3D Topology optimization of Stokes flow problems
DEFF Research Database (Denmark)
Gersborg-Hansen, Allan; Dammann, Bernd
of energy efficient devices for 2D Stokes flow. Creeping flow problems are described by the Stokes equations which model very viscous fluids at macro scales or ordinary fluids at very small scales. The latter gives the motivation for topology optimization problems based on the Stokes equations being a model...... the designs are 3D. Moreover, preliminary results show that a formulation of an optimization problem that maximizes mixing with a constraint on the pressure drop across the device gives promising results. To measure the mixing a step temperature profile is convected through the design and the resulting...
Topology optimization of 3D Stokes flow problems
DEFF Research Database (Denmark)
Gersborg-Hansen, Allan
to different flow problems. However, this research has focused on 2D fluid modelling, which limits the practical impact of the computed designs. The explanation of the limitation is that the finite size domain used in topology optimization problems ensures that the velocity components couples, even for Stokes...... flow [3]. Furthermore, it is questionable if such a coupling can be captured by a 2D model especially in non-trivial geometries as typically seen in topology design. This statement is widely accepted in the fluid mechanics community, i.e. that planar fluid models are useful for academic test problems...... fundamental aspects of the topology optimization method applied to the Stokes equations as described below. This work consists of two parts. The main part elaborates on effects caused by 3D fluid modelling on the design. Numerical examples are shown where the design is planar - relevant to micro fluidic...
Topology optimization of 3D Stokes flow problems
DEFF Research Database (Denmark)
Gersborg-Hansen, Allan; Sigmund, Ole; Bendsøe, Martin P.
is caused by the finite size domain used in topology optimization problems which ensures that the velocity components couples, even for Stokes flow [3]. Physically Stokes flow is an exotic inertia free flow, which in practice complicates mixing by passive devices. Passive mixing devices are relevant......The design of MEMS devices have benefitted from the topology optimization tool and complicated layout problems have been solved, see [1] for an overview. This research is aimed at micro fluidic devices known as micro-Total-Analysis-Systems (muTAS) where the main physical phenomena originate from...... fluid mechanics. In future practice a muTAS could be used by doctors, engineers etc. as a hand held device with short reaction time that provides on-site analysis of a flowing substance such as blood, polluted water or similar. Borrvall and Petersson [2] paved the road for using the topology...
Topology optimization of 3D Stokes flow problems
DEFF Research Database (Denmark)
Gersborg-Hansen, Allan
to different flow problems. However, this research has focused on 2D fluid modelling, which limits the practical impact of the computed designs. The explanation of the limitation is that the finite size domain used in topology optimization problems ensures that the velocity components couples, even for Stokes......Topology optimization has been applied to a multitude of physical systems and is now a mature technology used in industrial practice, see [1] for an overview. Borrvall and Petersson [2] introduced topology optimization of Stokes flow problems which initiated works on extending topology optimization...... flow [3]. Furthermore, it is questionable if such a coupling can be captured by a 2D model especially in non-trivial geometries as typically seen in topology design. This statement is widely accepted in the fluid mechanics community, i.e. that planar fluid models are useful for academic test problems...
3D Topology optimization of Stokes flow problems
DEFF Research Database (Denmark)
Gersborg-Hansen, Allan; Dammann, Bernd
for the fluid behavior in a micro fluidic device. Such a device has finite size and a large degree of freedom for the design of geometry. Physically Stokes flow is an exotic inertia free flow. This, however, complicates mixing by passive devices. Passive devices, that is, devices without moving parts, are often......, the optimizer suggests a design that stretches the hot-cold interface, which is encouraging since "stretching and folding" is known to be key ingredients in efficient mixing. The modelling is performed using a finite element based solver, with analytically derived sensitivities that drives a gradient based...... Program Interface, http://www.openmp.org/...
Topology optimization of 3D Stokes flow problems
DEFF Research Database (Denmark)
Gersborg-Hansen, Allan; Sigmund, Ole; Bendsøe, Martin P.
examples relevant for optimal micro fluidic mixer design are shown where the design is planar - compliant with micro fabrication techniques - and where the designs are 3D. In addition issues related to the parallel solution of the linear algebra problems are discussed. The implementation uses...... the commercial COMSOL multiphysics programme which is sufficiently flexible to provide semi--automated analytical sensitivities. 1. M. P. Bendsoe and O. Sigmund, "Topology Optimization - Theory, Methods and Applications", Springer Verlag, Berlin Heidelberg, 2003. 2. T. Borrvall and J. Petersson, "Topology...
The FMM-BEM Method for the 3D Particulate Stokes Flow
Directory of Open Access Journals (Sweden)
Hassib Selmi
2014-01-01
Full Text Available This work introduces new functions based on the spherical harmonics and the solid harmonics which have been used to construct a multipole development for the 3D Stokes problem in order to reduce the operations costs in the BEM method. We show that the major properties of those functions are inherited from the solid harmonics. The contribution of this paper is the introduction of new formulas that serve to calculate the multipole moments and the transfer functions that are necessary for the schemes of order O(NlogN. Moreover, new translation formulas are introduced to obtain an O(N scheme. The error truncation of the resulting scheme is discussed. In comparison to the BEM that attains a limit storage at O(104, we present here a method based on FMM-BEM that attains a storage at a limit of O(106. The implementation of the method achieves a high accuracy level at a reasonable cost.
Computation of 3D steady Navier-Stokes flow with free-surface gravity waves
Lewis, M.R.; Koren, B.; Raven, H.C.
2003-01-01
In this paper an iterative method for the computation of stationary gravity-wave solutions is investigated, using a novel formulation of the free-surface (FS) boundary-value problem. This method requires the solution of a sequence of stationary Reynolds-Averaged Navier-Stokes subproblems employing t
Computation of 3D Steady Navier-Stokes Flow with Free-Surface Gravity Waves
Lewis, M.R.; Koren, B.; Raven, H.C.
2003-01-01
In this paper an iterative method for the computation of stationary gravity-wave solutions is investigated, using a novel formulation of the free-surface (FS) boundary-value problem. This method requires the solution of a sequence of stationary Reynolds-Averaged Navier-Stokes subproblems employing t
Simulating Ice-Flow and Calving on Store Glacier, West Greenland, with a 3D Full Stokes Model
Todd, J.; Christoffersen, P.; Zwinger, T.; Luckman, A. J.; Benn, D.
2015-12-01
The mass balance and long-term stability of the ice sheets in Greenland and Antarctica depend heavily on the dynamics of their ice-ocean margins. Iceberg calving accounts for the majority of the net annual loss of ice in Antarctica and around half of that from Greenland. Furthermore, climate driven changes to dynamics at these calving margins can be transmitted far inland. Thus, predicting future sea level contribution from the cryosphere requires an improved understanding of calving, and the processes which link it to climate and ice-sheet flow. We present results from a new 3D calving model coupled to a full-Stokes, time evolving glacier dynamic model, implemented for Store Glacier, a 5-km-wide calving glacier in the Uummannaq region of West Greenland, which flows at a rate of 20 m/day at its terminus. The model is developed using the open source finite element package Elmer/Ice, with the criterion that calving occurs when surface and basal crevasses meet. Crevasses open in response to tensile stresses near the terminus and water pressure at the bed. When the model was applied in 2D for the central flowline of Store Glacier, we found that basal topography exerts overarching control on the long term position of the calving front, while ice mélange buttressing allows the seasonal extension of a floating tongue, which collapses in early summer. New results emerging from implementation of calving in a 3D model indicate significant spatial heterogeneity in calving dynamics because the northern half of the terminus is grounded whereas the southern half is floating. This contrasting setting affects calving dynamics, further underlining the importance of geometry and basal topography, and suggesting that lower dimensional calving models may miss important aspects of calving dynamics. Our results also suggest that implementing grounding line dynamics is important for modelling calving, even for glaciers which are, for the most part, firmly grounded.
Dual Variational Principles for 3-D Navier-Stokes Equations
Liu, G. L.
Just recently the exact variational principles (VP) of the full 3-D Navier-Stokes equations of viscous flow have been successfully established for the first time by the present author by means of a systematic reversed deduction method via the undetermined function. As a continuation and further development of that - a pair of new dual (reciprocal)VP is generated herein by means of the Friedrichs involutory transformation. These VP have the advantage over the previous ones that they possess apparent physical meaning of energy, providing a new rigorous theoretical basis for the finite element analysis of 3-D viscous flow.
Young, D. L.; Tsai, C. H.; Wu, C. S.
2015-11-01
An alternative vector potential formulation is used to solve the Navier-Stokes (N-S) equations in 3D incompressible viscous flow problems with and without through-flow boundaries. Difficulties of the vector potential formulation include the implementation of boundary conditions for through-flow boundaries and the numerical treatment of fourth-order partial differential equations. The advantages on the other hand are the automatic satisfaction of the continuity equation; and pressure is decoupled from the velocity. The objective of this paper is to introduce the appropriate gauge and boundary conditions on the vector potential formulation by a localized meshless method. To handle the divergence-free property, a Coulomb gauge condition is enforced on the vector potential to ensure its existence and uniqueness mathematically. We further improve the algorithm to through-flow problems for the boundary conditions of vector potential by introducing the concept of Stokes' theorem. Based on this innovation, there is no need to include an additional variable to tackle the through-flow fields. This process will greatly simplify the imposition of boundary conditions by the vector potential approach. Under certain conditions, the coupled fourth-order partial differential equations can be easily solved by using this meshless local differential quadrature (LDQ) method. Due to the LDQ capability to deal with the high order differential equations, this algorithm is very attractive to solve this fourth-order vector potential formulation for the N-S equations as comparing to the conventional numerical schemes such as finite element or finite difference methods. The proposed vector potential formulation is simpler and has improved accuracy and efficiency compared to other pressure-free or pressure-coupled algorithms. This investigation can be regarded as the first complete study to obtain the N-S solutions by vector potential formulation through a LDQ method. Two classic 3D benchmark
Persistence of Steady 3D Euler Solutions for 3D Navier-Stokes Equations
Li, Y Charles
2008-01-01
In the classical plane Couette flow, certain 3D steady solution (the so-called lower branch state) of the Navier-Stokes equations has a nontrivial limit as the Reynolds number approaches infinity \\cite{WGW07}. The limit is a shear of the form ($U(y,z), 0, 0$) in velocity variables. On the other hand, all the shears of this form are solutions of the corresponding 3D Euler equations. This note derives a necessary condition for such a shear to be a limit shear. The condition is $\\int \\Dl U f(U) dy dz = 0$ for any function $f$ satisfying certain boundary condition. Similar conditions are also derived for plane Poiseuille flow and pipe Poiseuille flow, which correspond to similar limit shears as revealed in \\cite{Wal03} \\cite{Vis08}.
Institute of Scientific and Technical Information of China (English)
Piotr Lampart; Andrzej Gardzilewicz; Sergey Yershov; Andrey Rusanov
2001-01-01
The effect of interaction of the main flow with root and tip leakage flows on the performance of an high pressure (HP) stage of an impulse turbine is studied numerically. The flow in blade-to-blade channels and axial gaps is computed with the aid of a 3D Navier-Stokes solver FlowER. The numerical scheme is modified to include the some/sink-type boundary conditions in places at the endwalls referring to design locations of injection of leakage and windage flows into, or extract from, the blade-to-blade passage. The turbine stage is computed in three configurations. First, computations are made without tip leakage and windage flows with source/sink slots closed.Second, tip leakage slots are open. Third, both tip leakage and windage flow slots are open, and the obtained flow characteristics including kinetic energy losses in the stage are compared so as to estimate the interaction of the main and leakage flows.
DEFF Research Database (Denmark)
Holbek, Simon
For the last decade, the field of ultrasonic vector flow imaging has gotten an increasingly attention, as the technique offers a variety of new applications for screening and diagnostics of cardiovascular pathologies. The main purpose of this PhD project was therefore to advance the field of 3-D...... ultrasonic vector flow estimation and bring it a step closer to a clinical application. A method for high frame rate 3-D vector flow estimation in a plane using the transverse oscillation method combined with a 1024 channel 2-D matrix array is presented. The proposed method is validated both through phantom......, if this significant reduction in the element count can still provide precise and robust 3-D vector flow estimates in a plane. The study concludes that the RC array is capable of estimating precise 3-D vector flow both in a plane and in a volume, despite the low channel count. However, some inherent new challenges...
DEFF Research Database (Denmark)
Holbek, Simon
studies and in vivo. Phantom measurements are compared with their corresponding reference value, whereas the in vivo measurement is validated against the current golden standard for non-invasive blood velocity estimates, based on magnetic resonance imaging (MRI). The study concludes, that a high precision......, if this significant reduction in the element count can still provide precise and robust 3-D vector flow estimates in a plane. The study concludes that the RC array is capable of estimating precise 3-D vector flow both in a plane and in a volume, despite the low channel count. However, some inherent new challenges......For the last decade, the field of ultrasonic vector flow imaging has gotten an increasingly attention, as the technique offers a variety of new applications for screening and diagnostics of cardiovascular pathologies. The main purpose of this PhD project was therefore to advance the field of 3-D...
3D IBFV : Hardware-Accelerated 3D Flow Visualization
Telea, Alexandru; Wijk, Jarke J. van
2003-01-01
We present a hardware-accelerated method for visualizing 3D flow fields. The method is based on insertion, advection, and decay of dye. To this aim, we extend the texture-based IBFV technique for 2D flow visualization in two main directions. First, we decompose the 3D flow visualization problem in a
DEFF Research Database (Denmark)
Pihl, Michael Johannes
The main purpose of this PhD project is to develop an ultrasonic method for 3D vector flow imaging. The motivation is to advance the field of velocity estimation in ultrasound, which plays an important role in the clinic. The velocity of blood has components in all three spatial dimensions, yet...... conventional methods can estimate only the axial component. Several approaches for 3D vector velocity estimation have been suggested, but none of these methods have so far produced convincing in vivo results nor have they been adopted by commercial manufacturers. The basis for this project is the Transverse...... on the TO fields are suggested. They can be used to optimize the TO method. In the third part, a TO method for 3D vector velocity estimation is proposed. It employs a 2D phased array transducer and decouples the velocity estimation into three velocity components, which are estimated simultaneously based on 5...
Energy Technology Data Exchange (ETDEWEB)
Henandez Rosete, Alejandro; Mazur C, Zdzislaw [Instituto de Investigaciones Electricas, Cuernavaca, Morelos (Mexico)
2007-11-15
The results of the simulation by CFD (Computacional Fluid Dynamics) realized to the first stage of a gas turbine GE Frame 7 are presented. The analysis includes the 3D modeling of the flow channel in the nozzle and the movable blade to know the velocities distributions, temperatures and pressures of the main hot gas flow that are developed in the Inter stage. The results are influenced by the imposed border conditions in the properties of the main flow, the rotation of the movable blade, as well as the simulation of cooling air injection in the nozzle. The present study focuses in the validation of the model of the meshes of the ensemble nozzle-blade, for later realize an analysis of conjugated heat transfer in a model with ceramic lining type heat barrier (THB) in the movable blade. The analysis is realized in a CFD commercial code oriented to turbo-machinery using the equations of unstable flows 3D of Navier Stokes. [Spanish] Se presentan los resultados de la simulacion por CFD (Computacional Fluid Dynamics) realizada a la primera etapa de una turbina de gas GE Frame 7. El analisis incluye la modelacion tridimensional del canal de flujo en la tobera y el alabe movil para conocer las distribuciones de las velocidades, temperaturas y presiones del flujo principal de gases calientes que se desarrollan en la inter etapa. Los resultados son influenciados por las condiciones de frontera impuestos en las propiedades del flujo principal, la rotacion del alabe movil, asi como la simulacion de inyeccion de aire de enfriamiento en la tobera. El presente estudio se enfoca en la validacion del modelo de la malla del conjunto tobera-alabe, para posteriormente realizar un analisis de transferencia de calor conjugada en un modelo con recubrimiento ceramico tipo barrera termica (TBC) en el alabe movil. El analisis es realizado en un codigo de CFD comercial orientado a turbomaquinaria utilizando las ecuaciones de flujos inestables 3D de Navier Stokes.
Free boundary value problem to 3D spherically symmetric compressible Navier-Stokes-Poisson equations
Kong, Huihui; Li, Hai-Liang
2017-02-01
In the paper, we consider the free boundary value problem to 3D spherically symmetric compressible isentropic Navier-Stokes-Poisson equations for self-gravitating gaseous stars with γ -law pressure density function for 6/5 <γ ≤ 4/3. For stress-free boundary condition and zero flow density continuously across the free boundary, the global existence of spherically symmetric weak solutions is shown, and the regularity and long time behavior of global solution are investigated for spherically symmetric initial data with the total mass smaller than a critical mass.
Topology Optimization of Large Scale Stokes Flow Problems
DEFF Research Database (Denmark)
Aage, Niels; Poulsen, Thomas Harpsøe; Gersborg-Hansen, Allan
2008-01-01
This note considers topology optimization of large scale 2D and 3D Stokes flow problems using parallel computations. We solve problems with up to 1.125.000 elements in 2D and 128.000 elements in 3D on a shared memory computer consisting of Sun UltraSparc IV CPUs.......This note considers topology optimization of large scale 2D and 3D Stokes flow problems using parallel computations. We solve problems with up to 1.125.000 elements in 2D and 128.000 elements in 3D on a shared memory computer consisting of Sun UltraSparc IV CPUs....
Exponential Mixing of the 3D Stochastic Navier-Stokes Equations Driven by Mildly Degenerate Noises
Energy Technology Data Exchange (ETDEWEB)
Albeverio, Sergio [Bonn University, Department of Applied Mathematics (Germany); Debussche, Arnaud, E-mail: arnaud.debussche@bretagne.ens-cachan.fr [ENS Cachan Bretagne and IRMAR Campus de Ker Lann (France); Xu Lihu, E-mail: Lihu.Xu@brunel.ac.uk [Brunel University, Mathematics Department (United Kingdom)
2012-10-15
We prove the strong Feller property and exponential mixing for 3D stochastic Navier-Stokes equation driven by mildly degenerate noises (i.e. all but finitely many Fourier modes being forced) via a Kolmogorov equation approach.
SOLUTION OF 3-D TURBULENCE NAVIER-STOKES EQUATIONS USING HYBRID GRIDS
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Hybrid grids are used for the solution of 3D turbulence Navier-Stokes equations. The prismatic grids are generated near the wall, and the tetrahedron grids are generated in the other field. A Navier-Stokes solver using ic Baldwin-Lomax turbulence model is adopted. The numerical tests show that the above method is very efficient.``
A least-squares finite element method for 3D incompressible Navier-Stokes equations
Jiang, Bo-Nan; Lin, T. L.; Hou, Lin-Jun; Povinelli, Louis A.
1993-01-01
The least-squares finite element method (LSFEM) based on the velocity-pressure-vorticity formulation is applied to three-dimensional steady incompressible Navier-Stokes problems. This method can accommodate equal-order interpolations, and results in symmetric, positive definite algebraic system. An additional compatibility equation, i.e., the divergence of vorticity vector should be zero, is included to make the first-order system elliptic. The Newton's method is employed to linearize the partial differential equations, the LSFEM is used to obtain discretized equations, and the system of algebraic equations is solved using the Jacobi preconditioned conjugate gradient method which avoids formation of either element or global matrices (matrix-free) to achieve high efficiency. The flow in a half of 3D cubic cavity is calculated at Re = 100, 400, and 1,000 with 50 x 52 x 25 trilinear elements. The Taylor-Gortler-like vortices are observed at Re = 1,000.
Two-equation turbulence modeling for 3-D hypersonic flows
Bardina, J. E.; Coakley, T. J.; Marvin, J. G.
1992-01-01
An investigation to verify, incorporate and develop two-equation turbulence models for three-dimensional high speed flows is presented. The current design effort of hypersonic vehicles has led to an intensive study of turbulence models for compressible hypersonic flows. This research complements an extensive review of experimental data and the current development of 2D turbulence models. The review of experimental data on 2D and 3D flows includes complex hypersonic flows with pressure profiles, skin friction, wall heat transfer, and turbulence statistics data. In a parallel effort, turbulence models for high speed flows have been tested against flat plate boundary layers, and are being tested against the 2D database. In the present paper, we present the results of 3D Navier-Stokes numerical simulations with an improved k-omega two-equation turbulence model against experimental data and empirical correlations of an adiabatic flat plate boundary layer, a cold wall flat plate boundary layer, and a 3D database flow, the interaction of an oblique shock wave and a thick turbulent boundary layer with a free stream Mach number = 8.18 and Reynolds number = 5 x 10 to the 6th.
Navier-Stokes Neutral and Plasma Fluid Modelling in 3D
Energy Technology Data Exchange (ETDEWEB)
Riemann, J; Borchardt, M; Schneider, R; Mutzke, A; Rognlien, T; Umansky, M
2004-05-17
The 3D finite volume transport code BoRiS is applied to a system of coupled plasma and neutral fluid equations in a slab. Demonstrating easy implementation of new equations, a new parallel BoRiS version is tested on three different models for the neutral fluid - diffusive, parallel Navier-Stokes and full Navier-Stokes - and the results are compared to each other. Typical effects like density enhancement by ionization of recycled neutrals in front of a target plate can be seen and differences are linked to the neutral models in use.
Existence and uniqueness of global solutions for the modified anisotropic 3D Navier−Stokes equations
Bessaih, Hakima
2016-01-27
We study a modified three-dimensional incompressible anisotropic Navier−Stokes equations. The modification consists in the addition of a power term to the nonlinear convective one. This modification appears naturally in porous media when a fluid obeys the Darcy−Forchheimer law instead of the classical Darcy law. We prove global in time existence and uniqueness of solutions without assuming the smallness condition on the initial data. This improves the result obtained for the classical 3D incompressible anisotropic Navier−Stokes equations.
Study of Tip-loss Using an Inverse 3D Navier-Stokes Method
DEFF Research Database (Denmark)
Mikkelsen, Robert; Sørensen, Jens Nørkær; Shen, Wen Zhong;
2003-01-01
The tip-correction for air-screws described by Prandtl (1919) and implemented into the Blade Element Momentum (BEM) theory by Glauert (1930), is founded on certain assumptions which the present analysis seeks to overcome. In the paper we propose a method to derive the tip-correction by solving...... the 3D Navier-Stokes equations combined with the actuator line technique where blade loading is applied using an inverse method. The numerical simulations shows that the method captures the tip-correction when comparing with the theories of Prandtl and Goldstein, however, the accuracy of the obtained...... results reveal that further refinements still is needed. Keywords: Tip-loss; Actuator line; 3D Navier-Stokes methods....
3D critical layers in fully-developed turbulent flows
Saxton-Fox, Theresa; McKeon, Beverley
2016-11-01
Recent work has shown that 3D critical layers drive self-sustaining behavior of exact coherent solutions of the Navier-Stokes equations (Wang et al. 2007; Hall and Sherwin 2010; Park and Graham 2015). This study investigates the role of 3D critical layers in fully-developed turbulent flows. 3D critical layer effects are identified in instantaneous snapshots of turbulent boundary layers in both experimental and DNS data (Wu et al. 2014). Additionally, a 3D critical layer effect is demonstrated to appear using only a few resolvent response modes from the resolvent analysis of McKeon and Sharma 2010, with phase relationships appropriately chosen. Connections are sought to the thin shear layers observed in turbulent boundary layers (Klewicki and Hirschi 2004; Eisma et al. 2015) and to amplitude modulation observations (Mathis et al. 2009; Duvvuri and McKeon 2014). This research is made possible by the Department of Defense through the National Defense & Engineering Graduate Fellowship (NDSEG) Program and by the Air Force Office of Scientific Research Grant # FA9550-12-1-0060. The support of the Center for Turbulence Research (CTR) summer program at Stanford is gratefully acknowledged.
XML3D and Xflow: combining declarative 3D for the Web with generic data flows.
Klein, Felix; Sons, Kristian; Rubinstein, Dmitri; Slusallek, Philipp
2013-01-01
Researchers have combined XML3D, which provides declarative, interactive 3D scene descriptions based on HTML5, with Xflow, a language for declarative, high-performance data processing. The result lets Web developers combine a 3D scene graph with data flows for dynamic meshes, animations, image processing, and postprocessing.
3-D numerical modelling of flow around a groin
DEFF Research Database (Denmark)
Miller, R.; Roulund, A.; Sumer, B. Mutlu
2003-01-01
A 3-D flow code, EllipSys3D, has been implemented to simulate the 3-D flow around a groin in steady current. The k turbulence model has been used for closure. Two kinds of groins are considered: (1) A vertical-wall groin, and (2) A groin with a side slope. Steady-flow simulations were conducted...
3D Flow reconstruction using ultrasound PIV
Poelma, C.; Mari, J.M.; Foin, N.; Tang, M.-X.; Krams, R.; Caro, C.G.; Weinberg, P.D.; Westerweel, J.
2009-01-01
Ultrasound particle image velocimetry (PIV) can be used to obtain velocity fields in non-transparent geometries and/or fluids. In the current study, we use this technique to document the flow in a curved tube, using ultrasound contrast bubbles as flow tracer particles. The performance of the techniq
Topology optimization of mass distribution problems in Stokes flow
DEFF Research Database (Denmark)
Gersborg-Hansen, Allan; Berggren, Martin; Dammann, Bernd
We consider topology optimization of mass distribution problems in 2D and 3D Stokes flow with the aim of designing devices that meet target outflow rates. For the purpose of validation, the designs have been post processed using the image processing tools available in FEMLAB. In turn, this has...... enabled an evaluation of the design with a body fitted mesh in a standard analysis software relevant in engineering practice prior to design manufacturing. This work investigates the proper choice of a maximum penalization value during the optimization process that ensures that the target outflow rates...
The new high resolution method of Godunov`s type for 3D viscous flow calculations
Energy Technology Data Exchange (ETDEWEB)
Yershov, S.V.; Rusanov, A.V. [Ukranian National Academy of Sciences, Kahrkov (Ukraine)
1996-12-31
The numerical method is suggested for the calculations of the 3D viscous compressible flows described by the thin-layer Reynolds-averaged Navier-Stokes equations. The method is based on the Godunov`s finite-difference scheme and it uses the ENO reconstruction suggested by Harten to achieve the uniformly high-order accuracy. The computational efficiency is provided with the simplified multi grid approach and the implicit step written in {delta} -form. The turbulent effects are simulated with the Baldwin - Lomax turbulence model. The application package FlowER is developed to calculate the 3D turbulent flows within complex-shape channels. The numerical results for the 3D flow around a cylinder and through the complex-shaped channels show the accuracy and the reliability of the suggested method. (author)
Ge, Liang; Sotiropoulos, Fotis
2007-08-01
A novel numerical method is developed that integrates boundary-conforming grids with a sharp interface, immersed boundary methodology. The method is intended for simulating internal flows containing complex, moving immersed boundaries such as those encountered in several cardiovascular applications. The background domain (e.g. the empty aorta) is discretized efficiently with a curvilinear boundary-fitted mesh while the complex moving immersed boundary (say a prosthetic heart valve) is treated with the sharp-interface, hybrid Cartesian/immersed-boundary approach of Gilmanov and Sotiropoulos [A. Gilmanov, F. Sotiropoulos, A hybrid cartesian/immersed boundary method for simulating flows with 3d, geometrically complex, moving bodies, Journal of Computational Physics 207 (2005) 457-492.]. To facilitate the implementation of this novel modeling paradigm in complex flow simulations, an accurate and efficient numerical method is developed for solving the unsteady, incompressible Navier-Stokes equations in generalized curvilinear coordinates. The method employs a novel, fully-curvilinear staggered grid discretization approach, which does not require either the explicit evaluation of the Christoffel symbols or the discretization of all three momentum equations at cell interfaces as done in previous formulations. The equations are integrated in time using an efficient, second-order accurate fractional step methodology coupled with a Jacobian-free, Newton-Krylov solver for the momentum equations and a GMRES solver enhanced with multigrid as preconditioner for the Poisson equation. Several numerical experiments are carried out on fine computational meshes to demonstrate the accuracy and efficiency of the proposed method for standard benchmark problems as well as for unsteady, pulsatile flow through a curved, pipe bend. To demonstrate the ability of the method to simulate flows with complex, moving immersed boundaries we apply it to calculate pulsatile, physiological flow
Analysis of wall shear stress around a competitive swimmer using 3D Navier-Stokes equations in CFD.
Popa, C V; Zaidi, H; Arfaoui, A; Polidori, G; Taiar, R; Fohanno, S
2011-01-01
This paper deals with the flow dynamics around a competitive swimmer during underwater glide phases occurring at the start and at every turn. The influence of the head position, namely lifted up, aligned and lowered, on the wall shear stress and the static pressure distributions is analyzed. The problem is considered as 3D and in steady hydrodynamic state. Three velocities (1.4 m/s, 2.2 m/s and 3.1 m/s) that correspond to inter-regional, national and international swimming levels are studied. The flow around the swimmer is assumed turbulent. The Reynolds-averaged Navier-Stokes (RANS) equations are solved with the standard k-ω turbulent model by using the CFD (computational fluid dynamics) numerical method based on a volume control approach. Numerical simulations are carried out with the ANSYS FLUENT® CFD code. The results show that the wall shear stress increases with the velocity and consequently the drag force opposing the movement of the swimmer increases as well. Also, high wall shear stresses are observed in the areas where the body shape, globally rigid in form, presents complex surface geometries such as the head, shoulders, buttocks, heel and chest.
Institute of Scientific and Technical Information of China (English)
He Zhi-guo; Mao Gen-hai; Yuan Xing-ming
2003-01-01
The 3-D turbulent flows in a valve pipe were described by the incompressible Reynolds-averaged Navier-Stokes equations with an RNG k-ε turbulence model. With the finite volume method and a body-fitted coordinate system, the discretised equations were solved by the SIMPLEST algorithm. The numerical result of a cut-off valve with curved inlet shows the flow characteristics and the main cause of energy loss when fluid flows through a valve. And then, the boundaries of valve were modified in order to reduce the energy loss. The computational results of modified valve show that the numerical value of turbulent kinetic energy is lower, and that the modified design of the 3-D valve boundaries is much better. The analysis of the result also shows that RNG k-ε turbulence model can successfully be used to predict the 3-D turbulent separated flows and the secondary flow inside valve pipes.
On the Coupling of Incompressible Stokes or Navier–Stokes and Darcy Flows Through Porous Media
Girault, V.
2012-11-03
In this chapter, we present the theoretical analysis of coupled incompressible Navier-Stokes (or Stokes) flows and Darcy flows with the Beavers-Joseph-Saffman interface condition. We discuss alternative interface and porous media models. We review some finite element methods used by several authors in this coupling and present numerical experiments.
Parallel Processor for 3D Recovery from Optical Flow
Directory of Open Access Journals (Sweden)
Jose Hugo Barron-Zambrano
2009-01-01
Full Text Available 3D recovery from motion has received a major effort in computer vision systems in the recent years. The main problem lies in the number of operations and memory accesses to be performed by the majority of the existing techniques when translated to hardware or software implementations. This paper proposes a parallel processor for 3D recovery from optical flow. Its main feature is the maximum reuse of data and the low number of clock cycles to calculate the optical flow, along with the precision with which 3D recovery is achieved. The results of the proposed architecture as well as those from processor synthesis are presented.
Frictionless dispersive hydrodynamics of Stokes flows
Maiden, Michelle D; Anderson, Dalton V; Schubert, Marika E; Hoefer, Mark A
2016-01-01
Effectively frictionless, dispersive flow characterizes superfluids, nonlinear optical diffraction, and geophysical fluid interfaces. Dispersive shock waves (DSWs) and solitons are fundamental nonlinear excitations in these media, but DSW studies to date have been severely constrained by a loss of coherence. Here we report on a novel dispersive hydrodynamics testbed: the effectively frictionless flow of interfacial waves between two high contrast, low Reynolds' number Stokes fluids. This system enables high fidelity observations of large amplitude DSWs, found to agree quantitatively with a nonlinear wave averaging theory. We then report on observations of highly coherent phenomena including DSW backflow, the refraction or absorption of solitons by DSWs, and multi-phase DSW-DSW merger. The complex, coherent, nonlinear mixing of DSWs and solitons observed here are universal features of dissipationless, dispersive hydrodynamic flows.
High Frame Rate Synthetic Aperture 3D Vector Flow Imaging
DEFF Research Database (Denmark)
Villagómez Hoyos, Carlos Armando; Holbek, Simon; Stuart, Matthias Bo
2016-01-01
3-D blood flow quantification with high spatial and temporal resolution would strongly benefit clinical research on cardiovascular pathologies. Ultrasonic velocity techniques are known for their ability to measure blood flow with high precision at high spatial and temporal resolution. However......, current volumetric ultrasonic flow methods are limited to one velocity component or restricted to a reduced field of view (FOV), e.g. fixed imaging planes, in exchange for higher temporal resolutions. To solve these problems, a previously proposed accurate 2-D high frame rate vector flow imaging (VFI......) technique is extended to estimate the 3-D velocity components inside a volume at high temporal resolutions (
Commercial turbofan engine exhaust nozzle flow analyses using PAB3D
Abdol-Hamid, Khaled S.; Uenishi, K.; Carlson, John R.; Keith, B. D.
1992-01-01
Recent developments of a three-dimensional (PAB3D) code have paved the way for a computational investigation of complex aircraft aerodynamic components. The PAB3D code was developed for solving the simplified Reynolds Averaged Navier-Stokes equations in a three-dimensional multiblock/multizone structured mesh domain. The present analysis was applied to commercial turbofan exhaust flow systems. Solution sensitivity to grid density is presented. Laminar flow solutions were developed for all grids and two-equation k-epsilon solutions were developed for selected grids. Static pressure distributions, mass flow and thrust quantities were calculated for on-design engine operating conditions. Good agreement between predicted surface static pressures and experimental data was observed at different locations. Mass flow was predicted within 0.2 percent of experimental data. Thrust forces were typically within 0.4 percent of experimental data.
An integral equation approach to smooth 3D Navier-Stokes solution
Costin, O.; Luo, G.; Tanveer, S.
2008-12-01
We summarize a recently developed integral equation (IE) approach to tackling the long-time existence problem for smooth solution v(x, t) to the 3D Navier-Stokes (NS) equation in the context of a periodic box problem with smooth time independent forcing and initial condition v0. Using an inverse-Laplace transform of {\\skew5\\hat v} (k, t) - {\\skew5\\hat v}_0 in 1/t, we arrive at an IE for {\\skew5\\hat U} (k, p) , where p is inverse-Laplace dual to 1/t and k is the Fourier variable dual to x. The advantage of this formulation is that the solution {\\skew5\\hat U} to the IE is known to exist a priori for p \\in \\mathbb{R}^+ and the solution is integrable and exponentially bounded at ∞. Global existence of NS solution in this formulation is reduced to an asymptotics question. If \\parallel\\!{\\skew5\\hat U} (\\cdot, p)\\!\\parallel_{{l^{1} (\\mathbb{Z}^3)}} has subexponential bounds as p→∞, then global existence to NS follows. Moreover, if f=0, then the converse is also true in the following sense: if NS has global solution, then there exists n>=1 for which the inverse-Laplace transform of {\\skew5\\hat v} (k, t) - {\\skew5\\hat v}_0 in 1/tn necessarily decays as q→∞, where q is the inverse-Laplace dual to 1/tn. We also present refined estimates of the exponential growth when the solution {\\skew5\\hat U} is known on a finite interval [0, p0]. We also show that for analytic v[0] and f, with finitely many nonzero Fourier-coefficients, the series for {\\skew5\\hat U} (k, p) in powers of p has a radius of convergence independent of initial condition and forcing; indeed the radius gets bigger for smaller viscosity. We also show that the IE can be solved numerically with controlled errors. Preliminary numerical calculations for Kida (1985 J. Phys. Soc. Japan 54 2132) initial conditions, though far from being optimized, and performed on a modest interval in the accelerated variable q show decay in q.
Numerical Simulation of Transient Flows around a 3D Pitching Hydrofoil
Directory of Open Access Journals (Sweden)
Qin Wu
2015-02-01
Full Text Available The objective of this paper is to investigate the hydrodynamic characteristics of the transient flows around a 3D pitching hydrofoil via numerical studies, where the effects of tunnel wall boundary layer and gap flows are considered. Simulations are performed using an unsteady Reynolds Average Navier-Stokes solver and the k-ω SST turbulence model, coupled with a two-equation γ-Reθ transition model. Hydrodynamic forces and flow structures are compared to the results with the equivalent 2D computations. During the upward pitching stage, the transition phenomenon is accurately captured by both the 2D and 3D simulations. The slightly lower lift and suction side loading coefficients predicted by the 3D simulation are due to the pressure effects caused by the tip gap flow. During the dynamic stall stage, the 2D case exhibits a clear overshoot on the hydrodynamic force coefficients and the 3D simulation results better agree with the experimental results. During the downward pitching stage, the flow transitions back to laminar. As for the effect of gap flow and the wall boundary condition, the gap flow causes disturbances to the formation and development of the vortex structures, resulting in the complex distribution of the three-dimensional streamlines and the particle path.
Yang, L. M.; Shu, C.; Wang, Y.; Sun, Y.
2016-08-01
The sphere function-based gas kinetic scheme (GKS), which was presented by Shu and his coworkers [23] for simulation of inviscid compressible flows, is extended to simulate 3D viscous incompressible and compressible flows in this work. Firstly, we use certain discrete points to represent the spherical surface in the phase velocity space. Then, integrals along the spherical surface for conservation forms of moments, which are needed to recover 3D Navier-Stokes equations, are approximated by integral quadrature. The basic requirement is that these conservation forms of moments can be exactly satisfied by weighted summation of distribution functions at discrete points. It was found that the integral quadrature by eight discrete points on the spherical surface, which forms the D3Q8 discrete velocity model, can exactly match the integral. In this way, the conservative variables and numerical fluxes can be computed by weighted summation of distribution functions at eight discrete points. That is, the application of complicated formulations resultant from integrals can be replaced by a simple solution process. Several numerical examples including laminar flat plate boundary layer, 3D lid-driven cavity flow, steady flow through a 90° bending square duct, transonic flow around DPW-W1 wing and supersonic flow around NACA0012 airfoil are chosen to validate the proposed scheme. Numerical results demonstrate that the present scheme can provide reasonable numerical results for 3D viscous flows.
3-D Viscous Flow Analysis of a Mixed Flow Pump Impeller
Directory of Open Access Journals (Sweden)
Steven M. Miner
2001-01-01
Full Text Available This paper presents the results of a study using a coarse grid to analyze the flow in the impeller of a mixed flow pump. A commercial computational fluid dynamics code (FLOTRAN is used to solve the 3-D Reynolds Averaged Navier Stokes equations in a rotating cylindrical coordinate system. The standard k-ε turbulence model is used. The mesh for this study uses 26,000 nodes and the model is run on a SPARCstation 20. This is in contrast to typical analyses using in excess of 100,000 nodes that are run on a super computer platform. The smaller mesh size has advantages in the design environment. Stage design parameters are, rotational speed 1185 rpm, flow coefficient φ=0.116, head coefficient ψ=0.094, and specific speed 2.01 (5475 US. Results for the model include circumferentially averaged results at the leading and trailing edges of the impeller, and analysis of the flow field within the impeller passage. Circumferentially averaged results include axial and tangential velocities, static pressure, and total pressure. Within the impeller passage the static pressure and velocity results are presented on surfaces from the leading edge to the trailing edge, the hub to the shroud, and the pressure surface to the suction surface. Results of this study are consistent with the expected flow characteristics of mixed flow impellers, indicating that small CFD models can be used to evaluate impeller performance in the design environment.
Large Time Behavior for Weak Solutions of the 3D Globally Modified Navier-Stokes Equations
Directory of Open Access Journals (Sweden)
Junbai Ren
2014-01-01
Full Text Available This paper is concerned with the large time behavior of the weak solutions for three-dimensional globally modified Navier-Stokes equations. With the aid of energy methods and auxiliary decay estimates together with Lp-Lq estimates of heat semigroup, we derive the optimal upper and lower decay estimates of the weak solutions for the globally modified Navier-Stokes equations as C1(1+t-3/4≤uL2≤C2(1+t-3/4, t>1. The decay rate is optimal since it coincides with that of heat equation.
ON THE REGULARITY CRITERIA OF THE 3D NAVIER-STOKES EQUATIONS IN CRITICAL SPACES
Institute of Scientific and Technical Information of China (English)
Dong Boqing; Sadek Gala; Chen Zhimin
2011-01-01
Regularity criteria of Leray-Hopf weak solutions to the three-dimensional Navier-Stokes equations in some critical spaces such as Lorentz space, Morrey space and multiplier space are derived in terms of two partial derivatives, 1u1, 2u2, of velocity fields.
3D Printed Micro Free-Flow Electrophoresis Device.
Anciaux, Sarah K; Geiger, Matthew; Bowser, Michael T
2016-08-02
The cost, time, and restrictions on creative flexibility associated with current fabrication methods present significant challenges in the development and application of microfluidic devices. Additive manufacturing, also referred to as three-dimensional (3D) printing, provides many advantages over existing methods. With 3D printing, devices can be made in a cost-effective manner with the ability to rapidly prototype new designs. We have fabricated a micro free-flow electrophoresis (μFFE) device using a low-cost, consumer-grade 3D printer. Test prints were performed to determine the minimum feature sizes that could be reproducibly produced using 3D printing fabrication. Microfluidic ridges could be fabricated with dimensions as small as 20 μm high × 640 μm wide. Minimum valley dimensions were 30 μm wide × 130 μm wide. An acetone vapor bath was used to smooth acrylonitrile-butadiene-styrene (ABS) surfaces and facilitate bonding of fully enclosed channels. The surfaces of the 3D-printed features were profiled and compared to a similar device fabricated in a glass substrate. Stable stream profiles were obtained in a 3D-printed μFFE device. Separations of fluorescent dyes in the 3D-printed device and its glass counterpart were comparable. A μFFE separation of myoglobin and cytochrome c was also demonstrated on a 3D-printed device. Limits of detection for rhodamine 110 were determined to be 2 and 0.3 nM for the 3D-printed and glass devices, respectively.
Energy Technology Data Exchange (ETDEWEB)
Chaviaropoulos, P.K. [CRES-Center for Renewable Energy Sources, Pikermi Attiki (Greece)
1997-08-01
The blade element codes provide surprisingly accurate predictions of the aerodynamic loads provided that they are `fed` with proper lift and drag - incidence curves for the profiles mounted on the rotor blades. The evident question is how one can obtain such data. It is common experience that the use of the mostly available steady two-dimensional profile data may lead to serious discrepancies between measured and simulated loads. Although several correction techniques have been proposed as a remedy during the last years, from simplified dynamic stall models suitably tuned for wind turbines to 3-D correction schemes for profile data, the problem is by no means over-passed. Especially for the three-dimensional effects it seems that part of the difficulty is due to our limited understanding of the physical mechanism which is responsible for the extra loading of the inner part of the blades. Recognizing the importance of the above aspects two relevant Joule projects have been launched, the concluded `Dynamic Stall and 3-D Effects` JOU2-CT93-0345 and the ongoing `VISCWIND` JOR3-CT95-0007 project. Part of the activities in the first and all the activities in the second project are devoted to the identification and quantification of the dynamic stall and three-dimensional effects experienced by the wind turbine blades using Navier-Stokes computations. The contribution of CRES in these two projects is briefly presented in this paper. (EG)
The 3D Flow Field Around an Embedded Planet
Fung, Jeffrey; Wu, Yanqin
2015-01-01
Understanding the 3D flow topology around a planet embedded in its natal disk is crucial to the study of planet formation. 3D modifications to the well-studied 2D flow topology have the potential to resolve longstanding problems in both planet migration and accretion. We present a detailed analysis of the 3D isothermal flow field around a 5 Earth-mass planet on a fixed circular orbit, simulated using our high-resolution multi-GPU hydrodynamics code PEnGUIn. We show that, overall, the horseshoe region has a columnar structure extending vertically much beyond the Hill sphere of the planet. This columnar structure is only broken for some of the widest horseshoe streamlines, along which high altitude fluid descends and converges rapidly toward the planet, enters its Bondi sphere, performs one horseshoe turn, and exits radially in the midplane. A portion of this flow gathers enough speed to exit the horseshoe region altogether. We call this newly identified feature the "transient" horseshoe flow. As the flow conti...
Zhai, Xiaoping; Yin, Zhaoyang
2017-02-01
The present paper is dedicated to the global well-posedness for the 3D inhomogeneous incompressible Navier-Stokes equations, in critical Besov spaces without smallness assumption on the variation of the density. We aim at extending the work by Abidi, Gui and Zhang (2012) [2], and (2013) [3] to a lower regularity index about the initial velocity. The key to that improvement is a new a priori estimate for an elliptic equation with nonconstant coefficients in Besov spaces which have the same degree as L2 in R3. Finally, we also generalize our well-posedness result to the inhomogeneous incompressible MHD equations.
Yu, Haibo; Zhao, Junning
2017-01-01
In this paper, we study the global existence for classical solutions to the 3D isentropic compressible Navier-Stokes equations in a cuboid domain. Compared to the Cauchy problem studied in Hoff (1995 J. Differ. Equ. 120 215-54), Hoff (2005 J. Math. Fluid Mech. 7 315-38), Huang et al (2012 Commun. Pure Appl. Math. 65 549-85), some new thoughts are applied to obtain upper bounds for density. Precisely, through piecewise estimation and some time-depending a priori estimates, we establish time-uniform upper bounds for density under the assumption that the initial energy is small. The initial vacuum is allowed.
An annotation system for 3D fluid flow visualization
Loughlin, Maria M.; Hughes, John F.
1995-01-01
Annotation is a key activity of data analysis. However, current systems for data analysis focus almost exclusively on visualization. We propose a system which integrates annotations into a visualization system. Annotations are embedded in 3D data space, using the Post-it metaphor. This embedding allows contextual-based information storage and retrieval, and facilitates information sharing in collaborative environments. We provide a traditional database filter and a Magic Lens filter to create specialized views of the data. The system has been customized for fluid flow applications, with features which allow users to store parameters of visualization tools and sketch 3D volumes.
Analysis of Stokes flow through periodic permeable tubules
Directory of Open Access Journals (Sweden)
A.M. Siddiqui
2017-03-01
Full Text Available This article reports the detailed analysis of the Stokes flow through permeable tubes. The objective of this investigation was to search for exact solutions to the Stokes flow and thereby observe the effects on radial flow component, provided the permeability on the tubular surface is an elementary trigonometric function. Mathematical expressions for the pressure distribution, velocity components, volume flux, average wall shear stress and leakage flux are presented explicitly. Graphical analysis of the fluid flow is presented for a set of parametric values. Important conclusions are drawn for Stokes flow through tubes with low as well as high permeability. The classical Poiseuille flow is presented as a limiting case of this immense study of Stokes flow.
Formation of coherent structures in 3D laminar mixing flows
Speetjens, Michel; Clercx, Herman
2009-11-01
Mixing under laminar flow conditions is key to a wide variety of industrial systems of size extending from microns to meters. Examples range from the traditional (and still very relevant) mixing of viscous fluids via compact processing equipment down to emerging micro-fluidics applications. Profound insight into laminar mixing mechanisms is imperative for further advancement of mixing technology (particularly for complex micro-fluidics systems) yet remains limited to date. The present study concentrates on a fundamental transport phenomenon of potential relevance to laminar mixing: the formation of coherent structures in the web of 3D fluid trajectories due to fluid inertia. Such coherent structures geometrically determine the transport properties of the flow and better understanding of their formation and characteristics may offer ways to control and manipulate the mixing properties of laminar flows. The formation of coherent structures and its impact upon 3D transport properties is demonstrated by way of examples.
Complex Singular Solutions of the 3-d Navier-Stokes Equations and Related Real Solutions
Boldrighini, Carlo; Li, Dong; Sinai, Yakov G.
2017-04-01
By applying methods of statistical physics Li and Sinai (J Eur Math Soc 10:267-313, 2008) proved that there are complex solutions of the Navier-Stokes equations in the whole space R3 which blow up at a finite time. We present a review of the results obtained so far, by theoretical work and computer simulations, for the singular complex solutions, and compare with the behavior of related real solutions. We also discuss the possible application of the techniques introduced in (J Eur Math Soc 10:267-313, 2008) to the study of the real ones.
Complex Singular Solutions of the 3-d Navier-Stokes Equations and Related Real Solutions
Boldrighini, Carlo; Li, Dong; Sinai, Yakov G.
2017-02-01
By applying methods of statistical physics Li and Sinai (J Eur Math Soc 10:267-313, 2008) proved that there are complex solutions of the Navier-Stokes equations in the whole space R3 which blow up at a finite time. We present a review of the results obtained so far, by theoretical work and computer simulations, for the singular complex solutions, and compare with the behavior of related real solutions. We also discuss the possible application of the techniques introduced in (J Eur Math Soc 10:267-313, 2008) to the study of the real ones.
Optimal propulsive flapping in Stokes flows
Was, Loic
2014-01-01
Swimming fish and flying insects use the flapping of fins and wings to generate thrust. In contrast, microscopic organisms typically deform their appendages in a wavelike fashion. Since a flapping motion with two degrees of freedom is able, in theory, to produce net forces from a time-periodic actuation at all Reynolds number, we compute in this paper the optimal flapping kinematics of a rigid spheroid in a Stokes flow. The hydrodynamics for the force generation and energetics of the flapping motion is solved exactly. We then compute analytically the gradient of a flapping efficiency in the space of all flapping gaits and employ it to derive numerically the optimal flapping kinematics as a function of the shape of the flapper and the amplitude of the motion. The kinematics of optimal flapping are observed to depend weakly on the flapper shape and are very similar to the figure-eight motion observed in the motion of insect wings. Our results suggest that flapping could be a exploited experimentally as a propul...
STOKES FLOW DUE TO FUNDAMENTAL SINGULARITIES BEFORE A PLANE BOUNDARY
Institute of Scientific and Technical Information of China (English)
N.Aktar; F. Rahman; S.K. Sen
2004-01-01
A representation for the velocity and pressure fields in three-dimensional Stokes flow was presented in terms of a biharmonic function A and a harmonic function B. This representation was used to establish a general theorem for the calculation of Stokes flow due to fundamental singularities in a region bounded by a stationary no-slip plane boundary.Collins' s theorem for axisymmetric Stokes flow before a rigid plane follows as a special case of the theorem. A few illustrative examples are given to show its usefulness.
Vanishing viscosity as a selection principle for the Euler equations: The case of 3D shear flow
Bardos, Claude; Wiedemann, Emil
2012-01-01
We show that for a certain family of initial data, there exist non-unique weak solutions to the 3D incompressible Euler equations satisfying the weak energy inequality, whereas the weak limit of every sequence of Leray-Hopf weak solutions for the Navier-Stokes equations, with the same initial data, and as the viscosity tends to zero, is uniquely determined and equals the shear flow solution of the Euler equations. This simple example suggests that, also in more general situations, the vanishing viscosity limit of the Navier-Stokes equations could serve as a uniqueness criterion for weak solutions of the Euler equations.
Mesh Resolution Effect on 3D RANS Turbomachinery Flow Simulations
Yershov, Sergiy
2016-01-01
The paper presents the study of the effect of a mesh refinement on numerical results of 3D RANS computations of turbomachinery flows. The CFD solver F, which based on the second-order accurate ENO scheme, is used in this study. The simplified multigrid algorithm and local time stepping permit decreasing computational time. The flow computations are performed for a number of turbine and compressor cascades and stages. In all flow cases, the successively refined meshes of H-type with an approximate orthogonalization near the solid walls were generated. The results obtained are compared in order to estimate their both mesh convergence and ability to resolve the transonic flow pattern. It is concluded that for thorough studying the fine phenomena of the 3D turbomachinery flows, it makes sense to use the computational meshes with the number of cells from several millions up to several hundred millions per a single turbomachinery blade channel, while for industrial computations, a mesh of about or less than one mil...
Preconditioning for modal discontinuous Galerkin methods for unsteady 3D Navier-Stokes equations
Birken, Philipp; Gassner, Gregor; Haas, Mark; Munz, Claus-Dieter
2013-05-01
We compare different block preconditioners in the context of parallel time adaptive higher order implicit time integration using Jacobian-free Newton-Krylov (JFNK) solvers for discontinuous Galerkin (DG) discretizations of the three dimensional time dependent Navier-Stokes equations. A special emphasis of this work is the performance for a relative high number of processors, i.e. with a low number of elements on the processor. For high order DG discretizations, a particular problem that needs to be addressed is the size of the blocks in the Jacobian. Thus, we propose a new class of preconditioners that exploits the hierarchy of modal basis functions and introduces a flexible order of the off-diagonal Jacobian blocks. While the standard preconditioners 'block Jacobi' (no off-blocks) and full symmetric Gauss-Seidel (full off-blocks) are included as special cases, the reduction of the off-block order results in the new scheme ROBO-SGS. This allows us to investigate the impact of the preconditioner's sparsity pattern with respect to the computational performance. Since the number of iterations is not well suited to judge the efficiency of a preconditioner, we additionally consider CPU time for the comparisons. We found that both block Jacobi and ROBO-SGS have good overall performance and good strong parallel scaling behavior.
A numerical study of the transition to oscillatory flow in 3D lid-driven cubic cavity flows
Chiu, Shang-Huan; He, Jiwen; Guo, Aixia; Glowinski, Roland
2016-01-01
In this article, three dimensional (3D) lid-driven cubic cavity flows have been studied numerically for various values of Reynolds number ($Re$). The numerical solution of the Navier-Stokes equations modeling incompressible viscous fluid flow in a cubic cavity is obtained via a methodology combining a first order accurate operator-splitting, $L^2$-projection Stokes solver, a wave-like equation treatment of the advection and finite element methods. The numerical results obtained for Re$=$400, 1000, and 3200 show a good agreement with available numerical and experimental results in literature. Simulation results predict that the critical Re$_{cr}$ for the transition from steady flow to oscillatory (a Hopf bifurcation) is somewhere in [1870, 1875] for the mesh size $h=1/96$. Via studying the flow field distortion of fluid flow at Re before and after Re$_{cr}$, the occurrence of the first pair of Taylor-G\\"ortler-like vortices is connected to the flow field distortion at the transition from steady flow to oscilla...
Preliminary examples of 3D vector flow imaging
DEFF Research Database (Denmark)
Pihl, Michael Johannes; Stuart, Matthias Bo; Tomov, Borislav Gueorguiev
2013-01-01
and visualized using three alternative approaches. Practically no in-plane motion (vx and vz) is measured, whereas the out-of-plane motion (vy) and the velocity magnitude exhibit the expected 2D circular-symmetric parabolic shape. It shown that the ultrasound method is suitable for real-time data acquisition...... ultrasound scanner SARUS on a flow rig system with steady flow. The vessel of the flow-rig is centered at a depth of 30 mm, and the flow has an expected 2D circular-symmetric parabolic prole with a peak velocity of 1 m/s. Ten frames of 3D vector flow images are acquired in a cross-sectional plane orthogonal...... to the center axis of the vessel, which coincides with the y-axis and the flow direction. Hence, only out-of-plane motion is expected. This motion cannot be measured by typical commercial scanners employing 1D arrays. Each frame consists of 16 flow lines steered from -15 to 15 degrees in steps of 2 degrees...
Slip flow through a converging microchannel: experiments and 3D simulations
Varade, Vijay; Agrawal, Amit; Pradeep, A. M.
2015-02-01
An experimental and 3D numerical study of gaseous slip flow through a converging microchannel is presented in this paper. The measurements reported are with nitrogen gas flowing through the microchannel with convergence angles (4°, 8° and 12°), hydraulic diameters (118, 147 and 177 µm) and lengths (10, 20 and 30 mm). The measurements cover the entire slip flow regime and a part of the continuum and transition regimes (the Knudsen number is between 0.0004 and 0.14); the flow is laminar (the Reynolds number is between 0.5 and 1015). The static pressure drop is measured for various mass flow rates. The overall pressure drop increases with a decrease in the convergence angle and has a relatively large contribution of the viscous component. The numerical solutions of the Navier-Stokes equations with Maxwell’s slip boundary condition explore two different flow behaviors: uniform centerline velocity with linear pressure variation in the initial and the middle part of the microchannel and flow acceleration with nonlinear pressure variation in the last part of the microchannel. The centerline velocity and the wall shear stress increase with a decrease in the convergence angle. The concept of a characteristic length scale for a converging microchannel is also explored. The location of the characteristic length is a function of the Knudsen number and approaches the microchannel outlet with rarefaction. These results on gaseous slip flow through converging microchannels are observed to be considerably different than continuum flow.
DNS of Sheared Particulate Flows with a 3D Explicit Finite-Difference Scheme
Perrin, Andrew; Hu, Howard
2007-11-01
A 3D explicit finite-difference code for direct simulation of the motion of solid particulates in fluids has been developed, and a periodic boundary condition implemented to study the effective viscosity of suspensions in shear. The code enforces the no-slip condition on the surface of spherical particles in a uniform Cartesian grid with a special particle boundary condition based on matching the Stokes flow solutions next to the particle surface with a numerical solution away from it. The method proceeds by approximating the flow next to the particle surface as a Stokes flow in the particle's local coordinates, which is then matched to the finite difference update in the bulk fluid on a ``cage'' of grid points near the particle surface. (The boundary condition is related to the PHYSALIS method (2003), but modified for explicit schemes and with an iterative process removed.) Advantages of the method include superior accuracy of the scheme on a relatively coarse grid for intermediate particle Reynolds numbers, ease of implementation, and the elimination of the need to track the particle surface. For the sheared suspension, the effects of fluid and solid inertia and solid volume fraction on effective viscosity at moderate particle Reynolds numbers and concentrated suspensions will be discussed.
3D couette flow of dusty fluid with transpiration cooling
Institute of Scientific and Technical Information of China (English)
GOVINDARAJAN A.; RAMAMURTHY V.; SUNDARAMMAL K.
2007-01-01
The couette dusty flow between two horizontal parallel porous flat plates with transverse sinusoidal injection of the dusty fluid at the stationary plate and its corresponding removal by constant suction through the plate in uniform motion was analyzed. Due to this type of injection velocity the dusty flow becomes 3D. Perturbation method is used to obtain the expressions for the velocity and temperature fields of both the fluid and dust. It was found that the velocity profiles of both the fluid and dust in the main flow direction decrease with the increase of the mass concentration of the dust panicles, and those in cross flow direction increase with an increase in the mass concentration of the dust particles up to the middle of the channel and thereafter decrease with increase in mass concentration of the dust particles. The skin friction components Tx and Tz in the main flow and transverse directions respectively increase with an increase in the mass concentration of the dust particles (or) injection parameter. The heat transfer coefficient decreases with the increase of the injection parameter and increases with the increase in the mass concentration of the dust particles.
Micro flow cytometer with 3D hydrodynamic focusing
Testa, Genni; Bernini, Romeo
2012-01-01
This paper reports a micro flow cytometer fabricated in Polymethylmethacrylate (PMMA) in which a 3d hydrodynamic flow focusing is employed in order to align the particles in a single line along the focused stream. The device has been fabricated by direct micro milling of two parts of PMMA that were finally bonded together. With a suitable choice of the fluidic channel geometry, a circular sample stream located in the center of the channel is obtained. Numerical simulations have been performed in order to investigate the flow characteristic of the structure and find the desiderated geometry. Three dimensional hydrofocusing of the sample fluid was analysed and demonstrated by cross sectional fluorescence imaging in good agreement with numerical simulations. Flow cytometry measurements have been performed by using 10μm particles. From the analysis of the fluorescence signals collected at each transit event we can confirm that the device was capable of creating a single-file particle stream. The results show that the device was capable of discriminating single microparticles with a good signal-to-noise ratio and a high throughput.
Modeling Electric Current Flow in 3D Fractured Media
Demirel, S.; Roubinet, D.; Irving, J.
2014-12-01
The study of fractured rocks is extremely important in a variety of research fields and applications such as hydrogeology, hydrocarbon extraction and long-term storage of toxic waste. As fractures are highly conductive structures in comparison to the surrounding rock, their presence can be either an advantage or a drawback. For hydrocarbon extraction, fractures allow for quick and easy access to the resource whereas for toxic waste storage their presence increases the risk of leakage and migration of pollutants. In both cases, the identification of fracture network characteristics is an essential step. Recently, we have developed an approach for modeling electric current flow in 2D fractured media. This approach is based on a discrete-dual-porosity model where fractures are represented explicitly, the matrix is coarsely discretized into blocks, and current flow exchange between the fractures and matrix is analytically evaluated at the fracture-scale and integrated at the block-scale [1]. Although this approach has shown much promise and has proven its efficiency for 2D simulations, its extension to 3D remains to be addressed. To this end, we assume that fractures can be represented as two-dimensional finite planes embedded in the surrounding matrix, and we express analytically the distribution of electric potential at the fracture scale. This fracture-scale expression takes into account the electric-current-flow exchange with the surrounding matrix and flow conservation is enforced at the fracture intersections. The fracture-matrix exchange is then integrated at the matrix-block scale where the electric current flow conservation at the block boundaries is formulated with a modified finite volume method. With the objective of providing a low-computational-cost modeling approach adapted to 3D simulations in fractured media, our model is (i) validated and compared to existing modeling approaches and, (ii) used to evaluate the impact of the presence of fractures on
Error estimation and adaptivity in Navier-Stokes incompressible flows
Wu, J.; Zhu, J. Z.; Szmelter, J.; Zienkiewicz, O. C.
1990-07-01
An adaptive remeshing procedure for solving Navier-Stokes incompressible fluid flow problems is presented in this paper. This procedure has been implemented using the error estimator developed by Zienkiewicz and Zhu (1987, 1989) and a semi-implicit time-marching scheme for Navier-Stokes flow problems (Zienkiewicz et al. 1990). Numerical examples are presented, showing that the error estimation and adaptive procedure are capable of monitoring the flow field, updating the mesh when necessary, and providing nearly optimal meshes throughout the calculation, thus making the solution reliable and the computation economical and efficient.
Multilevel local refinement and multigrid methods for 3-D turbulent flow
Energy Technology Data Exchange (ETDEWEB)
Liao, C.; Liu, C. [UCD, Denver, CO (United States); Sung, C.H.; Huang, T.T. [David Taylor Model Basin, Bethesda, MD (United States)
1996-12-31
A numerical approach based on multigrid, multilevel local refinement, and preconditioning methods for solving incompressible Reynolds-averaged Navier-Stokes equations is presented. 3-D turbulent flow around an underwater vehicle is computed. 3 multigrid levels and 2 local refinement grid levels are used. The global grid is 24 x 8 x 12. The first patch is 40 x 16 x 20 and the second patch is 72 x 32 x 36. 4th order artificial dissipation are used for numerical stability. The conservative artificial compressibility method are used for further improvement of convergence. To improve the accuracy of coarse/fine grid interface of local refinement, flux interpolation method for refined grid boundary is used. The numerical results are in good agreement with experimental data. The local refinement can improve the prediction accuracy significantly. The flux interpolation method for local refinement can keep conservation for a composite grid, therefore further modify the prediction accuracy.
Lagragian 3D tracking of fluorescent microscopic objects under flow
Darnige, T; Bohec, P; Lindner, A; Clément, E
2016-01-01
We detail the elaboration of a tracking device mounted on an epifluorescent inverted microscope and suited to obtain time resolved 3D Lagrangian tracks of fluorescent micro-objects. The system is based on a real-time image processing driving a mechanical X-Y stage displacement and a Z refocusing piezo mover such as to keep the designed object at a fixed position in a moving frame. Track coordinates with respect to the microfluidic device, as well as images of the object in the laboratory reference frame are thus obtained at a frequency of several tenths of Hertz. This device is particularly adapted to follow the trajectory of motile micro-organisms in microfluidic devices with or without flow.
Energy flow in passive and active 3D cochlear model
Energy Technology Data Exchange (ETDEWEB)
Wang, Yanli; Steele, Charles [Department of Mechanical Engineering, Stanford University, Stanford, California (United States); Puria, Sunil [Department of Mechanical Engineering, Stanford University, Stanford, California (United States); Department of Otolaryngology, Head and Neck Surgery, Stanford University, Stanford, California (United States)
2015-12-31
Energy flow in the cochlea is an important characteristic of the cochlear traveling wave, and many investigators, such as von Békésy and Lighthill, have discussed this phenomenon. Particularly after the discovery of the motility of the outer hair cells (OHCs), the nature of the power gain of the cochlea has been a fundamental research question. In the present work, direct three-dimensional (3D) calculations of the power on cross sections of the cochlea and on the basilar membrane are performed based on a box model of the mouse cochlea. The distributions of the fluid pressure and fluid velocity in the scala vestibuli are presented. The power output from the OHCs and the power loss due to fluid viscous damping are calculated along the length of the cochlea. This work provides a basis for theoretical calculations of the power gain of the OHCs from mechanical considerations.
Reynolds-stress model prediction of 3-D duct flows
Gerolymos, G A
2014-01-01
The paper examines the impact of different modelling choices in second-moment closures by assessing model performance in predicting 3-D duct flows. The test-cases (developing flow in a square duct [Gessner F.B., Emery A.F.: {\\em ASME J. Fluids Eng.} {\\bf 103} (1981) 445--455], circular-to-rectangular transition-duct [Davis D.O., Gessner F.B.: {\\em AIAA J.} {\\bf 30} (1992) 367--375], and \\tsn{S}-duct with large separation [Wellborn S.R., Reichert B.A., Okiishi T.H.: {\\em J. Prop. Power} {\\bf 10} (1994) 668--675]) include progressively more complex strains. Comparison of experimental data with selected 7-equation models (6 Reynolds-stress-transport and 1 scale-determining equations), which differ in the closure of the velocity/pressure-gradient tensor $\\Pi_{ij}$, suggests that rapid redistribution controls separation and secondary-flow prediction, whereas, inclusion of pressure-diffusion modelling improves reattachment and relaxation behaviour.
Finite element solution of 3-D turbulent Navier-Stokes equations for propeller-driven slender bodies
Thomas, Russell Hicks
1987-12-01
Three-dimensional turbulent flow over the aft end of a slender propeller driven body with the wake from a slender, planar appendage was calculated for 4 configurations. The finite element method in the form of the weak Galerkin formulation with the penalty method was used to solve the Reynolds averaged Navier-Stokes equations. The actual code was FIDAP, modified with a propeller body force and turbulence model, used for the solution. The turbulence model included an Inner Layer Integrated TKE model, and Outer Layer mixing length model, and a Planar Wake model. No separate boundary layer method was used for the body, rather modifications to the Integrated TKE model were made to account for the primary effects of the surface boundary layer on the flow. The flow was calculated at two levels of thrust and corresponding swirl, selfpropelled and 100 percent overthrust, as well as with selfpropelled thrust but no torque simulating an ideal rotor stator combination. Also, the selfpropelled case was calculated with a simplified turbulence model using only the Inner Layer and Planar Wake model. The results compared favorably with experiments.
Dynamics near the subcritical transition of the 3D Couette flow I: Below threshold case
Bedrossian, Jacob; Masmoudi, Nader
2015-01-01
We study small disturbances to the periodic, plane Couette flow in the 3D incompressible Navier-Stokes equations at high Reynolds number $\\textbf{Re}$. We prove that for sufficiently regular initial data of size $\\epsilon \\leq c_0\\textbf{Re}^{-1}$ for some universal $c_0 > 0$, the solution is global, remains within $O(c_0)$ of the Couette flow in $L^2$, and returns to the Couette flow as $t \\rightarrow \\infty$. For times $t \\gtrsim \\textbf{Re}^{1/3}$, the streamwise dependence is damped by a mixing-enhanced dissipation effect and the solution is rapidly attracted to the class of "2.5 dimensional" streamwise-independent solutions referred to as streaks. Our analysis contains perturbations that experience a transient growth of kinetic energy from $O(\\textbf{Re}^{-1})$ to $O(c_0)$ due to the algebraic linear instability known as the lift-up effect. Furthermore, solutions can exhibit a direct cascade of energy to small scales. The behavior is very different from the 2D Couette flow, in which stability is independ...
Ultrasonic 3-D vector flow method for quantitative in vivo peak velocity and flow rate estimation
DEFF Research Database (Denmark)
Holbek, Simon; Ewertsen, Caroline; Bouzari, Hamed;
2017-01-01
Current clinical ultrasound systems are limited to show blood flow movement in either 1-D or 2-D. In this paper, a method for estimating 3-D vector velocities in a plane using the Transverse Oscillation (TO) method, a 32 x 32 element matrix array, and the experimental ultrasound scanner SARUS...... is presented. The aim of this paper is to estimate precise flow rates and peak velocities derived from 3-D vector flow estimates. The emission sequence provides 3-D vector flow estimates at up to 1.145 frames per second in a plane, and was used to estimate 3-D vector flow in a cross sectional image plane....... The method is validated in two phantom studies, where flow rates are measured in a flow-rig, providing a constant parabolic flow, and in a straight-vessel phantom (ø = 8 mm) connected to a flow pump capable of generating time varying waveforms. Flow rates are estimated to be 82.1 ± 2.8 L/min in the flow...
Directory of Open Access Journals (Sweden)
Aiwen Wang
2012-01-01
Full Text Available We investigate an Oseen two-level stabilized finite-element method based on the local pressure projection for the 2D/3D steady Navier-Stokes equations by the lowest order conforming finite-element pairs (i.e., Q1−P0 and P1−P0. Firstly, in contrast to other stabilized methods, they are parameter free, no calculation of higher-order derivatives and edge-based data structures, implemented at the element level with minimal cost. In addition, the Oseen two-level stabilized method involves solving one small nonlinear Navier-Stokes problem on the coarse mesh with mesh size H, a large general Stokes equation on the fine mesh with mesh size h=O(H2. The Oseen two-level stabilized finite-element method provides an approximate solution (uh,ph with the convergence rate of the same order as the usual stabilized finite-element solutions, which involves solving a large Navier-Stokes problem on a fine mesh with mesh size h. Therefore, the method presented in this paper can save a large amount of computational time. Finally, numerical tests confirm the theoretical results. Conclusion can be drawn that the Oseen two-level stabilized finite-element method is simple and efficient for solving the 2D/3D steady Navier-Stokes equations.
Gerke, Kirill; Vasilyev, Roman; Khirevich, Siarhei; Karsanina, Marina; Collins, Daniel; Korost, Dmitry; Mallants, Dirk
2015-04-01
In this contribution we introduce a novel free software which solves the Stokes equation to obtain velocity fields for low Reynolds-number flows within externally generated 3D pore geometries. Provided with velocity fields, one can calculate permeability for known pressure gradient boundary conditions via Darcy's equation. Finite-difference schemes of 2nd and 4th order of accuracy are used together with an artificial compressibility method to iteratively converge to a steady-state solution of Stokes' equation. This numerical approach is much faster and less computationally demanding than the majority of open-source or commercial softwares employing other algorithms (finite elements/volumes, lattice Boltzmann, etc.) The software consists of two parts: 1) a pre and post-processing graphical interface, and 2) a solver. The latter is efficiently parallelized to use any number of available cores (the speedup on 16 threads was up to 10-12 depending on hardware). Due to parallelization and memory optimization our software can be used to obtain solutions for 300x300x300 voxels geometries on modern desktop PCs. The software was successfully verified by testing it against lattice Boltzmann simulations and analytical solutions. To illustrate the software's applicability for numerous problems in Earth Sciences, a number of case studies have been developed: 1) identifying the representative elementary volume for permeability determination within a sandstone sample, 2) derivation of permeability/hydraulic conductivity values for rock and soil samples and comparing those with experimentally obtained values, 3) revealing the influence of the amount of fine-textured material such as clay on filtration properties of sandy soil. This work was partially supported by RSF grant 14-17-00658 (pore-scale modelling) and RFBR grants 13-04-00409-a and 13-05-01176-a.
Gerke, Kirill
2015-04-01
In this contribution we introduce a novel free software which solves the Stokes equation to obtain velocity fields for low Reynolds-number flows within externally generated 3D pore geometries. Provided with velocity fields, one can calculate permeability for known pressure gradient boundary conditions via Darcy\\'s equation. Finite-difference schemes of 2nd and 4th order of accuracy are used together with an artificial compressibility method to iteratively converge to a steady-state solution of Stokes\\' equation. This numerical approach is much faster and less computationally demanding than the majority of open-source or commercial softwares employing other algorithms (finite elements/volumes, lattice Boltzmann, etc.) The software consists of two parts: 1) a pre and post-processing graphical interface, and 2) a solver. The latter is efficiently parallelized to use any number of available cores (the speedup on 16 threads was up to 10-12 depending on hardware). Due to parallelization and memory optimization our software can be used to obtain solutions for 300x300x300 voxels geometries on modern desktop PCs. The software was successfully verified by testing it against lattice Boltzmann simulations and analytical solutions. To illustrate the software\\'s applicability for numerous problems in Earth Sciences, a number of case studies have been developed: 1) identifying the representative elementary volume for permeability determination within a sandstone sample, 2) derivation of permeability/hydraulic conductivity values for rock and soil samples and comparing those with experimentally obtained values, 3) revealing the influence of the amount of fine-textured material such as clay on filtration properties of sandy soil. This work was partially supported by RSF grant 14-17-00658 (pore-scale modelling) and RFBR grants 13-04-00409-a and 13-05-01176-a.
Stokes flow near the contact line of an evaporating drop
Gelderblom, Hanneke; Bloemen, Oscar; Snoeijer, Jacco H.
2011-01-01
The evaporation of sessile drops in quiescent air is usually governed by vapour diffusion. For contact angles below $90^\\circ$, the evaporative flux from the droplet tends to diverge in the vicinity of the contact line. Therefore, the description of the flow inside an evaporating drop has remained a challenge. Here, we focus on the asymptotic behaviour near the pinned contact line, by analytically solving the Stokes equations in a wedge geometry of arbitrary contact angle. The flow field is d...
Generalized Method of Variational Analysis for 3-D Flow
Institute of Scientific and Technical Information of China (English)
兰伟仁; 黄思训; 项杰
2004-01-01
The generalized method of variational analysis (GMVA) suggested for 2-D wind observations by Huang et al. is extended to 3-D cases. Just as in 2-D cases, the regularization idea is applied. But due to the complexity of the 3-D cases, the vertical vorticity is taken as a stable functional. The results indicate that wind observations can be both variationally optimized and filtered. The efficiency of GMVA is also checked in a numerical test. Finally, 3-D wind observations with random disturbances are manipulated by GMVA after being filtered.
Stabilization of Navier-Stokes flows
Barbu, Viorel
2010-01-01
This volume presents recent and notable progress in the mathematical theory of stabilization of Newtonian fluid flows. It avoids the tedious technical details often seen in mathematical treatments of the subject and will thus appeal to a wide range of readers.
Navier-Stokes predictions of multifunction nozzle flows
Wilmoth, Richard G.; Leavitt, Laurence D.
1987-10-01
A two-dimensional, Navier-Stokes code developed by Imlay based on the implicit, finite-volume method of MacCormack has been applied to the prediction of the flow fields and performance of several nonaxisymmetric, convergent-divergent nozzles with and without thrust vectoring. Comparisons of predictions with experiment show that the Navier-Stokes code can accurately predict both the flow fields and performance for nonaxisymmetric nozzles where the flow is predominantly two-dimensional and at nozzle pressure ratios at or above the design values. Discrepancies between predictions and experiment are noted at lower nozzle pressure ratios where separation typically occurs in portions of the nozzle. The overall trends versus parameters such as nozzle pressure ratio, flap angle, and vector angle were generally predicted correctly.
Coupling nonlinear Stokes and Darcy flow using mortar finite elements
Ervin, Vincent J.
2011-11-01
We study a system composed of a nonlinear Stokes flow in one subdomain coupled with a nonlinear porous medium flow in another subdomain. Special attention is paid to the mathematical consequence of the shear-dependent fluid viscosity for the Stokes flow and the velocity-dependent effective viscosity for the Darcy flow. Motivated by the physical setting, we consider the case where only flow rates are specified on the inflow and outflow boundaries in both subdomains. We recast the coupled Stokes-Darcy system as a reduced matching problem on the interface using a mortar space approach. We prove a number of properties of the nonlinear interface operator associated with the reduced problem, which directly yield the existence, uniqueness and regularity of a variational solution to the system. We further propose and analyze a numerical algorithm based on mortar finite elements for the interface problem and conforming finite elements for the subdomain problems. Optimal a priori error estimates are established for the interface and subdomain problems, and a number of compatibility conditions for the finite element spaces used are discussed. Numerical simulations are presented to illustrate the algorithm and to compare two treatments of the defective boundary conditions. © 2010 Published by Elsevier B.V. on behalf of IMACS.
Institute of Scientific and Technical Information of China (English)
Yu.V. STARODUBTSEV; I.G. GOGOLEV; V.G. SOLODOV
2005-01-01
@@ The paper describes 3D numerical Reynolds Averaged Navier-Stokes (RANS) model and approximate sector approach for viscous turbulent flow through flow path of one stage axial supercharge gas turbine of marine diesel engine. Computational data are tested by comparison with experimental data. The back step flow path opening and tip clearance jet are taken into account.This approach could be applied for variety of turbine theory and design tasks: for offer optimal design in order to minimize kinetic energy stage losses; for solution of partial supply problem; for analysis of flow pattern in near extraction stages; for estimation of rotational frequency variable forces on blades; for sector vane adjustment (with thin leading edges mainly), for direct flow modeling in the turbine etc. The development of this work could be seen in the direction of unsteady stage model application.
Steady State Stokes Flow Interpolation for Fluid Control
DEFF Research Database (Denmark)
Bhatacharya, Haimasree; Nielsen, Michael Bang; Bridson, Robert
2012-01-01
Fluid control methods often require surface velocities interpolated throughout the interior of a shape to use the velocity as a feedback force or as a boundary condition. Prior methods for interpolation in computer graphics — velocity extrapolation in the normal direction and potential flow...... — suffer from a common problem. They fail to capture the rotational components of the velocity field, although extrapolation in the normal direction does consider the tangential component. We address this problem by casting the interpolation as a steady state Stokes flow. This type of flow captures...... the rotational components and is suitable for controlling liquid animations where tangential motion is pronounced, such as in a breaking wave...
Wu, Guochun
2017-01-01
In this paper, we investigate the global existence and uniqueness of strong solutions to the initial boundary value problem for the 3D compressible Navier-Stokes equations without heat conductivity in a bounded domain with slip boundary. The global existence and uniqueness of strong solutions are obtained when the initial data is near its equilibrium in H2 (Ω). Furthermore, the exponential convergence rates of the pressure and velocity are also proved by delicate energy methods.
Validation of a Node-Centered Wall Function Model for the Unstructured Flow Code FUN3D
Carlson, Jan-Renee; Vasta, Veer N.; White, Jeffery
2015-01-01
In this paper, the implementation of two wall function models in the Reynolds averaged Navier-Stokes (RANS) computational uid dynamics (CFD) code FUN3D is described. FUN3D is a node centered method for solving the three-dimensional Navier-Stokes equations on unstructured computational grids. The first wall function model, based on the work of Knopp et al., is used in conjunction with the one-equation turbulence model of Spalart-Allmaras. The second wall function model, also based on the work of Knopp, is used in conjunction with the two-equation k-! turbulence model of Menter. The wall function models compute the wall momentum and energy flux, which are used to weakly enforce the wall velocity and pressure flux boundary conditions in the mean flow momentum and energy equations. These wall conditions are implemented in an implicit form where the contribution of the wall function model to the Jacobian are also included. The boundary conditions of the turbulence transport equations are enforced explicitly (strongly) on all solid boundaries. The use of the wall function models is demonstrated on four test cases: a at plate boundary layer, a subsonic di user, a 2D airfoil, and a 3D semi-span wing. Where possible, different near-wall viscous spacing tactics are examined. Iterative residual convergence was obtained in most cases. Solution results are compared with theoretical and experimental data for several variations of grid spacing. In general, very good comparisons with data were achieved.
Dumbbell formation for elastic capsules in nonlinear extensional Stokes flows
Dimitrakopoulos, P.
2017-06-01
Cross-slot and four-roll-mill microdevices are commonly used for particle manipulation and characterization owing to the stagnation-point flow at the device center. Because of the solid boundaries, these devices may generate extensional Stokes flows where the velocity is a nonlinear function of position associated with a decreased pressure at the particle edges and an increased pressure at the particle middle. Our computational investigation shows that in this class of Stokes flows, an elastic capsule made of a strain-hardening membrane develops two distinct steady-state conformations at strong flows, i.e., an elongated weak dumbbell shape with rounded edges at low flow nonlinearity and a laterally extended dumbbell shape at high flow nonlinearity. These effects are more pronounced for the less strain-hardening capsules which develop a flat extended middle where the two sides of the membrane approach each other. The strong stability properties of the strain-hardening capsules (owing to the development of strong membrane tensions) contrast significantly with the behavior of droplets in these nonlinear flows which are unable to achieve highly deformed steady-state dumbbell shapes owing to their constant surface tension.
On the emergence of the Navier-Stokes-α model for turbulent channel flows
Foias, Ciprian; Tian, Jing; Zhang, Bingsheng
2016-08-01
In a series of papers (see Foias et al. [J. Dyn. Differ. Equations 14(1), 1-35 (2002)] and the pertinent references therein), the 3D Navier-Stokes-α model was shown to be a useful complement to the 3D Navier-Stokes equations, and in particular, to be a good Reynolds version of the latter equations. In this work, we introduce a simple Reynolds averaging which, due to the wall roughness, transforms the Navier-Stokes equations into the Navier-Stokes-α model.
Stokes Flow with Slip and Kuwabara Boundary Conditions
Indian Academy of Sciences (India)
Sunil Datta; Satya Deo
2002-08-01
The forces experienced by randomly and homogeneously distributed parallel circular cylinder or spheres in uniform viscous flow are investigated with slip boundary condition under Stokes approximation using particle-in-cell model technique and the result compared with the no-slip case. The corresponding problem of streaming flow past spheroidal particles departing but little in shape from a sphere is also investigated. The explicit expression for the stream function is obtained to the first order in the small parameter characterizing the deformation. As a particular case of this we considered an oblate spheroid and evaluate the drag on it.
Rezania, Vahid; Tuszynski, Jack
2016-01-01
In this paper, we develop a spatio-temporal modeling approach to describe blood and drug flow, as well as drug uptake and elimination, on an approximation of the liver. Extending on previously developed computational approaches, we generate an approximation of a liver, which consists of a portal and hepatic vein vasculature structure, embedded in the surrounding liver tissue. The vasculature is generated via constrained constructive optimization, and then converted to a spatial grid of a selected grid size. Estimates for surrounding upscaled lobule tissue properties are then presented appropriate to the same grid size. Simulation of fluid flow and drug metabolism (hepatic clearance) are completed using discretized forms of the relevant convective-diffusive-reactive partial differential equations for these processes. This results in a single stage, uniformly consistent method to simulate equations for blood and drug flow, as well as drug metabolism, on a 3D structure representative of a liver. PMID:27649537
Stereo Scene Flow for 3D Motion Analysis
Wedel, Andreas
2011-01-01
This book presents methods for estimating optical flow and scene flow motion with high accuracy, focusing on the practical application of these methods in camera-based driver assistance systems. Clearly and logically structured, the book builds from basic themes to more advanced concepts, culminating in the development of a novel, accurate and robust optic flow method. Features: reviews the major advances in motion estimation and motion analysis, and the latest progress of dense optical flow algorithms; investigates the use of residual images for optical flow; examines methods for deriving mot
3D pressure imaging of an aircraft propeller blade-tip flow by phase-locked stereoscopic PIV
Energy Technology Data Exchange (ETDEWEB)
Ragni, D.; Oudheusden, B.W. van; Scarano, F. [Delft University of Technology, Faculty of Aerospace Engineering, Delft (Netherlands)
2012-02-15
The flow field at the tip region of a scaled DHC Beaver aircraft propeller, running at transonic speed, has been investigated by means of a multi-plane stereoscopic particle image velocimetry setup. Velocity fields, phase-locked with the blade rotational motion, are acquired across several planes perpendicular to the blade axis and merged to form a 3D measurement volume. Transonic conditions have been reached at the tip region, with a revolution frequency of 19,800 rpm and a relative free-stream Mach number of 0.73 at the tip. The pressure field and the surface pressure distribution are inferred from the 3D velocity data through integration of the momentum Navier-Stokes equation in differential form, allowing for the simultaneous flow visualization and the aerodynamic loads computation, with respect to a reference frame moving with the blade. The momentum and pressure data are further integrated by means of a contour-approach to yield the aerodynamic sectional force components as well as the blade torsional moment. A steady Reynolds averaged Navier-Stokes numerical simulation of the entire propeller model has been used for comparison to the measurement data. (orig.)
Bardina, J. E.
1994-01-01
A new computational efficient 3-D compressible Reynolds-averaged implicit Navier-Stokes method with advanced two equation turbulence models for high speed flows is presented. All convective terms are modeled using an entropy satisfying higher-order Total Variation Diminishing (TVD) scheme based on implicit upwind flux-difference split approximations and arithmetic averaging procedure of primitive variables. This method combines the best features of data management and computational efficiency of space marching procedures with the generality and stability of time dependent Navier-Stokes procedures to solve flows with mixed supersonic and subsonic zones, including streamwise separated flows. Its robust stability derives from a combination of conservative implicit upwind flux-difference splitting with Roe's property U to provide accurate shock capturing capability that non-conservative schemes do not guarantee, alternating symmetric Gauss-Seidel 'method of planes' relaxation procedure coupled with a three-dimensional two-factor diagonal-dominant approximate factorization scheme, TVD flux limiters of higher-order flux differences satisfying realizability, and well-posed characteristic-based implicit boundary-point a'pproximations consistent with the local characteristics domain of dependence. The efficiency of the method is highly increased with Newton Raphson acceleration which allows convergence in essentially one forward sweep for supersonic flows. The method is verified by comparing with experiment and other Navier-Stokes methods. Here, results of adiabatic and cooled flat plate flows, compression corner flow, and 3-D hypersonic shock-wave/turbulent boundary layer interaction flows are presented. The robust 3-D method achieves a better computational efficiency of at least one order of magnitude over the CNS Navier-Stokes code. It provides cost-effective aerodynamic predictions in agreement with experiment, and the capability of predicting complex flow structures in
On Approximation and Computation of Navier-Stokes Flow
Institute of Scientific and Technical Information of China (English)
VARNHORN Werner; ZANGER Florian
2013-01-01
We present an approximation method for the non-stationary nonlinear incompressible Navier-Stokes equations in a cylindrical domain (0,T)×G,where G （C） IR3is a smoothly bounded domain.Our method is applicable to general three-dimensional flow without any symmetry restrictions and relies on existence,uniqueness and representation results from mathematical fluid dynamics.After a suitable time delay in the nonlinear convective term v·▽v we obtain globally (in time) uniquely solvable equations,which-by using semi-implicit time differences-can be transformed into a finite number of Stokes-type boundary value problems.For the latter a boundary element method based on a corresponding hydrodynamical potential theory is carried out.The method is reported in short outlines ranging from approximation theory up to numerical test calculations.
An elastic two-sphere swimmer in Stokes flow
Nasouri, Babak; Elfring, Gwynn J
2016-01-01
Swimming at low Reynolds number in Newtonian fluids is only possible through non-reciprocal body deformations due to the kinematic reversibility of the Stokes equations. We consider here a model swimmer consisting of two linked spheres, wherein one sphere is rigid and the other an incompressible neo-Hookean solid. The two spheres are connected by a rod which changes its length periodically. We show that the deformations of the body are non-reciprocal despite the reversible actuation and hence, the elastic two-sphere swimmer propels forward. Our results indicate that even weak elastic deformations of a body can qualitatively alter swimming dynamics and should not be neglected in analyzing swimming in Stokes flows.
An elastic two-sphere swimmer in Stokes flow
Nasouri, Babak; Elfring, Gwynn
2016-11-01
Swimming at low Reynolds number in Newtonian fluids is only possible through non-reciprocal body deformations due to the kinematic reversibility of the Stokes equations. We consider here a model swimmer consisting of two linked spheres, wherein one sphere is rigid and the other an incompressible neo-Hookean solid. The two spheres are connected by a rod which changes its length periodically. We show that the deformations of the body are non-reciprocal despite the reversible actuation and hence, the elastic two-sphere swimmer propels forward. Our results indicate that even weak elastic deformations of a body can qualitatively alter swimming dynamics and should not be neglected in analyzing swimming in Stokes flows.
Berselli, Luigi C.; Spirito, Stefano
2017-03-01
In this paper we consider the Navier-Stokes equations supplemented with either the Dirichlet or vorticity-based Navier slip boundary conditions. We prove that weak solutions obtained as limits of solutions of the Navier-Stokes-Voigt model satisfy the local energy inequality, and we also prove certain regularity results for the pressure. Moreover, in the periodic setting we prove that if the parameters are chosen in an appropriate way, then we can construct suitable weak solutions through a Fourier-Galerkin finite-dimensional approximation in the space variables.
Shalaev, V. I.
2016-10-01
Singularities appearing in solutions of 3D laminar boundary layer (BL) equations, when two streamline families are collided, are discussed. For conical bodies, equations are investigated using asymptotic methods. Analytical solutions are obtained for the outer BL region; their singularities in the runoff plane are studied. The asymptotic flow structure near the singularity is constructed on the base of Navier-Stokes equations at large Reynolds numbers. For different flow regions analytical solutions are found and are matched with BL equation solutions. Properties of BL equations for the near-wall region in the runoff plane are investigated and a criterion of the solution disappearing is found. It is shown that this criterion separates two different topological flow structures and corresponds to the singularity appearance in this plane in solutions of full equations. Calculations confirmed obtained results are presented.
Implementation for blow up of tornado-type solutions for complex version of 3D Navier-Stokes system
Arnold, M D
2008-01-01
We consider Cauchy problem for Fourier transformation of 3-dimensional Navier-Stokes system with zero external force. Using initial data purposed by Dong Li and Ya.G.Sinai we implement self-similar regime producing fast growing behavior of the energy of solution while time tends to critical value.
Institute of Scientific and Technical Information of China (English)
LI Jun; LIU Li-jun; FENG Zhen-ping
2004-01-01
Hydrodynamic optimization design of the bend pipe from pump using the Navier-Stokes solver and evolutionary algorithms was conducted. The minimization of the total pressure loss of the bend pipe was chosen as the design object in order to obtain the uniform exit flows through suppressing the secondary flows. The 3-D Navier-Stokes solver was applied to evaluate the hydrodynamic performance of the bend-pipe flows. A 7th-order Bezier curve was used to parameterize the meridional section and elliptic representation was adopted to represent the cross-section profiles of the bend pipe. Evolutionary algorithms were applied in optimization. The obtained results show that the designed bend pipe shape has much more uniform exit flows compared with the initial one and much weaker secondary flows, and that the evolutionary algorithms and CFD technique are the powerful optimization tools for the fluid machinery design.
Energy Technology Data Exchange (ETDEWEB)
Rusanov, A.V.; Yershov, S.V. [Institute of Mechanical Engineering Problems of National Academy of Sciences of Ukraine Kharkov (Ukraine)
1997-12-31
The numerical method is suggested for the calculation of the 3D periodically unsteady viscous cascade flow evoked by the aerodynamics interaction of blade rows. Such flow is described by the thin-layer Reynolds-averaged unsteady Navier-Stokes equations. The turbulent effects are simulated with the modified Baldwin-Lomax turbulence model. The problem statement allows to consider an unsteady flow through either a single turbo-machine stage or a multi stage turbomachine. The sliding mesh techniques and the time-space non-oscillatory square interpolation are used in axial spacings to calculate the flow in a computational domain that contains the reciprocally moving elements. The gasdynamical equations are integrated numerically with the implicit quasi-monotonous Godunov`s type ENO scheme of the second or third order of accuracy. The suggested numerical method is incorporated in the FlowER code developed by authors for calculations of the 3D viscous compressible flows through multi stage turbomachines. The numerical results are presented for unsteady turbine stage throughflows. The method suggested is shown to simulate qualitatively properly the main unsteady cascade effects in particular the periodically blade loadings, the propagation of stator wakes through rotor blade passage and the unsteady temperature flowfields for stages with cooled stator blades. (author) 21 refs.
Navier–Stokes flow in converging–diverging distensible tubes
Directory of Open Access Journals (Sweden)
Taha Sochi
2015-09-01
Full Text Available We use a method based on the lubrication approximation in conjunction with a residual-based mass-continuity iterative solution scheme to compute the flow rate and pressure field in distensible converging–diverging tubes for Navier–Stokes fluids. We employ an analytical formula derived from a one-dimensional version of the Navier–Stokes equations to describe the underlying flow model that provides the residual function. This formula correlates the flow rate to the boundary pressures in straight cylindrical elastic tubes with constant-radius. We validate our findings by the convergence toward a final solution with fine discretization as well as by comparison to the Poiseuille-type flow in its convergence toward analytic solutions found earlier in rigid converging–diverging tubes. We also tested the method on limiting special cases of cylindrical elastic tubes with constant-radius where the numerical solutions converged to the expected analytical solutions. The distensible model has also been endorsed by its convergence toward the rigid Poiseuille-type model with increasing the tube wall stiffness. Lubrication-based one-dimensional finite element method was also used for verification. In this investigation five converging–diverging geometries are used for demonstration, validation and as prototypes for modeling converging–diverging geometries in general.
Parallel Simulation of 3-D Turbulent Flow Through Hydraulic Machinery
Institute of Scientific and Technical Information of China (English)
徐宇; 吴玉林
2003-01-01
Parallel calculational methods were used to analyze incompressible turbulent flow through hydraulic machinery. Two parallel methods were used to simulate the complex flow field. The space decomposition method divides the computational domain into several sub-ranges. Parallel discrete event simulation divides the whole task into several parts according to their functions. The simulation results were compared with the serial simulation results and particle image velocimetry (PIV) experimental results. The results give the distribution and configuration of the complex vortices and illustrate the effectiveness of the parallel algorithms for numerical simulation of turbulent flows.
An implementation of the LHCb level 0 muon trigger using the 3D-Flow ASIC
Corti, G; Crosetto, D; Nelson, K
1998-01-01
The implementation of the LHCb level 0 muon trigger using the 3D-flow technique is discussed. The connection of the LHCb muon detector front-end electronics to the L0 3D-flow processor is also discussed.1
Angelidis, Dionysios; Chawdhary, Saurabh; Sotiropoulos, Fotis
2016-11-01
A novel numerical method is developed for solving the 3D, unsteady, incompressible Navier-Stokes equations on locally refined fully unstructured Cartesian grids in domains with arbitrarily complex immersed boundaries. Owing to the utilization of the fractional step method on an unstructured Cartesian hybrid staggered/non-staggered grid layout, flux mismatch and pressure discontinuity issues are avoided and the divergence free constraint is inherently satisfied to machine zero. Auxiliary/hanging nodes are used to facilitate the discretization of the governing equations. The second-order accuracy of the solver is ensured by using multi-dimension Lagrange interpolation operators and appropriate differencing schemes at the interface of regions with different levels of refinement. The sharp interface immersed boundary method is augmented with local near-boundary refinement to handle arbitrarily complex boundaries. The discrete momentum equation is solved with the matrix free Newton-Krylov method and the Krylov-subspace method is employed to solve the Poisson equation. The second-order accuracy of the proposed method on unstructured Cartesian grids is demonstrated by solving the Poisson equation with a known analytical solution. A number of three-dimensional laminar flow simulations of increasing complexity illustrate the ability of the method to handle flows across a range of Reynolds numbers and flow regimes. Laminar steady and unsteady flows past a sphere and the oblique vortex shedding from a circular cylinder mounted between two end walls demonstrate the accuracy, the efficiency and the smooth transition of scales and coherent structures across refinement levels. Large-eddy simulation (LES) past a miniature wind turbine rotor, parameterized using the actuator line approach, indicates the ability of the fully unstructured solver to simulate complex turbulent flows. Finally, a geometry resolving LES of turbulent flow past a complete hydrokinetic turbine illustrates
Segmented Domain Decomposition Multigrid For 3-D Turbomachinery Flows
Celestina, M. L.; Adamczyk, J. J.; Rubin, S. G.
2001-01-01
A Segmented Domain Decomposition Multigrid (SDDMG) procedure was developed for three-dimensional viscous flow problems as they apply to turbomachinery flows. The procedure divides the computational domain into a coarse mesh comprised of uniformly spaced cells. To resolve smaller length scales such as the viscous layer near a surface, segments of the coarse mesh are subdivided into a finer mesh. This is repeated until adequate resolution of the smallest relevant length scale is obtained. Multigrid is used to communicate information between the different grid levels. To test the procedure, simulation results will be presented for a compressor and turbine cascade. These simulations are intended to show the ability of the present method to generate grid independent solutions. Comparisons with data will also be presented. These comparisons will further demonstrate the usefulness of the present work for they allow an estimate of the accuracy of the flow modeling equations independent of error attributed to numerical discretization.
Laser direct writing 3D structures for microfluidic channels: flow meter and mixer
Lin, Chih-Lang; Liu, Yi-Jui; Lin, Zheng-Da; Wu, Bo-Long; Lee, Yi-Hsiung; Shin, Chow-Shing; Baldeck, Patrice L.
2015-03-01
The 3D laser direct-writing technology is aimed at the modeling of arbitrary three-dimensional (3D) complex microstructures by scanning a laser-focusing point along predetermined trajectories. Through the perspective technique, the details of designed 3D structures can be properly fabricated in a microchannel. This study introduces a direct reading flow meter and a 3D passive mixer fabricated by laser direct writing for microfluidic applications. The flow meter consists of two rod-shaped springs, a pillar, an anchor, and a wedge-shaped indicator, installed inside a microfluidic channel. The indicator is deflected by the flowing fluid while restrained by the spring to establish an equilibrium indication according to the flow rate. The measurement is readily carried out by optical microscopy observation. The 3D passive Archimedes-screw-shaped mixer is designed to disturb the laminar flow 3D direction for enhancing the mixing efficiency. The simulation results indicate that the screw provides 3D disturbance of streamlines in the microchannel. The mixing demonstration for fluids flowing in the micrchannel approximately agrees with the simulation result. Thanks to the advantage of the laser direct writing technology, this study performs the ingenious applications of 3D structures for microchannels.
Comparison of OpenFOAM and EllipSys3D for neutral atmospheric flow over complex terrain
DEFF Research Database (Denmark)
Cavar, Dalibor; Réthoré, Pierre-Elouan; Bechmann, Andreas;
2016-01-01
The flow solvers OpenFOAM and EllipSys3D are compared in the case of neutral atmospheric flow over terrain using the test cases of Askervein and Bolund hills. Both solvers are run using the steady-state Reynolds-averaged Navier–Stokes k– turbulence model. One of the main modeling differences...... between the two solvers is the wall-function approach. The Open-FOAM v.1.7.1 uses a Nikuradse’s sand roughness model, while EllipSys3D uses a model based on the atmospheric roughness length. It is found that Nikuradse’s model introduces an error dependent on the near-wall cell height. To mitigate...... this error the near-wall cells should be at least 10 times larger than the surface roughness. It is nonetheless possible to obtain very similar results between EllipSys3D and OpenFOAM v.1.7.1. The more recent OpenFOAM v.2.2.1, which includes the atmospheric roughness length wall-function approach, has also...
Simulation of 3D Flow in Turbine Blade Rows including the Effects of Coolant Ejection
Institute of Scientific and Technical Information of China (English)
Jian-Jun LIU; Bai-Tao AN; Yun-Tao ZENG
2008-01-01
This paper describes the numerical simulation of three-dimensional viscous flows in air-cooled turbine blade rows with the effects of coolant ejection. A TVD Navier-Stokes flow solver incorporated with Baldwin-Lomax turbulence model and multi-grid convergence acceleration algorithm are used for the simulation. The influences of coolant ejection on the main flow are accounted by volumetric coolant source terms. Numerical results for a four-stage turbine are presented and discussed.
Hydrodynamics beyond Navier-Stokes: the slip flow model.
Yudistiawan, Wahyu P; Ansumali, Santosh; Karlin, Iliya V
2008-07-01
Recently, analytical solutions for the nonlinear Couette flow demonstrated the relevance of the lattice Boltzmann (LB) models to hydrodynamics beyond the continuum limit [S. Ansumali, Phys. Rev. Lett. 98, 124502 (2007)]. In this paper, we present a systematic study of the simplest LB kinetic equation-the nine-bit model in two dimensions--in order to quantify it as a slip flow approximation. Details of the aforementioned analytical solution are presented, and results are extended to include a general shear- and force-driven unidirectional flow in confined geometry. Exact solutions for the velocity, as well as for pertinent higher-order moments of the distribution functions, are obtained in both Couette and Poiseuille steady-state flows for all values of rarefaction parameter (Knudsen number). Results are compared with the slip flow solution by Cercignani, and a good quantitative agreement is found for both flow situations. Thus, the standard nine-bit LB model is characterized as a valid and self-consistent slip flow model for simulations beyond the Navier-Stokes approximation.
3D Reacting Flow Analysis of LANTR Nozzles
Stewart, Mark E. M.; Krivanek, Thomas M.; Hemminger, Joseph A.; Bulman, M. J.
2006-01-01
This paper presents performance predictions for LANTR nozzles and the system implications for their use in a manned Mars mission. The LANTR concept is rocket thrust augmentation by injecting Oxygen into the nozzle to combust the Hydrogen exhaust of a Nuclear Thermal Rocket. The performance predictions are based on three-dimensional reacting flow simulations using VULCAN. These simulations explore a range of O2/H2 mixture ratios, injector configurations, and concepts. These performance predictions are used for a trade analysis within a system study for a manned Mars mission. Results indicate that the greatest benefit of LANTR will occur with In-Situ Resource Utilization (ISRU). However, Hydrogen propellant volume reductions may allow greater margins for fitting tanks within the launch vehicle where packaging issues occur.
3d Forced multiphase flow on the pore scale
Scholl, Hagen; Singh, Kamaljit; Scheel, Mario; Dimichiel, Marco; Herminghaus, Stephan; Seemann, Ralf
2013-11-01
Using ultra fast x-ray tomography the forced imbibition of an aqueous phase into an initially oil filled matrix is studied. The water is volume controlled flushed into cylindrical columns filled with oil saturated spherical bead packs. The oil displacement is imaged in real time having a spacial resolution of 11 microns and a temporal resolution of about 1 second. To clearly distinguish the aqueous from the oily phase a contrast agent was added to the aqueous phase. The influence of wettability, oil viscosity, gravity and flow velocity was explored and analyzed in terms of temporal development of oil saturation and front shape. It turned out that capillary forces are the key to understand the forced multiphase behavior in the explored parameter range. Funding was provided by the BP-ExploRe project.
Numerical simulation of 3D backward facing step flows at various Reynolds numbers
Directory of Open Access Journals (Sweden)
Louda Petr
2015-01-01
Full Text Available The work deals with the numerical simulation of 3D turbulent flow over backward facing step in a narrow channel. The mathematical model is based on the RANS equations with an explicit algebraic Reynolds stress model (EARSM. The numerical method uses implicit finite volume upwind discretization. While the eddy viscosity models fail in predicting complex 3D flows, the EARSM model is shown to provide results which agree well with experimental PIV data. The reference experimental data provide the 3D flow field. The simulations are compared with experiment for 3 values of Reynolds number.
Multi-GPU three dimensional Stokes solver for simulating glacier flow
Licul, Aleksandar; Herman, Frédéric; Podladchikov, Yuri; Räss, Ludovic; Omlin, Samuel
2016-04-01
Here we present how we have recently developed a three-dimensional Stokes solver on the GPUs and apply it to a glacier flow. We numerically solve the Stokes momentum balance equations together with the incompressibility equation, while also taking into account strong nonlinearities for ice rheology. We have developed a fully three-dimensional numerical MATLAB application based on an iterative finite difference scheme with preconditioning of residuals. Differential equations are discretized on a regular staggered grid. We have ported it to C-CUDA to run it on GPU's in parallel, using MPI. We demonstrate the accuracy and efficiency of our developed model by manufactured analytical solution test for three-dimensional Stokes ice sheet models (Leng et al.,2013) and by comparison with other well-established ice sheet models on diagnostic ISMIP-HOM benchmark experiments (Pattyn et al., 2008). The results show that our developed model is capable to accurately and efficiently solve Stokes system of equations in a variety of different test scenarios, while preserving good parallel efficiency on up to 80 GPU's. For example, in 3D test scenarios with 250000 grid points our solver converges in around 3 minutes for single precision computations and around 10 minutes for double precision computations. We have also optimized the developed code to efficiently run on our newly acquired state-of-the-art GPU cluster octopus. This allows us to solve our problem on more than 20 million grid points, by just increasing the number of GPU used, while keeping the computation time the same. In future work we will apply our solver to real world applications and implement the free surface evolution capabilities. REFERENCES Leng,W.,Ju,L.,Gunzburger,M. & Price,S., 2013. Manufactured solutions and the verification of three-dimensional stokes ice-sheet models. Cryosphere 7,19-29. Pattyn, F., Perichon, L., Aschwanden, A., Breuer, B., de Smedt, B., Gagliardini, O., Gudmundsson,G.H., Hindmarsh, R
EXPERIMENTAL STUDY OF 3-D TURBULENT BEND FLOWS IN OPEN CHANNEL
Institute of Scientific and Technical Information of China (English)
LIU Yue-qin; ZHENG Shao-wen; WU Qiang
2005-01-01
A generalized bend flow model, treating a 90° single bend and 60° continuous bends, was designed to quantitatively describe 3-D turbulence mechanism of circulating not-fully-developed flow in open channels with bends.The 3-D fluctuating velocities of turbulent flow were measured and analyzed with a 3-D acoustic-Doppler velocimeter.Formula for 3-D turbulent intensity was derived using the dimension analysis approach.Expressions of vertical turbulent-intensity distributions were obtained with the multivariant-regression theory, which agree with experiment data.Distributions of turbulent intensity and turbulent stress were characterized, and their relationships were concluded.In the bend-turbulent-flow core region, longitudinal and lateral turbulent-intensity distributions are coincident with linear distribution, but in near-wall region are coincident with the Gamma distribution.Vertical turbulent intensity distributions are coincident with the Rayleigh distribution.Herein, it is concluded that the bend turbulence is anisotropic.
A continuous flow microfluidic calorimeter: 3-D numerical modeling with aqueous reactants
Sen, Mehmet A.; Kowalski, Gregory J.; Fiering, Jason; Larson, Dale
2015-01-01
A computational analysis of the reacting flow field, species diffusion and heat transfer processes with thermal boundary layer effects in a microchannel reactor with a coflow configuration was performed. Two parallel adjacent streams of aqueous reactants flow along a wide, shallow, enclosed channel in contact with a substrate, which is affixed to a temperature controlled plate. The Fluent computational fluid dynamics package solved the Navier–Stokes, mass transport and energy equations. The e...
Axisymmetric and 3D calculations of melt flow during VCz growth
Bänsch, E.; Davis, D.; Langmach, H.; Miller, W.; Rehse, U.; Reinhardt, G.; Uhle, M.
2004-05-01
Axisymmetric and 3D calculations of melt flow have been performed for a configuration used at the vapour-pressure-controlled Czochalski growth of GaAs single crystals. Thermal boundary conditions were adapted from a global simulation of the temperature field. The axisymmetric calculations with the code NAVIER confirmed the ones previously perfomed with FIDAP TM. The 3D calculations showed that the flow exhibits an asymmetric transient behaviour beyond a certain critical Reynolds number.
Propulsion of micro-structures in Oscillatory Stokes Flow
Jo, Ikhee; Huang, Yangyang; Zimmerman, Walter; Kanso, Eva
2015-11-01
Drug delivery often necessitates specific site-targeting within the human body. The use of micro and/or nano devices swimming through the bloodstream provides an attractive mechanism for targeted drug targeting, however the design and practical implementation of such devices remain very challenging. Inspired by flapping wings, we construct a two-dimensional wedge-like device, consisting of two links connected by a linear torsional spring and released in an oscillatory Stokes flow. We vary the stiffness and rest angle of the linear spring and the oscillation amplitude and frequency of the background flow to explore the behavior of the device. We find that the device achieves a net displacement, or propulsion, in oscillatory flows even when no elastic energy is stored initially, thus breaking Purcell's scallop's theorem. More importantly, the vehicle tends to align with the background flow under perturbations. We conclude by commenting on how to control the parameters of the device and the fluid to achieve desired behavior of the device. These findings may have significant implications on the design of micro devices in viscous fluids.
Determining 3D flow fields via multi-camera light field imaging.
Truscott, Tadd T; Belden, Jesse; Nielson, Joseph R; Daily, David J; Thomson, Scott L
2013-03-06
In the field of fluid mechanics, the resolution of computational schemes has outpaced experimental methods and widened the gap between predicted and observed phenomena in fluid flows. Thus, a need exists for an accessible method capable of resolving three-dimensional (3D) data sets for a range of problems. We present a novel technique for performing quantitative 3D imaging of many types of flow fields. The 3D technique enables investigation of complicated velocity fields and bubbly flows. Measurements of these types present a variety of challenges to the instrument. For instance, optically dense bubbly multiphase flows cannot be readily imaged by traditional, non-invasive flow measurement techniques due to the bubbles occluding optical access to the interior regions of the volume of interest. By using Light Field Imaging we are able to reparameterize images captured by an array of cameras to reconstruct a 3D volumetric map for every time instance, despite partial occlusions in the volume. The technique makes use of an algorithm known as synthetic aperture (SA) refocusing, whereby a 3D focal stack is generated by combining images from several cameras post-capture (1). Light Field Imaging allows for the capture of angular as well as spatial information about the light rays, and hence enables 3D scene reconstruction. Quantitative information can then be extracted from the 3D reconstructions using a variety of processing algorithms. In particular, we have developed measurement methods based on Light Field Imaging for performing 3D particle image velocimetry (PIV), extracting bubbles in a 3D field and tracking the boundary of a flickering flame. We present the fundamentals of the Light Field Imaging methodology in the context of our setup for performing 3DPIV of the airflow passing over a set of synthetic vocal folds, and show representative results from application of the technique to a bubble-entraining plunging jet.
Three-dimensional potential flows from functions of a 3D complex variable
Kelly, Patrick; Panton, Ronald L.; Martin, E. D.
1990-01-01
Potential, or ideal, flow velocities can be found from the gradient of an harmonic function. An ordinary complex valued analytic function can be written as the sum of two real valued functions, both of which are harmonic. Thus, 2D complex valued functions serve as a source of functions that describe two-dimensional potential flows. However, this use of complex variables has been limited to two-dimensions. Recently, a new system of three-dimensional complex variables has been developed at the NASA Ames Research Center. As a step toward application of this theory to the analysis of 3D potential flow, several functions of a three-dimensional complex variable have been investigated. The results for two such functions, the 3D exponential and 3D logarithm, are presented in this paper. Potential flows found from these functions are investigated. Important characteristics of these flows fields are noted.
Computational studies of hard-body and 3-D effects in plume flows
Venkatapathy, Ethiraj; Feiereisen, William J.; Obayashi, Shigeru
1989-01-01
Axisymmetric and three-dimensional, multi-nozzle plume flows around generic rocket geometries are investigated with a three-dimensional Navier-Stokes solver to study the interactive effects between hard body and the plume. Time-asymptotic, laminar, ideal-gas solutions obtained with a two-factor, flux-split scheme and a diagonal, upwind scheme are presented. Computed solutions to three-dimensional, multi-nozzle problems and single-nozzle, axisymmetric problems demonstrate flow field features including three-dimensionality and hard-body effects. Geometry and three-dimensional effects are shown to be significant in multi-nozzle flows.
3D-printed devices for continuous-flow organic chemistry
Directory of Open Access Journals (Sweden)
Vincenza Dragone
2013-05-01
Full Text Available We present a study in which the versatility of 3D-printing is combined with the processing advantages of flow chemistry for the synthesis of organic compounds. Robust and inexpensive 3D-printed reactionware devices are easily connected using standard fittings resulting in complex, custom-made flow systems, including multiple reactors in a series with in-line, real-time analysis using an ATR-IR flow cell. As a proof of concept, we utilized two types of organic reactions, imine syntheses and imine reductions, to show how different reactor configurations and substrates give different products.
3D-printed devices for continuous-flow organic chemistry
Dragone, Vincenza; Sans, Victor; Rosnes, Mali H; Kitson, Philip J
2013-01-01
Summary We present a study in which the versatility of 3D-printing is combined with the processing advantages of flow chemistry for the synthesis of organic compounds. Robust and inexpensive 3D-printed reactionware devices are easily connected using standard fittings resulting in complex, custom-made flow systems, including multiple reactors in a series with in-line, real-time analysis using an ATR-IR flow cell. As a proof of concept, we utilized two types of organic reactions, imine syntheses and imine reductions, to show how different reactor configurations and substrates give different products. PMID:23766811
The performance & flow visualization studies of three-dimensional (3-D) wind turbine blade models
Sutrisno, Prajitno, Purnomo, W., Setyawan B.
2016-06-01
Recently, studies on the design of 3-D wind turbine blades have a less attention even though 3-D blade products are widely sold. In contrary, advanced studies in 3-D helicopter blade tip have been studied rigorously. Studies in wind turbine blade modeling are mostly assumed that blade spanwise sections behave as independent two-dimensional airfoils, implying that there is no exchange of momentum in the spanwise direction. Moreover, flow visualization experiments are infrequently conducted. Therefore, a modeling study of wind turbine blade with visualization experiment is needed to be improved to obtain a better understanding. The purpose of this study is to investigate the performance of 3-D wind turbine blade models with backward-forward swept and verify the flow patterns using flow visualization. In this research, the blade models are constructed based on the twist and chord distributions following Schmitz's formula. Forward and backward swept are added to the rotating blades. Based on this, the additional swept would enhance or diminish outward flow disturbance or stall development propagation on the spanwise blade surfaces to give better blade design. Some combinations, i. e., b lades with backward swept, provide a better 3-D favorable rotational force of the rotor system. The performance of the 3-D wind turbine system model is measured by a torque meter, employing Prony's braking system. Furthermore, the 3-D flow patterns around the rotating blade models are investigated by applying "tuft-visualization technique", to study the appearance of laminar, separated, and boundary layer flow patterns surrounding the 3-dimentional blade system.
Quantification of blood perfusion using 3D power Doppler: an in-vitro flow phantom study
Raine-Fenning, N. J.; Ramnarine, K. V.; Nordin, N. M.; Campbell, B. K.
2004-01-01
Three-dimensional (3D) power Doppler data is increasingly used to assess and quantify blood flow and tissue perfusion. The objective of this study was to assess the validity of common 3D power Doppler vascularity indices by quantification in well characterised in-vitro flow models. A computer driven gear pump was used to circulate a steady flow of a blood mimicking fluid through various well characterised flow phantoms to investigate the effect of the number of flow channels, flow rate, depth dependent tissue attenuation, blood mimic scatter particle concentration and ultrasound settings. 3D Power Doppler data were acquired with a Voluson 530D scanner and 7.5 MHz transvaginal transducer (GE Kretz). Virtual Organ Computer-aided Analysis software (VOCAL) was used to quantify the vascularisation index (VI), flow index (FI) and vascularisation-flow index (VFI). The vascular indices were affected by many factors, some intuitive and some with more complex or unexpected relationships (e.g. VI increased linearly with an increase in flow rate, blood mimic scatter particle concentration and number of flow channels, and had a complex dependence on pulse repetition frequency). Use of standardised settings and appropriate calibration are required in any attempt at relating vascularity indices with flow.
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz
2000-01-01
The 3D-LIM has as yet been used to simulate the following two three-dimensional problems. First, the method has been used to simulete for viscoelastic end-plate instability that occurs under certain conditions in the transient filament stretching apparatus for pressure sensitive adhesives...... (polymeric melts) and polymeric solutions. Secondly, the 3D-LIM has also been applied to calculate the inflation of a thick sheet of a polymer melt into an elliptic cylinder. These problems all include free surfaces. As the governing equations are solved for the particle positions, the motion of surfaces can...... be followed easily even in 3D viscoelastic flow....
Institute of Scientific and Technical Information of China (English)
裴吉; 袁寿其; 李晓俊; 袁建平
2014-01-01
Numerical simulation and 3-D periodic flow unsteadiness analysis for a centrifugal pump with volute are carried out in whole flow passage, including the impeller with twisted blades, the volute and the side chamber channels under a part-load condition. The pressure fluctuation intensity coefficient (PFIC) based on the standard deviation method, the time-averaged velocity unsteadi-ness intensity coefficient (VUIC) and the time-averaged turbulence intensity coefficient (TIC) are defined by averaging the results at each grid node for an entire impeller revolution period. Therefore, the strength distributions of the periodic flow unsteadiness based on the unsteady Reynolds-averaged Navier-Stokes (URANS) equations can be analyzed directly and in detail. It is shown that under the des.0.6Q condition, the pressure fluctuation intensity is larger near the blade pressure side than near the suction side, and a high fluctuation intensity can be observed at the beginning section of the spiral of the volute. The flow velocity unsteadiness intensity is larger near the blade suction side than near the pressure side. A strong turbulence intensity can be found near the blade suction side, the impeller shroud side as well as in the side chamber. The leakage flow has a significant effect on the inflow of the impeller, and can increase both the flow velocity unsteadiness intensity and the turbulence intensity near the wall. The accumulative flow unstea-diness results of an impeller revolution can be an important aspect to be considered in the centrifugal pump optimum design for ob-taining a more stable inner flow of the pump and reducing the flow-induced vibration and noise in certain components.
Directory of Open Access Journals (Sweden)
N. Wilkens
2014-09-01
Full Text Available Pine Island Glacier is one of the fastest changing glaciers in the Antarctic Ice Sheet and therefore in scientific focus. The glacier holds enough ice to raise global sea level significantly (∼0.5 m, when fully melted. The question addressed by numerous modelling studies of the glacier focuses on whether the observed changes are a start for an uncontrolled and accelerating retreat. The movement of the glacier is, in the fast flowing areas, dominated by basal motion. In modelling studies the parametrisation of the basal motion is therefore crucial. Inversion methods are commonly applied to reproduce the complex surface flow structure at Pine Island Glacier, which use information of the observed surface velocity field, to constrain basal sliding. We introduce two different approaches of combining a physical parameter, the basal roughness, with basal sliding parametrisations. This way basal sliding is connected again to its original formulation. We show that the basal roughness is an important and helpful parameter to consider and that many features of the flow structure could be reproduced with these approaches.
Recursive estimation of 3D motion and surface structure from local affine flow parameters.
Calway, Andrew
2005-04-01
A recursive structure from motion algorithm based on optical flow measurements taken from an image sequence is described. It provides estimates of surface normals in addition to 3D motion and depth. The measurements are affine motion parameters which approximate the local flow fields associated with near-planar surface patches in the scene. These are integrated over time to give estimates of the 3D parameters using an extended Kalman filter. This also estimates the camera focal length and, so, the 3D estimates are metric. The use of parametric measurements means that the algorithm is computationally less demanding than previous optical flow approaches and the recursive filter builds in a degree of noise robustness. Results of experiments on synthetic and real image sequences demonstrate that the algorithm performs well.
Improvements on digital inline holographic PTV for 3D wall-bounded turbulent flow measurements
Toloui, Mostafa; Mallery, Kevin; Hong, Jiarong
2017-04-01
Three-dimensional (3D) particle image velocimetry (PIV) and particle tracking velocimetry (PTV) provide the most comprehensive flow information for unraveling the physical phenomena in a wide range of fluid problems, from microfluidics to wall-bounded turbulent flows. Compared with other 3D PIV techniques, such as tomographic PIV and defocusing PIV, the digital inline holographic PTV (DIH-PTV) provides 3D flow measurement solution with high spatial resolution, low cost optical setup, and easy alignment and calibration. Despite these advantages, DIH-PTV suffers from major limitations including poor longitudinal resolution, human intervention (i.e. requirement for manually determined tuning parameters during tracer field reconstruction and extraction), limited tracer concentration, small sampling volume and expensive computations, limiting its broad use for 3D flow measurements. In this study, we present our latest developments on minimizing these challenges, which enables high-fidelity DIH-PTV implementation to larger sampling volumes with significantly higher particle seeding densities suitable for wall-bounded turbulent flow measurements. The improvements include: (1) adjustable window thresholding; (2) multi-pass 3D tracking; (3) automatic wall localization; and (4) continuity-based out-of-plane velocity component computation. The accuracy of the proposed DIH-PTV method is validated with conventional 2D PIV and double-view holographic PTV measurements in smooth-wall turbulent channel flow experiments. The capability of the technique in characterization of wall-bounded turbulence is further demonstrated through its application to flow measurements for smooth- and rough-wall turbulent channel flows. In these experiments, 3D velocity fields are measured within sampling volumes of 14.7 × 50.0 × 14.4 mm3 (covering the entire depth of the channel) with a velocity resolution of presented DIH-PTV method and measurements highlight the
Islam, Md Zahurul
In this thesis, development of a novel microfluidic flow model, and, fabrication and testing of microfluidic cytometer for potential cell detection and sorting applications are described. The model is formulated by decomposing the flow profile along the height of microfluidic device into a Fourier series that converts the 3D flow equations into a series of coupled 2D equations and is applicable to planar microfluidic devices only. It is validated against the analytical solution for flow in a straight rectangular channel and the full 3D solution of a commercial Navier-Stokes solver for flow in a T-channel. Comparable accuracy to the full 3D numerical solution is achieved by using only three Fourier terms with significant decrease in computation time. The model is also extended to the problems with time-varying boundary conditions. We fabricated two first generation miniaturized cytometer prototypes and used them for preliminary proof-of-concepts experiments. They were built by cutting fluidic channels into two different polymer materials and bonding them between two standard glass slides with epoxy and fusion bonding. We fabricated a second generation of flow cytometer chip consisting of an integrated 2D hydrodynamic focusing system, solid-core optical waveguides and a hydrodynamic side-flow switching system on an all-PDMS platform. Optical propagation losses of the integrated waveguides and signal-to-noise ratio (SNR) of its detection system were characterized. The propagation losses were found to be 1.6 and 1.5 dB/cm for the green and red light, respectively. Detection of fluorescent signal through the waveguide yielded improved SNR than the conventional method of under-chip detection. Fluid flow speeds were estimated from volumetric flow measurements and fluorescent particle tracking experiments and the width of the hydrodynamically focused stream was extracted from microscope flow images. The results were compared to the simulation values obtained from the Q3D
Deformation analysis of 3D tagged cardiac images using an optical flow method
Directory of Open Access Journals (Sweden)
Gorman Robert C
2010-03-01
Full Text Available Abstract Background This study proposes and validates a method of measuring 3D strain in myocardium using a 3D Cardiovascular Magnetic Resonance (CMR tissue-tagging sequence and a 3D optical flow method (OFM. Methods Initially, a 3D tag MR sequence was developed and the parameters of the sequence and 3D OFM were optimized using phantom images with simulated deformation. This method then was validated in-vivo and utilized to quantify normal sheep left ventricular functions. Results Optimizing imaging and OFM parameters in the phantom study produced sub-pixel root-mean square error (RMS between the estimated and known displacements in the x (RMSx = 0.62 pixels (0.43 mm, y (RMSy = 0.64 pixels (0.45 mm and z (RMSz = 0.68 pixels (1 mm direction, respectively. In-vivo validation demonstrated excellent correlation between the displacement measured by manually tracking tag intersections and that generated by 3D OFM (R ≥ 0.98. Technique performance was maintained even with 20% Gaussian noise added to the phantom images. Furthermore, 3D tracking of 3D cardiac motions resulted in a 51% decrease in in-plane tracking error as compared to 2D tracking. The in-vivo function studies showed that maximum wall thickening was greatest in the lateral wall, and increased from both apex and base towards the mid-ventricular region. Regional deformation patterns are in agreement with previous studies on LV function. Conclusion A novel method was developed to measure 3D LV wall deformation rapidly with high in-plane and through-plane resolution from one 3D cine acquisition.
Parallel Finite Element Solution of 3D Rayleigh-Benard-Marangoni Flows
Carey, G. F.; McLay, R.; Bicken, G.; Barth, B.; Pehlivanov, A.
1999-01-01
A domain decomposition strategy and parallel gradient-type iterative solution scheme have been developed and implemented for computation of complex 3D viscous flow problems involving heat transfer and surface tension effects. Details of the implementation issues are described together with associated performance and scalability studies. Representative Rayleigh-Benard and microgravity Marangoni flow calculations and performance results on the Cray T3D and T3E are presented. The work is currently being extended to tightly-coupled parallel "Beowulf-type" PC clusters and we present some preliminary performance results on this platform. We also describe progress on related work on hierarchic data extraction for visualization.
3D-printed and CNC milled flow-cells for chemiluminescence detection.
Spilstead, Kara B; Learey, Jessica J; Doeven, Egan H; Barbante, Gregory J; Mohr, Stephan; Barnett, Neil W; Terry, Jessica M; Hall, Robynne M; Francis, Paul S
2014-08-01
Herein we explore modern fabrication techniques for the development of chemiluminescence detection flow-cells with features not attainable using the traditional coiled tubing approach. This includes the first 3D-printed chemiluminescence flow-cells, and a milled flow-cell designed to split the analyte stream into two separate detection zones within the same polymer chip. The flow-cells are compared to conventional detection systems using flow injection analysis (FIA) and high performance liquid chromatography (HPLC), with the fast chemiluminescence reactions of an acidic potassium permanganate reagent with morphine and a series of adrenergic phenolic amines.
3-D model of a radial flow sub-watt methanol fuel processor
Energy Technology Data Exchange (ETDEWEB)
Holladay, J. D.; Wang, Y.
2015-10-01
A 3-D model is presented for a novel sub-watt packed bed reactor. The reactor uses an annular inlet flow combined with a radial flow packed bed reactor. The baseline reactor is compared to a reactor with multiple outlets and a reactor with 3 internal fins. Increasing the outlets from 1 to 4 did improve the flow distribution, but did not increase the performance in the simulation. However, inserting fins allowed a decrease in temperature with same inlet flow of approximately 35K. Or the inlet flow rate could be increased by a factor of 2.8x while maintaining >99% conversion.
Effects of texture component orientation on orientation flow visibility for 3-D shape perception.
Fowler, Michelle L; Li, Andrea
2013-01-01
In images of textured 3-D surfaces, orientation flows created by the texture components parallel to the surface slant play a critical role in conveying the surface slant and shape. This study examines the visibility of these orientation flows in complex patterns. Specifically, we examine the effect of orientation of neighboring texture components on orientation flow visibility. Complex plaids consisting of gratings equally spaced in orientation were mapped onto planar and curved surfaces. The visibility of the component that creates the orientation flows was quantified by measuring its contrast threshold (CT) while varying the combination of neighboring components present in the pattern. CTs were consistently lowest only when components closest in orientation to that of the orientation flows were subtracted from the pattern. This finding suggests that a previously reported frequency-selective cross-orientation suppression mechanism involved with the perception of 3-D shape from texture is affected by proximity in orientation of concurrent texture components.
Effects of texture component orientation on orientation flow visibility for 3-D shape perception.
Directory of Open Access Journals (Sweden)
Michelle L Fowler
Full Text Available In images of textured 3-D surfaces, orientation flows created by the texture components parallel to the surface slant play a critical role in conveying the surface slant and shape. This study examines the visibility of these orientation flows in complex patterns. Specifically, we examine the effect of orientation of neighboring texture components on orientation flow visibility. Complex plaids consisting of gratings equally spaced in orientation were mapped onto planar and curved surfaces. The visibility of the component that creates the orientation flows was quantified by measuring its contrast threshold (CT while varying the combination of neighboring components present in the pattern. CTs were consistently lowest only when components closest in orientation to that of the orientation flows were subtracted from the pattern. This finding suggests that a previously reported frequency-selective cross-orientation suppression mechanism involved with the perception of 3-D shape from texture is affected by proximity in orientation of concurrent texture components.
Kinematics and flow fields in 3D around swimming lamprey using light field PIV
Lehn, Andrea M.; Techet, Alexandra H.
2016-11-01
The fully time-resolved 3D kinematics and flow field velocities around freely swimming sea lamprey are derived using 3D light field imaging PIV. Lighthill's Elongated Body Theory (EBT) predicts that swimmers with anguilliform kinematics likened to lamprey, and similarly eels, will exhibit relatively poor propulsive efficiency. However, previous experimental studies of eel locomotion utilizing 2D PIV suggest disagreement with EBT estimates of wake properties; although, the thrust force generated by such swimmers has yet to be fully resolved using 3D measurements. A light field imaging array of multiple high-speed cameras is used to perform 3D synthetic aperture PIV around ammocoete sea lamprey (Petromyzon marinus). Fluid mechanics equations are used to determine thrust force generation, leading experimental studies closer to underpinning the physical mechanisms that enable aquatic locomotion of long, slender undulatory swimmers.
Dynamics of Capillary-Driven Flow in 3D Printed Open Microchannels.
Lade, Robert K; Hippchen, Erik J; Macosko, Christopher W; Francis, Lorraine F
2017-03-28
Microchannels have applications in microfluidic devices, patterns for micromolding, and even flexible electronic devices. Three-dimensional (3D) printing presents a promising alternative manufacturing route for these microchannels due to the technology's relative speed and the design freedom it affords its users. However, the roughness of 3D printed surfaces can significantly influence flow dynamics inside of a microchannel. In this work, open microchannels are fabricated using four different 3D printing techniques: fused deposition modeling (FDM), stereolithography (SLA), selective laser sintering, and multi jet modeling. Microchannels printed with each technology are evaluated with respect to their surface roughness, morphology, and how conducive they are to spontaneous capillary filling. Based on this initial assessment, microchannels printed with FDM and SLA are chosen as models to study spontaneous, capillary-driven flow dynamics in 3D printed microchannels. Flow dynamics are investigated over short (∼10(-3) s), intermediate (∼1 s), and long (∼10(2) s) time scales. Surface roughness causes a start-stop motion down the channel due to contact line pinning, while the cross-sectional shape imparted onto the channels during the printing process is shown to reduce the expected filling velocity. A significant delay in the onset of Lucas-Washburn dynamics (a long-time equilibrium state where meniscus position advances proportionally to the square root of time) is also observed. Flow dynamics are assessed as a function of printing technology, print orientation, channel dimensions, and liquid properties. This study provides the first in-depth investigation of the effect of 3D printing on microchannel flow dynamics as well as a set of rules on how to account for these effects in practice. The extension of these effects to closed microchannels and microchannels fabricated with other 3D printing technologies is also discussed.
New P3D Hydraulic Fracturing Model Based on the Radial Flow
Institute of Scientific and Technical Information of China (English)
鲁连军; 孙逢春; 肖海华; 安申法
2004-01-01
Pseudo three-dimension (P3D) hydraulic fracturing models often overpredict the fracture height for a poorly contained fracture. To solve this problem, a new method is presented in shaping the P3D fracture geometry on the basis of the fundamental theory and the original 1D fluid flow is replaced with a more representatively radial flow. The distribution of the fluid in the modified fluid field is analyzed and a sound explanation to the problem is given. Due to the consideration of the fluid flow in the vertical direction, the modified model can predict the fracture height much better. To validate the rationality of the radial fluid flow assumption, the distribution of the fluid in the modified fluid field is simulated with the plane potential flow by using finite element method. And the results agree effectively with those from the assumption. Through comparing with the full 3D model, the results show that this new P3D model can be used to aid the fracturing design and predict the fracture height under poorly contained situation.
Symplectic Exact Solution for Stokes Flow in the Thin Film Coating Applications
Directory of Open Access Journals (Sweden)
Yan Wang
2014-01-01
Full Text Available The symplectic analytical method is introduced to solve the problem of the stokes flow in the thin film coating applications. Based on the variational principle, the Lagrangian function of the stokes flow is established. By using the Legendre transformation, the dual variables of velocities and the Hamiltonian function are derived. Considering velocities and stresses as the basic variables, the equations of stokes flow problems are transformed into Hamiltonian system. The method of separation of variables and expansion of eigenfunctions are developed to solve the governing equations in Hamiltonian system, and the analytical solutions of the stokes flow are obtained. Several numerical simulations are carried out to verify the analytical solutions in the present study and discuss the effects of the driven lids of the square cavity on the dynamic behavior of the flow structure.
3D-SIFT-Flow for atlas-based CT liver image segmentation
Energy Technology Data Exchange (ETDEWEB)
Xu, Yan, E-mail: xuyan04@gmail.com [State Key Laboratory of Software Development Environment and Key Laboratory of Biomechanics and Mechanobiology of Ministry of Education, Beihang University, Beijing 100191, China and Research Institute of Beihang University in Shenzhen and Microsoft Research, Beijing 100080 (China); Xu, Chenchao, E-mail: chenchaoxu33@gmail.com; Kuang, Xiao, E-mail: kuangxiao.ace@gmail.com [School of Biological Science and Medical Engineering, Beihang University, Beijing 100191 (China); Wang, Hongkai, E-mail: wang.hongkai@gmail.com [Department of Biomedical Engineering, Dalian University of Technology, Dalian 116024 (China); Chang, Eric I-Chao, E-mail: eric.chang@microsoft.com [Microsoft Research, Beijing 100080 (China); Huang, Weimin, E-mail: wmhuang@i2r.a-star.edu.sg [Institute for Infocomm Research (I2R), Singapore 138632 (Singapore); Fan, Yubo, E-mail: yubofan@buaa.edu.cn [Key Laboratory of Biomechanics and Mechanobiology of Ministry of Education, Beihang University, Beijing 100191 (China)
2016-05-15
Purpose: In this paper, the authors proposed a new 3D registration algorithm, 3D-scale invariant feature transform (SIFT)-Flow, for multiatlas-based liver segmentation in computed tomography (CT) images. Methods: In the registration work, the authors developed a new registration method that takes advantage of dense correspondence using the informative and robust SIFT feature. The authors computed the dense SIFT features for the source image and the target image and designed an objective function to obtain the correspondence between these two images. Labeling of the source image was then mapped to the target image according to the former correspondence, resulting in accurate segmentation. In the fusion work, the 2D-based nonparametric label transfer method was extended to 3D for fusing the registered 3D atlases. Results: Compared with existing registration algorithms, 3D-SIFT-Flow has its particular advantage in matching anatomical structures (such as the liver) that observe large variation/deformation. The authors observed consistent improvement over widely adopted state-of-the-art registration methods such as ELASTIX, ANTS, and multiatlas fusion methods such as joint label fusion. Experimental results of liver segmentation on the MICCAI 2007 Grand Challenge are encouraging, e.g., Dice overlap ratio 96.27% ± 0.96% by our method compared with the previous state-of-the-art result of 94.90% ± 2.86%. Conclusions: Experimental results show that 3D-SIFT-Flow is robust for segmenting the liver from CT images, which has large tissue deformation and blurry boundary, and 3D label transfer is effective and efficient for improving the registration accuracy.
3D-SIFT-Flow for atlas-based CT liver image segmentation.
Xu, Yan; Xu, Chenchao; Kuang, Xiao; Wang, Hongkai; Chang, Eric I-Chao; Huang, Weimin; Fan, Yubo
2016-05-01
In this paper, the authors proposed a new 3D registration algorithm, 3D-scale invariant feature transform (SIFT)-Flow, for multiatlas-based liver segmentation in computed tomography (CT) images. In the registration work, the authors developed a new registration method that takes advantage of dense correspondence using the informative and robust SIFT feature. The authors computed the dense SIFT features for the source image and the target image and designed an objective function to obtain the correspondence between these two images. Labeling of the source image was then mapped to the target image according to the former correspondence, resulting in accurate segmentation. In the fusion work, the 2D-based nonparametric label transfer method was extended to 3D for fusing the registered 3D atlases. Compared with existing registration algorithms, 3D-SIFT-Flow has its particular advantage in matching anatomical structures (such as the liver) that observe large variation/deformation. The authors observed consistent improvement over widely adopted state-of-the-art registration methods such as ELASTIX, ANTS, and multiatlas fusion methods such as joint label fusion. Experimental results of liver segmentation on the MICCAI 2007 Grand Challenge are encouraging, e.g., Dice overlap ratio 96.27% ± 0.96% by our method compared with the previous state-of-the-art result of 94.90% ± 2.86%. Experimental results show that 3D-SIFT-Flow is robust for segmenting the liver from CT images, which has large tissue deformation and blurry boundary, and 3D label transfer is effective and efficient for improving the registration accuracy.
Simulation of Flow Pattern around Inclined Bridge Group Pier using FLOW-3D Software
Directory of Open Access Journals (Sweden)
Malihesadat Jafari
2017-03-01
Full Text Available Introduction: Bridges are certainly one of the most important structures but costly service elements in a transport system. The bridges are very required to access the damaged areas in emergency situations such as floods and earthquakes. Scour around the foundations of bridge piers exposed to the flowing water than can destroy the bridge itself is a subject of major concern. Flow pattern is known as responsible for all changes in stream bed. Any obstacle in the channel can form new flow patterns causing additional shear stress exerted on the bed than the equilibrium condition of the absence of the obstacle. Appropriate shaping of flow pattern and proper selecting of pier geometry and the location of bridge piers can be one of the proper methods in reduction of scour amount which is the main subject of the present study. Materials and Methods: Inclined bridge group pier is a type of bridges with modern geometry based on development in building technology of structures. Many of these bridges have been built all around the world and the 8th bridge built crossing the Karun River in Ahvaz is a sample of the Iranian ones considered in this research. Hydrodynamic behavior of flow is investigated around the inclined bridge group pier settled on foundation using the FLOW-3D numerical model. Inclined bridge group pier investigated in this study, includes two rectangular piers which are 2.5 cm long and 3.5 cm wide and set in an angle of 28 degree on rectangular foundation which is 16 cm long and 10 cm wide and installed in three different foundation levels namely at, above and below the bed levels. The physical model of prototype pier considered in this study was constructed to the scale of 1:190 of the Ahvaz 8th bridge. In order to verify the accuracy of the numerical model, velocity data obtained from image processing technique were used. Results and Discussion: Due to non- linearity and interactions between various phenomena involved, flow pattern
3-D Vector Flow Using a Row-Column Addressed CMUT Array
DEFF Research Database (Denmark)
Holbek, Simon; Christiansen, Thomas Lehrmann; Engholm, Mathias;
2016-01-01
This paper presents an in-house developed 2-D capacitive micromachined ultrasonic transducer (CMUT) appliedfor 3-D blood flow estimation. The probe breaks with conventional transducers in two ways; first, the ultrasonicpressure field is generated from thousands of small vibrating micromachined...
Negahdar, M J; Kadbi, Mo; Cha, J; Cebral, J; Amini, A
2013-01-01
Use of phase-contrast (PC) MRI in assessment of hemodynamics has significant clinical importance. In this paper we develop a novel approach to determination of hemodynamic pressures. 3D gradients of pressure obtained from Navier-Stokes equation are expanded into a series of orthogonal basis functions, and are subsequently projected onto an integrable subspace. Before the projection step however, a scheme is devised to eliminate the discontinuity at the vessel and image boundaries. In terms of the computation time, the proposed approach significantly improves on previous iterative methods for pressure calculations. The method has been validated using computational fluid dynamic simulations and in-vitro MRI studies of stenotic flows.
Numerical simulation of a combined oxidation ditch flow using 3D k-εturbulence model
Institute of Scientific and Technical Information of China (English)
LUO Lin; LI Wei-min; DENG Yong-sen; WANG Tao
2005-01-01
The standard three dimensional(3D) k-ε turbulence model was applied to simulate the flow field of a small scale combined oxidation ditch. The moving mesh approach was used to model the rotor of the ditch. Comparison of the computed and the measured data is acceptable. A vertical reverse flow zone in the ditch was found, and it played a very important role in the ditch flow behavior. The flow pattern in the ditch is discussed in detail, and approaches are suggested to improve the hydrodynamic performance in the ditch.
3D Flow in the Axial—Radial Exhaust Hood of a Steam Turbine
Institute of Scientific and Technical Information of China (English)
STASTNYM．，SKODA; KOLARP．，
1997-01-01
The computation model of the 3D viscous flow is used for the analysis of the flow conditions in the model of steam turbine exhaust hood,that was in previous time investigated experimentally,The computation method and the obtained results are described.The calculation is concentrated on the finding of the influence of inlet velocity field and on the influence of compressibility of the flow medium.Especially it followed the fluid motion in the outlte vortex and the occurrence of the areas with flow separation.
Energy Technology Data Exchange (ETDEWEB)
Stadlbauer, Andreas [Landesklinikum St. Poelten, MR Physics Group, Department of Radiology, St. Poelten (Austria); University of Erlangen-Nuremberg, Department of Neurosurgery, Erlangen (Germany); Salomonowitz, Erich [Landesklinikum St. Poelten, MR Physics Group, Department of Radiology, St. Poelten (Austria); Brenneis, Christian [Landesklinikum St. Poelten, Department of Neurology, St. Poelten (Austria); Ungersboeck, Karl [Landesklinikum St. Poelten, Department of Neurosurgery, St. Poelten (Austria); Riet, Wilma van der [European MRI Consultancy (EMRIC), Strasbourg (France); Buchfelder, Michael; Ganslandt, Oliver [University of Erlangen-Nuremberg, Department of Neurosurgery, Erlangen (Germany)
2012-01-15
To investigate the detectability of CSF flow alterations in the ventricular system of patients with hydrocephalus using time-resolved 3D MR velocity mapping. MR velocity mapping was performed in 21 consecutive hydrocephalus patients and 21 age-matched volunteers using a 3D phase-contrast (PC) sequence. Velocity vectors and particle path lines were calculated for visualisation of flow dynamics. CSF flow was classified as ''hypomotile flow'' if it showed attenuated dynamics and as ''hypermotile flow'' if it showed increased dynamics compared with volunteers. Diagnostic efficacy was compared with routine 2D cine PC-MRI. Seven patients showed hypomotile CSF flow: six had non-communicating hydrocephalus due to aqueductal stenosis. One showed oscillating flow between the lateral ventricles after craniotomy for intracranial haemorrhage. Seven patients showed normal flow: six had hydrocephalus ex vacuo due to brain atrophy. One patient who underwent ventriculostomy 10 years ago showed a flow path through the opening. Seven patients showed hypermotile flow: three had normal pressure hydrocephalus, three had dementia, and in one the diagnosis remained unclear. The diagnostic efficacy of velocity mapping was significantly higher except for that of aqueductal stenosis. Our approach may be useful for diagnosis, therapy planning, and follow-up of different kinds of hydrocephalus. (orig.)
In vivo analysis of physiological 3D blood flow of cerebral veins
Energy Technology Data Exchange (ETDEWEB)
Schuchardt, Florian; Schroeder, Laure; Baeuerle, Jochen; Harloff, Andreas [University Medical Centre, Department of Neurology, Freiburg (Germany); Anastasopoulos, Constantin [University Medical Center, Department of Neuropaediatrics and Muscle Disorders, Freiburg (Germany); University Medical Centre, Department of Neuroradiology, Freiburg (Germany); Markl, Michael [Northwestern University, Department of Radiology, Feinberg School of Medicine and McCormick School of Engineering, Chicago, IL (United States); Hennemuth, Anja; Drexl, Johann [Fraunhofer MEVIS, Bremen (Germany); Valdueza, Jose M. [Neurological Center, Segeberger Kliniken, Bad Segeberg (Germany); Mader, Irina [University Medical Centre, Department of Neuroradiology, Freiburg (Germany)
2015-08-15
To visualize and quantify physiological blood flow of intracranial veins in vivo using time-resolved, 3D phase-contrast MRI (4D flow MRI), and to test measurement accuracy. Fifteen healthy volunteers underwent repeated ECG-triggered 4D flow MRI (3 Tesla, 32-channel head coil). Intracranial venous blood flow was analysed using dedicated software allowing for blood flow visualization and quantification in analysis planes at the superior sagittal, straight, and transverse sinuses. MRI was evaluated for intra- and inter-observer agreement and scan-rescan reproducibility. Measurements of the transverse sinuses were compared with transcranial two-dimensional duplex ultrasound. Visualization of 3D blood flow within cerebral sinuses was feasible in 100 % and within at least one deep cerebral vein in 87 % of the volunteers. Blood flow velocity/volume increased along the superior sagittal sinus and was lower in the left compared to the right transverse sinus. Intra- and inter-observer reliability and reproducibility of blood flow velocity (mean difference 0.01/0.02/0.02 m/s) and volume (mean difference 0.0002/-0.0003/0.00003 l/s) were good to excellent. High/low velocities were more pronounced (8 % overestimation/9 % underestimation) in MRI compared to ultrasound. Four-dimensional flow MRI reliably visualizes and quantifies three-dimensional cerebral venous blood flow in vivo and is promising for studies in patients with sinus thrombosis and related diseases. (orig.)
Comparison of Tomo-PIV and 3D-PTV for microfluidic flows
Kim, Hyoungsoo; Westerweel, Jerry; Elsinga, Gerrit E.
2013-02-01
Two 3D-3C velocimetry techniques for micro-scale measurements are compared: tomographic particle image velocimetry (Tomo-PIV) and 3D particle-tracking velocimetry (3D-PTV). Both methods are applied to experimental data from a confined shear-driven liquid droplet over a moving surface. The droplet has 200 μm height and 2 mm diameter. Micro 3D-PTV and Tomo-PIV are used to obtain the tracer particle distribution and the flow velocity field for the same set of images. It is shown that the reconstructed particle distributions are distinctly different, where Tomo-PIV returns a nearly uniform distribution over the height of the volume, as expected, and PTV reveals a clear peak in the particle distribution near the plane of focus. In Tomo-PIV, however, the reconstructed particle peak intensity decreases in proportion to the distance from the plane of focus. Due to the differences in particle distributions, the measured flow velocities are also different. In particular, we observe Tomo-PIV to be in closer agreement with mass conservation. Furthermore, the random noise level is found to increase with distance to the plane of focus at a higher rate for 3D-PTV as compared to Tomo-PIV. Thus, for a given noise threshold value, the latter method can measure reliably over a thicker volume.
Obstacle detection and terrain characterization using optical flow without 3-D reconstruction
Young, Gin-Shu; Hong, Tsai Hong; Herman, Martin; Yang, Jackson C. S.
1992-11-01
For many applications in computer vision, it is important to recover range, 3-D motion, and/or scene geometry from a sequence of images. However, there are many robot behaviors which can be achieved by extracting relevant 2-D information from the imagery and using this information directly, without recovery of such information. In this paper, we focus on two behaviors, obstacle avoidance and terrain navigation. A novel method of these two behaviors has been developed without 3-D reconstruction. This approach is often called purposive active vision. A linear relationship, plotted as a line and called a reference flow line, has been found. The difference between a plotted line and the reference flow line can be used to detect discrete obstacles above or below the reference terrain. For terrain characterization, slopes of surface regions can be calculated directly from optical flow. Some error analysis is also done. The main features of this approach are that (1) discrete obstacles are detected directly from 2-D optical flow, no 3-D reconstruction is performed; (2) terrain slopes are also calculated from 2- D optical flow; (3) knowledge about the terrain model, camera-to-ground coordinate transformation, or vehicle (or camera) motion is not required; (4) the error sources involved are reduced to a minimum, since the only information required is a component of optical flow. An initial experiment using noisy synthetic data is also included to demonstrate the applicability and robustness of the method.
A σ-coordinate model for 3D free-surface flows using an unstructured finite-volume technique
Uh Zapata, Miguel
2016-11-01
The aim of this work is to develop a numerical solution of three-dimensional free-surface flows using a σ-coordinate model, a projection method and an unstructured finite-volume technique. The coordinate transformation is used in order to overcome difficulties arising from free surface elevation and irregular geometry. The projection method consists to combine the momentum and continuity equations in order to establish a Poisson-type equation for the non-hydrostatic pressure. A cell-centered finite volume method with a triangular mesh in the horizontal direction is used to simulate the flows with free-surfaces, in which the average values of conserved variables are stored at the centre of each element. A parallel algorithm is also presented for the finite volume discretization of the 3D Navier-Stokes equations. The proposed parallel method is formulated by using a multi-color SOR method, a block domain decomposition and interprocessor data communication techniques with Message Passing Interface. The model has been validated by several benchmarks which numerical simulations are in good agreement with the corresponding analytical and existing experimental results.
Institute of Scientific and Technical Information of China (English)
J. Li; W. Liu; Y.Q. Lai; Q.Y. Li; Y.X. Liu
2006-01-01
Two full 3D steady mathematical models are developed by finite element method (FEM) to calculate coupled physics fields: the electro-magnetic model is built and solved first and so is the fluid motion model with the acquired electromagnetic force as source body forces in Navier-Stokes equations. Effects caused by the ferromagnetic shell, busbar system around, and open boundary problem as well as inside induced current were considered in terms of the magnetic field. Furthermore, a new modeling method is found to set up solid models and then mesh them entirely with so-called structuralized grids, namely hex-mesh. Examples of 75kA prebaked cell with two kinds of busbar arrangements are presented. Results agree with those disclosed in the literature and confirm that the coupled simulation is valid. It is also concluded that the usage of these models facilitates the consistent analysis of the electric field to magnetic field and then flow motion to the greater extent, local distributions of current density and magnetic flux density are very much dependent on the cell structure, the steel shell is a shield to reduce the magnetic field and flow pattern is two dimensional in the main body of the metal pad.
DEFF Research Database (Denmark)
Holbek, Simon; Hansen, Kristoffer Lindskov; Bouzari, Hamed
2017-01-01
Ultrasound (US) examination of the common carotid artery was compared with a through-plane magnetic resonance imaging (MRI) sequence to validate a recently proposed technique for 3-D US vector flow imaging. Data from the first volunteer examined were used as the training set, before volume flow a...
Shrewsbury, George D.; Vadyak, Joseph; Schuster, David M.; Smith, Marilyn J.
1989-01-01
A computer analysis was developed for calculating steady (or unsteady) three-dimensional aircraft component flow fields. This algorithm, called ENS3D, can compute the flow field for the following configurations: diffuser duct/thrust nozzle, isolated wing, isolated fuselage, wing/fuselage with or without integrated inlet and exhaust, nacelle/inlet, nacelle (fuselage) afterbody/exhaust jet, complete transport engine installation, and multicomponent configurations using zonal grid generation technique. Solutions can be obtained for subsonic, transonic, or hypersonic freestream speeds. The algorithm can solve either the Euler equations for inviscid flow, the thin shear layer Navier-Stokes equations for viscous flow, or the full Navier-Stokes equations for viscous flow. The flow field solution is determined on a body-fitted computational grid. A fully-implicit alternating direction implicit method is employed for the solution of the finite difference equations. For viscous computations, either a two layer eddy-viscosity turbulence model or the k-epsilon two equation transport model can be used to achieve mathematical closure.
3-D Vector Flow Estimation With Row–Column-Addressed Arrays
DEFF Research Database (Denmark)
Holbek, Simon; Christiansen, Thomas Lehrmann; Stuart, Matthias Bo;
2016-01-01
.7, −0.9, 0.4)% with a relative standard deviation of (8.7, 5.1, 0.8)% for (vx , vy, vz). The estimated peak velocity is 48.5 ± 3 cm/s giving a −3% bias. The out-of-plane velocity component perpendicular to the cross section is used to estimate volumetric flow rates in the flow rig at a 90° beam......-to-flow angle. The estimated mean flow rate in this setup is 91.2 ± 3.1 L/h corresponding to a bias of −11.1%. In a pulsating flow setup, flow rate measured during five cycles is 2.3 ± 0.1 mL/stroke giving a negative 9.7% bias. It is concluded that accurate 3-D vector flow estimation can be obtained using a 2-D...
Structural elements and collapse regimes in 3D flows on a slope
Energy Technology Data Exchange (ETDEWEB)
Goncharov, V. P., E-mail: v.goncharov@rambler.ru [Russian Academy of Sciences, Obukhov Institute of Atmospheric Physics (Russian Federation)
2011-10-15
The mechanisms and structural elements of an instability whose development results in the collapse of flow fragments have been studied in the scope of the Hamilton version of the 'shallow water' 3D model on a slope. The study indicated that the 3D model differs from its 2D analog in a more varied set of collapsing solutions. In particular, the solutions describing anisotropic collapse, during which the area of a collapsing fragment in contact with the slope contracts into a segment rather than a point, exist together with the solutions describing radially symmetric (isotropic) collapse.
An improved parallel SPH approach to solve 3D transient generalized Newtonian free surface flows
Ren, Jinlian; Jiang, Tao; Lu, Weigang; Li, Gang
2016-08-01
In this paper, a corrected parallel smoothed particle hydrodynamics (C-SPH) method is proposed to simulate the 3D generalized Newtonian free surface flows with low Reynolds number, especially the 3D viscous jets buckling problems are investigated. The proposed C-SPH method is achieved by coupling an improved SPH method based on the incompressible condition with the traditional SPH (TSPH), that is, the improved SPH with diffusive term and first-order Kernel gradient correction scheme is used in the interior of the fluid domain, and the TSPH is used near the free surface. Thus the C-SPH method possesses the advantages of two methods. Meanwhile, an effective and convenient boundary treatment is presented to deal with 3D multiple-boundary problem, and the MPI parallelization technique with a dynamic cells neighbor particle searching method is considered to improve the computational efficiency. The validity and the merits of the C-SPH are first verified by solving several benchmarks and compared with other results. Then the viscous jet folding/coiling based on the Cross model is simulated by the C-SPH method and compared with other experimental or numerical results. Specially, the influences of macroscopic parameters on the flow are discussed. All the numerical results agree well with available data, and show that the C-SPH method has higher accuracy and better stability for solving 3D moving free surface flows over other particle methods.
Numerical simulation of 3-D incompressible, multi-phase flows over cavitating projectiles
Energy Technology Data Exchange (ETDEWEB)
Owis, F.M.; Nayfeh, A.H. [Blacksburg State University, Dept. of Engineering Science and Mechanics, MC 0219, Virginia Polytechnic Institute, VA (United States)
2004-04-01
The hydrodynamic cavitation over axisymmetric projectiles is computed using the unsteady incompressible Navier-Stokes equations for multi-fluid elements. The governing equations are discretized on a structured grid using an upwind difference scheme with flux limits. A preconditioning dual-time stepping method is used for the unsteady computations. The Eigen-system is derived for the Jacobian matrices. This Eigen-system is suitable for high-density ratio multi-fluid flows and it provides high numerical stability and fast convergence. This method can be used to compute single- as well as multi-phase flows. Cavitating flows over projectiles with different geometries are computed and the results are in good agreement with available experimental data and other published computations. (authors)
Parallel Adaptive Computation of Blood Flow in a 3D ``Whole'' Body Model
Zhou, M.; Figueroa, C. A.; Taylor, C. A.; Sahni, O.; Jansen, K. E.
2008-11-01
Accurate numerical simulations of vascular trauma require the consideration of a larger portion of the vasculature than previously considered, due to the systemic nature of the human body's response. A patient-specific 3D model composed of 78 connected arterial branches extending from the neck to the lower legs is constructed to effectively represent the entire body. Recently developed outflow boundary conditions that appropriately represent the downstream vasculature bed which is not included in the 3D computational domain are applied at 78 outlets. In this work, the pulsatile blood flow simulations are started on a fairly uniform, unstructured mesh that is subsequently adapted using a solution-based approach to efficiently resolve the flow features. The adapted mesh contains non-uniform, anisotropic elements resulting in resolution that conforms with the physical length scales present in the problem. The effects of the mesh resolution on the flow field are studied, specifically on relevant quantities of pressure, velocity and wall shear stress.
Computational fluid dynamics simulations of blood flow regularized by 3D phase contrast MRI
DEFF Research Database (Denmark)
Rispoli, Vinicius C; Nielsen, Jon; Nayak, Krishna S
2015-01-01
approach in regularizing 3D flow fields is evaluated. METHODS: The proposed algorithm incorporates both a Newtonian fluid physics model and a linear PC-MRI signal model. The model equations are solved numerically using a modified CFD algorithm. The numerical solution corresponds to the optimal solution......BACKGROUND: Phase contrast magnetic resonance imaging (PC-MRI) is used clinically for quantitative assessment of cardiovascular flow and function, as it is capable of providing directly-measured 3D velocity maps. Alternatively, vascular flow can be estimated from model-based computation fluid...... dynamics (CFD) calculations. CFD provides arbitrarily high resolution, but its accuracy hinges on model assumptions, while velocity fields measured with PC-MRI generally do not satisfy the equations of fluid dynamics, provide limited resolution, and suffer from partial volume effects. The purpose...
Selecting 3D Chaotic Flow States for Accelerated DNA Replication in Micro Scale Convective PCR
Priye, Aashish; Hassan, Yassin; Ugaz, Victor
2016-01-01
Micro-scale flow in cylindrical geometries can harness chaotic advection to perform complex thermally activated biochemical reactions such as the polymerase chain reaction (PCR). We have applied a 3D computational fluid dynamics model to resolve the complex flow patterns in such geometries. The resulting 3D flow trajectories are then used as input to a kinetic model to resolve the time evolution of DNA replication process. A simple mass action kinetic model was developed to couple these biochemical reactions with the intricate flow. Residence time analysis of virtual particles in the flow revealed that the flow has a strong chaotic component in wider geometries in comparison with taller geometries (quasi periodic motion). This work shows, for the first time that the chaotic aspect of the flow field plays a key role in determining the strength of the coupling between the reactions and the flow. Our model can quantify the doubling times of these reactions capturing the lag, exponential and plateau phases of PCR...
Delft3D-FLOW on PRACE infrastructures for real life hydrodynamic applications.
Donners, John; Genseberger, Menno; Jagers, Bert; de Goede, Erik; Mourits, Adri
2013-04-01
PRACE, the Partnership for Advanced Computing in Europe, offers access to the largest high-performance computing systems in Europe. PRACE invites and helps industry to increase their innovative potential through the use of the PRACE infrastructure. This poster describes different efforts to assist Deltares with porting the open-source simulation software Delft3D-FLOW to PRACE infrastructures. Analysis of the performance on these infrastructures has been done for real life flow applications. Delft3D-FLOW is a 2D and 3D shallow water solver which calculates non-steady flow and transport phenomena resulting from tidal and meteorological forcing on a curvilinear, boundary fitted grid in Cartesian or spherical coordinates. It also includes a module which sediment transport (both suspended and bed total load) and morphological changes for an arbitrary number of cohesive and non-cohesive fractions. As Delft3D-FLOW has been developed over several decades, with a variety of functionality and over 350k lines of source code, porting to PRACE infrastructures needs some effort. At the moment Delft3D-FLOW uses MPI with domain decomposition in one direction as its parallellisation approach. Because it is hard to identify scaling issues if one immediately starts with a complex case with many features enabled, different cases with increasing complexity have been used to investigate scaling of this parallellisation approach on several PRACE platforms. As a base reference case we started with a schematic high-resolution 2D hydrodynamic model of the river Waal that turned out to be surprisingly well-suited to the highly-parallel PRACE machines. Although Delft3D-FLOW employs a sophisticated build system, several modifications were required to port it to most PRACE systems due to the use of specific, highly-tuned compilers and MPI-libraries. After this we moved to a 3D hydrodynamic model of Rotterdam harbour that includes sections of the rivers Rhine and Meuse and a part of the North
Discretizations in isogeometric analysis of Navier-Stokes flow
DEFF Research Database (Denmark)
Nielsen, Peter Nørtoft; Gersborg, Allan Roulund; Gravesen, Jens;
2011-01-01
for the simplified Stokes problem confirm the existence of many stable discretizations of the velocity and pressure spaces, and in particular show that stability may be achieved by means of knot refinement of the velocity space. Error convergence studies for the full Navier-Stokes problem show optimal convergence...... rates for this type of discretizations. Finally, a comparison of the results of the method to data from the literature for the lid-driven square cavity for Reynolds numbers up to 10,000 serves as benchmarking of the discretizations and confirms the robustness of the method. © 2011 Elsevier B.V....
Capturing 3D Water Flow in Rooted Soil by Ultra-fast Neutron Tomography.
Tötzke, Christian; Kardjilov, Nikolay; Manke, Ingo; Oswald, Sascha E
2017-07-21
Water infiltration in soil is not only affected by the inherent heterogeneities of soil, but even more by the interaction with plant roots and their water uptake. Neutron tomography is a unique non-invasive 3D tool to visualize plant root systems together with the soil water distribution in situ. So far, acquisition times in the range of hours have been the major limitation for imaging 3D water dynamics. Implementing an alternative acquisition procedure we boosted the speed of acquisition capturing an entire tomogram within 10 s. This allows, for the first time, tracking of a water front ascending in a rooted soil column upon infiltration of deuterated water time-resolved in 3D. Image quality and resolution could be sustained to a level allowing for capturing the root system in high detail. Good signal-to-noise ratio and contrast were the key to visualize dynamic changes in water content and to localize the root uptake. We demonstrated the ability of ultra-fast tomography to quantitatively image quick changes of water content in the rhizosphere and outlined the value of such imaging data for 3D water uptake modelling. The presented method paves the way for time-resolved studies of various 3D flow and transport phenomena in porous systems.
3D mathematical model for suspended load transport by turbulent flows and its applications
Institute of Scientific and Technical Information of China (English)
LU; Yongjun; DOU; Guoren; HAN; Longxi; SHAO; Xuejun; YANG
2004-01-01
This paper presents a 3D mathematical model for suspended load transport in turbulent flows. Based on Dou's stochastic theory of turbulent flow, numerical schemes of Reynolds stresses for anisotropic turbulent flows were obtained. A refined wall function was employed to treat solid wall boundaries. The equations for 2D suspended load motion and sorting of bed material have been expanded into 3D cases. Numerical results are validated by the measured data of the Gezhouba Project, and proved to be in good agreement with the experimental. The present method has been employed to simulate sediment erosion and deposition in the dam area of Three Gorges Project, and for the operation of the project, siltation process and deposition pattern in the near-dam area of the reservoir, size distribution of the deposits and bed material, and flow fields and sediment concentration fields at different time and elevations are predicted. The predicted results are close to the experimental observations in physical model studies. Thus, a new method is established for 3D simulation of sediment motion in dam areas of multi-purpose water projects.
Understanding thermal Marangoni flow in water sessile evaporating drops via 3D-PTV
Rossi, Massimiliano; Marin, Alvaro; Kaehler, Christian J.
2016-11-01
Understanding the flow inside sessile evaporating drops is of great interest both from a fundamental and technological point of view. Despite strong research efforts in the recent years, a complete picture on the phenomena involved in this process and a way to control them is still far to be reached. This is due to a lack of reliable experimental data on the internal flow but more dramatically on the interfacial flow. A relevant open debate concerns the role played by the Marangoni flow induced by thermal gradients. We recently show how 3D particle tracking techniques are suitable to measure the internal flow of drops and to derive quantities such as surface shear and surface tension differences. Such experiments also indicated an increase of the thermal Marangoni flow as the droplet becomes thinner, in disagreement with current theoretical models and simulations. A possible reason for that could be a discrepancy of the imposed boundary conditions in the simulations and the experimental ones. This work follows up these observations with fully 3D time-resolved measurements of the flow inside drops evaporating on a quartz substrate, which temperature is controlled using a feedback temperature control and a microscope incubator system. Supported by DFG, Grant No. KA 1808/22.
Switchable 3D optofluidic Y-branch waveguides tuned by Dean flows
Li, L.; Zhu, X. Q.; Liang, L.; Zuo, Y. F.; Xu, Y. S.; Yang, Y.; Yuan, Y. J.; Huang, Q. Q.
2016-12-01
Optical branch waveguides are one of the most important optical elements and have been widely exploited for optical communication systems. However, prevailing devices are typically solid and have limit in tunability. Liquid optical devices have attracted more interest for the advantage of tunability of liquid media, but their signals suffer serious leakage if the refractive index (RI) of liquid is smaller than that of solid channels. This paper demonstrates the tunable three-dimensional (3D) optofluidic Y-branch waveguides in plannar microchannels by simply introducing Dean flow. This device can reconfigure 3D Y-branch profiles and separate the intensity of light as tunable ratio from 0 to 1 by adjusting the flow rates with low loss. Different from the prevailing 2D liquid counterparts, the 3D configuration offer much more freedom in the selection of liquid media as liquid’s RI can be totally independent to the solid channel structure. The transmission loss through the device is estimated to 0.97 db when the splitting angle is 10°, which shows the light is confined better in the 3D liquid structures than traditional 2D liquid counterparts. The Y-branch waveguides show potential in applications of integrated optofluidic devices.
Assessment of 3D-RANS models for the simulation of topographically forced shallow flows
Directory of Open Access Journals (Sweden)
Safarzadeh Akbar
2016-03-01
Full Text Available In this work the performance of Reynolds Averaged Navier-Stokes (RANS simulations to predict the flow structure developed by the presence of a sidewall obstacle in a uniform open-channel shallow flow is discussed. The tested geometry was selected due to its important role in several fluvial applications, such as the control of riverbank erosion and the creation of improved ecological conditions in river restoration applications. The results are compared against experimental laboratory velocity fields obtained after Large Scale Particle Image Velocimetry (LSPIV measurements. It is shown that the length of reattachment of the separated shear layer generated by the obstacle is well predicted by a Reynolds Stress Model, while classical two-equation models show important limitations. All the performed RANS simulations are unable to properly predict the formation of a secondary gyre region, which develops immediately downstream the obstacle.
Nonlinear analysis of chaotic flow in a 3D closed-loop pulsating heat pipe
Pouryoussefi, S M
2016-01-01
Numerical simulation has been conducted for the chaotic flow in a 3D closed-loop pulsating heat pipe (PHP). Heat flux and constant temperature boundary conditions were applied for evaporator and condenser sections, respectively. Water and ethanol were used as working fluids. Volume of Fluid (VOF) method has been employed for two-phase flow simulation. Spectral analysis of temperature time series was carried out using Power Spectrum Density (PSD) method. Existence of dominant peak in PSD diagram indicated periodic or quasi-periodic behavior in temperature oscillations at particular frequencies. Correlation dimension values for ethanol as working fluid was found to be higher than that for water under the same operating conditions. Similar range of Lyapunov exponent values for the PHP with water and ethanol as working fluids indicated strong dependency of Lyapunov exponent to the structure and dimensions of the PHP. An O-ring structure pattern was obtained for reconstructed 3D attractor at periodic or quasi-peri...
Sand transverse dune aerodynamics: 3D Coherent Flow Structures from a computational study
Bruno, Luca
2015-01-01
The engineering interest about dune fields is dictated by the their interaction with a number of human infrastructures in arid environments. The aerodynamic behaviour of sand dunes in atmospheric boundary layer belongs to the class of bluff bodies. Because of their simple geometry and their frequent occurrence in desert area, transverse sand dunes are usually adopted in literature as a benchmark to investigate dune aerodynamics by means of both computational or experimental approach, usually in nominally 2D setups. The writers suspect the flow in the wake is characterised by 3D features and affected by wind tunnel setup - e.g. blockage effect, duct side wall boundary layer, incoming velocity profile - when experimental studies are carried out. The present study aims at evaluating the 3D flow features of an idealised transverse dune under different setup conditions by means of computational simulations and to compare the obtained results with experimental measurements.
Quantification of smoothing requirement for 3D optic flow calculation of volumetric images
DEFF Research Database (Denmark)
Bab-Hadiashar, Alireza; Tennakoon, Ruwan B.; de Bruijne, Marleen
2013-01-01
that a (surprisingly) small amount of local smoothing is required to satisfy both the necessary and sufficient conditions for accurate optic flow estimation. This notion is called 'just enough' smoothing, and its proper implementation has a profound effect on the preservation of local information in processing 3D...... dynamic scans. To demonstrate the effect of 'just enough' smoothing, a robust 3D optic flow method with quantized local smoothing is presented, and the effect of local smoothing on the accuracy of motion estimation in dynamic lung CT images is examined using both synthetic and real image sequences......Complexities of dynamic volumetric imaging challenge the available computer vision techniques on a number of different fronts. This paper examines the relationship between the estimation accuracy and required amount of smoothness for a general solution from a robust statistics perspective. We show...
INTRINSIC FEATURES OF TURBULENT FLOW IN STRONGLY 3-D SKEW BLADE PASSAGE OF A FRANCIS TURBINE
Institute of Scientific and Technical Information of China (English)
ZHANG Li-xiang; WANG Wen-quan; GUO Yakun
2007-01-01
The turbulent flow, with the Reynolds number of 5.9 105, in the strongly 3-D skew blade passage of a true Francis hydro turbine was simulated by the Large Eddy Simulation (LES) approach to investigate the spatial and temporal distributions of the fully developed turbulence in the passage with strongly 3-D complex geometry. The simulations show that the strong three-dimensionality of the passage has a great amplification effect on the turbulence in the passage, and the distributions of the turbulence are diversely nonuniform, for instance, the rise of turbulent kinetic energy in the lower 1/3 region of the passage is more than 45%, whereas its rise in the upper 1/3 region is less than 1%. With the LES approach, the details of the flow structures at the near-wall surfaces of the blades could be obtained. Several turbulent spots were captured.
Fundamental Experimental and Numerical Investigation of Active Control of 3-D Flows
2011-10-06
on hot - wire anemometry and therefore, it was noted that understanding 3-D flow structures in detail was difficult. Nevertheless, prominent features...S.G., Reizes, J.A., Hong, G. and Westbury, P.S., 2004, “Analysis of Hot - wire Anemometry Data Obtained in a Synthetic Jet Flow”, Experimental Thermal...Measurements were made using three different techniques, namely, Particle Image Velocimetry (PIV), Laser Doppler Velocimetry (LDV), and hot - wire
Shepard, Lauren; Sommer, Kelsey; Izzo, Richard; Podgorsak, Alexander; Wilson, Michael; Said, Zaid; Rybicki, Frank J.; Mitsouras, Dimitrios; Rudin, Stephen; Angel, Erin; Ionita, Ciprian N.
2017-03-01
Purpose: Accurate patient-specific phantoms for device testing or endovascular treatment planning can be 3D printed. We expand the applicability of this approach for cardiovascular disease, in particular, for CT-geometry derived benchtop measurements of Fractional Flow Reserve, the reference standard for determination of significant individual coronary artery atherosclerotic lesions. Materials and Methods: Coronary CT Angiography (CTA) images during a single heartbeat were acquired with a 320x0.5mm detector row scanner (Toshiba Aquilion ONE). These coronary CTA images were used to create 4 patientspecific cardiovascular models with various grades of stenosis: severe, stenosis using pressure transducers. Compliance chambers were used before and after the model to modulate the pressure wave. A flow sensor was used to ensure flow rates within physiological reported values. Results: 3D model based FFR measurements correlated well with stenosis severity. FFR measurements for each stenosis grade were: 0.8 severe, 0.7 moderate and 0.88 mild. Conclusions: 3D printed models of patient-specific coronary arteries allows for accurate benchtop diagnosis of FFR. This approach can be used as a future diagnostic tool or for testing CT image-based FFR methods.
Electric Current Filamentation Induced by 3D Plasma Flows in the Solar Corona
Nickeler, Dieter H.; Wiegelmann, Thomas; Karlický, Marian; Kraus, Michaela
2017-03-01
Many magnetic structures in the solar atmosphere evolve rather slowly, so they can be assumed as (quasi-)static or (quasi-)stationary and represented via magnetohydrostatic (MHS) or stationary magnetohydrodynamic (MHD) equilibria, respectively. While exact 3D solutions would be desired, they are extremely difficult to find in stationary MHD. We construct solutions with magnetic and flow vector fields that have three components depending on all three coordinates. We show that the noncanonical transformation method produces quasi-3D solutions of stationary MHD by mapping 2D or 2.5D MHS equilibria to corresponding stationary MHD states, that is, states that display the same field-line structure as the original MHS equilibria. These stationary MHD states exist on magnetic flux surfaces of the original 2D MHS states. Although the flux surfaces and therefore also the equilibria have a 2D character, these stationary MHD states depend on all three coordinates and display highly complex currents. The existence of geometrically complex 3D currents within symmetric field-line structures provides the basis for efficient dissipation of the magnetic energy in the solar corona by ohmic heating. We also discuss the possibility of maintaining an important subset of nonlinear MHS states, namely force-free fields, by stationary flows. We find that force-free fields with nonlinear flows only arise under severe restrictions of the field-line geometry and of the magnetic flux density distribution.
Numerical investigations on cavitation intensity for 3D homogeneous unsteady viscous flows
Leclercq, C.; Archer, A.; Fortes-Patella, R.
2016-11-01
The cavitation erosion remains an industrial issue. In this paper, we deal with the cavitation intensity which can be described as the aggressiveness - or erosive capacity - of a cavitating flow. The estimation of this intensity is a challenging problem both in terms of modelling the cavitating flow and predicting the erosion due to cavitation. For this purpose, a model was proposed to estimate cavitation intensity from 3D unsteady cavitating flow simulations. An intensity model based on pressure and void fraction derivatives was developped and applied to a NACA 65012 hydrofoil tested at LMH-EPFL (École Polytechnique Fédérale de Lausanne) [1]. 2D and 3D unsteady cavitating simulations were performed using a homogeneous model with void fraction transport equation included in Code_Saturne with cavitating module [2]. The article presents a description of the numerical code and the physical approach considered. Comparisons between 2D and 3D simulations, as well as between numerical and experimental results obtained by pitting tests, are analyzed in the paper.
Nonhydrostatic granular flow over 3-D terrain: New Boussinesq-type gravity waves?
Castro-Orgaz, Oscar; Hutter, Kolumban; Giraldez, Juan V.; Hager, Willi H.
2015-01-01
granular mass flow is a basic step in the prediction and control of natural or man-made disasters related to avalanches on the Earth. Savage and Hutter (1989) pioneered the mathematical modeling of these geophysical flows introducing Saint-Venant-type mass and momentum depth-averaged hydrostatic equations using the continuum mechanics approach. However, Denlinger and Iverson (2004) found that vertical accelerations in granular mass flows are of the same order as the gravity acceleration, requiring the consideration of nonhydrostatic modeling of granular mass flows. Although free surface water flow simulations based on nonhydrostatic depth-averaged models are commonly used since the works of Boussinesq (1872, 1877), they have not yet been applied to the modeling of debris flow. Can granular mass flow be described by Boussinesq-type gravity waves? This is a fundamental question to which an answer is required, given the potential to expand the successful Boussinesq-type water theory to granular flow over 3-D terrain. This issue is explored in this work by generalizing the basic Boussinesq-type theory used in civil and coastal engineering for more than a century to an arbitrary granular mass flow using the continuum mechanics approach. Using simple test cases, it is demonstrated that the above question can be answered in the affirmative way, thereby opening a new framework for the physical and mathematical modeling of granular mass flow in geophysics, whereby the effect of vertical motion is mathematically included without the need of ad hoc assumptions.
NUMERICAL SIMULATION OF 3-D FLOW FIELD IN ARCIFORM PLUNGE POOL
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
The 3-D complex turbulent flow fields in aplunge pool with arciform bottom are simulated by using thek-ε model in body-fitted coordinates. The calculated results re-veal the flow characteristics in the arciform plunge pool underthe different flood discharge conditions, which can not be easi-ly obtained in the physical model test because the measure-ment of the complex velocity is very difficult. The calculatedflow fields are helpful to understand in depth the hydrauliccharacteristics of plunge pool. The calculated and the meas-ured pressure distributions on the pool bottom are comparedand in good agreement.
Bridging from Eulerian to Lagrangian statistics in 3D hydro- and magnetohydrodynamic turbulent flows
Energy Technology Data Exchange (ETDEWEB)
Homann, H [CNRS, Universite de Nice-Sophia Antipolis, Observatoire de la Cote d' Azur, Lab. Cassiopee, Bd. de l' Observatoire, 06300 Nice (France); Kamps, O [Center for Nonlinear Science, Universitaet Muenster, 48149 Muenster (Germany); Friedrich, R [Theoretische Physik, Universitaet Muenster, 48149 Muenster (Germany); Grauer, R [Theoretische Physik I, Ruhr-Universitaet, 44780 Bochum (Germany)], E-mail: grauer@tp1.rub.de
2009-07-15
We present measurements of conditional probability density functions (PDFs) that allow one to systematically bridge from Eulerian to Lagrangian statistics in fully developed 3D turbulence. The transition is investigated for hydro- as well as magnetohydrodynamic flows and comparisons are drawn. Significant differences in the transition PDFs are observed for these flows and traced back to the differing coherent structures. In particular, we address the problem of an increasing degree of intermittency going from Eulerian to Lagrangian coordinates by means of the conditional PDFs involved in this transformation. First simple models of these PDFs are investigated in order to distinguish different contributions to the degree of Lagrangian intermittency.
Numerical Simulations of Flow in a 3-D Supersonic Intake at High Mach Numbers
Directory of Open Access Journals (Sweden)
R. Sivakumar
2006-10-01
Full Text Available Numerical simulations of the compressible, 3-D non reacting flow in the engine inlet sectionof a concept hypersonic air-breathing vehicle are presented. These simulations have been carriedout using FLUENT. For all the results reported, the mesh has been refined to achieve areaaveragedwall y+ about 105. Mass flow rate through the intake and stagnation pressure recoveryare used to compare the performance at various angles of attack. The calculations are able topredict the mode of air-intake operation (critical and subcritical for different angles of attack.Flow distortion at the intake for various angles of attack is also calculated and discussed. Thenumerical results are validated by simulating the flow through a 2-D mixed compression hypersonicintake model and comparing with the experimental data.
Incorporating preferential flow into a 3D model of a forested headwater catchment
Glaser, Barbara; Jackisch, Conrad; Hopp, Luisa; Pfister, Laurent; Klaus, Julian
2016-04-01
Preferential flow plays an important role for water flow and solute transport. The inclusion of preferential flow, for example with dual porosity or dual permeability approaches, is a common feature in transport simulations at the plot scale. But at hillslope and catchment scales, incorporation of macropore and fracture flow into distributed hydrologic 3D models is rare, often due to limited data availability for model parameterisation. In this study, we incorporated preferential flow into an existing 3D integrated surface subsurface hydrologic model (HydroGeoSphere) of a headwater region (6 ha) of the forested Weierbach catchment in western Luxembourg. Our model philosophy was a strong link between measured data and the model setup. The model setup we used previously had been parameterised and validated based on various field data. But existing macropores and fractures had not been considered in this initial model setup. The multi-criteria validation revealed a good model performance but also suggested potential for further improvement by incorporating preferential flow as additional process. In order to pursue the data driven model philosophy for the implementation of preferential flow, we analysed the results of plot scale bromide sprinkling and infiltration experiments carried out in the vicinity of the Weierbach catchment. Three 1 sqm plots were sprinkled for one hour and excavated one day later for bromide depth profile sampling. We simulated these sprinkling experiments at the soil column scale, using the parameterisation of the base headwater model extended by a second permeability domain. Representing the bromide depth profiles was successful without changing this initial parameterisation. Moreover, to explain the variability between the three bromide depth profiles it was sufficient to adapt the dual permeability properties, indicating the spatial heterogeneity of preferential flow. Subsequently, we incorporated the dual permeability simulation in the
A numerical study of two-phase Stokes flow in an axisymmetric flow-focusing device
DEFF Research Database (Denmark)
Jensen, Mads Jakob; Stone, H.A.; Bruus, Henrik
2006-01-01
in MATLAB, which interfaces with the finite-element software FEMLAB. We derive scaling laws for the volume of a created bubble and for the gas flow rate, and confirm them numerically. Our results are consistent with existing experimental results by Garstecki et al. [Phys. Rev. Lett. 94, 164501 (2005......We present a numerical investigation of the time-dependent dynamics of the creation of gas bubbles in an axisymmetric flow-focusing device. The liquid motion is treated as a Stokes flow, and using a generic framework we implement a second-order time-integration scheme and a free-surface model......)], and predict a scaling yet to be observed: the bubble volume scales with the outlet channel radius to the power of 4 and the surface tension. Our axisymmetric simulations further show that the collapse of the gas thread before bubble snap-off is different from the recent experimental results. We suggest...
3D Simulation of Flow with Free Surface Based on Adaptive Octree Mesh System
Institute of Scientific and Technical Information of China (English)
Li Shaowu; Zhuang Qian; Huang Xiaoyun; Wang Dong
2015-01-01
The technique of adaptive tree mesh is an effective way to reduce computational cost through automatic adjustment of cell size according to necessity. In the present study, the 2D numerical N-S solver based on the adaptive quadtree mesh system was extended to a 3D one, in which a spatially adaptive octree mesh system and multiple parti-cle level set method were adopted for the convenience to deal with the air-water-structure multiple-medium coexisting domain. The stretching process of a dumbbell was simulated and the results indicate that the meshes are well adaptable to the free surface. The collapsing process of water column impinging a circle cylinder was simulated and from the results, it can be seen that the processes of fluid splitting and merging are properly simulated. The interaction of sec-ond-order Stokes waves with a square cylinder was simulated and the obtained drag force is consistent with the result by the Morison’s wave force formula with the coefficient values of the stable drag component and the inertial force component being set as 2.54.
3D Laboratory Measurements of Forces, Flows, and Collimation in Arched Flux Tubes
Haw, Magnus; Bellan, Paul
2016-10-01
Fully 3D, vector MHD force measurements from an arched, current carrying flux tube (flux rope) are presented. The experiment consists of two arched plasma-filled flux ropes each powered by a capacitor bank. The two loops are partially overlapped, as in a Venn diagram, and collide and reconnect during their evolution. B-field data is taken on the lower plasma arch using a 54 channel B-dot probe. 3D volumetric data is acquired by placing the probe at 2700 locations and taking 5 plasma shots at each location. The resulting data set gives high resolution (2cm, 10ns) volumetric B-field data with high reproducibility (deviation of 3% between shots). Taking the curl of the measured 3D B-field gives current densities (J) in good agreement with measured capacitor bank current. The JxB forces calculated from the data have a strong axial component at the base of the current channel and are shown to scale linearly with axial gradients in current density. Assuming force balance in the flux tube minor radius direction, we infer near-Alfvenic axial flows from the footpoint regions which are consistent with the measured axial forces. Flux tube collimation is observed in conjunction with these axial flows. These dynamic processes are relevant to the stability and dynamics of coronal loops. Supported provided by NSF, AFOSR.
Pipe Flow and Wall Turbulence Using a Modified Navier-Stokes Equation
Institute of Scientific and Technical Information of China (English)
L. Jirkovsky; A. Muriel
2012-01-01
We use a derived incompressible modified Navier-Stokes equation to model pipe flow and wall turbulence. We reproduce the observed flattened paraboloid velocity profiles of turbulence that cannot be obtained directly using standard incompressible Navier-Stokes equation. The solutions found are in harmony with multi-valued velocity fields as a definition of turbulence. Repeating the procedure for the flow of turbulent fluid between two parallel flat plates we find similar flattened velocity profiles. We extend the analysis to the turbulent flow along a single wall and compare the results with experimental data and the established controversial yon Karman logarithmic law of the wall.
A continuous flow microfluidic calorimeter: 3-D numerical modeling with aqueous reactants
Energy Technology Data Exchange (ETDEWEB)
Sen, Mehmet A., E-mail: mehmet.sen@mathworks.com [Northeastern University, Department of Mechanical and Industrial Engineering, 360 Hungtington Avenue, 334 Snell Engineering Center, Boston, MA 02115 (United States); Kowalski, Gregory J., E-mail: gkowal@coe.neu.edu [Northeastern University, Department of Mechanical and Industrial Engineering, 360 Hungtington Avenue, 334 Snell Engineering Center, Boston, MA 02115 (United States); Fiering, Jason, E-mail: jfiering@draper.com [Charles Stark Draper Laboratory, 555 Technology Square, Cambridge, MA 02139 (United States); Larson, Dale, E-mail: dlarson@draper.com [Charles Stark Draper Laboratory, 555 Technology Square, Cambridge, MA 02139 (United States)
2015-03-10
Highlights: • A co-flow microreactor is modeled in flow, reaction/diffusion, and thermal domains. • Analysis shows how arrayed temperature sensors can provide enthalpy of reaction. • Optical plasmonic temperature sensors could be arrayed suitably for calorimetry. • The reactor studied has a volume of 25 nL. - Abstract: A computational analysis of the reacting flow field, species diffusion and heat transfer processes with thermal boundary layer effects in a microchannel reactor with a coflow configuration was performed. Two parallel adjacent streams of aqueous reactants flow along a wide, shallow, enclosed channel in contact with a substrate, which is affixed to a temperature controlled plate. The Fluent computational fluid dynamics package solved the Navier–Stokes, mass transport and energy equations. The energy model, including the enthalpy of reaction as a nonuniform heat source, was validated by calculating the energy balance at several control volumes in the microchannel. Analysis reveals that the temperature is nearly uniform across the channel thickness, in the direction normal to the substrate surface; hence, measurements made by sensors at or near the surface are representative of the average temperature. Additionally, modeling the channel with a glass substrate and a silicone cover shows that heat transfer is predominantly due to the glass substrate. Finally, using the numerical results, we suggest that a microcalorimeter could be based on this configuration, and that temperature sensors such as optical nanohole array sensors could have sufficient spatial resolution to determine enthalpy of reaction.
Cauchy's almost forgotten Lagrangian formulation of the Euler equation for 3D incompressible flow
Frisch, Uriel
2014-01-01
Two prized papers, one by Augustin Cauchy in 1815, presented to the French Academy and the other by Hermann Hankel in 1861, presented to G\\"ottingen University, contain major discoveries on vorticity dynamics whose impact is now quickly increasing. Cauchy found a Lagrangian formulation of 3D ideal incompressible flow in terms of three invariants that generalize to three dimensions the now well-known law of conservation of vorticity along fluid particle trajectories for two-dimensional flow. This has very recently been used to prove analyticity in time of fluid particle trajectories for 3D incompressible Euler flow and can be extended to compressible flow, in particular to cosmological dark matter. Hankel showed that Cauchy's formulation gives a very simple Lagrangian derivation of the Helmholtz vorticity-flux invariants and, in the middle of the proof, derived an intermediate result which is the conservation of the circulation of the velocity around a closed contour moving with the fluid. This circulation the...
Intrathoracic tumour motion estimation from CT imaging using the 3D optical flow method
Guerrero, Thomas; Zhang, Geoffrey; Huang, Tzung-Chi; Lin, Kang-Ping
2004-09-01
The purpose of this work was to develop and validate an automated method for intrathoracic tumour motion estimation from breath-hold computed tomography (BH CT) imaging using the three-dimensional optical flow method (3D OFM). A modified 3D OFM algorithm provided 3D displacement vectors for each voxel which were used to map tumour voxels on expiration BH CT onto inspiration BH CT images. A thoracic phantom and simulated expiration/inspiration BH CT pairs were used for validation. The 3D OFM was applied to the measured inspiration and expiration BH CT images from one lung cancer and one oesophageal cancer patient. The resulting displacements were plotted in histogram format and analysed to provide insight regarding the tumour motion. The phantom tumour displacement was measured as 1.20 and 2.40 cm with full-width at tenth maximum (FWTM) for the distribution of displacement estimates of 0.008 and 0.006 cm, respectively. The maximum error of any single voxel's motion estimate was 1.1 mm along the z-dimension or approximately one-third of the z-dimension voxel size. The simulated BH CT pairs revealed an rms error of less than 0.25 mm. The displacement of the oesophageal tumours was nonuniform and up to 1.4 cm, this was a new finding. A lung tumour maximum displacement of 2.4 cm was found in the case evaluated. In conclusion, 3D OFM provided an accurate estimation of intrathoracic tumour motion, with estimated errors less than the voxel dimension in a simulated motion phantom study. Surprisingly, oesophageal tumour motion was large and nonuniform, with greatest motion occurring at the gastro-oesophageal junction. Presented at The IASTED Second International Conference on Biomedical Engineering (BioMED 2004), Innsbruck, Austria, 16-18 February 2004.
Bifurcations and degenerate periodic points in a 3D chaotic fluid flow
Smith, Lachlan D; Lester, Daniel R; Metcalfe, Guy
2016-01-01
Analysis of the periodic points of a conservative periodic dynamical system uncovers the basic kinematic structure of the transport dynamics, and identifies regions of local stability or chaos. While elliptic and hyperbolic points typically govern such behaviour in 3D systems, degenerate (parabolic) points play a more important role than expected. These points represent a bifurcation in local stability and Lagrangian topology. In this study we consider the ramifications of the two types of degenerate periodic points that occur in a model 3D fluid flow. (1) Period-tripling bifurcations occur when the local rotation angle associated with elliptic points is reversed, creating a reversal in the orientation of associated Lagrangian structures. Even though a single unstable point is created, the bifurcation in local stability has a large influence on local transport and the global arrangement of manifolds as the unstable degenerate point has three stable and three unstable directions, similar to hyperbolic points, ...
PIV Measurement of Pulsatile Flows in 3D Curved Tubes Using Refractive Index Matching Method
Energy Technology Data Exchange (ETDEWEB)
Hong, Hyeon Ji; Ji, Ho Seong; Kim, Kyung Chun [Pusan Nat’l Univ., Busan (Korea, Republic of)
2016-08-15
Three-dimensional models of stenosis blood vessels were prepared using a 3D printer. The models included a straight pipe with axisymmetric stenosis and a pipe that was bent 10° from the center of stenosis. A refractive index matching method was utilized to measure accurate velocity fields inside the 3D tubes. Three different pulsatile flows were generated and controlled by changing the rotational speed frequency of the peristaltic pump. Unsteady velocity fields were measured by a time-resolved particle image velocimetry method. Periodic shedding of vortices occurred and moves depended on the maximum velocity region. The sizes and the positions of the vortices and symmetry are influenced by mean Reynolds number and tube geometry. In the case of the bent pipe, a recirculation zone observed at the post-stenosis could explain the possibility of blood clot formation and blood clot adhesion in view of hemodynamics.
Squire's transformation and 3D Optimal Perturbations in Bounded Parallel Shear Flows
Chomaz, Jean-Marc; Soundar Jerome, J. John
2011-11-01
The aim of this short communication is to present the implication of Squire's transformation on the optimal transient growth of arbitrary 3D disturbances in parallel shear flow bounded in the cross-stream direction. To our best knowledge this simple property has never been discussed before. In particular it allows to express the long-time optimal growth for perturbations of arbitrary wavenumbers as the product of the gains from the 2D optimal at a lower Reynolds number itself due to the Orr-mechanism by a term that may be identified as due to the lift-up mechanism. This property predict scalings for the 3D optimal perturbation well verified by direct computation. It may be extended to take into account buoyancy effect.
A 3-D nonisothermal flow simulation and pulling force model for injection pultrusion processes
Mustafa, Ibrahim
1998-12-01
Injected Pultrusion (IP) is an efficient way of producing high quality, low cost, high volume and constant cross-section polymeric composites. This process has been developed recently, and the efforts to optimize it are still underway. This work is related to the development of a 3-D non-isothermal flow model for the IP processes. The governing equations for transport of mass, momentum and, energy are formulated by using a local volume averaging approach, and the Finite Element/Control Volume method is used to solve the system of equations numerically. The chemical species balance equation is solved in the Lagrangian frame of reference whereas the energy equation is solved using Galerkin, SU (Streamline Upwind), and SUPG (Streamline Upwind Petrov Galerkin) approaches. By varying degrees of freedom and the flow rates of the resin, it is shown that at high Peclet numbers the SUPG formulation performs better than the SU and the Galerkin methods in all cases. The 3-D model predictions for degree of cure and temperature are compared with a one dimensional analytical solution and the results are found satisfactory. Moreover, by varying the Brinkman Number, it is shown that the effect of viscous dissipation is insignificant. The 3-D flow simulations have been carried out for both thin and thick parts and the results are compared with the 2-D model. It is shown that for thick parts 2-D simulations render erroneous results. The effect of changing permeability on the flow fronts is also addressed. The effect of increasing taper angle on the model prediction is also investigated. A parametric study is conducted to isolate optimum conditions for both isothermal and non-isothermal cases using a straight rectangular die and a die with a tapered inlet. Finally, a simple pulling force model is developed and the pulling force required to pull the carbon-epoxy fiber resin system is estimated for dies of varying tapered inlet.
Biedron, Robert T.; Vatsa, Veer N.; Atkins, Harold L.
2005-01-01
We apply an unsteady Reynolds-averaged Navier-Stokes (URANS) solver for unstructured grids to unsteady flows on moving and stationary grids. Example problems considered are relevant to active flow control and stability and control. Computational results are presented using the Spalart-Allmaras turbulence model and are compared to experimental data. The effect of grid and time-step refinement are examined.
Predictions of bubbly flows in vertical pipes using two-fluid models in CFDS-FLOW3D code
Energy Technology Data Exchange (ETDEWEB)
Banas, A.O.; Carver, M.B. [Chalk River Laboratories (Canada); Unrau, D. [Univ. of Toronto (Canada)
1995-09-01
This paper reports the results of a preliminary study exploring the performance of two sets of two-fluid closure relationships applied to the simulation of turbulent air-water bubbly upflows through vertical pipes. Predictions obtained with the default CFDS-FLOW3D model for dispersed flows were compared with the predictions of a new model (based on the work of Lee), and with the experimental data of Liu. The new model, implemented in the CFDS-FLOW3D code, included additional source terms in the {open_quotes}standard{close_quotes} {kappa}-{epsilon} transport equations for the liquid phase, as well as modified model coefficients and wall functions. All simulations were carried out in a 2-D axisymmetric format, collapsing the general multifluid framework of CFDS-FLOW3D to the two-fluid (air-water) case. The newly implemented model consistently improved predictions of radial-velocity profiles of both phases, but failed to accurately reproduce the experimental phase-distribution data. This shortcoming was traced to the neglect of anisotropic effects in the modelling of liquid-phase turbulence. In this sense, the present investigation should be considered as the first step toward the ultimate goal of developing a theoretically sound and universal CFD-type two-fluid model for bubbly flows in channels.
Measurement and inverse estimation of 3D anisotropic flow resistivity for porous materials
Göransson, Peter; Guastavino, Rémi; Hörlin, Nils-Erik
2009-11-01
This paper presents a new methodology for estimating the anisotropic flow resistivity for porous materials. From pressure measurements on a cubic or parallelepiped sample of a porous material, the flow resistivities are determined using inverse estimation. The core of the estimation is a series of 3D solutions to Darcy's law, where the flow resistivity tensor is varied until the sum of the quadratic errors between measured and computed pressures is minimised. The overall approach and experimental set-up used, enabling efficient measurements of high quality, are described in some detail together with the main steps of the measurement and estimation procedures. Results from a fibrous glass wool and a polyurethane foam are discussed and compared to standard measurement data.
Simulation of 3D material flow in friction stir welding of AA6061-T6
Institute of Scientific and Technical Information of China (English)
Zhang Zhao; Zhang Hongwu
2008-01-01
This paper reports the numerical simulation of the 3D material flow in friction stir welding process by using finite element methods based on solid mechanics. It is found that the material flow behind the pin is much faster than that in front of the pin. The material in front of the pin moves upwards and then rotates with the pin due to the effect of the rotating tool. Behind of the pin, the material moves downwards. This process of material movement is the real cause to make the friction stir welding process continuing successfully. With the increase of the translational velocity or the rotational velocity of the pin, the material flow becomes faster.
Costa, J E R
2009-01-01
Polars (or AM Her systems) are cataclysmic variables without a disc due to the strong magnetic field of the white dwarf. Most of their emission comes from the region where the accretion column impacts the white dwarf and cools through cyclotron and bremsstrahlung processes. We present a new code, CYCLOPS, to model the optical emission from these systems including the four Stokes parameters. It considers a three-dimensional region with the electronic density and temperature varying following a \\textit{shock-like} profile and a dipolar magnetic field. The radiative transfer is solved in steps considering the solution with non-null input radiation. The footprint of the column in the white-dwarf surface is determined by the threading region in the equatorial plane, i.e., the region from where the flow follows the magnetic lines. The extinction caused by Thomson scattering above the emitting region is optionally included. The fittings of observational data are done using a hybrid approach: a genetic algorithm is u...
Numerical Study on the 3-D Complex Characteristics of Flow Around the Hull Structure of TLP
Institute of Scientific and Technical Information of China (English)
谷家扬; 朱新耀; 杨建民; 卢燕祥; 肖龙飞
2015-01-01
Vortex-induced motion is based on the complex characteristics of the flow around the tension leg platform (TLP) hull. By considering the flow field of the South China Sea and the configuration of the platform, three typical flow velocities and three flow directions are chosen to study the numerical simulation of the flow field characteristics around the TLP hull. Reynolds-averaged Navier–Stokes equations combined with the detached eddy simulation turbulence model are employed in the numerical study. The hydrodynamic coefficients of columns and pontoons, the total drag and lift coefficients of the TLP, the formation and development of the wake, and the vorticity iso-surfaces for different inlet velocities and current directions are discussed in this paper. The average value of the drag coefficient of the upstream columns is considerably larger than that of the downstream columns in the inlet direction of 0°. Although the time history of the lift coefficient demonstrates a “beating” behavior, the plot shows regularity in general. The Strouhal number decreases as the inlet velocity increases from the power spectral density plot at different flow velocities. The mean root values of the lift and drag coefficients of the front column decrease as the current direction increases. Under the symmetrical configuration of 45°, the streamwise force on C4 is the smallest, whereas the transverse force is the largest. The broken vortex conditions in current directions of 22.5° and 45° are more serious than that in the current direction of 0°. In addition, turbulence at the bottom of the TLP becomes stronger when the current direction changes from 0° to 45°. However, a high inlet velocity indicates a large region influenced by the broken vortex and shows the emergence of the wake behind the TLP under the same current angle.
Numerical simulation of unsteady flow characteristics for cavitation around a 3-D hydrofoil
Ahn, S. H.; Xiao, Y. X.; Wang, Z. W.
2015-01-01
At present it is possible to predict more accurately by various numerical methods established for cavitation simulation around a hydrofoil. However, for the solution of the complex unsteady cavity flow, it is still marginal. In this paper, numerical method is adopted to simulate cavitation around 3-D NACA0015 hydrofoil with homogeneous two-phase flow calculation using commercial code CFX-solver with two turbulence models, the standard RNG k-epsilon turbulence model and the modified RNG k-epsilon turbulence model respectively. First, pressure coefficient for non-cavitating flow, time averaged values of unsteady cavity flow around a hydrofoil are verified to simulate more closely to an actual cavity flow. And then frequency analysis is performed with Fast Fourier Transform. The results show that the calculation results with modified RNG k-epsilon turbulence model agree with experimental results in terms of mean cavity length and pressure drop, but the unsteady flow characteristics of oscillating cavitation still deviate slightly in terms of unsteady cavity flow.
3D visualization of the material flow in friction stir welding process
Institute of Scientific and Technical Information of China (English)
Zhao Yanhua; Lin Sanbao; Shen Jiajie; Wu Lin
2005-01-01
The material flow in friction stir welded 2014 Al alloy has been investigated using a marker insert technique (MIT). Results of the flow visualization show that the material flow is asymmetrical during the friction stir welding(FSW)process and there are also significant differences in the flow patterns observed on advancing side and retreating side. On advancing side, some material transport forward and some move backward, but on retreating side, material only transport backward. At the top surface of the weld, significant material traasport forward due to the action of the rotating tool shoulder.Combining the data from all the markers, a three-dimensional flow visualization, similar to the 3D image reconstruction technique, was obtained. The three-dimensional plot gives the tendency chart of material flow in friction stir welding process and from the plot it can be seen that there is a vertical, circular motion around the longitudinal axis of the weld. On the advancing side of the weld, the material is pushed downward but on the retreating side, the material is pushed toward the crown of the weld. The net result of the two relative motions in both side of the advancing and the retreating is that a circular motion comes into being. Comparatively, the material flow around the longitudinal axis is a secondary motion.
A Laminar Flow-Based Microfluidic Tesla Pump via Lithography Enabled 3D Printing.
Habhab, Mohammed-Baker; Ismail, Tania; Lo, Joe Fujiou
2016-11-23
Tesla turbine and its applications in power generation and fluid flow were demonstrated by Nicholas Tesla in 1913. However, its real-world implementations were limited by the difficulty to maintain laminar flow between rotor disks, transient efficiencies during rotor acceleration, and the lack of other applications that fully utilize the continuous flow outputs. All of the aforementioned limits of Tesla turbines can be addressed by scaling to the microfluidic flow regime. Demonstrated here is a microscale Tesla pump designed and fabricated using a Digital Light Processing (DLP) based 3D printer with 43 µm lateral and 30 µm thickness resolutions. The miniaturized pump is characterized by low Reynolds number of 1000 and a flow rate of up to 12.6 mL/min at 1200 rpm, unloaded. It is capable of driving a mixer network to generate microfluidic gradient. The continuous, laminar flow from Tesla turbines is well-suited to the needs of flow-sensitive microfluidics, where the integrated pump will enable numerous compact lab-on-a-chip applications.
A Laminar Flow-Based Microfluidic Tesla Pump via Lithography Enabled 3D Printing
Directory of Open Access Journals (Sweden)
Mohammed-Baker Habhab
2016-11-01
Full Text Available Tesla turbine and its applications in power generation and fluid flow were demonstrated by Nicholas Tesla in 1913. However, its real-world implementations were limited by the difficulty to maintain laminar flow between rotor disks, transient efficiencies during rotor acceleration, and the lack of other applications that fully utilize the continuous flow outputs. All of the aforementioned limits of Tesla turbines can be addressed by scaling to the microfluidic flow regime. Demonstrated here is a microscale Tesla pump designed and fabricated using a Digital Light Processing (DLP based 3D printer with 43 µm lateral and 30 µm thickness resolutions. The miniaturized pump is characterized by low Reynolds number of 1000 and a flow rate of up to 12.6 mL/min at 1200 rpm, unloaded. It is capable of driving a mixer network to generate microfluidic gradient. The continuous, laminar flow from Tesla turbines is well-suited to the needs of flow-sensitive microfluidics, where the integrated pump will enable numerous compact lab-on-a-chip applications.
A Laminar Flow-Based Microfluidic Tesla Pump via Lithography Enabled 3D Printing
Habhab, Mohammed-Baker; Ismail, Tania; Lo, Joe Fujiou
2016-01-01
Tesla turbine and its applications in power generation and fluid flow were demonstrated by Nicholas Tesla in 1913. However, its real-world implementations were limited by the difficulty to maintain laminar flow between rotor disks, transient efficiencies during rotor acceleration, and the lack of other applications that fully utilize the continuous flow outputs. All of the aforementioned limits of Tesla turbines can be addressed by scaling to the microfluidic flow regime. Demonstrated here is a microscale Tesla pump designed and fabricated using a Digital Light Processing (DLP) based 3D printer with 43 µm lateral and 30 µm thickness resolutions. The miniaturized pump is characterized by low Reynolds number of 1000 and a flow rate of up to 12.6 mL/min at 1200 rpm, unloaded. It is capable of driving a mixer network to generate microfluidic gradient. The continuous, laminar flow from Tesla turbines is well-suited to the needs of flow-sensitive microfluidics, where the integrated pump will enable numerous compact lab-on-a-chip applications. PMID:27886051
Simulation of suspension flow of finite-size spherical particles in a 3D square channel
Gao, Hui; Wang, Lian-Ping
2008-11-01
Suspension flow of finite-size particles in a turbulent gas is of importance to many engineering applications and natural phenomena. As a first step, the present work focuses on the motion and hydrodynamic interaction of finite-size particles in the absence of background carrier-fluid turbulence. The major challenge for an accurate simulation is twofold: an efficient implementation of no-slip boundary conditions on the moving particle surface and an accurate representation of short-range lubrication effects that typically are not resolved numerically. A Navier-Stokes based hybrid approach (i.e., Physalis) developed by Prosperetti and co-workers is employed to solve the suspension flows of a pair of finite-size, freely-moving particles at finite particle Reynolds numbers. A lubrication force representation, designed by Ladd, involving particle relative location and velocity, is incorporated to capture the short-range interactions between particles. The accuracy of the representation and its compatibility with the flow simulation will be examined. A mesoscopic lattice Boltzmann equation (LBE) approach is also used to simulate the same problem for cross validation. Specific implementation issues will be addressed. Comparison with available numerical data will also be discussed.
Pressure moderation and effective pressure in Navier-Stokes flows
Tran, Chuong V.; Yu, Xinwei
2016-10-01
We study the Cauchy problem of the Navier-Stokes equations by both semi-analytic and classical energy methods. The former approach provides a physical picture of how viscous effects may or may not be able to suppress singularity development. In the latter approach, we examine the pressure term that drives the dynamics of the velocity norms \\parallel u{{\\parallel}{{Lq}}} , for q≥slant 3 . A key idea behind this investigation is due to the fact that the pressure p in this term is determined up to a function of both space and |u| , say P(x,|u|) , which may assume relatively broad forms. This allows us to use P as a pressure moderator in the evolution equation for \\parallel u{{\\parallel}{{Lq}}} , whereby optimal regularity criteria can be sought by varying P within its admissible classes. New regularity criteria are derived with and without making use of the moderator. The results obtained in the absence of the moderator feature some improvement over existing criteria in the literature. Several criteria are derived in terms of the moderated (effective) pressure p+P . A simple moderation scheme and the plausibility of the present approach to the problem of Navier-Stokes regularity are discussed.
Landslide Displacement Monitoring Using 3D Range Flow on Airborne and Terrestrial LiDAR Data
Directory of Open Access Journals (Sweden)
Norbert Pfeifer
2013-05-01
Full Text Available An active landslide in Doren, Austria, has been studied by multitemporal airborne and terrestrial laser scanning from 2003 to 2012. To evaluate the changes, we have determined the 3D motion using the range flow algorithm, an established method in computer vision, but not yet used for studying landslides. The generated digital terrain models are the input for motion estimation; the range flow algorithm has been combined with the coarse-to-fine resolution concept and robust adjustment to be able to determine the various motions over the landslide. The algorithm yields fully automatic dense 3D motion vectors for the whole time series of the available data. We present reliability measures for determining the accuracy of the estimated motion vectors, based on the standard deviation of components. The differential motion pattern is mapped by the algorithm: parts of the landslide show displacements up to 10 m, whereas some parts do not change for several years. The results have also been compared to pointwise reference data acquired by independent geodetic measurements; reference data are in good agreement in most of the cases with the results of range flow algorithm; only some special points (e.g., reflectors fixed on trees show considerably differing motions.
Quasi 3D refined simulation of flow and pollutant transport in a meandering River Reach
Directory of Open Access Journals (Sweden)
Li-ren Yu
2013-03-01
Full Text Available This paper reports a quasi 3D numerical simulation in a meandering river reach of the Yellow River, aiming to develop a tool for modeling turbulent flows and pollutant transport in complex natural waters. The recently built depth-averaged two-equation turbulence model, together with and models, were used to close non-simplified quasi 3D hydrodynamic fundamental governing equations. The discretized equations were solved by advanced multi-grid iterative method under non-orthogonal body-fitted coarse and fine two-levels’ grids with collocated variable arrangement. Except for steady flow and transport computation, the processes of contaminant inpouring and plume development, caused by the side-discharge from a tribytary, also have been investigated numerically. The used three closure approaches are suitable for modeling strong mixing turbulence. The established model with higher order of magnitude of transported variable provides a possibility to elevate the computational precision. Based on the developed mathematical model, a CFD (Computational Fluid Dynamics software, namely Q3drm1.0, was developed. This numerical tool focuses on the refined simulations of the steady and unsteady problems of flow and temperature/contaminant transports in complicated computational domains with the strong ability to deal with different discharge situations: side-discharge, point-source discharge/point-sink, and area-source discharge from the slope along bank. In this article, the study of side-discharge is presented only.
Vascular centerline extraction in 3D MR angiograms for phase contrast MRI blood flow measurement
Energy Technology Data Exchange (ETDEWEB)
Hernandez Hoyos, M. [CREATIS, CNRS 5515 et INSERM U630 Research Unit, INSA de Lyon, 69 - Villeurbanne (France); Universidad de los Andes, Bogota (Colombia). Grupo Imagine, Grupo de Ingenieria Biomedica; Orlowski, P.; Piatkowska-Janko, E.; Bogorodzki, P. [Warsaw Univ. of Tech. (Poland). ZEJM-BINSK, Inst. of Radioelectronics; Orkisz, M. [CREATIS, CNRS 5515 et INSERM U630 Research Unit, INSA de Lyon, 69 - Villeurbanne (France)
2006-03-15
The accuracy of 2D phase contrast (PC) magnetic resonance angiography (MRA) depends on the alignment between the vessels and the imaging plane. PC MRA imaging of blood flow is challenging when the flow in several vessels is to be evaluated with one acquisition. For this purpose, semi-automatic determination of the plane most perpendicular to several vessels is proposed based on centerlines extracted from 3D MRA. Arterial centerlines are extracted from 3D MRA based on iterative estimation-prediction, multi-scale analysis of image moments, and a second-order shape model. The optimal plane is determined by minimizing misalignment between its normal vector and the centerlines' tangent vectors. The method was evaluated on a phantom and on 35 patients, by seeking the optimal plane for cerebral blood flow quantification simultaneously in internal carotids and vertebral arteries. In the phantom, difference of orientation and of height between known and calculated planes was 1.2 and 2.5 mm, respectively. In the patients, all but one centerline were correctly extracted and the misalignment of the plane was within 12 per artery. Semi-automatic centerline extraction simplifies and automates determination of the plane orthogonal to one vessel, thereby permitting automatic simultaneous minimization of the misalignment with several vessels in PC MRA. (orig.)
Influence of Underhood Flow on Engine Cooling Using 1-D And 3-D Approach
Directory of Open Access Journals (Sweden)
Bolehovský Ondřej
2015-12-01
Full Text Available This work deals with numerical simulation of complete cooling system of internal combustion engine (GT-SUITE, which also involves the simulation of flow in underhood using the computationally undemanding simulation. A detailed model of the internal combustion engine is extended to a cooling circuit model which is then coupled to a simplified underhood model which is created with the help of GT-COOL application as a 3-D model and afterwards transferred to a 1-D form. The approaches, one using 1-D solution of arrangement of the heat exchangers and the other 3-D approach using the underhood model, were investigated in two steady states corresponding to various vehicle speeds and engine load. These simulations have shown the inappropriateness of 1-D approach when solving the flow in the heat exchangers in the underhood and helped to explore a relatively undemanding method of flow simulation in the underhood, which enables to detect the interaction between the models of the cooling system and the internal combustion engine and the issue of arrangement of the heat exchangers in the underhood.
Matching-index-of-refraction of transparent 3D printing models for flow visualization
Energy Technology Data Exchange (ETDEWEB)
Song, Min Seop; Choi, Hae Yoon; Seong, Jee Hyun; Kim, Eung Soo, E-mail: kes7741@snu.ac.kr
2015-04-01
Matching-index-of-refraction (MIR) has been used for obtaining high-quality flow visualization data for the fundamental nuclear thermal-hydraulic researches. By this method, distortions of the optical measurements such as PIV and LDV have been successfully minimized using various combinations of the model materials and the working fluids. This study investigated a novel 3D printing technology for manufacturing models and an oil-based working fluid for matching the refractive indices. Transparent test samples were fabricated by various rapid prototyping methods including selective layer sintering (SLS), stereolithography (SLA), and vacuum casting. As a result, the SLA direct 3D printing was evaluated to be the most suitable for flow visualization considering manufacturability, transparency, and refractive index. In order to match the refractive indices of the 3D printing models, a working fluid was developed based on the mixture of herb essential oils, which exhibit high refractive index, high transparency, high density, low viscosity, low toxicity, and low price. The refractive index and viscosity of the working fluid range 1.453–1.555 and 2.37–6.94 cP, respectively. In order to validate the MIR method, a simple test using a twisted prism made by the SLA technique and the oil mixture (anise and light mineral oil) was conducted. The experimental results show that the MIR can be successfully achieved at the refractive index of 1.51, and the proposed MIR method is expected to be widely used for flow visualization studies and CFD validation for the nuclear thermal-hydraulic researches.
Computing 3-D steady supersonic flow via a new Lagrangian approach
Loh, C. Y.; Liou, M.-S.
1993-01-01
The new Lagrangian method introduced by Loh and Hui (1990) is extended for 3-D steady supersonic flow computation. Details of the conservation form, the implementation of the local Riemann solver, and the Godunov and the high resolution TVD schemes are presented. The new approach is robust yet accurate, capable of handling complicated geometry and reactions between discontinuous waves. It keeps all the advantages claimed in the 2-D method of Loh and Hui, e.g., crisp resolution for a slip surface (contact discontinuity) and automatic grid generation along the stream.
Reactive Flow Modeling of Liquid Explosives via ALE3D/Cheetah Simulations
Energy Technology Data Exchange (ETDEWEB)
Kuo, I W; Bastea, S; Fried, L E
2010-03-10
We carried out reactive flow simulations of liquid explosives such as nitromethane using the hydrodynamic code ALE3D coupled with equations of state and reaction kinetics modeled by the thermochemical code Cheetah. The simulation set-up was chosen to mimic cylinder experiments. For pure unconfined nitromethane we find that the failure diameter and detonation velocity dependence on charge diameter are in agreement with available experimental results. Such simulations are likely to be useful for determining detonability and failure behavior for a wide range of experimental conditions and explosive compounds.
Rotary slanted single wire CTA – a useful tool for 3D flows investigations
Directory of Open Access Journals (Sweden)
Jonáš P.
2013-04-01
Full Text Available The procedure is described of experimental investigation of a statistically stationary generally nonisothermal 3D flow by means of a constant temperature anemometer (CTA using single slanted heated wire, rotary round the fixed axis. The principle of this procedure is quite clear. The change of the heated wire temperature modifies ratio of CTA sensitivities to temperature and velocity fluctuations. Turning the heated wire through a proper angle changes the sensitivity to components of the instantaneous velocity vector. Some recommendations are presented based on long time experiences, e.g. on the choice of probe, on the probe calibration, to the measurement organization and to the evaluation of results.
Slanted channel microfluidic chip for 3D fluorescence imaging of cells in flow.
Jagannadh, Veerendra Kalyan; Mackenzie, Mark D; Pal, Parama; Kar, Ajoy K; Gorthi, Sai Siva
2016-09-19
Three-dimensional cellular imaging techniques have become indispensable tools in biological research and medical diagnostics. Conventional 3D imaging approaches employ focal stack collection to image different planes of the cell. In this work, we present the design and fabrication of a slanted channel microfluidic chip for 3D fluorescence imaging of cells in flow. The approach employs slanted microfluidic channels fabricated in glass using ultrafast laser inscription. The slanted nature of the microfluidic channels ensures that samples come into and go out of focus, as they pass through the microscope imaging field of view. This novel approach enables the collection of focal stacks in a straight-forward and automated manner, even with off-the-shelf microscopes that are not equipped with any motorized translation/rotation sample stages. The presented approach not only simplifies conventional focal stack collection, but also enhances the capabilities of a regular widefield fluorescence microscope to match the features of a sophisticated confocal microscope. We demonstrate the retrieval of sectioned slices of microspheres and cells, with the use of computational algorithms to enhance the signal-to-noise ratio (SNR) in the collected raw images. The retrieved sectioned images have been used to visualize fluorescent microspheres and bovine sperm cell nucleus in 3D while using a regular widefield fluorescence microscope. We have been able to achieve sectioning of approximately 200 slices per cell, which corresponds to a spatial translation of ∼ 15 nm per slice along the optical axis of the microscope.
Directory of Open Access Journals (Sweden)
Baocheng Shi
2014-06-01
Full Text Available For numerically simulating 3D solid-liquid turbulent flow in low specific speed centrifugal pumps, the iteration convergence problem caused by complex internal structure and high rotational speed of pump is always a problem for numeral simulation researchers. To solve this problem, the combination of three measures of dynamic underrelaxation factor adjustment, step method, and rotational velocity control means according to residual curves trends of operating parameters was used to improve the numerical convergence. Numeral simulation of 3D turbulent flow in a low specific speed solid-liquid centrifugal pump was performed, and the results showed that the improved solution strategy is greatly helpful to the numerical convergence. Moreover, the 3D turbulent flow fields in pumps have been simulated for the bottom ash-particles with the volume fraction of 10%, 20%, and 30% at the same particle diameter of 0.1 mm. The two-phase calculation results are compared with those of single-phase clean water flow. The calculated results gave the main region of the abrasion of the impeller and volute casing and improve the hydraulic design of the impeller in order to decrease the abrasion and increase the service life of the pump.
Numerical Investigation of Nozzle Geometry Effect on Turbulent 3-D Water Offset Jet Flows
Directory of Open Access Journals (Sweden)
Negar Mohammad Aliha
2016-01-01
Full Text Available Using the Yang-Shih low Reynolds k-ε turbulence model, the mean flow field of a turbulent offset jet issuing from a long circular pipe was numerically investigated. The experimental results were used to verify the numerical results such as decay rate of streamwise velocity, locus of maximum streamwise velocity, jet half width in the wall normal and lateral directions, and jet velocity profiles. The present study focused attention on the influence of nozzle geometry on the evolution of a 3D incompressible turbulent offset jet. Circular, square-shaped, and rectangular nozzles were considered here. A comparison between the mean flow characteristics of offset jets issuing from circular and square-shaped nozzles, which had equal area and mean exit velocity, were made numerically. Moreover, the effect of aspect ratio of rectangular nozzles on the main features of the flow was investigated. It was shown that the spread rate, flow entrainment, and mixing rate of an offset jet issuing from circular nozzle are lower than square-shaped one. In addition, it was demonstrated that the aspect ratio of the rectangular nozzles only affects the mean flow field of the offset jet in the near field (up to 15 times greater than equivalent diameter of the nozzles. Furthermore, other parameters including the wall shear stress, flow entrainment and the length of potential core were also investigated.
Method of internal 3D flow field numerical simulation for hydrodynamic torque converter
Institute of Scientific and Technical Information of China (English)
Tao SHANG; Dingxuan ZHAO; Yuankun ZHANG; Xiangen GUO; Xiangzhong SHI
2008-01-01
To enhance the performance of a hydrody-namic torque converter and thoroughly understand the trait of inside flow, a numerical simulation method of internal 3D flow for the three-element centrifugal hydrodynamic torque converter was systematically researched and expatiated in this paper. First, the internal flow field of each impeller was calculated. The curves that illustrate the relationships between the pressure differences of the inlet and outlet versus flux were drawn. Second, the concurrent working point of each impeller was approximately estimated. Finally, a calculation was performed considering the influence on each impeller. The flow field of a working point was solved by multiple calculations and the actual working condition was gradually determined. The pressure and velocity distributions of the flow field were proposed. The performance parameters of the hydrodynamic torque converter were predicted. The calculation method, and the proposed pressure and velocity distribution of the flow field, have practical significance for the design and improvement of a hydrodynamic torque converter.
Navier-Stokes computations of separated vortical flows past prolate spheroid at incidence
Wong, Tin-Chee; Kandil, Osama A.; Liu, C. H.
1989-01-01
The problem of steady incompressible viscous flow past prolate spheroids at incidence is formulated using the unsteady incompressible and compressible thin-layer Navier-Stokes equations. The two sets of Navier-Stokes equations are solved using a pseudotime stepping of the implicit flux-difference splitting scheme on a curvilinear grid, which is generated by a transfinite grid generator. The Baldwin and Lomax (1978) algebraic eddy-viscosity model is used to model the turbulent flow. The computational applications cover a 6:1 prolate spheroid at different angles of attack and Reynolds numbers. The results are compared with experimental data.
Method of coupling 1-D unsaturated flow with 3-D saturated flow on large scale
Directory of Open Access Journals (Sweden)
Yan ZHU
2011-12-01
Full Text Available A coupled unsaturated-saturated water flow numerical model was developed. The water flow in the unsaturated zone is considered the one-dimensional vertical flow, which changes in the horizontal direction according to the groundwater table and the atmospheric boundary conditions. The groundwater flow is treated as the three-dimensional water flow. The recharge flux to groundwater from soil water is considered the bottom flux for the numerical simulation in the unsaturated zone, and the upper flux for the groundwater simulation. It connects and unites the two separated water flow systems. The soil water equation is solved based on the assumed groundwater table and the subsequent predicted recharge flux. Then, the groundwater equation is solved with the predicted recharge flux as the upper boundary condition. Iteration continues until the discrepancy between the assumed and calculated groundwater nodal heads have a certain accuracy. Illustrative examples with different water flow scenarios regarding the Dirichlet boundary condition, the Neumann boundary condition, the atmospheric boundary condition, and the source or sink term were calculated by the coupled model. The results are compared with those of other models, including Hydrus-1D, SWMS-2D, and FEFLOW, which demonstrate that the coupled model is effective and accurate and can significantly reduce the computational time for the large number of nodes in saturated-unsaturated water flow simulation.
Rivers, Melissa; Hunter, Craig; Vatsa, Veer
2017-01-01
Two Navier-Stokes codes were used to compute flow over the High-Lift Common Research Model (HL-CRM) in preparation for a wind tunnel test to be performed at the NASA Langley Research Center 14-by-22-Foot Subsonic Tunnel in fiscal year 2018. Both flight and wind tunnel conditions were simulated by the two codes at set Mach numbers and Reynolds numbers over a full angle-of-attack range for three configurations: cruise, landing and takeoff. Force curves, drag polars and surface pressure contour comparisons are shown for the two codes. The lift and drag curves compare well for the cruise configuration up to 10deg angle of attack but not as well for the other two configurations. The drag polars compare reasonably well for all three configurations. The surface pressure contours compare well for some of the conditions modeled but not as well for others.
Multi-cellular 3D human primary liver cell culture elevates metabolic activity under fluidic flow.
Esch, Mandy B; Prot, Jean-Matthieu; Wang, Ying I; Miller, Paula; Llamas-Vidales, Jose Ricardo; Naughton, Brian A; Applegate, Dawn R; Shuler, Michael L
2015-05-21
We have developed a low-cost liver cell culture device that creates fluidic flow over a 3D primary liver cell culture that consists of multiple liver cell types, including hepatocytes and non-parenchymal cells (fibroblasts, stellate cells, and Kupffer cells). We tested the performance of the cell culture under fluidic flow for 14 days, finding that hepatocytes produced albumin and urea at elevated levels compared to static cultures. Hepatocytes also responded with induction of P450 (CYP1A1 and CYP3A4) enzyme activity when challenged with P450 inducers, although we did not find significant differences between static and fluidic cultures. Non-parenchymal cells were similarly responsive, producing interleukin 8 (IL-8) when challenged with 10 μM bacterial lipoprotein (LPS). To create the fluidic flow in an inexpensive manner, we used a rocking platform that tilts the cell culture devices at angles between ±12°, resulting in a periodically changing hydrostatic pressure drop between reservoirs and the accompanying periodically changing fluidic flow (average flow rate of 650 μL min(-1), and a maximum shear stress of 0.64 dyne cm(-2)). The increase in metabolic activity is consistent with the hypothesis that, similar to unidirectional fluidic flow, primary liver cell cultures increase their metabolic activity in response to fluidic flow periodically changes direction. Since fluidic flow that changes direction periodically drastically changes the behavior of other cells types that are shear sensitive, our findings support the theory that the increase in hepatic metabolic activity associated with fluidic flow is either activated by mechanisms other than shear sensing (for example increased opportunities for gas and metabolite exchange), or that it follows a shear sensing mechanism that does not depend on the direction of shear. Our mode of device operation allows us to evaluate drugs under fluidic cell culture conditions and at low device manufacturing and operation
Thermoelectric DC conductivities and Stokes flows on black hole horizons
Banks, Elliot; Gauntlett, Jerome P
2015-01-01
We consider a general class of electrically charged black holes of Einstein-Maxwell-scalar theory that are holographically dual to conformal field theories at finite charge density which break translation invariance explicitly. We examine the linearised perturbations about the solutions that are associated with the thermoelectric DC conductivity. We show that there is a decoupled sector at the black hole horizon which must solve generalised Stokes equations for a charged fluid. By solving these equations we can obtain the DC conductivity of the dual field theory. For one-dimensional lattices we solve the fluid equations to obtain closed form expressions for the DC conductivity in terms of the solution at the black hole horizon. We also determine the leading order DC conductivity for lattices that can be expanded as a perturbative series about translationally invariant solutions.
A continuous flow microfluidic calorimeter: 3-D numerical modeling with aqueous reactants.
Sen, Mehmet A; Kowalski, Gregory J; Fiering, Jason; Larson, Dale
2015-03-10
A computational analysis of the reacting flow field, species diffusion and heat transfer processes with thermal boundary layer effects in a microchannel reactor with a coflow configuration was performed. Two parallel adjacent streams of aqueous reactants flow along a wide, shallow, enclosed channel in contact with a substrate, which is affixed to a temperature controlled plate. The Fluent computational fluid dynamics package solved the Navier-Stokes, mass transport and energy equations. The energy model, including the enthalpy of reaction as a nonuniform heat source, was validated by calculating the energy balance at several control volumes in the microchannel. Analysis reveals that the temperature is nearly uniform across the channel thickness, in the direction normal to the substrate surface; hence, measurements made by sensors at or near the surface are representative of the average temperature. Additionally, modeling the channel with a glass substrate and a silicone cover shows that heat transfer is predominantly due to the glass substrate. Finally, using the numerical results, we suggest that a microcalorimeter could be based on this configuration, and that temperature sensors such as optical nanohole array sensors could have sufficient spatial resolution to determine enthalpy of reaction.
CFD SIMULATION OF 3D FLOW IN LARGE-BORE AXIAL-FLOW PUMP WITH HALF-ELBOW SUCTION SUMP
Institute of Scientific and Technical Information of China (English)
WANG Fu-jun; LI Yao-jun; CONG Guo-hui; WANG Wen-e; WANG Hai-song
2006-01-01
Numerical simulations of 3D turbulent flow in a large-bore axial-flow pump coupled with half-elbow suction sump were performed by using CFD approach. The numerical model and velocity and pressure distributions in entire flow passage were presented. The obvious backflow in half-elbow suction sump and strong flow nonuniformity at suction sump outlet were observed, whereas these phenomena were not observed in existing studies performed for a separate suction sump by either experimental or numerical approach. This result indicates that the interaction between half-elbow suction sump and impeller has significant effect on the flow distribution in the pump passage. The change of pump efficiency caused by the interaction was discussed.
3D FLOW INSIDE BUBBLE-TYPE VORTEX BREAKDOWN: AN EXPERIMENTAL INVESTIGATION VIA LDV
Institute of Scientific and Technical Information of China (English)
Liu Ying-zheng; Chen Han-ping; Koyama Hide S.
2003-01-01
Bubble-type vortex breakdown of the swirling flow inside a closed cylindrical container with a rotating upper endwall was experimentally investigated via LDV.3D measurement of the steady bubble at H/R=1.5 was firstly carried out with very fine grid arrangement.Flow details inside the bubble and its Re-dependent structure were made clear.Abrupt waves of the azimuthal velocity component were always found to be between the bottom stationary endwall and the upstream stagnation point, which might be the reason of bubble formation.Variation of bubble structure and bubble center with the increasing Re gives the explanation for the disappearance of the breakdown region.
Resuspension of particles in an oscillating grid turbulent flow using PIV and 3D-PTV
Energy Technology Data Exchange (ETDEWEB)
Traugott, H; Liberzon, A [Turbulence Structure Laboratory, School of Mechanical Engineering, Tel Aviv University, Tel Aviv 69978 (Israel); Hayse, T, E-mail: alexlib@eng.tau.ac.il [Department of Civil Engineering, Massachusetts Institute of Technology, MA (United States)
2011-12-22
Description of the mechanisms responsible for the initiation of particle motion from a surface and re-entrainment of particles into suspension remains a challenge, partially due to the technical difficulties to quantify the forces applied on the particles and the collection of high resolution data of particle displacements simultaneously. In this study we explore the process of initial entrainment of spherical particles from smooth beds into zero-mean-shear turbulent flow in an oscillating grid chamber. Particle image velocimetry (PIV) and three-dimensional particle tracking velocimetry (3D-PTV) are used to correlate in a quantitative manner the turbulent flow properties responsible for pick-up, detachment and re-entrainment of particles. The results are compared to the existing models of critical shear velocity and provide further insight into the resuspension process of spherical particles in the transitional range of particle size Reynolds numbers 2 {<=} Re{sub p} {<=} 500.
3D conformation of a flexible fiber in a turbulent flow
Verhille, Gautier; Bartoli, Adrien
2016-07-01
A growing number of studies is devoted to anisotropic particles in turbulent flows. In most cases, the particles are assumed to be rigid and their deformations are neglected. We present an adaptation of classical computer vision tools to reconstruct from two different images the 3D conformation of a fiber distorted by the turbulent fluctuations in a von Kármán flow. This technique allows us notably to characterize the fiber deformation by computing the correlation function of the orientation of the tangent vector. This function allows us to tackle the analogy between polymers and flexible fibers proposed by Brouzet et al. (Phys Rev Lett 112(7):074501, 2014). We show that this function depends on an elastic length ℓ _e which characterizes the particle flexibility, as is the case for polymers, but also on the fiber length L, contrary to polymers.
A 3D Spectral Anelastic Hydrodynamic Code for Shearing, Stratified Flows
Barranco, J A; Barranco, Joseph A.; Marcus, Philip S.
2005-01-01
We have developed a three-dimensional (3D) spectral hydrodynamic code to study vortex dynamics in rotating, shearing, stratified systems (e.g. the atmosphere of gas giant planets, protoplanetary disks around newly forming protostars). The time-independent background state is stably stratified in the vertical direction and has a unidirectional linear shear flow aligned with one horizontal axis. Superposed on this background state is an unsteady, subsonic flow that is evolved with the Euler equations subject to the anelastic approximation to filter acoustic phenomena. A Fourier-Fourier basis in a set of quasi-Lagrangian coordinates that advect with the background shear is used for spectral expansions in the two horizontal directions. For the vertical direction, two different sets of basis functions have been implemented: (1) Chebyshev polynomials on a truncated, finite domain, and (2) rational Chebyshev functions on an infinite domain. Use of this latter set is equivalent to transforming the infinite domain to ...
A NUMERICAL SIMULATION OF 3-D INNER FLOW IN UP-STREAM PUMPING MECHANICAL SEAL
Institute of Scientific and Technical Information of China (English)
ZHANG Jin-feng; YUAN Shou-qi; FU Yong-hong; FANG Yu-jian
2006-01-01
Numerical simulation of 3-D inner flow between Up-stream Pumping Mechanical Face Seals (UPMFS) faces was initially done by CFD software, which made the flow visualization come true.Simulation results directly discover the action of hydrodynamic lubrication, and by comparison with that of Conventional Mechanic Face Seals (CMFS), the advantage over bigger bearing capability, less friction and much less leakage are explained clearly.Otherwise there are also some different ideas and results from precedent analysis and computational research results: dynamic and static pressure profiles can be obtained respectively instead of the analytic total pressure distribution only, pressure distribution is nonlinear, while always be solved as linear, lower pressure is observed at the area of inner diameter caused by the grooves, but its possible cavitations effects to the performance of UPMFS still need further study.
Measuring the orientation and rotation rate of 3D printed particles in turbulent flow
Voth, Greg; Kramel, Stefan; Cole, Brendan
2015-03-01
The orientation distribution and rotations of anisotropic particles plays a key role in many applications ranging from icy clouds to papermaking and drag reduction in pipe flow. Experimental access to time resolved orientations of anisotropic particles has not been easy to achieve. We have found that 3D printing technology can be used to fabricate a wide range of particle shapes with smallest dimension down to 300 ?m. So far we have studied rods, crosses, jacks, tetrads, and helical shapes. We extract the particle orientations from stereoscopic video images using a method of least squares optimization in Euler angle space. We find that in turbulence the orientation and rotation rate of many particles can be understood using a simple picture of alignment of both the vorticity and a long axis of the particle with the Lagrangian stretching direction of the flow.
Casting directly from a computer model by using advanced simulation software FLOW-3D Cast ®
Directory of Open Access Journals (Sweden)
M. Sirviö
2009-01-01
Full Text Available ConiferRob - A patternless casting technique, originally conceived at VTT Technical Research Centre of Finland and furtherdeveloped at its spin-off company, Simtech Systems, offers up to 40% savings in product development costs, and up to two months shorterdevelopment times compared to conventional techniques. Savings of this order can be very valuable on today's highly competitivemarkets. Casting simulation is commonly used for designing of casting systems. However, most of the software are today old fashioned and predicting just shrinkage porosity. Flow Science, VTT and Simtech have developed new software called FLOW-3D Cast ® , whichcan simulate surface defects, air entrainment, filters, core gas problems and even a cavitation.
Coupled Aeroelastic Oscillations of a Turbine Blade Row in 3D Transonic Flow
Institute of Scientific and Technical Information of China (English)
Vitaly Gnesin; Lyubov Kolodyazhnaya; Romuald Rzadkowski
2001-01-01
This paper presents the mutual time - marching method to predict the aeroelastic stability of an oscillating blade row in 3D transonic flow. The ideal gas flow through a blade row is governed by the time dependent Euler equations in conservative form which are integrated by using the explicit monotonous second order accurate Godunov-Kolgan finite volume scheme and moving hybrid H-O grid. The structure analysis uses the modal approach and 3D finite element dynamic model of blade. The blade movement is assumed as a linear combination of the fast modes of blade natural oscillations with the modal coefficients depending on time. To demonstrate the capability and correctness of the method, two experimentally investigated test cases have been selected, in which the blades had performed tuned harmonic bending or torsional vibrations (The 1th and 4th standard configurations of the "Workshop on Aeroelasticity in Turbomachines" by Bolcs and Fransson, 1986). The calculated results of aeroelastic behaviour of the blade row (4th standard configuration), are presented over a wide frequency range under different start regimes of interblade phase angle.
LHCb base-line level-0 trigger 3D-flow implementation
Crosetto, D
1999-01-01
The LHCb Level-0 trigger implementation with the 3D-Flow system offers full programmability, allowing it to adapt to unexpected operating conditions and enabling new, unpredicted physics. The implementation is described in detail and refers to components and technology available today. The 3D-Flow Processor system is a new, technology-independent concept in very fast, real-time system architectures. Based on the replication of a single type of circuit of 100 k gates, which communicates in six directions: bi-directional with North, East, West, and South neighbors, unidirectional from Top to Bottom, the system offers full programmability, modularity, ease of expansion and adaptation to the latest technology. A complete study of its applicability to the LHCb calorimeter triggers is presented. Full description of the input data handling, either in digital or mixed digital-analog form, of the data processing, and the transmission of results to the global level-0 trigger decision unit are provided. Any level-0 trig...
3D reconstruction of a compressible flow by synchronized multi-camera BOS
Nicolas, F.; Donjat, D.; Léon, O.; Le Besnerais, G.; Champagnat, F.; Micheli, F.
2017-05-01
This paper investigates the application of a 3D density reconstruction from a limited number of background-oriented schlieren (BOS) images as recently proposed in Nicolas et al. (Exp Fluids 57(1):1-21, 2016), to the case of compressible flows, such as underexpanded jets. First, an optimization of a 2D BOS setup is conducted to mitigate the intense local blurs observed in raw BOS images and caused by strong density gradients present in the jets. It is demonstrated that a careful choice of experimental conditions enables one to obtain sharp deviation fields from 2D BOS images. Second, a 3DBOS experimental bench involving 12 synchronized cameras is specifically designed for the present study. It is shown that the 3DBOS method can provide physically consistent 3D reconstructions of instantaneous and mean density fields for various underexpanded jet flows issued into quiescent air. Finally, an analysis of the density structure of a moderately underexpanded jet is conducted through phase-averaging, highlighting the development of a large-scale coherent structure associated with a jet shear layer instability.
Negara, Ardiansyah
2013-01-01
Anisotropy of hydraulic properties of subsurface geologic formations is an essential feature that has been established as a consequence of the different geologic processes that they undergo during the longer geologic time scale. With respect to petroleum reservoirs, in many cases, anisotropy plays significant role in dictating the direction of flow that becomes no longer dependent only on the pressure gradient direction but also on the principal directions of anisotropy. Furthermore, in complex systems involving the flow of multiphase fluids in which the gravity and the capillarity play an important role, anisotropy can also have important influences. Therefore, there has been great deal of motivation to consider anisotropy when solving the governing conservation laws numerically. Unfortunately, the two-point flux approximation of finite difference approach is not capable of handling full tensor permeability fields. Lately, however, it has been possible to adapt the multipoint flux approximation that can handle anisotropy to the framework of finite difference schemes. In multipoint flux approximation method, the stencil of approximation is more involved, i.e., it requires the involvement of 9-point stencil for the 2-D model and 27-point stencil for the 3-D model. This is apparently challenging and cumbersome when making the global system of equations. In this work, we apply the equation-type approach, which is the experimenting pressure field approach that enables the solution of the global problem breaks into the solution of multitude of local problems that significantly reduce the complexity without affecting the accuracy of numerical solution. This approach also leads in reducing the computational cost during the simulation. We have applied this technique to a variety of anisotropy scenarios of 3-D subsurface flow problems and the numerical results demonstrate that the experimenting pressure field technique fits very well with the multipoint flux approximation
Effect of span length and temperature on the 3-D confined flow around a vortex promoter
Energy Technology Data Exchange (ETDEWEB)
Martin, E. [Fluid Mechanics Area, School of Industrial Engineering, Universidad de Vigo, Campus Lagoas-Marcosende, 36310 Vigo (Spain); Velazquez, A., E-mail: angel.velazquez@upm.es [Aerospace Propulsion and Fluid Mechanics Department, School of Aeronautics, Universidad Politecnica de Madrid, Plaza del Cardenal Cisneros 3, 28040 Madrid (Spain)
2011-12-15
Highlights: Black-Right-Pointing-Pointer The article deals with study of vortex promoter flow in a 3-D micro-channel. Black-Right-Pointing-Pointer Aspects studied are: channel aspect ratio and prism surface temperature. Black-Right-Pointing-Pointer Flow is classified into three different regimes depending on different parameters. Black-Right-Pointing-Pointer Results could be used for practical engineering design purposes. - Abstract: This article presents a numerical study on the influence of span length and wall temperature on the 3-D flow pattern around a square section vortex promoter located inside a micro-channel in the low Reynolds number regime. The first objective of the work is to quantify the critical Reynolds number that defines the onset of vortex shedding and to identify the different regimes that appear as a function of the channel aspect ratio (span to height ratio). We found that the critical Reynolds number for the onset of the Karman street regime increases as the aspect ratio decreases. In particular, for the aspect ratio of 1/2 the critical Reynolds number is nearly six times the critical Reynolds number of the 2-D problem. An intermediate oscillating regime between the steady and the Karman street solutions was also found to exist within a rather wide range of Reynolds numbers for small channel aspect ratios. The second objective was to investigate the influence of the vortex promoter wall temperature on both vortex shedding and flow pattern. This has practical engineering implications because the working fluid considered in the article is water that has a viscosity that depends significantly on temperature and promotes a strong coupling between the momentum and energy equations that influences the system behaviour. Results indicate that high surface temperature on the prism promotes the onset of the Karman street, suggesting design guidelines for micro-channel based heat sinks that make use of vortex promoters.
Interstitial solute transport in 3D reconstructed neuropil occurs by diffusion rather than bulk flow
Holter, Karl Erik; Kehlet, Benjamin; Devor, Anna; Sejnowski, Terrence J.; Dale, Anders M.; Omholt, Stig W.; Ottersen, Ole Petter; Nagelhus, Erlend Arnulf; Mardal, Kent-André; Pettersen, Klas H.
2017-01-01
The brain lacks lymph vessels and must rely on other mechanisms for clearance of waste products, including amyloid β that may form pathological aggregates if not effectively cleared. It has been proposed that flow of interstitial fluid through the brain’s interstitial space provides a mechanism for waste clearance. Here we compute the permeability and simulate pressure-mediated bulk flow through 3D electron microscope (EM) reconstructions of interstitial space. The space was divided into sheets (i.e., space between two parallel membranes) and tunnels (where three or more membranes meet). Simulation results indicate that even for larger extracellular volume fractions than what is reported for sleep and for geometries with a high tunnel volume fraction, the permeability was too low to allow for any substantial bulk flow at physiological hydrostatic pressure gradients. For two different geometries with the same extracellular volume fraction the geometry with the most tunnel volume had 36% higher permeability, but the bulk flow was still insignificant. These simulation results suggest that even large molecule solutes would be more easily cleared from the brain interstitium by diffusion than by bulk flow. Thus, diffusion within the interstitial space combined with advection along vessels is likely to substitute for the lymphatic drainage system in other organs. PMID:28847942
Computed Tomography 3-D Imaging of the Metal Deformation Flow Path in Friction Stir Welding
Schneider, Judy; Beshears, Ronald; Nunes, Arthur C., Jr.
2005-01-01
In friction stir welding (FSW), a rotating threaded pin tool is inserted into a weld seam and literally stirs the edges of the seam together. To determine optimal processing parameters for producing a defect free weld, a better understanding of the resulting metal deformation flow path is required. Marker studies are the principal method of studying the metal deformation flow path around the FSW pin tool. In our study, we have used computed tomography (CT) scans to reveal the flow pattern of a lead wire embedded in a FSW weld seam. At the welding temperature of aluminum, the lead becomes molten and is carried with the macro-flow of the weld metal. By using CT images, a 3-dimensional (3D) image of the lead flow pattern can be reconstructed. CT imaging was found to be a convenient and comprehensive way of collecting and displaying tracer data. It marks an advance over previous more tedious and ambiguous radiographic/metallographic data collection methods.
DeJong, Andrew
Numerical models of fluid-structure interaction have grown in importance due to increasing interest in environmental energy harvesting, airfoil-gust interactions, and bio-inspired formation flying. Powered by increasingly powerful parallel computers, such models seek to explain the fundamental physics behind the complex, unsteady fluid-structure phenomena. To this end, a high-fidelity computational model based on the high-order spectral difference method on 3D unstructured, dynamic meshes has been developed. The spectral difference method constructs continuous solution fields within each element with a Riemann solver to compute the inviscid fluxes at the element interfaces and an averaging mechanism to compute the viscous fluxes. This method has shown promise in the past as a highly accurate, yet sufficiently fast method for solving unsteady viscous compressible flows. The solver is monolithically coupled to the equations of motion of an elastically mounted 3-degree of freedom rigid bluff body undergoing flow-induced lift, drag, and torque. The mesh is deformed using 4 methods: an analytic function, Laplace equation, biharmonic equation, and a bi-elliptic equation with variable diffusivity. This single system of equations -- fluid and structure -- is advanced through time using a 5-stage, 4th-order Runge-Kutta scheme. Message Passing Interface is used to run the coupled system in parallel on up to 240 processors. The solver is validated against previously published numerical and experimental data for an elastically mounted cylinder. The effect of adding an upstream body and inducing wake galloping is observed.
Shirsath, S.S.; Padding, J.T.; Clercx, H.J.H.; Kuipers, J.A.M.
2015-01-01
Three-dimensional particle tracking velocimetry (3D-PTV) is a promising technique to study the behavior of granular flows. The aim of this paper is to cross-validate 3D-PTV against independent or more established techniques, such as particle image velocimetry (PIV), electronic ultrasonic sensor meas
Cosmic dynamo analogue and decay of magnetic fields in 3D Ricci flows
de Andrade, Garcia
2009-01-01
Magnetic curvature effects, investigated by Barrow and Tsagas (BT) [Phys Rev D \\textbf{77},(2008)],as a mechanism for magnetic field decay in open Friedmann universes (${\\Lambda}<0$), are applied to dynamo geometric Ricci flows in 3D curved substrate in laboratory. By simple derivation, a covariant three-dimensional magnetic self-induced equation, presence of these curvature effects, indicates that de Sitter cosmological constant (${\\Lambda}\\ge{0}$), leads to enhancement in the fast kinematic dynamo action which adds to stretching of plasma flows. From the magnetic growth rate, the strong shear case, anti-de Sitter case (${\\Lambda}<0$) BT magnetic decaying fields are possible while for weak shear, fast dynamos are possible. The self-induced equation in Ricci flows is similar to the equation derived by BT in $(3+1)$-spacetime continuum. Lyapunov-de Sitter metric is obtained from Ricci flow eigenvalue problem. In de Sitter analogue there is a decay rate of ${\\gamma}\\approx{-{\\Lambda}}\\approx{-10^{-35}s^{-...
A 3D velocimetry study of the flow through prosthetic heart valves
Ledesma, R.; Zenit, R.; Pulos, G.; Sanchez, E.; Juarez, A.
2006-11-01
Blood damage commonly appears in medical valve prothesis. It is a mayor concern for the designers and surgeons. It is well known that this damage and other complications result from the modified fluid dynamics through the replacement valve. To evaluate the performance of prosthetic heart valves, it is necessary to study the flow through them. To conduct this study , we have built a flow channel that emulates cardiac conditions and allows optical access such that a 3D-PIV velocimetry system could be used. The experiments are aimed to reconstruct the downstream structure of the flow through a mechanical and a bio-material tricuspid heart valve prothesis. Preliminary results show that the observed coherent structures can be related with haemolysis and trombosis, illnesses commonly found in valve prothesis recipients. The mean flow, the levels of strain rate and the turbulence intensity generated by the valves can also be directly related to blood damage. In general, bio-material made valves tend to reduce these complications.
Simulation of a Synthetic Jet in Quiescent Air Using TLNS3D Flow Code
Vatsa, Veer N.; Turkel, Eli
2007-01-01
Although the actuator geometry is highly three-dimensional, the outer flowfield is nominally two-dimensional because of the high aspect ratio of the rectangular slot. For the present study, this configuration is modeled as a two-dimensional problem. A multi-block structured grid available at the CFDVAL2004 website is used as a baseline grid. The periodic motion of the diaphragm is simulated by specifying a sinusoidal velocity at the diaphragm surface with a frequency of 450 Hz, corresponding to the experimental setup. The amplitude is chosen so that the maximum Mach number at the jet exit is approximately 0.1, to replicate the experimental conditions. At the solid walls zero slip, zero injection, adiabatic temperature and zero pressure gradient conditions are imposed. In the external region, symmetry conditions are imposed on the side (vertical) boundaries and far-field conditions are imposed on the top boundary. A nominal free-stream Mach number of 0.001 is imposed in the free stream to simulate incompressible flow conditions in the TLNS3D code, which solves compressible flow equations. The code was run in unsteady (URANS) mode until the periodicity was established. The time-mean quantities were obtained by running the code for at least another 15 periods and averaging the flow quantities over these periods. The phase-locked average of flow quantities were assumed to be coincident with their values during the last full time period.
Micro flow cytometer with self-aligned 3D hydrodynamic focusing.
Testa, Genni; Persichetti, Gianluca; Bernini, Romeo
2015-01-01
A micro flow cytometer with a single step 3D hydrodynamic flow focusing has been developed. The proposed design is capable to create a single-file particle stream that is self-aligned with an integrated optical fiber-based detection system, regardless of the flow rate ratio between the focusing and core liquids. The design approach provides the ability to adjust the stream size while keeping the position of the focused stream centered with respect to the focusing channel. The device has been fabricated by direct micro milling of PMMA sheets. Experimental validation of the hydrodynamic sheath focusing effect has been presented and sample stream with tuneable size from about 18 to 50 μm was measured. Flow cytometry measurements have been performed by using 10-23 μm fluorescent particles. From the analysis of the signals collected at each transit event we can confirm that the device was capable to align and measure microparticles with a good coefficient of variance.
Numerical simulation of compressible Navier-Stokes flow in a double throat nozzle
Scott, James N.; Visbal, Miguel R.
The flow through a double-throat nozzle is computed using the complete time-dependent compressible Navier-Stokes equations. The computations were performed by using an existing working code with no special modifications for this particular application. The computations were performed on a Cyber 845 computer and a CRAY XMP-48 computer using three different grid sizes.
Actuator Line/Navier-Stokes Computations for Flows past the Yawed MEXICO Rotor
DEFF Research Database (Denmark)
Shen, Wen Zhong; Sørensen, Jens Nørkær; Yang, H.
2011-01-01
In the paper the Actuator Line/Navier-Stokes model has been used to simulate flows past the yawed MEXICO rotor. The computed loads as well as the velocity field behind the yawed rotor are compared to detailed pressure and PIV measurements which were carried out in the EU funded MEXICO project...
High Re Separated Flow Solutions Using the Navier-Stokes and Approximate Equations,
1985-01-01
flow field. In the present study the incremental block-line Gauss- Seidel method proposed in Ref. 17 is used as an efficient numerical tool for solving...Incremental Block-Line-Gauss- Seidel Method for the Navier-Stokes Equations", AIAA Paper 85-0033. 18. Beam, R. M. and Warming, R. F., "An Implicit Factored
Tomographic imaging of reacting flows in 3D by laser absorption spectroscopy
Foo, J.; Martin, P. A.
2017-05-01
This paper describes the development of an infrared laser absorption tomography system for the 3D volumetric imaging of chemical species and temperature in reacting flows. The system is based on high-resolution near-infrared tunable diode laser absorption spectroscopy (TDLAS) for the measurement of water vapour above twin, mixed fuel gas burners arranged with an asymmetrical output. Four parallel laser beams pass through the sample region and are rotated rapidly in a plane to produce a wide range of projection angles. A rotation of 180° with 0.5° sampling was achieved in 3.6 s. The effects of changes to the burner fuel flow were monitored in real time for the 2D distributions. The monitoring plane was then moved vertically relative to the burners enabling a stack of 2D images to be produced which were then interpolated to form a 3D volumetric image of the temperature and water concentrations above the burners. The optical transmission of each beam was rapidly scanned around 1392 nm and the spectrum was fitted to find the integrated absorbance of the water transitions and although several are probed in each scan, two of these transitions possess opposite temperature dependencies. The projections of the integrated absorbances at each angle form the sinogram from which the 2D image of integrated absorbance of each line can be reconstructed by the direct Fourier reconstruction based on the Fourier slice theorem. The ratio of the integrated absorbances of the two lines can then be related to temperature alone in a method termed, two-line thermometry. The 2D temperature distribution obtained was validated for pattern and accuracy by thermocouple measurements. With the reconstructed temperature distribution, the temperature-dependent line strengths could be determined and subsequently the concentration distribution of water across the 2D plane whilst variations in burner condition were carried out. These results show that the measurement system based on TDLAS can be
Spacetime Stereo and 3D Flow via Binocular Spatiotemporal Orientation Analysis.
Sizintsev, Mikhail; Wildes, Richard P
2014-11-01
This paper presents a novel approach to recovering estimates of 3D structure and motion of a dynamic scene from a sequence of binocular stereo images. The approach is based on matching spatiotemporal orientation distributions between left and right temporal image streams, which encapsulates both local spatial and temporal structure for disparity estimation. By capturing spatial and temporal structure in this unified fashion, both sources of information combine to yield disparity estimates that are naturally temporal coherent, while helping to resolve matches that might be ambiguous when either source is considered alone. Further, by allowing subsets of the orientation measurements to support different disparity estimates, an approach to recovering multilayer disparity from spacetime stereo is realized. Similarly, the matched distributions allow for direct recovery of dense, robust estimates of 3D scene flow. The approach has been implemented with real-time performance on commodity GPUs using OpenCL. Empirical evaluation shows that the proposed approach yields qualitatively and quantitatively superior estimates in comparison to various alternative approaches, including the ability to provide accurate multilayer estimates in the presence of (semi)transparent and specular surfaces.
Uniqueness of weak solutions of the Navier-Stokes equations of compressible flow
Ariane Piovezan Entringer
2009-01-01
Resumo: Este trabalho consiste de uma exposição detalhada do resultado provado no artigo Uniqueness of Weak Solutions of the Navier-Stokes Equations of Multidimensional, Compressible Flow de D. Hoff (SIAM J. Math. Anal - 2006) sobre a unicidade de solução fraca e a dependência contínua da solução fraca nos dados iniciais para as equações de Navier-Stokes para fluídos compressíveis...Observação: O resumo, na integra, podera ser visualizado no texto completo da tese digital Abstract: Uniquen...
A strongly conservative finite element method for the coupling of Stokes and Darcy flow
Kanschat, G.
2010-08-01
We consider a model of coupled free and porous media flow governed by Stokes and Darcy equations with the Beavers-Joseph-Saffman interface condition. This model is discretized using divergence-conforming finite elements for the velocities in the whole domain. Discontinuous Galerkin techniques and mixed methods are used in the Stokes and Darcy subdomains, respectively. This discretization is strongly conservative in Hdiv(Ω) and we show convergence. Numerical results validate our findings and indicate optimal convergence orders. © 2010 Elsevier Inc.
Global smooth flows for compressible Navier-Stokes-Maxwell equations
Xu, Jiang; Cao, Hongmei
2016-08-01
Umeda et al. (Jpn J Appl Math 1:435-457, 1984) considered a rather general class of symmetric hyperbolic-parabolic systems: A0zt+sum_{j=1}nAjz_{xj}+Lz=sum_{j,k=1}nB^{jk}z_{xjxk} and showed optimal decay rates with certain dissipative assumptions. In their results, the dissipation matrices {L} and {B^{jk}(j,k=1,ldots,n)} are both assumed to be real symmetric. So far there are no general results in case that {L} and {B^{jk}} are not necessarily symmetric, which is left open now. In this paper, we investigate compressible Navier-Stokes-Maxwell (N-S-M) equations arising in plasmas physics, which is a concrete example of hyperbolic-parabolic composite systems with non-symmetric dissipation. It is observed that the Cauchy problem for N-S-M equations admits the dissipative mechanism of regularity-loss type. Consequently, extra higher regularity is usually needed to obtain the optimal decay rate of {L1({mathbb{R}}^3)}-{L^2({mathbb{R}}^3)} type, in comparison with that for the global-in-time existence of smooth solutions. In this paper, we obtain the minimal decay regularity of global smooth solutions to N-S-M equations, with aid of {L^p({mathbb{R}}^n)}-{Lq({mathbb{R}}^n)}-{Lr({mathbb{R}}^n)} estimates. It is worth noting that the relation between decay derivative orders and the regularity index of initial data is firstly found in the optimal decay estimates.
A Novel Flow-Perfusion Bioreactor Supports 3D Dynamic Cell Culture
Directory of Open Access Journals (Sweden)
Alexander M. Sailon
2009-01-01
Full Text Available Background. Bone engineering requires thicker three-dimensional constructs than the maximum thickness supported by standard cell-culture techniques (2 mm. A flow-perfusion bioreactor was developed to provide chemotransportation to thick (6 mm scaffolds. Methods. Polyurethane scaffolds, seeded with murine preosteoblasts, were loaded into a novel bioreactor. Control scaffolds remained in static culture. Samples were harvested at days 2, 4, 6, and 8 and analyzed for cellular distribution, viability, metabolic activity, and density at the periphery and core. Results. By day 8, static scaffolds had a periphery cell density of 67%±5.0%, while in the core it was 0.3%±0.3%. Flow-perfused scaffolds demonstrated peripheral cell density of 94%±8.3% and core density of 76%±3.1% at day 8. Conclusions. Flow perfusion provides chemotransportation to thick scaffolds. This system may permit high throughput study of 3D tissues in vitro and enable prefabrication of biological constructs large enough to solve clinical problems.
Lattice Boltzmann Model of 3D Multiphase Flow in Artery Bifurcation Aneurysm Problem
Abas, Aizat; Mokhtar, N. Hafizah; Ishak, M. H. H.; Abdullah, M. Z.; Ho Tian, Ang
2016-01-01
This paper simulates and predicts the laminar flow inside the 3D aneurysm geometry, since the hemodynamic situation in the blood vessels is difficult to determine and visualize using standard imaging techniques, for example, magnetic resonance imaging (MRI). Three different types of Lattice Boltzmann (LB) models are computed, namely, single relaxation time (SRT), multiple relaxation time (MRT), and regularized BGK models. The results obtained using these different versions of the LB-based code will then be validated with ANSYS FLUENT, a commercially available finite volume- (FV-) based CFD solver. The simulated flow profiles that include velocity, pressure, and wall shear stress (WSS) are then compared between the two solvers. The predicted outcomes show that all the LB models are comparable and in good agreement with the FVM solver for complex blood flow simulation. The findings also show minor differences in their WSS profiles. The performance of the parallel implementation for each solver is also included and discussed in this paper. In terms of parallelization, it was shown that LBM-based code performed better in terms of the computation time required. PMID:27239221
Lattice Boltzmann Model of 3D Multiphase Flow in Artery Bifurcation Aneurysm Problem.
Abas, Aizat; Mokhtar, N Hafizah; Ishak, M H H; Abdullah, M Z; Ho Tian, Ang
2016-01-01
This paper simulates and predicts the laminar flow inside the 3D aneurysm geometry, since the hemodynamic situation in the blood vessels is difficult to determine and visualize using standard imaging techniques, for example, magnetic resonance imaging (MRI). Three different types of Lattice Boltzmann (LB) models are computed, namely, single relaxation time (SRT), multiple relaxation time (MRT), and regularized BGK models. The results obtained using these different versions of the LB-based code will then be validated with ANSYS FLUENT, a commercially available finite volume- (FV-) based CFD solver. The simulated flow profiles that include velocity, pressure, and wall shear stress (WSS) are then compared between the two solvers. The predicted outcomes show that all the LB models are comparable and in good agreement with the FVM solver for complex blood flow simulation. The findings also show minor differences in their WSS profiles. The performance of the parallel implementation for each solver is also included and discussed in this paper. In terms of parallelization, it was shown that LBM-based code performed better in terms of the computation time required.
Lattice Boltzmann Model of 3D Multiphase Flow in Artery Bifurcation Aneurysm Problem
Directory of Open Access Journals (Sweden)
Aizat Abas
2016-01-01
Full Text Available This paper simulates and predicts the laminar flow inside the 3D aneurysm geometry, since the hemodynamic situation in the blood vessels is difficult to determine and visualize using standard imaging techniques, for example, magnetic resonance imaging (MRI. Three different types of Lattice Boltzmann (LB models are computed, namely, single relaxation time (SRT, multiple relaxation time (MRT, and regularized BGK models. The results obtained using these different versions of the LB-based code will then be validated with ANSYS FLUENT, a commercially available finite volume- (FV- based CFD solver. The simulated flow profiles that include velocity, pressure, and wall shear stress (WSS are then compared between the two solvers. The predicted outcomes show that all the LB models are comparable and in good agreement with the FVM solver for complex blood flow simulation. The findings also show minor differences in their WSS profiles. The performance of the parallel implementation for each solver is also included and discussed in this paper. In terms of parallelization, it was shown that LBM-based code performed better in terms of the computation time required.
Institute of Scientific and Technical Information of China (English)
KOUKOUVINIS P.; BERGELES G.; GAVAISES M
2015-01-01
The paper proposes a methodology within the Reynolds averaged Navier Stokes (RANS) solvers for cavitating flows capable of predicting the flow regions of bubble collapse and the potential aggressiveness to material damage. An aggressiveness index is introduced, called cavitation aggressiveness index (CAI) based on the total derivative of pressure which identifies surface areas exposed to bubble collapses, the index is tested in two known cases documented in the open literature and seems to identify regions of potential cavitation damage.
Investigation of the effect of wall friction on the flow rate in 2D and 3D Granular Flow
Carballo-Ramirez, Brenda; Pleau, Mollie; Easwar, Nalini; Birwa, Sumit; Shah, Neil; Tewari, Shubha
We have measured the mass flow rate of spherical steel spheres under gravity in vertical, straight-walled 2 and 3-dimensional hoppers, where the flow velocity is controlled by the opening size. Our measurements focus on the role of friction and its placement along the walls of the hopper. In the 2D case, an increase in the coefficient of static friction from μ = 0.2 to 0.6 is seen to decrease the flow rate significantly. We have changed the placement of frictional boundaries/regions from the front and back walls of the 2D hopper to the side walls and floor to investigate the relative importance of the different regions in determining the flow rate. Fits to the Beverloo equation show significant departure from the expected exponent of 1.5 in the case of 2D flow. In contrast, 3D flow rates do not show much dependence on wall friction and its placement. We compare the experimental data to numerical simulations of gravity driven hopper granular flow with varying frictional walls constructed using LAMMPS*. *http://lammps.sandia.gov Supported by NSF MRSEC DMR 0820506.
Development of seismic anisotropy during subduction-induced 3D mantle flow
Faccenda, M.; capitanio, F. A.
2012-12-01
Subduction zones are convergent margins where the rigid lithosphere sinks into the Earth's mantle inducing complex 3D flow patterns. Seismic anisotropy generated by strain-induced lattice/crystal preferred orientation (LPO/CPO) of intrinsically anisotropic minerals is commonly used to study flow in the mantle and its relations with plate motions. As the development of seismic anisotropy due to upper and lower plate motions occurs at depths and timescales such that it is not directly observable, numerical modelling provides a useful tool to investigate these processes. We computed the seismic anisotropy of dry olivine-enstatite aggregates due to strain-induced LPO in 3D mechanical models of dynamic subduction by using, respectively, D-Rex and Underworld. Subsequently, FSTRACK was used to compute seismogram synthetics and SKS splitting patterns. We found that for relatively narrow subducting plates, retreat motions are maximized producing strong subslab trench-parallel anisotropy. Here, synthetic data reproduce quite well the observations in analogous subduction systems like Calabria and South Sandwich, where the fast azimuths orients parallel to the trench in the forearc and follow the toroidal flow patterns on the slab edges. Furthermore, we found that the amount of anisotropy is proportional to the amount of subduction, while it does not depend on the rate at which the plate subducts. On the other hand, larger subducting plates subducts mainly by plate advance, favoring poloidal motions and trench-perpendicular anisotropy. Additional Earth-like plate geometries involving along-trench variation of the subducting plate age that induces differential slab retreat motions are considered. We also tested different olivine fabrics (A, B, C, E type), yielding distinct SKS splitting patterns that may help to constrain the composition of the upper mantle. Although more sophisticated numerical modelling taking into account temperature-dependent mantle rock rheologies and P
Turbulence characteristics of open channel flow over non-equilibrium 3-D mobile dunes
Indian Academy of Sciences (India)
PRASHANTH REDDY HANMAIAHGARI; RAM BALACHANDAR
2016-09-01
This paper reports velocity measurements over mobile dunes using an acoustic Doppler velocimetry (ADV). Experiments were conducted with two different flow conditions resulting in the formation of two different size mobile dunes. Dunes height, wavelength and velocity of dunes found to be increasing with increase in average flow velocity for a constant flow depth. The quasi-stationary bed condition was assumed while measuring the velocity distribution along the depth. The effect of the non-equilibrium mobile dunes on the flow characteristics and turbulence is examined by computing turbulent intensities, turbulent kinetic energy and Reynolds shear stresses using time averaged and time–space averaged velocity measurements. The magnitudes of transverse velocities are approximately 1/10 of streamwise velocities and vertical velocities are approximately half of the transverse velocities. The considerable magnitudes of transverse velocities over mobile bedforms necessitate measurement of 3-D velocity components to analyze the flow field. Computed turbulence intensities are found to be maximum in the region consisting of the trough and the reattachment point of the dunes. It is observed that streamwise turbulence intensities near the bed are twice the transverse turbulence intensities, and transverse turbulence intensities are twice the vertical turbulence intensities. Reynolds stresses (transverse fluxes of streamwise and vertical momentum) are observed to be high on mobile bedforms which shows mobile dunes reinforce the secondary currents. Peak values of turbulent kinetic energy (TKE) and Reynolds stresses are also found in the region consisting of the trough and the reattachment point. It is visually observed in the present experiments that maximum erosion takes place at the reattachment point and eroded sediment is carried as totalload and dropped on the lee slope of the subsequent downstream dune. This phenomenon is caused by flow expansion in the separation zone
Carlsohn, Matthias F.; Kemmling, André; Petersen, Arne; Wietzke, Lennart
2016-04-01
Cerebral aneurysms require endovascular treatment to eliminate potentially lethal hemorrhagic rupture by hemostasis of blood flow within the aneurysm. Devices (e.g. coils and flow diverters) promote homeostasis, however, measurement of blood flow within an aneurysm or cerebral vessel before and after device placement on a microscopic level has not been possible so far. This would allow better individualized treatment planning and improve manufacture design of devices. For experimental analysis, direct measurement of real-time microscopic cerebrovascular flow in micro-structures may be an alternative to computed flow simulations. An application of microscopic aneurysm flow measurement on a regular basis to empirically assess a high number of different anatomic shapes and the corresponding effect of different devices would require a fast and reliable method at low cost with high throughout assessment. Transparent three dimensional 3D models of brain vessels and aneurysms may be used for microscopic flow measurements by particle image velocimetry (PIV), however, up to now the size of structures has set the limits for conventional 3D-imaging camera set-ups. On line flow assessment requires additional computational power to cope with the processing large amounts of data generated by sequences of multi-view stereo images, e.g. generated by a light field camera capturing the 3D information by plenoptic imaging of complex flow processes. Recently, a fast and low cost workflow for producing patient specific three dimensional models of cerebral arteries has been established by stereo-lithographic (SLA) 3D printing. These 3D arterial models are transparent an exhibit a replication precision within a submillimeter range required for accurate flow measurements under physiological conditions. We therefore test the feasibility of microscopic flow measurements by PIV analysis using a plenoptic camera system capturing light field image sequences. Averaging across a sequence of
Stokes flow near the contact line of an evaporating drop
Gelderblom, H.; Bloemen, O.; Snoeijer, J.H.
2012-01-01
The evaporation of sessile drops in quiescent air is usually governed by vapour diffusion. For contact angles below , the evaporative flux from the droplet tends to diverge in the vicinity of the contact line. Therefore, the description of the flow inside an evaporating drop has remained a challenge
Continuum Navier-Stokes modelling of water flow past fullerene molecules
Walther, J. H.; Popadic, A.; Koumoutsakos, P.; Praprotnik, M.
2015-11-01
We present continuum simulations of water flow past fullerene molecules. The governing Navier-Stokes equations are complemented with the Navier slip boundary condition with a slip length that is extracted from related molecular dynamics simulations. We find that several quantities of interest as computed by the present model are in good agreement with results from atomistic and atomistic-continuum simulations at a fraction of the computational cost. We simulate the flow past a single fullerene and an array of fullerenes and demonstrate that such nanoscale flows can be computed efficiently by continuum flow solvers, allowing for investigations into spatiotemporal scales inaccessible to atomistic simulations.
A digital holography set-up for 3D vortex flow dynamics
Lebon, Benoît; Perret, Gaële; Coëtmellec, Sébastien; Godard, Gilles; Gréhan, Gérard; Lebrun, Denis; Brossard, Jérôme
2016-06-01
In the present paper, a digital in-line holography (DIH) set-up, with a converging beam, is used to take three-dimensional (3D) velocity measurements of vortices. The vortices are formed periodically at the edges of a submerged horizontal plate submitted to regular waves. They take the form of vortex filaments that extend from side to side of the channel. They undergo strongly three-dimensional instability mechanisms that remain very complicated to characterize experimentally. The experiments are performed in a 10 × 0.3 × 0.3 m3 wave flume. The DIH set-up is performed using a modulated laser diode emitting at the wavelength of 640 nm and a lensless CCD camera. The beam crosses the channel side to side. To reveal the flow dynamics, 30-μm hydrogen bubbles are generated at the edge of the plate to serve as tracers. Their locations are recorded on the holograms multiple times to access the dynamics of the flow. This method leads to an accuracy in the order of 100 μm on the axial location. Those measurements have been validated with stereo-PIV measurements. A very good agreement is found on time-averaged velocity fields between the two techniques.
3D Markov Process for Traffic Flow Prediction in Real-Time
Directory of Open Access Journals (Sweden)
Eunjeong Ko
2016-01-01
Full Text Available Recently, the correct estimation of traffic flow has begun to be considered an essential component in intelligent transportation systems. In this paper, a new statistical method to predict traffic flows using time series analyses and geometric correlations is proposed. The novelty of the proposed method is two-fold: (1 a 3D heat map is designed to describe the traffic conditions between roads, which can effectively represent the correlations between spatially- and temporally-adjacent traffic states; and (2 the relationship between the adjacent roads on the spatiotemporal domain is represented by cliques in MRF and the clique parameters are obtained by example-based learning. In order to assess the validity of the proposed method, it is tested using data from expressway traffic that are provided by the Korean Expressway Corporation, and the performance of the proposed method is compared with existing approaches. The results demonstrate that the proposed method can predict traffic conditions with an accuracy of 85%, and this accuracy can be improved further.
USM3D Simulations of Saturn V Plume Induced Flow Separation
Deere, Karen; Elmlilgui, Alaa; Abdol-Hamid, K. S.
2011-01-01
The NASA Constellation Program included the Ares V heavy lift cargo vehicle. During the design stage, engineers questioned if the Plume Induced Flow Separation (PIFS) that occurred along Saturn V rocket during moon missions at some flight conditions, would also plague the newly proposed rocket. Computational fluid dynamics (CFD) was offered as a tool for initiating the investigation of PIFS along the Ares V rocket. However, CFD best practice guidelines were not available for such an investigation. In an effort to establish a CFD process and define guidelines for Ares V powered simulations, the Saturn V vehicle was used because PIFS flight data existed. The ideal gas, computational flow solver USM3D was evaluated for its viability in computing PIFS along the Saturn V vehicle with F-1 engines firing. Solutions were computed at supersonic freestream conditions, zero degree angle of attack, zero degree sideslip, and at flight Reynolds numbers. The effects of solution sensitivity to grid refinement, turbulence models, and the engine boundary conditions on the predicted PIFS distance along the Saturn V were discussed and compared to flight data from the Apollo 11 mission AS-506.
A 3D moving mesh Finite Element Method for two-phase flows
Anjos, G. R.; Borhani, N.; Mangiavacchi, N.; Thome, J. R.
2014-08-01
A 3D ALE Finite Element Method is developed to study two-phase flow phenomena using a new discretization method to compute the surface tension forces. The computational method is based on the Arbitrary Lagrangian-Eulerian formulation (ALE) and the Finite Element Method (FEM), creating a two-phase method with an improved model for the liquid-gas interface. An adaptive mesh update procedure is also proposed for effective management of the mesh to remove, add and repair elements, since the computational mesh nodes move according to the flow. The ALE description explicitly defines the two-phase interface position by a set of interconnected nodes which ensures a sharp representation of the boundary, including the role of the surface tension. The proposed methodology for computing the curvature leads to accurate results with moderate programming effort and computational cost. Static and dynamic tests have been carried out to validate the method and the results have compared well to analytical solutions and experimental results found in the literature, demonstrating that the new proposed methodology provides good accuracy to describe the interfacial forces and bubble dynamics. This paper focuses on the description of the proposed methodology, with particular emphasis on the discretization of the surface tension force, the new remeshing technique, and the validation results. Additionally, a microchannel simulation in complex geometry is presented for two elongated bubbles.
Framework system and research flow of uncertainty in 3D geological structure models
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
Uncertainty in 3D geological structure models has become a bottleneck that restricts the development and application of 3D geological modeling.In order to solve this problem during periods of accuracy assessment,error detection and dynamic correction in 3D geological structure models,we have reviewed the current situation and development trends in 3D geological modeling.The main context of uncertainty in 3D geological structure models is discussed.Major research issues and a general framework system of unce...
Software Package \\Nesvetay-3D" for modeling three-dimensional flows of monatomic rarefied gas
Directory of Open Access Journals (Sweden)
V. A. Titarev
2014-01-01
Full Text Available Analysis of three-dimensional rarefied gas flowsin microdevices (micropipes, micropumps etc and over re-entry vehicles requires development of methods of computational modelling. One of such methods is the direct numerical solution of the Boltzmann kinetic equation for the velocity distribution function with either exact or approximate (model collision integral. At present, for flows of monatomic rarefied gas the Shakhov model kinetic equation, also called S-model, has gained wide-spread use. The equation can be regarded as a model equation of the incomplete thirdorder approximation. Despite its relative simplicity, the S-model is still a complicated integrodifferential equation of high dimension. The numerical solution of such an equation requires high-accuracy parallel methods.The present work is a review of recent results concerning the development and application of three-dimensional computer package Nesvetay-3D intended for modelling of rarefied gas flows. The package solves Boltzmann kinetic equation with the BGK (Krook and Shakhov model collision integrals using the discrete velocity approach. Calculations are carried out in non-dimensional variables. A finite integration domain and a mesh are introduced in the molecular velocity space. Next, the kinetic equation is re-written as a system of kinetic equations for each of the discrete velocities. The system is solved using an implicit finite-volume method of Godunov type. The steady-state solution is computed by a time marching method. High order of spatial accuracy is achieved by using a piece-wise linear representation of the distribution function in each spatial cell. In general, the coefficients of such an approximation are found using the least-square method. Arbitrary unstructured meshes in the physical space can be used in calculations, which allow considering flows over objects of general geometrical shape. Conservative property of the method with respect to the model collision
Schafhitzel, Tobias; Rößler, Friedemann; Weiskopf, Daniel; Ertl, Thomas
2007-03-01
Modern medical imaging provides a variety of techniques for the acquisition of multi-modality data. A typical example is the combination of functional and anatomical data from functional Magnetic Resonance Imaging (fMRI) and anatomical MRI measurements. Usually, the data resulting from each of these two methods is transformed to 3D scalar-field representations to facilitate visualization. A common method for the visualization of anatomical/functional multi-modalities combines semi-transparent isosurfaces (SSD, surface shaded display) with other scalar visualization techniques like direct volume rendering (DVR). However, partial occlusion and visual clutter that typically result from the overlay of these traditional 3D scalar-field visualization techniques make it difficult for the user to perceive and recognize visual structures. This paper addresses these perceptual issues by a new visualization approach for anatomical/functional multi-modalities. The idea is to reduce the occlusion effects of an isosurface by replacing its surface representation by a sparser line representation. Those lines are chosen along the principal curvature directions of the isosurface and rendered by a flow visualization method called line integral convolution (LIC). Applying the LIC algorithm results in fine line structures that improve the perception of the isosurface's shape in a way that it is possible to render it with small opacity values. An interactive visualization is achieved by executing the algorithm completely on the graphics processing unit (GPU) of modern graphics hardware. Furthermore, several illumination techniques and image compositing strategies are discussed for emphasizing the isosurface structure. We demonstrate our method for the example of fMRI/MRI measurements, visualizing the spatial relationship between brain activation and brain tissue.
Energy Technology Data Exchange (ETDEWEB)
Grafenberger, P.; Klinner, P.; Nefischer, P. [BMW Motoren GmbH, Steyr (Austria); Klingebiel, F. [AMSTRAL Engineering fuer Stroemungsmechanik GmbH, Idstein (Germany)
2000-04-01
Shorting the development time for new engines and vehicles is leading to the increasing use of computational design and simulation methods in the automotive industry. For several years now, both one-dimensional and three-dimensional flow computation have been used successfully in the development of cooling systems. However, the fact that less hardware is used in the early development stages makes new demands on the quality and quantity of these simulation results. BMW's diesel development division has been able to improve the quality of the results and to reduce the processing time by improving the model quality and by coupling existing 1D and 3D computational fluid dynamic programmes. (orig.) [German] Die Verkuerzung der Entwicklungszeit neuer Motoren und Automobile fuehrt zu einem verstaerkten Einsatz von rechnergestuetzten Konstruktions- und Simulationsmethoden in der Fahrzeugindustrie. Sowohl eindimensionale als auch dreidimensionale Stroemungsberechnungen werden seit Jahren erfolgreich bei der Entwicklung von Kuehlsystemen eingesetzt. Der Entfall von Hardware-Baugruppen in der fruehen Entwicklungsphase stellt jedoch neue Anforderungen an die Qualitaet und Quantitaet dieser Simulationsergebnisse. Durch Verbesserung der Modellqualitaet und durch Kopplung vorhandener 1D- und 3D-Stroemungsberechnungsprogramme konnten in der Dieselmotorenentwicklung von BMW die Qualitaet der Ergebnisse und die Bearbeitungsgeschwindigkeit deutlich gesteigert werden. (orig.)
Directory of Open Access Journals (Sweden)
B. Panic
2013-04-01
Full Text Available The results of experimental investigations concerning radial distribution of powder accumulation in bed and static pressure were presented in this paper. To realize this research physical model of gas-powder two phase flow with descending bed was projected and constructed. Amounts of “dynamic” and “static” powder accumulated in bed, in dependence on gas velocity and of bed particles were investigated. In 3D model “static” powder (with its radial distribution at the tuyere level and in the higher part of bed was measured. The influence of bed particles, powder and gas radial distribution on values of interaction forces between flow phases in investigated system was defined.
Experimental Investigation of Material Flows Within FSWs Using 3D Tomography
Energy Technology Data Exchange (ETDEWEB)
Charles R. Tolle; Timothy A. White; Karen S. Miller; Denis E. Clark; Herschel B. Smartt
2008-06-01
There exists significant prior work using tracers or pre-placed hardened markers within friction stir welding (FSWing) to experimentally explore material flow within the FSW process. Our experiments replaced markers with a thin sheet of copper foil placed between the 6061 aluminum lap and butt joints that were then welded. The absorption characteristics of x-rays for copper and aluminum are significantly different allowing for non-destructive evaluation (NDE) methods such as x-ray computed tomography (CT) to be used to demonstrate the material movement within the weldment on a much larger scale than previously shown. 3D CT reconstruction of the copper components of the weldment allows for a unique view into the final turbulent state of the welding process as process parameters are varied. The x-ray CT data of a section of the weld region was collected using a cone-beam x-ray imaging system developed at the INL. Six-hundred projections were collected over 360-degrees using a 160-kVp Bremsstrahlung x-ray generator (25-micrometer focal spot) and amorphoussilicon x-ray detector. The region of the object that was imaged was about 3cm tall and 1.5cm x 1cm in cross section, and was imaged at a magnification of about 3.6x. The data were reconstructed on a 0.5x0.5x0.5 mm3 voxel grid. After reconstruction, the aluminum and copper could be easily discriminated using a gray level threshold allowing visualization of the copper components. Fractal analysis of the tomographic reconstructed material topology is investigated as a means to quantify macro level material flow based on process parameters. The results of multi-pass FSWs show increased refinement of the copper trace material. Implications of these techniques for quantifying process flow are discussed.
A comparative analysis of 3D flow fields between straight and bowed blades in a steam turbine
Institute of Scientific and Technical Information of China (English)
M.HASSANVAND; WANG Zhong-qi 王仲奇; WANG Song-tao 王松涛
2004-01-01
A commercial Navier-Stokes flow solver has been employed tor simulating steady subsonic flow characteristics and analyzing the comparative features of flow fields between straight and bowed blades applied to the stator of a high pressure steam turbine. For comparison, we have studied the effects of bowed blades on the wakes of stator trailing edge and horse shoe vortex in the rotor. It was found that the position of wakes for bowed blades is shifted toward the blade suction side. Also, we have discussed and compared the entropy generation and energy loss caused by dissipation mechanism within the boundary layers on the hub and shroud; and temperature gradient in meridional plane.
Solving microscopic flow problems using Stokes equations in SPH
Van Liedekerke, P.; Smeets, B.; Odenthal, T.; Tijskens, E.; Ramon, H.
2013-07-01
Starting from the Smoothed Particle Hydrodynamics method (SPH), we propose an alternative way to solve flow problems at a very low Reynolds number. The method is based on an explicit drop out of the inertial terms in the normal SPH equations, and solves the coupled system to find the velocities of the particles using the conjugate gradient method. The method will be called NSPH which refers to the non-inertial character of the equations. Whereas the time-step in standard SPH formulations for low Reynolds numbers is linearly restricted by the inverse of the viscosity and quadratically by the particle resolution, the stability of the NSPH solution benefits from a higher viscosity and is independent of the particle resolution. Since this method allows for a much higher time-step, it solves creeping flow problems with a high resolution and a long timescale up to three orders of magnitude faster than SPH. In this paper, we compare the accuracy and capabilities of the new NSPH method to canonical SPH solutions considering a number of standard problems in fluid dynamics. In addition, we show that NSPH is capable of modeling more complex physical phenomena such as the motion of a red blood cell in plasma.
Directory of Open Access Journals (Sweden)
Kuznetsov Vladimir V.
2016-01-01
Full Text Available New full-statement 3D mathematical model of joint motion of thin liquid film and gas in a microchannel at local heating developed by taking into account the heat transfer by flows, evaporation and condensation, as well as the heat transfer at the gas-liquid interface is derived. The model is based on the full system of the Navier-Stokes equations, taking into account the convective terms of motion equations in the phases. Comparison of the numerical results obtained using the model based on the full Navier-Stokes equations and using the simplified model developed in the framework of the thin layer approximation has been performed. The comparison shows that at low Reynolds numbers, simplified model well describes all the main characteristics of the gas and liquid motion. With the gas Reynolds numbers significant increase difference between numerical results starts to grow.
PARTIALLY AVERAGED NAVIER-STOKES METHOD FOR TIME DEPENDENT TURBULENT CAVITATING FLOWS
Institute of Scientific and Technical Information of China (English)
HUANG Biao; WANG Guo-yu
2011-01-01
Cavitation typically occurs when the fluid pressure is lower than the vapor pressure in a local thermodynamic state, and the flow is frequently unsteady and turbulent. The Reynolds-Averaged Navier-Stokes (RANS) approach has been popular for turbulent flow computations. The most widely used ones, such as the standard k-ε model, have well-recognized deficiencies when treating time dependent flow field. To identify ways to improve the predictive capability of the current RANS-based engineering turbulence closures, conditional averaging is adopted for the Navier-Stokes equation, and one more parameter, based on the filter size, is introduced into the k-ε model. In the Partially Averaged Navier-Stokes (PANS) model, the filter width is mainly controlled by the ratio of unresolved-to-total kinetic energy f1. This model is assessed in unsteady cavitating flows over a Clark-Y hydrofoil. From the experimental validations regarding the forces, frequencies, cavity visualizations and velocity distributions, the PANS model is shown to improve the predictive capability considerably, in comparison to the standard k-ε model, and also, it is observed the value of f1 in the PANS model has substantial influence on the predicting result. As the filter width f1 is decreased, the PANS model can effectively reduce the eddy viscosity near the closure region which can significantly influence the capture of the detach cavity, and this model can reproduce the time-averaged velocity quantitatively around the hydrofoil.
Stokes flow paths separation and recirculation cells in X-junctions of varying angle
Cachile, Mario; Gomba, Juan M; Hulin, Jean-Pierre; Auradou, Harold
2012-01-01
Fluid and solute transfer in X-junctions between straight channels is shown to depend critically on the junction angle in the Stokes flow regime. Experimentally, water and a water-dye solution are injected at equal flow rates in two facing channels of the junction: Planar Laser Induced fluorescence (PLIF) measurements show that the largest part of each injected fluid "bounces back" preferentially into the outlet channel at the lowest angle to the injection; this is opposite to the inertial case and requires a high curvature of the corresponding streamlines. The proportion of this fluid in the other channel decreases from 50% at 90\\degree to zero at a threshold angle. These counterintuitive features reflect the minimization of energy dissipation for Stokes flows. Finite elements numerical simulations of a 2D Stokes flow of equivalent geometry con rm these results and show that, below the threshold angle 33.8\\degree recirculation cells are present in the center part of the junction and separate the two injected...
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz
2000-01-01
Lagrangian Integral Method) is a finite element method where Galerkons method is used for solving the governing equation in rectangular coordinates numerically. In the present implementation the velocity and pressure fields are approximated with tri-linear and constant shape functions, respectivly.The 3D LIM......) and polymeric solutions. Secondly, the 3D-LIM has also been applied to calculate the inflation of a thick sheet of a polymeric melt into a elliptic cylinder. These problems all include free surfaces. As the governing equations are solved for the particle positions, the motion of surfaces can be followed easily......A new technique for the numerical 3D simulation of time dependent flow of viscoelastic fluid is presented. The technique is based on a Lagrangian kinematics description of the fluid flow. The fluid is described by the Rivlin Sawyer integral constitutive equation. The method (referred to as the 3D...
ANALYSIS AND MEASUREMENT OF STOKES LAYER FLOWS IN AN OSCILLATING NARROW CHANNEL
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
The velocities of boundary layer flows between two parallel oscillating plates separated by small distance, i.e., in so called narrow channel, were theoretically and experimentally studied. The focus was on the laminar case where the Reynolds number is much smaller than the transition value. The theoretical analysis of the Stokes layer in oscillating flow over a narrow channel was made first. Then Laser Doppler Velocimeter (LDV) was employed to measure the Stokes boundary layer above an oscillating flat plate and inside the oscillating narrow channel at various numbers. At the same time, the phase angle difference along the vertical direction in both analysis and experiment were provided. The good agreements are shown between the measured results and the theoretical solution.
Interfacial tension based on-chip extraction of microparticles confined in microfluidic Stokes flows
Huang, Haishui; He, Xiaoming
2014-10-01
Microfluidics involving two immiscible fluids (oil and water) has been increasingly used to produce hydrogel microparticles with wide applications. However, it is difficult to extract the microparticles out of the microfluidic Stokes flows of oil that have a Reynolds number (the ratio of inertia to viscous force) much less than one, where the dominant viscous force tends to drive the microparticles to move together with the surrounding oil. Here, we present a passive method for extracting hydrogel microparticles in microfluidic Stokes flow from oil into aqueous extracting solution on-chip by utilizing the intrinsic interfacial tension between oil and the microparticles. We further reveal that the thickness of an "extended confining layer" of oil next to the interface between oil and aqueous extracting solution must be smaller than the radius of microparticles for effective extraction. This method uses a simple planar merging microchannel design that can be readily fabricated and further integrated into a fluidic system to extract microparticles for wide applications.
Hong, Jiarong; Toloui, Mostafa; Mallery, Kevin
2016-11-01
Three-dimensional PIV and PTV provides the most comprehensive flow information for unraveling the physical phenomena in a wide range of fluid problems, from microfluidics to wall-bounded turbulent flows. Compared with other commercialized 3D PIV techniques, such as tomographic PIV and defocusing PIV, the digital inline holographic PTV (namely DIH-PTV) provides 3D flow measurement solution with high spatial resolution, low cost optical setup, and easy alignment and calibration. Despite these advantages, DIH-PTV suffers from major limitations including poor longitudinal resolution, human intervention (i.e. requirement for manually determined tuning parameters during tracer field reconstruction and extraction), limited tracer concentration, small sampling volume and expensive computations, limiting its broad use for 3D flow measurements. Here we will report our latest work on improving DIH-PTV method through an integration of deconvolution algorithm, iterative removal method and GPU computation to overcome some of abovementioned limitations. We will also present the application of our DIH-PTV for measurements in the following sample cases: (i) flows in bio-filmed microchannel with 50-60 μm vector spacing within sampling volumes of 1 mm (streamwise) x 1 mm (wall-normal) x 1 mm (spanwise); (ii) turbulent flows over smooth and rough surfaces (1.1 mm vector spacing within 15 mm x 50 mm x 15 mm); (iii) 3D distribution and kinematics of inertial particles in turbulent air duct flow.
Quasi-periodic non-stationary solutions of 3D Euler equations for incompressible flow
Ershkov, Sergey V
2015-01-01
A novel derivation of non-stationary solutions of 3D Euler equations for incompressible inviscid flow is considered here. Such a solution is the product of 2 separated parts: - one consisting of the spatial component and the other being related to the time dependent part. Spatial part of a solution could be determined if we substitute such a solution to the equations of motion (equation of momentum) with the requirement of scale-similarity in regard to the proper component of spatial velocity. So, the time-dependent part of equations of momentum should depend on the time-parameter only. The main result, which should be outlined, is that the governing (time-dependent) ODE-system consist of 2 Riccati-type equations in regard to each other, which has no solution in general case. But we obtain conditions when each component of time-dependent part is proved to be determined by the proper elliptical integral in regard to the time-parameter t, which is a generalization of the class of inverse periodic functions.
Stability of 3D Gaussian vortices in rotating stratified Boussinesq flows: Linear analysis
Mahdinia, Mani; Jiang, Chung-Hsiang
2016-01-01
The linear stability of three-dimensional (3D) vortices in rotating, stratified flows has been studied by analyzing the non-hydrostatic inviscid Boussinesq equations. We have focused on a widely-used model of geophysical and astrophysical vortices, which assumes an axisymmetric Gaussian structure for pressure anomalies in the horizontal and vertical directions. For a range of Rossby number ($-0.5 < Ro < 0.5$) and Burger number ($0.02 < Bu < 2.3$) relevant to observed long-lived vortices, the growth rate and spatial structure of the most unstable eigenmodes have been numerically calculated and presented as a function of $Ro-Bu$. We have found neutrally-stable vortices only over a small region of the $Ro-Bu$ parameter space: cyclones with $Ro \\sim 0.02-0.05$ and $Bu \\sim 0.85-0.95$. However, we have also found that anticyclones in general have slower growth rates compared to cyclones. In particular, growth rate of the most unstable eigenmode for anticyclones in a large region of the parameter space ...
Thermocapillary bubble flow and coalescence in a rotating cylinder: A 3D study
Alhendal, Yousuf; Turan, A.; Al-mazidi, M.
2015-12-01
The process of thermocapillary bubbles rising in a rotating 3D cylinder in zero gravity was analysed and presented numerically with the aid of computational fluid dynamics (CFD) by means of the volume of fluid (VOF) method. Calculations were carried out to investigate in detail the effect of the rotational speed of the hosted liquid on the trajectory of both single and group bubbles driven by the Marangoni force in zero-gravity conditions. For rotational speeds from 0.25 to 2 rad/s, bubble displacement with angular motion was found to be directed between the hotter surface and the rotational axis. This is contrary to the conventional bubble flow from areas of high pressure to low pressure, radial direction, or from cold to hot regions, axial direction. The results demonstrate that for the ratio of rotational speeds to the thermocapillary bubble velocity larger than unity, the surface tension gradient is the dominant force and the bubble motion towards the hotter. On the other hand, for ratio less than 1, the bubble motion is dominated and is significantly affected by centrifugal force. As rotation speed increases, the amount of deflection increases and the Marangoni effect vanishes. The current study is novel in the sense that single- and multi-bubble motion incorporating thermocapillary forces in a rotating liquid in a zero-gravity environment has never been numerically investigated.
Leigh, S. J.; Purssell, C. P.; Billson, D. R.; Hutchins, D. A.
2014-09-01
Flow sensing is an essential technique required for a wide range of application environments ranging from liquid dispensing to utility monitoring. A number of different methodologies and deployment strategies have been devised to cover the diverse range of potential application areas. The ability to easily create new bespoke sensors for new applications is therefore of natural interest. Fused deposition modelling is a 3D printing technology based upon the fabrication of 3D structures in a layer-by-layer fashion using extruded strands of molten thermoplastic. The technology was developed in the late 1980s but has only recently come to more wide-scale attention outside of specialist applications and rapid prototyping due to the advent of low-cost 3D printing platforms such as the RepRap. Due to the relatively low-cost of the printers and feedstock materials, these printers are ideal candidates for wide-scale installation as localized manufacturing platforms to quickly produce replacement parts when components fail. One of the current limitations with the technology is the availability of functional printing materials to facilitate production of complex functional 3D objects and devices beyond mere concept prototypes. This paper presents the formulation of a simple magnetite nanoparticle-loaded thermoplastic composite and its incorporation into a 3D printed flow-sensor in order to mimic the function of a commercially available flow-sensing device. Using the multi-material printing capability of the 3D printer allows a much smaller amount of functional material to be used in comparison to the commercial flow sensor by only placing the material where it is specifically required. Analysis of the printed sensor also revealed a much more linear response to increasing flow rate of water showing that 3D printed devices have the potential to at least perform as well as a conventionally produced sensor.
Custom 3D printer and resin for 18 μm × 20 μm microfluidic flow channels.
Gong, Hua; Bickham, Bryce P; Woolley, Adam T; Nordin, Gregory P
2017-08-22
While there is great interest in 3D printing for microfluidic device fabrication, to-date the achieved feature sizes have not been in the truly microfluidic regime (digital light processor stereolithographic (DLP-SLA) 3D printer and a specifically-designed, low cost, custom resin can readily achieve flow channel cross sections as small as 18 μm × 20 μm. Our 3D printer has a projected image plane resolution of 7.6 μm and uses a 385 nm LED, which dramatically increases the available selection of UV absorbers for resin formulation compared to 3D printers with 405 nm LEDs. Beginning with 20 candidate absorbers, we demonstrate the evaluation criteria and process flow required to develop a high-resolution resin. In doing so, we introduce a new mathematical model for characterizing the resin optical penetration depth based only on measurement of the absorber's molar absorptivity. Our final resin formulation uses 2-nitrophenyl phenyl sulfide (NPS) as the UV absorber. We also develop a novel channel narrowing technique that, together with the new resin and 3D printer resolution, enables small flow channel fabrication. We demonstrate the efficacy of our approach by fabricating 3D serpentine flow channels 41 mm long in a volume of only 0.12 mm(3), and by printing high aspect ratio flow channels <25 μm wide and 3 mm tall. These results indicate that 3D printing is finally positioned to challenge the pre-eminence of methods such as soft lithography for microfluidic device prototyping and fabrication.
Accurate calculation of Stokes drag for point-particle tracking in two-way coupled flows
Horwitz, Jeremy
2015-01-01
In this work, we propose and test a method for calculating Stokes drag applicable to particle-laden fluid flows where two-way momentum coupling is important. In the point-particle formulation, particle dynamics are coupled to fluid dynamics via a source term that appears in the respective momentum equations. When the particle Reynolds number is small and the particle diameter is smaller than the fluid scales, it is common to approximate the momentum coupling source term as the Stokes drag. The Stokes drag force depends on the difference between the undisturbed fluid velocity evaluated at the particle location, and the particle velocity. However, owing to two-way coupling, the fluid velocity is modified in the neighborhood of a particle, relative to its undisturbed value. This causes the computed Stokes drag force to be underestimated in two-way coupled point-particle simulations. We develop estimates for the drag force error as function of the particle size relative to the grid size. We then develop a correct...
National Aeronautics and Space Administration — This SBIR project proposes to develop a gas-kinetic Navier-Stokes solver for simulation of hypersonic flows in thermal and chemical non-equilibrium. The...
Directory of Open Access Journals (Sweden)
Deininger Martina
2013-01-01
Full Text Available Numerical simulations of complete hydraulic systems (e.g. diesel injectors can, due to high computational costs, currently not be done entirely in three dimensions. Our aim is to substitute the 3D solver by a corresponding 1D method in some parts of the system and develop a solver coupling with suitable interface models. Firstly, we investigate an interface model for non-cavitating flow passing the interface. A flux-coupling with a thin interface approach is considered and the jump in dimensions at the interface is transferred to an additional variable φ, which switches between the 3D and the 1D domain. As shown in two testcases, the error introduced in the vicinity of the interface is quite small. Two numerical flux formulations for the flux over the 3D-1D interface are compared and the Roe-type flux formulation is recommended. Secondly, extending the first method to cavitating flows passing the interface, we divide the density equation in two equations - one for liquid and one for vapor phase of the two-phase fluid - and couple the two equations by source terms depending on the free enthalpy. We propose two interface models for coupling 3D and 1D compressible density-based Euler methods that have potential for considering the entire (non- cavitating hydraulic system behaviour by a 1D method in combination with an embedded detailed 3D simulation at much lower computational costs than the pure 3D simulation.
Investigation of foam flow in a 3D printed porous medium in the presence of oil.
Osei-Bonsu, Kofi; Grassia, Paul; Shokri, Nima
2017-03-15
Foams demonstrate great potential for displacing fluids in porous media which is applicable to a variety of subsurface operations such as the enhanced oil recovery and soil remediation. The application of foam in these processes is due to its unique ability to reduce gas mobility by increasing its effective viscosity and to divert gas to un-swept low permeability zones in porous media. The presence of oil in porous media is detrimental to the stability of foams which can influence its success as a displacing fluid. In the present work, we have conducted a systematic series of experiments using a well-characterised porous medium manufactured by 3D printing technique to evaluate the influence of oil on the dynamics of foam displacement under different boundary conditions. The effects of the type of oil, foam quality and foam flow rate were investigated. Our results reveal that generation of stable foam is delayed in the presence of light oil in the porous medium compared to heavy oil. Additionally, it was observed that the dynamics of oil entrapment was dictated by the stability of foam in the presence of oil. Furthermore, foams with high gas fraction appeared to be less stable in the presence of oil lowering its recovery efficiency. Pore-scale inspection of foam-oil dynamics during displacement revealed formation of a less stable front as the foam quality increased, leading to less oil recovery. This study extends the physical understanding of oil displacement by foam in porous media and provides new physical insights regarding the parameters influencing this process.
Fox, Rodney O.; Vie, Aymeric; Laurent, Frederique; Chalons, Christophe; Massot, Marc
2012-11-01
Numerous applications involve a disperse phase carried by a gaseous flow. To simulate such flows, one can resort to a number density function (NDF) governed a kinetic equation. Traditionally, Lagrangian Monte-Carlo methods are used to solve for the NDF, but are expensive as the number of numerical particles needed must be large to control statistical errors. Moreover, such methods are not well adapted to high-performance computing because of the intrinsic inhomogeneity of the NDF. To overcome these issues, Eulerian methods can be used to solve for the moments of the NDF resulting in an unclosed Eulerian system of hyperbolic conservation laws. To obtain closure, in this work a multivariate bi-Gaussian quadrature is used, which can account for particle trajectory crossing (PTC) over a large range of Stokes numbers. This closure uses up to four quadrature points in 2-D velocity phase space to capture large-scale PTC, and an anisotropic Gaussian distribution around each quadrature point to model small-scale PTC. Simulations of 2-D particle-laden isotropic turbulence at different Stokes numbers are employed to validate the Eulerian models against results from the Lagrangian approach. Good agreement is found for the number density fields over the entire range of Stokes numbers tested. Research carried out at the Center for Turbulence Research 2012 Summer Program.
On Exact Solutions of the Navier-Stokes Equations for Uni-directional Flows
Lam, F
2015-01-01
In the present note, we show that the uni-directional flows in a rectangular channel and in a circular pipe are exact spatio-temporal solutions of the Navier-Stokes equations over a short time interval. We assert that the classical plane Poiseuille-Couette flow and Hagen-Poiseuille flow are time-independent approximations of the exact solutions if an appropriate initial velocity distribution at starting location is specified. Conceptually, there do not exist absolute steady flows starting from unspecified initial data. The classic experimental measurements by Poiseuille can be explained in terms of the evolutional solutions. In particular, the pipe flow does not have a time-independent characteristic velocity. The orthodox notion that the parabolic profile exists for arbitrary Reynolds numbers is unwarranted.
Chen, Y. K.; Henline, W. D.
1993-01-01
The general boundary conditions including mass and energy balances of chemically equilibrated or nonequilibrated gas adjacent to ablating surfaces have been derived. A computer procedure based on these conditions was developed and interfaced with the Navier-Stokes solver for predictions of the flow field, surface temperature, and surface ablation rates over re-entry space vehicles with ablating Thermal Protection Systems (TPS). The Navier-Stokes solver with general surface thermochemistry boundary conditions can predict more realistic solutions and provide useful information for the design of TPS. A test case with a proposed hypersonic test vehicle configuration and associated free stream conditions was developed. Solutions with various surface boundary conditions were obtained, and the effect of nonequilibrium gas as well as surface chemistry on surface heating and ablation rate were examined. The solutions of the GASP code with complete ablating surface conditions were compared with those of the ASC code. The direction of future work is also discussed.
Zhu, Liang-sheng; Yu, Long-fei
2016-10-01
Aimed at the hydrodynamic response for marine structures slamming into water, based on the mechanism analysis to the slamming process, and by combining 3D N-S equation and k- ɛ turbulent kinetic equation with structure fully 6DOF motion equation, a mathematical model for the wind-fluid-solid interaction is established in 3D marine structure slamming wave at free poses and wind-wave-flow complex environments. Compared with the results of physical model test, the numerical results from the slamming wave well correspond with the experimental results. Through the mathematical model, the wave-making issue of 3D marine structure at initial pose falls into water in different complex wind, wave and flow environments is investigated. The research results show that various kinds of natural factors and structure initial poses have different influence on the slamming wave, and there is an obvious rule in this process.
Institute of Scientific and Technical Information of China (English)
罗志强; 陈志敏
2013-01-01
A three-dimensional (3D) predictor-corrector finite difference method for standing wave is developed. It is applied to solve the 3D nonlinear potential flow equa-tions with a free surface. The 3D irregular tank is mapped onto a fixed cubic tank through the proper coordinate transform schemes. The cubic tank is distributed by the staggered meshgrid, and the staggered meshgrid is used to denote the variables of the flow field. The predictor-corrector finite difference method is given to develop the difference equa-tions of the dynamic boundary equation and kinematic boundary equation. Experimental results show that, using the finite difference method of the predictor-corrector scheme, the numerical solutions agree well with the published results. The wave profiles of the standing wave with different amplitudes and wave lengths are studied. The numerical solutions are also analyzed and presented graphically.
Well-Posed Stokes/Brinkman and Stokes/Darcy Problems for Coupled Fluid-Porous Viscous Flows
Angot, Philippe
2010-09-01
We present a well-posed model for the Stokes/Brinkman problem with a family of jump embedded boundary conditions (J.E.B.C.) on an immersed interface with weak regularity assumptions. It is issued from a general framework recently proposed for fictitious domain problems. Our model is based on algebraic transmission conditions combining the stress and velocity jumps on the interface Σ separating the fluid and porous domains. These conditions, well chosen to get the coercivity of the operator, are sufficiently general to get the usual immersed boundary conditions on Σ when fictitious domain methods are concerned: Stefan-like, Robin (Fourier), Neumann or Dirichlet… Moreover, the general framework allows to prove the global solvability of some models with physically relevant stress or velocity jump boundary conditions for the momentum transport at a fluid-porous interface. The Stokes/Brinkman problem with Ochoa-Tapia & Whitaker (1995) interface conditions and the Stokes/Darcy problem with Beavers & Joseph (1967) conditions are both proved to be well-posed by an asymptotic analysis. Up to our knowledge, only the Stokes/Darcy problem with Saffman (1971) approximate interface conditions was known to be well-posed.
Mao, Mingxu; Ye, Jiamin; Wang, Haigang; Yang, Wuqiang
2016-09-01
The hydrodynamics of gas-solids flow in the bottom of a circulating fluidized bed (CFB) are complicated. Three-dimensional (3D) electrical capacitance tomography (ECT) has been used to investigate the hydrodynamics in risers of different shapes. Four different ECT sensors with 12 electrodes each are designed according to the dimension of risers, including two circular ECT sensors, a square ECT sensor and a rectangular ECT sensor. The electrodes are evenly arranged in three planes to obtain capacitance in different heights and to reconstruct the 3D images by linear back projection (LBP) algorithm. Experiments were carried out on the four risers using sands as the solids material. The capacitance and differential pressure are measured under the gas superficial velocity from 0.6 m s-1 to 3.0 m s-1 with a step of 0.2 m s-1. The flow regime is investigated according to the solids concentration and differential pressure. The dynamic property of bubbling flows is analyzed theoretically and the performance of the 3D ECT sensors is evaluated. The experimental results show that 3D ECT can be used in the CFB with different risers to predict the hydrodynamics of gas-solids bubbling flows.
Energy Technology Data Exchange (ETDEWEB)
Ramazani, A., E-mail: ali.ramazani@iehk.rwth-aachen.de [Department of Ferrous Metallurgy, RWTH Aachen University, Intzestr.1, D-52072 Aachen (Germany); Mukherjee, K.; Quade, H.; Prahl, U.; Bleck, W. [Department of Ferrous Metallurgy, RWTH Aachen University, Intzestr.1, D-52072 Aachen (Germany)
2013-01-10
A microstructure-based approach by means of representative volume elements (RVEs) is employed to evaluate the flow curve of DP steels using virtual tensile tests. Microstructures with different martensite fractions and morphologies are studied in two- and three-dimensional approaches. Micro sections of DP microstructures with various amounts of martensite have been converted to 2D RVEs, while 3D RVEs were constructed statistically with randomly distributed phases. A dislocation-based model is used to describe the flow curve of each ferrite and martensite phase separately as a function of carbon partitioning and microstructural features. Numerical tensile tests of RVE were carried out using the ABAQUS/Standard code to predict the flow behaviour of DP steels. It is observed that 2D plane strain modelling gives an underpredicted flow curve for DP steels, while the 3D modelling gives a quantitatively reasonable description of flow curve in comparison to the experimental data. In this work, a von Mises stress correlation factor {sigma}{sub 3D}/{sigma}{sub 2D} has been identified to compare the predicted flow curves of these two dimensionalities showing a third order polynomial relation with respect to martensite fraction and a second order polynomial relation with respect to equivalent plastic strain, respectively. The quantification of this polynomial correlation factor is performed based on laboratory-annealed DP600 chemistry with varying martensite content and it is validated for industrially produced DP qualities with various chemistry, strength level and martensite fraction.
Euler/Navier-Stokes flow computations on flexible configurations for stability analysis
Guruswamy, G.; Tu, E.
1995-01-01
Longitudinal dynamic stability derivatives required for design of aircraft are computed by using the state-of-the-art numerical methods for wing-body configurations. The flow is modeled using the Euler/Navier-Stokes equations with turbulence models and solved using an efficient finite-difference scheme suitable for patched structured grids. Computations are made at a flow regime that is beyond the limits of the current linear methods mostly used for computing stability derivatives. Flow conditions include shockwaves and viscous dominated vortical flows. Effect of Mach number and angle-of-attack on stability derivatives are demonstrated for a typical wing-body configuration. For the same configuration the effects of wing flexibility on the magnitude and phase angles of stability derivatives are also demonstrated.
Pore-Scale Modeling of Navier-Stokes Flow in Distensible Networks and Porous Media
Sochi, Taha
2013-01-01
In this paper, a pore-scale network modeling method, based on the flow continuity residual in conjunction with a Newton-Raphson non-linear iterative solving technique, is proposed and used to obtain the pressure and flow fields in a network of interconnected distensible ducts representing, for instance, blood vasculature or deformable porous media. A previously derived analytical expression correlating boundary pressures to volumetric flow rate in compliant tubes for a pressure-area constitutive elastic relation has been used to represent the underlying flow model. Comparison to a preceding equivalent method, the one-dimensional Navier-Stokes finite element, was made and the results were analyzed. The advantages of the new method have been highlighted and practical computational issues, related mainly to the rate and speed of convergence, have been discussed.
3D CFD modeling of subsonic and transonic flowing-gas DPALs with different pumping geometries
Yacoby, Eyal; Sadot, Oren; Barmashenko, Boris D.; Rosenwaks, Salman
2015-10-01
Three-dimensional computational fluid dynamics (3D CFD) modeling of subsonic (Mach number M ~ 0.2) and transonic (M ~ 0.9) diode pumped alkali lasers (DPALs), taking into account fluid dynamics and kinetic processes in the lasing medium is reported. The performance of these lasers is compared with that of supersonic (M ~ 2.7 for Cs and M ~ 2.4 for K) DPALs. The motivation for this study stems from the fact that subsonic and transonic DPALs require much simpler hardware than supersonic ones where supersonic nozzle, diffuser and high power mechanical pump (due to a drop in the gas total pressure in the nozzle) are required for continuous closed cycle operation. For Cs DPALs with 5 x 5 cm2 flow cross section pumped by large cross section (5 x 2 cm2) beam the maximum achievable power of supersonic devices is higher than that of the transonic and subsonic devices by only ~ 3% and ~ 10%, respectively. Thus in this case the supersonic operation mode has no substantial advantage over the transonic one. The main processes limiting the power of Cs supersonic DPALs are saturation of the D2 transition and large ~ 60% losses of alkali atoms due to ionization, whereas the influence of gas heating is negligible. For K transonic DPALs both the gas heating and ionization effects are shown to be unimportant. The maximum values of the power are higher than those in Cs transonic laser by ~ 11%. The power achieved in the supersonic and transonic K DPAL is higher than for the subsonic version, with the same resonator and K density at the inlet, by ~ 84% and ~ 27%, respectively, showing a considerable advantaged of the supersonic device over the transonic one. For pumping by rectangular beams of the same (5 x 2 cm2) cross section, comparison between end-pumping - where the laser beam and pump beam both propagate at along the same axis, and transverse-pumping - where they propagate perpendicularly to each other, shows that the output power and optical-to-optical efficiency are not
Navier-Stokes analysis of solid propellant rocket motor internal flows
Sabnis, J. S.; Gibeling, H. J.; Mcdonald, H.
1989-01-01
A multidimensional implicit Navier-Stokes analysis that uses numerical solution of the ensemble-averaged Navier-Stokes equations in a nonorthogonal, body-fitted, cylindrical coordinate system has been applied to the simulation of the steady mean flow in solid propellant rocket motor chambers. The calculation procedure incorporates a two-equation (k-epsilon) turbulence model and utilizes a consistently split, linearized block-implicit algorithm for numerical solution of the governing equations. The code was validated by comparing computed results with the experimental data obtained in cylindrical-port cold-flow tests. The agreement between the computed and experimentally measured mean axial velocities is excellent. The axial location of transition to turbulent flow predicted by the two-equation (k-epsilon) turbulence model used in the computations also agrees well with the experimental data. Computations performed to simulate the axisymmetric flowfield in the vicinity of the aft field joint in the Space Shuttle solid rocket motor using 14,725 grid points show the presence of a region of reversed axial flow near the downstream edge of the slot.
Navier-Stokes analysis of solid propellant rocket motor internal flows
Sabnis, J. S.; Gibeling, H. J.; Mcdonald, H.
1989-01-01
A multidimensional implicit Navier-Stokes analysis that uses numerical solution of the ensemble-averaged Navier-Stokes equations in a nonorthogonal, body-fitted, cylindrical coordinate system has been applied to the simulation of the steady mean flow in solid propellant rocket motor chambers. The calculation procedure incorporates a two-equation (k-epsilon) turbulence model and utilizes a consistently split, linearized block-implicit algorithm for numerical solution of the governing equations. The code was validated by comparing computed results with the experimental data obtained in cylindrical-port cold-flow tests. The agreement between the computed and experimentally measured mean axial velocities is excellent. The axial location of transition to turbulent flow predicted by the two-equation (k-epsilon) turbulence model used in the computations also agrees well with the experimental data. Computations performed to simulate the axisymmetric flowfield in the vicinity of the aft field joint in the Space Shuttle solid rocket motor using 14,725 grid points show the presence of a region of reversed axial flow near the downstream edge of the slot.
Jung, Yookyung; Tam, Joshua; Jalian, H. Ray; Anderson, R. Rox; Evans, Conor L.
2014-01-01
Sebaceous glands perform complex functions, and are centrally involved in the pathogenesis of acne vulgaris. Current techniques for studying sebaceous glands are mostly static in nature, whereas the gland’s main function – excretion of sebum via the holocrine mechanism – can only be evaluated over time. We present a longitudinal, real-time alternative – the in vivo, label-free imaging of sebaceous glands using Coherent Anti-Stokes Raman Scattering (CARS) microscopy, which is used to selectively visualize lipids. In mouse ears, CARS microscopy revealed dynamic changes in sebaceous glands during the holocrine secretion process, as well as in response to damage to the glands caused by cooling. Detailed gland structure, plus the active migration of individual sebocytes and cohorts of sebocytes were measured. Cooling produced characteristic changes in sebocyte structure and migration. This study demonstrates that CARS microscopy is a promising tool for studying the sebaceous gland and its associated disorders in three-dimensions in vivo. PMID:25026458
Bruno, Oscar
2015-01-01
This paper introduces alternating-direction implicit (ADI) solvers of higher order of time-accuracy (orders two to six) for the compressible Navier-Stokes equations in two- and three-dimensional curvilinear domains. The higher-order accuracy in time results from 1) An application of the backward differentiation formulae time-stepping algorithm (BDF) in conjunction with 2) A BDF-like extrapolation technique for certain components of the nonlinear terms (which makes use of nonlinear solves unnecessary), as well as 3) A novel application of the Douglas-Gunn splitting (which greatly facilitates handling of boundary conditions while preserving higher-order accuracy in time). As suggested by our theoretical analysis of the algorithms for a variety of special cases, an extensive set of numerical experiments clearly indicate that all of the BDF-based ADI algorithms proposed in this paper are "quasi-unconditionally stable" in the following sense: each algorithm is stable for all couples $(h,\\Delta t)$ of spatial and t...
Mixed mimetic spectral element method for Stokes flow: A pointwise divergence-free solution
Kreeft, Jasper; Gerritsma, Marc
2013-05-01
In this paper we apply the recently developed mimetic discretization method to the mixed formulation of the Stokes problem in terms of vorticity, velocity and pressure. The mimetic discretization presented in this paper and in Kreeft et al. [51] is a higher-order method for curvilinear quadrilaterals and hexahedrals. Fundamental is the underlying structure of oriented geometric objects, the relation between these objects through the boundary operator and how this defines the exterior derivative, representing the grad, curl and div, through the generalized Stokes theorem. The mimetic method presented here uses the language of differential k-forms with k-cochains as their discrete counterpart, and the relations between them in terms of the mimetic operators: reduction, reconstruction and projection. The reconstruction consists of the recently developed mimetic spectral interpolation functions. The most important result of the mimetic framework is the commutation between differentiation at the continuous level with that on the finite dimensional and discrete level. As a result operators like gradient, curl and divergence are discretized exactly. For Stokes flow, this implies a pointwise divergence-free solution. This is confirmed using a set of test cases on both Cartesian and curvilinear meshes. It will be shown that the method converges optimally for all admissible boundary conditions.
Wang, ChengYue; Gao, Qi; Wei, RunJie; Li, Tian; Wang, JinJun
2016-06-01
Volumetric measurement for the leading-edge vortex (LEV) breakdown of a delta wing has been conducted by three-dimensional (3D) flow visualization and tomographic particle image velocimetry (TPIV). The 3D flow visualization is employed to show the vortex structures, which was recorded by four cameras with high resolution. 3D dye streaklines of the visualization are reconstructed using a similar way of particle reconstruction in TPIV. Tomographic PIV is carried out at the same time using same cameras with the dye visualization. Q criterion is employed to identify the LEV. Results of tomographic PIV agree well with the reconstructed 3D dye streaklines, which proves the validity of the measurements. The time-averaged flow field based on TPIV is shown and described by sections of velocity and streamwise vorticity. Combining the two measurement methods sheds light on the complex structures of both bubble type and spiral type of breakdown. The breakdown position is recognized by investigating both the streaklines and TPIV velocity fields. Proper orthogonal decomposition is applied to extract a pair of conjugated helical instability modes from TPIV data. Therefore, the dominant frequency of the instability modes is obtained from the corresponding POD coefficients of the modes based on wavelet transform analysis.
Kim, Ho Jun; Lee, Hae June
2016-06-01
The wide applicability of capacitively coupled plasma (CCP) deposition has increased the interest in developing comprehensive numerical models, but CCP imposes a tremendous computational cost when conducting a transient analysis in a three-dimensional (3D) model which reflects the real geometry of reactors. In particular, the detailed flow features of reactive gases induced by 3D geometric effects need to be considered for the precise calculation of radical distribution of reactive species. Thus, an alternative inclusive method for the numerical simulation of CCP deposition is proposed to simulate a two-dimensional (2D) CCP model based on the 3D gas flow results by simulating flow, temperature, and species fields in a 3D space at first without calculating the plasma chemistry. A numerical study of a cylindrical showerhead-electrode CCP reactor was conducted for particular cases of SiH4/NH3/N2/He gas mixture to deposit a hydrogenated silicon nitride (SiN x H y ) film. The proposed methodology produces numerical results for a 300 mm wafer deposition reactor which agree very well with the deposition rate profile measured experimentally along the wafer radius.
Hybrid solution of the averaged Navier-Stokes equations for turbulent flow
Lima, J. A.; Perez-Guerrero, J. S.; Cotta, R. M.
The Generalized Integral Transform Technique (GITT) is utilized in the hybrid numerical-analytical solution of the Reynolds averaged Navier-Stokes equations, for developing turbulent flow inside a parallel-plates channel. An algebraic turbulence model is employed in modelling the turbulent diffusivity. The automatic global error control feature inherent to this approach, permits the determination of fully converged reference results for the validation of purely numerical methods. Therefore, numerical results for different values of Reynolds number are obtained, both for illustrating the convergence characteristics of the integral transform approach, and for critical comparisons with previously reported results through different models and numerical schemes.
NON-STATIONARY STOKES FLOWS UNDER LEAK BOUNDARY CONDITIONS OF FRICTION TYPE
Institute of Scientific and Technical Information of China (English)
Hiroshi Fujita
2001-01-01
This paper is concerned with the initial value problem for non-stationary Stokes flows,under a certain non-linear boundary condition which can be called the leak boundarycondition of friction type. Theoretically, our main purpose is to show the strong solvability(i.e.,the unique existence of the L2-strong solution) of this initial value problem by meansof the non-linear semi-group theory originated with Y. Komura. The method of analysiscan be applied to other boundary or interface conditions of friction type. It should benoted that the result yields a sound basis of simulation methods for evolution problemsinvolving these conditions.
OPTIMAL MIXED H- P FINITE ELEMENT METHODS FOR STOKES AND NON-NEWTONIAN FLOW
Institute of Scientific and Technical Information of China (English)
Ping-bing Ming; Zhong-ci Shi
2001-01-01
Based upon a new mixed variational formulation for the three-field Stokes equations and linearized Non-Newtonian flow, an h -p finite element method is presented with or without a stabilization. As to the variational formulation without stabilization, optimal error bounds in h as well as in p are obtained. As with stabilization, optimal error bounds are obtained which is optimal in h and one order deterioration in p for the pressure, that is consistent with numerical results in [9, 12] and therefore solved the problem therein.Moreover, we proposed a stabilized formulation which is optimal in both h and p.
Stokes coupling method for the exterior flowPart III: regularity
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Based on the Stokes coupling method for solving the two-dimensional exterior unsteady Navier-Stokes equations, the existence of the strong solution of the Stokes coupling equations is proven. And the regularity of the solution for the reduced Stokes coupling equations is discussed.
Simultaneous 3D turbulent large-scale structures in a flood flow by multi-channels measuring systems
Hino, Mikio; Meng, Yang; Murayama, Nobuyoshi; 日野 幹雄; Meng, Y.; 村山 宣義
1992-01-01
Field measurements on turbulent large-scale structure of a flood flow in the Hinuma river at a high Reynolds number of the order of 10 (exp 6) were conducted with 16-channels electromagnetic velocimeters. The turbulent velocity components (u, v) at eight points in a plane perpendicular to the mean flow have been sampled and recorded simultaneously by a A/D converter. The quasi-instantaneous 3D images of coherent structures in the flood flow were reconstructed from these data by using a new me...
Massively Parallel Linear Stability Analysis with P_ARPACK for 3D Fluid Flow Modeled with MPSalsa
Energy Technology Data Exchange (ETDEWEB)
Lehoucq, R.B.; Salinger, A.G.
1998-10-13
We are interested in the stability of three-dimensional fluid flows to small dkturbances. One computational approach is to solve a sequence of large sparse generalized eigenvalue problems for the leading modes that arise from discretizating the differential equations modeling the flow. The modes of interest are the eigenvalues of largest real part and their associated eigenvectors. We discuss our work to develop an effi- cient and reliable eigensolver for use by the massively parallel simulation code MPSalsa. MPSalsa allows simulation of complex 3D fluid flow, heat transfer, and mass transfer with detailed bulk fluid and surface chemical reaction kinetics.
A PARTIALLY-AVERAGED NAVIER-STOKES MODEL FOR HILL AND CURVED DUCT FLOW
Institute of Scientific and Technical Information of China (English)
MA Jia-mei; WANG Fu-jun; YU Xin; LIU Zhu-qing
2011-01-01
Turbulent flows past hill and curved ducts exist in many engineering applications.Simulations of the turbulent flow are carried out based on a newly developed technique,the Partially-Averaged Navier-Stokes(PANS)model,including separation,recirculation,reattachment,turbulent vortex mechanism.The focus is on how to accurately predict typical separating,reattaching and secondary motion at a reasonable computational expense.The effect of the parameter,the unresolved-to-total ratio of kinetic energy (fk),is examined with a given unresolved-to-total ratio of dissipation(fε)for the hill flow with a much coarser grid system than required by the LES.An optimal value of fk can be obtained to predict the separation and reattachment locations and for more accurate simulation of the resolved turbulence.In addition,the turbulent secondary motions are captured by a smaller fk as compared with the RANS method with the same grid.
Institute of Scientific and Technical Information of China (English)
V.I. GNESIN; L.V. KOLODYAZHNAYA; R. RZADKOWSKI
2005-01-01
Fiszera st., 14, Gdansk, 80 952 PolandIn this study presented the algorithm proposed involves the coupled solution of 3-D unsteady flow through a turbine stage and the dynamics problem for rotor-blade motion by the action of aerodynamic forces, without separating the outer and inner flow fluctuations. The partially integrated method involves the solution of the fluid and structural equations separately, but information is exchanged at each time step, so that solution from one domain is used as a boundary condition for the other domain. 3-D transonic gas flow through the stator and rotor blades in relative motion with periodicity on the whole annulus is described by the unsteady Euler conservation equations, which are integrated using the explicit monotonous finite-volume difference scheme of GodunovKolgan. The structural analysis uses the modal approach and a 3-D finite element model of a blade. A calculation has been done for the last stage of the steam turbine, under design and off-design regimes. It is shown that the amplitude-frequency spectrum of blade oscillations contains the high frequency harmonics, corresponding to the rotor moving past one stator blade pitch, and low frequency harmonics caused by blade oscillations and flow nonunifonnity downstream from the blade row; moreover, the spectrum involves the harmonics which are not multiples of the rotation frequency.
Recent Enhancements To The FUN3D Flow Solver For Moving-Mesh Applications
Biedron, Robert T,; Thomas, James L.
2009-01-01
An unsteady Reynolds-averaged Navier-Stokes solver for unstructured grids has been extended to handle general mesh movement involving rigid, deforming, and overset meshes. Mesh deformation is achieved through analogy to elastic media by solving the linear elasticity equations. A general method for specifying the motion of moving bodies within the mesh has been implemented that allows for inherited motion through parent-child relationships, enabling simulations involving multiple moving bodies. Several example calculations are shown to illustrate the range of potential applications. For problems in which an isolated body is rotating with a fixed rate, a noninertial reference-frame formulation is available. An example calculation for a tilt-wing rotor is used to demonstrate that the time-dependent moving grid and noninertial formulations produce the same results in the limit of zero time-step size.
Flow-through 3D biofuel cell anode for NAD{sup +}-dependent enzymes
Energy Technology Data Exchange (ETDEWEB)
Rincon, Rosalba A.; Lau, Carolin; Garcia, Kristen E. [Department of Chemical and Nuclear Engineering, Center for Emerging Energy Technologies, University of New Mexico, Albuquerque, NM 87131 (United States); Atanassov, Plamen, E-mail: plamen@unm.ed [Department of Chemical and Nuclear Engineering, Center for Emerging Energy Technologies, University of New Mexico, Albuquerque, NM 87131 (United States)
2011-02-01
NAD{sup +}-dependent enzymes require the presence of catalysts for cofactor regeneration in order to be employed in enzymatic biofuel cells. Poly-(methylene green) catalysts have proven to help the oxidation reaction of NADH allowing for the use of such enzymes in electrocatalytic oxidation reactions. In this paper we present the development of 3D anode based on NAD{sup +}-dependent malate dehydrogenase. The 3D material chosen was reticulated vitreous carbon (RVC) which was modified with poly-(MG) for NADH oxidation and it also accommodated the porous immobilization matrix for MDH consisting of MWCNTs embedded in chitosan; allowing for mass transport of the substrate to the electrode. Scanning electron microscopy was used in order to characterize the poly-(MG)-modified RVC, and electrochemical evaluation of the anode was performed.
Numerical Simulation and Experimental Investigation of 3-D Separated Flow Field around a Blunt Body
Institute of Scientific and Technical Information of China (English)
无
1999-01-01
@@Motivated by re-designing a fuselage in engineering application, the numerical and experimental investigation of the separated flow field around a special blunt body is described in this thesis. The aerodynamic response of the blunt body is successively studied. The thesis consists of four parts: the numerical simulation of the flow field around a two-dimensional blunt body; the numerical simulation of the flow field around a three-dimensional blunt body; the flow
Directory of Open Access Journals (Sweden)
Xingwen Zhu
2015-01-01
Full Text Available Smoothing analysis process of distributive red-black Jacobi relaxation in multigrid method for solving 2D Stokes flow is mainly investigated on the nonstaggered grid by using local Fourier analysis (LFA. For multigrid relaxation, the nonstaggered discretizing scheme of Stokes flow is generally stabilized by adding an artificial pressure term. Therefore, an important problem is how to determine the zone of parameter in adding artificial pressure term in order to make stabilization of the algorithm for multigrid relaxation. To end that, a distributive red-black Jacobi relaxation technique for the 2D Stokes flow is established. According to the 2h-harmonics invariant subspaces in LFA, the Fourier representation of the distributive red-black Jacobi relaxation for discretizing Stokes flow is given by the form of square matrix, whose eigenvalues are meanwhile analytically computed. Based on optimal one-stage relaxation, a mathematical relation of the parameter in artificial pressure term between the optimal relaxation parameter and related smoothing factor is well yielded. The analysis results show that the numerical schemes for solving 2D Stokes flow by multigrid method on the distributive red-black Jacobi relaxation have a specified convergence parameter zone of the added artificial pressure term.
3D flows near a HAWT rotor: A dissection of blade and wake contributions
Micallef, D.
2012-01-01
Investigating the flow physics in the vicinity of the wind turbine blade is a challenging endeavour. In the past, focus was placed on the understanding of near wake flows arising from wake vorticity and the rotor loading. In this work, a different approach is taken by considering the flow field in t
Stokes flow through a slit with periodic reabsorption: An application to renal tubule
Directory of Open Access Journals (Sweden)
T. Haroon
2016-06-01
Full Text Available This paper is concerned with the Stokes flow of an incompressible viscous fluid through a slit with periodic reabsorption at the walls. The momentum equation for the two dimensional flow is exactly solved in terms of stream function for two different cases of boundary conditions. Dimensional forms of stream function, velocity components, axial flow rate, pressure distribution, mean pressure drop, wall shear stress, fractional reabsorption and leakage flux are obtained. The points of maximum velocity components are also identified for fixed axial distance. Using physiological data of rat kidney, the theoretical values of periodic reabsorption and pressure drop for various values of fractional reabsorption are tabulated. The graphs of flow properties for both the cases are compared with the case of uniform reabsorption. It is shown that the periodic reabsorption parameter for both the cases plays a vital role in altering the flow properties, which are useful in analyzing flow behavior during the reabsorption of glomerular filtrate through a renal tubule in normal and diseased conditions. It is found that 50% reabsorption of fluid from a single nephron can be achieved by setting α=3.197500134cm for one of the cases which indicates that there is a need of artificial kidney for survival. In case 2, a minor treatment is needed as the value of α for 80% reabsorption is not possible. Streamlines are also drawn to analyze the flow behavior through an abnormal renal tubule.
Computer modeling of flow and transport interactions for compressible Navier-Stokes equations
Rahman, Mohamed Mizanur
A unified numerical algorithm to simulate viscous flow with heat transfer over a wide range of Mach number and Reynolds number is developed. The governing equations used to model the numerical simulations are the 2-D compressible viscous Navier-Stokes equations. The numerical procedure is based on MacCormack's explicit 'predictor corrector' time dependent finite difference scheme. For an explicit scheme, a great number of iterations is required to get a converged steady solution because of a small time step. Vectorizing and parallelizing the code greatly alleviates this problem by reducing the total job running time manifold. The numerical algorithm, thus developed, is used to simulate such demanding and interacting flow problems as convection heat transfer in a cavity flow heat transfer enhancement by eddy-promoters, laminar/turbulent shock boundary layer interactions and unsteady shock boundary layer interactions over a compression corner. A detailed analysis of all important flow features that characterize such flows and the mechanisms that are involved, is performed for each individual case. The flow physics are discussed and new insights are provided. Results are compared with experimental data where available and the empirical relations between different flow properties or parameters are either established or verified where possible. Apart from these, some algorithm related questions, such as grid sensitivity, boundary conditions, convergence criteria, effects of artificial viscosity and the numerical stability are investigated.
3-D hybrid LES-RANS model for simulation of open-channel T-diversion flows
Institute of Scientific and Technical Information of China (English)
Jie ZHOU; Cheng ZENG
2009-01-01
The study of flow diversions in open channels plays an important practical role in the design and management of open-channel networks for irrigation or drainage.To accurately predict the mean flow and turbulence characteristics of open-channel dividing flows,a hybrid LES-RANS model,which combines the large eddy simulation (LES) model with the Reynolds-averaged Navier-Stokes (RANS) model,is proposed in the present study.The unsteady RANS model was used to simulate the upstream and downstream regions of a main channel,as well as the downstream region of a branch channel.The LES model was used to simulate the channel diversion region,where turbulent flow characteristics ate complicated.Isotropic velocity fluctuations were added at the inflow interface of the LES region to trigger the generation of resolved turbulence.A method based on the virtual body force is proposed to impose Reynolds-averaged velocity fields near the outlet of the LES region in order to take downstream flow effects computed by the RANS model into account and dissipate the excessive turbulent fluctuations.This hybrid approach saves computational effort and makes it easier to properly specify inlet and outlet boundary conditions.Comparison between computational results and experimental data indicates that this relatively new modeling approach can accurately predict open-channel T-diversion flows.
NUMERICAL ANALYSIS OF THE 3-D FLOW FIELD OF PRESSURE ATOMIZERS WITH V-SHAPED CUT AT ORIFICE
Institute of Scientific and Technical Information of China (English)
ZHOU Hua
2011-01-01
Axisymmetric liquid jets have been studied extensively for more than one century, while non-axisymmetric jets are also very common in engineering applications but attract less concern. Based on Eulerian fluid-fluid model in Fluent software, this article analysizes the 3-D flow fields of pressure atomizers with V-shaped cut at orifice, which will result in a non-axisymmetric liquid jet.Flow rate analysis and jet structure analysis are carried out, the results show that the flow rate can be formulated by adding a correction coefficient to the formula of inviscid axisymmetric jets in atomization regime, when the Weber number is low enough to make the flow fall out of atomization regime, and the jet structure together with the flow rate formula will change. Analysis shows that the evolution of the spray and therefore the structure of the liquid jet are affected much by relative velocity and the local volume fraction of liquid phase.
SIMULATION PROCESS OF REMOVING NON-METALLIC INCLUSIONS IN ALUMINUM ALLOYS USING THE PROGRAM FLOW-3D
Directory of Open Access Journals (Sweden)
N. V. Sletova
2013-01-01
Full Text Available The perspective materials for making fining preparations for the silumins are the calcium and strontium carbonates from the environmental safety point of view are shown. Principle possibility of using dispersed carbonates in the fining mixtures is confirmed by late inoculation process research using simulation FLOW-3D.The high efficiency of the fining mixture with the inoculants effect is confirmed by the industrial tests
Wang, Min; Chen, Yi-Feng; Ma, Guo-Wei; Zhou, Jia-Qing; Zhou, Chuang-Bing
2016-10-01
This study investigates the impacts of surface roughness on the nonlinear fluid flow through three-dimensional (3D) self-affine rock fractures, whose original surface roughness is decomposed into primary roughness (i.e. the large-scale waviness of the fracture morphology) and secondary roughness (i.e. the small-scale unevenness) with a wavelet analysis technique. A 3D Lattice Boltzmann method (LBM) is adopted to predict the flow physics in rock fractures numerically created with and without consideration of the secondary roughness, respectively. The simulation results show that the primary roughness mostly controls the pressure distribution and fracture flow paths at a large scale, whereas the secondary roughness determines the nonlinear properties of the fluid flow at a local scale. As the pressure gradient increases, the secondary roughness enhances the local complexity of velocity distribution by generating and expanding the eddy flow and back flow regions in the vicinity of asperities. It was found that the Forchheimer's law characterizes well the nonlinear flow behavior in fractures of varying roughness. The inertial effects induced by the primary roughness differ only marginally in fractures with the roughness exponent varying from 0.5 to 0.8, and it is the secondary roughness that significantly enhances the nonlinear flow and leads to earlier onset of nonlinearity. Further examined were the effects of surface roughness on the transmissivity, hydraulic aperture and the tortuosity of flow paths, demonstrating again the dominant role of the secondary roughness, especially for the apparent transmissivity and the equivalent hydraulic aperture at high pressure gradient or high Reynolds number. The results may enhance our understanding of the role of surface roughness in the nonlinear flow behaviors in natural rock fractures.
Chatelin, Robin; Poncet, Philippe
2014-07-01
Particle methods are very convenient to compute transport equations in fluid mechanics as their computational cost is linear and they are not limited by convection stability conditions. To achieve large 3D computations the method must be coupled to efficient algorithms for velocity computations, including a good treatment of non-homogeneities and complex moving geometries. The Penalization method enables to consider moving bodies interaction by adding a term in the conservation of momentum equation. This work introduces a new computational algorithm to solve implicitly in the same step the Penalization term and the Laplace operators, since explicit computations are limited by stability issues, especially at low Reynolds number. This computational algorithm is based on the Sherman-Morrison-Woodbury formula coupled to a GMRES iterative method to reduce the computations to a sequence of Poisson problems: this allows to formulate a penalized Poisson equation as a large perturbation of a standard Poisson, by means of algebraic relations. A direct consequence is the possibility to use fast solvers based on Fast Fourier Transforms for this problem with good efficiency from both the computational and the memory consumption point of views, since these solvers are recursive and they do not perform any matrix assembling. The resulting fluid mechanics computations are very fast and they consume a small amount of memory, compared to a reference solver or a linear system resolution. The present applications focus mainly on a coupling between transport equation and 3D Stokes equations, for studying biological organisms motion in a highly viscous flows with variable viscosity.
Validation of Wall Friction Model in SPACE-3D Module with Two-Phase Cross Flow Experiment
Energy Technology Data Exchange (ETDEWEB)
Choi, Chi-Jin; Yang, Jin-Hwa; Cho, Hyoung-Kyu; Park, Goon-Cher [Seoul National University, Seoul (Korea, Republic of); Euh, Dong-Jin [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2015-10-15
In this study, SPACE-3D was used to simulate the Yang's experiment, and obtained the local variables. Then, the wall friction model used in SPACE-3D was validated by comparing the two-phase cross flow experimental results with the calculated local variables. In this study, the two-phase cross flow experiment was modeled by SPACE-3D to validate the wall friction model in multi-dimensional module. Considering the realistic phenomena in the reactor, however, recent trends in safety analysis codes have tended to adopt multi-dimensional module to simulate the complex flow more accurately. Even though the module was applied to deal the multi-dimensional phenomena, implemented models in that are one-dimensional empirical models. Therefore, prior to applying the multi-dimensional module, the constitutive models implemented in the codes need to be validated. In the downcomer of Advanced Power Reactor 1400 (APR1400) which has direct vessel injection (DVI) lines as an emergency core cooling system, multi-dimensional two-phase flow may occur due to the Loss-of-Coolant-Accident (LOCA). The accurate prediction about that is high relevance to evaluation of the integrity of the reactor core. For this reason, Yang performed an experiment that was to investigate the two-dimensional film flow which simulated the two-phase cross flow in the upper downcomer, and obtained the local liquid film velocity and thickness data. From these data, it could be possible to validate the friction models in multi-dimensional module of system analysis codes. Compared with the experiment, SPACE-3D underestimated the liquid film velocity and overestimated the liquid film thickness. From these results, it was clarified that the Wallis correlation which is used as a wall friction model in SPACE-3D overestimates the wall friction. On the other hand, H.T.F.S. correlation which is used as the wall friction in MARS-multiD underestimates the wall friction.
3-D flow and scour near a submerged wing dike: ADCP measurements on the Missouri River
Jamieson, E.C.; Rennie, C.D.; Jacobson, R.B.; Townsend, R.D.
2011-01-01
Detailed mapping of bathymetry and three-dimensional water velocities using a boat-mounted single-beam sonar and acoustic Doppler current profiler (ADCP) was carried out in the vicinity of two submerged wing dikes located in the Lower Missouri River near Columbia, Missouri. During high spring flows the wing dikes become submerged, creating a unique combination of vertical flow separation and overtopping (plunging) flow conditions, causing large-scale three-dimensional turbulent flow structures to form. On three different days and for a range of discharges, sampling transects at 5 and 20 m spacing were completed, covering the area adjacent to and upstream and downstream from two different wing dikes. The objectives of this research are to evaluate whether an ADCP can identify and measure large-scale flow features such as recirculating flow and vortex shedding that develop in the vicinity of a submerged wing dike; and whether or not moving-boat (single-transect) data are sufficient for resolving complex three-dimensional flow fields. Results indicate that spatial averaging from multiple nearby single transects may be more representative of an inherently complex (temporally and spatially variable) three-dimensional flow field than repeated single transects. Results also indicate a correspondence between the location of calculated vortex cores (resolved from the interpolated three-dimensional flow field) and the nearby scour holes, providing new insight into the connections between vertically oriented coherent structures and local scour, with the unique perspective of flow and morphology in a large river.
Directory of Open Access Journals (Sweden)
Ping Zhang
2014-01-01
Full Text Available The variational multiscale element free Galerkin method is extended to simulate the Stokes flow problems in a circular cavity as an irregular geometry. The method is combined with Hughes’s variational multiscale formulation and element free Galerkin method; thus it inherits the advantages of variational multiscale and meshless methods. Meanwhile, a simple technique is adopted to impose the essential boundary conditions which makes it easy to solve problems with complex area. Finally, two examples are solved and good results are obtained as compared with solutions of analytical and numerical methods, which demonstrates that the proposed method is an attractive approach for solving incompressible fluid flow problems in terms of accuracy and stability, even for complex irregular boundaries.
PARALLEL ALGORITHM FOR THREE-DIMENSIONAL STOKES FLOW SIMULATION USING BOUNDARY ELEMENT METHOD
Directory of Open Access Journals (Sweden)
D. G. Pribytok
2016-01-01
Full Text Available Parallel computing technique for modeling three-dimensional viscous flow (Stokes flow using direct boundary element method is presented. The problem is solved in three phases: sampling and construction of system of linear algebraic equations (SLAE, its decision and finding the velocity of liquid at predetermined points. For construction of the system and finding the velocity, the parallel algorithms using graphics CUDA cards programming technology have been developed and implemented. To solve the system of linear algebraic equations the implemented software libraries are used. A comparison of time consumption for three main algorithms on the example of calculation of viscous fluid motion in three-dimensional cavity is performed.
Exact Solutions for Stokes' Flow of a Non-Newtonian Nanofluid Model: A Lie Similarity Approach
Aziz, Taha; Aziz, A.; Khalique, C. M.
2016-07-01
The fully developed time-dependent flow of an incompressible, thermodynamically compatible non-Newtonian third-grade nanofluid is investigated. The classical Stokes model is considered in which the flow is generated due to the motion of the plate in its own plane with an impulsive velocity. The Lie symmetry approach is utilised to convert the governing nonlinear partial differential equation into different linear and nonlinear ordinary differential equations. The reduced ordinary differential equations are then solved by using the compatibility and generalised group method. Exact solutions for the model equation are deduced in the form of closed-form exponential functions which are not available in the literature before. In addition, we also derived the conservation laws associated with the governing model. Finally, the physical features of the pertinent parameters are discussed in detail through several graphs.
A comparison of two incompressible Navier-Stokes algorithms for unsteady internal flow
Wiltberger, N. Lyn; Rogers, Stuart E.; Kwak, Dochan
1993-01-01
A comparative study of two different incompressible Navier-Stokes algorithms for solving an unsteady, incompressible, internal flow problem is performed. The first algorithm uses an artificial compressibility method coupled with upwind differencing and a line relaxation scheme. The second algorithm uses a fractional step method with a staggered grid, finite volume approach. Unsteady, viscous, incompressible, internal flow through a channel with a constriction is computed using the first algorithm. A grid resolution study and parameter studies on the artificial compressibility coefficient and the maximum allowable residual of the continuity equation are performed. The periodicity of the solution is examined and several periodic data sets are generated using the first algorithm. These computational results are compared with previously published results computed using the second algorithm and experimental data.
Algebraic approach to non-integrability of Bajer-Moffattʼs steady Stokes flow
Nishiyama, Takahiro
2014-12-01
Non-integrability of the streamline system of equations for a steady Stokes flow, which Bajer and Moffatt introduced by the name of stretch-twist-fold flow, is discussed by an algebraic method without assuming its closeness to an integrable system. In the author's previous paper, the non-existence of a real meromorphic first integral of the streamline system was proved on the basis of Ziglin's theory and the differential Galois theory, where a parameter was assumed not to belong to a set of exceptional values. In this paper, this assumption is proved to be removable by making further use of some results from the differential Galois theory. The road to this result is explained in the form of a recipe in order to make clear how the differential Galois theory is applied.
Application of A Fast Multipole BIEM for Flow Diffraction from A 3D Body
Institute of Scientific and Technical Information of China (English)
滕斌; 宁德志
2004-01-01
A Fast Multipole Method (FMM) is developed as a numerical approach to the reduction of the computational cost and requirement memory capacity for a large in solving large-scale problems. In this paper it is applied to the boundary integral equation method (BIEM) for current diffraction from arbitrary 3D bodies. The boundary integral equation is discretized by higher order elements, the FMM is applied to avoid the matrix/vector product, and the resulting algebraic equation is solved by the Generalized Conjugate Residual method (GCR). Numerical examination shows that the FMM is more efficient than the direct evaluation method in computational cost and storage of computers.
Axisymmetric Granular Collapse: A Transient 3D Flow Test of Viscoplasticity
Lacaze, Laurent; Kerswell, Rich R.
2009-03-01
A viscoplastic continuum theory has recently been proposed to model dense, cohesionless granular flows [P. Jop , Nature (London)NATUAS0028-0836 441, 727 (2006)10.1038/nature04801]. We confront this theory for the first time with a transient, three-dimensional flow situation—the simple collapse of a cylinder of granular matter onto a horizontal plane—by extracting stress and strain rate tensors directly from soft particle simulations. These simulations faithfully reproduce the different flow regimes and capture the observed scaling laws for the final deposit. Remarkably, the theoretical hypothesis that there is a simple stress-strain rate tensorial relationship does seem to hold across the whole flow even close to the rough boundary provided the flow is dense enough. These encouraging results suggest viscoplastic theory is more generally applicable to transient, multidirectional, dense flows and open the way for quantitative predictions in real applications.
Science Letters: Research on 3D fiber orientation distribution in arbitrary planar flows
Institute of Scientific and Technical Information of China (English)
ZHOU Kun; LIN Jian-zhong
2007-01-01
A non-stretchable fiber rotation in planar flows has been solved. The fiber will rotate periodically or run to the asymptotical direction decided by a discriminant defined in the paper involving the fiber aspect ratio and the flow characteristics.Subsequently the fiber orientation distribution is derived directly without the bother of solving the Fokker-Planck equation. The research clearly indicates the overall configuration of a fiber rotation movement in planar flows.
Optic flow-based vision system for autonomous 3D localization and control of small aerial vehicles
Kendoul, Farid; Fantoni, Isabelle; Nonami, Kenzo
2009-01-01
International audience; The problem considered in this paper involves the design of a vision-based autopilot for small and micro Unmanned Aerial Vehicles (UAVs). The proposed autopilot is based on an optic flow-based vision system for autonomous localization and scene mapping, and a nonlinear control system for flight control and guidance. This paper focusses on the development of a real-time 3D vision algorithm for estimating optic flow, aircraft self-motion and depth map, using a low-resolu...
NUMERICAL SIMULATION OF 3-D TURBULENT FLOW IN THE MULTI- INTAKES SUMP OF THE PUMP STATION
Institute of Scientific and Technical Information of China (English)
CHEN Hong-xun; GUO Jia-hong
2007-01-01
In this article, a numerical model for three-dimensional turbulent flow in the sump of the pump station was presented. A reasonable boundary condition for the flow in the sump with several water intakes at different flow rates was proposed. The finite volume method was employed to solve the governing equations with the body fitted grid generated by the multi-block grid technique. By using the Fluent software, the fluid flow in a model sump of the pump station was calculated. Compared with the experimental result, the numerical result of the example is fairly good.
Water flow prediction for Membranes using 3D simulations with detailed morphology
Shi, Meixia
2015-04-01
The membrane morphology significantly influences membrane performance. For osmotically driven membrane processes, the morphology strongly affects the internal concentration polarization. Different membrane morphologies were generated by simulation and their influence on membrane performance was studied, using a 3D model. The simulation results were experimentally validated for two classical phase-inversion membrane morphologies: sponge- and finger-like structures. Membrane porosity and scanning electron microscopy image information were used as model input. The permeance results from the simulation fit well the experimentally measured permeances. Water permeances were predicted for different kinds of finger-like cavity membranes with different finger-like cavity lengths and various finger-like cavity sets, as well as for membranes with cylindrical cavities. The results provide realistic information on how to increase water permeance, and also illustrate that membrane’s complete morphology is important for the accurate water permeance evaluation. Evaluations only based on porosity might be misleading, and the new 3D simulation approach gives a more realistic representation.
Tomographic iterative reconstruction of a passive scalar in a 3D turbulent flow
Pisso, Ignacio; Kylling, Arve; Cassiani, Massimo; Solveig Dinger, Anne; Stebel, Kerstin; Schmidbauer, Norbert; Stohl, Andreas
2017-04-01
Turbulence in stable planetary boundary layers often encountered in high latitudes influences the exchange fluxes of heat, momentum, water vapor and greenhouse gases between the Earth's surface and the atmosphere. In climate and meteorological models, such effects of turbulence need to be parameterized, ultimately based on experimental data. A novel experimental approach is being developed within the COMTESSA project in order to study turbulence statistics at high resolution. Using controlled tracer releases, high-resolution camera images and estimates of the background radiation, different tomographic algorithms can be applied in order to obtain time series of 3D representations of the scalar dispersion. In this preliminary work, using synthetic data, we investigate different reconstruction algorithms with emphasis on algebraic methods. We study the dependence of the reconstruction quality on the discretization resolution and the geometry of the experimental device in both 2 and 3-D cases. We assess the computational aspects of the iterative algorithms focusing of the phenomenon of semi-convergence applying a variety of stopping rules. We discuss different strategies for error reduction and regularization of the ill-posed problem.
Energy Technology Data Exchange (ETDEWEB)
Sarkar, Avik; Milioli, Fernando E.; Ozarkar, Shailesh; Li, Tingwen; Sun, Xin; Sundaresan, Sankaran
2016-10-01
The accuracy of fluidized-bed CFD predictions using the two-fluid model can be improved significantly, even when using coarse grids, by replacing the microscopic kinetic-theory-based closures with coarse-grained constitutive models. These coarse-grained constitutive relationships, called filtered models, account for the unresolved gas-particle structures (clusters and bubbles) via sub-grid corrections. Following the previous 2-D approaches of Igci et al. [AIChE J., 54(6), 1431-1448, 2008] and Milioli et al. [AIChE J., 59(9), 3265-3275, 2013], new filtered models are constructed from highly-resolved 3-D simulations of gas-particle flows. Although qualitatively similar to the older 2-D models, the new 3-D relationships exhibit noticeable quantitative and functional differences. In particular, the filtered stresses are strongly dependent on the gas-particle slip velocity. Closures for the filtered inter-phase drag, gas- and solids-phase pressures and viscosities are reported. A new model for solids stress anisotropy is also presented. These new filtered 3-D constitutive relationships are better suited to practical coarse-grid 3-D simulations of large, commercial-scale devices.
LDA measurement of the passage flow field in a 3-D airfoil cascade
Stauter, R. C.; Fleeter, S.
1986-01-01
Three-dimensional internal flow computational models are currently being developed to predict the flow through turbomachinery blade rows. For these codes to be of quantitative value, they must be verified with data obtained in experiments which model the fundamental flow phenomena. In this paper, the complete three-dimensional flow field through a subsonic annular cascade of cambered airfoils is experimentally quantified. In particular, detailed three-dimensional data are obtained to quantify the inlet velocity profile, the cascade passage velocity field, and the exit region flow field. The primary instrumentation for acquiring these data is a single-channel Laser Doppler Anemometer operating in the backscatter mode, with chordwise distributions of airfoil surface static pressure taps also utilized. Appropriate data are correlated with predictions from the MERIDL/TSONIC codes.
Moscibrodzka, Monika; Shiokawa, Hotaka; Gammie, Charles F
2014-01-01
Radiatively inefficient accretion flows (RIAFs) are believed to power supermassive black holes (SMBH) in the underluminous cores of galaxies. Such black holes are typically accompanied by flat-spectrum radio cores indicating the presence of moderately relativistic jets. One of the best constrained RIAFs is associated with the SMBH in the Galactic center, Sgr A*. Since the plasma in RIAFs is only weakly collisional, the dynamics and the radiative properties of these systems are very uncertain. Here we want to study the impact of varying electron temperature on the appearance of accretion flows and jets. Using 3-D GRMHD accretion flow simulations, we use ray tracing methods to predict spectra and radio images of RIAFs allowing for different electron heating mechanisms in the in- and outflowing parts of the simulations. We find that small changes in the electron temperature can result in dramatic differences in the relative dominance of jets and accretion flows. Application to Sgr A* shows that radio spectrum an...
Vignon-Clementel, Irene; Jansen, K E; Taylor, C A; 10.1080/10255840903413565
2010-01-01
The simulation of blood flow and pressure in arteries requires outflow boundary conditions that incorporate models of downstream domains. We previously described a coupled multidomain method to couple analytical models of the downstream domains with 3D numerical models of the upstream vasculature. This prior work either included pure resistance boundary conditions or impedance boundary conditions based on assumed periodicity of the solution. However, flow and pressure in arteries are not necessarily periodic in time due to heart rate variability, respiration, complex transitional flow or acute physiological changes. We present herein an approach for prescribing lumped parameter outflow boundary conditions that accommodate transient phenomena. We have applied this method to compute haemodynamic quantities in different physiologically relevant cardiovascular models, including patient-specific examples, to study non-periodic flow phenomena often observed in normal subjects and in patients with acquired or congen...
Packing, alignment and flow of shape-anisotropic grains in a 3D silo experiment
Börzsönyi, Tamás; Somfai, Ellák; Szabó, Balázs; Wegner, Sandra; Mier, Pascal; Rose, Georg; Stannarius, Ralf
2016-09-01
Granular material flowing through bottlenecks, like the openings of silos, tend to clog and thus inhibit further flow. We study this phenomenon in a three-dimensional hopper for spherical and shape-anisotropic particles by means of x-ray tomography. The x-ray tomograms provide information on the bulk of the granular filling, and allows us to determine the particle positions and orientations inside the silo. In addition, it allows us to calculate local packing densities in different parts of the container. We find that in the flowing zone of the silo particles show a preferred orientation and thereby a higher order. Similarly to simple shear flows, the average orientation of the particles is not parallel to the streamlines but encloses a certain angle with it. In most parts of the hopper, the angular distribution of the particles did not reach the one corresponding to stationary shear flow, thus the average orientation angle in the hopper deviates more from the streamlines than in stationary shear flows. In the flowing parts of the silo, shear induced dilation is observed, which is more pronounced for elongated grains than for nearly spherical particles. The clogged state is characterized by a dome, i.e. the geometry of the layer of grains blocking the outflow. The shape of the dome depends on the particle shape.
One-way spatial integration of Navier-Stokes equations: stability of wall-bounded flows
Rigas, Georgios; Colonius, Tim; Towne, Aaron; Beyar, Michael
2016-11-01
For three-dimensional flows, questions of stability, receptivity, secondary flows, and coherent structures require the solution of large partial-derivative eigenvalue problems. Reduced-order approximations are thus required for engineering prediction since these problems are often computationally intractable or prohibitively expensive. For spatially slowly evolving flows, such as jets and boundary layers, a regularization of the equations of motion sometimes permits a fast spatial marching procedure that results in a huge reduction in computational cost. Recently, a novel one-way spatial marching algorithm has been developed by Towne & Colonius. The new method overcomes the principle flaw observed in Parabolized Stability Equations (PSE), namely the ad hoc regularization that removes upstream propagating modes. The one-way method correctly parabolizes the flow equations based on estimating, in a computationally efficient way, the local spectrum in each cross-stream plane and an efficient spectral filter eliminates modes with upstream group velocity. Results from the application of the method to wall-bounded flows will be presented and compared with predictions from the full linearized compressible Navier-Stokes equations and PSE.
Simulation of 3-D viscous flow within a multi-stage turbine
Adamczyk, John J.; Celestina, Mark L.; Beach, Tim A.; Barnett, Mark
1989-01-01
This work outlines a procedure for simulating the flow field within multistage turbomachinery which includes the effects of unsteadiness, compressibility, and viscosity. The associated modeling equations are the average passage equation system which governs the time-averaged flow field within a typical passage of a blade row embedded within a multistage configuration. The results from a simulation of a low aspect ratio stage and a one-half turbine will be presented and compared with experimental measurements. It will be shown that the secondary flow field generated by the rotor causes the aerodynamic performance of the downstream vane to be significantly different from that of an isolated blade row.
A Stable Parametric Finite Element Discretization of Two-Phase Navier--Stokes Flow
Barrett, John W; Nürnberg, Robert
2013-01-01
We present a parametric finite element approximation of two-phase flow. This free boundary problem is given by the Navier--Stokes equations in the two phases, which are coupled via jump conditions across the interface. Using a novel variational formulation for the interface evolution gives rise to a natural discretization of the mean curvature of the interface. The parametric finite element approximation of the evolving interface is then coupled to a standard finite element approximation of the two-phase Navier--Stokes equations in the bulk. Here enriching the pressure approximation space with the help of an XFEM function ensures good volume conservation properties for the two phase regions. In addition, the mesh quality of the parametric approximation of the interface in general does not deteriorate over time, and an equidistribution property can be shown for a semidiscrete continuous-in-time variant of our scheme in two space dimensions. Moreover, our finite element approximation can be shown to be uncondit...
Lattice Boltzmann method simulations of Stokes number effects on particle motion in a channel flow
Zhang, Lenan; Jebakumar, Anand Samuel; Abraham, John
2016-06-01
In a recent experimental study by Lau and Nathan ["Influence of Stokes number on the velocity and concentration distributions in particle-laden jets," J. Fluid Mech. 757, 432 (2014)], it was found that particles in a turbulent pipe flow tend to migrate preferentially toward the wall or the axis depending on their Stokes number (St). Particles with a higher St (>10) are concentrated near the axis while those with lower St (effects on particle trajectories in a wall-bounded flow," Comput. Fluids 124, 208 (2016)] have carried out simulations of a particle in a laminar channel flow to investigate this behavior. In their work, they report a similar behavior where particles with low St migrate toward the wall and oscillate about a mean position near the wall while those with high St oscillate about the channel center plane. They have explained this behavior in terms of the Saffman lift, Magnus lift, and wall repulsion forces acting on the particle. The present work extends the previous work done by Jebakumar et al. and aims to study the behavior of particles at intermediate St ranging from 10 to 20. It is in this range where the equilibrium position of the particle changes from near the wall to the axis and the particle starts oscillating about the axis. The Lattice Boltzmann method is employed to carry out this study. It is shown that the change in mean equilibrium position is related to increasing oscillations of the particle with mean position near the wall which results in the particle moving past the center plane to the opposite side. The responsible mechanisms are explained in detail.
Leprince, S.; Lin, J.; Ayoub, F.; Herman, F.; Avouac, J.
2013-12-01
We present the latest capabilities added to the Co-Registration of Optically Sensed Images and Correlation (COSI-Corr) software, which aim at analyzing time-series of stereoscopic imagery to document 3D variations of the ground surface. We review the processing chain and present the new and improved modules for satellite pushbroom imagery, in particular the N-image bundle block adjustment to jointly optimize the viewing geometry of multiple acquisitions, the improved multi-scale image matching based on Semi-Global Matching (SGM) to extract high resolution topography, and the triangulation of multi-temporal disparity maps to derive 3D ground motion. In particular, processes are optimized to run on a cluster computing environment. This new suite of algorithms is applied to the study of Worldview stereo imagery above the Franz Josef, Fox, and Tasman Glaciers, New Zealand, acquired on 01/30/2013, 02/09/2013, and 02/28/2013. We derive high resolution (1m post-spacing) maps of ice flow in three dimensions, where ice velocities of up to 4 m/day are recorded. Images were collected in early summer during a dry and sunny period, which followed two weeks of unsettled weather with several heavy rainfall events across the Southern Alps. The 3D tracking of ice flow highlights the surface response of the glaciers to changes in effective pressure at the ice-bedrock interface due to heavy rainfall, at an unprecedented spatial resolution.
Brown, Donald L.
2011-09-11
In this paper we establish corrector estimates for Stokes flow in slowly varying perforated media via two scale asymptotic analysis. Current methods and techniques are often not able to deal with changing geometries prevalent in applied problems. For example, in a deformable porous medium environment, the geometry does not remain periodic under mechanical deformation and if slow variation in the geometry occurs. For such problems, one cannot use classical homogenization results directly and new homogenization results and estimates are needed. Our work uses asymptotic techniques of Marusic-Paloka and Mikelic (Bollettino U. M. I 7:661-671, 1996) where the authors constructed a downscaled velocity which converges to the fine-scale velocity at a rate of ε1/6 where ε is the characteristic length scale. We assume a slowly varying porous medium and study homogenization and corrector estimates for the Stokes equations. Slowly varying media arise, e. g., in fluid-structure interaction (FSI) problems (Popov et al. in Iterative upscaling of flows in deformable porous media, 2008), carbonation of porous concrete (Peter in C. R. Mecanique 335:357-362, 2007a; C. R. Mecanique 335:679-684, 2007b), and various other multiphysics processes. To homogenize Stokes flows in such media we restate the cell problems of Marusic-Paloka and Mikelic (Bollettino U. M. I 7:661-671, 1996) in a moving RVE framework. Further, to recover the same convergence properties it is necessary to solve an additional cell problem and add one more corrector term to the downscaled velocity. We further extend the framework of Marusic-Paloka and Mikelic (Bollettino U. M. I 7:661-671, 1996) to three spatial dimensions in both periodic and variable pore-space cases. Next, we also propose an efficient algorithm for computing the correctors by solving a limited number of cell problems at selected spatial locations. We present two computational examples: one for a constructed medium of elliptical perforations, and
Liepsch, D; Pflugbeil, G; Matsuo, T; Lesniak, B
1998-04-01
Pulsatile flow, wall distensibility, non-Newtonian flow characteristics of blood in flow separation regions, and high/low blood pressure were studied in elastic silicon rubber models having a compliance similar to human vessels and the same surface structure as the biological intima models of (1) a healthy carotid artery model, (2) a 90% stenosis in the ICA, and (3) 80% stenosis in both the internal and external carotid arteries. Flow was visualized for steady flow and pulsatile studies to localize flow separation regions and reattachment points. Local velocity was measured with a 1-, 2-, or 3-D laser-Doppler-anemometer (LDA). Flow in the unstenosed model was Re = 250. In the stenosed models, the Re number decreased to Re = 180 and 213 under the same experimental conditions. High velocity fluctuations with vortices were found in the stenosed models. The jet flow in the stenosis increased up to 4 m/s. With an increasing bifurcation angle, the separation regions in the ECA and ICA increased. Increased flow (Re = 350) led to an increase in flow separation and high velocity shear gradients. The highest shear stresses were nearly 20 times higher than normal. The 90% stenosis created high velocity shear gradients and velocity fluctuations. Downstream of the stenoses, eddies were found over the whole cross-section. In the healthy model a slight flow separation region was observed in the ICA at the branching cross-section whereas in the stenosed models, the flow separation regions extended far into the ICA. We conclude that a detailed understanding of flow is necessary before vascular surgery is performed especially before artificial grafts or patches are implanted.
Using the UM dynamical cores to reproduce idealised 3D flows
Mayne, N J; Acreman, David M; Smith, Chris; Wood, Nigel; Amundsen, David Skålid; Thuburn, John; Jackson, David R
2013-01-01
We demonstrate that both the current (New Dynamics), and next generation (ENDGame) dynamical cores of the UK Met Office global circulation model, the UM, reproduce consistently, the long-term, large-scale flows found in several published idealised tests. The cases presented are the Held-Suarez test, a simplified model of Earth (including a stratosphere), and a hypothetical tidally locked Earth. Furthermore, we show that using simplifications to the dynamical equations, which are expected to be justified for the physical domains and flow regimes we have studied, and which are supported by the ENDGame dynamical core, also produces matching long-term, large-scale flows. Finally, we present evidence for differences in the detail of the planetary flows and circulations resulting from improvements in the ENDGame formulation over New Dynamics.
3D Simulations of a Pyroclastic Surge as an Example of a Compressible Suspension Flow
National Research Council Canada - National Science Library
ISHIMINE, Yasuhiro
2004-01-01
.... As a conspicuous example of such a flow, we present three-dimensional numerical simulations of a pyroclastic surge, which spreads laterally over the ground surface during some volcanic eruptions...
Numerical research on the 3D fiber orientation distribution in arbitrary planar flows
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The fiber orientation distribution in a fiber suspension flow was investigated by a finite difference scheme in spherical coordinates. The diffusivity was transformed between Cartesian and spherical coordinates through tensor analysis to obtain efficiency. It is found that under simple shear flow condition the diffusivity in the azimuthal direction, Dry, has greater effect on the orientation distribution than that in the colatitude direction, Drθθ.
Sea-surface temperature effects on 3D bora-like flow
Energy Technology Data Exchange (ETDEWEB)
Kraljevic, L. [Meteorological and Hydrological Service of Croatia, Zagreb (Croatia); Grisogono, B. [Dept. of Geophysics, Zagreb (Croatia)
2006-04-15
A COAMPS (TM) nonhydrostatic numerical model with a higher order turbulence closure scheme is used to study the effect of the sea-surface temperature (SST) on the idealized nonlinear flow over an idealized mountain in the presence of rotation. The low-level jet (LLJ) that develops at both flanks of the mountain is intensified by the Coriolis effect on the northern flank for a westerly flow. Shooting flow develops down the slope ending over the sea while resembling a hydraulic jump. This is considered as bora (bura) like flow. The front is related to the abrupt slowdown of the shooting flow through the hydraulic jump. Seven different idealized cases are addressed, the control run, nearly linear case with Fr = 1.2, and the cases with the SST 10 K colder, and 2.5 K, 5 K, 7.5 K and 10 K warmer than the control run. The maximum wind speeds in the shooting flow and the LLJs are around two times higher than the background wind speeds. The interplay of SST effects and the effects of the asymmetric lee-side vortices modify the location and the shape of the bora front which is found not to be parallel with the shoreline. The front is not stationary in time but exhibits vibrations which are more pronounced at the southern flank associated with the weaker LLJ. (orig.)
Secondary flow structure in a model curved artery: 3D morphology and circulation budget analysis
Bulusu, Kartik V.; Plesniak, Michael W.
2015-11-01
In this study, we examined the rate of change of circulation within control regions encompassing the large-scale vortical structures associated with secondary flows, i.e. deformed Dean-, Lyne- and Wall-type (D-L-W) vortices at planar cross-sections in a 180° curved artery model (curvature ratio, 1/7). Magnetic resonance velocimetry (MRV) and particle image velocimetry (PIV) experiments were performed independently, under the same physiological inflow conditions (Womersley number, 4.2) and using Newtonian blood-analog fluids. The MRV-technique performed at Stanford University produced phase-averaged, three-dimensional velocity fields. Secondary flow field comparisons of MRV-data to PIV-data at various cross-sectional planes and inflow phases were made. A wavelet-decomposition-based approach was implemented to characterize various secondary flow morphologies. We hypothesize that the persistence and decay of arterial secondary flow vortices is intrinsically related to the influence of the out-of-plane flow, tilting, in-plane convection and diffusion-related factors within the control regions. Evaluation of these factors will elucidate secondary flow structures in arterial hemodynamics. Supported by the National Science Foundation under Grant Number CBET-0828903, and GW Center for Biomimetics and Bioinspired Engineering (COBRE). The MRV data were acquired at Stanford University in collaboration with Christopher Elkins and John Eaton.
Using 3D CFD to reconcile different views of confluence flow structure
Lane, S. N.
2001-05-01
River channel confluences have seen considerable attention in recent years. The aim of this presentation is to demonstrate how CFD has been used to evaluate and expand some of the results that have emerged from field and laboratory studies. Central to this research has been the use of three-dimensional numerical modelling techniques that are able to represent key hydrodynamic processes in confluences (e.g. water surface super-elevation, topographic forcing of flow, shear-driven turbulence), and to provide predictions of important explanatory variables (e.g. dynamic pressure). The research design is based upon using numerical simulation to explore interactions between amongst governing variables (e.g. tributary momentum ratio, degree of asymmetry, junction angle, tributary bed discordance). On the basis of more than 50 simulations of 'laboratory-style' confluences and a smaller number of field cases, this paper identifies the key controls upon confluence flow structures, and the potential influence of these structures upon geomorphological processes within the confluence. This demonstrates: (i) how divergence of opinion over confluence flow processes has resulted from different methods of instrument rotation in the field; (ii) the importance of both streamline curvature and flow separation as controls upon flow structure development; and (iii) the periodic nature of the flow structures that are seen in confluence environments, and which may be misunderstood when a series of time-averaged measurements are made in the field.
Development of 3-D Flow Analysis Code for Fuel Assembly using Unstructured Grid System
Energy Technology Data Exchange (ETDEWEB)
Myong, Hyon Kook; Kim, Jong Eun; Ahn, Jong Ki; Yang, Seung Yong [Kookmin Univ., Seoul (Korea, Republic of)
2007-03-15
The flow through a nuclear rod bundle with mixing vanes are very complex and required a suitable turbulence model to be predicted accurately. Final objective of this study is to develop a CFD code for fluid flow and heat transfer analysis in a nuclear fuel assembly using unstructured grid system. In order to develop a CFD code for fluid flow and heat transfer analysis in a nuclear fuel assembly using unstructured grid system, the following researches are made: - Development of numerical algorithm for CFD code's solver - Grid and geometric connectivity data - Development of software(PowerCFD code) for fluid flow and heat transfer analysis in a nuclear fuel assembly using unstructured grid system - Modulation of software(PowerCFD code) - Development of turbulence model - Development of analysis module of RANS/LES hybrid models - Analysis of turbulent flow and heat transfer - Basic study on LES analysis - Development of main frame on pre/post processors based on GUI - Algorithm for fully-developed flow.
Investigation of seasonal thermal flow in a real dam reservoir using 3-D numerical modeling
Directory of Open Access Journals (Sweden)
Üneş Fatih
2015-03-01
Full Text Available Investigations indicate that correct estimation of seasonal thermal stratification in a dam reservoir is very important for the dam reservoir water quality modeling and water management problems. The main aim of this study is to develop a hydrodynamics model of an actual dam reservoir in three dimensions for simulating a real dam reservoir flows for different seasons. The model is developed using nonlinear and unsteady continuity, momentum, energy and k-ε turbulence model equations. In order to include the Coriolis force effect on the flow in a dam reservoir, Coriolis force parameter is also added the model equations. Those equations are constructed using actual dimensions, shape, boundary and initial conditions of the dam and reservoir. Temperature profiles and flow visualizations are used to evaluate flow conditions in the reservoir. Reservoir flow’s process and parameters are determined all over the reservoir. The mathematical model developed is capable of simulating the flow and thermal characteristics of the reservoir system for seasonal heat exchanges. Model simulations results obtained are compared with field measurements obtained from gauging stations for flows in different seasons. The results show a good agreement with the field measurements.
Bocanegra Evans, Humberto; Gorumlu, Serdar; Aksak, Burak; Castillo, Luciano; Sheng, Jian
2016-06-01
Understanding how fluid flow interacts with micro-textured surfaces is crucial for a broad range of key biological processes and engineering applications including particle dispersion, pathogenic infections, and drag manipulation by surface topology. We use high-speed digital holographic microscopy (DHM) in combination with a correlation based de-noising algorithm to overcome the optical interference generated by surface roughness and to capture a large number of 3D particle trajectories in a microfluidic channel with one surface patterned with micropillars. It allows us to obtain a 3D ensembled velocity field with an uncertainty of 0.06% and 2D wall shear stress distribution at the resolution of ~65 μPa. Contrary to laminar flow in most microfluidics, we find that the flow is three-dimensional and complex for the textured microchannel. While the micropillars affect the velocity flow field locally, their presence is felt globally in terms of wall shear stresses at the channel walls. These findings imply that micro-scale mixing and wall stress sensing/manipulation can be achieved through hydro-dynamically smooth but topologically rough micropillars.
Pedersen, John A; Lichter, Seth; Swartz, Melody A
2010-03-22
Interstitial flow is an important regulator of various cell behaviors both in vitro and in vivo, yet the forces that fluid flow imposes on cells embedded in a 3D extracellular matrix (ECM), and the effects of matrix architecture on those forces, are not well understood. Here, we demonstrate how fiber alignment can affect the shear and pressure forces on the cell and ECM. Using computational fluid dynamics simulations, we show that while the solutions of the Brinkman equation accurately estimate the average fluid shear stress and the drag forces on a cell within a 3D fibrous medium, the distribution of shear stress on the cellular surface as well as the peak shear stresses remain intimately related to the pericellular fiber architecture and cannot be estimated using bulk-averaged properties. We demonstrate that perpendicular fiber alignment of the ECM yields lower shear stress and pressure forces on the cells and higher stresses on the ECM, leading to decreased permeability, while parallel fiber alignment leads to higher stresses on cells and increased permeability, as compared to a cubic lattice arrangement. The Spielman-Goren permeability relationships for fibrous media agreed well with CFD simulations of flow with explicitly considered fibers. These results suggest that the experimentally observed active remodeling of ECM fibers by fibroblasts under interstitial flow to a perpendicular alignment could serve to decrease the shear and drag forces on the cell.
An axis-free overset grid in spherical polar coordinates for simulating 3D self-gravitating flows
Wongwathanarat, Annop; Müller, Ewald
2010-01-01
A type of overlapping grid in spherical coordinates called the Yin-Yang grid is successfully implemented into a 3D version of the explicit Eulerian grid-based code PROMETHEUS including self-gravity. The modified code successfully passed several standard hydrodynamic tests producing results which are in very good agreement with analytic solutions. Moreover, the solutions obtained with the Yin-Yang grid exhibit no peculiar behaviour at the boundary between the two grid patches. The code has also been successfully used to model astrophysically relevant situations, namely equilibrium polytropes, a Taylor-Sedov explosion, and Rayleigh-Taylor instabilities. According to our results, the usage of the Yin-Yang grid greatly enhances the suitability and efficiency of 3D explicit Eulerian codes based on spherical polar coordinates for astrophysical flows.
Reflux venous flow in dural sinus and internal jugular vein on 3D time-of-flight MR angiography
Energy Technology Data Exchange (ETDEWEB)
Jang, Jinhee; Kim, Bum-soo; Kim, Bom-yi; Choi, Hyun Seok; Jung, So-Lyung; Ahn, Kook-Jin; Byun, Jae Young [The Catholic University of Korea, Department of Radiology, Seoul St. Mary' s Hospital, School of Medicine, Seoul (Korea, Republic of)
2013-10-15
Reflux venous signal on the brain and neck time-of-flight magnetic resonance angiography (TOF MRA) is thought to be related to a compressed left brachiocephalic vein. This study is aimed to assess the prevalence of venous reflux flow in internal jugular vein (IJV), sigmoid sinus/transverse sinus (SS/TS), and inferior petrosal sinus (IPS) on the brain and neck TOF MRA and its pattern. From the radiology database, 3,475 patients (1,526 men, 1,949 women, age range 19-94, median age 62 years) with brain and neck standard 3D TOF MRA at 3 T and 1.5 T were identified. Rotational maximal intensity projection images of 3D TOF MRA were assessed for the presence of reflux flow in IJV, IPS, and SS/TS. Fifty-five patients (1.6 %) had reflux flow, all in the left side. It was more prevalent in females (n = 43/1,949, 2.2 %) than in males (n = 12/1,526, 0.8 %) (p = 0.001). The mean age of patients with reflux flow (66 years old) was older than those (60 years old) without reflux flow (p = 0.001). Three patients had arteriovenous shunt in the left arm for hemodialysis. Of the remaining 52 patients, reflux was seen on IJV in 35 patients (67.3 %). There were more patients with reflux flow seen on SS/TS (n = 34) than on IPS (n = 25). Venous reflux flow on TOF MRA is infrequently observed, and reflux pattern is variable. Because it is exclusively located in the left side, the reflux signal on TOF MRA could be an alarm for an undesirable candidate for a contrast injection on the left side for contrast-enhanced imaging study. (orig.)
Buoyancy effects on the 3D MHD stagnation-point flow of a Newtonian fluid
Borrelli, A.; Giantesio, G.; Patria, M. C.; Roşca, N. C.; Roşca, A. V.; Pop, I.
2017-02-01
This work examines the steady three-dimensional stagnation-point flow of an electrically conducting Newtonian fluid in the presence of a uniform external magnetic field H0 under the Oberbeck-Boussinesq approximation. We neglect the induced magnetic field and examine the three possible directions of H0 which coincide with the directions of the axes. In all cases it is shown that the governing nonlinear partial differential equations admit similarity solutions. We find that the flow has to satisfy an ordinary differential problem whose solution depends on the Hartmann number M, the buoyancy parameter λ and the Prandtl number Pr. The skin-friction components along the axes are computed and the stagnation-point is classified. The numerical integration shows the existence of dual solutions and the occurrence of the reverse flow for some values of the parameters.
Navier-Stokes-Fourier analytic solutions for non-isothermal Couette slip gas flow
Directory of Open Access Journals (Sweden)
Milićev Snežana S.
2016-01-01
Full Text Available The explicit and reliable analytical solutions for steady plane compressible non-isothermal Couette gas flow are presented. These solutions for velocity and temperature are developed by macroscopic approach from Navier-Stokes-Fourier system of continuum equations and the velocity slip and the temperature jump first order boundary conditions. Variability of the viscosity and thermal conductivity with temperature is involved in the model. The known result for the gas flow with constant and equal temperatures of the walls (isothermal walls is verified and a new solution for the case of different temperature of the walls is obtained. Evan though the solution for isothermal walls correspond to the gas flow of the Knudsen number Kn≤0.1, i.e. to the slip and continuum flow, it is shown that the gas velocity and related shear stress are also valid for the whole range of the Knudsen number. The deviation from numerical results for the same system is less than 1%. The reliability of the solution is confirmed by comparing with results of other authors which are obtained numerically by microscopic approach. The advantage of the presented solution compared to previous is in a very simple applicability along with high accuracy. [Projekat Ministarstva nauke Republike Srbije, br. 35046 i 174014
Heat or mass transfer from a sphere in Stokes flow at low Péclet number
Bell, Christopher G.
2013-04-01
We consider the low Péclet number, Pe≪1, asymptotic solution for steady-state heat or mass transfer from a sphere immersed in Stokes flow with a Robin boundary condition on its surface, representing Newton cooling or a first-order chemical reaction. The application of Van Dyke\\'s rule up to terms of O(Pe3) shows that the O(Pe3logPe) terms in the expression for the average Nusselt/Sherwood number are twice those previously derived in the literature. Inclusion of the O(Pe3) terms is shown to increase the range of validity of the expansion. © 2012 Elsevier Ltd. All rights reserved.
Unsteady rotating laminar flow: analytical solution of relevant Navier-Stokes equations
Bocci, Alessio; Ritelli, Daniele
2016-01-01
We provide a integration of Navier-Stokes equations concerning the unsteady-state laminar flow of an incompressible, isothermal (newtonian) fluid in a cylindrical vessel spinning about its symmetry axis, say $z$, and inside which the liquid velocity starts with a non-zero axial component as well. Basic physical assumptions are that the pressure axial gradient keeps itself on its hydrostatic value and that no radial velocity exists. In such a way the PDEs become uncoupled and can be faced separately from each other. We succeed in computing both the unsteady velocities, i.e. the axial $v_z$ and the circumferential $v_\\theta$ as well, by means of infinite series expansions of Fourier-Bessel type under time exponential damping. Following this, we also find the unsteady surfaces of dynamical equilibrium, the wall shear stress and the Stokesian streamlines
An exact solution for Stokes flow in a channel with arbitrarily large wall permeability
Herschlag, Gregory J; Layton, Anita T
2014-01-01
We derive an exact solution for Stokes flow in an in a channel with permeable walls. We assume that at the channel walls, the normal component of the fluid velocity is described by Darcy's law and the tangential component of the fluid velocity is described by the no slip condition. The pressure exterior to the channel is assumed to be constant. Although this problem has been well studied, typical studies assume that the permeability of the wall is small relative to other non-dimensional parameters; this work relaxes this assumption and explores a regime in parameter space that has not yet been well studied. A consequence of this relaxation is that transverse velocity is no longer necessarily small when compared with the axial velocity. We use our result to explore how existing asymptotic theories break down in the limit of large permeability.
Modelling 3D Steam Turbine Flow Using Thermodynamic Properties of Steam Iapws-95
Directory of Open Access Journals (Sweden)
Rusanow A.V.
2016-01-01
Full Text Available An approach to approximate equations of state for water and steam (IAPWS-95 for the calculation of three-dimensional flows of steam in turbomachinery in a range of operation of the present and future steam turbines is described. Test calculations of three-dimensional viscous flow in an LP steam turbine using various equations of state (perfect gas, Van der Waals equation, equation of state for water and steam IAPWS-95 are made. The comparison of numerical results with experimental data is also presented.
3D numerical simulation of gaseous flows structure in semidetached binaries
Bisikalo, D V; Chechetkin, V M; Kuznetsov, O A; Molteni, D
1998-01-01
The results of 3D hydrodynamic simulation of mass transfer in semidetached binaries of different types (cataclysmic variables and low-mass X-ray binaries) are presented. We find that taking into account of a circumbinary envelope leads to significant changes in the stream-disc morphology. In particular, the obtained steady-state self-consistent solutions show an absence of impact between gas stream from the inner Lagrangian point L1 and forming accretion disc. The stream deviates under the action of gas of circumbinary envelope, and does not cause the shock perturbation of the disc boundary (traditional `hotspot'). At the same time, the gas of circumbinary envelope interacts with the stream and causes the formation of an extended shock wave, located on the stream edge. We discuss the implication of this model without `hotspot' (but with a shock wave located outside the disc) for interpretation of observations. The comparison of synthetic light curves with observations proves the validity of the discussed hydr...
MOTION AND DEFORMATION OF VISCOUS DROP IN STOKES FLOW NEAR RIGID WALL
Institute of Scientific and Technical Information of China (English)
LU Hua-jian; ZHANG Hui-sheng
2005-01-01
A boundary integral method was developed for simulating the motion and deformation of a viscous drop in an axisymmetric ambient Stokes flow near a rigid wall and for direct calculating the stress on the wall. Numerical experiments by the method were performed for different initial stand-off distances of the drop to the wall, viscosity ratios, combined surface tension and buoyancy parameters and ambient flow parameters. Numerical results show that due to the action of ambient flow and buoyancy the drop is compressed and stretched respectively in axial and radial directions when time goes. When the ambient flow action is weaker than that of the buoyancy the drop raises and bends upward and the stress on the wall induced by drop motion decreases when time advances. When the ambient flow action is stronger than that of the buoyancy the drop descends and becomes flatter and flatter as time goes. In this case when the initial stand-off distance is large the stress on the wall increases as the drop evolutes but when the stand-off distance is small the stress on the wall decreases as a result of combined effects of ambient flow, buoyancy and the stronger wall action to the flow. The action of the stress on the wall induced by drop motion is restricted in an area near the symmetric axis, which increases when the initial stand-off distance increases.When the initial stand-off distance increases the stress induced by drop motion decreases substantially. The surface tension effects resist the deformation and smooth the profile of the drop surfaces. The drop viscosity will reduce the deformation and migration of the drop.
Wall shear stress characterization of a 3D bluff-body separated flow
Fourrié, Grégoire; Keirsbulck, Laurent; Labraga, Larbi
2013-10-01
Efficient flow control strategies aimed at reducing the aerodynamic drag of road vehicles require a detailed knowledge of the reference flow. In this work, the flow around the rear slanted window of a generic car model was experimentally studied through wall shear stress measurements using an electrochemical method. The mean and fluctuating wall shear stress within the wall impact regions of the recirculation bubble and the main longitudinal vortex structures which develop above the rear window are presented. Correlations allow a more detailed characterization of the recirculation phenomenon within the separation bubble. In the model symmetry plane the recirculation structure compares well with simpler 2D configurations; specific lengths, flapping motion and shedding of large-scale vortices are observed, these similarities diminish when leaving the middle plane due to the strong three-dimensionality of the flow. A specific attention is paid to the convection processes occurring within the recirculation: a downstream convection velocity is observed, in accordance with 2D recirculations from the literature, and an upstream convection is highlighted along the entire bubble length which has not been underlined in some previous canonical configurations.
Rosenauer, M.; Buchegger, W.; Finoulst, I.; Verhaert, P.D.E.M.; Vellekoop, M.
2010-01-01
In this study, the design, realization and measurement results of a novel optofluidic system capable of performing absorbance-based flow cytometric analysis is presented. This miniaturized laboratory platform, fabricated using SU-8 on a silicon substrate, comprises integrated polymer-based waveguide
3D flow organization and dynamics in subsonic jets: Aeroacoustic source analysis by tomographic PIV
Violato, D.V.
2013-01-01
To meet the increasingly stringent noise regulation, aircraft manufacturers are searching for solutions to jet noise. This, which constitutes a significant amount of the total noise emitted by civil aircrafts, is generated by the mixing processes between the exhaust flow leaving the engine and the a
Investigation on 3D t wake flow structures of swimming bionic fish
Shen, G.-X.; Tan, G.-K.; Lai, G.-J.
2012-10-01
A bionic experimental platform was designed for the purpose of investigating time accurate three-dimensional flow field, using digital particle image velocimetry (DSPIV). The wake behind the flapping trail of a robotic fish model was studied at high spatial resolution. The study was performed in a water channel. A robot fish model was designed and built. The model was fixed onto a rigid support framework using a cable-supporting method, with twelve stretched wires. The entire tail of the model can perform prescribed motions in two degrees of freedom, mainly in carangiform mode, by driving its afterbody and lunate caudal fin respectively. The DSPIV system was set up to operate in a translational manner, measuring velocity field in a series of parallel slices. Phase locked measurements were repeated for a number of runs, allowing reconstruction of phase average flow field. Vortex structures with phase history of the wake were obtained. The study reveals some new and complex three-dimensional flow structures in the wake of the fish, including "reverse hairpin vortex" and "reverse Karman S-H vortex rings", allowing insight into physics of this complex flow.
Computer Tomography 3-D Imaging of the Metal Deformation Flow Path in Friction Stir Welding
Schneider, Judy; Beshears, Ronald; Nunes, Arthur C., Jr.
2004-01-01
In friction stir welding, a rotating threaded pin tool is inserted into a weld seam and literally stirs the edges of the seam together. This solid-state technique has been successfully used in the joining of materials that are difficult to fusion weld such as aluminum alloys. To determine optimal processing parameters for producing a defect free weld, a better understanding of the resulting metal deformation flow path is required. Marker studies are the principal method of studying the metal deformation flow path around the FSW pin tool. In our study, we have used computed tomography (CT) scans to reveal the flow pattern of a lead wire embedded in a FSW weld seam. At the welding temperature of aluminum, the lead becomes molten and thus tracks the aluminum deformation flow paths in a unique 3-dimensional manner. CT scanning is a convenient and comprehensive way of collecting and displaying tracer data. It marks an advance over previous more tedious and ambiguous radiographic/metallographic data collection methods.
3D time-dependent flow computations using a molecular stress function model with constraint release
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz
2002-01-01
The numerical simulation of time dependent viscoelastic flow (in three dimensions) is of interest in connection with a variety of polymer processing operations. The application of the numerical simulation techniques is in the analysis and design of polymer processing problems. This is operations,...
Sommer, Kelsey; Izzo, Rick L.; Shepard, Lauren; Podgorsak, Alexander R.; Rudin, Stephen; Siddiqui, Adnan H.; Wilson, Michael F.; Angel, Erin; Said, Zaid; Springer, Michael; Ionita, Ciprian N.
2017-03-01
3D printing has been used to create complex arterial phantoms to advance device testing and physiological condition evaluation. Stereolithographic (STL) files of patient-specific cardiovascular anatomy are acquired to build cardiac vasculature through advanced mesh-manipulation techniques. Management of distal branches in the arterial tree is important to make such phantoms practicable. We investigated methods to manage the distal arterial flow resistance and pressure thus creating physiologically and geometrically accurate phantoms that can be used for simulations of image-guided interventional procedures with new devices. Patient specific CT data were imported into a Vital Imaging workstation, segmented, and exported as STL files. Using a mesh-manipulation program (Meshmixer) we created flow models of the coronary tree. Distal arteries were connected to a compliance chamber. The phantom was then printed using a Stratasys Connex3 multimaterial printer: the vessel in TangoPlus and the fluid flow simulation chamber in Vero. The model was connected to a programmable pump and pressure sensors measured flow characteristics through the phantoms. Physiological flow simulations for patient-specific vasculature were done for six cardiac models (three different vasculatures comparing two new designs). For the coronary phantom we obtained physiologically relevant waves which oscillated between 80 and 120 mmHg and a flow rate of 125 ml/min, within the literature reported values. The pressure wave was similar with those acquired in human patients. Thus we demonstrated that 3D printed phantoms can be used not only to reproduce the correct patient anatomy for device testing in image-guided interventions, but also for physiological simulations. This has great potential to advance treatment assessment and diagnosis.
Institute of Scientific and Technical Information of China (English)
Naoto Miyama; Kazuaki Inaba; Makoto Yamamoto
2008-01-01
In these years, a lot of environmental problems such as air pollution and exhaustion of fossil fuels have been discussed intensively. In our laboratory, a hydrogen-fueled propulsion system has been researched as an alternative to conventional systems. A hydrogen-fueled propulsion system is expected to have higher power, lighter weight and lower emissions. However, for the practical use, there exist many problems that must be overcome. Considering these backgrounds, jet engines with hydrogen-fueled combustion within a turbine blade passage have been studied. Although some studies have been made on injecting and burning hydrogen fuel from a stator surface, little is known about the interaction between a tip leakage vortex near the suction side of a rotor tip and hydrogen-fueled combustion.The purpose of this study is to clarify the influence of the tip leakage vortex on the characteristics of the 3-dimensional flow field with hydrogen-fueled combustion within a turbine blade passage. Reynolds-averaged compressible Navier-Stokes equations are solved with incorporating a k-ε turbulence and a reduced chemical mechanism models. Using the computational results, the 3-dimensional turbulent flow field with chemical reactions is numerically visualized, and the three-dimensional turbulent flow fields with hydrogen combustion and the structure of the tip leakage vortex are investigated.
Prediction and analysis of 3D hydrofoil and propeller under potential flow using panel method
Directory of Open Access Journals (Sweden)
Chen Chen-Wei
2016-01-01
Full Text Available Potential flow over an airfoil plays an important historical role in the theory of airfoil. The governing equation for potential flow is Laplace’s equation. One of Green’s identities can be used to write a solution to Laplace’s equation as a boundary integral. Using distributions of singularity solutions and determining their strength via the boundary conditions is the essence of panel method. This paper introduces a quick prediction method of three-dimensional hydrofoil and propeller performance based on panel method. The surface of hydrofoil and propeller is divided into numbers of quadrilateral panels. Combined sources with doublets singularities will be distributed on the corners of panels. Calculated blade pressure distributions of hydrofoil and propeller agree well with experimental data. Several sample calculations have been included using panel method.
Reconstructing 3D Tree Models Using Motion Capture and Particle Flow
Directory of Open Access Journals (Sweden)
Jie Long
2013-01-01
Full Text Available Recovering tree shape from motion capture data is a first step toward efficient and accurate animation of trees in wind using motion capture data. Existing algorithms for generating models of tree branching structures for image synthesis in computer graphics are not adapted to the unique data set provided by motion capture. We present a method for tree shape reconstruction using particle flow on input data obtained from a passive optical motion capture system. Initial branch tip positions are estimated from averaged and smoothed motion capture data. Branch tips, as particles, are also generated within a bounding space defined by a stack of bounding boxes or a convex hull. The particle flow, starting at branch tips within the bounding volume under forces, creates tree branches. The forces are composed of gravity, internal force, and external force. The resulting shapes are realistic and similar to the original tree crown shape. Several tunable parameters provide control over branch shape and arrangement.
Time-resolved fuel injector flow characterisation based on 3D laser Doppler vibrometry
Crua, Cyril
2015-01-01
In order to enable investigations of the fuel flow inside unmodified injectors, we have developed a new experimental approach to measure time-resolved vibration spectra of diesel nozzles using a three dimensional laser vibrometer. The technique we propose is based on the triangulation of the vibrometer and fuel pressure transducer signals, and enables the quantitative characterisation of quasi-cyclic internal flows without requiring modifications to the injector, the working fluid, or limiting the fuel injection pressure. The vibrometer, which uses the Doppler effect to measure the velocity of a vibrating object, was used to scan injector nozzle tips during the injection event. The data were processed using a discrete Fourier transform to provide time-resolved spectra for valve-closed-orifice, minisac and microsac nozzle geometries, and injection pressures ranging from 60 to 160MPa, hence offering unprecedented insight into cyclic cavitation and internal mechanical dynamic processes. A peak was consistently f...
2009-08-14
involving particle simu- lation of fluid flows at the mesoscale. The Smooth Dissipative Particle Dynamics (SDPD) method developed by Espanol and...coefficients in the SDPD model equations are given in Espanol and Revenga (2003), 30 2.1 SDPD Computational Implementation The SDPD model has been...pp. 786-793. 10 Espanol , P. and Revenga, M. Smoothed Dissipative Particle Dynamics. Physical Review, 2003, Vol. 67. 31 Liu G.R. and Liu, M.B
Numerical analysis of 3-D unsteady flow in a vaneless counter-rotating turbine
Institute of Scientific and Technical Information of China (English)
ZHAO Qingjun; WANG Huishe; ZHAO Xiaolu; XU Jianzhong
2007-01-01
To reveal the unsteady flow characteristics of a vaneless counter-rotating turbine (VCRT),a threedimensional,viscous,unsteady computational fluid dynamics (CFD) analysis was performed.The results show that unsteady simulation is superior to steady simulation because more flow characteristics can be obtained.The unsteady effects in upstream airfoil rows are weaker than those in downstream airfoil rows in the VCRT.The static pressure distribution along the span in the pressure surface of a high pressure turbine stator is more uniform than that in the suction surface.The static pressure distributions along the span in the pressure surfaces and the suction surfaces of a high pressure turbine rotor and a low pressure turbine rotor are all uneven.The numerical results also indicate that the load of a high pressure turbine rotor will increase with the increase of the span.The deviation is very big between the direction of air flow at the outlet of a high pressure turbine rotor and the axial direction.A similar result can also be obtained in the outlet of a low pressure turbine rotor.This means that the specific work of a high pressure turbine rotor and a low pressure turbine rotor is big enough to reach the design objectives.
Single-Camera Stereoscopy Setup to Visualize 3D Dusty Plasma Flows
Romero-Talamas, C. A.; Lemma, T.; Bates, E. M.; Birmingham, W. J.; Rivera, W. F.
2016-10-01
A setup to visualize and track individual particles in multi-layered dusty plasma flows is presented. The setup consists of a single camera with variable frame rate, and a pair of adjustable mirrors that project the same field of view from two different angles to the camera, allowing for three-dimensional tracking of particles. Flows are generated by inclining the plane in which the dust is levitated using a specially designed setup that allows for external motion control without compromising vacuum. Dust illumination is achieved with an optics arrangement that includes a Powell lens that creates a laser fan with adjustable thickness and with approximately constant intensity everywhere. Both the illumination and the stereoscopy setup allow for the camera to be placed at right angles with respect to the levitation plane, in preparation for magnetized dusty plasma experiments in which there will be no direct optical access to the levitation plane. Image data and analysis of unmagnetized dusty plasma flows acquired with this setup are presented.
3D flow study in a mildly stenotic coronary artery phantom using a whole volume PIV method.
Brunette, J; Mongrain, R; Laurier, J; Galaz, R; Tardif, J C
2008-11-01
Blood flow dynamics has an important role in atherosclerosis initiation, progression, plaque rupture and thrombosis eventually causing myocardial infarction. In particular, shear stress is involved in platelet activation, endothelium function and secondary flows have been proposed as possible variables in plaque erosion. In order to investigate these three-dimensional flow characteristics in the context of a mild stenotic coronary artery, a whole volume PIV method has been developed and applied to a scaled-up transparent phantom. Experimental three-dimensional velocity data was processed to estimate the 3D shear stress distributions and secondary flows within the flow volume. The results show that shear stress reaches values out of the normal and atheroprotective range at an early stage of the obstructive pathology and that important secondary flows are also initiated at an early stage of the disease. The results also support the concept of a vena contracta associated with the jet in the context of a coronary artery stenosis with the consequence of higher shear stresses in the post-stenotic region in the blood domain than at the vascular wall.
Hou, Hui-Hsiung; Tsai, Chien-Hsiung; Fu, Lung-Ming; Yang, Ruey-Jen
2009-07-01
This study presents a novel 3-D hydrodynamic focusing technique for micro-flow cytometers. In the proposed approach, the sample stream is compressed initially in the horizontal direction by a set of sheath flows such that it is constrained to the central region of the microchannel and is then focused in the vertical direction by a second pair of sheath flows. Thereafter, the focused sample stream passes over a micro-weir structure positioned directly beneath an optical detection system to capture polystyrene beads fluorescent signal. The microchannel configuration and operational parameters are optimized by performing a series of numerical simulations. An experimental investigation is then performed using a micro-flow cytometer fabricated using conventional micro-electro-mechanical systems techniques and an isotropic wet etching method. The results indicate that the two sets of sheath flows successfully constrain the sample stream within a narrow, well-defined region of the microchannel. Furthermore, the micro-weir structure prompts the separation of a mixed sample of 5 and 10 microm polystyrene beads in the vertical direction and ensures that the beads flow through the detection region of the microchannel in a sequential fashion and can therefore be reliably detected and counted.
Directory of Open Access Journals (Sweden)
Rui Wu
2011-09-01
Full Text Available In order to achieve high efficiency and low cost cathode designing, improve stability of process in NC precision electrochemical machining of integer impeller, a method of applying Computational Fluid Dynamics (CFD to aid designing flow field structure of cathode and parameters for NC-ECM has been proposed in this study. The designing of flow field is the key point in cathode design and a suitable flow field design guarantees the process stability in electrochemical machining. A numerical model of the three-dimension flow field was built according to the geometrical model of interelectrode gap and cathode outline. Then the numerical simulation of 3-D flow field was performed by using the standard k-, turbulence model when the turbulence state in electrochemical machining had been determined. The effect of cathode’s structure and initial electrolyte pressure on the electrolyte flow field was analyzed according to the results of numerical simulation. A series of results similar to the actual experimental results are obtained. The method deduced in this paper could be used to achieve high efficiency and low cost cathode design, select of initial electrolyte pressure, and consequently a lot of “trial and error” cycles will be deduced.
Institute of Scientific and Technical Information of China (English)
WANG Liang; FU Song
2009-01-01
Based on Reynolds-averaged Navier-Stokes approach, a laminar-turbulence transition model is proposed in this study that takes into account the effects of different instability modes associated with the variations in Mach numbers of compressible boundary layer flows. The model is based on k-ω-γ three-equation eddy-viscosity concept with k representing the fluctuating kinetic energy, ωthe specific dissipation rate and the intermittency factor γ.The particular features of the model are that: 1) k includes the non-turbulent, as well as turbulent fluctuations; 2) a transport equation for the intermittency factor γis proposed here with a source term set to trigger the transition onset; 3) through the introduction of a new length scale normal to wall, the present model employs the local variables only avoiding the use of the integral parameters, like the boundary layer thickness δ,which are often cost-ineffective with the modern CFD (Computational Fluid Dynamics) methods; 4) in the fully turbulent region, the model retreats to the well-known k-ωSST (Shear Stress Transport) model. This model is validated with a number of available experiments on boundary layer transitions including the incompressible, supersonic and hypersonic flows past flat plates, straight/flared cones at zero incidences, etc. It is demonstrated that the present model can be successfully applied to the engineering calculations of a variety of aerodynamic flow transition.
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Based on Reynolds-averaged Navier-Stokes approach,a laminar-turbulence transition model is proposed in this study that takes into account the effects of different instability modes associated with the variations in Mach numbers of compressible boundary layer flows.The model is based on k-ω-γ three-equation eddy-viscosity concept with k representing the fluctuating kinetic energy,ωthe specific dissipation rate and the intermittency factorγ.The particular features of the model are that:1)k includes the non-turbulent,as well as turbulent fluctuations;2)a transport equation for the intermittency factorγis proposed here with a source term set to trigger the transition onset;3)through the introduction of a new length scale normal to wall,the present model employs the local variables only avoiding the use of the integral parameters,like the boundary layer thicknessδ,which are often cost-ineffective with the modern CFD(Computational Fluid Dynamics)methods;4)in the fully turbulent region,the model retreats to the well-known k-ωSST(Shear Stress Transport)model.This model is validated with a number of available experiments on boundary layer transitions including the incompressible,supersonic and hypersonic flows past flat plates,straight/flared cones at zero incidences,etc.It is demonstrated that the present model can be successfully applied to the engineering calculations of a variety of aerodynamic flow transition.
DEFF Research Database (Denmark)
Yang, Yang; Kær, Søren Knudsen
2012-01-01
The flow structure of one isothermal swirling case in the Sydney swirl flame database was studied using two numerical methods. Results from the Reynolds-averaged Navier-Stokes (RANS) approach and large eddy simulation (LES) were compared with experimental measurements. The simulations were applied...
PIV measurements in a microfluidic 3D-sheathing structure with three-dimensional flow behaviour
DEFF Research Database (Denmark)
Klank, Henning; Goranovic, Goran; Kutter, Jörg Peter
2002-01-01
The design and production time for complex microfluidic systems is considerable, often up to several months. It is therefore important to be able to understand and predict the flow phenomena prior to design and fabrication of the microdevice in order to save costly fabrication resources. The stru......, a stereoscopic principle was applied to obtain all three velocity components, showing the feasibility of obtaining full volume mapping (x, y, z, U, V, W) from micro-PIV measurements. The results are compared with computational fluid dynamics (CFD) simulations....
2011-01-01
equipped backpack and with an echosounder-equipped electric kayak . The meandering reach (Figure 2) is a deep (~10m) channel with flows around 0.5m/s...Kootenai River, ID on 12-16 August 2010. The study reach contained a number of natural channel features, such as a pool-riffle sequence and bank...irregularities, which influence transverse mixing. The dye was released at a constant rate for one hour from a kayak fixed in the center of the channel
3-D modelling the electric field due to ocean tidal flow and comparison with observations
DEFF Research Database (Denmark)
Kuvshinov, A.; Junge, A.; Utada, H.
2006-01-01
of the global distribution of the electric signal due to tidal ocean flow. We simulate the electric signals for two tidal constituents - lunar semidiurnal (M2) and diurnal (O1) tides. We assume a realistic Earth's conductivity model with a surface thin shell and 1-D mantle underneath. Simulations demonstrate......The tidal motion of the ocean water through the ambient magnetic field, generates secondary electric field. This motionally induced electric field can be detected in the sea or inland and has a potential for electrical soundings of the Earth. A first goal of the paper is to gain an understanding...
Farrell, C.; Adamczyk, J.
1981-01-01
The three-dimensional flow in a turbomachinery blade row was approximated by correcting for streamtube convergence and radius change in the throughflow direction. The method is a fully conservative solution of the full potential equation incorporating the finite volume technique on body fitted periodic mesh, with an artificial density imposed in the transonic region to insure stability and the capture of shock waves. Comparison of results for several supercritical blades shows good agreement with their hodograph solutions. Other calculations for these profiles as well as standard NACA blade sections indicate that this is a useful scheme analyzing both the design and off-design performance of turbomachinery blading.
Simplified 3d CFD flow simulation of a turbojet disc cavity with conjugate heat transfer
CSIR Research Space (South Africa)
Snedden, Glen C
2003-09-01
Full Text Available of the first disc (refer to Figure 1). This assumption is well founded as the seal has close tolerances and consists of two serial sections of seal. The second assumption is that there is no flow through the top of the seal under the nozzle guide vane (NGV... size limitations imposed by hardware constraints circa 1999. 4 All wall boundaries are default, as Star-CD automatically assigns spin parameters to walls in spinning ‘zones’ and stationary walls in zones without spin velocities. Furthermore...
Armandine Les Landes, Antoine; Guillon, Théophile; Peter-Borie, Mariane; Rachez, Xavier
2017-04-01
(DFN) and 3D elements to simulate groundwater flow in the 3D regional fault network and in sedimentary deposits, respectively. Firstly, the geometry of the 3D fracture network and its hydraulic connections with 3D elements (sedimentary cover) is built in accordance with the tectonic history and based on geological and geophysical evidences. Secondly, data from previous studies and site-specific geological knowledge provide information on the fault zones family sets and on respective hydraulic properties. Then, from the simulated 3D groundwater flow model and based on a particle tracking methodology, groundwater flow paths are constructed. The regional groundwater flow paths results are extracted and analysed to delineate preferential zones to explore at finer scale and so to define the potential positions of the exploration wells. This work is conducted in the framework of the IMAGE project (Integrated Methods for Advanced Geothermal Exploration, grant agreement No. 608553), which aims to develop new methods for better siting of exploitation wells.
Time resolved PIV and flow visualization of 3D sheet cavitation
Energy Technology Data Exchange (ETDEWEB)
Foeth, E.J.; Doorne, C.W.H. van; Terwisga, T. van [Delft University of Technology, Laboratory of Ship Hydromechanics, Delft (Netherlands); Wieneke, B. [LaVision GmbH, Goettingen (Germany)
2006-04-15
Time-resolved PIV was applied to study fully developed sheet cavitation on a hydrofoil with a spanwise varying angle of attack. The hydrofoil was designed to have a three-dimensional cavitation pattern closely related to propeller cavitation, studied for its adverse effects as vibration, noise, and erosion production. For the PIV measurements, fluorescent tracer particles were applied in combination with an optical filter, in order to remove the reflections of the laser lightsheet by the cavitation. An adaptive mask was developed to find the interface between the vapor and liquid phase. The velocity at the interface of the cavity was found to be very close to the velocity predicted by a simple streamline model. For a visualization of the global flow dynamics, the laser beam was expanded and used to illuminate the entire hydrofoil and cavitation structure. The time-resolved recordings reveal the growth of the attached cavity and the cloud shedding. Our investigation proves the viability of accurate PIV measurements around developed sheet cavitation. The presented results will further be made available as a benchmark for the validation of numerical simulations of this complicated flow. (orig.)
3D Acoustic Modelling of Dissipative Silencers with Nonhomogeneous Properties and Mean Flow
Directory of Open Access Journals (Sweden)
E. M. Sánchez-Orgaz
2014-07-01
Full Text Available A finite element approach is proposed for the acoustic analysis of automotive silencers including a perforated duct with uniform axial mean flow and an outer chamber with heterogeneous absorbent material. This material can be characterized by means of its equivalent acoustic properties, considered coordinate-dependent via the introduction of a heterogeneous bulk density, and the corresponding material airflow resistivity variations. An approach has been implemented to solve the pressure wave equation for a nonmoving heterogeneous medium, associated with the problem of sound propagation in the outer chamber. On the other hand, the governing equation in the central duct has been solved in terms of the acoustic velocity potential considering the presence of a moving medium. The coupling between both regions and the corresponding acoustic fields has been carried out by means of a perforated duct and its acoustic impedance, adapted here to include absorbent material heterogeneities and mean flow effects simultaneously. It has been found that bulk density heterogeneities have a considerable influence on the silencer transmission loss.
Zeinali, Soheila; Çetin, Barbaros; Oliaei, Samad Nadimi Bavil; Karpat, Yiğit
2015-07-01
Microfluidics is the combination of micro/nano fabrication techniques with fluid flow at microscale to pursue powerful techniques in controlling and manipulating chemical and biological processes. Sorting and separation of bio-particles are highly considered in diagnostics and biological analyses. Dielectrophoresis (DEP) has offered unique advantages for microfluidic devices. In DEP devices, asymmetric pair of planar electrodes could be employed to generate non-uniform electric fields. In DEP applications, facing 3D sidewall electrodes is considered to be one of the key solutions to increase device throughput due to the generated homogeneous electric fields along the height of microchannels. Despite the advantages, fabrication of 3D vertical electrodes requires a considerable challenge. In this study, two alternative fabrication techniques have been proposed for the fabrication of a microfluidic device with 3D sidewall electrodes. In the first method, both the mold and the electrodes are fabricated using high precision machining. In the second method, the mold with tilted sidewalls is fabricated using high precision machining and the electrodes are deposited on the sidewall using sputtering together with a shadow mask fabricated by electric discharge machining. Both fabrication processes are assessed as highly repeatable and robust. Moreover, the two methods are found to be complementary with respect to the channel height. Only the manipulation of particles with negative-DEP is demonstrated in the experiments, and the throughput values up to 105 particles / min is reached in a continuous flow. The experimental results are compared with the simulation results and the limitations on the fabrication techniques are also discussed.
Code and Solution Verification of 3D Numerical Modeling of Flow in the Gust Erosion Chamber
Yuen, A.; Bombardelli, F. A.
2014-12-01
Erosion microcosms are devices commonly used to investigate the erosion and transport characteristics of sediments at the bed of rivers, lakes, or estuaries. In order to understand the results these devices provide, the bed shear stress and flow field need to be accurately described. In this research, the UMCES Gust Erosion Microcosm System (U-GEMS) is numerically modeled using Finite Volume Method. The primary aims are to simulate the bed shear stress distribution at the surface of the sediment core/bottom of the microcosm, and to validate the U-GEMS produces uniform bed shear stress at the bottom of the microcosm. The mathematical model equations are solved by on a Cartesian non-uniform grid. Multiple numerical runs were developed with different input conditions and configurations. Prior to developing the U-GEMS model, the General Moving Objects (GMO) model and different momentum algorithms in the code were verified. Code verification of these solvers was done via simulating the flow inside the top wall driven square cavity on different mesh sizes to obtain order of convergence. The GMO model was used to simulate the top wall in the top wall driven square cavity as well as the rotating disk in the U-GEMS. Components simulated with the GMO model were rigid bodies that could have any type of motion. In addition cross-verification was conducted as results were compared with numerical results by Ghia et al. (1982), and good agreement was found. Next, CFD results were validated by simulating the flow within the conventional microcosm system without suction and injection. Good agreement was found when the experimental results by Khalili et al. (2008) were compared. After the ability of the CFD solver was proved through the above code verification steps. The model was utilized to simulate the U-GEMS. The solution was verified via classic mesh convergence study on four consecutive mesh sizes, in addition to that Grid Convergence Index (GCI) was calculated and based on
Quasi 3D modelling of water flow in the sandy soil
Rezaei, Meisam; Seuntjens, Piet; Joris, Ingeborg; Boënne, Wesley; De Pue, Jan; Cornelis, Wim
2016-04-01
Monitoring and modeling tools may improve irrigation strategies in precision agriculture. Spatial interpolation is required for analyzing the effects of soil hydraulic parameters, soil layer thickness and groundwater level on irrigation management using hydrological models at field scale. We used non-invasive soil sensor, a crop growth (LINGRA-N) and a soil hydrological model (Hydrus-1D) to predict soil-water content fluctuations and crop yield in a heterogeneous sandy grassland soil under supplementary irrigation. In the first step, the sensitivity of the soil hydrological model to hydraulic parameters, water stress, crop yield and lower boundary conditions was assessed after integrating models at one soil column. Free drainage and incremental constant head conditions were implemented in a lower boundary sensitivity analysis. In the second step, to predict Ks over the whole field, the spatial distributions of Ks and its relationship between co-located soil ECa measured by a DUALEM-21S sensor were investigated. Measured groundwater levels and soil layer thickness were interpolated using ordinary point kriging (OK) to a 0.5 by 0.5 m in aim of digital elevation maps. In the third step, a quasi 3D modelling approach was conducted using interpolated data as input hydraulic parameter, geometric information and boundary conditions in the integrated model. In addition, three different irrigation scenarios namely current, no irrigation and optimized irrigations were carried out to find out the most efficient irrigation regime. In this approach, detailed field scale maps of soil water stress, water storage and crop yield were produced at each specific time interval to evaluate the best and most efficient distribution of water using standard gun sprinkler irrigation. The results show that the effect of the position of the groundwater level was dominant in soil-water content prediction and associated water stress. A time-dependent sensitivity analysis of the hydraulic
Moortgat, Joachim; Soltanian, Mohamad Reza
2016-01-01
We present a new implicit higher-order finite element (FE) approach to efficiently model compressible multicomponent fluid flow on unstructured grids and in fractured porous subsurface formations. The scheme is sequential implicit: pressures and fluxes are updated with an implicit Mixed Hybrid Finite Element (MHFE) method, and the transport of each species is approximated with an implicit second-order Discontinuous Galerkin (DG) FE method. Discrete fractures are incorporated with a cross-flow equilibrium approach. This is the first investigation of all-implicit higher-order MHFE-DG for unstructured triangular, quadrilateral (2D), and hexahedral (3D) grids and discrete fractures. A lowest-order implicit finite volume (FV) transport update is also developed for the same grid types. The implicit methods are compared to an Implicit-Pressure-Explicit-Composition (IMPEC) scheme. For fractured domains, the unconditionally stable implicit transport update is shown to increase computational efficiency by orders of mag...
Moortgat, Joachim
2016-01-01
Problems of interest in hydrogeology and hydrocarbon resources involve complex heterogeneous geological formations. Such domains are most accurately represented in reservoir simulations by unstructured computational grids. Finite element methods accurately describe flow on unstructured meshes with complex geometries, and their flexible formulation allows implementation on different grid types. In this work, we consider for the first time the challenging problem of fully compositional three-phase flow in 3D unstructured grids, discretized by any combination of tetrahedra, prisms, and hexahedra. We employ a mass conserving mixed hybrid finite element (MHFE) method to solve for the pressure and flux fields. The transport equations are approximated with a higher-order vertex-based discontinuous Galerkin (DG) discretization. We show that this approach outperforms a face-based implementation of the same polynomial order. These methods are well suited for heterogeneous and fractured reservoirs, because they provide ...
Validation of PSF-based 3D reconstruction for myocardial blood flow measurements with Rb-82 PET
DEFF Research Database (Denmark)
Tolbod, Lars Poulsen; Christensen, Nana Louise; Møller, Lone W.;
Aim:The use of PSF-based 3D reconstruction algorithms (PSF) is desirable in most clinical PET-exams due to their superior image quality. Rb-82 cardiac PET is inherently noisy due to short half-life and prompt gammas and would presumably benefit from PSF. However, the quantitative behavior of PSF......-scans performed on a GE Discovery 690 PET/CT were included. Images were reconstructed in an isotropic matrix (3.27x3.27x3.27 mm) using PSF (SharpIR: 3 iterations and 21 subsets) and FBP (FORE FBP) with the same edge-preserving filter (3D Butterworth: cut-off 10 mm, power 10). Analysis: The dynamic PET...... is not well validated and problems with both edge-effects and unphysical contrast-recovery have been reported.1 In this study, we compare myocardial blood flow (MBF) and coronary flow reserve (CFR) obtained using GEs implementation of PSF, SharpIR, with the conventional method for reconstruction of dynamic...
Farrell, C.; Adamczyk, J.
1981-01-01
A reliable method is presented for calculating the flowfield about a cascade of arbitrary 2-D airfoils. The method approximates the three-dimensional flow in a turbomachinery blade row by correcting for streamtube convergence and radius change in the throughflow direction. The method is a fully conservative solution of the full potential equation incorporating the finite volume technique on a body-fitted periodic mesh, with an artificial density imposed in the transonic region to ensure stability and the capture of shock waves. Comparison of results for several supercritical blades shows good agreement with their hodograph solutions. Other calculations for these profiles as well as standard NACA blade sections indicate that this is a useful scheme for analyzing both the design and off-design performance of turbomachinery blading.
Institute of Scientific and Technical Information of China (English)
Yaghobi Nakisa; Ghoreishy Mir Hamid Reza
2009-01-01
The oxidative coupling of methane (OCM) over titanate perovskite catalyst has been developed by three-dimensional numerical simulations of flow field coupled with heat transfer as well as heterogeneous kinetic model.The reaction was assumed to take place both in the gas phase and on the catalytic surface.Kinetic rate constants were experimentally obtained using a ten step kinetic model.The simulation results agree quite well with the data of OCM experiments,which were used to investigate the effect of temperature on the selectivity and conversion obtained in the methane oxidative coupling process.The conversion of methane linearly increased with temperature and the selectivity of C2 was practically constant in the temperature range of 973-1073 K.The study shows that CFD tools make it possible to implement the heterogeneous kinetic model even for high exothermic reaction such as OCM.
Benchmark Study of 3D Pore-scale Flow and Solute Transport Simulation Methods
Scheibe, T. D.; Yang, X.; Mehmani, Y.; Perkins, W. A.; Pasquali, A.; Schoenherr, M.; Kim, K.; Perego, M.; Parks, M. L.; Trask, N.; Balhoff, M.; Richmond, M. C.; Geier, M.; Krafczyk, M.; Luo, L. S.; Tartakovsky, A. M.
2015-12-01
Multiple numerical approaches have been developed to simulate porous media fluid flow and solute transport at the pore scale. These include 1) methods that explicitly model the three-dimensional geometry of pore spaces and 2) methods that conceptualize the pore space as a topologically consistent set of stylized pore bodies and pore throats. In previous work we validated a model of the first type, using computational fluid dynamics (CFD) codes employing standard finite volume method (FVM), against magnetic resonance velocimetry (MRV) measurements of pore-scale velocities. Here we expand that benchmark study to include additional models of the first type based on the immersed-boundary method (IMB), lattice Boltzmann method (LBM), and smoothed particle hydrodynamics (SPH), as well as a model of the second type, a pore-network model (PNM). While the PNM approach is computationally much less demanding than direct numerical simulation methods, the effect of conceptualizing complex three-dimensional pore geometries in the manner of PNMs has not been fully determined. We apply all five approaches (FVM-based CFD, IMB, LBM, SPH and PNM) to simulate pore-scale velocity distributions and nonreactive solute transport, and intercompare the model results. Comparisons are drawn both in terms of macroscopic variables (e.g., permeability, solute breakthrough curves) and microscopic variables (e.g., local velocities and concentrations). Generally good agreement was achieved among the various approaches, but some differences were observed depending on the model context. The benchmark study was challenging because of variable capabilities of the codes, and inspired some code enhancements to allow consistent comparison of flow and transport simulations across the full suite of methods. This study provides support for confidence in a variety of pore-scale modeling methods, and motivates further development and application of pore-scale simulation methods.
Intercomparison of 3D pore-scale flow and solute transport simulation methods
Yang, Xiaofan; Mehmani, Yashar; Perkins, William A.; Pasquali, Andrea; Schönherr, Martin; Kim, Kyungjoo; Perego, Mauro; Parks, Michael L.; Trask, Nathaniel; Balhoff, Matthew T.; Richmond, Marshall C.; Geier, Martin; Krafczyk, Manfred; Luo, Li-Shi; Tartakovsky, Alexandre M.; Scheibe, Timothy D.
2016-09-01
Multiple numerical approaches have been developed to simulate porous media fluid flow and solute transport at the pore scale. These include 1) methods that explicitly model the three-dimensional geometry of pore spaces and 2) methods that conceptualize the pore space as a topologically consistent set of stylized pore bodies and pore throats. In previous work we validated a model of the first type, using computational fluid dynamics (CFD) codes employing a standard finite volume method (FVM), against magnetic resonance velocimetry (MRV) measurements of pore-scale velocities. Here we expand that validation to include additional models of the first type based on the lattice Boltzmann method (LBM) and smoothed particle hydrodynamics (SPH), as well as a model of the second type, a pore-network model (PNM). The PNM approach used in the current study was recently improved and demonstrated to accurately simulate solute transport in a two-dimensional experiment. While the PNM approach is computationally much less demanding than direct numerical simulation methods, the effect of conceptualizing complex three-dimensional pore geometries on solute transport in the manner of PNMs has not been fully determined. We apply all four approaches (FVM-based CFD, LBM, SPH and PNM) to simulate pore-scale velocity distributions and (for capable codes) nonreactive solute transport, and intercompare the model results. Comparisons are drawn both in terms of macroscopic variables (e.g., permeability, solute breakthrough curves) and microscopic variables (e.g., local velocities and concentrations). Generally good agreement was achieved among the various approaches, but some differences were observed depending on the model context. The intercomparison work was challenging because of variable capabilities of the codes, and inspired some code enhancements to allow consistent comparison of flow and transport simulations across the full suite of methods. This study provides support for confidence
Energy Technology Data Exchange (ETDEWEB)
Millan Barrera, Cecia; Ramirez Leon, Hermilo [Instituto Mexicano de Tecnologia del Agua, Jiutepec, Morelos (Mexico)
2001-12-01
A numerical analysis is applied to a flow in an open channel and deformed by a three dimensional obstacle. The proposed model solves the 3-D Navier-Stokes equations, to which a {kappa}-{epsilon} turbulence model is coupled. The numerical analysis was constructed using a finite difference formulation for time evaluation purposed and staggered cells for space evaluation. The main goal of the present work was to study the turbulent structures and patterns of the flow due to an obstacle at the bottom of the channel plate. Our results are according to those found in the related literature. Flow patterns allow establishing the generation of turbulent structures by means of a comparison between this study and a most recent related work that evaluates the vorticity of the flow. [Spanish] Se reportan los resultados obtenidos, mediante simulaciones numericas, del movimiento del flujo en un canal con superficie libre y un obstaculo en el fondo. El sistema ecuaciones utilizado resuelve las ecuaciones de Navier-Stokes en tres dimensiones, al cual se le acoplo un modelo de turbulencia tipo {kappa}-{epsilon}. La solucion se obtiene numericamente utilizando un esquema en diferencias finitas para la evaluacion temporal de las variables y una celda escalonada para la evaluacion espacial de las mismas. El objetivo del modelo es estudiar los patrones de flujo y las estructuras turbulentas que se generan debido a la presencia del obstaculo. El estudio se realizo para un flujo en tres dimensiones. Los resultados son satisfactorios, ya que muestran concordancia con otros estudios numericos y experimentales encontrados en la literatura.
Comparison of predicting drag methods using computational fluid dynamics in 2d/3d viscous flow
Institute of Scientific and Technical Information of China (English)
ZHU; ZiQiang; WANG; XiaoLu; LIU; Jie; LIU; Zhou
2007-01-01
As a result of the necessity of aircraft engineering design and the progress of computational fluid dynamics (CFD), techniques of accurately predicting aerodynamic drag are being increasingly explored. According to the momentum balance, the drag can be represented by an integral over a cross-flow plane (called wake integration method) at an arbitrary distance behind the configuration. A formulation to reduce the size of the wake cross plane region required for calculating the drag is developed by using cutoff parameters of vorticity and entropy. This increases the calculation accuracy and decreases the computation time required. Numerical experiments are made to obtain the threshold values of these cutoff parameters. The wake integration method is applied to predict drags of some examples including airfoil, a variety of wings and wing-body combination. Numerical results are compared with those of traditional surface integration method, showing that the predicting drag values with the wake integration method are closer to the experimental data. The results also show that drag prediction within engineering accuracy is possible by using CFD and the numerical drag optimization of complex aircraft configurations is possible, too.
Field observations of swash zone flow patterns and 3D morphodynamics
Puelo, Jack A.; Holland, K. Todd; Kooney, Timothy N.; Sallenger,, Asbury H.; Edge, Billy L.
2001-01-01
Rapid video measurements of foreshore morphology and velocity were collected at Duck, NC in 1997 to investigate sediment transport processes in the swash zone. Estimates of foreshore evolution over a roughly 30 m cross-shore by 80 m alongshore study area were determined using a stereogrammetric technique. During the passage of a small storm (offshore wave heights increased from 1.4 to 2.5 m), the foreshore eroded nearly 40 cm in less than 4 hours. Dense, horizontal surface velocities were measured over a sub-region (roughly 30 m by 40 m) of the study area using a new particle image velocimetry technique. This technique was able to quantify velocities across the bore front approaching 5 m s–1 as well as the rapid velocities in the very shallow backwash flows. The velocity and foreshore topography measurements were used to test a three-dimensional energetics-based sediment transport model. Even though these data represent the most extensive and highly resolved swash measurements to date, the results showed that while the model could predict some of the qualitative trends in the observed foreshore change, it was a poor predictor of the observed magnitudes of foreshore change. Model — data comparisons differed by roughly an order of magnitude with observed foreshore changes on the order of 10's of centimeters and model predictions on the order of meters. This poor comparison suggests that future models of swash-zone sediment transport may require the inclusion of other physical processes such as bore turbulence, fluid accelerations and skewness, infiltration/exfiltration, water depth variations, and variable friction factors (to name a few).
Directory of Open Access Journals (Sweden)
K. Majidi
2000-01-01
Full Text Available The flow field in volute and circular casings interacting with a centrifugal impeller is obtained by numerical analysis. In the present study, effects of the volute and circular casings on the flow pattern have been investigated by successively combining a volute casing and a circular casing with a single centrifugal impeller. The numerical calculations are carried out with a multiple frame of reference to predict the flow field inside the entire impeller and casings. The impeller flow field is solved in a rotating frame and the flow field in the casings in a stationary frame. The static pressure and velocity in the casing and impeller, and the static pressures and secondary velocity vectors at several cross-sectional planes of the casings are calculated. The calculations show that the curvature of the casings creates pressure gradients that cause vortices at cross-sectional planes of the casings.
Saha, Debashish; Babler, Matthaus U; Holzner, Markus; Soos, Miroslav; Lüthi, Beat; Liberzon, Alex; Kinzelbach, Wolfgang
2016-01-12
Aggregates grown in mild shear flow are released, one at a time, into homogeneous isotropic turbulence, where their motion and intermittent breakup is recorded by three-dimensional particle tracking velocimetry (3D-PTV). The aggregates have an open structure with a fractal dimension of ∼2.2, and their size is 1.4 ± 0.4 mm, which is large, compared to the Kolmogorov length scale (η = 0.15 mm). 3D-PTV of flow tracers allows for the simultaneous measurement of aggregate trajectories and the full velocity gradient tensor along their pathlines, which enables us to access the Lagrangian stress history of individual breakup events. From this data, we found no consistent pattern that relates breakup to the local flow properties at the point of breakup. Also, the correlation between the aggregate size and both shear stress and normal stress at the location of breakage is found to be weaker, when compared with the correlation between size and drag stress. The analysis suggests that the aggregates are mostly broken due to the accumulation of the drag stress over a time lag on the order of the Kolmogorov time scale. This finding is explained by the fact that the aggregates are large, which gives their motion inertia and increases the time for stress propagation inside the aggregate. Furthermore, it is found that the scaling of the largest fragment and the accumulated stress at breakup follows an earlier established power law, i.e., dfrag ∼ σ(-0.6) obtained from laminar nozzle experiments. This indicates that, despite the large size and the different type of hydrodynamic stress, the microscopic mechanism causing breakup is consistent over a wide range of aggregate size and stress magnitude.
Rao, Satish
2015-03-01
Experimental studies show strong strengthening effects for micrometer-scale FCC as well as two-phase superalloy crystals, even at high initial dislocation densities. This talk shows results from large-scale 3-D discrete dislocation simulations (DDS) used to explicitly model the deformation behavior of FCC Ni (flow stress and strain-hardening) as well as superalloy microcrystals for diameters ranging from 1 - 20 microns. The work shows that two size-sensitive athermal hardening processes, beyond forest and precipitation hardening, are sufficient to develop the dimensional scaling of the flow stress, stochastic stress variation, flow intermittency and, high initial strain-hardening rates, similar to experimental observations for various materials. In addition, 3D dislocation dynamics simulations are used to investigate strain-hardening characteristics and dislocation microstructure evolution with strain in large 20 micron size Ni microcrystals (bulk-like) under three different loading axes: 111, 001 and 110. Three different multi-slip loading axes, , and , are explored for shear strains of ~0.03 and final dislocation densities of ~1013/m2. The orientation dependence of initial strain hardening rates and dislocation microstructure evolution with strain are discussed. The simulated strain hardening results are compared with experimental data under similar loading conditions from bulk single-crystal Ni. Finally, atomistic simulation results on the operation of single arm sources in Ni bipillars with a large angle grain boundary is discussed. The atomistic simulation results are compared with experimental mechanical behavior data on Cu bipillars with a similar large angle grain boundary. This work was supported by AFOSR (Dr. David Stargel), and by a grant of computer time from the DOD High Performance Computing Modernization Program, at the Aeronautical Systems Center/Major Shared Resource Center.
Moortgat, Joachim; Amooie, Mohammad Amin; Soltanian, Mohamad Reza
2016-10-01
We present a new implicit higher-order finite element (FE) approach to efficiently model compressible multicomponent fluid flow on unstructured grids and in fractured porous subsurface formations. The scheme is sequential implicit: pressures and fluxes are updated with an implicit Mixed Hybrid Finite Element (MHFE) method, and the transport of each species is approximated with an implicit second-order Discontinuous Galerkin (DG) FE method. Discrete fractures are incorporated with a cross-flow equilibrium approach. This is the first investigation of all-implicit higher-order MHFE-DG for unstructured triangular, quadrilateral (2D), and hexahedral (3D) grids and discrete fractures. A lowest-order implicit finite volume (FV) transport update is also developed for the same grid types. The implicit methods are compared to an Implicit-Pressure-Explicit-Composition (IMPEC) scheme. For fractured domains, the unconditionally stable implicit transport update is shown to increase computational efficiency by orders of magnitude as compared to IMPEC, which has a time-step constraint proportional to the pore volume of discrete fracture grid cells. However, when lowest-order Euler time-discretizations are used, numerical errors increase linearly with the larger implicit time-steps, resulting in high numerical dispersion. Second-order Crank-Nicolson implicit MHFE-DG and MHFE-FV are therefore presented as well. Convergence analyses show twice the convergence rate for the DG methods as compared to FV, resulting in two to three orders of magnitude higher computational efficiency. Numerical experiments demonstrate the efficiency and robustness in modeling compressible multicomponent flow on irregular and fractured 2D and 3D grids, even in the presence of fingering instabilities.
3D numerical study on flow structure and heat transfer in a circular tube with V-baffles☆
Institute of Scientific and Technical Information of China (English)
Withada Jedsadaratanachai; Nuthvipa Jayranaiwachira; Pongjet Promvonge
2015-01-01
A 3D numerical investigation has been carried out to examine periodic laminar flow and heat transfer character-istics in a circular tube with 45° V-baffles with isothermal wal . The computations are based on the finite volume method (FVM), and the SIMPLE algorithm has been implemented. The fluid flow and heat transfer characteristics are presented for Reynolds numbers ranging from 100 to 2000. To generate main longitudinal vortex flows through the tested section, V-baffles with an attack angle of 45° are mounted in tandem and in-line arrangement on the opposite positions of the circular tube. Effects of tube blockage ratio, flow direction on heat transfer and pressure drop in the tube are studied. It is apparent that a pair of longitudinal twisted vortices (P-vortex) created by a V-baffle can induce impingement on a wal of the inter-baffle cavity and lead a drastic increase in heat trans-fer rate at tube wall. In addition, the larger blockage ratio results in the higher Nusselt number and friction factor values. The computational results show that the optimum thermal enhancement factor is around 3.20 at baffle height of B=0.20 and B=0.25 times of the tube diameter for the V-upstream and V-downstream, respectively. © 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. Al rights reserved.
Moortgat, Joachim; Firoozabadi, Abbas
2016-06-01
Problems of interest in hydrogeology and hydrocarbon resources involve complex heterogeneous geological formations. Such domains are most accurately represented in reservoir simulations by unstructured computational grids. Finite element methods accurately describe flow on unstructured meshes with complex geometries, and their flexible formulation allows implementation on different grid types. In this work, we consider for the first time the challenging problem of fully compositional three-phase flow in 3D unstructured grids, discretized by any combination of tetrahedra, prisms, and hexahedra. We employ a mass conserving mixed hybrid finite element (MHFE) method to solve for the pressure and flux fields. The transport equations are approximated with a higher-order vertex-based discontinuous Galerkin (DG) discretization. We show that this approach outperforms a face-based implementation of the same polynomial order. These methods are well suited for heterogeneous and fractured reservoirs, because they provide globally continuous pressure and flux fields, while allowing for sharp discontinuities in compositions and saturations. The higher-order accuracy improves the modeling of strongly non-linear flow, such as gravitational and viscous fingering. We review the literature on unstructured reservoir simulation models, and present many examples that consider gravity depletion, water flooding, and gas injection in oil saturated reservoirs. We study convergence rates, mesh sensitivity, and demonstrate the wide applicability of our chosen finite element methods for challenging multiphase flow problems in geometrically complex subsurface media.
Avettand-Fènoël, Marie-Noëlle; Taillard, Roland; Laye, Julien; Odièvre, Thierry
2014-02-01
The current microstructural investigation performed at various scales deals with the three-dimensional (3-D) material flow in thick dissimilar Airware™ 2050 friction-stir butt welds (Airware, Newport Beach, CA) because of the scarcity of the results obtained with thicker than 8 mm joints and the lack of detailed interpretation of features in the longitudinal direction. An additional originality consists in the study of material flow under the probe tip. In the current case of thick plates, the variation of local temperature along the weld depth is of key importance for the material flow. Indeed, it governs the slight difference of local mechanical behavior between both materials and therefore the shift of the interface, which was clearly put into evidence by means of a difference of Mn content as small as 0.3 pct between both alloys. This importance of temperature for the malleability also entails the pear shape of the nugget as well as a change of grains orientation along the depth in the thermomechanically affected zone. Due to the modification of tool-material adhesion with temperature, a new phenomenological model of material flow for thick friction-stir welds is proposed. In accordance with their difference of origin, the coexistence of onion rings and serrated interface is also highlighted.
Dual FIB-SEM 3D Imaging and Lattice Boltzmann Modeling of Porosimetry and Multiphase Flow in Chalk
Rinehart, A. J.; Yoon, H.; Dewers, T. A.; Heath, J. E.; Petrusak, R.
2010-12-01
Mercury intrusion porosimetry (MIP) is an often-applied technique for determining pore throat distributions and seal analysis of fine-grained rocks. Due to closure effects, potential pore collapse, and complex pore network topologies, MIP data interpretation can be ambiguous, and often biased toward smaller pores in the distribution. We apply 3D imaging techniques and lattice-Boltzmann modeling in interpreting MIP data for samples of the Cretaceous Selma Group Chalk. In the Mississippi Interior Salt Basin, the Selma Chalk is the apparent seal for oil and gas fields in the underlying Eutaw Fm., and, where unfractured, the Selma Chalk is one of the regional-scale seals identified by the Southeast Regional Carbon Sequestration Partnership for CO2 injection sites. Dual focused ion - scanning electron beam and laser scanning confocal microscopy methods are used for 3D imaging of nanometer-to-micron scale microcrack and pore distributions in the Selma Chalk. A combination of image analysis software is used to obtain geometric pore body and throat distributions and other topological properties, which are compared to MIP results. 3D data sets of pore-microfracture networks are used in Lattice Boltzmann simulations of drainage (wetting fluid displaced by non-wetting fluid via the Shan-Chen algorithm), which in turn are used to model MIP procedures. Results are used in interpreting MIP results, understanding microfracture-matrix interaction during multiphase flow, and seal analysis for underground CO2 storage. This work was supported by the US Department of Energy, Office of Basic Energy Sciences as part of an Energy Frontier Research Center. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
Kierkegaard, Axel; Boij, Susann; Efraimsson, Gunilla
2010-02-01
Acoustic wave propagation in flow ducts is commonly modeled with time-domain non-linear Navier-Stokes equation methodologies. To reduce computational effort, investigations of a linearized approach in frequency domain are carried out. Calculations of sound wave propagation in a straight duct are presented with an orifice plate and a mean flow present. Results of transmission and reflections at the orifice are presented on a two-port scattering matrix form and are compared to measurements with good agreement. The wave propagation is modeled with a frequency domain linearized Navier-Stokes equation methodology. This methodology is found to be efficient for cases where the acoustic field does not alter the mean flow field, i.e., when whistling does not occur.
Pederzani, Jean-Noel; Haj-Hariri, Hossein
2012-11-01
An embedded-boundary (or cut-cell) method for complex geometry with moving boundaries is used to solve the three dimensional Navier-Stokes equation around a self-propelling manta swimming at moderately high Reynolds numbers. The motion of the ray is prescribed using a kinematic model fitted to actual biological data. The dependence of thrust production mechanism on Strouhal and Reynolds numbers is investigated. The vortex core structures are accurately plotted and a correlation between wake structures and propulsive performance is established. This insight is critical in understanding the key flow features that a bio-inspired autonomous vehicle should reproduce in order to swim efficiently. The solution method is implemented, on a block-structured Cartesian grid using a cut-cell approach enabling the code to correctly evaluate the wall shear-stress, a key feature necessary at higher Reynolds. To enhance computational efficiency, a parallel adaptive mesh refinement technique is used. The present method is validated against published experimental results. Supported by ONR MURI.
Directory of Open Access Journals (Sweden)
Diego Santiago
2009-09-01
Full Text Available The process of Friction Stir Welding (FSW is a welding method developed by the "The Welding Institute" (TWI of England in 1991. The welding equipment consists of a tool that rotates and progresses along the joint of two restrained sheets. The joint is produced by frictional heating which causes the softening of both components into a viscous-plastic condition and also by the resultant flow between the sheets to be joined. Numerical Modeling of the process can provide realistic prediction of the main variables of the process, reducing the number of experimental tests, thus accelerating the design processes while reducing costs and optimizing the involved technological variables. In this study the friction stir welding process is modeled using a general purpose finite element based program, reproducing the material thermal map and the corresponding mass flow. Numerical thermal results are compared against experimental thermographic maps and numerical material flow results are compared with material flow visualization techniques, with acceptable concordance.O processo denominado "Friction Stir Welding" (FSW é um método de soldagem desenvolvido pelo "The Welding Institute" (TWI na Inglaterra em 1991. O equipamento de soldagem consiste de uma ferramenta que gira e avança ao longo da interface entre duas chapas fixas. A junção é produzida pelo calor gerado por fricção o qual causa o amolecimento de ambos os componentes atingindo uma condição visco-plástica e também pelo escoamento resultante entre as laminas a ser unidas. A modelagem numérica do processo pode fornecer uma predição real das principais variáveis do processo, reduzindo o número de testes experimentais, acelerando, portanto os processos de projeto ao mesmo tempo em que reduz custos e permite a otimização das variáveis tecnológicas envolvidas. Neste trabalho, o processo de soldagem por fricção é modelado empregando um programa de propósito geral baseado no m
Nickeler, D H; Nickeler, Dieter H.; Fahr, Hans-Joerg
2005-01-01
We make some remarks on reconnection in plasmas and want to present some calculations related to the problem of finding velocity fields which conserve magnetic flux or at least magnetic field lines. Hereby we start from views and definitions of ideal and non-ideal flows on one hand, and of reconnective and non-reconnective plasma dynamics on the other hand. Our considerations give additional insights into the discussion on violations of the frozen--in field concept which started recently with the papers by Baranov & Fahr (2003a; 2003b). We find a correlation between the nonidealness which is given by a generalized form of the Ohm's law and a general transporting velocity, which is field line conserving.
Gemmell, Brad; Buskey, Edward; Sheng, Jian
2009-11-01
Copepods are an important planktonic food source for fish species. High predation has led to the development of effective escape responses with short reaction times (less than 2 ms), maximum escape velocities of over 500 body lengths per second and shear sensitivity as low as 1.5s-1. Using high speed digital holography (2 kfps), we measure 3-D distributions of velocity generated by a dwarf seahorse (Hippocampus zosterae) during attacks on its copepod prey, Acartia tonsa. It is found that successful attacks often produce smaller or even no detectable hydrodynamic disturbances around the strike zone, when compared to unsuccessful attempts. In this paper, we will provide quantitative characterization of this ``low-flow'' zone. Further, to elucidate the role of a possible geometrical advantage of the seahorse's head in minimizing its bow wave, high-speed time resolved PIV measurements are conducted in a low-speed water tunnel. On-going analysis will provide insights and implications in understanding the dynamics of flows around the stagnation point at high Reynolds number flow. Sponsored by NSF.
Study on Bubbly Two-Phase Flow Across Twisted Tube Bundles Based on Quasi 3D High Speed Video
Directory of Open Access Journals (Sweden)
Jicheng Zhou
2013-12-01
Full Text Available In flooded evaporators, refrigerants are boiling outside the tubes. This paper focuses on the bubbly two-phase flow characteristics in twisted tube bundles. The quasi 3-D high speed video method and computational fluid dynamics are carried out to understand the effects which angles between the major axis of the cylinder and vertical direction ( and bubble diameters have on the motion behaviours of bubbly flow. is adjusted to 0°, 30°, 45° and 60°，respectively. Bubble diameter is 4mm, 6mm and 8mm, respectively. The turbulence intensity of fluid outside the tubes which is resulted by bubble rising behaviour is also investigated. The results show that the elliptical cylinders with different s lead to bubble sliding out the surface of tubes, rising steadily and spreading widely in tube bundles. And larger bubbles have a stronger effect on turbulence intensity of liquid phase flow. It also can be concluded that the surface geometry of twisted tube plays an active role in heat transfer enhancement of the twisted tube evaporator
A full 3D model of fluid flow and heat transfer in an E.B. heated liquid metal bath
Matveichev, A.; Jardy, A.; Bellot, J. P.
2016-07-01
In order to study the dissolution of exogeneous inclusions in the liquid metal during processing of titanium alloys, a series of dipping experiments has been performed in an Electron Beam Melting laboratory furnace. Precise determination of the dissolution kinetics requires knowing and mastering the exact thermohydrodynamic behavior of the melt pool, which implies full 3D modeling of the process. To achieve this goal, one needs to describe momentum and heat transfer, phase change, as well as the development of flow turbulence in the liquid. EB power input, thermal radiation, heat loss through the cooling circuit, surface tension effects (i.e. Marangoni-induced flow) must also be addressed in the model. Therefore a new solver dealing with all these phenomena was implemented within OpenFOAM platform. Numerical results were compared with experimental data from actual Ti melting, showing a pretty good agreement. In the second stage, the immersion of a refractory sample rod in the liquid pool was simulated. Results of the simulations showed that the introduction of the sample slightly disturbs the flow field inside the bath. The amount of such disturbance depends on the exact location of the dipping.
Institute of Scientific and Technical Information of China (English)
Qiang LI; Shu-lian LIU; Xiao-hong PAN; Shui-ying ZHENG
2012-01-01
The effects of journal misalignment on the transient flow of a finite grooved journal bearing are presented in this study.A new 3D computational fluid dynamics (CFD) analysis method is applied.Also,the quasi-coupling calculation of transient fluid dynamics of oil film in journal bearing and rotor dynamics is considered in the analysis.Based on the structured mesh,a new approach for mesh movement is proposed to update the mesh volume when the journal moves during the fluid dynamics simulation of an oil film.Existing dynamic mesh models provided by FLUENT are not suitable for the transient oil flow in journal bearings.The movement of the journal is obtained by solving the moving equations of the rotor-bearing system with the calculated film pressure as the boundary condition of the load.The data exchange between fluid dynamics and rotor dynamics is realized by data files.Results obtained from the CFD model were consistent with previous experimental results on misalignedjournal bearings.Film pressure,oil film force,friction torque,misalignment moment and attitude angle were calculated and compared for misaligned and aligned journal bearings.The results indicate that bearing performances are greatly affected by misalignment which is caused by unbalanced excitation,and the CFD method based on the fluid-structure interaction (FSI) technique can effectively predict the transient flow field ofa misaligned journal bearing in a rotor-bearing system.
Coupling Motion and Energy Harvesting of Two Side-by-Side Flexible Plates in a 3D Uniform Flow
Directory of Open Access Journals (Sweden)
Dibo Dong
2016-05-01
Full Text Available The fluid-structure interaction problems of two side-by-side flexible plates with a finite aspect ratio in a three-dimensional (3D uniform flow are numerically studied. The plates’ motions are entirely passive under the force of surrounding fluid. By changing the aspect ratio and transverse distance, the coupling motions, drag force and energy capture performance are analyzed. The mechanisms underlying the plates’ motion and flow characteristics are discussed systematically. The adopted algorithm is verified and validated by the simulation of flow past a square flexible plate. The results show that the plate’s passive flapping behavior contains transverse and spanwise deformation, and the flapping amplitude is proportional to the aspect ratio. In the side-by-side configuration, three distinct coupling modes of the plates’ motion are identified, including single-plate mode, symmetrical flapping mode and decoupled mode. The plate with a lower aspect ratio may suffer less drag force and capture less bending energy than in the isolated situation. The optimized selection for obtaining higher energy conversion efficiency is the plate flapping in single-plate mode, especially the plate with a higher aspect ratio. The findings of this work provide several new physical insights into the understanding of fish schooling and are expected to inspire the developments of underwater robots or energy harvesters.
A 3-dimensional Navier-Stokes-Euler code for blunt-body flow computations
Li, C. P.
1985-01-01
The shock-layer flowfield is obtained with or without viscous and heat-conducting dissipations from the conservative laws of fluid dynamics equations using a shock-fitting implicity finite-difference technique. The governing equations are cast in curvilinear-orthogonal coordinates and transformed to the domain between the shock and the body. Another set of equations is used for the singular coordinate axis, which, together with a cone generator away from the stagnation point, encloses the computation domain. A time-dependent alternating direction implicit factorization technique is applied to integrate the equations with local-time increment until a steady solution is reached. The shock location is updated after the flowfield computation, but the wall conditions are implemented into the implicit procedure. Innovative procedures are introduced to define the initial flowfield, to treat both perfect and equilibrium gases, to advance the solution on a coarse-to-fine grid sequence, and to start viscous flow computations from their corresponding inviscid solutions. The results are obtained from a grid no greater than 28 by 18 by 7 and converged within 300 integration steps. They are of sufficient accuracy to start parabolized Navier-Stokes or Euler calculations beyond the nose region, to compare with flight and wind-tunnel data, and to evaluate conceptual designs of reentry spacecraft.
Modelling debris transport within glaciers by advection in a full-Stokes ice flow model
Wirbel, Anna; Jarosch, Alexander H.; Nicholson, Lindsey
2017-04-01
As mountain glaciers recede worldwide, an increasing proportion of the remaining glacierized area is expected to become debris covered. The spatio-temporal development of a surface debris cover has profound effects on the glacier behaviour and meltwater generation, yet little is known about how glacier dynamics influence the spatial distribution of an emerging debris cover. Motivated by this lack of understanding, we present a coupled model to simulate advection and resulting deformation of debris features within glaciers. The finite element model developed in python consists of an advection scheme coupled to a full-Stokes ice flow model, using FEniCS as the numerical framework. We show results from numerical tests that demonstrate its suitability to model advection-dominated transport of concentration in a divergence-free velocity field. The capabilities of the coupled model are demonstrated by simulating transport of debris features of different initial size, shape and location through modelled velocity fields of representative mountain glaciers. The results indicate that deformation of initial debris inputs, as a consequence of being transported through the glacier, plays an important role in determining the location and rate of debris emergence at the glacier surface. The presented work lays the foundation for comprehensive simulations of realistic patterns of debris cover, their spatial and temporal variability and the timescales over which debris covers can form.
Precession in Stokes flow: spin and revolution of a bacterial flagellum
Ishikawa, Takuji; Sawano, Yoichiro; Wakebe, Hiromichi; Inoue, Yuichi; Ishijima, Akihiko; Shimogonya, Yuji
2016-11-01
The bacterial flagellar motor is an ion-driven rotary machine in the cell envelope of bacteria. When we performed a bead assay, in which the cell body was affixed to a glass surface to observe the rotation of a truncated flagellum via the positioning of a 250 nm-diameter gold nanoparticle, we often observed that the filament motion consisted of two types of rotation: spin and revolution, which resulted in precession. Since the mechanism of flagella precession was unknown, we investigated it using numerical simulations. The results show that the precession occurred due to hydrodynamic interactions between the flagellum and the wall in the Stokes flow regime. We also developed a simple theory of the precession, which validity was confirmed by comparing with the simulation. The theory could be utilized to predict both the filament tilt angle and motor torque from experimental flagellar precession data. The knowledge obtained is important in understanding mechanical properties of the bacterial motor and hook. This work was supported in part by a Japan Society Promotion of Science Grants-in-Aid for Scientific Research (JSPS KAKENHI) (Grant Nos. 25000008 and 26242039).
Energy integral of the Stokes flow in a singularly perturbed exterior domain
Directory of Open Access Journals (Sweden)
Matteo Dalla Riva
2012-01-01
Full Text Available We consider a pair of domains \\(\\Omega ^b\\ and \\(\\Omega ^s\\ in \\(\\mathbb{R}^n\\ and we assume that the closure of \\(\\Omega ^b\\ does not intersect the closure of \\(\\epsilon \\Omega ^s\\ for \\(\\epsilon \\in (0,\\epsilon _0\\. Then for a fixed \\(\\epsilon \\in (0,\\epsilon_0\\ we consider a boundary value problem in \\(\\mathbb{R}^n \\setminus (\\Omega ^b \\cup \\epsilon \\Omega ^s\\ which describes the steady state Stokes flow of an incompressible viscous fluid past a body occupying the domain \\(\\Omega ^b\\ and past a small impurity occupying the domain \\(\\epsilon \\Omega ^s\\. The unknown of the problem are the velocity field \\(u\\ and the pressure field \\(p\\, and we impose the value of the velocity field \\(u\\ on the boundary both of the body and of the impurity. We assume that the boundary velocity on the impurity displays an arbitrarily strong singularity when \\(\\epsilon\\ tends to 0. The goal is to understand the behaviour of the strain energy of \\( (u, p\\ for \\(\\epsilon\\ small and positive. The methods developed aim at representing the limiting behaviour in terms of analytic maps and possibly singular but completely known functions of \\(\\epsilon\\, such as \\(\\epsilon ^{-1}\\, \\(\\log \\epsilon\\.
A spectral numerical method for the Navier-Stokes equations with applications to Taylor-Couette flow
Moser, R. D.; Moin, P.; Leonard, A.
1983-01-01
A new spectral method for solving the incompressible Navier-Stokes equations in a plane channel and between concentric cylinders is presented. The method uses spectral expansions which inherently satisfy the boundary conditions and the continuity equation and yield banded matrices which are efficiently solved at each time step. In addition, the number of dependent variables is reduced, resulting in a reduction in computer memory requirements. Several test problems have been computed for the channel flow and for flow between concentric cylinders, including Taylor-Couette flow with axisymmetric Taylor vortices and wavy vortices. In all cases, agreement with available experimental and theoretical results is very good.
Navier-Stokes flow field analysis of compressible flow in a high pressure safety relief valve
Vu, Bruce; Wang, Ten-See; Shih, Ming-Hsin; Soni, Bharat
1993-12-01
The objective of this study is to investigate the complex three-dimensional flowfield of an oxygen safety pressure relieve valve during an incident, with a computational fluid dynamic (CFD) analysis. Specifically, the analysis will provide a flow pattern that would lead to the expansion of the eventual erosion pattern of the hardware, so as to combine it with other findings to piece together a most likely scenario for the investigation. The CFD model is a pressure based solver. An adaptive upwind difference scheme is employed for the spatial discretization, and a predictor, multiple corrector method is used for the velocity-pressure coupling. The computational result indicated vortices formation near the opening of the valve which matched the erosion pattern of the damaged hardware.
Coupling Navier-stokes and Cahn-hilliard Equations in a Two-dimensional Annular flow Configuration
Vignal, Philippe
2015-06-01
In this work, we present a novel isogeometric analysis discretization for the Navier-Stokes- Cahn-Hilliard equation, which uses divergence-conforming spaces. Basis functions generated with this method can have higher-order continuity, and allow to directly discretize the higher- order operators present in the equation. The discretization is implemented in PetIGA-MF, a high-performance framework for discrete differential forms. We present solutions in a two- dimensional annulus, and model spinodal decomposition under shear flow.
Zhai, Lu-Sheng; Zong, Yan-Bo; Wang, Hong-Mei; Yan, Cong; Gao, Zhong-Ke; Jin, Ning-De
2017-03-01
Horizontal oil-water two-phase flows often exist in many industrial processes. Uncovering the dynamic mechanism of the flow pattern transition is of great significance for modeling the flow parameters. In this study we propose a method called multi-scale distribution entropy (MSDE) in a coupled 3D phase space, and use it to characterize the flow pattern transitions in horizontal oil-water two-phase flows. Firstly, the proposed MSDE is validated with Lorenz system and ARFIMA processes. Interestingly, it is found that the MSDE is dramatically associated with the cross-correlations of the coupled time series. Then, through conducting the experiment of horizontal oil-water two-phase flows, the upstream and downstream flow information is collected using a conductance cross-correlation velocity probe. The coupled cross-correlated signals are investigated using the MSDE method, and the results indicate that the MSDE is an effective tool uncovering the complex dynamic behaviors of flow pattern transitions.
Directory of Open Access Journals (Sweden)
F. Rezanezhad
2009-05-01
Full Text Available The hydraulic conductivity of unsaturated peat soils is controlled by the peat structure which affects the air-filled porosity, pore size distribution and shape. This study investigates how the size and shape of pores affects the flow of water through peat soils. In this study we used X-ray Computed Tomography (CT, at 45 µm resolution under 5 specific soil-water pressure head levels to provide 3-D, high-resolution images that were used to detect the inner pore structure of peat samples under a changing water regime. Pore structure and configuration were found to be irregular, which affected the rate of water transmission through peat soils. The 3-D analysis suggested that pore distribution is dominated by a single large pore-space. At low pressure head, this single large air-filled pore imparted a more effective flowpath compared to smaller pores. Smaller pores were disconnected and the flowpath was more tortuous than in the single large air-filled pore, and their contribution to flow was negligible when the single large pore was active. We quantify the pore structure of peat soil that affects the hydraulic conductivity in the unsaturated condition, and demonstrate the validity of our estimation of peat unsaturated hydraulic conductivity by making a comparison with a standard permeameter-based method. Estimates of unsaturated hydraulic conductivities were made for the purpose of testing the sensitivity of pore shape and geometry parameters on the hydraulic properties of peats and how to evaluate the structure of the peat and its affects on parameterization. We also studied the ability to quantify these factors for different soil moisture contents in order to define how the factors controlling the shape coefficient vary with changes in soil water pressure head. The relation between measured and estimated unsaturated hydraulic conductivity at various heads shows that rapid initial drainage, that changes the air-filled pore properties, creates a
A New Approach to Sap Flow Measurement Using 3D Printed Gauges and Open-source Electronics
Ham, J. M.; Miner, G. L.; Kluitenberg, G. J.
2015-12-01
A new type of sap flow gauge was developed to measure transpiration from herbaceous plants using a modified heat pulse technique. Gauges were fabricated using 3D-printing technology and low-cost electronics to keep the materials cost under $20 (U.S.) per sensor. Each gauge consisted of small-diameter needle probes fastened to a 3D-printed frame. One needle contained a resistance heater to provide a 6 to 8 second heat pulse while the other probes measured the resultant temperature increase at two distances from the heat source. The data acquisition system for the gauges was built from a low-cost Arduino microcontroller. The system read the gauges every 10 minutes and stored the results on a SD card. Different numerical techniques were evaluated for estimating sap velocity from the heat pulse data - including analytical solutions and parameter estimation approaches . Prototype gauges were tested in the greenhouse on containerized corn and sunflower. Sap velocities measured by the gauges were compared to independent gravimetric measurements of whole plant transpiration. Results showed the system could measure daily transpiration to within 3% of the gravimetric measurements. Excellent agreement was observed when two gauges were attached the same stem. Accuracy was not affected by rapidly changing transpiration rates observed under partly cloudy conditions. The gauge-based estimates of stem thermal properties suggested the system may also detect the onset of water stress. A field study showed the gauges could run for 1 to 2 weeks on a small battery pack. Sap flow measurements on multiple corn stems were scaled up by population to estimate field-scale transpiration. During full canopy cover, excellent agreement was observed between the scaled-up sap flow measurements and reference crop evapotranspiration calculated from weather data. Data also showed promise as a way to estimate real-time canopy resistance required for model verification and development. Given the low
Energy Technology Data Exchange (ETDEWEB)
Liu, C.; Liu, Z. [Univ. of Colorado, Denver, CO (United States)
1994-12-31
A new multilevel technology was developed in this study which provides a successful numerical simulation for the whole process of flow transition in 3-D flat plate boundary layers, including linear growth, secondary instability, breakdown, and transition on a relatively coarse grid with low CPU cost. A fourth-order finite difference scheme on stretched and staggered grids, a fully implicit time-marching technique, a semi-coarsening multigrid based on the so-called approximate line-box relaxation, and a buffer domain for the outflow boundary conditions were all employed for high-order accuracy, good stability, and fast convergence. A new fine-coarse-fine grid mapping technique was developed to catch the large eddies and represent main roles of small eddies to keep the code running after the laminar flow breaks down. The computational results are in good agreement with linear stability theory, secondary instability theory, and some experiments. The computation also reproduced the K-type and C-type transition observed by laboratory experiments. The CPU cost for a typical case is around 2-9 CRAY-YMP hours.
3D visualization of two-phase flow in the micro-tube by a simple but effective method
Fu, X; Hu, H; Huang, C J; Huang, Y; Wang, R Z
2009-01-01
The present study presents a simple but effective method for 3D visualization of the two-phase flow in the micro-tube. An isosceles right-angle prism combined with a mirror located 45^o bevel to the prism is employed to obtain synchronously the front and side views of the flow patterns with a single camera, where the locations of the prism and the micro-tube for clearly imaging should satisfy a fixed relationship which is specified in the present study. The optical design is proven successfully by the tough visualization work at the cryogenic temperature range. The image deformation due to the refraction and geometrical configuration of the test section is quantitatively investigated. It is calculated that the image is enlarged by about 20% in inner diameter compared to the real object, which is validated by the experimental results. Meanwhile, the image deformation by adding a rectangular optical correction box outside the circular tube is comparatively investigated. It is calculated that the image is reduce...
Effect of Catch Cup Geometry on 3D Boundary Layer Flow over the Wafer Surface in a Spin Coating
Institute of Scientific and Technical Information of China (English)
Mizue MUNEKATA; Seiichi KIMURA; Hiroaki KURISHIMA; Jinsuke TANAKA; Sohei YAMAMOTO; Hiroyuki YOSHIKAWA; Kazuyoshi MATSUZAKI; Hideki OHBA
2008-01-01
Recently, development of high technology has been required for the formation of thin uniform fdm in manufacturing processes of semiconductor as the semiconductor instruments become more sophisticated. Spin coating is usually used for spreading photoresist on a wafer surface. However, since rotating speed of the disk is very high in spin coating, the dropped photoresist scatters outward and reattaches on the film surface. A catch cup is set up outside the wafer in spin coating, and scattered photoresist mist is removed from the wafer edge by the exhaust flow generated at the gap between the wafer edge and the catch cup. In the dry process of a spin coating, it is a serious concern that the film thickness increases near the wafer edge in the case of low rotating speed. The purpose of this study is to make clear the effect of the catch cup geometry on the 3D boundary layer flow over the wafer surface and the drying rate of liquid film.
Influence of external 3D magnetic fields on helical equilibrium and plasma flow in RFX-mod
Energy Technology Data Exchange (ETDEWEB)
Piovesan, P; Bonfiglio, D; Bonomo, F; Cappello, S; Carraro, L; Cavazzana, R; Gobbin, M; Marrelli, L; Martin, P; Martines, E; Momo, B; Piron, L; Puiatti, M E; Soppelsa, A; Valisa, M; Zanca, P; Zaniol, B [Consorzio RFX, EURATOM-ENEA Association, Corso Stati Uniti 4, 35127 Padova (Italy)
2011-08-15
A spontaneous transition to a helical equilibrium with an electron internal transport barrier is observed in RFX-mod as the plasma current is raised above 1 MA (Lorenzini R et al 2009 Nature Phys. 5 570). The helical magnetic equilibrium can be controlled with external three-dimensional (3D) magnetic fields applied by 192 active coils, providing proper helical boundary conditions either rotating or static. The persistence of the helical equilibrium is strongly increased in this way. A slight reduction in the energy confinement time of about 15% is observed, likely due to the increased plasma-wall interaction associated with the finite radial magnetic field imposed at the edge. A global helical flow develops in these states and is expected to play a role in the helical self-organization. In particular, its shear may contribute to the ITB formation and is observed to increase with the externally applied radial field. The possible origins of this flow, from nonlinear visco-resistive magnetohydrodynamic (MHD) and/or ambipolar electric fields, will be discussed.
A 3D-CFD code for accurate prediction of fluid flows and fluid forces in seals
Athavale, M. M.; Przekwas, A. J.; Hendricks, R. C.
1994-01-01
Current and future turbomachinery requires advanced seal configurations to control leakage, inhibit mixing of incompatible fluids and to control the rotodynamic response. In recognition of a deficiency in the existing predictive methodology for seals, a seven year effort was established in 1990 by NASA's Office of Aeronautics Exploration and Technology, under the Earth-to-Orbit Propulsion program, to develop validated Computational Fluid Dynamics (CFD) concepts, codes and analyses for seals. The effort will provide NASA and the U.S. Aerospace Industry with advanced CFD scientific codes and industrial codes for analyzing and designing turbomachinery seals. An advanced 3D CFD cylindrical seal code has been developed, incorporating state-of-the-art computational methodology for flow analysis in straight, tapered and stepped seals. Relevant computational features of the code include: stationary/rotating coordinates, cylindrical and general Body Fitted Coordinates (BFC) systems, high order differencing schemes, colocated variable arrangement, advanced turbulence models, incompressible/compressible flows, and moving grids. This paper presents the current status of code development, code demonstration for predicting rotordynamic coefficients, numerical parametric study of entrance loss coefficients for generic annular seals, and plans for code extensions to labyrinth, damping, and other seal configurations.
3D NUMERICAL SIMULATION ON WATER AND AIR TWO-PHASE FLOWS OF THE STEPS AND FLARING GATE PIER
Institute of Scientific and Technical Information of China (English)
ZHANG Ting; WU Chao; LIAO Hua-sheng; HU Yao-hua
2005-01-01
A new-style flood discharging dam, which consolidates the flaring gate pier and the stepped spillway for discharging the flood through the dam surface, had been applied in China. The theoretical study on it is in a beginning stage at present. The three-dimensional numerical simulation has not been reported. In this paper, the 3D numerical calculation on the two-phase flow of water and air with discharge per unit width 195m3/s* m is presented . The results indicate that there is negative pressure on the juncture of the spillway surface and the first step. There forms obvious longitudinal and transverse eddies on the steps and the velocity decreases obviously compared with the smooth spillway. The figures of the velocity distributions and the water-air two-phase flows are plotted. The results calculated on the pressure are in agreement with the experimental data. Based on the position of the negative pressure obtained from calculation, measurement points of pressure are arranged in physical model. The experimental results validate the existence of the negative pressure. Being an applied and trial study, the results obtained are of theoretical and practical significance.
Furuichi, M.
2009-12-01
We are interested in solving a large-scale plate-mantle simulation enables capture of the large and complex deformation of a subducting plate. In our earlier study (Furuichi, et al 2008), we developed a numerical method toward plate-mantle simulation especially for the highly parallel vector supercomputer system (e.g. Earth Simulator). Our scheme is based on the finite volume method combines (i) the multigrid technique together with ACuTE smoother algorithm (Kameyama et al., 2005), and (ii) the low diffusive CIP-CSLR advection. The validity test of our simulation code by using a fluid rope coiling event (Furuichi, et al 2009) showed that our method enable us to reproduce large non-linear deformation problems of a rigid plate surrounded by soft material without serious quantitative errors. Then as a next step, I am trying to create a Stokes flow solver scalable against a large jump in a viscosity profile, for moving surface (geometrically free boundary) problems. It is for solving the Stokes flow motion under the same condition as real earth. In this presentation, I propose to apply BFBt preconditioner and AMG techniques for the problems of large viscosity contrast and moving free surface boundary condition respectively. I would like to show some numerical experiments for a self-gravitating motion of the layered Stokes flow.
3D CFD modeling of flowing-gas DPALs with different pumping geometries and various flow velocities
Yacoby, Eyal; Waichman, Karol; Sadot, Oren; Barmashenko, Boris D.; Rosenwaks, Salman
2017-01-01
Scaling-up flowing-gas diode pumped alkali lasers (DPALs) to megawatt class power is studied using accurate three-dimensional computational fluid dynamics model, taking into account the effects of temperature rise and losses of alkali atoms due to ionization. Both the maximum achievable power and laser beam quality are estimated for Cs and K lasers. We examined the influence of the flow velocity and Mach number M on the maximum achievable power of subsonic and supersonic lasers. For Cs DPAL devices with M = 0.2 - 3 the output power increases with increasing M by only 20%, implying that supersonic operation mode has only small advantage over subsonic. In contrast, the power achievable in K DPALs strongly depends on M. The output power increases by 100% when M increases from 0.2 to 4, showing a considerable advantage of supersonic device over subsonic. The reason for the increase of the power with M in both Cs and K DPALs is the decrease of the temperature due to the gas expansion in the flow system. However, the power increase for K lasers is much larger than for the Cs devices mainly due to the much smaller fine-structure splitting of the 2P states ( 58 cm-1 for K and 554 cm-1 for Cs), which results in a much stronger effect of the temperature decrease in K DPALs. For pumping by beams of the same rectangular cross section, comparison between end-pumping and transverse-pumping shows that the output power is not affected by the pump geometry. However, the intensity of the output laser beam in the case of transverse-pumped DPALs is strongly non-uniform in the laser beam cross section resulting in higher brightness and better beam quality in the far field for the end-pumping geometry where the intensity of the output beam is uniform.
Bartzke, Gerhard; Kuhlmann, Jannis; Huhn, Katrin
2016-04-01
The entrainment of single grains and, hence, their erosion characteristics are dependent on fluid forcing, grain size and density, but also shape variations. To quantitatively describe and capture the hydrodynamic conditions around individual grains, researchers commonly use empirical approaches such as laboratory flume tanks. Nonetheless, it is difficult with such physical experiments to measure the flow velocities in the direct vicinity or within the pore spaces of sediments, at a sufficient resolution and in a non-invasive way. As a result, the hydrodynamic conditions in the water column, at the fluid-porous interface and within pore spaces of a granular medium of various grain shapes is not yet fully understood. For that reason, there is a strong need for numerical models, since these are capable of quantifying fluid speeds within a granular medium. A 3D-SPH (Smooth Particle Hydrodynamics) numerical wave tank model was set up to provide quantitative evidence on the flow velocities in the direct vicinity and in the interior of granular beds composed of two shapes as a complementary method to the difficult task of in situ measurement. On the basis of previous successful numerical wave tank models with SPH, the model geometry was chosen in dimensions of X=2.68 [m], Y=0.48 [m], and Z=0.8 [m]. Three suites of experiments were designed with a range of particle shape models: (1) ellipsoids with the long axis oriented in the across-stream direction, (2) ellipsoids with the long axis oriented in the along-stream direction, and (3) spheres. Particle diameters ranged from 0.04 [m] to 0.08 [m]. A wave was introduced by a vertical paddle that accelerated to 0.8 [m/s] perpendicular to the granular bed. Flow measurements showed that the flow velocity values into the beds were highest when the grains were oriented across the stream direction and lowest in case when the grains were oriented parallel to the stream, indicating that the model was capable to simulate simultaneously
Institute of Scientific and Technical Information of China (English)
XIA Lin-sheng; CHENG Yong-guang; ZHOU Da-qing
2013-01-01
The 3-D characteristics of the water-air flow patterns in a corridor-shaped air-cushion surge chamber during hydraulic transients need to be considered in the shape optimization.To verify the reliability of the water-air two-phase model,namely,the volume of fluid model,the process of charging water into a closed air chamber is successfully simulated.Using the model,the 3-D flow characteristics under the load rejection and acceptance conditions within the air-cushion surge chamber of a specific hydropower station are studied.The flee surface waves,the flow patterns,and the pressure changes during the surge wave process are analyzed in detail.The longitudinal flow of water in the long corridor-shaped surge chamber is similar to the open channel flow with respect to the wave propagation,reflection and superposition characteristics.The lumped parameters of the 3-D numerical simulation agree with the results of a 1-D calculation of hydraulic transients in the whole water conveying system,which validates the 3-D method.The 3-D flow structures obtained can be applied to the shape optimization of the chamber.
Moreno, P. A.; Bombardelli, F. A.
2012-12-01
-dimensional (HR3D) velocity field can be used as a representation of near bed open-channel flows. Both approaches are used to simulate saltating sediment particles using a 3D Lagrangian particle tracking model. This tracking model is composed by generalized sub-models for particle collision with the bed, bed-roughness representation, and particle free-flight between wall collisions. We analyze the hydrodynamic forces (drag, virtual mass, lift, Basset, Magnus and buoyancy) involved in particle saltation. For validation purposes, we compare our simulation results with experimental data from Niño and García (1998) and Lee and Hsu (1994). Finally we use the logarithmic velocity profile to analyze the importance of particle-particle collision using a sub-model based on the conservation of linear and angular momentum during collision. We analyze simulation results with different particle sizes within the sand range, different flow intensities, and different particle concentrations, in terms of particle diffusion and changes in velocity, rotation and trajectory during collision. To identify the importance of particle-particle collisions, simulations with and without collision among particles were carried out.
Calhoun, Ronald; Gouveia, Frank; Shinn, Joseph; Chan, Stevens; Stevens, Dave; Lee, Robert; Leone, John
2004-05-01
An experiment investigating flow around a single complex building was performed in 2000. Sonic anemometers were placed around the building, and two-dimensional wind velocities were recorded. An energy-budget and wind-measuring station was located upstream to provide stability and inflow conditions. In general, the sonic anemometers were located in a horizontal plane around the building at a height of 2.6 m above the ground. However, at the upwind wind station, two levels of the wind were measured. The resulting database can be sampled to produce mean wind fields associated with specific wind directions such as 210°, 225°, and 240°. The data are available generally and should be useful for testing computational fluid dynamical models for flow around a building. An in-house Reynolds-averaged Navier Stokes approach was used to compare with the mean wind fields for the predominant wind directions. The numerical model assumed neutral flow and included effects from a complex array of trees in the vicinity of the building. Two kinds of comparisons are presented: 1) direct experimental versus modeled vector comparisons and 2) a numerical metric approach that focuses on wind magnitude and direction errors. The numerical evaluation generally corroborates the vector-to-vector inspection, showing reasonable agreement for the mean wind fields around the building. However, regions with special challenges for the model were identified. In particular, recirculation regions were especially difficult for the model to capture correctly. In the 240° case, there is a tendency for the model to exaggerate the turning effect in the wind caused by the effect of the building. Two different kinds of simulations were performed: 1) predictive calculations with a reasonable but not high-fidelity representation of the building's architectural complexity and 2) postexperiment calculations in which a large number of architectural features were well represented. Although qualitative evidence
Fast chemical reaction in two-dimensional Navier-Stokes flow: initial regime.
Ait-Chaalal, Farid; Bourqui, Michel S; Bartello, Peter
2012-04-01
This paper studies an infinitely fast bimolecular chemical reaction in a two-dimensional biperiodic Navier-Stokes flow. The reactants in stoichiometric quantities are initially segregated by infinite gradients. The focus is placed on the initial stage of the reaction characterized by a well-defined one-dimensional material contact line between the reactants. Particular attention is given to the effect of the diffusion κ of the reactants. This study is an idealized framework for isentropic mixing in the lower stratosphere and is motivated by the need to better understand the effect of resolution on stratospheric chemistry in climate-chemistry models. Adopting a Lagrangian straining theory approach, we relate theoretically the ensemble mean of the length of the contact line, of the gradients along it, and of the modulus of the time derivative of the space-average reactant concentrations (here called the chemical speed) to the joint probability density function of the finite-time Lyapunov exponent λ with two times τ and τ[over ̃]. The time 1/λ measures the stretching time scale of a Lagrangian parcel on a chaotic orbit up to a finite time t, while τ measures it in the recent past before t, and τ[over ̃] in the early part of the trajectory. We show that the chemical speed scales like κ(1/2) and that its time evolution is determined by rare large events in the finite-time Lyapunov exponent distribution. The case of smooth initial gradients is also discussed. The theoretical results are tested with an ensemble of direct numerical simulations (DNSs) using a pseudospectral model.
Krank, Benjamin; Wall, Wolfgang A; Kronbichler, Martin
2016-01-01
We present an efficient discontinuous Galerkin scheme for simulation of the incompressible Navier-Stokes equations including laminar and turbulent flow. We consider a semi-explicit high-order velocity-correction method for time integration as well as nodal equal-order discretizations for velocity and pressure. The non-linear convective term is treated explicitly while a linear system is solved for the pressure Poisson equation and the viscous term. The key feature of our solver is a consistent penalty term reducing the local divergence error in order to overcome recently reported instabilities in spatially under-resolved high-Reynolds-number flows as well as small time steps. This penalty method is similar to the grad-div stabilization widely used in continuous finite elements. We further review and compare our method to several other techniques recently proposed in literature to stabilize the method for such flow configurations. The solver is specifically designed for large-scale computations through matrix-...
Esposti Ongaro, Tomaso; Cerminara, Matteo
2016-10-01
In the framework of the IAVCEI (International Association of Volcanology and Chemistry of the Earth Interior) initiative on volcanic plume models intercomparison, we discuss three-dimensional numerical simulations performed with the multiphase flow model PDAC (Pyroclastic Dispersal Analysis Code). The model describes the dynamics of volcanic and atmospheric gases (in absence of wind) and two pyroclastic phases by adopting a non-equilibrium Eulerian-Eulerian formulation. Accordingly, gas and particulate phases are treated as interpenetrating fluids, interacting with each other through momentum (drag) and heat exchange. Numerical results describe the time-wise and spatial evolution of weak (mass eruption rate: 1.5 × 106 kg/s) and strong (mass eruption rate: 1.5 × 109 kg/s) plumes. The two tested cases display a remarkably different phenomenology, associated with the different roles of atmospheric stratification, compressibility and mechanism of buoyancy reversal, reflecting in a different structure of the plume, of the turbulent eddies and of the atmospheric circulation. This also brings about different rates of turbulent mixing and atmospheric air entrainment. The adopted multiphase flow model allows to quantify temperature and velocity differences between the gas and particles, including settling, preferential concentration by turbulence and thermal non-equilibrium, as a function of their Stokes number, i.e., the ratio between their kinetic equilibrium time and the characteristic large-eddy turnover time of the turbulent plume. As a result, the spatial and temporal distribution of coarse ash in the atmosphere significantly differs from that of the fine ash, leading to a modification of the plume shape. Finally, three-dimensional numerical results have been averaged in time and across horizontal slices in order to obtain a one-dimensional picture of the plume in a stationary regime. For the weak plume, the results are consistent with one-dimensional models, at
Wu, Wenming; Trinh, Kieu The Loan; Lee, Nae Yoon
2015-03-07
We introduce a new strategy for fabricating a seamless three-dimensional (3D) helical microreactor utilizing a silicone tube and a paraffin mold. With this method, various shapes and sizes of 3D helical microreactors were fabricated, and a complicated and laborious photolithographic process, or 3D printing, was eliminated. With dramatically enhanced portability at a significantly reduced fabrication cost, such a device can be considered to be the simplest microreactor, developed to date, for performing the flow-through polymerase chain reaction (PCR).
Viegas, J. R.; Rubesin, M. W.
1983-01-01
To make computer codes for two-dimensional compressible flows more robust and economical, wall functions for these flows, under adiabatic conditions, have been developed and tested. These wall functions have been applied to three two-equation models of turbulence. The tests consist of comparisons of calculated and experimental results for transonic and supersonic flow over a flat plate and for two-dimensional and axisymmetrical transonic shock-wave/boundary-layer interaction flows with and without separation. The calculations are performed with an implicit algorithm that solves the Reynolds-averaged Navier-Stokes equations. It is shown that results obtained agree very well with the data for the complex compressible flows tested, provided criteria for use of the wall functions are followed. The expected savings in cost of the computations and improved robustness of the code were achieved.
Numerical model of water flow and solute accumulation in vertisols using HYDRUS 2D/3D code
Weiss, Tomáš; Dahan, Ofer; Turkeltub, Tuvia
2015-04-01
Keywords: dessication-crack-induced-salinization, preferential flow, conceptual model, numerical model, vadose zone, vertisols, soil water retention function, HYDRUS 2D/3D Vertisols cover a hydrologically very significant area of semi-arid regions often through which water infiltrates to groundwater aquifers. Understanding of water flow and solute accumulation is thus very relevant to agricultural activity and water resources management. Previous works suggest a conceptual model of dessication-crack-induced-salinization where salinization of sediment in the deep section of the vadose zone (up to 4 m) is induced by subsurface evaporation due to convective air flow in the dessication cracks. It suggests that the salinization is induced by the hydraulic gradient between the dry sediment in the vicinity of cracks (low potential) and the relatively wet sediment further from the main cracks (high potential). This paper presents a modified previously suggested conceptual model and a numerical model. The model uses a simple uniform flow approach but unconventionally prescribes the boundary conditions and the hydraulic parameters of soil. The numerical model is bound to one location close to a dairy farm waste lagoon, but the application of the suggested conceptual model could be possibly extended to all semi-arid regions with vertisols. Simulations were conducted using several modeling approaches with an ultimate goal of fitting the simulation results to the controlling variables measured in the field: temporal variation in water content across thick layer of unsaturated clay sediment (>10 m), sediment salinity and salinity the water draining down the vadose zone to the water table. The development of the model was engineered in several steps; all computed as forward solutions by try-and-error approach. The model suggests very deep instant infiltration of fresh water up to 12 m, which is also supported by the field data. The paper suggests prescribing a special atmospheric
Directory of Open Access Journals (Sweden)
Tanguy Janin
2010-01-01
Full Text Available In the course of a postulated severe accident in an NPP, Direct Containment Heating (DCH may occur after an eventual failure of the vessel. DCH is related to dynamical, thermal, and chemical phenomena involved by the eventual fine fragmentation and dispersal of the corium melt out of the vessel pit. It may threaten the integrity of the containment by pressurization of its atmosphere. Several simplified modellings have been proposed in the past but they require a very strong fitting which renders any extrapolation regarding geometry, material, and scales rather doubtful. With the development of multidimensional multiphase flow computer codes, it is now possible to investigate the phenomenon numerically with more details. We present an analysis of the potential of the MC3D code to support the analysis of this phenomenon, restricting our discussion to the dynamical processes. The analysis is applied to the case of French 1300 MWe PWR reactors for which we derive a correlation for the corium dispersal rate for application in a Probabilistic Safety Analysis (PSA level 2 study.
Zhilkin, A G; Mason, P A; 10.1134/S1063772912040087
2012-01-01
We performed 3D MHD calculations of stream accretion in cataclysmic variable stars for which the white dwarf primary star possesses a strong and complex magnetic field. These calculations are motivated by observations of polars; cataclysmic variables containing white dwarfs with magnetic fields sufficiently strong to prevent the formation of an accretion disk. So an accretion stream flows from the L1 point and impacts directly onto one or more spots on the surface of the white dwarf. Observations indicate that the white dwarf, in some binaries, possesses a complex (non-dipolar) magnetic field. We perform simulations of 10 polars or equivalently one asynchronous polar at 10 different beat phases. Our models have an aligned dipole plus quadrupole magnetic field centered on the white dwarf primary. We find that for a sufficiently strong quadrupole component an accretion spot occurs near the magnetic equator for slightly less than half of our simulations while a polar accretion zone is active for most of the rest...
Knobloch, Gesine; Lauff, Marie-Teres; Hirsch, Sebastian; Schwenke, Carsten; Hamm, Bernd; Wagner, Moritz
2016-12-01
To prospectively compare 3D flow-dependent subtractive MRA vs. 2D flow-independent non-subtractive MRA for assessment of the calf arteries at 3 Tesla. Forty-two patients with peripheral arterial occlusive disease underwent nonenhanced MRA of calf arteries at 3 Tesla with 3D flow-dependent subtractive MRA (fast spin echo sequence; 3D-FSE-MRA) and 2D flow-independent non-subtractive MRA (balanced steady-state-free-precession sequence; 2D-bSSFP-MRA). Moreover, all patients underwent contrast-enhanced MRA (CE-MRA) as standard-of-reference. Two readers performed a per-segment evaluation for image quality (4 = excellent to 0 = non-diagnostic) and severity of stenosis. Image quality scores of 2D-bSSFP-MRA were significantly higher compared to 3D-FSE-MRA (medians across readers: 4 vs. 3; p Tesla with significantly higher image quality and diagnostic accuracy compared to 3D flow-dependent subtractive MRA (3D-FSE-MRA). • 2D flow-independent non-subtractive MRA (2D-bSSFP-MRA) is a robust NE-MRA technique at 3T • 2D-bSSFP-MRA outperforms 3D flow-dependent subtractive MRA (3D-FSE-MRA) as NE-MRA of calf arteries • 2D-bSSFP-MRA is a promising alternative to CE-MRA for calf PAOD evaluation.
Nicolas, F.; Donjat, D.; Plyer, A.; Champagnat, F.; Le Besnerais, G.; Micheli, F.; Cornic, P.; Le Sant, Y.; Deluc, J. M.
2017-08-01
This paper describes the first application of 3D density reconstruction from a limited number of background oriented schlieren (BOS) images in a large research-type low speed wind tunnel. The tested flow is an ad hoc co-flowing hot jet generated at the wingtip of a simplified airfoil. Ray deviation maps captured by 12 synchronized cameras are combined to reconstruct the three dimensional density field of the jet, in the line of the direct 3D BOS technique described in Nicolas et al (2016 Exp. Fluids 57 1-21). A comparison with thermocouple sampling shows consistent results and highlights the efficiency of this new method for thermal measurement of a low speed convective flow. Finally, we underline the new possibilities for fluid dynamic characterization offered by combining stereo particle image velocimetry and 3D BOS measurements.
Kim, Jin-Tae; Liberzon, Alex; Chamorro, Leonardo P.
2015-11-01
The distinctive differences between two jet flows that share the same hydraulic diameter dh = 0.01 m and Re ~ 6000, but different (nozzle) shape are explored via 3D Particle Tracking Velocimetry using OpenPTV (http://www.openptv.net). The two jets are formed from circular and semicircular pipes and released in a quiescent water tank of 40 dh height, 40 dh wide, and 200 dh long. The recirculating system is seeded with 100 μm particles, where flow measurements are performed in the intermediate flow field (14.5 < x /dh <18.5) at 550Hz for a total of ~ 30,000 frames. Analysis is focused on the spatial distribution of the local flow acceleration and curvature of the Lagrangian trajectories. The velocity and acceleration of particles are estimated by low-pass filtering their position with a moving cubic spline fitting, while the curvature is obtained from the Frenet-Serret equations. Probability density functions (p.d.f.) of these quantities are obtained at various sub-volumes containing a given streamwise velocity range, and compared between the two cases to evaluate the memory effects in the intermediate flow field.
Simulation of self-propelled chemotactic bacteria in a stokes flow*
Directory of Open Access Journals (Sweden)
Maury B.
2010-12-01
Full Text Available We prescrit a method to simulate the motion of self-propelled rigid particles in a twodimensional Stokesian fluid, taking into account chemotactic behaviour. Self-propulsion is modelled as a point force associated to each particle, placed at a certain distance from its gravity centre. The method for solving the fluid flow and the motion of the bacteria is based on a variational formulation on the whole domain, including fluid and particles: rigid motion is enforced by penalizing the strain rate tensor on the rigid domain, while incompressibility is treated by duality. This leads to a minimisation problem over unconstrained functional spaces which cari lie easily implemented from any finite element Stokes solver. In order to ensure robustness, a projection algorithm is used to deal with contacts between particles. The particles are meant to represent bacteria of the Escherichia coli type, which interact with their chemical environment through consumption of nutrients and orientation in some favorable direction. Our mode’ takes into account the interaction with oxygen. An advection-diffusion equation on the oxygen concentration is solved in the fluid domain, with a source term accounting for oxygen consumption by the bacteria. In addition, self-propulsion is deactivated for those particles which cannot consume enough oxygen. Finally, the mode’ includes random changes in the orientation of the individual bacteria, with a frequency that depends on the surrounding oxygen concentration, in order to favor the direction of the concentration gradient and thus to reproduce chemotactic behaviour. Numerical simulations implemented with FreeFem++ are presented. Nous présentons une méthode de simulation du mouvement de particules rigides autopropulsées dans un fluide de Stokes en dimension 2. en prenant en compte leur comportement chimiotactique. L’auto-propulsion est modélisée par une force (presque ponctuelle associée à chaque particule et plac
Institute of Scientific and Technical Information of China (English)
HU De-chao; FAN Bei-lin; WANG Guang-qian; ZHANG Hong-wu
2011-01-01
A 3-D numerical formulation is proposed on the horizontal Cartesian, vertical sigma-coordinate grid for modeling non-hydrostatic pressure free-surface flows.The pressure decomposition technique and θ semi-implicit method are used, with the solution procedure being split into two steps.First, with the implicit parts of non-hydrostatic pressures excluded, the provisional velocity field and free surface are obtained by solving a 2-D Poisson equation.Second, the theory of the differential operator is employed to derive the 3-D Poisson equation for non-hydrostatic pressures, which is solved to obtain the non-hydrostatic pressures and to update the provisional velocity field.When the non-orthogonal sigma-coordinate transformation is introduced, additional terms come into being, resulting in a 15-diagonal, diagonally dominant but unsymmetric linear system in the 3-D Poisson equation for non-hydrostatic pressures.The Biconjugate Gradient Stabilized (BiCGstab) method is used to solve the resulting 3-D unsymmetric linear system instead of the conjugate gradient method, which can only be used for symmetric, positive-definite linear systems.Three test cases are used for validations.The successful simulations of the small-amplitude wave, a supercritical flow over a ramp and a turbulent flow in the open channel indicate that the new model can simulate well non-hydrostatic flows, supercritical flows and turbulent flows.
Sanghera, Bal; Banerjee, Debasish; Khan, Aftab; Simcock, Ian; Stirling, J James; Glynne-Jones, Rob; Goh, Vicky
2012-06-01
To characterize the two-dimensional (2D) and three-dimensional (3D) fractal properties of rectal cancer regional blood flow assessed by using volumetric helical perfusion computed tomography (CT) and to determine its reproducibility. Institutional review board approval and informed consent were obtained. Ten prospective patients (eight men, two women; mean age, 72.3 years) with rectal adenocarcinoma underwent two repeated volumetric helical perfusion CT studies (four-dimensional adaptive spiral mode, 11.4-cm z-axis coverage) without intervening treatment within 24 hours, with regional blood flow derived by using deconvolution analysis. Two-dimensional and 3D fractal analyses of the rectal tumor were performed, after segmentation from surrounding structures by using thresholding, to derive fractal dimension and fractal abundance. Reproducibility was quantitatively assessed by using Bland-Altman statistics. Two-dimensional and 3D lacunarity plots were also generated, allowing qualitative assessment of reproducibility. Statistical significance was at 5%. Mean blood flow was 63.50 mL/min/100 mL ± 8.95 (standard deviation). Good agreement was noted between the repeated studies for fractal dimension; mean difference was -0.024 (95% limits of agreement: -0.212, 0.372) for 2D fractal analysis and -0.024 (95% limits of agreement: -0.307, 0.355) for 3D fractal analysis. Mean difference for fractal abundance was -0.355 (95% limits of agreement: -0.869, 1.579) for 2D fractal analysis and -0.043 (95% limits of agreement: -1.154, 1.239) for 3D fractal analysis. The 95% limits of agreement were narrower for 3D than 2D analysis. Lacunarity plots also visually confirmed close agreement between repeat studies. Regional blood flow in rectal cancer exhibits fractal properties. Good reproducibility was achieved between repeated studies with 2D and 3D fractal analysis.
HOMOGENIZATION OF A STATIONARY NAVIER-STOKES FLOW IN POROUS MEDIUM WITH THIN FILM
Institute of Scientific and Technical Information of China (English)
Yao Zhengan; Zhao Hongxing
2008-01-01
The article studies the homogenization of a stationary Navier-Stokes fluid in porous medium with thin film under Dirichlet boundary condition. At the end of the article, "Darcy's law" is rigorously derived from this model as the parameter e tends to zero, which is independent of the coordinates towards the thickness.
Energy Technology Data Exchange (ETDEWEB)
Holford, D.J.
1994-01-01
This document is a user`s manual for the Rn3D finite element code. Rn3D was developed to simulate gas flow and radon transport in variably saturated, nonisothermal porous media. The Rn3D model is applicable to a wide range of problems involving radon transport in soil because it can simulate either steady-state or transient flow and transport in one-, two- or three-dimensions (including radially symmetric two-dimensional problems). The porous materials may be heterogeneous and anisotropic. This manual describes all pertinent mathematics related to the governing, boundary, and constitutive equations of the model, as well as the development of the finite element equations used in the code. Instructions are given for constructing Rn3D input files and executing the code, as well as a description of all output files generated by the code. Five verification problems are given that test various aspects of code operation, complete with example input files, FORTRAN programs for the respective analytical solutions, and plots of model results. An example simulation is presented to illustrate the type of problem Rn3D is designed to solve. Finally, instructions are given on how to convert Rn3D to simulate systems other than radon, air, and water.
Lagrangian 3D particle tracking in high-speed flows: Shake-The-Box for multi-pulse systems
Novara, Matteo; Schanz, Daniel; Reuther, Nico; Kähler, Christian J.; Schröder, Andreas
2016-08-01
The Shake-The-Box (STB) particle tracking technique, recently introduced for time-resolved 3D particle image velocimetry (PIV) images, is applied here to data from a multi-pulse investigation of a turbulent boundary layer flow with adverse pressure gradient in air at 36 m/s ( Re τ = 10,650). The multi-pulse acquisition strategy allows for the recording of four-pulse long time-resolved sequences with a time separation of a few microseconds. The experimental setup consists of a dual-imaging system and a dual-double-cavity laser emitting orthogonal polarization directions to separate the four pulses. The STB particle triangulation and tracking strategy is adapted here to cope with the limited amount of realizations available along the time sequence and to take advantage of the ghost track reduction offered by the use of two independent imaging systems. Furthermore, a correction scheme to compensate for camera vibrations is discussed, together with a method to accurately identify the position of the wall within the measurement domain. Results show that approximately 80,000 tracks can be instantaneously reconstructed within the measurement volume, enabling the evaluation of both dense velocity fields, suitable for spatial gradients evaluation, and highly spatially resolved boundary layer profiles. Turbulent boundary layer profiles obtained from ensemble averaging of the STB tracks are compared to results from 2D-PIV and long-range micro particle tracking velocimetry; the comparison shows the capability of the STB approach in delivering accurate results across a wide range of scales.
Ongaro, T. E.; Clarke, A.; Neri, A.; Voight, B.; Widiwijayanti, C.
2005-12-01
For the first time the dynamics of directed blasts from explosive lava-dome decompression have been investigated by means of transient, multiphase flow simulations in 2D and 3D. Multiphase flow models developed for the analysis of pyroclastic dispersal from explosive eruptions have been so far limited to 2D axisymmetric or Cartesian formulations which cannot properly account for important 3D features of the volcanic system such as complex morphology and fluid turbulence. Here we use a new parallel multiphase flow code, named PDAC (Pyroclastic Dispersal Analysis Code) (Esposti Ongaro et al., 2005), able to simulate the transient and 3D thermofluid-dynamics of pyroclastic dispersal produced by collapsing columns and volcanic blasts. The code solves the equations of the multiparticle flow model of Neri et al. (2003) on 3D domains extending up to several kilometres in 3D and includes a new description of the boundary conditions over topography which is automatically acquired from a DEM. The initial conditions are represented by a compact volume of gas and pyroclasts, with clasts of different sizes and densities, at high temperature and pressure. Different dome porosities and pressurization models were tested in 2D to assess the sensitivity of the results to the distribution of initial gas pressure, and to the total mass and energy stored in the dome, prior to 3D modeling. The simulations have used topographies appropriate for the 1997 Boxing Day directed blast on Montserrat, which eradicated the village of St. Patricks. Some simulations tested the runout of pyroclastic density currents over the ocean surface, corresponding to observations of over-water surges to several km distances at both locations. The PDAC code was used to perform 3D simulations of the explosive event on the actual volcano topography. The results highlight the strong topographic control on the propagation of the dense pyroclastic flows, the triggering of thermal instabilities, and the elutriation
Directory of Open Access Journals (Sweden)
Zhong-Dong Shi
Full Text Available BACKGROUND: Interstitial flow directly affects cells that reside in tissues and regulates tissue physiology and pathology by modulating important cellular processes including proliferation, differentiation, and migration. However, the structures that cells utilize to sense interstitial flow in a 3-dimensional (3D environment have not yet been elucidated. Previously, we have shown that interstitial flow upregulates matrix metalloproteinase (MMP expression in rat vascular smooth muscle cells (SMCs and fibroblasts/myofibroblasts via activation of an ERK1/2-c-Jun pathway, which in turn promotes cell migration in collagen. Herein, we focused on uncovering the flow-induced mechanotransduction mechanism in 3D. METHODOLOGY/PRINCIPAL FINDINGS: Cleavage of rat vascular SMC surface glycocalyx heparan sulfate (HS chains from proteoglycan (PG core proteins by heparinase or disruption of HS biosynthesis by silencing N-deacetylase/N-sulfotransferase 1 (NDST1 suppressed interstitial flow-induced ERK1/2 activation, interstitial collagenase (MMP-13 expression, and SMC motility in 3D collagen. Inhibition or knockdown of focal adhesion kinase (FAK also attenuated or blocked flow-induced ERK1/2 activation, MMP-13 expression, and cell motility. Interstitial flow induced FAK phosphorylation at Tyr925, and this activation was blocked when heparan sulfate proteoglycans (HSPGs were disrupted. These data suggest that HSPGs mediate interstitial flow-induced mechanotransduction through FAK-ERK. In addition, we show that integrins are crucial for mechanotransduction through HSPGs as they mediate cell spreading and maintain cytoskeletal rigidity. CONCLUSIONS/SIGNIFICANCE: We propose a conceptual mechanotransduction model wherein cell surface glycocalyx HSPGs, in the presence of integrin-mediated cell-matrix adhesions and cytoskeleton organization, sense interstitial flow and activate the FAK-ERK signaling axis, leading to upregulation of MMP expression and cell motility in 3D
Codding, William H.; Lombard, C. K.; Yang, J. Y.
1988-01-01
The Conservative Supra-Characteristic Method (CSCM) Navier-Stokes solver is applied to ascertain the problems inherent in the design of a nominal Mach 14 nozzle for NASA-Ames' 3.5-ft Hypersonic Wind Tunnel; attention is given to the effects of boundary layer cooling systems on the aerodynamic redesign of the nozzle throat region. Complete nozzle flowfields are calculated with and without slot injection of either hot or cold fluid into the boundary layer just upstream of the throat, as well as with alternatively adiabatic and cold walls. The CSCM method is capable of resolving subtle differences in the flows.
Kweon, Jae Ryong
2016-09-01
In this paper, when the initial density has a jump across an interior curve in a bounded domain, we show unique existence, piecewise regularity and jump discontinuity dynamics for the density and the velocity vector governed by the Navier-Stokes equations of compressible viscous barotropic flows. A critical difficulty is in controlling the gradient of the pressure across the jump curve. This is resolved by constructing a vector function associated with the pressure jump value on the convecting curve and extending it to the whole domain.
Numerical Solution of Stokes Flow in a Circular Cavity Using Mesh-free Local RBF-DQ
DEFF Research Database (Denmark)
Kutanaai, S Soleimani; Roshan, Naeem; Vosoughi, A;
2012-01-01
This work reports the results of a numerical investigation of Stokes flow problem in a circular cavity as an irregular geometry using mesh-free local radial basis function-based differential quadrature (RBF-DQ) method. This method is the combination of differential quadrature approximation...... is applied on a two-dimensional geometry. The obtained results from the numerical simulations are compared with those gained by previous works. Outcomes prove that the current technique is in very good agreement with previous investigations and this fact that RBF-DQ method is an accurate and flexible method...... in solution of partial differential equations (PDEs)....
Institute of Scientific and Technical Information of China (English)
Ying-hui ZHANG; Zhong TAN
2011-01-01
In this paper,we are concerned with the asymptotic behaviour of a weak solution to the NavierStokes equations for compressible barotropic flow in two space dimensions with the pressure function satisfying p(ρ) =a(ρ)logd(ρ) for large (ρ).Here d ＞ 2,a ＞ 0.We introduce useful tools from the theory of Orlicz spaces and construct a suitable function which approximates the density for time going to infinity.Using properties of this function,we can prove the strong convergence of the density to its limit state.The behaviour of the velocity field and kinetic energy is also briefly discussed.
Martyr-Koller, R.C.; Kernkamp, H.W.J.; Van Dam, Anne A.; Mick van der Wegen,; Lucas, Lisa; Knowles, N.; Jaffe, B.; Fregoso, T.A.
2017-01-01
A linked modeling approach has been undertaken to understand the impacts of climate and infrastructure on aquatic ecology and water quality in the San Francisco Bay-Delta region. The Delft3D Flexible Mesh modeling suite is used in this effort for its 3D hydrodynamics, salinity, temperature and sediment dynamics, phytoplankton and water-quality coupling infrastructure, and linkage to a habitat suitability model. The hydrodynamic model component of the suite is D-Flow FM, a new 3D unstructured finite-volume model based on the Delft3D model. In this paper, D-Flow FM is applied to the San Francisco Bay-Delta to investigate tidal, seasonal and annual dynamics of water levels, river flows and salinity under historical environmental and infrastructural conditions. The model is driven by historical winds, tides, ocean salinity, and river flows, and includes federal, state, and local freshwater withdrawals, and regional gate and barrier operations. The model is calibrated over a 9-month period, and subsequently validated for water levels, flows, and 3D salinity dynamics over a 2 year period.Model performance was quantified using several model assessment metrics and visualized through target diagrams. These metrics indicate that the model accurately estimated water levels, flows, and salinity over wide-ranging tidal and fluvial conditions, and the model can be used to investigate detailed circulation and salinity patterns throughout the Bay-Delta. The hydrodynamics produced through this effort will be used to drive affiliated sediment, phytoplankton, and contaminant hindcast efforts and habitat suitability assessments for fish and bivalves. The modeling framework applied here will serve as a baseline to ultimately shed light on potential ecosystem change over the current century.
On the validity of the Navier-Stokes equations for nanoscale liquid flows: The role of channel size
Directory of Open Access Journals (Sweden)
Chong Liu
2011-09-01
Full Text Available In this work, we investigate the validity of the Navier-Stokes (NS equations for nanoscale liquid flows through molecular dynamics simulations. We focus on the role of channel size by considering the fluid-wall interaction. Liquid flows between two planar parallel walls driven by an external force with channel size ranging from 2 to 80 nm are studied. The volumetric flux is computed and the dependence of the volumetric flux on the channel size is explained both qualitatively and quantitatively. It is found that the flow is sensitive to the fluid-wall binding energy and the classical fluid mechanics falls apart in small nanochannels. However, the wall effects become insignificant and the NS equations are valid when the channel size is larger than about 150 molecular diameters (∼ 50 nm.
Directory of Open Access Journals (Sweden)
Zhengrong Zhang
2012-01-01
Full Text Available Numerical manifold method was applied to directly solve Navier-Stokes (N-S equations for incompressible viscous flow in this paper, and numerical manifold schemes for N-S equations coupled velocity and pressure were derived based on Galerkin weighted residuals method as well. Mixed cover with linear polynomial function for velocity and constant function for pressure was employed in finite element cover system. As an application, mixed cover 4-node rectangular manifold element has been used to simulate the incompressible viscous flow around a square cylinder in a channel. Numerical tests illustrate that NMM is an effective and high-order accurate numerical method for incompressible viscous flow N-S equations.
Muñoz-Cobo, José; Chiva, Sergio; El Aziz Essa, Mohamed; Mendes, Santos
2012-08-01
Two phase flow experiments with different superficial velocities of gas and water were performed in a vertical upward isothermal cocurrent air-water flow column with conditions ranging from bubbly flow, with very low void fraction, to transition flow with some cap and slug bubbles and void fractions around 25%. The superficial velocities of the liquid and the gas phases were varied from 0.5 to 3 m/s and from 0 to 0.6 m/s, respectively. Also to check the effect of changing the surface tension on the previous experiments small amounts of 1-butanol were added to the water. These amounts range from 9 to 75 ppm and change the surface tension. This study is interesting because in real cases the surface tension of the water diminishes with temperature, and with this kind of experiments we can study indirectly the effect of changing the temperature on the void fraction distribution. The following axial and radial distributions were measured in all these experiments: void fraction, interfacial area concentration, interfacial velocity, Sauter mean diameter and turbulence intensity. The range of values of the gas superficial velocities in these experiments covered the range from bubbly flow to the transition to cap/slug flow. Also with transition flow conditions we distinguish two groups of bubbles in the experiments, the small spherical bubbles and the cap/slug bubbles. Special interest was devoted to the transition region from bubbly to cap/slug flow; the goal was to understand the physical phenomena that take place during this transition A set of numerical simulations of some of these experiments for bubbly flow conditions has been performed by coupling a Lagrangian code, that tracks the three dimensional motion of the individual bubbles in cylindrical coordinates inside the field of the carrier liquid, to an Eulerian model that computes the magnitudes of continuous phase and to a 3D random walk model that takes on account the fluctuation in the velocity field of the
Faizan-Ur-Rab, M.; Zahiri, S. H.; Masood, S. H.; Jahedi, M.; Nagarajah, R.
2017-06-01
This study presents the validation of a developed three-dimensional multicomponent model for cold spray process using two particle image velocimetry (PIV) experiments. The k- ɛ type 3D model developed for spherical titanium particles was validated with the measured titanium particle velocity within a nitrogen and helium supersonic jet. The 3D model predicted lower values of particle velocity than the PIV experimental study that used irregularly shaped titanium particles. The results of the 3D model were consistent with the PIV experiment that used spherical titanium powder. The 3D model simulation of particle velocity within the helium and nitrogen jet was coupled with an estimation of titanium particle temperature. This was achieved with the consideration of the fact that cold spray particle temperature is difficult and expensive to measure due to considerably lower temperature of particles than thermal spray. The model predicted an interesting pattern of particle size distribution with respect to the location of impact with a concentration of finer particles close to the jet center. It is believed that the 3D model outcomes for particle velocity, temperature and location could be a useful tool to optimize system design, deposition process and mechanical properties of the additively manufactured cold spray structures.
Xie, Yifan; Wu, Jichun; Nan, Tongchao; Xue, Yuqun; Xie, Chunhong; Ji, Haifeng
2017-03-01
In this paper, an efficient triple-grid multiscale finite element method (ETMSFEM) is proposed for 3D groundwater simulation in heterogeneous porous media. The main idea of this method is to employ new 3D linear base functions and the domain decomposition technique to solve the local reduced elliptical problem, thereby simplifying the base function construction process and improving the efficiency. Furthermore, by using the ETMSFEM base functions, this method can solve Darcy's equation with high efficiency to obtain a continuous velocity field. Therefore, this method can considerably reduce the computational cost of solving for heads and velocities, which is crucial for large-scale 3D groundwater simulations. In the application section, we present numerical examples to compare the ETMSFEM with several classical methods to demonstrate its efficiency and effectiveness.
Is the water flow more or less than that predicted by the Navier-Stokes equation in micro-orifices?
Hasegawa, Tomiichi; Ushida, Akiomi; Narumi, Takatsune; Goda, Masaki
2016-09-01
Micro-fluid mechanics is an important field in modern fluid mechanics. However, flows through microscale short tubes (micro-orifices) are not yet fully understood. Thus far, experiments on the flow through micro-orifices have been conducted by two methods: the pressure-given method (PGM), in which the pressure is given and the rate of flow is measured, and the flow-given method (FGM), in which the flow rate is given and the pressure is measured. According to conventional fluid mechanics, these two methods should give the same result; however, studies have found lower fluidity (lower flow rate) in PGM and higher fluidity (lower pressure drop) in FGM than that predicted by the Navier-Stokes equation, suggesting that the difference is caused by the method used. To clarify the cause of this difference, we examined the flow of ultra-pure water (UPW) with elapsed time by PGM. UPW was passed through Ni or Ti micro-orifices with 20-μm diameter at applied pressures of 50-1000 Pa. The difference in the shape and material of the orifices did not have a great effect on the flow property. The flow rate was frequently higher than that predicted at the start of the flow experiment; however, it subsequently fell and finally reached zero as time elapsed. This fact suggests that UPW inherently flows at velocities higher than those predicted by the Navier-Stokes equation; however, the flow is then resisted by something that develops over time. We removed an orifice in which flow had stopped from the experimental apparatus, observed it by phase contrast microscope and electron probe micro analyzer, and revealed that a visible membrane, a transparent lattice-like structure, or nothing existed in the orifice. Dissolved air was reduced by deaerating the air from UPW (deaeration), bubbling UPW with Ar (Ar-bubbling), or preventing UPW from contact with air after UPW production (air-prevention). Deaeration, Ar-bubbling, and air-prevention reduced the probability of formation of the visible
A data-driven adaptive Reynolds-averaged Navier-Stokes k-ω model for turbulent flow
Li, Zhiyong; Zhang, Huaibao; Bailey, Sean C. C.; Hoagg, Jesse B.; Martin, Alexandre
2017-09-01
This paper presents a new data-driven adaptive computational model for simulating turbulent flow, where partial-but-incomplete measurement data is available. The model automatically adjusts the closure coefficients of the Reynolds-averaged Navier-Stokes (RANS) k- ω turbulence equations to improve agreement between the simulated flow and the measurements. This data-driven adaptive RANS k- ω (D-DARK) model is validated with 3 canonical flow geometries: pipe flow, backward-facing step, and flow around an airfoil. For all test cases, the D-DARK model improves agreement with experimental data in comparison to the results from a non-adaptive RANS k- ω model that uses standard values of the closure coefficients. For the pipe flow, adaptation is driven by mean stream-wise velocity data from 42 measurement locations along the pipe radius, and the D-DARK model reduces the average error from 5.2% to 1.1%. For the 2-dimensional backward-facing step, adaptation is driven by mean stream-wise velocity data from 100 measurement locations at 4 cross-sections of the flow. In this case, D-DARK reduces the average error from 40% to 12%. For the NACA 0012 airfoil, adaptation is driven by surface-pressure data at 25 measurement locations. The D-DARK model reduces the average error in surface-pressure coefficients from 45% to 12%.
Application of the Poor Man's Navier-Stokes Equations to Real-Time Control of Fluid Flow
Directory of Open Access Journals (Sweden)
James B. Polly
2012-01-01
Full Text Available Control of fluid flow is an important, underutilized process possessing potential benefits ranging from avoidance of separation and stall on aircraft wings to reduction of friction in oil and gas pipelines to mitigation of noise from wind turbines. But the Navier-Stokes (N.-S. equations, whose solutions describe such flows, consist of a system of time-dependent, multidimensional, nonlinear partial differential equations (PDEs which cannot be solved in real time using current computing hardware. The poor man's Navier-Stokes (PMNS equations comprise a discrete dynamical system that is algebraic—hence, easily (and rapidly solved—and yet which retains many (possibly all of the temporal behaviors of the PDE N.-S. system at specific spatial locations. Herein, we outline derivation of these equations and discuss their basic properties. We consider application of these equations to the control problem by adding a control force. We examine the range of behaviors that can be achieved by changing this control force and, in particular, consider controllability of this (nonlinear system via numerical experiments. Moreover, we observe that the derivation leading to the PMNS equations is very general and may be applied to a wide variety of problems governed by PDEs and (possibly time-delay ordinary differential equations such as, for example, models of machining processes.
Directory of Open Access Journals (Sweden)
Jin-feng Zou
2016-01-01
Full Text Available In order to investigate the influence of the intermediate principal stress on the stress and displacement of surrounding rock, a novel approach based on 3D Hoek-Brown (H-B failure criterion was proposed. Taking the strain-softening characteristic of rock mass into account, the potential plastic zone is subdivided into a finite number of concentric annulus and a numerical procedure for calculating the stress and displacement of each annulus was presented. Strains were obtained based on the nonassociated and associated flow rule and 3D plastic potential function. Stresses were achieved by the stress equilibrium equation and generalized Hoek-Brown failure criterion. Using the proposed approach, we can get the solutions of the stress and displacement of the surrounding rock considering the intermediate principal stress. Moreover, the proposed approach was validated with the published results. Compared with the results based on generalized Hoek-Brown failure criterion, it is shown that the plastic radius calculated by 3D Hoek-Brown failure criterion is smaller than those solved by generalized H-B failure criterion, and the influences of dilatancy effect on the results based on the generalized H-B failure criterion are greater than those based on 3D H-B failure criterion. The displacements considering the nonassociated flow rule are smaller than those considering associated flow rules.
DEFF Research Database (Denmark)
Sørensen, Niels N.; Bechmann, Andreas; Réthoré, Pierre-Elouan
2014-01-01
In the present paper, Reynolds-averaged Navier–Stokes predictions of the flow field around the MEXICO rotor in yawed conditions are compared with measurements. The paper illustrates the high degree of qualitative and quantitative agreement that can be obtained for this highly unsteady flow...
Podliński, J.; Kocik, M.; Barbucha, R.; Niewulis, A.; Mizeraczyk, J.; Mizuno, A.
2006-10-01
The results of 3-dimensional (3D) Particle Image Velocimetry (PIV) measurements of the electrohydrodynamic (EHD) flow patterns in a narrow electrostatic precipitator (ESP) are presented in this paper. The ESP was an acrylic parallelepiped with a wire discharge electrode and two plane collecting electrodes. In contrary to typical ESPs the wire electrode was placed along the gas flow, in the ESP centre, in the halfway between collecting electrodes. Either two smooth stainless steel plates or two stainless steel meshes with nylon flocks were used as the collecting electrodes. They were placed on the top and bottom of the ESP. The PIV measurements were carried out in two parallel planes, placed perpendicularly to the collecting electrodes and parallel to the wire electrode. The obtained results showed some similarities and differences of a 3D particle flow in the ESP with plate or flocking electrodes.
Energy Technology Data Exchange (ETDEWEB)
Blanchard, M., E-mail: mathieu.blanchard@ladhyx.polytechnique.fr [LadHyX, CNRS and Ecole Polytechnique, 91128 Palaiseau (France); Schuller, T. [CNRS, UPR 288, Laboratoire d’Energétique Moléculaire et Macroscopique Combustion (EM2C), Grande Voie des Vignes, 92290 Châtenay-Malabry (France); Centrale-Supélec, Grande Voie des Vignes, 92290 Châtenay-Malabry (France); Sipp, D. [ONERA-DAFE, 8 rue des Vertugadins, 92190 Meudon (France); Schmid, P. J. [Department of Mathematics, Imperial College London, London SW7 2AZ (United Kingdom)
2015-04-15
The response of a laminar premixed methane-air flame subjected to flow perturbations around a steady state is examined experimentally and using a linearized compressible Navier-Stokes solver with a one-step chemistry mechanism to describe combustion. The unperturbed flame takes an M-shape stabilized both by a central bluff body and by the external rim of a cylindrical nozzle. This base flow is computed by a nonlinear direct simulation of the steady reacting flow, and the flame topology is shown to qualitatively correspond to experiments conducted under comparable conditions. The flame is then subjected to acoustic disturbances produced at different locations in the numerical domain, and its response is examined using the linearized solver. This linear numerical model then allows the componentwise investigation of the effects of flow disturbances on unsteady combustion and the feedback from the flame on the unsteady flow field. It is shown that a wrinkled reaction layer produces hydrodynamic disturbances in the fresh reactant flow field that superimpose on the acoustic field. This phenomenon, observed in several experiments, is fully interpreted here. The additional perturbations convected by the mean flow stem from the feedback of the perturbed flame sheet dynamics onto the flow field by a mechanism similar to that of a perturbed vortex sheet. The different regimes where this mechanism prevails are investigated by examining the phase and group velocities of flow disturbances along an axis oriented along the main direction of the flow in the fresh reactant flow field. It is shown that this mechanism dominates the low-frequency response of the wrinkled shape taken by the flame and, in particular, that it fully determines the dynamics of the flame tip from where the bulk of noise is radiated.
PSH3D fast Poisson solver for petascale DNS
Adams, Darren; Dodd, Michael; Ferrante, Antonino
2016-11-01
Direct numerical simulation (DNS) of high Reynolds number, Re >= O (105) , turbulent flows requires computational meshes >= O (1012) grid points, and, thus, the use of petascale supercomputers. DNS often requires the solution of a Helmholtz (or Poisson) equation for pressure, which constitutes the bottleneck of the solver. We have developed a parallel solver of the Helmholtz equation in 3D, PSH3D. The numerical method underlying PSH3D combines a parallel 2D Fast Fourier transform in two spatial directions, and a parallel linear solver in the third direction. For computational meshes up to 81923 grid points, our numerical results show that PSH3D scales up to at least 262k cores of Cray XT5 (Blue Waters). PSH3D has a peak performance 6 × faster than 3D FFT-based methods when used with the 'partial-global' optimization, and for a 81923 mesh solves the Poisson equation in 1 sec using 128k cores. Also, we have verified that the use of PSH3D with the 'partial-global' optimization in our DNS solver does not reduce the accuracy of the numerical solution of the incompressible Navier-Stokes equations.
Oliveira, J.L.G.; Geld, van der C.W.M.; Kuerten, J.G.M.
2013-01-01
Three-dimensional particle tracking velocimetry (3D-PTV) measurements have provided accurate Eulerian and Lagrangian high-order statistics of velocity and acceleration fluctuations and correlations at Reynolds number 10,300, based on the bulk velocity and the pipe diameter. Spatial resolution requir
Kuiper, Logan K
2016-01-01
An approximate solution to the two dimensional Navier Stokes equation with periodic boundary conditions is obtained by representing the x any y components of fluid velocity with complex Fourier basis vectors. The chosen space of basis vectors is finite to allow for numerical calculations, but of variable size. Comparisons of the resulting approximate solutions as they vary with the size of the chosen vector space allow for extrapolation to an infinite basis vector space. Results suggest that such a solution, with the full basis vector space and which would give the exact solution, would fail for certain initial velocity configurations when initial velocity and time t exceed certain limits.