A model for transonic plasma flow
Energy Technology Data Exchange (ETDEWEB)
Guazzotto, Luca, E-mail: luca.guazzotto@rochester.edu [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States); Hameiri, Eliezer, E-mail: hameiri@cims.nyu.edu [Courant Institute of Mathematical Sciences, New York University, New York, New York 10012 (United States)
2014-02-15
A linear, two-dimensional model of a transonic plasma flow in equilibrium is constructed and given an explicit solution in the form of a complex Laplace integral. The solution indicates that the transonic state can be solved as an elliptic boundary value problem, as is done in the numerical code FLOW [Guazzotto et al., Phys. Plasmas 11, 604 (2004)]. Moreover, the presence of a hyperbolic region does not necessarily imply the presence of a discontinuity or any other singularity of the solution.
Transonic swirling nozzle flow
Keith, Theo G., Jr.; Pawlas, Gary E.
1991-06-01
A numerical model of viscous transonic swirling flow in axisymmetric nozzles is developed. MacCormack's implicit Gauss-Seidel method is applied to the thin-layer Navier-Stokes equations in transformed coordinates. Numerical results are compared with experimental data to validate the method. The effect of swirl and viscosity on nozzle performance are demonstrated by examining wall pressures, Mach contours, and integral parameters.
Janus Spectra in Two-Dimensional Flows
Liu, Chien-Chia; Cerbus, Rory T.; Chakraborty, Pinaki
2016-09-01
In large-scale atmospheric flows, soap-film flows, and other two-dimensional flows, the exponent of the turbulent energy spectra, α , may theoretically take either of two distinct values, 3 or 5 /3 , but measurements downstream of obstacles have invariably revealed α =3 . Here we report experiments on soap-film flows where downstream of obstacles there exists a sizable interval in which α transitions from 3 to 5 /3 for the streamwise fluctuations but remains equal to 3 for the transverse fluctuations, as if two mutually independent turbulent fields of disparate dynamics were concurrently active within the flow. This species of turbulent energy spectra, which we term the Janus spectra, has never been observed or predicted theoretically. Our results may open up new vistas in the study of turbulence and geophysical flows.
Janus spectra in two-dimensional flows
Liu, Chien-Chia; Chakraborty, Pinaki
2016-01-01
In theory, large-scale atmospheric flows, soap-film flows and other two-dimensional flows may host two distinct types of turbulent energy spectra---in one, $\\alpha$, the spectral exponent of velocity fluctuations, equals $3$ and the fluctuations are dissipated at the small scales, and in the other, $\\alpha=5/3$ and the fluctuations are dissipated at the large scales---but measurements downstream of obstacles have invariably revealed $\\alpha = 3$. Here we report experiments on soap-film flows where downstream of obstacles there exists a sizable interval in which $\\alpha$ has transitioned from $3$ to $5/3$ for the streamwise fluctuations but remains equal to $3$ for the transverse fluctuations, as if two mutually independent turbulent fields of disparate dynamics were concurrently active within the flow. This species of turbulent energy spectra, which we term the Janus spectra, has never been observed or predicted theoretically. Our results may open up new vistas in the study of turbulence and geophysical flows...
Transonic flow theory of airfoils and wings
Energy Technology Data Exchange (ETDEWEB)
Garabedian, P R
1976-01-01
Supercritical wing technology is expected to have a significant influence on the next generation of commercial aircraft. Computational fluid dynamics is playing a central role in the development of new supercritical wing sections. One of the principal tools is a fast and reliable code that simulates two-dimensional wind tunnel data for transonic flow at high Reynolds numbers. This is used widely by industry to assess drag creep and drag rise. Codes for the design of shockless airfoils by the hodograph method have not been so well received because they usually require a lot of trial and error. However, a more advanced mathematical approach makes it possible to assign the pressure as a function of the arc length and then obtain a shockless airfoil that nearly achieves the given distribution of pressure. This tool should enable engineers to design families of transonic airfoils more easily both for airplane wings and for compressor blades in cascade.
Semidirect computations for transonic flow
Swisshelm, J. M.; Adamczyk, J. J.
1983-01-01
A semidirect method, driven by a Poisson solver, was developed for inviscid transonic flow computations. It is an extension of a recently introduced algorithm for solving subsonic rotational flows. Shocks are captured by implementing a form of artificial compressibility. Nonisentropic cases are computed using a shock tracking procedure coupled with the Rankine-Hugoniot relationships. Results are presented for both subsonic and transonic flows. For the test geometry, an unstaggered cascade of 20 percent thick circular arc airfoils at zero angle of attack, shocks are crisply resolved in supercritical situations and the algorithm converges rapidly. In addition, the convergence rate appears to be nearly independent of the entropy and vorticity production at the shock.
Numerical simulation of transonic flows in diffusers
Liou, M.-S.; Coakley, T. J.; Bergmann, M. Y.
1981-01-01
Numerical simulations were made of two-dimensional transonic flows in diffusers, including flow separation induced by a shock or adverse pressure gradient. The mass-averaged, time-dependent, compressible Navier-Stokes equations, simplified by the thin-layer approximation, were solved using MacCormack's hybrid method. The eddy-viscosity formulation was described by the Wilcox-Rubesin's two-equation, k-omega model. Detailed comparison of the computed results with measurements showed good agreement in all cases, including one with massive separation induced by a strong shock. The computation correctly predicted the details of a distinct lambda shock pattern, closely duplicating the configuration observed experimentally in spark-schlieren photographs.
Unsteady transonic flow in cascades
Surampudi, S. P.; Adamczyk, J. J.
1984-01-01
There is a need for methods to predict the unsteady air loads associated with flutter of turbomachinery blading at transonic speeds. The results of such an analysis in which the steady relative flow approaching a cascade of thin airfoils is assumed to be transonic, irrotational, and isentropic is presented. The blades in the cascade are allowed to undergo a small amplitude harmonic oscillation which generates a small unsteady flow superimposed on the existing steady flow. The blades are assumed to oscillate with a prescribed motion of constant amplitude and interblade phase angle. The equations of motion are obtained by linearizing about a uniform flow the inviscid nonheat conducting continuity and momentum equations. The resulting equations are solved by employing the Weiner Hopf technique. The solution yields the unsteady aerodynamic forces acting on the cascade at Mach number equal to 1. Making use of an unsteady transonic similarity law, these results are compared with the results obtained from linear unsteady subsonic and supersonic cascade theories. A parametric study is conducted to find the effects of reduced frequency, solidity, stagger angle, and position of pitching axis on the flutter.
Transonic Investigation of Two-Dimensional Nozzles Designed for Supersonic Cruise
Capone, Francis J.; Deere, Karen A.
2015-01-01
An experimental and computational investigation has been conducted to determine the off-design uninstalled drag characteristics of a two-dimensional convergent-divergent nozzle designed for a supersonic cruise civil transport. The overall objectives were to: (1) determine the effects of nozzle external flap curvature and sidewall boattail variations on boattail drag; (2) develop an experimental data base for 2D nozzles with long divergent flaps and small boattail angles and (3) provide data for correlating computational fluid dynamic predictions of nozzle boattail drag. The experimental investigation was conducted in the Langley 16-Foot Transonic Tunnel at Mach numbers from 0.80 to 1.20 at nozzle pressure ratios up to 9. Three-dimensional simulations of nozzle performance were obtained with the computational fluid dynamics code PAB3D using turbulence closure and nonlinear Reynolds stress modeling. The results of this investigation indicate that excellent correlation between experimental and predicted results was obtained for the nozzle with a moderate amount of boattail curvature. The nozzle with an external flap having a sharp shoulder (no curvature) had the lowest nozzle pressure drag. At a Mach number of 1.2, sidewall pressure drag doubled as sidewall boattail angle was increased from 4deg to 8deg. Reducing the height of the sidewall caused large decreases in both the sidewall and flap pressure drags. Summary
Flow Control in a Transonic Diffuser
Gartner, Jeremy; Amitay, Michael
2014-11-01
In some airplanes such as fighter jets and UAV, short inlet ducts replace the more conventional ducts due to their shorter length. However, these ducts are associated with low length-to-diameter ratio and low aspect ratio and, thus, experience massive separation and the presence of secondary flow structures. These flow phenomena are undesirable as they lead to pressure losses and distortion at the Aerodynamic Interface Plane (AIP), where the engine face is located. It causes the engine to perform with a lower efficiency as it would with a straight duct diffuser. Different flow control techniques were studied on the short inlet duct, with the goal to reattach the flow and minimize the distortions at the AIP. Due to the complex interaction between the separation and the secondary flow structures, the necessity to understand the flow mechanisms, and how to control them at a more fundamental level, a new transonic diffuser with an upper ramp and a straight floor was designed and built. The objective of this project is to explore the effectiveness of different flow control techniques in a high subsonic (up to Mach 0.8) diffuser, so that the quasi two-dimensional separation and the formation of secondary flow structure can be isolated using a canonical flow field. Supported by Northrop Grumman.
Finite elements and finite differences for transonic flow calculations
Hafez, M. M.; Murman, E. M.; Wellford, L. C.
1978-01-01
The paper reviews the chief finite difference and finite element techniques used for numerical solution of nonlinear mixed elliptic-hyperbolic equations governing transonic flow. The forms of the governing equations for unsteady two-dimensional transonic flow considered are the Euler equation, the full potential equation in both conservative and nonconservative form, the transonic small-disturbance equation in both conservative and nonconservative form, and the hodograph equations for the small-disturbance case and the full-potential case. Finite difference methods considered include time-dependent methods, relaxation methods, semidirect methods, and hybrid methods. Finite element methods include finite element Lax-Wendroff schemes, implicit Galerkin method, mixed variational principles, dual iterative procedures, optimal control methods and least squares.
Two dimensional axisymmetric smooth lattice Ricci flow
Brewin, Leo
2015-01-01
A lattice based method will be presented for numerical investigations of Ricci flow. The method will be applied to the particular case of 2-dimensional axially symmetric initial data on manifolds with S^2 topology. Results will be presented that show that the method works well and agrees with results obtained using contemporary finite difference methods.
Steady and unsteady transonic flow
Seegmiller, H. L.; Marvin, J. G.; Levy, L. L., Jr.
1978-01-01
An investigation of the transonic flow over a circular arc airfoil was conducted to obtain basic information for turbulence modeling of shock-induced separated flows and to verify numerical computer codes which are being developed to simulate such flows. The investigation included the employment of a laser velocimeter to obtain data concerning the mean velocity, the shear stress, and the turbulent kinetic energy profiles in the flowfield downstream of the airfoil midchord where the flow features are more complex. Depending on the free-stream Mach number, the flowfield developed was either steady with shock-wave-induced separation extending from the foot of the shock wave to beyond the trailing edge or unsteady with a periodic motion also undergoing shock-induced separation. The experimental data were compared with the results of numerical simulations in which a computer code was employed that solved the time-dependent Reynolds' averaged compressible Navier-Stokes equations.
Mohan, S. R.
1983-01-01
This thesis is divided into, two distinct parts. Part I describes the design and development of an intermittent cryogenic wind-tunnel, in which the cold conditions are generated by the expansion of high pressure gas. The device uses a light piston moving in a tube and conditions during the running time are maintained constant by 'tuning' the piston motion, i. e. by Imatchingt the volumetric flow rate entering and leaving the tube. The results of the pilot tunnel (running tim...
On the use of wall functions as boundary conditions for two-dimensional separated compressible flows
Viegas, J. R.; Rubesin, M. W.; Horstman, C. C.
1985-01-01
A new and improved wall function method for compressible turbulent flows has been developed and tested. This method is applicable to attached and separated flows, to both high- and low-Reynolds number flows, and to flows with adiabatic and nonadiabatic surfaces. This wall function method has been applied to the Launder-Spalding k-epsilon two-equation model of turbulence. The tests consist of comparisons of calculated and experimental results for: (1) an axisymmetrical transonic shock-wave/boundary-wave interaction flow at low Reynolds number in an adiabatic tube, (2) an axisymmetrical high-Reynolds number transonic flow over a nonadiabatic bump, and (3) a two-dimensional supersonic high-Reynolds number flow on a nonadiabatic deflected flap. Each of these experiments had significant regions of flow separation. The calculations are performed with an implicit algorithm that solves the Reynolds-averaged Navier-Stokes equations. It is shown that the results obtained agree very well with the data for the complex compressible flows tested.
Unsteady transonic flow over cascade blades
Surampudi, S. P.; Adamczyk, J. J.
1986-01-01
An attempt is made to develop an efficient staggered cascade blade unsteady aerodynamics model for the neighborhood of March 1, representing the blade row by a rectilinear two-dimensional cascade of thin, flat plate airfoils. The equations of motion are derived on the basis of linearized transonic small perturbation theory, and an analytical solution is obtained by means of the Wiener-Hopf procedure. Making use of the transonic similarity law, the results obtained are compared with those of other linearized cascade analyses. A parametric study is conducted to find the effects of reduced frequency, stagger angle, solidity, and the location of the pitching axis on cascade stability.
Phase separation under two-dimensional Poiseuille flow.
Kiwata, H
2001-05-01
The spinodal decomposition of a two-dimensional binary fluid under Poiseuille flow is studied by numerical simulation. We investigated time dependence of domain sizes in directions parallel and perpendicular to the flow. In an effective region of the flow, the power-law growth of a characteristic length in the direction parallel to the flow changes from the diffusive regime with the growth exponent alpha=1/3 to a new regime. The scaling invariance of the growth in the perpendicular direction is destroyed after the diffusive regime. A recurrent prevalence of thick and thin domains which determines log-time periodic oscillations has not been observed in our model. The growth exponents in the infinite system under two-dimensional Poiseuille flow are obtained by the renormalization group.
Dynamics of vortex interactions in two-dimensional flows
DEFF Research Database (Denmark)
Juul Rasmussen, J.; Nielsen, A.H.; Naulin, V.
2002-01-01
a critical value, a(c). Using the Weiss-field, a(c) is estimated for vortex patches. Introducing an effective radius for vortices with distributed vorticity, we find that 3.3 a(c) ...The dynamics and interaction of like-signed vortex structures in two dimensional flows are investigated by means of direct numerical solutions of the two-dimensional Navier-Stokes equations. Two vortices with distributed vorticity merge when their distance relative to their radius, d/R-0l. is below...
Numerical Study of Two-Dimensional Viscous Flow over Dams
Institute of Scientific and Technical Information of China (English)
王利兵; 刘宇陆; 涂敏杰
2003-01-01
In this paper, the characteristics of two-dimensional viscous flow over two dams were numerically investigated. The results show that the behavior of the vortices is closely related to the space between two dams, water depth, Fr number and Reynolds number. In addition, the flow properties behind each dam are different, and the changes over two dams are more complex than over one dam. Finally, the relevant turbulent characteristics were analyzed.
Hot-wire anemometry in transonic flow
Horstman, C. C.; Rose, W. C.
1977-01-01
The use of hot-wire anemometry for obtaining fluctuating data in transonic flows has been evaluated. From hot-wire heat loss correlations based on previous transonic data, the sensitivity coefficients for velocity, density, and total temperature fluctuations have been calculated for a wide range of test conditions and sensor parameters. For sensor Reynolds number greater than 20 and high sensor overheat ratios, the velocity sensitivity remains independent of Mach number and equal to the density sensitivity. These conditions were verified by comparisons of predicted sensitivities with those from recent direct calibrations in transonic flows. Based on these results, techniques are presented to obtain meaningful measurements of fluctuating velocity, density, and Reynolds shear stress using hot-wire and hot-film anemometers. Example of these measurements are presented for two transonic boundary layers.
Hot wire anemometry in transonic flow
Horstman, C. C.; Rose, W. C.
1975-01-01
The use of hot-wire anemometry for obtaining fluctuating data in transonic flows has been evaluated. From hot-wire heat loss correlations based on previous transonic data, the sensitivity coefficients for velocity, density, and total temperature fluctuations have been calculated for a wide range of test conditions and sensor parameters. For sensor Reynolds numbers greater than 20 and high sensor overheat ratios, the velocity sensitivity remains independent of Mach number and equal to the density sensitivity. These conclusions were verified by comparisons of predicted sensitivities with those from recent direct calibrations in transonic flows. Based on these results, techniques are presented to obtain meaningful measurements of fluctuating velocity, density, and Reynolds shear stress using hot-wire and hot-film anemometers. Examples of these measurements are presented for two transonic boundary layers.
Mean flow generation in rotating anelastic two-dimensional convection
Currie, Laura K
2016-01-01
We investigate the processes that lead to the generation of mean flows in two-dimensional anelastic convection. The simple model consists of a plane layer that is rotating about an axis inclined to gravity. The results are two-fold: firstly we numerically investigate the onset of convection in three-dimensions, paying particular attention to the role of stratification and highlight a curious symmetry. Secondly, we investigate the mechanisms that drive both zonal and meridional flows in two dimensions. We find that, in general, non-trivial Reynolds stresses can lead to systematic flows and, using statistical measures, we quantify the role of stratification in modifying the coherence of these flows.
Statistical mechanics of two-dimensional and geophysical flows
Bouchet, Freddy
2011-01-01
The theoretical study of the self-organization of two-dimensional and geophysical turbulent flows is addressed based on statistical mechanics methods. This review is a self-contained presentation of classical and recent works on this subject; from the statistical mechanics basis of the theory up to applications to Jupiter's troposphere and ocean vortices and jets. Emphasize has been placed on examples with available analytical treatment in order to favor better understanding of the physics and dynamics. The equilibrium microcanonical measure is built from the Liouville theorem. On this theoretical basis, we predict the output of the long time evolution of complex turbulent flows as statistical equilibria. This is applied to make quantitative models of two-dimensional turbulence, the Great Red Spot and other Jovian vortices, ocean jets like the Gulf-Stream, and ocean vortices. We also present recent results for non-equilibrium situations, for the studies of either the relaxation towards equilibrium or non-equi...
Two Dimensional Lattice Boltzmann Method for Cavity Flow Simulation
Directory of Open Access Journals (Sweden)
Panjit MUSIK
2004-01-01
Full Text Available This paper presents a simulation of incompressible viscous flow within a two-dimensional square cavity. The objective is to develop a method originated from Lattice Gas (cellular Automata (LGA, which utilises discrete lattice as well as discrete time and can be parallelised easily. Lattice Boltzmann Method (LBM, known as discrete Lattice kinetics which provide an alternative for solving the Navier–Stokes equations and are generally used for fluid simulation, is chosen for the study. A specific two-dimensional nine-velocity square Lattice model (D2Q9 Model is used in the simulation with the velocity at the top of the cavity kept fixed. LBM is an efficient method for reproducing the dynamics of cavity flow and the results which are comparable to those of previous work.
AN APPROACH IN MODELING TWO-DIMENSIONAL PARTIALLY CAVITATING FLOW
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
An approach of modeling viscosity, unsteady partially cavitating flows around lifting bodies is presented. By employing an one-fluid Navier-Stokers solver, the algorithm is proved to be able to handle two-dimensional laminar cavitating flows at moderate Reynolds number. Based on the state equation of water-vapor mixture, the constructive relations of densities and pressures are established. To numerically simulate the cavity wall, different pseudo transition of density models are presumed. The finite-volume method is adopted and the algorithm can be extended to three-dimensional cavitating flows.
Phase Transitions in Two-Dimensional Traffic Flow Models
Cuesta, J A; Molera, J M; Cuesta, José A; Martinez, Froilán C; Molera, Juan M
1993-01-01
Abstract: We introduce two simple two-dimensional lattice models to study traffic flow in cities. We have found that a few basic elements give rise to the characteristic phase diagram of a first-order phase transition from a freely moving phase to a jammed state, with a critical point. The jammed phase presents new transitions corresponding to structural transformations of the jam. We discuss their relevance in the infinite size limit.
Phase Transitions in Two-Dimensional Traffic Flow Models
Cuesta, José A; Molera, Juan M; Escuela, Angel Sánchez; 10.1103/PhysRevE.48.R4175
2009-01-01
We introduce two simple two-dimensional lattice models to study traffic flow in cities. We have found that a few basic elements give rise to the characteristic phase diagram of a first-order phase transition from a freely moving phase to a jammed state, with a critical point. The jammed phase presents new transitions corresponding to structural transformations of the jam. We discuss their relevance in the infinite size limit.
ANALYSIS OF TRANSONIC FLOW PAST CUSPED AIRFOILS
Directory of Open Access Journals (Sweden)
Jiří Stodůlka
2015-06-01
Full Text Available Transonic flow past two cusped airfoils is numerically solved and achieved results are analyzed by means of flow behavior and oblique shocks formation.Regions around sharp trailing edges are studied in detail and parameters of shock waves are solved and compared using classical shock polar approach and verified by reduction parameters for symmetric configurations.
Nonclassical Symmetry Analysis of Heated Two-Dimensional Flow Problems
Naeem, Imran; Naz, Rehana; Khan, Muhammad Danish
2015-12-01
This article analyses the nonclassical symmetries and group invariant solution of boundary layer equations for two-dimensional heated flows. First, we derive the nonclassical symmetry determining equations with the aid of the computer package SADE. We solve these equations directly to obtain nonclassical symmetries. We follow standard procedure of computing nonclassical symmetries and consider two different scenarios, ξ1≠0 and ξ1=0, ξ2≠0. Several nonclassical symmetries are reported for both scenarios. Furthermore, numerous group invariant solutions for nonclassical symmetries are derived. The similarity variables associated with each nonclassical symmetry are computed. The similarity variables reduce the system of partial differential equations (PDEs) to a system of ordinary differential equations (ODEs) in terms of similarity variables. The reduced system of ODEs are solved to obtain group invariant solution for governing boundary layer equations for two-dimensional heated flow problems. We successfully formulate a physical problem of heat transfer analysis for fluid flow over a linearly stretching porous plat and, with suitable boundary conditions, we solve this problem.
Epi-two-dimensional flow and generalized enstrophy
Yoshida, Zensho
2016-01-01
The conservation of the enstrophy ($L^2$ norm of the vorticity $\\omega$) plays an essential role in the physics and mathematics of two-dimensional (2D) Euler fluids. Generalizing to compressible ideal (inviscid and barotropic) fluids, the generalized enstrophy $\\int_{\\Sigma(t)} f(\\omega/\\rho)\\rho\\, d^2 x$, ($f$ an arbitrary smooth function, $\\rho$ the density, and $\\Sigma(t)$ an arbitrary 2D domain co-moving with the fluid) is a constant of motion, and plays the same role. On the other hand, for the three-dimensional (3D) ideal fluid, the helicity $\\int_{M} {V}\\cdot\\omega\\,d^3x$, ($V$ the flow velocity, $\\omega=\
Flow of foams in two-dimensional disordered porous media
Dollet, Benjamin; Geraud, Baudouin; Jones, Sian A.; Meheust, Yves; Cantat, Isabelle; Institut de Physique de Rennes Team; Geosciences Rennes Team
2015-11-01
Liquid foams are a yield stress fluid with elastic properties. When a foam flow is confined by solid walls, viscous dissipation arises from the contact zones between soap films and walls, giving very peculiar friction laws. In particular, foams potentially invade narrow pores much more efficiently than Newtonian fluids, which is of great importance for enhanced oil recovery. To quantify this effect, we study experimentally flows of foam in a model two-dimensional porous medium, consisting of an assembly of circular obstacles placed randomly in a Hele-Shaw cell, and use image analysis to quantify foam flow at the local scale. We show that bubbles split as they flow through the porous medium, by a mechanism of film pinching during contact with an obstacle, yielding two daughter bubbles per split bubble. We quantify the evolution of the bubble size distribution as a function of the distance along the porous medium, the splitting probability as a function of bubble size, and the probability distribution function of the daughter bubbles. We propose an evolution equation to model this splitting phenomenon and compare it successfully to the experiments, showing how at long distance, the porous medium itself dictates the size distribution of the foam.
ACCRETION DISKS IN TWO-DIMENSIONAL HOYLE-LYTTLETON FLOW
Energy Technology Data Exchange (ETDEWEB)
Blondin, John M., E-mail: John_Blondin@ncsu.edu [Department of Physics, North Carolina State University, Raleigh, NC 27695-8202 (United States)
2013-04-20
We investigate the flip-flop instability observed in two-dimensional planar hydrodynamic simulations of Hoyle-Lyttleton accretion in the case of an accreting object with a radius much smaller than the nominal accretion radius, as one would expect in astrophysically relevant situations. Contrary to previous results with larger accretors, accretion from a homogenous medium onto a small accretor is characterized by a robust, quasi-Keplerian accretion disk. For gas with a ratio of specific heats of 5/3, such a disk remains locked in one direction for a uniform ambient medium. The accretion flow is more variable for gas with a ratio of specific heats of 4/3, with more dynamical interaction of the disk flow with the bow shock leading to occasional flips in the direction of rotation of the accretion disk. In both cases the accretion of angular momentum is determined by the flow pattern behind the accretion shock rather than by the parameters of the upstream flow.
Thin films flowing down inverted substrates: two dimensional flow
Lin, Te-sheng
2009-01-01
We consider free surface instabilities of films flowing on inverted substrates within the framework of lubrication approximation. We allow for the presence of fronts and related contact lines, and explore the role which they play in instability development. It is found that a contact line, modeled by a commonly used precursor film model, leads to free surface instabilities of convective type without any additional natural or excited perturbations. A single parameter D=(3Ca)^{1/3}cot\\alpha, where Ca is the capillary number and \\alpha is the inclination angle, is identified as a governing parameter in the problem. This parameter may be interpreted to reflect the combined effect of inclination angle, film thickness, Reynolds number and the fluid flux. Variation of D leads to change of the wave-like properties of the instabilities, allowing to observe traveling wave behavior, mixed waves, and the waves resembling solitary ones.
Recent developments of axial flow compressors under transonic flow conditions
Srinivas, G.; Raghunandana, K.; Satish Shenoy, B.
2017-05-01
The objective of this paper is to give a holistic view of the most advanced technology and procedures that are practiced in the field of turbomachinery design. Compressor flow solver is the turbulence model used in the CFD to solve viscous problems. The popular techniques like Jameson’s rotated difference scheme was used to solve potential flow equation in transonic condition for two dimensional aero foils and later three dimensional wings. The gradient base method is also a popular method especially for compressor blade shape optimization. Various other types of optimization techniques available are Evolutionary algorithms (EAs) and Response surface methodology (RSM). It is observed that in order to improve compressor flow solver and to get agreeable results careful attention need to be paid towards viscous relations, grid resolution, turbulent modeling and artificial viscosity, in CFD. The advanced techniques like Jameson’s rotated difference had most substantial impact on wing design and aero foil. For compressor blade shape optimization, Evolutionary algorithm is quite simple than gradient based technique because it can solve the parameters simultaneously by searching from multiple points in the given design space. Response surface methodology (RSM) is a method basically used to design empirical models of the response that were observed and to study systematically the experimental data. This methodology analyses the correct relationship between expected responses (output) and design variables (input). RSM solves the function systematically in a series of mathematical and statistical processes. For turbomachinery blade optimization recently RSM has been implemented successfully. The well-designed high performance axial flow compressors finds its application in any air-breathing jet engines.
Intermittent Flow Regimes in a Transonic Fan Airfoil Cascade
Directory of Open Access Journals (Sweden)
J. Lepicovsky
2004-01-01
velocity.To date, this flow behavior has only been observed in a linear transonic cascade. Further research is necessary to confirm this phenomenon occurs in actual transonic fans and is not the by-product of an endwall restricted linear cascade.
Unsteady separated boundary layer in a transonic diffuser flow with self-excited oscillations
Hsieh, T.; Coakley, T. J.
1986-01-01
A numerical investigation of two-dimensional unsteady boundary layer in a transonic diffuser flow with self-excited oscillations and strong flow separation by solving the compressible, Reynolds-averaged, thin-layer Navier-Stokes equations with two-equations turbulence model is described. Three different meshes with constant streamwise mesh distribution and varying vertical mesh distribution were used. Results obtained indicate that a refinement of mesh studied here has minimal effect on the mean boundary layer flow but significantly increases the amplitude of oscillation of all flow variables. Comparisons of unsteady wall pressure, velocity profile, terminal shock, and separation pocket among computations and with experiment are presented.
The two-dimensional Godunov scheme and what it means for macroscopic pedestrian flow models
Van Wageningen-Kessels, F.L.M.; Daamen, W.; Hoogendoorn, S.P.
2015-01-01
An efficient simulation method for two-dimensional continuum pedestrian flow models is introduced. It is a two-dimensional and multi-class extension of the Go-dunov scheme for one-dimensional road traffic flow models introduced in the mid 1990’s. The method can be applied to continuum pedestrian flo
Elliptic Length Scales in Laminar, Two-Dimensional Supersonic Flows
2015-06-01
adiabatic wall flows over compression ramps and flows with shock impingements. The new correlations are derived from existing numerical data and...developed for 2D, laminar adiabatic wall flows over compression ramps and flows with shock impingements. These correlations are derived from existing...characterizing the influence of shocks and compression ramps on flat plate flows is presented. New correlations for laminar compressive interactions on
Flow Modelling for partially Cavitating Two-dimensional Hydrofoils
DEFF Research Database (Denmark)
Krishnaswamy, Paddy
2001-01-01
The present work addresses te computational analysis of partial sheet hydrofoil cavitation in two dimensions. Particular attention is given to the method of simulating the flow at the end of the cavity. A fixed-length partially cavitating panel method is used to predict the height of the re...... of the model and comparing the present calculations with numerical results. The flow around the partially cavitating hydrofoil with a re-entrant jet has also been treated with a viscous/inviscid interactive method. The viscous flow model is based on boundary layer theory applied on the compound foil......, consisting of the union of the cavity and the hydrofoil surface. The change in the flow direction in the cavity closure region is seen to have a slightly adverse effect on the viscous pressure distribution. Otherwise, it is seen that the viscous re-entrant jet solution compares favourably with experimental...
Two-Dimensional Turbulent Separated Flow. Volume 1
1985-06-01
of detached turbulent boundary layers, even when the sign of U is changed to account for mean backflows. Thus, earlier researchers, such as Kuhn and...Turbulent Shear Layer," Third Symposium on Turbulent Shear Flows, pp. 16.23-16.29. Hillier, R., Latour , M.E.M.P., and Cherry, N.J. (1983), "Unsteady...344. Kuhn , G.D. and Nielsen, J.N. (1971), "An Analytical Method for Calculating Turbulent Separated Flows Due to Adverse Pressure Gradients
Bubbly flows around a two-dimensional circular cylinder
Lee, Jubeom; Park, Hyungmin
2016-11-01
Two-phase cross flows around a bluff body occur in many thermal-fluid systems like steam generators, heat exchangers and nuclear reactors. However, our current knowledge on the interactions among bubbles, bubble-induced flows and the bluff body are limited. In the present study, the gas-liquid bubbly flows around a solid circular cylinder are experimentally investigated while varying the mean void fraction from 5 to 27%. The surrounding liquid (water) is initially static and the liquid flow is only induced by the air bubbles. For the measurements, we use the high-speed two-phase particle image velocimetry techniques. First, depending on the mean void fraction, two regimes are classified with different preferential concentration of bubbles in the cylinder wake, which are explained in terms of hydrodynamic force balances acting on rising bubbles. Second, the differences between the two-phase and single-phase flows (while matching their Reynolds numbers) around a circular cylinder will be discussed in relation to effects of bubble dynamics and the bubble-induced turbulence on the cylinder wake. Supported by a Grant (MPSS-CG-2016-02) through the Disaster and Safety Management Institute funded by Ministry of Public Safety and Security of Korean government.
Two-dimensional nonlinear travelling waves in magnetohydrodynamic channel flow
Hagan, Jonathan
2013-01-01
The present study is concerned with the stability of a flow of viscous conducting liquid driven by pressure gradient in the channel between two parallel walls subject to a transverse magnetic field. Although the magnetic field has a strong stabilizing effect, this flow, similarly to its hydrodynamic counterpart -- plane Poiseuille flow, is known to become turbulent significantly below the threshold predicted by linear stability theory. We investigate the effect of the magnetic field on 2D nonlinear travelling-wave states which are found at substantially subcritical Reynolds numbers starting from $Re_n=2939$ without the magnetic field and from $Re_n\\sim6.50\\times10^3Ha$ in a sufficiently strong magnetic field defined by the Hartmann number $Ha.$ Although the latter value is by a factor of seven lower than the linear stability threshold $Re_l\\sim4.83\\times10^4Ha$,it is still more by an order of magnitude higher than the experimentally observed value for the onset of turbulence in this flow.
Hsieh, T.
1986-10-01
Investigation of downstream boundary effects on the frequency of self-excited oscillations in two-dimensional, separated transonic diffuser flows were conducted numerically by solving the compressible, Reynolds-averaged, thin-layer Navier-Stokes equation with two equation turbulence models. It was found that the flow fields are very sensitive to the location of the downstream boundary. Extension of the diffuser downstream boundary significantly reduces the frequency and amplitude of oscillations for pressure, velocity, and shock. The existence of a suction slot in the experimental setpup obscures the physical downstream boundary and therefore presents a difficulty for quantitative comparisons between computation and experiment.
Two-Dimensional Graphs Moving by Mean Curvature Flow
Institute of Scientific and Technical Information of China (English)
CHEN Jing Yi; LI Jia Yu; TIAN Gang
2002-01-01
A surface Σ is a graph in R4 if there is a unit constant 2-form ω on R4 such that initial surface, then the mean curvature flow has a global solution and the scaled surfaces converge to a self-similar solution. A surface ∑ is a graph in M1 × M2 where M1 and M2 are Riemann surfaces,surface with scalar curvature R, v0 ≥1/√2 on the initial surface, then the mean curvature flow has a global solution and it sub-converges to a minimal surface, if, in addition, R ≥ 0 it converges to a totally geodesic surface which is holomorphic.
Two dimensional RG flows and Yang-Mills instantons
Gava, Edi; Narain, K S
2010-01-01
We study RG flow solutions in (1,0) six dimensional supergravity coupled to an anti-symmetric tensor and Yang-Mills multiplets corresponding to a semisimple group $G$. We turn on $G$ instanton gauge fields, with instanton number $N$, in the conformally flat part of the 6D metric. The solution interpolates between two (4,0) supersymmetric $AdS_3\\times S^3$ backgrounds with two different values of $AdS_3$ and $S^3$ radii and describes an RG flow in the dual 2D SCFT. For the single instanton case and $G=SU(2)$, there exist a consistent reduction ansatz to three dimensions, and the solution in this case can be interpreted as an uplifted 3D solution. Correspondingly, we present the solution in the framework of N=4 $(SU(2)\\ltimes \\mathbf{R}^3)^2$ three dimensional gauged supergravity. The flows studied here are of v.e.v. type, driven by a vacuum expectation value of a (not exactly) marginal operator of dimension two in the UV. We give an interpretation of the supergravity solution in terms of the D1/D5 system in ty...
Efficient solution of two-dimensional steady separated flows
Napolitano, M.
This work is concerned with the numerical solution of 2D incompressible steady laminar separated flows at moderate-to-high values of Re. The vorticity-stream function Navier-Stokes equations, as well as approximate models based upon the boundary-layer theory, will be considered. The main objective of the paper is to present the development of an efficient approach for solving a class of problems usually referred to as high Re weakly separated flows. A description is given of a block-alternating-direction-implicit method, which applies the approximate factorization scheme of Beam and Warming to the vorticity-stream function equations, using the delta form of the deferred correction procedure of Khosla and Rubin to combine the stability of upwind schemes with the accuracy of central differences. The logical steps which led to the development of a more efficient incremental block-line Gauss-Seidel method and to a simple multigrid strategy particularly suited for this kind of numerical scheme are then outlined. Finally, benchmark-quality solutions for separated flows inside diffusers and channels with smooth as well as sudden expansions are presented.
Pfeiffer, F.; Meyer-Koenig, W.
1949-01-01
By means of characteristics theory, formulas for the numerical treatment of stationary compressible supersonic flows for the two-dimensional and rotationally symmetrical cases have been obtained from their differential equations.
Wu, Chung-Hua
1993-01-01
This report represents a general theory applicable to axial, radial, and mixed flow turbomachines operating at subsonic and supersonic speeds with a finite number of blades of finite thickness. References reflect the evolution of computational methods used, from the inception of the theory in the 50's to the high-speed computer era of the 90's. Two kinds of relative stream surfaces, S(sub 1) and S(sub 2), are introduced for the purpose of obtaining a three-dimensional flow solution through the combination of two-dimensional flow solutions. Nonorthogonal curvilinear coordinates are used for the governing equations. Methods of computing transonic flow along S(sub 1) and S(sub 2) stream surfaces are given for special cases as well as for fully three-dimensional transonic flows. Procedures pertaining to the direct solutions and inverse solutions are presented. Information on shock wave locations and shapes needed for computations are discussed. Experimental data from a Deutsche Forschungs- und Versuchsanstalt fur Luft- und Raumfahrt e.V. (DFVLR) rotor and from a Chinese Academy of Sciences (CAS) transonic compressor rotor are compared with the computed flow properties.
Blast shocks in quasi-two-dimensional supersonic granular flows.
Boudet, J F; Cassagne, J; Kellay, H
2009-11-27
In a thin, dilute, and fast flowing granular layer, the impact of a small sphere generates a fast growing hole devoid of matter. The growth of this hole is studied in detail, and its dynamics is found to mimic that of blast shocks in gases. This dynamics can be decomposed into two stages: a fast initial stage (the blast) and a slower growth regime whose growth velocity is given by the speed of sound in the medium used. A simple model using ingredients already invoked for the case of blast shocks in gases but including the inelastic nature of collisions between grains accounts accurately for our results. The system studied here allows for a detailed study of the full dynamics of a blast as it relaxes from a strong to a weak shock and later to an acoustic disturbance.
Topology of streamlines and vorticity contours for two - dimensional flows
DEFF Research Database (Denmark)
Andersen, Morten
Considering a coordinate-free formulation of helical symmetry rather than more traditional definitions based on coordinates, we discuss basic properties of helical vector fields and compare results from the literature. For inviscid flow where a velocity field is generated by a sum of helical vortex...... generated by a helical vortex filament in an ideal fluid. The classical expression for the stream function obtained by Hardin (Phys. Fluids 25, 1982) contains an infinite sum of modified Bessel functions. Using the approach by Okulov (Russ. J. Eng. Thermophys. 5, 1995) we obtain a closed-form approximation...... by a point vortex above a wall in inviscid fluid. There is no reason to a priori expect equivalent results of the three vortex definitions. However, the study is mainly motivated by the findings of Kudela & Malecha (Fluid Dyn. Res. 41, 2009) who find good agreement between the vorticity and streamlines...
Renouf, M.; Bonamy, D.; Dubois, F.; Alart, P.
2005-10-01
The rheology of two-dimensional steady surface flow of cohesionless cylinders in a rotating drum is investigated through nonsmooth contact dynamics simulations. Profiles of volume fraction, translational and angular velocity, rms velocity, strain rate, and stress tensor are measured at the midpoint along the length of the surface-flowing layer, where the flow is generally considered as steady and homogeneous. Analysis of these data and their interrelations suggest the local inertial number—defined as the ratio between local inertial forces and local confinement forces—to be the relevant dimensionless parameter to describe the transition from the quasistatic part of the packing to the flowing part at the surface of the heap. Variations of the components of the stress tensor as well as the ones of rms velocity as a function of the inertial number are analyzed within both the quasistatic and the flowing phases. Their implications are discussed.
Stability of a Two-Dimensional Poiseuille-Type Flow for a Viscoelastic Fluid
Endo, Masakazu; Giga, Yoshikazu; Götz, Dario; Liu, Chun
2017-03-01
A viscoelastic flow in a two-dimensional layer domain is considered. An L 2-stability of the Poiseuille-type flow is established provided that both Poiseuille flow and perturbation is sufficiently small. Our analysis is based on a stream function formulation introduced by Lin et al. (Commun Pure Appl Math 58(11):1437-1471, 2005).
Numerical studies of transverse curvature effects on transonic flow stability
Macaraeg, M. G.; Daudpota, Q. I.
1992-01-01
A numerical study of transverse curvature effects on compressible flow temporal stability for transonic to low supersonic Mach numbers is presented for axisymmetric modes. The mean flows studied include a similar boundary-layer profile and a nonsimilar axisymmetric boundary-layer solution. The effect of neglecting curvature in the mean flow produces only small quantitative changes in the disturbance growth rate. For transonic Mach numbers (1-1.4) and aerodynamically relevant Reynolds numbers (5000-10,000 based on displacement thickness), the maximum growth rate is found to increase with curvature - the maximum occurring at a nondimensional radius (based on displacement thickness) between 30 and 100.
DEFF Research Database (Denmark)
Ruban, V.P.; Senchenko, Sergey
2004-01-01
The evolution of piecewise constant distributions of a conserved quantity related to the frozen-in canonical vorticity in effectively two-dimensional incompressible ideal EMHD flows is analytically investigated by the Hamiltonian method. The study includes the case of axisymmetric flows with zero...
Computation of two-dimensional isothermal flow in shell-and-tube heat exchangers
Energy Technology Data Exchange (ETDEWEB)
Carlucci, L.N.; Galpin, P.F.; Brown, J.D.; Frisina, V.
1983-07-01
A computational procedure is outlined whereby two-dimensional isothermal shell-side flow distributions can be calculated for tube bundles having arbitrary boundaries and flow blocking devices, such as sealing strips, defined in arbitrary locations. The procedure is described in some detail and several computed results are presented to illustrate the robustness and generality of the method. 11 figs.
Intermittent Flow Regimes in a Transonic Fan Airfoil Cascade
Lepicovsky, J.; McFarland, E. R.; Chima, R. V.; Capece, V. R.; Hayden, J.
2002-01-01
A study was conducted in the NASA Glenn Research Center linear cascade on the intermittent flow on the suction surface of an airfoil section from the tip region of a modern low aspect ratio fan blade. Experimental results revealed that, at a large incidence angle, a range of transonic inlet Mach numbers exist where the leading-edge shock-wave pattern was unstable. Flush mounted high frequency response pressure transducers indicated large local jumps in the pressure in the leading edge area, which generates large intermittent loading on the blade leading edge. These measurements suggest that for an inlet Mach number between 0.9 and 1.0 the flow is bi-stable, randomly switching between subsonic and supersonic flows. Hence, it appears that the change in overall flow conditions in the transonic region is based on the frequency of switching between two stable flow states rather than on the continuous increase of the flow velocity. To date, this flow behavior has only been observed in a linear transonic cascade. Further research is necessary to confirm this phenomenon occurs in actual transonic fans and is not the byproduct of an endwall restricted linear cascade.
Design considerations for pulsed-flow comprehensive two-dimensional GC: dynamic flow model approach.
Harvey, Paul McA; Shellie, Robert A; Haddad, Paul R
2010-04-01
A dynamic flow model, which maps carrier gas pressures and carrier gas flow rates through the first dimension separation column, the modulator sample loop, and the second dimension separation column(s) in a pulsed-flow modulation comprehensive two-dimensional gas chromatography (PFM-GCxGC) system is described. The dynamic flow model assists design of a PFM-GCxGC modulator and leads to rapid determination of pneumatic conditions, timing parameters, and the dimensions of the separation columns and connecting tubing used to construct the PFM-GCxGC system. Three significant innovations are introduced in this manuscript, which were all uncovered by using the dynamic flow model. A symmetric flow path modulator improves baseline stability, appropriate selection of the flow restrictors in the first dimension column assembly provides a generally more stable and robust system, and these restrictors increase the modulation period flexibility of the PFM-GCxGC system. The flexibility of a PFM-GCxGC system resulting from these innovations is illustrated using the same modulation interface to analyze Special Antarctic Blend (SAB) diesel using 3 s and 9 s modulation periods.
New insight into flow development and two dimensionality of turbulent channel flows
Vinuesa, Ricardo; Bartrons, Eduard; Chiu, Daniel; Dressler, Kristofer M.; Rüedi, J.-D.; Suzuki, Yasumasa; Nagib, Hassan M.
2014-06-01
The experimental conditions required for a turbulent channel flow to be considered fully developed and nominally two dimensional remain a challenging objective. In this study, we show that the flow obtained in a high-aspect-ratio channel facility cannot be reproduced by direct numerical simulations (DNSs) of spanwise-periodic channel flows; therefore, we reserve the term "channel" for spanwise-periodic DNSs and denote the experimental flow by the term "duct." Oil film interferometry (OFI) and static pressure measurements were carried out over the range in an adjustable-geometry duct flow facility. Three-dimensional effects were studied by considering different aspect ratio (AR) configurations and also by fixing the AR and modifying the hydraulic diameter of the section. The conditions at the centerplane of the duct were characterized through the local skin friction from the OFI and the centerline velocity at four different streamwise locations and through the wall shear based on the streamwise global pressure gradient. The skin friction obtained from pressure gradient overestimated the local shear measurements obtained from the OFI and did not reproduce the same AR dependence observed with OFI. Differences between the local and global techniques were also reflected in the flow development. For the range of Reynolds numbers tested, the development length of high-aspect-ratio ducts scales with the duct full-height and is around , much larger than the values of around 100-150 H previously reported in the literature.
Interaction of two-dimensional turbulence with a sheared channel flow: a numerical study
Kamp, Leon; Marques Rosas Fernandes, Vitor; van Heijst, Gertjan; Clercx, Herman
2015-11-01
Interaction of large-scale flows with turbulence is of fundamental and widespread importance in geophysical fluid dynamics and also, more recently for the dynamics of fusion plasma. More specifically the interplay between two-dimensional turbulence and so-called zonal flows has gained considerable interest because of its relevance for transport and associated barriers. We present numerical results on the interaction of driven two-dimensional turbulence with typical sheared channel flows (Couette and Poiseuille). It turns out that a linear shear rate that is being sustained by moving channel walls (Couette flow) is far more effective in suppressing turbulence and associated transport than a Poiseuille flow. We explore the mechanisms behind this in relation to the width of the channel and the strength of the shear of the background flow. Also the prominent role played by the no-slip boundaries and the Reynolds stress is discussed.
On the existence of two-dimensional nonlinear steady states in plane Couette flow
Rincon, Francois
2007-01-01
The problem of two-dimensional steady nonlinear dynamics in plane Couette flow is revisited using homotopy from either plane Poiseuille flow or from plane Couette flow perturbed by a small symmetry-preserving identity operator. Our results show that it is not possible to obtain the nonlinear plane Couette flow solutions reported by Cherhabili and Ehrenstein [Eur. J. Mech. B/Fluids, 14, 667 (1995)] using their Poiseuille-Couette homotopy. We also demonstrate that the steady solutions obtained by Mehta and Healey [Phys. Fluids, 17, 4108 (2005)] for small symmetry-preserving perturbations are influenced by an artefact of the modified system of equations used in their paper. However, using a modified version of their model does not help to find plane Couette flow solution in the limit of vanishing symmetry-preserving perturbations either. The issue of the existence of two-dimensional nonlinear steady states in plane Couette flow remains unsettled.
Two-dimensional cellular automaton model of traffic flow with open boundaries
Tadaki, S I
1996-01-01
A two-dimensional cellular automaton model of traffic flow with open boundaries are investigated by computer simulations. The outflow of cars from the system and the average velocity are investigated. The time sequences of the outflow and average velocity have flicker noises in a jamming phase. The low density behavior are discussed with simple jam-free approximation.
DEFF Research Database (Denmark)
Brøns, Morten; Hartnack, Johan Nicolai
1999-01-01
Streamline patterns and their bifurcations in two-dimensional incompressible flow are investigated from a topological point of view. The velocity field is expanded at a point in the fluid, and the expansion coefficients are considered as bifurcation parameters. A series of nonlinear coordinate...
DEFF Research Database (Denmark)
Brøns, Morten; Hartnack, Johan Nicolai
1998-01-01
Streamline patterns and their bifurcations in two-dimensional incompressible flow are investigated from a topological point of view. The velocity field is expanded at a point in the fluid, and the expansion coefficients are considered as bifurcation parameters. A series of non-linear coordinate...
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The dynamic effects in measurements of unsteady flow when using a probe with quasi-steady calibration curves has been investigated in this paper by numerical simulation of the compressible flow around a fixed two-dimensional 3-hole probe. The unsteady velocity and pressure distributions, as well as the hole-pressures, are calculated for high frequency flow variations. The measurement errors caused by the dynamic effects indicate that considerable measurement errors may occur for high frequency flow fluctuation, e.g., 2000Hz, especially, when the flow around the probe head approaches separation. This work shows how numerical simulation can be used to investigate and correct for the dynamic effects.
On the origins of vortex shedding in two-dimensional incompressible flows
Boghosian, M. E.; Cassel, K. W.
2016-12-01
An exegesis of a novel mechanism leading to vortex splitting and subsequent shedding that is valid for two-dimensional incompressible, inviscid or viscous, and external or internal or wall-bounded flows, is detailed in this research. The mechanism, termed the vortex shedding mechanism (VSM) is simple and intuitive, requiring only two coincident conditions in the flow: (1) the existence of a location with zero momentum and (2) the presence of a net force having a positive divergence. Numerical solutions of several model problems illustrate causality of the VSM. Moreover, the VSM criteria is proved to be a necessary and sufficient condition for a vortex splitting event in any two-dimensional, incompressible flow. The VSM is shown to exist in several canonical problems including the external flow past a circular cylinder. Suppression of the von Kármán vortex street is demonstrated for Reynolds numbers of 100 and 400 by mitigating the VSM.
A review of hot wire anemometry in transonic flows
Stainback, P. C.
1985-01-01
The present paper provides a review of hot wire anemometry for compressible flows, giving particular attention to the transonic flow problem. It is pointed out that the first and most important definitive work in hot wire anemometry for compressible flows was reported by Kovasznay (1953). The existence of three independent fluctuating modes in compressible flows for small perturbations was found, taking into account the vorticity mode, the entropy mode, and the sound-wave mode. A review of Kovasznays' method for supersonic flows is also presented, and advances reported by Markovin (1956) are examined. Attention is given to experiments conducted by Horstman and Rose (1977), a general solution to the hot wire problem at transonic conditions sought by Stainback et al. (1983), and some apparent problems.
Coexistence of two dissipative mechanisms in two-dimensional turbulent flows
Energy Technology Data Exchange (ETDEWEB)
Yen, Romain Nguyen van [FB Mathematik und Informatik, Freie Universitaet, Berlin (Germany); Farge, Marie [LMD-CNRS-IPSL, ENS Paris (France); Schneider, Kai, E-mail: rnguyen@zedat.fu-berlin.de [M2P2-CNRS, Universite d' Aix-Marseille (France)
2011-12-22
Two distinct dissipative mechanisms occurring in two-dimensional fully developed turbulent flows in the limit of vanishing viscosity have been highlighted by means of direct numerical simulation. First, molecular energy dissipation is triggered by the production of localized vortices at the walls. Second, instabilities intrinsic to the flow itself generate a noisy component which can be quantified by wavelet analysis. The possibilities of competition and coexistence of the two mechanisms are discussed.
Two-Dimensional Automatic Measurement for Nozzle Flow Distribution Using Improved Ultrasonic Sensor
Changyuan Zhai; Chunjiang Zhao; Xiu Wang; Ning Wang; Wei Zou; Wei Li
2015-01-01
Spray deposition and distribution are affected by many factors, one of which is nozzle flow distribution. A two-dimensional automatic measurement system, which consisted of a conveying unit, a system control unit, an ultrasonic sensor, and a deposition collecting dish, was designed and developed. The system could precisely move an ultrasonic sensor above a pesticide deposition collecting dish to measure the nozzle flow distribution. A sensor sleeve with a PVC tube was designed for the ultras...
Transition to two-dimensionality in magnetohydrodynamic turbulent Taylor-Couette flow.
Zhao, Yurong; Tao, Jianjun; Zikanov, Oleg
2014-03-01
Transition from a Taylor-Couette turbulent flow to a completely two-dimensional axisymmetric turbulent state is realized numerically by increasing gradually the strength of the azimuthal magnetic field produced by electric current flowing through the axial rod. With the increase of the Hartmann number, the Taylor-vortex-like structures shrink, move closer to the inner cylinder, and turn into unsteady but perfect tori at sufficiently high Hartmann numbers.
TWO-DIMENSIONAL PLANE WATER FLOW AND WATER QUALITY DISTRIBUTION IN BOSTEN LAKE
Institute of Scientific and Technical Information of China (English)
Feng Min-quan; Zhou Xiao-de; Zheng Bang-min; Min Tao; Zhao Ke-yu
2003-01-01
The two-dimensional plane water flow and water quality was developed by using the techniques of coordinate transformation, alternating directions, staggered grid, linear recurrence, and implicit scheme in the study of large water body in lakes. The model was proved to be suitable for treating the irregular boundary and predicting quickly water flow and water quality. The application of the model to the Bosten Lake in Xinjiang Uygur Autonomous Region of China shows that it is reasonable and practicable.
Double-Humped Transverse Density Profile in Two-Dimensional Chute Flow with Rough Sidewalls
Institute of Scientific and Technical Information of China (English)
HU Guo-Qi; ZHANG Xun-Sheng; BAO De-Song; TANG Xiao-Wei
2006-01-01
@@ We study a two-dimensional granular rapid flow with rough sidewalls stuck with the same size discs by molecular dynamics simulation. A transient state of the double-humped density profile in the flowing process has been found, which appears and moves as travelling wave and is the same as the phenomena in the recent experiments [Acta Phys. Sin. 53 (2004) 3389 (in Chinese)].
Fourier time spectral method for subsonic and transonic flows
Institute of Scientific and Technical Information of China (English)
Lei Zhan; Feng Liu; Dimitri Papamoschou
2016-01-01
The time accuracy of the exponentially accu-rate Fourier time spectral method (TSM) is examined and compared with a conventional 2nd-order backward differ-ence formula (BDF) method for periodic unsteady flows. In particular, detailed error analysis based on numerical com-putations is performed on the accuracy of resolving the local pressure coefficient and global integrated force coefficients for smooth subsonic and non-smooth transonic flows with moving shock waves on a pitching airfoil. For smooth sub-sonic flows, the Fourier TSM method offers a significant accuracy advantage over the BDF method for the predic-tion of both the local pressure coefficient and integrated force coefficients. For transonic flows where the motion of the discontinuous shock wave contributes significant higher-order harmonic contents to the local pressure fluctuations, a sufficient number of modes must be included before the Fourier TSM provides an advantage over the BDF method. The Fourier TSM, however, still offers better accuracy than the BDF method for integrated force coefficients even for transonic flows. A problem of non-symmetric solutions for symmetric periodic flows due to the use of odd numbers of intervals is uncovered and analyzed. A frequency-searching method is proposed for problems where the frequency is not known a priori. The method is tested on the vortex shedding problem of the flow over a circular cylinder.
Modeling two-dimensional water flow and bromide transport in a heterogeneous lignitic mine soil
Energy Technology Data Exchange (ETDEWEB)
Buczko, U.; Gerke, H.H. [Brandenburg University of Technology, Cottbus (Germany)
2006-02-15
Water and solute fluxes in lignitic mine soils and in many other soils are often highly heterogeneous. Here, heterogeneity reflects dumping-induced inclined structures and embedded heterogeneous distributions of sediment mixtures and of lignitic fragments. Such two-scale heterogeneity effects may be analyzed through the application of two-dimensional models for calculating water and solute fluxes. The objective of this study was to gain more insight to what extent spatial heterogeneity of soil hydraulic parameters contributes to preferential flow at a lignitic mine soil. The simulations pertained to the 'Barenbrucker Hohe' site in Germany where previously water fluxes and applied tracers had been monitored with a cell lysimeter, and from where a soil block had been excavated for detailed two-dimensional characterization of the hydraulic parameters using pedotransfer functions. Based on those previous studies, scenarios with different distributions of hydraulic parameters were simulated. The results show that spatial variability of hydraulic parameters alone can hardly explain the observed flow patterns. The observed preferential flow at the site was probably caused by additional factors such as hydrophobicity, the presence of root channels, anisotropy in the hydraulic conductivity, and heterogeneous root distributions. To study the relative importance of these other factors by applying two-dimensional flow models to such sites, the experimental database must be improved. Single-continuum model approaches may be insufficient for such sites.
Characterizing Mixing in a Quasi-Two-Dimensional Flow using Persistent Homology
Tithof, Jeffrey; Kelley, Douglas
2016-11-01
Fluid mixing is a tremendously important phenomenon present in numerous physical systems, both natural and human-made. Describing, understanding, and predicting the mixing behavior of fluid flows poses an immense challenge. In this work, we explore the utility of topological data analysis in quantifying fluid mixing. We analyze Eulerian and Lagrangian quantities obtained from a quasi-two-dimensional flow realized by driving a thin layer of fluid with electromagnetic forces. Our analysis employs persistent homology, which offers a unique framework for quantifying topological features associated with connectivity in the fluid flow. Preliminary results suggest that this topological approach offers new physical insight, complementing existing methods for quantifying fluid mixing.
EXPERIMENTAL INVESTIGATION ON TWO-DIMENSIONAL UNSTEADY COLD FLOW IN MPC EXHAUST MANIFOLD
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The gas flow in exhaust manifolds has much effect on scavenge, pumping loss and exhaust energy utilization of turbocharged diesel engines. This paper presented experimental investigation on two-dimensional unsteady flow in MPC(modular pulse converter) exhaust manifold model. The pressure and velocity distributions in six sections of the manifold model were measured when the diesel engine was motored. The probe with slitted sleeve was used to determine flow direction. The experimental results show that velocity distributions vary with place and time; the pressure traces at different points of the same section are not different obviously.
Two Dimensional Subsonic Euler Flows Past a Wall or a Symmetric Body
Chen, Chao; Du, Lili; Xie, Chunjing; Xin, Zhouping
2016-08-01
The existence and uniqueness of two dimensional steady compressible Euler flows past a wall or a symmetric body are established. More precisely, given positive convex horizontal velocity in the upstream, there exists a critical value {ρ_cr} such that if the incoming density in the upstream is larger than {ρ_cr}, then there exists a subsonic flow past a wall. Furthermore, {ρ_cr} is critical in the sense that there is no such subsonic flow if the density of the incoming flow is less than {ρ_cr}. The subsonic flows possess large vorticity and positive horizontal velocity above the wall except at the corner points on the boundary. Moreover, the existence and uniqueness of a two dimensional subsonic Euler flow past a symmetric body are also obtained when the incoming velocity field is a general small perturbation of a constant velocity field and the density of the incoming flow is larger than a critical value. The asymptotic behavior of the flows is obtained with the aid of some integral estimates for the difference between the velocity field and its far field states.
Yatou, Hiroki
2010-01-01
We find three types of steady solutions and remarkable flow pattern transitions between them in a two-dimensional wavy-walled channel for low to moderate Reynolds (Re) and Weissenberg (Wi) numbers using direct numerical simulations with spectral element method. The solutions are called "convective", "transition", and "elastic" in ascending order of Wi. In the convective region in the Re-Wi parameter space, the convective effect and the pressure gradient balance on average. As Wi increases, th...
Group classification of steady two-dimensional boundary-layer stagnation-point flow equations
Nadjafikhah, Mehdi; Hejazi, Seyed Reza
2010-01-01
Lie symmetry group method is applied to study the boundary-layer equations for two-dimensional steady flow of an incompressible, viscous fluid near a stagnation point at a heated stretching sheet placed in a porous medium equation. The symmetry group and its optimal system are given, and group invariant solutions associated to the symmetries are obtained. Finally the structure of the Lie algebra symmetries is determined.
Analytical Studies of Two-Dimensional Channel Turbulent Flow Subjected to Coriolis Force
鬼頭, 修己; 中林, 功一; キトウ, オサミ; Kito, Osami
1992-01-01
Coriolis effects on fully developed turbulent flow in a two-dimensional channel rotating about an axis perpendicular to its axis are considered. The Coriolis force has stabilizing/destabilizing effects on turbulence, and the mean velocity distribution changes accordingly. Experimental and numerical studies on the velocity characteristics have already been conducted by other researchers for various conditions. However, we cannot assemble the overall picture of the Coriolis effect on the veloci...
An immersed interface method for two-dimensional modelling of stratified flow in pipes
Berthelsen, Petter Andreas
2004-01-01
This thesis deals with the construction of a numerical method for solving two-dimensional elliptic interface problems, such as fully developed stratified flow in pipes. Interface problems are characterized by its non-smooth and often discontinuous behaviour along a sharp boundary separating the fluids or other materials. Classical numerical schemes are not suitable for these problems due to the irregular geometry of the interface. Standard finite difference discretization across the interface...
Spatial statistics of magnetic field in two-dimensional chaotic flow in the resistive growth stage
Kolokolov, I. V.
2017-03-01
The correlation tensors of magnetic field in a two-dimensional chaotic flow of conducting fluid are studied. It is shown that there is a stage of resistive evolution where the field correlators grow exponentially with time. The two- and four-point field correlation tensors are computed explicitly in this stage in the framework of Batchelor-Kraichnan-Kazantsev model. They demonstrate strong temporal intermittency of the field fluctuations and high level of non-Gaussianity in spatial field distribution.
Determination of two-dimensional magnetostatic equilibria and analogous Euler flows
Linardatos, D.
1993-01-01
A modified computational procedure with an improved time-stepping algorithm for two-dimensional magnetic relaxation is developed. The procedure is used to determine a family of flows in a closed (square) domain with a single elliptic stagnation point. In addition, the problem of saddle point collapse is investigated, and the tendency to form discontinuities is confirmed in the manner described by Bajer (1989).
Directory of Open Access Journals (Sweden)
Taha Aziz
2013-01-01
Full Text Available The simplest equation method is employed to construct some new exact closed-form solutions of the general Prandtl's boundary layer equation for two-dimensional flow with vanishing or uniform mainstream velocity. We obtain solutions for the case when the simplest equation is the Bernoulli equation or the Riccati equation. Prandtl's boundary layer equation arises in the study of various physical models of fluid dynamics. Thus finding the exact solutions of this equation is of great importance and interest.
Flow Rate in the Discharge of a Two-dimensional Silo
Zuriguel, I.; Janda, A.; Garcimartín, A.; Maza, D.
2009-06-01
We present an experimental study of the flow rate in the discharge of a flat bottomed two-dimensional silo. The results of the flow rate dependence on the size of the orifice evidence that the Beverloo expression is not valid for small outlet sizes. This behavior is related with the properties of the flow rate which has been found to fluctuate in a gaussian like form for large orifices. On the contrary, for small orifices extreme events appear at zero flow rates causing a significant slow down of the average flow rate. These events are explained in terms of the existence of arches that block the outlet instantaneously but are unstable to permanently halt the flow.
Numerical simulation of the interaction of a vortex with stationary airfoil in transonic flow
Srinivasan, G. R.; Mccroskey, W. J.; Kutler, P.
1984-01-01
A perturbation form of an implicit conservative, noniterative numerical algorithm for the two-dimensional thin layer Navier-Stokes and Euler equations is used to compute the interaction flow-field of a vortex with stationary airfoil. A Lamb-like analytical vortex having a finite core is chosen to interact with a thick (NACA 0012) and a thin (NACA 64A006) airfoil independently in transonic flow. Two different configurations of vortex interaction are studied, viz., (1) when the vortex is fixed at one location in the flowfield, and (2) when the vortex is convecting past the airfoil at freestream velocity. Parallel computations of this interacting flowfield are also done using a version of the Transonic Small Disturbance Code (ATRAN2). A special treatment of the leading edge region for thin airfoils is included in this code. With this, the three methods gave qualitatively similar results for the weaker interactions considered in this study. However, the strongest interactions considered proved to be beyond the capabilities of the small disturbance code. The results also show a far greater influence of the vortex on the airfoil flowfield when the vortex is stationary than when it is convecting with the flow.
Basic numerical methods. [of unsteady and transonic flow
Steger, Joseph L.; Van Dalsem, William R.
1989-01-01
Some of the basic finite-difference schemes that can be used to solve the nonlinear equations that describe unsteady inviscid and viscous transonic flow are reviewed. Numerical schemes for solving the unsteady Euler and Navier-Stokes, boundary-layer, and nonlinear potential equations are described. Emphasis is given to the elementary ideas used in constructing various numerical procedures, not specific details of any one procedure.
Two-dimensional surface river flow patterns measured with paired RiverSondes
Teague, C.C.; Barrick, D.E.; Lilleboe, P.M.; Cheng, R.T.
2008-01-01
Two RiverSondes were operated simultaneously in close proximity in order to provide a two-dimensional map of river surface velocity. The initial test was carried out at Threemile Slough in central California. The two radars were installed about 135 m apart on the same bank of the channel. Each radar used a 3-yagi antenna array and determined signal directions using direction finding. The slough is approximately 200 m wide, and each radar processed data out to about 300 m, with a range resolution of 15 m and an angular resolution of 1 degree. Overlapping radial vector data from the two radars were combined to produce total current vectors at a grid spacing of 10 m, with updates every 5 minutes. The river flow in the region, which has a maximum velocity of about 0.8 m/s, is tidally driven with flow reversals every 6 hours, and complex flow patterns were seen during flow reversal. The system performed well with minimal mutual interference. The ability to provide continuous, non-contact two-dimensional river surface flow measurements will be useful in several unique settings, such as studies of flow at river junctions where impacts to juvenile fish migration are significant. Additional field experiments are planned this year on the Sacramento River. ?? 2007 IEEE.
Liu, Yifan; Shen, Yusheng; Duan, Lian; Yobas, Levent
2016-10-01
Two-dimensional hydrodynamic flow focusing is demonstrated through a microfluidic device featuring a monolithic integrated glass micronozzle inside a flow-focusing geometry. Such a coaxial configuration allows simple one-step focusing of a sample fluid stream, jetted from the micronozzle tip, in both in-plane and out-of-plane directions. The width of the focused filament can be precisely controlled and further scaled down to the submicrometer regime to facilitate rapid hydrodynamic mixing. Fluorescence quenching experiments reveal ultra-fast microsecond mixing of the denaturant into the focused filament. This device offers new possibilities to a set of applications such as the study of protein folding kinetics.
Seshasayanan, Kannabiran; Alexakis, Alexandros
2016-01-01
We investigate the critical transition from an inverse cascade of energy to a forward energy cascade in a two-dimensional magnetohydrodynamic flow as the ratio of magnetic to mechanical forcing amplitude is varied. It is found that the critical transition is the result of two competing processes. The first process is due to hydrodynamic interactions and cascades the energy to the large scales. The second process couples small-scale magnetic fields to large-scale flows, transferring the energy back to the small scales via a nonlocal mechanism. At marginality the two cascades are both present and cancel each other. The phase space diagram of the transition is sketched.
Flow of an aqueous foam through a two-dimensional porous medium: a pore scale investigation
Meheust, Y.; Jones, S. A.; Dollet, B.; Cox, S.; Cantat, I.
2012-12-01
Flowing foams are used in many engineering and technical applications. A well-known application is oil recovery. Another one is the remediation of polluted soil: the foam is injected into the ground in order to mobilize chemical species present in the medium. Apart from potential interesting physico-chemical and biochemical properties, foams have peculiar flow properties that might be of benefit to the application. We address here this physical aspect of the topic. As a precursor to the study of foam flow through a complex porous material, we first study the behavior of an aqueous two-dimensional foam flowing through a medium consisting of two parallel channels with different widths, at fixed medium porosity, that is, at fixed total combined width of the two channels. The flow velocity, and hence flux, in each channel is measured by analyzing images of the flowing foam. It is then compared to a theoretical model, the basic assumption of which is that the pressure drop along a channel is identical for both channels. This pressure drop both consists of (i) a dynamic pressure drop, which is controlled by bubble-wall friction and depends on the foam velocity in the channel, and (ii) a capillary pressure drop over the bubble films that emerge at the channel outlet, the latter pressure drop being controlled by the radius of curvature of the bubble film. Based on this assumption, the dependence of the ratio of the foam velocities in the two channels is inferred as a function of the channel width ratio. It compares well to the measurements and shows that the flow behavior is highly dependent on the foam structure within the narrowest of the two channels, especially when a "bamboo" structure is obtained. Consequently, the flux in a channel is found to have a more complicated relation to the channel width than expected for the flow of a standard Newtonian fluid in the same geometry. We provide a comparison to this reference configuration. We then study the flow of the same
Implementation of the Log-Conformation Formulation for Two-Dimensional Viscoelastic Flow
Jensen, K E; Okkels, F
2015-01-01
We have implemented the log-conformation method for two-dimensional viscoelastic flow in COMSOL, a commercial high-level finite element package. The code is verified for an Oldroyd-B fluid flowing past a confined cylinder. We are also able to describe the well-known bistability of the viscoelastic flow in a cross-slot geometry for a FENE-CR fluid, and we describe the changes required for performing simulations with the Phan-Thien-Tanner (PTT), Giesekus and FENE-P models. Finally, we calculate the flow of a FENE-CR fluid in a geometry with three in- and outlets. The implementation is included in the supplementary material, and we hope that it can inspire new as well as experienced researchers in the field of differential constitutive equations for viscoelastic flow.
Experimental study on two-dimensional film flow with local measurement methods
Energy Technology Data Exchange (ETDEWEB)
Yang, Jin-Hwa, E-mail: evo03@snu.ac.kr [Nuclear Thermal-Hydraulic Engineering Laboratory, Seoul National University, Gwanak 599, Gwanak-ro, Gwanak-gu, Seoul 151-742 (Korea, Republic of); Korea Atomic Energy Research Institute, 989-111, Daedeok-daero, Yuseong-gu, Daejeon 305-600 (Korea, Republic of); Cho, Hyoung-Kyu [Nuclear Thermal-Hydraulic Engineering Laboratory, Seoul National University, Gwanak 599, Gwanak-ro, Gwanak-gu, Seoul 151-742 (Korea, Republic of); Kim, Seok [Korea Atomic Energy Research Institute, 989-111, Daedeok-daero, Yuseong-gu, Daejeon 305-600 (Korea, Republic of); Euh, Dong-Jin, E-mail: djeuh@kaeri.re.kr [Korea Atomic Energy Research Institute, 989-111, Daedeok-daero, Yuseong-gu, Daejeon 305-600 (Korea, Republic of); Park, Goon-Cherl [Nuclear Thermal-Hydraulic Engineering Laboratory, Seoul National University, Gwanak 599, Gwanak-ro, Gwanak-gu, Seoul 151-742 (Korea, Republic of)
2015-12-01
Highlights: • An experimental study on the two-dimensional film flow with lateral air injection was performed. • The ultrasonic thickness gauge was used to measure the local liquid film thickness. • The depth-averaged PIV (Particle Image Velocimetry) method was applied to measure the local liquid film velocity. • The uncertainty of the depth-averaged PIV was quantified with a validation experiment. • Characteristics of two-dimensional film flow were classified following the four different flow patterns. - Abstract: In an accident condition of a nuclear reactor, multidimensional two-phase flows may occur in the reactor vessel downcomer and reactor core. Therefore, those have been regarded as important issues for an advanced thermal-hydraulic safety analysis. In particular, the multi-dimensional two-phase flow in the upper downcomer during the reflood phase of large break loss of coolant accident appears with an interaction between a downward liquid and a transverse gas flow, which determines the bypass flow rate of the emergency core coolant and subsequently, the reflood coolant flow rate. At present, some thermal-hydraulic analysis codes incorporate multidimensional modules for the nuclear reactor safety analysis. However, their prediction capability for the two-phase cross flow in the upper downcomer has not been validated sufficiently against experimental data based on local measurements. For this reason, an experimental study was carried out for the two-phase cross flow to clarify the hydraulic phenomenon and provide local measurement data for the validation of the computational tools. The experiment was performed in a 1/10 scale unfolded downcomer of Advanced Power Reactor 1400 (APR1400). Pitot tubes, a depth-averaged PIV method and ultrasonic thickness gauge were applied for local measurement of the air velocity, the liquid film velocity and the liquid film thickness, respectively. The uncertainty of the depth-averaged PIV method for the averaged
Energy Technology Data Exchange (ETDEWEB)
Goldberg, L.F. [Univ. of Minnesota, Minneapolis, MN (United States)
1990-08-01
The activities described in this report do not constitute a continuum but rather a series of linked smaller investigations in the general area of one- and two-dimensional Stirling machine simulation. The initial impetus for these investigations was the development and construction of the Mechanical Engineering Test Rig (METR) under a grant awarded by NASA to Dr. Terry Simon at the Department of Mechanical Engineering, University of Minnesota. The purpose of the METR is to provide experimental data on oscillating turbulent flows in Stirling machine working fluid flow path components (heater, cooler, regenerator, etc.) with particular emphasis on laminar/turbulent flow transitions. Hence, the initial goals for the grant awarded by NASA were, broadly, to provide computer simulation backup for the design of the METR and to analyze the results produced. This was envisaged in two phases: First, to apply an existing one-dimensional Stirling machine simulation code to the METR and second, to adapt a two-dimensional fluid mechanics code which had been developed for simulating high Rayleigh number buoyant cavity flows to the METR. The key aspect of this latter component was the development of an appropriate turbulence model suitable for generalized application to Stirling simulation. A final-step was then to apply the two-dimensional code to an existing Stirling machine for which adequate experimental data exist. The work described herein was carried out over a period of three years on a part-time basis. Forty percent of the first year`s funding was provided as a match to the NASA funds by the Underground Space Center, University of Minnesota, which also made its computing facilities available to the project at no charge.
Water-channel study of flow and turbulence past a two-dimensional array of obstacles
Di Bernardino, Annalisa; Leuzzi, Giovanni; Querzoli, Giorgio
2016-01-01
A neutral boundary layer was generated in the laboratory to analyze the mean velocity field and the turbulence field within and above an array of two-dimensional obstacles simulating an urban canopy. Different geometrical configurations were considered in order to investigate the main characteristics of the flow as a function of the aspect ratio (AR) of the canopy. To this end, a summary of the two-dimensional fields of the fundamental turbulence parameters is given for AR ranging from 1 to 2. The results show that the flow field depends strongly on AR only within the canyon, while the outer flow seems to be less sensitive to this parameter. This is not true for the vertical momentum flux, which is one of the parameters most affected by AR, both within and outside the canyon. The experiments also indicate that, when (i.e. the skimming flow regime), the roughness sub-layer extends up to a height equal to 1.25 times the height of the obstacles (H), surmounted by an inertial sub-layer that extends up to 2.7 H. I...
Hydrodynamic aspects of premixed flame stripes in two-dimensional stagnation-point flows
Energy Technology Data Exchange (ETDEWEB)
Lee, H.; Sohrab, S.H. [Northwestern Univ., Evanston, IL (United States). Dept. of Mechanical Engineering
1995-06-01
The behavior of cellular premixed flames of rich butane-air in the two-dimensional stagnation-point flow configuration has been investigated. It is found that the stretching of the cellular flame results in the alignment f the ridge (extinction) and the trough (combustion) zones of the individual cells such as to form a series of parallel flame stripes. The number of flame stripes as a function of the equivalence ratio for three different mean velocities at the nozzle have been determined. Through the introduction of a generalized form of the stream function periodic velocity fields are obtained as the exact solutions of the Euler equation for the nonreactive finite-jet two-dimensional stagnation flow. The predicted periodic velocity profiles are confirmed by the experimental observation of the streamlines in nonreactive flow made visible by laser-sheet lighting. The observed average size of the flame stripes is found to be in good agreement with the predicted value. Similar periodic velocity profiles are also obtained for the viscous flow within the laminar boundary layer by treatment of the unsteady vorticity equation first described by Taylor. The results support an earlier prediction by Williams that cellular flame structures that are affected mainly by diffusive-thermal phenomena may in fact be initiated by the hydrodynamic instability.
Jun, Brian; Giarra, Matthew; Golz, Brian; Main, Russell; Vlachos, Pavlos
2016-11-01
We present a methodology to mitigate the major sources of error associated with two-dimensional confocal laser scanning microscopy (CLSM) images of nanoparticles flowing through a microfluidic channel. The correlation-based velocity measurements from CLSM images are subject to random error due to the Brownian motion of nanometer-sized tracer particles, and a bias error due to the formation of images by raster scanning. Here, we develop a novel ensemble phase correlation with dynamic optimal filter that maximizes the correlation strength, which diminishes the random error. In addition, we introduce an analytical model of CLSM measurement bias error correction due to two-dimensional image scanning of tracer particles. We tested our technique using both synthetic and experimental images of nanoparticles flowing through a microfluidic channel. We observed that our technique reduced the error by up to a factor of ten compared to ensemble standard cross correlation (SCC) for the images tested in the present work. Subsequently, we will assess our framework further, by interrogating nanoscale flow in the cell culture environment (transport within the lacunar-canalicular system) to demonstrate our ability to accurately resolve flow measurements in a biological system.
NUMERICAL SIMULATION OF TWO-DIMENSIONAL DAM-BREAK FLOWS IN CURVED CHANNELS
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Two-dimensional transient dam-break flows in a river with bends were theoretically studied. The river was modeled as a curved channel with a constant width and a flat bottom. The water was assumed to be an incompressible and homogeneous fluid. A channel-fitted orthogonal curvilinear coordinate system was established and the corresponding two-dimensional shallow-water equations were derived for this system. The governing equations with well-posed initial and boundary conditions were numerically solved in a rectangular domain by use of the Godunov-type finite-difference scheme, which can capture the hydraulic jump of dam-break flows. The comparison between the obtained numerical results and the experimental data of Miller and Chaudry in a semicircle channel shows the validity of the present numerical scheme. The mathematical model and the numerical method were applied to the dam-break flows in channels with various curvatures. Based on the numerical results, the influence of river curvatures on the dam-break flows was analyzed in details.
Wake structure and thrust generation of a flapping foil in two-dimensional flow
DEFF Research Database (Denmark)
Andersen, Anders Peter; Bohr, Tomas; Schnipper, Teis
2017-01-01
We present a combined numerical (particle vortex method) and experimental (soap film tunnel) study of a symmetric foil undergoing prescribed oscillations in a two-dimensional free stream. We explore pure pitching and pure heaving, and contrast these two generic types of kinematics. We compare...... measurements and simulations when the foil is forced with pitching oscillations, and we find a close correspondence between flow visualisations using thickness variations in the soap film and the numerically determined vortex structures. Numerically, we determine wake maps spanned by oscillation frequency...
Two-dimensional motion of unstable steps induced by flow in solution
Sato, Masahide
2011-01-01
By carrying out Monte Carlo simulation, we study step instabilities during crystal growth from solution. In previous studies [M. Sato. J. Phys. Soc. Jpn. 79 (2010) 064606; M. Sato, J. Cryst. Growth 318 (2011) 5; M. Sato. J. Phys. Soc. Jpn. 80 (2011) 024604], we used a one-dimensional model, so that we were unable to study another type of instability, step wandering. In this research, we use a two-dimensional model to study both step wandering and step bunching. When the flow of solutes is in ...
Spatial statistics of magnetic field in two-dimensional chaotic flow in the resistive growth stage
Kolokolov, Igor
2016-01-01
The correlation tensors of magnetic field in a two-dimensional chaotic flow of conducting fluid are studied. It is shown that there is a stage of resistive evolution where the field correlators grow exponentially with time what contradicts to the statements present in literature. The two- and four-point field correlation tensors are computed explicitly in this stage in the framework of Batchelor-Kraichnan-Kazantsev model. These tensors demonstrate highly intermittent statistics of the field fluctuations both in space and time.
Two-dimensional numerical simulation of flow around three-stranded rope
Wang, Xinxin; Wan, Rong; Huang, Liuyi; Zhao, Fenfang; Sun, Peng
2016-08-01
Three-stranded rope is widely used in fishing gear and mooring system. Results of numerical simulation are presented for flow around a three-stranded rope in uniform flow. The simulation was carried out to study the hydrodynamic characteristics of pressure and velocity fields of steady incompressible laminar and turbulent wakes behind a three-stranded rope. A three-cylinder configuration and single circular cylinder configuration are used to model the three-stranded rope in the two-dimensional simulation. The governing equations, Navier-Stokes equations, are solved by using two-dimensional finite volume method. The turbulence flow is simulated using Standard κ-ɛ model and Shear-Stress Transport κ-ω (SST) model. The drag of the three-cylinder model and single cylinder model is calculated for different Reynolds numbers by using control volume analysis method. The pressure coefficient is also calculated for the turbulent model and laminar model based on the control surface method. From the comparison of the drag coefficient and the pressure of the single cylinder and three-cylinder models, it is found that the drag coefficients of the three-cylinder model are generally 1.3-1.5 times those of the single circular cylinder for different Reynolds numbers. Comparing the numerical results with water tank test data, the results of the three-cylinder model are closer to the experiment results than the single cylinder model results.
Simulated transonic flows for aircraft with nacelles, pylons, and winglets
Boppe, C. W.; Stern, M. A.
1980-01-01
A computational method which simulates transonic flow about wing-fuselage configurations has been extended to include the treatment of multiple body and non-planar wing surfaces. The finite difference relaxation scheme is characterized by a modified small disturbance flow equation and multiple embedded grid system. Wing-body combinations with as many as four nacelles/pods, four pylons, and wing-tip-mounted winglets can be analyzed. A scheme for modeling inlet spillage and engine exhaust interference effects has been included. Computed results are correlated with experimental data for three transport configurations.
Wind-US Unstructured Flow Solutions for a Transonic Diffuser
Mohler, Stanley R., Jr.
2005-01-01
The Wind-US Computational Fluid Dynamics flow solver computed flow solutions for a transonic diffusing duct. The calculations used an unstructured (hexahedral) grid. The Spalart-Allmaras turbulence model was used. Static pressures along the upper and lower wall agreed well with experiment, as did velocity profiles. The effect of the smoothing input parameters on convergence and solution accuracy was investigated. The meaning and proper use of these parameters are discussed for the benefit of Wind-US users. Finally, the unstructured solver is compared to the structured solver in terms of run times and solution accuracy.
The direct enstrophy cascade of two-dimensional soap film flows
Rivera, Mike; Ecke, Robert
2013-01-01
We investigate the direct enstrophy cascade of two-dimensional decaying turbulence in a flowing soap film channel. We use a coarse-graining approach that allows us to resolve the nonlinear dynamics and scale-coupling simultaneously in scale and in space. From our data, we calculate the transfer of enstrophy across scale $\\ell$ at every point $\\bx$ in the flow domain. We verify an exact relation due to Eyink (1995) between traditional 3rd-order structure function and the enstrophy flux obtained by coarse-graining. We also present experimental evidence that enstrophy cascades to smaller (larger) scales with a 60% (40%) probability, in support of theoretical predictions by Merilees & Warn (1975). Using an Eulerian coherent structure identification technique, we then determine the effect of flow topology on the enstrophy cascade. A key finding is that "centers" are inefficient at transferring enstrophy between scales, in contrast to "saddle" regions which transfer enstrophy to small scales with high efficienc...
Venaille, Antoine
2010-01-01
Using explicit analytical computations, generic occurrence of inequivalence between two or more statistical ensembles is obtained for a large class of equilibrium states of two-dimensional and geophysical turbulent flows. The occurrence of statistical ensemble inequivalence is shown to be related to previously observed phase transitions in the equilibrium flow topology. We find in these turbulent flow equilibria, two mechanisms for the appearance of ensemble equivalences, that were not observed in any physical systems before. These mechanisms are associated respectively with second-order azeotropy (simultaneous appearance of two second-order phase transitions), and with bicritical points (bifurcation from a first-order to two second-order phase transition lines). The important roles of domain geometry, of topography, and of a screening length scale (the Rossby radius of deformation) are discussed. It is found that decreasing the screening length scale (making interactions more local) surprisingly widens the r...
Gas-kinetic numerical schemes for one- and two-dimensional inner flows
Institute of Scientific and Technical Information of China (English)
Zhi-hui LI; Lin BI; Zhi-gong TANG
2009-01-01
Several kinds of explicit and implicit finite-difference schemes directly solving the discretized velocity distribution functions are designed with precision of different orders by analyzing the inner characteristics of the gas-kinetic numerical algorithm for Boltzmann model equation.The peculiar flow phenomena and mechanism from various flow regimes are revealed in the numerical simulations of the unsteady Sod shock-tube problems and the two-dimensional channel flows with different Knudsen numbers.The numerical remainder-effects of the difference schemes are investigated and analyzed based on the computed results.The ways of improving the computational efficiency of the gaskinetic numerical method and the computing principles of difference discretization are discussed.
A characteristic mapping method for two-dimensional incompressible Euler flows
Yadav, Badal; Mercier, Olivier; Nave, Jean-Christophe; Schneider, Kai
2016-11-01
We propose an efficient semi-Lagrangian method for solving the two-dimensional incompressible Euler equations with high precision on a coarse grid. The new approach evolves the flow map using the gradient-augmented level set method (GALSM). Since the flow map can be decomposed into submaps (each over a finite time interval), the error can be controlled by choosing the remapping times appropriately. This leads to a numerical scheme that has exponential resolution in linear time. The computational efficiency and the high precision of the method are illustrated for a vortex merger and a four mode flow. Comparisons with a Cauchy-Lagrangian method are also presented. KS thankfully acknowledges financial support from the French Research Federation for Fusion Studies within the framework of the European Fusion Development Agreement (EFDA).
Solution of Two-Dimensional Viscous Flow Driven by Motion of Flexible Walls
Directory of Open Access Journals (Sweden)
Mohamed Gad-el-Hak
2010-03-01
Full Text Available An exact solution of the Navier–Stokes equations for a flow driven by motion of flexible wall is developed. A simple two-dimensional channel with deforming walls is considered as domain. The governing equations are linearized for low Reynolds number and large Womersley number Newtonian flows. Appropriate boundary conditions for general deformation are decomposed into harmonic excitations in space by Fourier series decomposition. A model of harmonic boundary deformation is considered and results are compared with computational fluid dynamics predictions. The results of velocity profiles across the channel and the centerline velocities of the channel are in good agreement with CFD solution. The analytical model developed provides quantitative descriptions of the flow field for a wide spectrum of actuating frequnecy and boundary conditions. The presented model can be used as an effective framework for preliminary design and optimization of displacement micropumps and other miniature applications.
An incompressible two-dimensional multiphase particle-in-cell model for dense particle flows
Energy Technology Data Exchange (ETDEWEB)
Snider, D.M. [SAIC, Albuquerque, NM (United States); O`Rourke, P.J. [Los Alamos National Lab., NM (United States); Andrews, M.J. [Texas A and M Univ., College Station, TX (United States). Dept. of Mechanical Engineering
1997-06-01
A two-dimensional, incompressible, multiphase particle-in-cell (MP-PIC) method is presented for dense particle flows. The numerical technique solves the governing equations of the fluid phase using a continuum model and those of the particle phase using a Lagrangian model. Difficulties associated with calculating interparticle interactions for dense particle flows with volume fractions above 5% have been eliminated by mapping particle properties to a Eulerian grid and then mapping back computed stress tensors to particle positions. This approach utilizes the best of Eulerian/Eulerian continuum models and Eulerian/Lagrangian discrete models. The solution scheme allows for distributions of types, sizes, and density of particles, with no numerical diffusion from the Lagrangian particle calculations. The computational method is implicit with respect to pressure, velocity, and volume fraction in the continuum solution thus avoiding courant limits on computational time advancement. MP-PIC simulations are compared with one-dimensional problems that have analytical solutions and with two-dimensional problems for which there are experimental data.
A two-dimensional CA model for traffic flow with car origin and destination
In-nami, Junji; Toyoki, Hiroyasu
2007-05-01
Dynamic phase transitions in a two-dimensional traffic flow model defined on a decorated square-lattice are studied numerically. The square-lattice point and the decorated site denote intersections and roads, respectively. In the present model, a car has a finite deterministic path between the origin and the destination, which is assigned to the car from the beginning. In this new model, we found a new phase between the free-flow phase and the frozen-jam phase that is absent from previous models. The new model is characterized by the persistence of a macroscopic cluster. Furthermore, the behavior in this macroscopic cluster phase is classified into three regions characterized by the shape of the cluster. The boundary of the three regions is phenomenologically estimated. When the trip length is short and the car density is high, both ends of the belt-like cluster connect to each other through the periodic boundary with some probability. This type of cluster is classified topologically as a string on a two-dimensional torus.
A two-dimensional adaptive spectral element method for the direct simulation of incompressible flow
Hsu, Li-Chieh
The spectral element method is a high order discretization scheme for the solution of nonlinear partial differential equations. The method draws its strengths from the finite element method for geometrical flexibility and spectral methods for high accuracy. Although the method is, in theory, very powerful for complex phenomena such as transitional flows, its practical implementation is limited by the arbitrary choice of domain discretization. For instance, it is hard to estimate the appropriate number of elements for a specific case. Selection of regions to be refined or coarsened is difficult especially as the flow becomes more complex and memory limits of the computer are stressed. We present an adaptive spectral element method in which the grid is automatically refined or coarsened in order to capture underresolved regions of the domain and to follow regions requiring high resolution as they develop in time. The objective is to provide the best and most efficient solution to a time-dependent nonlinear problem by continually optimizing resource allocation. The adaptivity is based on an error estimator which determines which regions need more resolution. The solution strategy is as follows: compute an initial solution with a suitable initial mesh, estimate errors in the solution locally in each element, modify the mesh according to the error estimators, interpolate old mesh solutions onto the new elements, and resume the numerical solution process. A two-dimensional adaptive spectral element method for the direct simulation of incompressible flows has been developed. The adaptive algorithm effectively diagnoses and refines regions of the flow where complexity of the solution requires increased resolution. The method has been demonstrated on two-dimensional examples in heat conduction, Stokes and Navier-Stokes flows.
The flow of an aqueous foam through a two-dimensional porous medium
Dollet, B.; Jones, S. A.; Géraud, B.; Meheust, Y.; Cox, S. J.; Cantat, I.
2013-12-01
Flowing foams are used in many engineering and technical applications. A well-known application is oil recovery. Another one is the remediation of polluted soils: the foam is injected into the ground in order to mobilize chemical species present in the medium. Apart from potential interesting physico-chemical and biochemical properties, foams have peculiar flow properties that applications might benefit of. In particular, viscous dissipation arises mostly from the contact zones between the soap films and the walls, which results in peculiar friction laws allowing the foam to invade narrow pores more efficiently than Newtonian fluids would. We investigate the flow of a two-dimensional foam in three geometrical configurations. The flow velocity field and pressure field can both be reconstructed from the kinematics of the foam bubbles. We first consider a medium consisting of two parallel channels with different widths, at fixed medium porosity, that is, at fixed total combined width of the two channels. The flow behavior is highly dependent on the foam structure within the narrowest of the two channels [1]; consequently, the flux ratio between the two channels exhibits a non-monotonic dependence on the ratio of their widths. We then consider two parallel channels that are respectively convergent and divergent. The resulting flow kinematics imposes asymmetric bubble deformations in the two channels; these deformations strongly impact the foam/wall friction, and consequently the flux distribution between the two channels, causing flow irreversibility. We quantitatively predict the flux ratio as a function of the channel widths by modeling pressure drops of both viscous and capillary origins. This study reveals the crucial importance of boundary-induced bubble deformation on the mobility of a flowing foam. We then study how film-wall friction, capillary pressures and bubble deformation impact the flow of a foam in a two-dimensional porous medium consisting of randomly
Mamatsashvili, G R; Gogichaishvili, D Z; Chagelishvili, G D; Horton, W
2014-04-01
We find and investigate via numerical simulations self-sustained two-dimensional turbulence in a magnetohydrodynamic flow with a maximally simple configuration: plane, noninflectional (with a constant shear of velocity), and threaded by a parallel uniform background magnetic field. This flow is spectrally stable, so the turbulence is subcritical by nature and hence it can be energetically supported just by a transient growth mechanism due to shear flow non-normality. This mechanism appears to be essentially anisotropic in the spectral (wave-number) plane and operates mainly for spatial Fourier harmonics with streamwise wave numbers less than the ratio of flow shear to Alfvén speed, kymagnetohydrodynamic (MHD) turbulence research. We find similarity of the nonlinear dynamics to the related dynamics in hydrodynamic flows: to the bypass concept of subcritical turbulence. The essence of the analyzed nonlinear MHD processes appears to be a transverse redistribution of kinetic and magnetic spectral energies in the wave-number plane [as occurs in the related hydrodynamic flow; see Horton et al., Phys. Rev. E 81, 066304 (2010)] and differs fundamentally from the existing concepts of (anisotropic direct and inverse) cascade processes in MHD shear flows.
Computational aspects of the prediction of multidimensional transonic flows in turbomachinery
Oliver, D. A.; Sparis, P.
1975-01-01
The analytical prediction and description of transonic flow in turbomachinery is complicated by three fundamental effects: (1) the fluid equations describing the transonic regime are inherently nonlinear, (2) shock waves may be present in the flow, and (3) turbomachine blading is geometrically complex, possessing large amounts of curvature, stagger, and twist. A three-dimensional computation procedure for the study of transonic turbomachine fluid mechanics is described. The fluid differential equations and corresponding difference operators are presented, the boundary conditions for complex blade shapes are described, and the computational implementation and mapping procedures are developed. Illustrative results of a typical unthrottled transonic rotor are also presented.
Yatou, Hiroki
2010-01-01
We find three types of steady solutions and remarkable flow pattern transitions between them in a two-dimensional wavy-walled channel for low to moderate Reynolds (Re) and Weissenberg (Wi) numbers using direct numerical simulations with spectral element method. The solutions are called "convective", "transition", and "elastic" in ascending order of Wi. In the convective region in the Re-Wi parameter space, the convective effect and the pressure gradient balance on average. As Wi increases, the elastic effect becomes suddenly comparable and the first transition sets in. Through the transition, a separation vortex disappears and a jet flow induced close to the wall by the viscoelasticity moves into the bulk; The viscous drag significantly drops and the elastic wall friction rises sharply. This transition is caused by an elastic force in the streamwise direction due to the competition of the convective and elastic effects. In the transition region, the convective and elastic effects balance. When the elastic eff...
Finite-time barriers to front propagation in two-dimensional fluid flows
Mahoney, John R
2015-01-01
Recent theoretical and experimental investigations have demonstrated the role of certain invariant manifolds, termed burning invariant manifolds (BIMs), as one-way dynamical barriers to reaction fronts propagating within a flowing fluid. These barriers form one-dimensional curves in a two-dimensional fluid flow. In prior studies, the fluid velocity field was required to be either time-independent or time-periodic. In the present study, we develop an approach to identify prominent one-way barriers based only on fluid velocity data over a finite time interval, which may have arbitrary time-dependence. We call such a barrier a burning Lagrangian coherent structure (bLCS) in analogy to Lagrangian coherent structures (LCSs) commonly used in passive advection. Our approach is based on the variational formulation of LCSs using curves of stationary "Lagrangian shear", introduced by Farazmand, Blazevski, and Haller [Physica D 278-279, 44 (2014)] in the context of passive advection. We numerically validate our techniqu...
Flow-rate fluctuations in the outpouring of grains from a two-dimensional silo.
Janda, A; Harich, R; Zuriguel, I; Maza, D; Cixous, P; Garcimartín, A
2009-03-01
We present experimental results obtained with a two-dimensional silo discharging under gravity through an orifice at the flat bottom. High-speed measurements provide enough time resolution to detect every single bead that goes out and this allows the measurement of the flow rate in short-time windows. Two different regimes are clearly distinguished: one for large orifices, which can be described by Gaussian fluctuations, and another for small orifices, in which extreme events appear. The frontier between those two regimes coincides with the outlet size below which jamming events are frequent. Moreover, it is shown that the power spectrum of the flow-rate oscillations is not dominated by any particular frequency.
A Hybrid Nodal Method for Time-Dependent Incompressible Flow in Two-Dimensional Arbitrary Geometries
Energy Technology Data Exchange (ETDEWEB)
Toreja, A J; Uddin, R
2002-10-21
A hybrid nodal-integral/finite-analytic method (NI-FAM) is developed for time-dependent, incompressible flow in two-dimensional arbitrary geometries. In this hybrid approach, the computational domain is divided into parallelepiped and wedge-shaped space-time nodes (cells). The conventional nodal integral method (NIM) is applied to the interfaces between adjacent parallelepiped nodes (cells), while a finite analytic approach is applied to the interfaces between parallelepiped and wedge-shaped nodes (cells). In this paper, the hybrid method is formally developed and an application of the NI-FAM to fluid flow in an enclosed cavity is presented. Results are compared with those obtained using a commercial computational fluid dynamics code.
Chan, B. C.
1986-05-01
A basic, limited scope, fast-running computer model is presented for the solution of two-dimensional, transient, thermally-coupled fluid flow problems. This model is to be the module in the SSC (an LMFBR thermal-hydraulic systems code) for predicting complex flow behavior, as occurs in the upper plenum of the loop-type design or in the sodium pool of the pool-type design. The nonlinear Navier-Stokes equations and the two-equation (two-variable) transport model of turbulence are reduced to a set of linear algebraic equations in an implicit finite difference scheme, based on the control volume approach. These equations are solved iteratively in a line-by-line procedure using the tri-diagonal matrix algorithm. The results of calculational examplers are shown in the computer-generated plots.
Numerical Algorithms for Two-Dimensional Dry Granular Flow with Deformable Elastic Grain
Energy Technology Data Exchange (ETDEWEB)
Boateng, H A; Elander, V; Jin, C; Li, Y; Vasquez, P; Fast, P
2005-08-11
The authors consider the dynamics of interacting elastic disks in the plane. This is an experimentally realizable two-dimensional model of dry granular flow where the stresses can be visualized using the photoelastic effect. As the elastic disks move in a vacuum, they interact through collisions with each other and with the surrounding geometry. Because of the finite propagation speed of deformations inside each grain it can be difficult to capture computationally even simple experiments involving just a few interacting grains. The goal of this project is to improve our ability to simulate dense granular flow in complex geometry. They begin this process by reviewing some past work, how they can improve upon previous work. the focus of this project is on capturing the elastic dynamics of each grain in an approximate, computationally tractable, model that can be coupled to a molecular dynamics scheme.
A minimum action method for small random perturbations of two-dimensional parallel shear flows
Wan, Xiaoliang
2013-02-01
In this work, we develop a parallel minimum action method for small random perturbations of Navier-Stokes equations to solve the optimization problem given by the large deviation theory. The Freidlin-Wentzell action functional is discretized by hp finite elements in time direction and spectral methods in physical space. A simple diagonal preconditioner is constructed for the nonlinear conjugate gradient solver of the optimization problem. A hybrid parallel strategy based on MPI and OpenMP is developed to improve numerical efficiency. Both h- and p-convergence are obtained when the discretization error from physical space can be neglected. We also present preliminary results for the transition in two-dimensional Poiseuille flow from the base flow to a non-attenuated traveling wave.
Laboratory setup and results of experiments on two-dimensional multiphase flow in porous media
Energy Technology Data Exchange (ETDEWEB)
McBride, J.F. (ed.) (Pacific Northwest Lab., Richland, WA (USA)); Graham, D.N. (ed.); Schiegg, H.O. (SIMULTEC Ltd., Meilen/Zurich (Switzerland))
1990-10-01
In the event of an accidental release into earth's subsurface of an immiscible organic liquid, such as a petroleum hydrocarbon or chlorinated organic solvent, the spatial and temporal distribution of the organic liquid is of great interest when considering efforts to prevent groundwater contamination or restore contaminated groundwater. An accurate prediction of immiscible organic liquid migration requires the incorporation of relevant physical principles in models of multiphase flow in porous media; these physical principles must be determined from physical experiments. This report presents a series of such experiments performed during the 1970s at the Swiss Federal Institute of Technology (ETH) in Zurich, Switzerland. The experiments were designed to study the transient, two-dimensional displacement of three immiscible fluids in a porous medium. This experimental study appears to be the most detailed published to date. The data obtained from these experiments are suitable for the validation and test calibration of multiphase flow codes. 73 refs., 140 figs.
Quasi-normal acoustic oscillations in the transonic Bondi flow
Chaverra, Eliana
2015-01-01
In recent work, we analyzed the dynamics of spherical and nonspherical acoustic perturbations of the Michel flow, describing the steady radial accretion of a relativistic perfect fluid into a nonrotating black hole. We showed that such perturbations undergo quasi-normal oscillations and computed the corresponding complex frequencies as a function of the black hole mass M and the radius r_c of the sonic horizon. It was found that when r_c is much larger than the Schwarzschild radius r_H = 2GM/c^2 of the black hole, these frequencies scale like the surface gravity of the analogue black hole associated with the acoustic metric. In this work, we analyze the Newtonian limit of the Michel solution and its acoustic perturbations. In this limit, the flow outside the sonic horizon reduces to the transonic Bondi flow, and the acoustic metric reduces to the one introduced by Unruh in the context of experimental black hole evaporation. We show that for the transonic Bondi flow, Unruh's acoustic metric describes an analog...
Enhanced Transport of Passive Tracers In A Time Periodic Two-dimensional Flow
Boffetta, G.; Cencini, M.; Espa, S.; Musacchio, S.
, investigating systems in which the second condition is violated is much more inter- esting. With this purpose, some experiments have shown how superdiffusion arises in a two-dimensional quasi-geostrophic (planetary-type) flow, where particles can jump for very long time in the same direction performing a Levy flight (Castiglione et al., 2001 ). Moreover, two recent papers (Vulpiani, 1998; Solomon, 2001) show how, also in very simple two-dimensional, time and space periodic cellular flows,anomalous diffusive behaviours can appear. In this paper we present an experimental study of transport in an electromagnetically forced time periodic two-dimensional flow. The flow is generated by applying an electromagnetic forcing on a thin layer of an elec- trolyte solution and reveals in a square grid of alternating vortices. Time dependence can be easily obtained by changing the time dependence of the electric fields. In par- ticular, considering certain values of the imposed oscillation frequencies, particles can display very long jump. Particle Tracking Velocimetry (PTV) is used to measure the flow field. This technique is the most suitable for studying dispersion phenomena in a Lagrangian framework allowing the direct evaluation of particle displacements and related quantities (Cenedese, Querzoli; 2000). Moreover, due to the characteristics of the analyzed flow and to the improvement of the tracking procedure, we have been able to track a great number of particles for time intervals greater than the charac- teristic time-scales of the flow. In order to characterize the time correlations we will evaluate the so-called jumps probabilities with memory which represent the probabil- ities to jump in a given direction conditioned to having experienced jumps in the same direction at previous times. Such statistics will revealed very useful and suitable for detecting the onset of the aforementioned correlations. 2
Riahi-Madvar, Hossien; Ayyoubzadeh, Seyed Ali; Namin, Masoud Montazeri; Seifi, Akram
2011-01-01
Flow in compound channels with overbank flows becomes more complex because of shear interactions between flows in main channel and flood plains, lateral momentum transfer and secondary flows. Compound channels have interesting applications in flood control, civil engineering and environmental management. Because it is difficult to obtain sufficiently accurate and comprehensive understandings of flow in natural compound rivers, the developed models of flow in overbank flows have many uncertain...
GIS-based two-dimensional numerical simulation of rainfall-induced debris flow
Directory of Open Access Journals (Sweden)
C. Wang
2008-02-01
Full Text Available This paper aims to present a useful numerical method to simulate the propagation and deposition of debris flow across the three dimensional complex terrain. A depth-averaged two-dimensional numerical model is developed, in which the debris and water mixture is assumed to be continuous, incompressible, unsteady flow. The model is based on the continuity equations and Navier-Stokes equations. Raster grid networks of digital elevation model in GIS provide a uniform grid system to describe complex topography. As the raster grid can be used as the finite difference mesh, the continuity and momentum equations are solved numerically using the finite difference method. The numerical model is applied to simulate the rainfall-induced debris flow occurred in 20 July 2003, in Minamata City of southern Kyushu, Japan. The simulation reproduces the propagation and deposition and the results are in good agreement with the field investigation. The synthesis of numerical method and GIS makes possible the solution of debris flow over a realistic terrain, and can be used to estimate the flow range, and to define potentially hazardous areas for homes and road section.
GIS-based two-dimensional numerical simulation of rainfall-induced debris flow
Wang, C.; Li, S.; Esaki, T.
2008-02-01
This paper aims to present a useful numerical method to simulate the propagation and deposition of debris flow across the three dimensional complex terrain. A depth-averaged two-dimensional numerical model is developed, in which the debris and water mixture is assumed to be continuous, incompressible, unsteady flow. The model is based on the continuity equations and Navier-Stokes equations. Raster grid networks of digital elevation model in GIS provide a uniform grid system to describe complex topography. As the raster grid can be used as the finite difference mesh, the continuity and momentum equations are solved numerically using the finite difference method. The numerical model is applied to simulate the rainfall-induced debris flow occurred in 20 July 2003, in Minamata City of southern Kyushu, Japan. The simulation reproduces the propagation and deposition and the results are in good agreement with the field investigation. The synthesis of numerical method and GIS makes possible the solution of debris flow over a realistic terrain, and can be used to estimate the flow range, and to define potentially hazardous areas for homes and road section.
Two-Dimensional Automatic Measurement for Nozzle Flow Distribution Using Improved Ultrasonic Sensor
Directory of Open Access Journals (Sweden)
Changyuan Zhai
2015-10-01
Full Text Available Spray deposition and distribution are affected by many factors, one of which is nozzle flow distribution. A two-dimensional automatic measurement system, which consisted of a conveying unit, a system control unit, an ultrasonic sensor, and a deposition collecting dish, was designed and developed. The system could precisely move an ultrasonic sensor above a pesticide deposition collecting dish to measure the nozzle flow distribution. A sensor sleeve with a PVC tube was designed for the ultrasonic sensor to limit its beam angle in order to measure the liquid level in the small troughs. System performance tests were conducted to verify the designed functions and measurement accuracy. A commercial spray nozzle was also used to measure its flow distribution. The test results showed that the relative error on volume measurement was less than 7.27% when the liquid volume was 2 mL in trough, while the error was less than 4.52% when the liquid volume was 4 mL or more. The developed system was also used to evaluate the flow distribution of a commercial nozzle. It was able to provide the shape and the spraying width of the flow distribution accurately.
Two-dimensional automatic measurement for nozzle flow distribution using improved ultrasonic sensor.
Zhai, Changyuan; Zhao, Chunjiang; Wang, Xiu; Wang, Ning; Zou, Wei; Li, Wei
2015-10-16
Spray deposition and distribution are affected by many factors, one of which is nozzle flow distribution. A two-dimensional automatic measurement system, which consisted of a conveying unit, a system control unit, an ultrasonic sensor, and a deposition collecting dish, was designed and developed. The system could precisely move an ultrasonic sensor above a pesticide deposition collecting dish to measure the nozzle flow distribution. A sensor sleeve with a PVC tube was designed for the ultrasonic sensor to limit its beam angle in order to measure the liquid level in the small troughs. System performance tests were conducted to verify the designed functions and measurement accuracy. A commercial spray nozzle was also used to measure its flow distribution. The test results showed that the relative error on volume measurement was less than 7.27% when the liquid volume was 2 mL in trough, while the error was less than 4.52% when the liquid volume was 4 mL or more. The developed system was also used to evaluate the flow distribution of a commercial nozzle. It was able to provide the shape and the spraying width of the flow distribution accurately.
Suri, Balachandra; Tithof, Jeffrey; Pallantla, Ravi Kumar; Grigoriev, Roman; Schatz, Michael
2015-11-01
The dynamical systems approach to fluid turbulence relies on understanding the role of unstable, non-chaotic solutions - such as equilibria, traveling waves, and periodic orbits - of the Navier-Stokes equations. These solutions, called Exact Coherent Structures, exist in the same parameter regime as turbulence, but being unstable, are observed in experiments only as short transients. In this talk, we present experimental evidence for the existence and dynamical relevance of unstable equilibria in a weakly turbulent quasi-two-dimensional (Q2D) Kolmogorov flow. In the experiment, this Q2D flow is generated in an electromagnetically driven shallow layer of electrolyte. The numerical simulations, however, use a strictly 2D model which incorporates the effects of the finite thickness of the fluid layer in the experiment. During its evolution, there are instances when the dynamics of a weakly turbulent flow slow down, rather dramatically. Using experimental flow fields from such instances, and by means of a Newton-Solver, we numerically compute several unstable equilibria. Additionally, using numerical simulations, we show that the dynamics of a turbulent flow in the neighbourhood of an equilibrium are accurately described by the unstable manifold of the equilibrium. This work is supported in part by the National Science Foundation under grants CBET-0900018, and CMMI-1234436.
Coherent Structures in Turbulent Flow over Two-Dimensional River Dunes
Omidyeganeh, Mohammad
2011-01-01
We performed large-eddy simulations of the flow over a typical two-dimensional dune geometry at laboratory scale (the Reynolds number based on the average channel height and mean velocity is 18,900) using the Lagrangian dynamic eddy-viscosity subgrid-scale model. The flow separates at the dune crest and reattaches downstream on the bed (at x=5.7h). A favorable pressure gradient accelerates the flow over the stoss-side (the upward-sloping region for x > 8h) and an unfavorable gradient for x < 8h decelerates the flow over the lee-side of the dune. Due to the separation of the flow, a shear layer is generated after the crest that expands in the wake region towards the next dune. The outer-layer turbulence structures are visualized through isosurfaces of pressure fluctuations colored by distance to the surface. Spanwise vortices are generated in the shear layer separating from the crest due to the Kelvin-Helmholtz instability. They are convected downstream and either interact with the wall or rise to the surfa...
PIV study on a shock-induced separation in a transonic flow
Energy Technology Data Exchange (ETDEWEB)
Sartor, Fulvio; Losfeld, Gilles; Bur, Reynald [ONERA, Meudon (France)
2012-09-15
A transonic interaction between a steady shock wave and a turbulent boundary layer in a Mach 1.4 channel flow is experimentally investigated by means of particle image velocimetry (PIV). In the test section, the lower wall is equipped with a contour profile shaped as a bump allowing flow separation. The transonic interaction, characterized by the existence in the outer flow of a lambda shock pattern, causes the separation of the boundary layer, and a low-speed recirculating bubble is observed downstream of the shock foot. Two-component PIV velocity measurements have been performed using an iterative gradient-based cross-correlation algorithm, providing high-speed and flexible calculations, instead of the classic multi-pass processing with FFT-based cross-correlation. The experiments are performed discussing all the hypotheses linked to the experimental set-up and the technique of investigation such as the two-dimensionality assumption of the flow, the particle response assessment, the seeding system, and the PIV correlation uncertainty. Mean velocity fields are presented for the whole interaction with particular attention for the recirculating bubble downstream of the detachment, especially in the mixing layer zone where the effects of the shear stress are most relevant. Turbulence is discussed in details, the results are compared to previous study, and new results are given for the turbulent production term and the return to isotropy mechanism. Finally, using different camera lens, a zoom in the vicinity of the wall presents mean and turbulent velocity fields for the incoming boundary layer. (orig.)
Flow of a two-dimensional aqueous foam in two parallel channels
Jones, S.; Cantat, I.; Dollet, B.; Meheust, Y.
2012-04-01
Flowing foams are used in many engineering and technical applications. A well-known application is oil recovery. Another one is the remediation of polluted soil: the foam is injected into the ground in order to mobilize chemical species that are initially present in the medium. Apart from potential interesting physico-chemical and biochemical properties, foams have pecular flow properties that might be used in order to reach regions of the medium that are normally the least permeable. We study here this physical aspect of the topic. As a precursor to the study of foam flow through a complex porous material, we study the behaviour of an aqueous two-dimensional foam flowing through a medium consisting of two parallel channels with different widths, at fixed medium porosity, that is, at fixed total combined width of the two channels. The flow velocity, and hence flux, in each channel is measured by analyzing images of the flowing foam. The corresponding pressure drop along each channel is calculated based on theoretical arguments involving both (i) a dynamic pressure drop, which is controlled by bubble-wall friction, and (ii) possibly a capillary pressure drop over the bubble films that emerge at the channel outlet, the latter pressure drop being controlled by the radius of curvature of the bubble film. The flow behaviour of the foam happens to not uniquely be determined by the channel width, as would be the case for a Newtonian fluid, but also to be highly dependent on the foam structure within the narrowest of the two channel, especially when a "bamboo" structure is obtained. Consequently, the flux in a channel is found to have a more complicated relation to the channel width than expected. We try to define a corresponding medium permeability and compare it to the permeability expected for the flow of a standard newtonian fluid in the same geometry.
Numerical Investigation on Two-dimensional Boundary Layer Flow with Transition
Institute of Scientific and Technical Information of China (English)
Yong Zhao; Tianlin Wang; Zhi Zong
2014-01-01
As a basic problem in many engineering applications, transition from laminar to turbulence still remains a difficult problem in computational fluid dynamics (CFD). A numerical study of one transitional flow in two-dimensional is conducted by Reynolds averaged numerical simulation (RANS) in this paper. Turbulence model plays a significant role in the complex flows’ simulation, and four advanced turbulence models are evaluated. Numerical solution of frictional resistance coefficient is compared with the measured one in the transitional zone, which indicates that Wilcox (2006) k-ω model with correction is the best candidate. Comparisons of numerical and analytical solutions for dimensionless velocity show that averaged streamwise dimensionless velocity profiles correct the shape rapidly in transitional region. Furthermore, turbulence quantities such as turbulence kinetic energy, eddy viscosity, and Reynolds stress are also studied, which are helpful to learn the transition’s behavior.
A numerical study of the alpha model for two-dimensional magnetohydrodynamic turbulent flows
Mininni, P D; Pouquet, A G
2004-01-01
We explore some consequences of the ``alpha model,'' also called the ``Lagrangian-averaged'' model, for two-dimensional incompressible magnetohydrodynamic (MHD) turbulence. This model is an extension of the smoothing procedure in fluid dynamics which filters velocity fields locally while leaving their associated vorticities unsmoothed, and has proved useful for high Reynolds number turbulence computations. We consider several known effects (selective decay, dynamic alignment, inverse cascades, and the probability distribution functions of fluctuating turbulent quantities) in magnetofluid turbulence and compare the results of numerical solutions of the primitive MHD equations with their alpha-model counterparts' performance for the same flows, in regimes where available resolution is adequate to explore both. The hope is to justify the use of the alpha model in regimes that lie outside currently available resolution, as will be the case in particular in three-dimensional geometry or for magnetic Prandtl number...
Experimental Analysis of Two-Dimensional Pedestrian Flow in front of the Bottleneck
cek, Marek Buká\\v; Krbálek, Milan
2014-01-01
This contribution presents experimental study of two-dimensional pedestrian flow with the aim to capture the pedestrian behaviour within the cluster formed in front of the bottleneck. Two experiments of passing through a room with one entrance and one exit were arranged according to phase transition study in Ezaki et al. (2012), the inflow rate was regulated to obtain different walking modes. By means of automatic image processing, pedestrians' paths are extracted from camera records to get actual velocity and local density. Macroscopic information is extracted by means of virtual detector and leaving times of pedestrians. The pedestrian's behaviour is evaluated by means of density and velocity. Different approaches of measurement are compared using several fundamental diagrams. Two phases of crowd behaviour have been recognized and the phase transition was described.
Two-dimensional behavior of three-dimensional magnetohydrodynamic flow with a strong guiding field.
Alexakis, Alexandros
2011-11-01
The magnetohydrodynamic (MHD) equations in the presence of a guiding magnetic field are investigated by means of direct numerical simulations. The basis of the investigation consists of nine runs forced at the small scales. The results demonstrate that for a large enough uniform magnetic field the large scale flow behaves as a two-dimensional (2D) (non-MHD) fluid exhibiting an inverse cascade of energy in the direction perpendicular to the magnetic field, while the small scales behave like a three-dimensional (3D) MHD fluid cascading the energy forwards. The amplitude of the inverse cascade is sensitive to the magnetic field amplitude, the domain size, the forcing mechanism, and the forcing scale. All these dependences are demonstrated by the varying parameters of the simulations. Furthermore, in the case that the system is forced anisotropically in the small parallel scales an inverse cascade in the parallel direction is observed that is feeding the 2D modes k(//)=0.
Two-Dimensional River Flow Patterns Observed with a Pair of UHF Radar System
Directory of Open Access Journals (Sweden)
Yidong Hou
2017-01-01
Full Text Available A pair of ultrahigh-frequency (UHF radars system for measuring the two-dimensional river flow patterns is presented. The system consists of two all-digital UHF radars with exactly the same hardware structure, operating separately at 329–339 MHz and 341–351 MHz. The adoption of direct radio frequency (RF sampling technique and digital pulse compression simplifies the structure of radar system and eliminates the distortion introduced by the analog mixer, which improves the SNR and dynamic range of the radar. The field experiment was conducted at Hanjiang River, Hubei province, China. Over a period of several weeks, the radar-derived surface velocity has been very highly correlated with the measurements of EKZ-I, with a correlation coefficient of 0.958 and a mean square error of 0.084 m/s.
Simulations of Viscous Accretion Flow around Black Holes in Two-Dimensional Cylindrical Geometry
Lee, Seong-Jae; Kumar, Rajiv; Hyung, Siek; Ryu, Dongsu
2016-01-01
We simulate shock-free and shocked viscous accretion flow onto a black hole in a two dimensional cylindrical geometry, where initial conditions were chosen from analytical solutions. The simulation code used the Lagrangian Total Variation Diminishing (LTVD) and remap routine, which enabled us to attain high accuracy in capturing shocks and to handle the angular momentum distribution correctly. Inviscid shock-free accretion disk solution produced a thick disk structure, while the viscous shock-free solution attained a Bondi-like structure, but in either case, no jet activity nor any QPO-like activity developed. The steady state shocked solution in the inviscid, as well as, in the viscous regime, matched theoretical predictions well. However, increasing viscosity renders the accretion shock unstable. Large amplitude shock oscillation is accompanied by intermittent, transient inner multiple shocks. Such oscillation of the inner part of disk is interpreted as the source of QPO in hard X-rays observed in micro-qua...
Turbulence models and Reynolds analogy for two-dimensional supersonic compression ramp flow
Wang, Chi R.; Bidek, Maleina C.
1994-01-01
Results of the application of turbulence models and the Reynolds analogy to the Navier-Stokes computations of Mach 2.9 two-dimensional compression ramp flows are presented. The Baldwin-Lomax eddy viscosity model and the kappa-epsilon turbulence transport equations for the turbulent momentum flux modeling in the Navier-Stokes equations are studied. The Reynolds analogy for the turbulent heat flux modeling in the energy equation was also studied. The Navier-Stokes equations and the energy equation were numerically solved for the flow properties. The Reynolds shear stress, the skin friction factor, and the surface heat transfer rate were calculated and compared with their measurements. It was concluded that with a hybrid kappa-epsilon turbulence model for turbulence modeling, the present computations predicted the skin friction factors of the 8 deg and 16 deg compression ramp flows and with the turbulent Prandtl number Pr(sub t) = 0.93 and the ratio of the turbulent thermal and momentum transport coefficients mu(sub q)/mu(sub t) = 2/Prt, the present computations also predicted the surface heat transfer rates beneath the boundary layer flow of the 16 compression ramp.
Wake Effects on Drift in Two-Dimensional Inviscid Incompressible Flows
Melkoumian, Sergei
2014-01-01
This investigation analyzes the effect of vortex wakes on the Lagrangian displacement of particles induced by the passage of an obstacle in a two-dimensional incompressible and inviscid fluid. In addition to the trajectories of individual particles, we also study their drift and the corresponding total drift areas in the F\\"oppl and Kirchhoff potential flow models. Our findings, which are obtained numerically and in some regimes are also supported by asymptotic analysis, are compared to the wakeless potential flow which serves as a reference. We show that in the presence of the F\\"oppl vortex wake some of the particles follow more complicated trajectories featuring a second loop. The appearance of an additional stagnation point in the F\\"oppl flow is identified as a source of this effect. It is also demonstrated that, while the total drift area increases with the size of the wake for large vortex strengths, it is actually decreased for small circulation values. On the other hand, the Kirchhoff flow model is s...
The onset of thermal instability of a two-dimensional hydromagnetic stagnation point flow
Energy Technology Data Exchange (ETDEWEB)
Amaouche, Mustapha; Bouda, Faical Nait [Laboratoire de physique theorique, Universite de Bejaia, Route de Targua Ouzemour Bejaia (Algeria); Sadat, Hamou [Laboratoire d' Etudes Thermiques, Universite de Poitiers, 40 Avenue du Recteur Pineau, 86022 Poitiers (France)
2005-10-01
The aim of the present paper is to examine the effects of a constant magnetic field on the thermal instability of a two-dimensional stagnation point flow. First, it is shown that a basic flow, described by an exact solution of the full Navier-Stokes equations exists under some conditions relating the orientation of the magnetic field in the plane of motion to the obliqueness of free stream. The stability of the basic flow is then investigated in the usual fashion by making use of the normal mode decomposition. The resulting eigenvalue problem is solved numerically by means of a pseudo spectral collocation method based upon Laguerre's functions. The use of this procedure is warranted by the exponential damping of disturbances far from the boundary layer and the appropriate distribution of the roots of Laguerre's polynomials to treat boundary layer problems. It is found through the calculation of neutral stability curves that magnetic field acts to increase the stability of the basic flow. (author)
Particle motion in unsteady two-dimensional peristaltic flow with application to the ureter
Jiménez-Lozano, Joel; Sen, Mihir; Dunn, Patrick F.
2009-04-01
Particle motion in an unsteady peristaltic fluid flow is analyzed. The fluid is incompressible and Newtonian in a two-dimensional planar geometry. A perturbation method based on a small ratio of wave height to wavelength is used to obtain a closed-form solution for the fluid velocity field. This analytical solution is used in conjunction with an equation of motion for a small rigid sphere in nonuniform flow taking Stokes drag, virtual mass, Faxén, Basset, and gravity forces into account. Fluid streamlines and velocity profiles are calculated. Theoretical values for pumping rates are compared with available experimental data. An application to ureteral peristaltic flow is considered since fluid flow in the ureter is sometimes accompanied by particles such as stones or bacteriuria. Particle trajectories for parameters that correspond to calcium oxalates for calculosis and Escherichia coli type for bacteria are analyzed. The findings show that retrograde or reflux motion of the particles is possible and bacterial transport can occur in the upper urinary tract when there is a partial occlusion of the wave. Dilute particle mixing is also investigated, and it is found that some of the particles participate in the formation of a recirculating bolus, and some of them are delayed in transit and eventually reach the walls. This can explain the failure of clearing residuals from the upper urinary tract calculi after successful extracorporeal shock wave lithotripsy. The results may also be relevant to the transport of other physiological fluids and industrial applications in which peristaltic pumping is used.
Numerical simulation of two-dimensional fluid flow with strong shocks
Energy Technology Data Exchange (ETDEWEB)
Woodward, P.; Colella, P.
1984-04-01
Results of an extensive comparison of numerical methods for simulating hydrodynamics are presented and discussed. This study focuses on the simulation of fluid flows with strong shocks in two dimensions. By ''strong shocks,'' we here refer to shocks in which there is substantial entropy production. For the case of shocks in air, we therefore refer to Mach numbers of three and greater. For flows containing such strong shocks we find that a careful treatment of flow discontinuities is of greatest importance in obtaining accurate numerical results. Three aproaches to treating discontinuities in the flow are discussed-artificial viscosity, blending of low- and high-order-accurate fluxes, and the use of nonlinear solutions to Riemann's problem. The advantages and disadvantages of each approach are discussed and illustrated by computed results for three test problems. In this comparison we have focused our attention entirely upon the performance of schemes for differencing the hydrodynamic equations. We have regarded the nature of the grid upon which such differencing schemes are applied as an independent issue outside the scope of this work. Therefore we have restricted our study to the case of uniform, square computational zones in Cartesian coordinates. For simplicity we have further restricted our attention to two-dimensional difference schemes which are built out of symmetrized products of one-dimensional difference operators.
Relaxation techniques for three-dimensional transonic flow about wings.
Bailey, F. R.; Steger, J. L.
1972-01-01
A relaxation procedure has been developed to treat the three-dimensional, transonic small perturbation equations about finite lifting wings. A combination of two schemes is employed. For flow forward of the wing trailing edge the equations are written in terms of a velocity potential in order to minimize computer algebra and storage. For the remaining flow field the equations are written in terms of the velocity components in order to simplify the enforcement of the Kutta condition. Difference equations and relaxation procedures are described for both schemes. The computational method automatically captures the imbedded shock wave in the three-dimensional flow field. Computed results are given and compared to experiment and other inviscid methods.
Dual-RiverSonde measurements of two-dimensional river flow patterns
Teague, C.C.; Barrick, D.E.; Lilleboe, P.M.; Cheng, R.T.; Stumpner, P.; Burau, J.R.
2008-01-01
Two-dimensional river flow patterns have been measured using a pair of RiverSondes in two experiments in the Sacramento-San Joaquin River Delta system of central California during April and October 2007. An experiment was conducted at Walnut Grove, California in order to explore the use of dual RiverSondes to measure flow patterns at a location which is important in the study of juvenile fish migration. The data available during the first experiment were limited by low wind, so a second experiment was conducted at Threemile Slough where wind conditions and surface turbulence historically have resulted in abundant data. Both experiments included ADCP near-surface velocity measurements from either manned or unmanned boats. Both experiments showed good comparisons between the RiverSonde and ADCP measurements. The flow conditions at both locations are dominated by tidal effects, with partial flow reversal at Walnut Grove and complete flow reversal at Threemile Slough. Both systems showed complex flow patterns during the flow reversals. Quantitative comparisons between the RiverSondes and an ADCP on a manned boat at Walnut Grove showed mean differences of 4.5 cm/s in the u (eastward) and 7.6 cm/s in the v (northward) components, and RMS differences of 14.7 cm/s in the u component and 21.0 cm/s in the v component. Quantitative comparisons between the RiverSondes and ADCPs on autonomous survey vessels at Threemile Slough showed mean differences of 0.007 cm/s in the u component and 0.5 cm/s in the v component, and RMS differences of 7.9 cm/s in the u component and 13.5 cm/s in the v component after obvious outliers were removed. ?? 2008 IEEE.
The flow of a foam in a two-dimensional porous medium
Géraud, Baudouin; Jones, Siân. A.; Cantat, Isabelle; Dollet, Benjamin; Méheust, Yves
2016-02-01
Foams have been used for decades as displacing fluids for enhanced oil recovery and aquifer remediation, and more recently, for remediation of the vadose zone, in which case foams carry chemical amendments. Foams are better injection fluids than aqueous solutions due to their low sensitivity to gravity and because they are less sensitive to permeability heterogeneities, thus allowing a more uniform sweep. The latter aspect results from their peculiar rheology, whose understanding motivates the present study. We investigate foam flow through a two-dimensional porous medium consisting of circular obstacles positioned randomly in a horizontal transparent Hele-Shaw cell. The local foam structure is recorded in situ, which provides a measure of the spatial distribution of bubble velocities and sizes at regular time intervals. The flow exhibits a rich phenomenology including preferential flow paths and local flow nonstationarity (intermittency) despite the imposed permanent global flow rate. Moreover, the medium selects the bubble size distribution through lamella division-triggered bubble fragmentation. Varying the mean bubble size of the injected foam, its water content, and mean velocity, we characterize those processes systematically. In particular, we measure the spatial evolution of the distribution of bubble areas, and infer the efficiency of bubble fragmentation depending on the various control parameters. We furthermore show that the distributions of bubble sizes and velocities are correlated. This study sheds new light on the local rheology of foams in porous media and opens the way toward quantitative characterization of the relationship between medium geometry and foam flow properties. It also suggests that large-scale models of foam flows in the subsurface should account for the correlation between bubble sizes and velocities.
One- and two-dimensional modelling of overland flow in semiarid shrubland, Jornada basin, New Mexico
Howes, David A.; Abrahams, Athol D.; Pitman, E. Bruce
2006-03-01
Two distributed parameter models, a one-dimensional (1D) model and a two-dimensional (2D) model, are developed to simulate overland flow in two small semiarid shrubland watersheds in the Jornada basin, southern New Mexico. The models are event-based and represent each watershed by an array of 1-m2 cells, in which the cell size is approximately equal to the average area of the shrubs.Each model uses only six parameters, for which values are obtained from field surveys and rainfall simulation experiments. In the 1D model, flow volumes through a fixed network are computed by a simple finite-difference solution to the 1D kinematic wave equation. In the 2D model, flow directions and volumes are computed by a second-order predictor-corrector finite-difference solution to the 2D kinematic wave equation, in which flow routing is implicit and may vary in response to flow conditions.The models are compared in terms of the runoff hydrograph and the spatial distribution of runoff. The simulation results suggest that both the 1D and the 2D models have much to offer as tools for the large-scale study of overland flow. Because it is based on a fixed flow network, the 1D model is better suited to the study of runoff due to individual rainfall events, whereas the 2D model may, with further development, be used to study both runoff and erosion during multiple rainfall events in which the dynamic nature of the terrain becomes an important consideration.
Two-Fluid Equilibrium for Transonic Poloidal Flows
Guazzotto, Luca; Betti, Riccardo
2012-03-01
Much analytical and numerical work has been done in the past on ideal MHD equilibrium in the presence of macroscopic flow. In recent years, several authors have worked on equilibrium formulations for a two-fluid system, in which inertial ions and massless electrons are treated as distinct fluids. In this work, we present our approach to the formulation of the two-fluid equilibrium problem. Particular attention is given to the relation between the two-fluid equations and the equilibrium equations for the single-fluid ideal MHD system. Our purpose is to reconsider the results of one-fluid calculation with the more accurate two-fluid model, referring in particular to the so-called transonic discontinuities, which occur when the poloidal velocity spans a range crossing the poloidal sound speed (i.e., the sound speed reduced by a factor Bp/B). It is expected that the one-fluid discontinuity will be resolved into a sharp gradient region by the two-fluid model. Also, contrary to the ideal MHD case, in the two-fluid model the equations governing the equilibrium are elliptic in the whole range of interest for transonic equilibria. The numerical solution of the two-fluid system of equations is going to be based on a code built on the structure of the existing ideal-MHD code FLOW.
Yatou, Hiroki
2010-09-01
We numerically find three types of steady solutions of viscoelastic flows and flow pattern transitions between them in a two-dimensional wavy-walled channel for low to moderate Weissenberg (Wi) and Reynolds (Re) numbers using a spectral element method. The solutions are called "convective," "transition," and "elastic" in ascending order of Wi. In the convective region in the Wi-Re parameter space, convective effect and pressure gradient balance on average. As Wi increases, elastic effect becomes comparable, and the first transition sets in. Through the transition, a separation vortex disappears, and a jet flow induced close to the wall by the viscoelasticity moves into the bulk; the viscous drag significantly drops, and the elastic wall friction rises sharply. This transition is caused by an elastic force in the streamwise direction due to the competition of the convective and elastic effects. In the transition region, the convective and elastic effects balance. When the elastic effect becomes greater than the convective effect, the second transition occurs but it is relatively moderate. The second transition seems to be governed by the so-called Weissenberg effect. These transitions are not sensitive to driving forces. By a scaling analysis, it is shown that the stress component is proportional to the Reynolds number on the boundary of the first transition in the Wi-Re space. This scaling coincides well with the numerical result.
Effect of a levee setback on aquatic resources using two-dimensional flow and bioenergetics models
Black, Robert W.; Czuba, Christiana R.; Magirl, Christopher S.; McCarthy, Sarah; Berge, Hans; Comanor, Kyle
2016-04-05
Watershed restoration is the focus of many resource managers and can include a multitude of restoration actions each with specific restoration objectives. For the White River flowing through the cities of Pacific and Sumner, Washington, a levee setback has been proposed to reconnect the river with its historical floodplain to help reduce flood risks, as well as provide increased habitat for federally listed species of salmonids. The study presented here documents the use of a modeling framework that integrates two-dimensional hydraulic modeling with process-based bioenergetics modeling for predicting how changes in flow from reconnecting the river with its floodplain affects invertebrate drift density and the net rate of energy intake of juvenile salmonids. Modeling results were calculated for flows of 25.9 and 49.3 cubic meters per second during the spring, summer, and fall. Predicted hypothetical future mean velocities and depths were significantly lower and more variable when compared to current conditions. The abundance of low energetic cost and positive growth locations for salmonids were predicted to increase significantly in the study reach following floodplain reconnection, particularly during the summer. This modeling framework presents a viable approach for evaluating the potential fisheries benefits of reconnecting a river to its historical floodplain that integrates our understanding of hydraulic, geomorphology, and organismal biology.
Unsteady Free-surface Waves Due to a Submerged Body in Two-dimensional Oseen Flows
Institute of Scientific and Technical Information of China (English)
LUDong-qiang; AllenT.CHWANG
2004-01-01
The two-dimensional unsteady free-surface waves due to a submerged body moving in an incompressible viscous fluid of infinite depth is considered.The disturbed flow is governed by the unsteadyOseen equations with the kinematic and dynamic boundary conditions linearized for the free-surface waves.Accordingly, the body is mathematically simulated by an Oseenlet with a periodically oscillating strength.By means of Fourier transforms,the exact solution for the free-surface waves is expressed by an integral with a complex dispersion function, which explicitly shows that the wave dynamics is characterized by a Reynolds number and a Strouhal number.By applying Lighthill's theorem, asymptotic representations are derived for the far-field waves with a sub-critical and a super-critical Strouhal number. It is found that the generated waves due to the oscillating Oseenlet consist of the steady-state and transient responses. For the viscous flow with a sub-critical Strouhal number, there exist four waves: three propagate downstream while one propagates upstream.However, for the viscous flow with a super-critical Strouhal number, there exist two waves only,which propagate downstream.
Two-dimensional relativistic space charge limited current flow in the drift space
Energy Technology Data Exchange (ETDEWEB)
Liu, Y. L.; Chen, S. H., E-mail: chensh@ncu.edu.tw [Department of Physics, National Central University, Jhongli 32001, Taiwan (China); Koh, W. S. [A-STAR Institute of High Performance Computing, Singapore 138632 (Singapore); Ang, L. K. [Engineering Product Development, Singapore University of Technology and Design, Singapore 138682 (Singapore)
2014-04-15
Relativistic two-dimensional (2D) electrostatic (ES) formulations have been derived for studying the steady-state space charge limited (SCL) current flow of a finite width W in a drift space with a gap distance D. The theoretical analyses show that the 2D SCL current density in terms of the 1D SCL current density monotonically increases with D/W, and the theory recovers the 1D classical Child-Langmuir law in the drift space under the approximation of uniform charge density in the transverse direction. A 2D static model has also been constructed to study the dynamical behaviors of the current flow with current density exceeding the SCL current density, and the static theory for evaluating the transmitted current fraction and minimum potential position have been verified by using 2D ES particle-in-cell simulation. The results show the 2D SCL current density is mainly determined by the geometrical effects, but the dynamical behaviors of the current flow are mainly determined by the relativistic effect at the current density exceeding the SCL current density.
Gelfgat, Alexander Yu.
2016-08-01
A visualization of three-dimensional incompressible flows by divergence-free quasi-two-dimensional projections of the velocity field onto three coordinate planes is revisited. An alternative and more general way to compute the projections is proposed. The approach is based on the Chorin projection combined with a SIMPLE-like iteration. Compared to the previous methodology based on divergence-free Galerkin-Chebyshev bases, this technique, formulated in general curvilinear coordinates, is applicable to any flow region and allows for faster computations. To illustrate this visualization method, examples in Cartesian and spherical coordinates, as well as post-processing of experimental 3D-PTV data, are presented.
Two-dimensional Rarefaction Waves in the High-speed Two-phase Flow
Nakagawa, Masafumi; Harada, Atsushi
Two-phase flow nozzles are used in the total flow system for geothermal power plants and in the ejector of the refrigerant cycle, etc. One of the most important functions of a two-phase flow nozzle is to convert the thermal energy to the kinetic energy of the two-phase flow. The kinetic energy of the two-phase flow exhausted from a nozzle is available for all applications of this type. There exist the shock waves or rarefaction waves at the outlet of a supersonic nozzle in the case of non-best fitting expansion conditions when the operation conditions of the nozzle are widely chosen. The purpose of the present study is to elucidate theoretically the character of the rarefaction waves at the outlet of the supersonic two-phase flow nozzle. Two-dimensional basic equations for the compressible two-phase flow are introduced considering the inter-phase momentum transfer. Sound velocities are obtained from these equations by using monochromatic wave approximation. Those depend on the relaxation time that determines the momentum transfer. The two-phase flow with large relaxation times has a frozen sound velocity, and with small one has an equilibrium sound velocity. Rarefaction waves which occurred behind the two-phase flow nozzle are calculated by the CIP method. Although the frozen Mach number, below one, controls these basic equations, the rarefaction waves appeared for small relaxation time. The Mach line behind which the expansion starts depends on the inlet velocity and the relaxation time. Those relationships are shown in this paper. The pressure expansion curves are only a function of the revolution angle around the corner of the nozzle outlet for the relaxation time less than 0.1. For the larger relaxation time, the pressure decays because of internal friction caused by inter phase momentum transfer, and the expansion curves are a function of not only the angle but also the flow direction. The calculated expansion curves are compared with the experimental ones
Al-Kouz, Wael; Alshare, Aiman; Alkhalidi, Ammar; Kiwan, Suhil
2016-01-01
A numerical simulation of the steady two-dimensional laminar natural convection heat transfer for the gaseous low-pressure flows in the annulus region between two concentric horizontal cylinders is carried out. This type of flow occurs in "evacuated" solar collectors and in the receivers of the solar parabolic trough collectors. A finite volume code is used to solve the coupled set of governing equations. Boussinesq approximation is utilized to model the buoyancy effect. A correlation for the thermal conductivity ratio (k r = k eff/k) in terms of Knudsen number and the modified Rayleigh number is proposed for Prandtl number (Pr = 0.701). It is found that as Knudsen number increases then the thermal conductivity ratio decreases for a given Rayleigh number. Also, it is shown that the thermal conductivity ratio k r increases as Rayleigh number increases. It appears that there is no consistent trend for varying the dimensionless gap spacing between the inner and the outer cylinder ([Formula: see text]) on the thermal conductivity ratio (k r) for the considered spacing range.
Two dimensional heat transfer problem in flow boiling in a rectangular minichannel
Directory of Open Access Journals (Sweden)
Hożejowska Sylwia
2015-01-01
Full Text Available The paper presents mathematical modelling of flow boiling heat transfer in a rectangular minichannel asymmetrically heated by a thin and one-sided enhanced foil. Both surfaces are available for observations due to the openings covered with glass sheets. Thus, changes in the colour of the plain foil surface can be registered and then processed. Plain side of the heating foil is covered with a base coat and liquid crystal paint. Observation of the opposite, enhanced surface of the minichannel allows for identification of the gas-liquid two-phase flow patterns and vapour quality. A two-dimensional mathematical model of heat transfer in three subsequent layers (sheet glass, heating foil, liquid was proposed. Heat transfer in all these layers was described with the respective equations: Laplace equation, Poisson equation and energy equation, subject to boundary conditions corresponding to the observed physical process. The solutions (temperature distributions in all three layers were obtained by Trefftz method. Additionally, the temperature of the boiling liquid was obtained by homotopy perturbation method (HPM combined with Trefftz method. The heat transfer coefficient, derived from Robin boundary condition, was estimated in both approaches. In comparison, the results by both methods show very good agreement especially when restricted to the thermal sublayer.
Formation of multiple shocklets in a transonic diffuser flow
Handa, T.; Miyazato, Y.; Masuda, M.; Matsuo, K.
Multiple shocklets are frequently generated in transonic diffuser flows. The present paper investigates the formation of these shocklets with a high-speed CCD camera combined with the schlieren method. It is observed that compression waves steepen while propagating upstream, and eventually become new shock waves. The ordinary shock wave is found to move upstream beyond the nozzle throat or to disappear while moving downstream depending on the pressure ratio across the nozzle. This phenomenon is also analyzed with the one-dimensional Euler equations by assuming a pressure disturbance given by the sine function at the channel exit. The calculated results are found to reproduce quite well the experimental behavior of the shocklets. The effect of the frequency of disturbance is also studied numerically, and it is shown that the multiple shocklet pattern appears when the amplitude of disturbance is not large and the diverging part of the channel downstream of the ordinary shock wave is long.
Institute of Scientific and Technical Information of China (English)
Mohammad Ali; S.Ahmed; A.K.M.Sadrul Islam
2003-01-01
A numerical investigation has been performed on supersonic mixing of hydrogen with air in a Scramjet(Supersonic Combustion Ramjet) combustor and its flame holding capability by solving Two-Dimensional full Navier-Stokes equations. The main flow is air entering through a finite width of inlet and gaseous hydrogen is injected perpendicularly from the side wall. An explicit Harten-Yee Non-MUSCL Modified-flux-type TVD scheme has been used to solve the system of equations, and a zero-equation algebraic turbulence model to calculate the eddy viscosity coefficient. In this study the enhancement of mixing and good flame holding capability of a supersonic combustor have been investigated by varying the distance of injector position from left boundary keeping constant the backward-facing step height and other calculation parameters. The results show that the configuration for small distance of injector position has high mixing efficiency but the upstream recirculation can not evolved properly which is an important factor for flame holding capability. On the other hand, the configuration for very long distance has lower mixing efficiency due to lower gradient of hydrogen mass concentration on the top of injector caused by the expansion of side jet in both upstream and downstream of injector. For moderate distance of injector position, large and elongated upstream recirculation can evolve which might be activated as a good flame holder.
Simulations of Viscous Accretion Flow around Black Holes in a Two-dimensional Cylindrical Geometry
Lee, Seong-Jae; Chattopadhyay, Indranil; Kumar, Rajiv; Hyung, Siek; Ryu, Dongsu
2016-11-01
We simulate shock-free and shocked viscous accretion flows onto a black hole in a two-dimensional cylindrical geometry, where initial conditions were chosen from analytical solutions. The simulation code used the Lagrangian total variation diminishing plus remap routine, which enabled us to attain high accuracy in capturing shocks and to handle the angular momentum distribution correctly. The inviscid shock-free accretion disk solution produced a thick disk structure, while the viscous shock-free solution attained a Bondi-like structure, but in either case, no jet activity nor any quasi-periodic oscillation (QPO)-like activity developed. The steady-state shocked solution in the inviscid as well as in the viscous regime matched theoretical predictions well. However, increasing viscosity renders the accretion shock unstable. Large-amplitude shock oscillation is accompanied by intermittent, transient inner multiple shocks. This oscillation of the inner part of the disk is interpreted as the source of QPO in hard X-rays observed in micro-quasars. Strong shock oscillation induces strong episodic jet emission. The jets also show the existence of shocks, which are produced as one shell hits the preceding one. The periodicities of the jets and shock oscillation are similar; the jets for the higher viscosity parameter appear to be stronger and faster.
Huang, Huaxiong; Takagi, Shu
2003-08-01
In this paper, we study the convergence property of PHYSALIS when it is applied to incompressible particle flows in two-dimensional space. PHYSALIS is a recently proposed iterative method which computes the solution without imposing the boundary conditions on the particle surfaces directly. Instead, a consistency equation based on the local (near particle) representation of the solution is used as the boundary conditions. One of the important issues needs to be addressed is the convergence properties of the iterative procedure. In this paper, we present the convergence analysis using Laplace and biharmonic equations as two model problems. It is shown that convergence of the method can be achieved but the rate of convergence depends on the relative locations of the cages. The results are directly related to potential and Stokes flows. However, they are also relevant to Navier-Stokes flows, heat conduction in composite media, and other problems.
Controlling Compressor Vane Flow Vectoring Angles at Transonic Speeds
Munson, Matthew; Rempfer, Dietmar; Williams, David; Acharya, Mukund
2003-11-01
The ability to control flow separation angles from compressor inlet guide vanes with a Coanda-type actuator is demonstrated using both wind tunnel experiments and finite element simulations. Vectoring angles up to 40 degrees from the uncontrolled baseline state were measured with helium schlieren visualization at transonic Mach numbers ranging from 0.1 to 0.6, and with airfoil chord Reynolds numbers ranging from 89,000 to 710,000. The magnitude of the vectoring angle is shown to depend upon the geometry of the trailing edge, and actuator slot size, and the momentum flux coefficient. Under certain conditions the blowing has no effect on the vectoring angle indicating that the Coanda effect is not present. DNS simulations with the finite element method investigated the effects of geometry changes and external flow. Continuous control of the vectoring angle is demonstrated, which has important implications for application to rotating machinery. The technique is shown to reduce the stall flow coefficient by 15 percent in an axial flow compressor.
Periodic transonic flow simulation using fourier-based algorithm
Energy Technology Data Exchange (ETDEWEB)
Mohaghegh, Mohammad Reza [Islamic Azad University, Tehran (Iran, Islamic Republic of); Malekjafarian, Majid [University of Birjand, Birjand (Iran, Islamic Republic of)
2014-10-15
The present research simulates time-periodic unsteady transonic flow around pitching airfoils via the solution of unsteady Euler and Navier-Stokes equations, using time spectral method (TSM) and compares it with the traditional methods like BDF and explicit structured adaptive grid method. The TSM uses a Fourier representation in time and hence solves for the periodic state directly without resolving transients (which consume most of the resources in a time-accurate scheme). Mathematical tools used here are discrete Fourier transformations. The TSM has been validated with 2D external aerodynamics test cases. These test cases are NACA 64A010 (CT6) and NACA 0012 (CT1 and CT5) pitching airfoils. Because of turbulent nature of flow, Baldwin-Lomax turbulence model has been used in viscous flow analysis with large oscillation amplitude (CT5 type). The results presented by the TSM are compared with experimental data and the two other methods. By enforcing periodicity and using Fourier representation in time that has a spectral accuracy, tremendous reduction of computational cost has been obtained compared to the conventional time-accurate methods. Results verify the small number of time intervals per pitching cycle (just four time intervals) required to capture the flow physics with small oscillation amplitude (CT6) and large oscillation amplitude (CT5) as compared to the other two methods.
Danila, Bogdan; Mocanu, Gabriela
2015-01-01
We investigate the transition to Self Organized Criticality in a two-dimensional model of a flux tube with a background flow. The magnetic induction equation, represented by a partial differential equation with a stochastic source term, is discretized and implemented on a two dimensional cellular automaton. The energy released by the automaton during one relaxation event is the magnetic energy. As a result of the simulations we obtain the time evolution of the energy release, of the system control parameter, of the event lifetime distribution and of the event size distribution, respectively, and we establish that a Self Organized Critical state is indeed reached by the system. Moreover, energetic initial impulses in the magnetohydrodynamic flow can lead to one dimensional signatures in the magnetic two dimensional system, once the Self Organized Critical regime is established. The applications of the model for the study of Gamma Ray Bursts is briefly considered, and it is shown that some astrophysical paramet...
Erdos, J. I.; Alzner, E.
1977-01-01
A numerical method of solution of the inviscid, compressible, two-dimensional unsteady flow on a blade-to-blade stream surface through a stage (rotor and stator) or a single blade row of an axial flow compressor or fan is described. A cyclic procedure has been developed for representation of adjacent blade-to-blade passages which asymptotically achieves the correct phase between all passages of a stage. A shock-capturing finite difference method is employed in the interior of the passage, and a method of characteristics technique is used at the boundaries. The blade slipstreams form two of the passage boundaries and are treated as moving contact surfaces capable of supporting jumps in entropy and tangential velocity. The Kutta condition is imposed by requiring the slipstreams to originate at the trailing edges, which are assumed to be sharp. Results are presented for several transonic fan rotors and compared with available experimental data, consisting of holographic observations of shock structure and pressure contour maps. A subcritical stator solution is also compared with results from a relaxation method. Finally, a periodic solution for a stage consisting of 44 rotor blades and 46 stator blades is discussed.
Energy Technology Data Exchange (ETDEWEB)
Huerst, C.; Schulz, A.; Wittig, S. [Univ. Karlsruhe (Germany). Lehrstuhl und Inst. fuer Thermische Stroemungsmaschinen
1995-04-01
The present study compares measured and computed heat transfer coefficients for high-speed boundary layer nozzle flows under engine Reynolds number conditions (U{sub {infinity}} = 230 {divided_by} 880 m/s, Re* = 0.37 {divided_by} 1.07 {times} 10{sup 6}). Experimental data have been obtained by heat transfer measurements in a two-dimensional, nonsymmetric, convergent-divergent nozzle. The nozzle wall is convectively cooled using water passages. The coolant heat transfer data and nozzle surface temperatures are used as boundary conditions for a three-dimensional finite-element code, which is employed to calculate the temperature distribution inside the nozzle wall. Heat transfer coefficients along the hot gas nozzle wall are derived from the temperature gradients normal to the surface. The results are compared with numerical heat transfer predictions using the low-Reynolds-number {kappa}-{epsilon} turbulence model by Lam and Bremhorst. Influence of compressibility in the transport equations for the turbulence properties is taken into account by using the local averaged density. The results confirm that this simplification leads to good results for transonic and low supersonic flows.
HO, Yat-Kiu; LIU, Chun-Ho
2015-04-01
The atmospheric boundary layer (ABL) immediately above the urban canopy is the roughness sublayer (RSL). In this layer, flows and turbulence are strongly affected by the roughness elements beneath, e.g. building obstacles. The wind flows over urban areas could be represented by conventional logarithmic law of the wall (log-law) in the neutrally stratified ABL. However, in the RSL region, the vertical wind profile deviates from that predicted from log-law and the effect could be extended from ground level up to several canopy heights. As a result, the Monin-Obukhov similarity theory (MOST) fails and an additional length scale is required to describe the flows. The key aim of this study is to introduce a simple wind profile model which accounts for the effect of the RSL in neutral stratification using wind tunnel experiments. Profile measurements of wind speeds and turbulence quantities over various two-dimensional (2D) idealised roughness elements are carried out in an open-circuit wind tunnel with test section of size 560 mm (width) × 560 mm (height) × 6 m (length). The separation between the roughness elements is varied systematically so that ten different types of surface forms are adopted. The velocity measurements are obtained by hot-wire anemometry using X-probe design (for UW- measurements) with a constant temperature anemometer. For each configuration, eight vertical profiles are collected over the canopy, including solid boundaries and cavities of the roughness elements. Firstly, we compute the measurement results using conventional MOST to determine different roughness parameters. Afterwards, we derive the RSL height from the Reynolds stress profiles. Since the profiles taken from different locations of the canopy are eventually converged with increasing height, we use this 'congregated height' to define the RSL height. Next, we introduce an alternative function, i.e. power-law function, instead of MOST, to describe the velocity profile in attempt to
The Second Las Cruces Trench Experiment: Experimental Results and Two-Dimensional Flow Predictions
Hills, R. G.; Wierenga, P. J.; Hudson, D. B.; Kirkland, M. R.
1991-10-01
As part of a comprehensive field study designed to provide data to test stochastic and deterministic models of water flow and contaminant transport in the vadose zone, several trench experiments were performed in the semiarid region of southern New Mexico. The first trench experiment is discussed by Wierenga et al. (this issue). During the second trench experiment, a 1.2 m wide by 12 m long area on the north side of and parallel to a 26.4 m long by 4.8 m wide by 6m deep trench was irrigated with water containing tracers using a carefully controlled drip irrigation system. The irrigated area was heavily instrumented with tensiometers and neutron probe access tubes to monitor water movement, and with suction samplers to monitor solute transport. Water containing tritium and bromide was. applied during the first 11.5 days of the study. Thereafter, water was applied without tracers for an additional 64 days. Both water movement and tracer movement were monitored in the subsoil during infiltration and redistribution. The experimental results indicate that water and bromide moved fairly uniformly during infiltration and the bromide moved ahead of the tritium due to anion exclusion during redistribution. Comparisons between measurements and predictions made with a two-dimensional model show qualitative agreement for two of the three water content measurement planes. Model predictions of tritium and bromide transport were not as satisfactory. Measurements of both tritium and bromide show localized areas of high relative concentrations and a large downward motion of bromide relative to tritium during redistribution. While the simple deterministic model does show larger downward motions for bromide than for tritium during redistribution, it does not predict the high concentrations of solute observed during infiltration, nor can it predict the heterogeneous behavior observed for tritium during infiltration and for bromide during redistribution.
Bouncing, rolling, energy flows, and cluster formation in a two-dimensional vibrated granular gas
Pérez-Ángel, Gabriel; Nahmad-Molinari, Yuri
2011-10-01
We study the formation of crystalline clusters for a two-dimensional (2D) sinusoidally vibrated granular gas, with maximum vertical acceleration smaller than gravity, using fully 3D simulations. It is found that this phenomenon arises from the spontaneous segregation of the granulate into two dynamical modes: one of grains that bounce in synchrony with the motion of the sustaining plate (“bouncers”) and another of grains that cease to bounce and simply rolls on the plate, without ever loosing contact with it (“rollers”). These two dynamical categories are quite robust with respect to perturbations. The populations for bouncers and rollers depend on the preparation of the granulate and can be made to take arbitrary values in all the range of accelerations where both dynamical modes are present. It is found that the dynamical mode with the largest population coalesces in clusters under the influence of the other mode, whose grains act as a higher pressure gas that compresses the clusters. In this way it is possible to produce clusters of rollers or clusters of bouncers. A gas made of grains from only one dynamical class shows only weak density fluctuations. When the occupation fractions for both modes are similar, one observes segregation and clusters of both types. The clustering of the gas is monitored using both the average coordination number and the local hexatic order parameter ψ6. Energy flows in the plane are monitored, and it is shown that roller-bouncer collisions increase horizontal kinetic energy, while all other types of collisions reduce this energy. We find that friction with the substrate is the main sink of horizontal energy for these granular gases.
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.
Energy Technology Data Exchange (ETDEWEB)
Costa-Cabral, M.C. [GKSS-Forschungszentrum Geesthacht GmbH (Germany). Inst. fuer Hydrophysik
1999-07-01
Current Lagrangian models for simulating advective transport of trace species in a discretized two-dimensional flow field use simplified descriptions of tracer sources, receptors and flow paths. When 'forward trajectories' are used, a diffuse source spread over a two-dimensional grid cell is treated as a single point source located at the cell's center, and its flow is projected in the downflow direction by a line. When 'backward trajectories' are used, each cell is treated as a point receptor and flow is projected back in time in the upflow direction by a line. In both cases, two-dimensional sources or receptors are treated as zero dimensional, and two-dimensional flow tubes are replaced by one-dimensional lines. While these simplifications may be acceptable in some cases, they can generate large errors when the flow field contains regions of considerable divergence of flow directions, or when fine scales are used. A new algorithm is introduced, called TUBES, which provides an exact solution to advective transport in a discretized two-dimensional flow field. TUBES uses two-dimensional flow tubes whose width expands and contracts over directionally divergent and convergent regions of the flow field, respectively. TUBES has applications in a wide variety of the earth sciences, including atmospheric science, oceanography, and surface and groundwater hydrology. (orig.) [German] Gegenwaertige Lagrange-Modelle zur Simulation advektiver Transporte von Tracern in einem diskretisierten zweidimensionalen Stroemungsfeld verwenden vereinfachte Beschreibungen der Quellen, Rezeptoren und Transportwege. Bei der Verwendung vorwaerts gerichteter Trajektorien ('forward trajectories') werden diffusive Quellen, die ueber eine zweidimensionale Gitterzelle verteilt sind, als Punktquelle behandelt, und der Transport mit der Stroemung erfolgt entlang einer Linie. Bei der Verwendung rueckwaerts gerichteter Trajektorien ('backward trajectories
Olson, L. E.; Dvorak, F. A.
1976-01-01
The viscous subsonic flow past two-dimensional and infinite-span swept multi-component airfoils is studied theoretically and experimentally. The computerized analysis is based on iteratively coupled boundary-layer and potential-flow analysis. The method, which is restricted to flows with only slight separation, gives surface pressure distribution, chordwise and spanwise boundary-layer characteristics, lift, drag, and pitching moment for airfoil configurations with up to four elements. Merging confluent boundary layers are treated. Theoretical predictions are compared with an exact theoretical potential flow solution and with experimental measures made in the Ames 40- by 80-Foot Wind Tunnel for both two-dimensional and infinite-span swept wing configurations. Section lift characteristics are accurately predicted for zero and moderate sweep angles where flow separation effects are negligible.
Olson, L. E.; Dvorak, F. A.
1975-01-01
The viscous subsonic flow past two-dimensional and infinite-span swept multi-component airfoils is studied theoretically and experimentally. The computerized analysis is based on iteratively coupled boundary layer and potential flow analysis. The method, which is restricted to flows with only slight separation, gives surface pressure distribution, chordwise and spanwise boundary layer characteristics, lift, drag, and pitching moment for airfoil configurations with up to four elements. Merging confluent boundary layers are treated. Theoretical predictions are compared with an exact theoretical potential flow solution and with experimental measures made in the Ames 40- by 80-Foot Wind Tunnel for both two-dimensional and infinite-span swept wing configurations. Section lift characteristics are accurately predicted for zero and moderate sweep angles where flow separation effects are negligible.
Three-dimensional flows in a transonic compressor rotor
Reid, Lonnie; Celestina, Mark L.; Dewitt, Kenneth; Keith, Theo
1991-01-01
This study involves an experimental and numerical investigation of the three-dimensional flows in a transonic compressor rotor. A variety of data which could be used, in a complementary fashion, to validate/calibrate the computational fluid dynamics turbomachinery code and improve understanding of the flow physics, were acquired. Detailed radial survey data which consisted of total pressure, total temperature, static pressure and flow angle were obtained at stations upstream and downstream of the rotor blade. Detailed velocity and turbulence profiles were obtained upstream of the rotor and used as the upstream boundary conditions for the numerical analysis. Calibrated flush-mounted hot film probes were used to measure wall shear stress on the hub and casing walls upstream of the rotor. The blade-to-blade shear-stress angle distributions were obtained at two axial locations on the rotor casing, using flush-mounted hot film probes. A numerical analysis conducted using a three-dimensional Navier-Stokes code was compared with the experimental results.
Performance of turbulence models for transonic flows in a diffuser
Liu, Yangwei; Wu, Jianuo; Lu, Lipeng
2016-09-01
Eight turbulence models frequently used in aerodynamics have been employed in the detailed numerical investigations for transonic flows in the Sajben diffuser, to assess the predictive capabilities of the turbulence models for shock wave/turbulent boundary layer interactions (SWTBLI) in internal flows. The eight turbulence models include: the Spalart-Allmaras model, the standard k - 𝜀 model, the RNG k - 𝜀 model, the realizable k - 𝜀 model, the standard k - ω model, the SST k - ω model, the v2¯ - f model and the Reynolds stress model. The performance of the different turbulence models adopted has been systematically assessed by comparing the numerical results with the available experimental data. The comparisons show that the predictive performance becomes worse as the shock wave becomes stronger. The v2¯ - f model and the SST k - ω model perform much better than other models, and the SST k - ω model predicts a little better than the v2¯ - f model for pressure on walls and velocity profile, whereas the v2¯ - f model predicts a little better than the SST k - ω model for separation location, reattachment location and separation length for strong shock case.
Wind Tunnel Study on Flows over Various Two-dimensional Idealized Urban-liked Surfaces
Ho, Yat-Kiu; Liu, Chun-Ho
2013-04-01
Extensive human activities (e.g. increased traffic emissions) emit a wide range of pollutants resulting in poor urban area air quality. Unlike open, flat and homogenous rural terrain, urban surface is complicated by the presence of buildings, obstacles and narrow streets. The irregular urban surfaces thus form a random roughness that further modifies the near-surface flows and pollutant dispersion. In this study, a physical modelling approach is employed to commence a series of wind tunnel experiments to study the urban-area air pollution problems. The flow characteristics over different hypothetical urban roughness surfaces were studied in a wind tunnel in isothermal conditions. Preliminary experiments were conducted based on six types of idealized two-dimensional (2D) street canyon models with various building-height-to-street-width (aspect) ratios (ARs) 1, 1/2, 1/4, 1/8, 1/10 and 1/12. The main instrumentation is an in-house 90o X-hotwire anemometry. In each set of configuration, a sampling street canyon was selected near the end of the streamwise domain. Its roof level, i.e. the transverse between the mid points of the upstream and downstream buildings, was divided into eight segments. The measurements were then recorded on the mid-plane of the spannwise domain along the vertical profile (from building roof level to the ceiling of wind tunnel) of the eight segments. All the data acquisition processes were handled by the NI data acquisition modules, NI 9239 and CompactDAQ-9188 hardware. Velocity calculation was carried out in the post-processing stage on a digital computer. The two-component flow velocities and velocity fluctuations were calculated at each sampling points, therefore, for each model, a streamwise average of eight vertical profiles of mean velocity and velocity fluctuations was presented. A plot of air-exchange rate (ACH) against ARs was also presented in order to examine the ventilation performance of different tested models. Preliminary results
Froessling, Nils
1958-01-01
The fundamental boundary layer equations for the flow, temperature and concentration fields are presented. Two dimensional symmetrical and unsymmetrical and rotationally symmetrical steady boundary layer flows are treated as well as the transfer boundary layer. Approximation methods for the calculation of the transfer layer are discussed and a brief survey of an investigation into the validity of the law that the Nusselt number is proportional to the cube root of the Prandtl number is presented.
水坝绕流的数值研究%Numerical Study of Two-Dimensional Viscous Flow over Dams
Institute of Scientific and Technical Information of China (English)
王利兵; 刘宇陆; 涂敏杰
2003-01-01
In this paper, the characteristics of two-dimensional viscous flow over two dams were numerically investigated. The results show that the behavior of the vortices is closely related to the space between two dams, water depth, Fr number and Reynolds number. In addition, the flow properties behind each dam are different, and the changes over two dams are more complex than over one dam. Finally, the relevant turbulent characteristics were analyzed.
Gallet, Basile
2015-01-01
We investigate the behavior of flows, including turbulent flows, driven by a horizontal body-force and subject to a vertical magnetic field, with the following question in mind: for very strong applied magnetic field, is the flow mostly two-dimensional, with remaining weak three-dimensional fluctuations, or does it become exactly 2D, with no dependence along the vertical? We first focus on the quasi-static approximation, i.e. the asymptotic limit of vanishing magnetic Reynolds number Rm << 1: we prove that the flow becomes exactly 2D asymptotically in time, regardless of the initial condition and provided the interaction parameter N is larger than a threshold value. We call this property "absolute two-dimensionalization": the attractor of the system is necessarily a (possibly turbulent) 2D flow. We then consider the full-magnetohydrodynamic equations and we prove that, for low enough Rm and large enough N, the flow becomes exactly two-dimensional in the long-time limit provided the initial vertically-de...
Shi, Xiao-Qiu; Wu, Yi-Qi; Li, Hong; Zhong, Rui
2007-11-01
Two-dimensional cellular automaton model has been broadly researched for traffic flow, as it reveals the main characteristics of the traffic networks in cities. Based on the BML models, a first-order phase transition occurs between the low-density moving phase in which all cars move at maximal speed and the high-density jammed phase in which all cars are stopped. However, it is not a physical result of a realistic system. We propose a new traffic rule in a two-dimensional traffic flow model containing road sections, which reflects that a car cannot enter into a road crossing if the road section in front of the crossing is occupied by another car. The simulation results reveal a second-order phase transition that separates the free flow phase from the jammed phase. In this way the system will not be entirely jammed (“don’t block the box” as in New York City).
Hot-wire calibration in subsonic/transonic flow regimes
Nagabushana, K. A.; Ash, Robert L.
1995-01-01
A different approach for calibrating hot-wires, which simplifies the calibration procedure and reduces the tunnel run-time by an order of magnitude was sought. In general, it is accepted that the directly measurable quantities in any flow are velocity, density, and total temperature. Very few facilities have the capability of varying the total temperature over an adequate range. However, if the overheat temperature parameter, a(sub w), is used to calibrate the hot-wire then the directly measurable quantity, voltage, will be a function of the flow variables and the overheat parameter i.e., E = f(u,p,a(sub w), T(sub w)) where a(sub w) will contain the needed total temperature information. In this report, various methods of evaluating sensitivities with different dependent and independent variables to calibrate a 3-Wire hot-wire probe using a constant temperature anemometer (CTA) in subsonic/transonic flow regimes is presented. The advantage of using a(sub w) as the independent variable instead of total temperature, t(sub o), or overheat temperature parameter, tau, is that while running a calibration test it is not necessary to know the recovery factor, the coefficients in a wire resistance to temperature relationship for a given probe. It was deduced that the method employing the relationship E = f (u,p,a(sub w)) should result in the most accurate calibration of hot wire probes. Any other method would require additional measurements. Also this method will allow calibration and determination of accurate temperature fluctuation information even in atmospheric wind tunnels where there is no ability to obtain any temperature sensitivity information at present. This technique greatly simplifies the calibration process for hot-wires, provides the required calibration information needed in obtaining temperature fluctuations, and reduces both the tunnel run-time and the test matrix required to calibrate hotwires. Some of the results using the above techniques are presented
Adaptivity techniques for the computation of two-dimensional viscous flows using structured meshes
Szmelter, J.; Evans, A.; Weatherill, N. P.
In this paper three different adaptivity techniques have been investigated on the base of structured meshes. All the techniques indicate the significance of using adaptivity for improving computational results. In particular, the technique of combining point enrichment and node movement strategies offers the best compromise. Although, the work presented here used two-dimensional structured meshes, the techniques can be readily applied to hybrid and unstructured meshes. Also, preliminary three-dimensional numerical results have been already obtained by coauthors.
Institute of Scientific and Technical Information of China (English)
Bai Jing-Song; Zhang Zhan-Ji; Li Ping; Zhong Min
2006-01-01
Based on the classical Roe method, we develop an interface capture method according to the general equation of state, and extend the single-fluid Roe method to the two-dimensional (2D) multi-fluid flows, as well as construct the continuous Roe matrix for the whole flow field. The interface capture equations and fluid dynamic conservative equations are coupled together and solved by using any high-resolution schemes that usually suit for the single-fluid flows. Some numerical examples are given to illustrate the solution of 1D and 2D multi-fluid Riemann problems.
Gelfgat, Alexander
2015-01-01
A visualization of three-dimensional incompressible flows by divergence-free quasi-two-dimensional projections of the velocity field on three coordinate planes was recently proposed. The projections were calculated using divergence-free Galerkin bases, which resulted in the whole procedure being complicated and CPU-time consuming. Here we propose an alternative way based on the Chorin projection combined with a SIMPLE-like iteration. The approach proposed is much easier in realization, allows...
Itoh, Tsubasa; Miura, Hideyuki; Yoneda, Tsuyoshi
2016-09-01
In this paper, we consider the two-dimensional Euler flow under a simple symmetry condition, with hyperbolic structure in a unit square {D = {(x_1,x_2):0 < x_1+x_2 < √{2},0 < -x_1+x_2 < √{2}}}. It is shown that the Lipschitz estimate of the vorticity on the boundary is at most a single exponential growth near the stagnation point.
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.
2015-01-01
A two-dimensional single-phase model is developed for the steady-state and transient analysis of polymer electrolyte membrane fuel cells (PEMFC). Based on diluted and concentrated solution theories, viscous flow is introduced into a phenomenological multi-component modeling framework in the membrane. Characteristic variables related to the water uptake are discussed. A ButlereVolmer formulation of the current-overpotential relationship is developed based on an elementary mechanism of elect...
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.
Numerical Simulation of the Flow around Two-dimensional Partially Cavitating Hydrofoils
Institute of Scientific and Technical Information of China (English)
Fahri Celik; Yasemin Arikan Ozden; Sakir Bal
2014-01-01
In the present study, a new approach is applied to the cavity prediction for two-dimensional (2D) hydrofoils by the potential based boundary element method (BEM). The boundary element method is treated with the source and doublet distributions on the panel surface and cavity surface by the use of the Dirichlet type boundary conditions. An iterative solution approach is used to determine the cavity shape on partially cavitating hydrofoils. In the case of a specified cavitation number and cavity length, the iterative solution method proceeds by addition or subtraction of a displacement thickness on the cavity surface of the hydrofoil. The appropriate cavity shape is obtained by the dynamic boundary condition of the cavity surface and the kinematic boundary condition of the whole foil surface including the cavity. For a given cavitation number the cavity length of the 2D hydrofoil is determined according to the minimum error criterion among different cavity lengths, which satisfies the dynamic boundary condition on the cavity surface. The NACA 16006, NACA 16012 and NACA 16015 hydrofoil sections are investigated for two angles of attack. The results are compared with other potential based boundary element codes, the PCPAN and a commercial CFD code (FLUENT). Consequently, it has been shown that the results obtained from the two dimensional approach are consistent with those obtained from the others.
Numerical simulation of the flow around two-dimensional partially cavitating hydrofoils
Celik, Fahri; Ozden, Yasemin Arikan; Bal, Sakir
2014-09-01
In the present study, a new approach is applied to the cavity prediction for two-dimensional (2D) hydrofoils by the potential based boundary element method (BEM). The boundary element method is treated with the source and doublet distributions on the panel surface and cavity surface by the use of the Dirichlet type boundary conditions. An iterative solution approach is used to determine the cavity shape on partially cavitating hydrofoils. In the case of a specified cavitation number and cavity length, the iterative solution method proceeds by addition or subtraction of a displacement thickness on the cavity surface of the hydrofoil. The appropriate cavity shape is obtained by the dynamic boundary condition of the cavity surface and the kinematic boundary condition of the whole foil surface including the cavity. For a given cavitation number the cavity length of the 2D hydrofoil is determined according to the minimum error criterion among different cavity lengths, which satisfies the dynamic boundary condition on the cavity surface. The NACA 16006, NACA 16012 and NACA 16015 hydrofoil sections are investigated for two angles of attack. The results are compared with other potential based boundary element codes, the PCPAN and a commercial CFD code (FLUENT). Consequently, it has been shown that the results obtained from the two dimensional approach are consistent with those obtained from the others.
Determination of instantaneous pressure in a transonic base flow using four-pulse tomographic PIV
Blinde, P.L.; Lynch, K.P.; Schrijer, F.F.J.; Van Oudheusden, B.W.
2015-01-01
A tomographic four-pulse PIV system is used in a transonic axisymmetric base flow experiment at a nominal free stream Mach number of 0.7, with the objective to obtain flow acceleration and pressure data. The PIV system, consisting of two double-pulse lasers and twelve cameras, allows acquiring two v
A solution of two-dimensional magnetohydrodynamic flow using the finite volume method
Directory of Open Access Journals (Sweden)
Naceur Sonia
2014-01-01
Full Text Available This paper presents the two dimensional numerical modeling of the coupling electromagnetic-hydrodynamic phenomena in a conduction MHD pump using the Finite volume Method. Magnetohydrodynamic problems are, thus, interdisciplinary and coupled, since the effect of the velocity field appears in the magnetic transport equations, and the interaction between the electric current and the magnetic field appears in the momentum transport equations. The resolution of the Maxwell's and Navier Stokes equations is obtained by introducing the magnetic vector potential A, the vorticity z and the stream function y. The flux density, the electromagnetic force, and the velocity are graphically presented. Also, the simulation results agree with those obtained by Ansys Workbench Fluent software.
Water Impact of Rigid Wedges in Two-Dimensional Fluid Flow
Directory of Open Access Journals (Sweden)
Sawan Shah
2015-01-01
Full Text Available A combined experimental and numerical investigation was conducted into impact of rigid wedges on water in two-dimensional fluid conditions. Drop test experiments were conducted involving symmetric rigid wedges of varying angle and mass impacted onto water. The kinematic behaviour of the wedge and water was characterised using high-speed video. Numerical models were analysed in LS-DYNA® that combined regions of Smoothed Particle Hydrodynamics particles and a Lagrangian element mesh. The analysis captured the majority of experimental results and trends, within the bounds of experimental variance. Further, the combined modelling technique presented a highly attractive combination of computational efficiency and accuracy, making it a suitable candidate for aircraft ditching investigations.
Meng, J. C. S.
1973-01-01
The laminar base flow field of a two-dimensional reentry body has been studied by Telenin's method. The flow domain was divided into strips along the x-axis, and the flow variations were represented by Lagrange interpolation polynomials in the transformed vertical coordinate. The complete Navier-Stokes equations were used in the near wake region, and the boundary layer equations were applied elsewhere. The boundary conditions consisted of the flat plate thermal boundary layer in the forebody region and the near wake profile in the downstream region. The resulting two-point boundary value problem of 33 ordinary differential equations was then solved by the multiple shooting method. The detailed flow field and thermal environment in the base region are presented in the form of temperature contours, Mach number contours, velocity vectors, pressure distributions, and heat transfer coefficients on the base surface. The maximum heating rate was found on the centerline, and the two-dimensional stagnation point flow solution was adquate to estimate the maximum heating rate so long as the local Reynolds number could be obtained.
Two-dimensionalization of the flow driven by a slowly rotating impeller in a rapidly rotating fluid
Machicoane, Nathanaël; Cortet, Pierre-Philippe
2016-01-01
We characterize the two-dimensionalization process in the turbulent flow produced by an impeller rotating at a rate $\\omega$ in a fluid rotating at a rate $\\Omega$ around the same axis for Rossby number $Ro=\\omega/\\Omega$ down to $10^{-2}$. The flow can be described as the superposition of a large-scale vertically invariant global rotation and small-scale shear layers detached from the impeller blades. As $Ro$ decreases, the large-scale flow is subjected to azimuthal modulations. In this regime, the shear layers can be described in terms of wakes of inertial waves traveling with the blades, originating from the velocity difference between the non-axisymmetric large-scale flow and the blade rotation. The wakes are well defined and stable at low Rossby number, but they become disordered at $Ro$ of order of 1. This experiment provides insight into the route towards pure two-dimensionalization induced by a background rotation for flows driven by a non-axisymmetric rotating forcing.
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
Based on the standark κ-ε turbulence model,a new compressible κ-ε model considering the pressure expansion influence due to the compressibility of fluid is developed and aplied to the simulation of 3D transonic turbulent flows in a nozzle and a cascade.The Reynolds averaged N-S equations in generalized curvilinear coordinates are solved with implementation of the new model,the high resolution TVD scheme is used to discretize the convective terms.The numerical results show that the compressible κ-ε odel behaves well in the simulation of transonic internal turbulent flows.
Investigation of Flow Separation in a Transonic-fan Linear Cascade Using Visualization Methods
Lepicovsky, Jan; Chima, Rodrick V.; Jett, Thomas A.; Bencic, Timothy J.; Weiland, Kenneth E.
2000-01-01
An extensive study into the nature of the separated flows on the suction side of modem transonic fan airfoils at high incidence is described in the paper. Suction surface.flow separation is an important flow characteristic that may significantly contribute to stall flutter in transonic fans. Flutter in axial turbomachines is a highly undesirable and dangerous self-excited mode of blade oscillations that can result in high cycle fatigue blade failure. The study basically focused on two visualization techniques: surface flow visualization using dye oils, and schlieren (and shadowgraph) flow visualization. The following key observations were made during the study. For subsonic inlet flow, the flow on the suction side of the blade is separated over a large portion of the blade, and the separated area increases with increasing inlet Mach number. For the supersonic inlet flow condition, the flow is attached from the leading edge up to the point where a bow shock from the upper neighboring blade hits the blade surface. Low cascade solidity, for the subsonic inlet flow, results in an increased area of separated flow. For supersonic flow conditions, a low solidity results in an improvement in flow over the suction surface. Finally, computational results modeling the transonic cascade flowfield illustrate our ability to simulate these flows numerically.
Multi-scale coupling strategy for fully two-dimensional and depth-averaged models for granular flows
Pudasaini, Shiva P.; Domnik, Birte; Miller, Stephen A.
2013-04-01
We developed a full two-dimensional Coulomb-viscoplastic model and applied it for inclined channel flows of granular materials from initiation to their deposition. The model includes the basic features and observed phenomena in dense granular flows like the exhibition of a yield strength and a non-zero slip velocity. A pressure-dependent yield strength is proposed to account for the frictional nature of granular materials. The yield strength can be related to the internal friction angle of the material and plays an important role, for example, in deposition processes. The interaction of the flow with the solid boundary is modelled by a pressure and rate-dependent Coulomb-viscoplastic sliding law. We developed an innovative multi-scale strategy to couple the full two-dimensional, non depth-averaged model (N-DAM) with a one-dimensional, depth-averaged model (DAM). The coupled model reduces computational complexity dramatically by using DAM only in regions with smooth changes of flow variables. The numerics uses N-DAM in regions where depth-averaging becomes inaccurate, for instance, in the initiation and deposition regions, and (particularly) when the flow hits an obstacle or a defense structure. In these regions, momentum transfer must be, and is, considered in all directions. We observe very high coupling performance, and show that the numerical results deviate only slightly from results of the much more cumbersome full two-dimensional model. This shows that the coupled model, which retains all the basic physics of the flow, is an attractive alternative to an expensive, full two-dimensional simulations. We compare simulation results with different experimental data for shock waves appearing in rapid granular flows down inclined channels and impacting a wall. The model predicts the evolution of the strong shock wave and the impact force on a rigid wall for different inclination angles and sliding surfaces. It is demonstrated that the internal friction angle plays an
The use of hot-wire anemometry in transonic periodic flow
Bodapati, S.; Lee, C.-S.
1984-01-01
The unsteady wake profiles of an airfoil with an oscillating flap were measured in the NASA Ames 11 x 11-foot transonic wind tunnel. Laser Doppler Velocimetry (LDV) and holography techniques were used in limited region where optical accessability is available. X-hot-film wire was used to measure the wake profiles in the complete region to obtain magnitude and direction of the flow. A thorough calibration was carried out to determine the sensitivity coefficients of the hot-wire in three different tunnels at transonic speeds. A calculation procedure is established to resolve the hot-wire signals at transonic speeds and applied in the measurements of steady and periodic wake profiles. The effect of flow incidence on the hot-wire signals is evaluated and incorporated in the analyses. Typical hot-wire results are compared with the results of LDV, holography and pitot-static tube embedded with Kulite transducers.
Jamming of particles in a two-dimensional fluid-driven flow
Guariguata, Alfredo; Pascall, Masika A.; Gilmer, Matthew W.; Sum, Amadeu K.; Sloan, E. Dendy; Koh, Carolyn A.; Wu, David T.
2012-12-01
The jamming of particles under flow is of critical importance in a broad range of natural and industrial settings, such as the jamming of ice in rivers, or the plugging of suspended solids in pipeline transport. Relatively few studies have been carried out on jamming of suspended particles under flow, in comparison to the many studies on jamming in gravity-driven flows that have revealed various features of the jamming process. Fluid-driven particle flows differ in several aspects from gravity-driven flows, particularly in being compatible with a range of particle concentrations and velocities. Additionally, there are fluid-particle interactions and hydrodynamic effects. To investigate particle jamming in fluid-driven flows, we have performed both experiments and computer simulations on the flow of circular particles floating over water in an open channel with a restriction. We determined the flow-rate boundary for a dilute-to-dense flow transition, similar to that seen in gravity-driven flows. The maximum particle throughput increased for larger restriction sizes consistent with a Beverloo equation form over the entire range of particle mixtures and restriction sizes. The exponent of ˜3/2 in the Beverloo equation is consistent with approximately constant acceleration of grains due to fluid drag in the immediate region of the opening. We verified that the jamming probability from the dense flow gave a geometric distribution in the number of particles escaping before a jam. The probability of jamming in both experiments and simulations was found to be dependent on the ratio of channel opening to particle size, but only weakly dependent on the fluid flow velocity. Flow entrance effects were measured and observed to affect the jamming probability, and dependence on particle friction coefficient was determined from simulation. A comprehensive model for the jamming probability integrating these observations from the different flow regimes was shown to be in good
ONE- AND TWO-DIMENSIONAL COUPLED HYDRODYNAMICS MODEL FOR DAM BREAK FLOW
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
1-D and 2-D mathematical models for dam break flow were established and verified with the measured data in laboratory. The 1-D and 2-D models were then coupled, and used to simulate the dam break flow from the reservoir tail to the dam site, the propagation of dam break waves in the downstream channel, and the submergence of dam break flow in the downstream town with the hydrodynamics method. As a numerical example, the presented model was employed to simulate dam break flow of a hydropower station under construction. In simulation, different dam-break durations, upstream flows and water levels in front of dam were considered, and these influencing factors of dam break flow were analyzed, which could be referenced in planning and designing hydropower stations.
Two-Dimensional Spectroscopy of Photospheric Shear Flows in a Small delta Spot
Denker, C; Tritschler, A; Yurchyshyn, V
2007-01-01
In recent high-resolution observations of complex active regions, long-lasting and well-defined regions of strong flows were identified in major flares and associated with bright kernels of visible, near-infrared, and X-ray radiation. These flows, which occurred in the proximity of the magnetic neutral line, significantly contributed to the generation of magnetic shear. Signatures of these shear flows are strongly curved penumbral filaments, which are almost tangential to sunspot umbrae rather than exhibiting the typical radial filamentary structure. Solar active region NOAA 10756 was a moderately complex, beta-delta sunspot group, which provided an opportunity to extend previous studies of such shear flows to quieter settings. We conclude that shear flows are a common phenomenon in complex active regions and delta spots. However, they are not necessarily a prerequisite condition for flaring. Indeed, in the present observations, the photospheric shear flows along the magnetic neutral line are not related to a...
The CABARET method for a weakly compressible fluid flows in one- and two-dimensional implementations
Kulikov, Yu M.; Son, E. E.
2016-11-01
The CABARET method implementation for a weakly compressible fluid flow is in the focus of present paper. Testing both one-dimensional pressure balancing problem and a classical plane Poiseuille flow, we analyze this method in terms of discontinuity resolution, dispersion and dissipation. The method is proved to have an adequate convergence to an analytical solution for a velocity profile. We also show that a flow formation process represents a set of self-similar solutions under varying pressure differential and sound speed.
Gupta, Akanksha; Ganesh, Rajaraman; Joy, Ashwin
2016-11-01
In Navier-Stokes fluids, shear flows are known to become unstable leading to instability and eventually to turbulence. A class of flow namely, Kolmogorov Flows (K-Flows) exhibit such transition at low Reynolds number. Using fluid and molecular dynamics, we address the physics of transition from laminar to turbulent regime in strongly correlated-liquids such as in multi-species plasmas and also in naturally occurring plasmas with K-Flows as initial condition. A 2D phenomenological generalized hydrodynamic model is invoked wherein the effect of strong correlations is incorporated via a viscoelastic memory. To study the stability of K-Flows or in general any shear flow, a generalized eigenvalue solver has been developed along with a spectral solver for the full nonlinear set of fluid equations. A study of the linear and nonlinear features of K-Flow in incompressible and compressible limit exhibits cyclicity and nonlinear pattern formation in vorticity. A first principles based molecular dynamics simulation of particles interacting via Yukawa potential is performed with features such as configurational and kinetic thermostats for K-Flows. This work reveals several interesting similarities and differences between hydrodynamics and molecular dynamics studies.
Effect of Moist Air on Transonic Internal Flow around a Plate
Hasan, A. B. M. Toufique; Matsuo, Shigeru; Setoguchi, Toshiaki; Kim, Heuy Dong
The unsteady phenomena in the transonic flow around airfoils are observed in the flow field of fan, compressor blades and butterfly valves, and this causes often serious problems such as the aeroacoustic noise and the vibration. In the transonic or supersonic flow where vapor is contained in the main flow, the rapid expansion of the flow may give rise to a non-equilibrium condensation. In the present study, the effect of non-equilibrium condensation of moist air on the shock induced flow field oscillation around a plate was investigated numerically. The results showed that in the case with non-equilibrium condensation, the flow field aerodynamic unsteadiness is reduced significantly compared with those without the non-equilibrium condensation.
Temperature and velocity field of the two-dimensional transverse hot-air jet in a freestream flow.
Tatom, J. W.; Cooper, M. A.; Hayden, T. K.
1972-01-01
Experimental investigation of the low subsonic, two-dimensional transverse hot-air jet. In the study jet-to-freestream angles of 90, 120, 135, and 150 deg and jet-to-freestream velocity ratios of 5, 10, and 20 were investigated. In the tests the jet velocity and temperature fields were measured using a temperature-compensated hot-wire anemometer. Photographs of the flowfield were also made. The tests results are compared with the available data and analysis. Results indicate a relatively minor deflection of the freestream by the jet and the presence of a large separated flow region behind the jet.
Miller, Benjamin L.; Baker, James E.; Sriram, Rashmi
2017-05-01
Because of their compatibility with standard CMOS fabrication, small footprint, and exceptional sensitivity, Two-Dimensional Photonic Crystals (2D PhCs) have been posited as attractive components for the development of real-time integrated photonic virus sensors. While detection of single virus-sized particles by 2D PhCs has been demonstrated, specific recognition of a virus simulant under conditions relevant to sensor use (including aqueous solution and microfluidic flow) has remained an unsolved challenge. This talk will describe the design and testing of a W1 waveguide-coupled 2D PhC in the context of addressing that challenge.
Uncertainty Quantification of Turbulence Model Closure Coefficients for Transonic Wall-Bounded Flows
Schaefer, John; West, Thomas; Hosder, Serhat; Rumsey, Christopher; Carlson, Jan-Renee; Kleb, William
2015-01-01
The goal of this work was to quantify the uncertainty and sensitivity of commonly used turbulence models in Reynolds-Averaged Navier-Stokes codes due to uncertainty in the values of closure coefficients for transonic, wall-bounded flows and to rank the contribution of each coefficient to uncertainty in various output flow quantities of interest. Specifically, uncertainty quantification of turbulence model closure coefficients was performed for transonic flow over an axisymmetric bump at zero degrees angle of attack and the RAE 2822 transonic airfoil at a lift coefficient of 0.744. Three turbulence models were considered: the Spalart-Allmaras Model, Wilcox (2006) k-w Model, and the Menter Shear-Stress Trans- port Model. The FUN3D code developed by NASA Langley Research Center was used as the flow solver. The uncertainty quantification analysis employed stochastic expansions based on non-intrusive polynomial chaos as an efficient means of uncertainty propagation. Several integrated and point-quantities are considered as uncertain outputs for both CFD problems. All closure coefficients were treated as epistemic uncertain variables represented with intervals. Sobol indices were used to rank the relative contributions of each closure coefficient to the total uncertainty in the output quantities of interest. This study identified a number of closure coefficients for each turbulence model for which more information will reduce the amount of uncertainty in the output significantly for transonic, wall-bounded flows.
Wake Behavior behind Turbine Cascades in Compressible Two-Dimensional Flows
Directory of Open Access Journals (Sweden)
Kurz Rainer
2005-01-01
Full Text Available The goal of the paper is to describe wake parameters of wakes from turbine cascades in compressible flows especially in planes where the leading edge of the following blade row would be located. Data from experiments with turbine cascades in compressible flow will be used to derive a theoretical approach which describes the wake growth and the recovery of the velocity deficit. The theory is based on similarity assumptions. The derived equations depend on simple and readily available parameters such as overall losses, exit angle, and Mach or Laval number. In compressible turbine flows, the influence of the inviscid flow field is of great importance. In this paper, an approach to take this influence into account when determining the behavior of the wake is presented. Correlations for basic characteristics of wakes in compressible flows are not readily available. Such correlations are necessary as input to unsteady flow and heat transfer calculation procedures for turbomachine blades. Based on available data on wake behavior in the compressible flow behind turbine blades, the correlations presented describe the wake behavior from the trailing edge to the confluence of the wakes of adjacent blades.
The effect of magnetic field on mean flow generation by rotating two-dimensional convection
Currie, Laura K
2016-01-01
Motivated by the significant interaction of convection, rotation and magnetic field in many astrophysical objects, we investigate the interplay between large-scale flows driven by rotating convection and an imposed magnetic field. We utilise a simple model in two dimensions comprised of a plane layer that is rotating about an axis inclined to gravity. It is known that this setup can result in strong mean flows; we numerically examine the effect of an imposed horizontal magnetic field on such flows. We show that increasing the field strength in general suppresses the time-dependent mean flows, but in some cases it organises them leading to stronger time-averaged flows. Further, we discuss the effect of the field on the correlations responsible for driving the flows and the competition between Reynolds and Maxwell stresses. A change in behaviour is observed when the (fluid and magnetic) Prandtl numbers are decreased. In the smaller Prandtl number regime, it is shown that significant mean flows can persist even ...
Two-Dimensional Stagnation-Point Velocity-Slip Flow and Heat Transfer over Porous Stretching Sheet
Directory of Open Access Journals (Sweden)
FEROZ AHMED SOOMRO
2016-10-01
Full Text Available Present paper investigates 2D (Two-Dimensional stagnation-point velocity-slip flow over porous stretching sheet. The governing non-linear PDEs (Partial Differential Equations are non-dimensionlized by using the similarity transformation technique that results into coupled non-linear ODEs (Ordinary Differential Equations. Such ODEs are then solved by using shooting technique with fourth-order Runge-Kutta method. Since the behavior of boundary layer stagnation-point flow depends on the rate of cooling and stretching. Therefore, the main objective of this paper is to analyze the effects of different working parameters on shear stress, heat transfer, velocity and temperature of fluid. The results revealed that the velocity-slip has significant effect on the fluid flow as well as on the heat transfer. The numerical results are also compared with existing work for no-slip condition and found to have good agreement with improved asymptotic behavior.
Cross-flow blowing of a two-dimensional stationary arc.
Bose, T. K.
1971-01-01
It is demonstrated in an analysis that the electrons emitted from the cathode undergo collisions with the heavy particles and are deflected in the flow direction by the component of a collisional force associated with the relative difference in flow velocities between electrons and heavy particles. The resultant motion of the electrons describing the arc is thus caused by a combined action of the collisional force that results from the externally applied electric field. An expression is given which enables computation of the arc shape to be made provided the velocity distribution of the cross-flow and the distribution of the externally applied electric field are prescribed.
Nonparallel stability of two-dimensional nonuniformly heated boundary-layer flows
Nayfeh, A. H.; El-Hady, N. M.
1979-01-01
An analysis is presented for the linear stability of water boundary-layer flows over nonuniformly flat plates. Included in the analysis are disturbances due to velocity, pressure, temperatures, density, and transport properties as well as variations of the liquid properties with temperature. The method of multiple scales is used to account for the nonparallelism of the mean flow. In contrast with previous analyses, the nonsimilarity of the mean flow is taken into account. No analysis agrees, even qualitatively, with the experimental data when similar profiles are used. However, both the parallel and nonparallel results qualitatively agree with the experimental results of Strazisar and Reshotko when nonsimilar profiles are used.
Numerical simulation of two-dimensional corner flows in a circulating water channel with guide vanes
Energy Technology Data Exchange (ETDEWEB)
Hung, Y.; Nishimoto, H.; Tamashima, M.; Yamazaki, R. [West Japan Fluid Engineering Co. Ltd., Nagasaki (Japan); Wang, G.
1998-09-04
A Navier-Stokes procedure is developed based on the Finite Volume Method to simulate the 2-D comer flows in a CWC. The staggered grid is adopted and a new method is presented to coupling the velocities and the pressure when the grid lines change direction by 90deg. The turbulince is approximated using {kappa} - {epsilon} model and a transfinite algebraic method is used to generate the body fitted coordinates. After validation of the computer code, the corner flows in a CWC was calculated and the effect of guide vanes was investigated. For laminar flows, the guide vanes may restrain the separations on the inner side but not so effective on the outside; for turbulent flows, separations on the inner side disappeared even without guide vanes but still remained on the outside. By incorporating guide vanes, the separation can be effectively controlled. 6 refs., 13 figs.
A two-dimensional parabolic model for vertical annular two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Fernandez, F.M.; Toledo, A. Alvarez; Paladino, E.E. [Graduate Program in Mechanical Engineering, Universidade Federal de Rio Grande do Norte, Natal, RN (Brazil)], e-mail: emilio@ct.ufrn.br
2010-07-01
This work presents a solution algorithm for predicting hydrodynamic parameters for developing and equilibrium, adiabatic, annular, vertical two-phase flow. It solves mass and momentum transport differential equations for both the core and the liquid film across their entire domains. Thus, the velocity and shear stress distributions from the tube center to the wall are obtained, together with the average film thickness and the pressure gradient, making no use of empirical closure relations nor assuming any known velocity profile to solve the triangular relationship in the liquid film. The model was developed using the Finite Volume Method and an iterative procedure is proposed to solve all flow variables for given phase superficial velocities. The procedure is validated against the analytical solution for laminar flow and experimental data for gas-liquid turbulent flow with entrainment. For the last case, an algebraic turbulence model is used for turbulent viscosity calculation for both, liquid film and gas core. (author)
Least Squares Shadowing Sensitivity Analysis of Chaotic Flow Around a Two-Dimensional Airfoil
Blonigan, Patrick J.; Wang, Qiqi; Nielsen, Eric J.; Diskin, Boris
2016-01-01
Gradient-based sensitivity analysis has proven to be an enabling technology for many applications, including design of aerospace vehicles. However, conventional sensitivity analysis methods break down when applied to long-time averages of chaotic systems. This breakdown is a serious limitation because many aerospace applications involve physical phenomena that exhibit chaotic dynamics, most notably high-resolution large-eddy and direct numerical simulations of turbulent aerodynamic flows. A recently proposed methodology, Least Squares Shadowing (LSS), avoids this breakdown and advances the state of the art in sensitivity analysis for chaotic flows. The first application of LSS to a chaotic flow simulated with a large-scale computational fluid dynamics solver is presented. The LSS sensitivity computed for this chaotic flow is verified and shown to be accurate, but the computational cost of the current LSS implementation is high.
Shunt flow evaluation in congenital heart disease based on two-dimensional speckle tracking.
Fadnes, Solveig; Nyrnes, Siri Ann; Torp, Hans; Lovstakken, Lasse
2014-10-01
High-frame-rate ultrasound speckle tracking was used for quantification of peak velocity in shunt flows resulting from septal defects in congenital heart disease. In a duplex acquisition scheme implemented on a research scanner, unfocused transmit beams and full parallel receive beamforming were used to achieve a frame rate of 107 frames/s for full field-of-view flow images with high accuracy, while also ensuring high-quality focused B-mode tissue imaging. The setup was evaluated in vivo for neonates with atrial and ventricular septal defects. The shunt position was automatically tracked in B-mode images and further used in blood speckle tracking to obtain calibrated shunt flow velocities throughout the cardiac cycle. Validation toward color flow imaging and pulsed wave Doppler with manual angle correction indicated that blood speckle tracking could provide accurate estimates of shunt flow velocities. The approach was less biased by clutter filtering compared with color flow imaging and was able to provide velocity estimates beyond the Nyquist range. Possible placements of sample volumes (and angle corrections) for conventional Doppler resulted in a peak shunt velocity variations of 0.49-0.56 m/s for the ventricular septal defect of patient 1 and 0.38-0.58 m/s for the atrial septal defect of patient 2. In comparison, the peak velocities found from speckle tracking were 0.77 and 0.33 m/s for patients 1 and 2, respectively. Results indicated that complex intraventricular flow velocity patterns could be quantified using high-frame-rate speckle tracking of both blood and tissue movement. This could potentially help increase diagnostic accuracy and decrease inter-observer variability when measuring peak velocity in shunt flows. Copyright © 2014 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.
Measuring two-dimensional components of a flow velocity vector using a hot-wire probe.
Kiełbasa, Jan
2007-08-01
The article presents a single-hot-wire probe adapted to detect the direction of flow velocity. The modification consists of the introduction of a third support which allows to measure voltage at the central point of the wire. The sign of voltage difference DeltaU between both parts of the wire is the measure of the direction of flow velocity in a system of coordinates associated with the probe.
Wake Behavior behind Turbine Cascades in Compressible Two-Dimensional Flows
2005-01-01
The goal of the paper is to describe wake parameters of wakes from turbine cascades in compressible flows especially in planes where the leading edge of the following blade row would be located. Data from experiments with turbine cascades in compressible flow will be used to derive a theoretical approach which describes the wake growth and the recovery of the velocity deficit. The theory is based on similarity assumptions. The derived equations depend on simple and readily available parameter...
Ensemble Distribution for Immiscible Two-Phase Flow in Two-Dimensional Networks
Savani, Isha; Kjelstrup, Signe; Vassvik, Morten; Sinha, Santanu; Hansen, Alex
2016-01-01
An ensemble distribution has been constructed to describe steady immiscible two-phase flow of two incompressible fluids in a network. The system is ergodic. The distribution relates the time that a bubble of the non-wetting fluid spends in a link to the local volume flow. The properties of the ensemble distribution are tested by two-phase flow simulations at the pore-scale for capillary numbers ranging from 0.1 to 0.001. It is shown that the distribution follows the postulated dependence on the local flow for Ca = 0.01 and 0.001. The distribution is used to compute the global flow performance of the network. In particular, we find the expression for the overall mobility of the system using the ensemble distribution. The entropy production at the scale of the network is shown to give the expected product of the average flow and its driving force, obtained from a black-box description. The distribution can be used to obtain macroscopic variables from local network information, for a practical range of capillary...
Investigation of Unsteady Flow Behavior in Transonic Compressor Rotors with LES and PIV Measurements
Hah, Chunill; Voges, Melanie; Mueller, Martin; Schiffer, Heinz-Peter
2009-01-01
In the present study, unsteady flow behavior in a modern transonic axial compressor rotor is studied in detail with large eddy simulation (LES) and particle image velocimetry (PIV). The main purpose of the study is to advance the current understanding of the flow field near the blade tip in an axial transonic compressor rotor near the stall and peak-efficiency conditions. Flow interaction between the tip leakage vortex and the passage shock is inherently unsteady in a transonic compressor. Casing-mounted unsteady pressure transducers have been widely applied to investigate steady and unsteady flow behavior near the casing. Although many aspects of flow have been revealed, flow structures below the casing cannot be studied with casing-mounted pressure transducers. In the present study, unsteady velocity fields are measured with a PIV system and the measured unsteady flow fields are compared with LES simulations. The currently applied PIV measurements indicate that the flow near the tip region is not steady even at the design condition. This self-induced unsteadiness increases significantly as the compressor rotor operates near the stall condition. Measured data from PIV show that the tip clearance vortex oscillates substantially near stall. The calculated unsteady characteristics of the flow from LES agree well with the PIV measurements. Calculated unsteady flow fields show that the formation of the tip clearance vortex is intermittent and the concept of vortex breakdown from steady flow analysis does not seem to apply in the current flow field. Fluid with low momentum near the pressure side of the blade close to the leading edge periodically spills over into the adjacent blade passage. The present study indicates that stall inception is heavily dependent on unsteady behavior of the flow field near the leading edge of the blade tip section for the present transonic compressor rotor.
Que, Ruiyi; Zhu, Rong
2013-12-31
This paper demonstrates a novel flow sensor with two-dimensional 360° direction sensitivity achieved with a simple structure and a novel data fusion algorithm. Four sensing elements with roundabout wires distributed in four quadrants of a circle compose the sensor probe, and work in constant temperature difference (CTD) mode as both Joule heaters and temperature detectors. The magnitude and direction of a fluid flow are measured by detecting flow-induced temperature differences among the four elements. The probe is made of Ti/Au thin-film with a diameter of 2 mm, and is fabricated using micromachining techniques. When a flow goes through the sensor, the flow-induced temperature differences are detected by the sensing elements that also serve as the heaters of the sensor. By measuring the temperature differences among the four sensing elements symmetrically distributed in the sensing area, a full 360° direction sensitivity can be obtained. By using a BP neural network to model the relationship between the readouts of the four sensor elements and flow parameters and execute data fusion, the magnitude and direction of the flow can be deduced. Validity of the sensor design was proven through both simulations and experiments. Wind tunnel experimental results show that the measurement accuracy of the airflow speed reaches 0.72 m/s in the range of 3 m/s-30 m/s and the measurement accuracy of flow direction angle reaches 1.9° in the range of 360°.
Directory of Open Access Journals (Sweden)
Ruiyi Que
2013-12-01
Full Text Available This paper demonstrates a novel flow sensor with two-dimensional 360° direction sensitivity achieved with a simple structure and a novel data fusion algorithm. Four sensing elements with roundabout wires distributed in four quadrants of a circle compose the sensor probe, and work in constant temperature difference (CTD mode as both Joule heaters and temperature detectors. The magnitude and direction of a fluid flow are measured by detecting flow-induced temperature differences among the four elements. The probe is made of Ti/Au thin-film with a diameter of 2 mm, and is fabricated using micromachining techniques. When a flow goes through the sensor, the flow-induced temperature differences are detected by the sensing elements that also serve as the heaters of the sensor. By measuring the temperature differences among the four sensing elements symmetrically distributed in the sensing area, a full 360° direction sensitivity can be obtained. By using a BP neural network to model the relationship between the readouts of the four sensor elements and flow parameters and execute data fusion, the magnitude and direction of the flow can be deduced. Validity of the sensor design was proven through both simulations and experiments. Wind tunnel experimental results show that the measurement accuracy of the airflow speed reaches 0.72 m/s in the range of 3 m/s–30 m/s and the measurement accuracy of flow direction angle reaches 1.9° in the range of 360°.
A least squares finite element scheme for transonic flow around harmonically oscillating airfoils
Cox, C. L.; Fix, G. J.; Gunzburger, M. D.
1983-01-01
The present investigation shows that a finite element scheme with a weighted least squares variational principle is applicable to the problem of transonic flow around a harmonically oscillating airfoil. For the flat plate case, numerical results compare favorably with the exact solution. The obtained numerical results for the transonic problem, for which an exact solution is not known, have the characteristics of known experimental results. It is demonstrated that the performance of the employed numerical method is independent of equation type (elliptic or hyperbolic) and frequency. The weighted least squares principle allows the appropriate modeling of singularities, which such a modeling of singularities is not possible with normal least squares.
Numerical computation of transonic flows by finite-element and finite-difference methods
Hafez, M. M.; Wellford, L. C.; Merkle, C. L.; Murman, E. M.
1978-01-01
Studies on applications of the finite element approach to transonic flow calculations are reported. Different discretization techniques of the differential equations and boundary conditions are compared. Finite element analogs of Murman's mixed type finite difference operators for small disturbance formulations were constructed and the time dependent approach (using finite differences in time and finite elements in space) was examined.
The Application of the Probabilistic Collocation Method to a Transonic Axial Flow Compressor
Loeven, G.J.A.; Bijl, H.
2010-01-01
In this paper the Probabilistic Collocation method is used for uncertainty quantification of operational uncertainties in a transonic axial flow compressor (i.e. NASA Rotor 37). Compressor rotors are components of a gas turbine that are highly sensitive to operational and geometrical uncertainties.
Moderately converging ion and electron flows in two-dimensional diodes
Cavenago, M.
2012-11-01
Flow of particles in diodes is solved selfconsistently assuming an approximated system of flow lines, that can be easily represented by an analytic transformation in a complex plane, with assumed uniformity in the third spatial direction. Beam current compression is tunable by an angle parameter α0; transformed coordinate lines are circular arcs, exactly matching to the curved cathode usually considered by rectilinear converging flows. The curvature of flow lines allows to partly balance the transverse effect of space charge. A self-contained discussion of the whole theory is reported, ranging from analytical solution for selfconsistent potential to electrode drawing to precise numerical simulation, which serves as a verification and as an illustration of typical electrode shapes. Motion and Poisson equation are written in a curved flow line system and their approximate consistency is shown to imply an ordinary differential equation for the beam edge potential. Transformations of this equation and their series solutions are given and discussed, showing that beam edge potential has a maximum, so supporting both diode (with α0 ≅ π/3) and triode design. Numerical simulations confirm the consistency of these solution. Geometrical details of diode design are discussed: the condition of a zero divergence beam, with the necessary anode lens effect included, is written and solved, as a function of beam compression; accurate relations for diode parameters and perveance are given. Weakly relativistic effects including self-magnetic field are finally discussed as a refinement.
Gai, Ya; Leong, Chia Min; Cai, Wei; Tang, Sindy K. Y.
2016-11-01
Here we report a surprising order in concentrated emulsion when flowing as a monolayer in a tapered microfluidic channel. The flow of droplets in micro-channels can be non-trivial, and may lead to unexpected phenomena such as long-period oscillations and chaos. Previously, there have been studies on concentrated emulsions in straight channels and channels with bends. The dynamics of how drops flow and rearrange in a tapered geometry has not yet been characterized. At sufficiently slow flow rates, the drops arrange into a hexagonal lattice. At a given x-position, the time-averaged droplet velocities are uniform. The instantaneous drop velocities, however, reveal a different, wave-like pattern. Within the rearrangement zone where the number of rows of drops decreases from N to N-1, there is always a drop moved faster than the others. Close examination reveals the anomalous velocity profile arises from a series of dislocations that are both spatial and temporal periodic. To our knowledge, such reproducible dislocation motion has not been reported before. Our results are useful in novel flow control and mixing strategies in droplet microfluidics as well as modeling crystal plasticity in low-dimensional nanomaterials.
New families of flows between two-dimensional conformal field theories
Dorey, P; Tateo, R; Dorey, Patrick; Dunning, Clare; Tateo, Roberto
2000-01-01
We present evidence for the existence of infinitely-many new families of renormalisation group flows between the nonunitary minimal models of conformal field theory. These are associated with perturbations by the $\\phi_{21}$ and In all of the new flows, the finite-volume effective central charge is a non-monotonic function of the system size. The evolution of this effective central charge is studied by means of a nonlinear integral equation, a massless variant of an equation recently found to describe certain massive perturbations of these same models. We also observe that a similar non-monotonicity arises in the more familiar $\\phi_{13}$ perturbations, when the flows induced are between nonunitary minimal models.
Exact two-dimensionalization of rapidly rotating large-Reynolds-number flows
Gallet, Basile
2015-01-01
We consider the flow of a Newtonian fluid in a three-dimensional domain, rotating about a vertical axis and driven by a vertically invariant horizontal body-force. This system admits vertically invariant solutions that satisfy the 2D Navier-Stokes equation. At high Reynolds number and without global rotation, such solutions are usually unstable to three-dimensional perturbations. By contrast, for strong enough global rotation, we prove rigorously that the 2D (and possibly turbulent) solutions are stable to vertically dependent perturbations: the flow becomes 2D in the long-time limit. These results shed some light on several fundamental questions of rotating turbulence: for arbitrary Reynolds number and small enough Rossby number, the system is attracted towards purely 2D flow solutions, which display no energy dissipation anomaly and no cyclone-anticyclone asymmetry. Finally, these results challenge the applicability of wave turbulence theory to describe stationary rotating turbulence in bounded domains.
Two dimensional analytical solution for a partially vegetated compound channel flow
Institute of Scientific and Technical Information of China (English)
HUAI Wen-xin; XU Zhi-gang; YANG Zhong-hua; ZENG Yu-hong
2008-01-01
The theory of an eddy viscosity model is applied to the study of the flow in a compound channel which is partially vegetated. The governing equation is constituted by analyzing the longitudinal forces acting on the unit volume where the effect of the vegetation on the flow is considered as a drag force item. The compound channel is di- vided into 3 sub-regions in the transverse direction, and the coefficients in every region's differential equations were solved simultaneously. Thus, the analytical solution of the transverse distribution of the depth-averaged velocity for uniform flow in a partially vege- tated compound channel was obtained. The results can be used to predict the transverse distribution of bed shear stress, which has an important effect on the transportation of sediment. By comparing the analytical results with the measured data, the analytical so- lution in this paper is shown to be sufficiently accurate to predict most hydraulic features for engineering design purposes.
A Finite-Element Solution of the Navier-Stokes Equations for Two-Dimensional and Axis-Symmetric Flow
Directory of Open Access Journals (Sweden)
Sven Ø. Wille
1980-04-01
Full Text Available The finite element formulation of the Navier-Stokes equations is derived for two-dimensional and axis-symmetric flow. The simple triangular, T6, isoparametric element is used. The velocities are interpolated by quadratic polynomials and the pressure is interpolated by linear polynomials. The non-linear simultaneous equations are solved iteratively by the Newton-Raphson method and the element matrix is given in the Newton-Raphson form. The finite element domain is organized in substructures and an equation solver which works on each substructure is specially designed. This equation solver needs less storage in the computer and is faster than the traditional banded equation solver. To reduce the amount of input data an automatic mesh generator is designed. The input consists of the coordinates of eight points defining each substructure with the corresponding boundary conditions. In order to interpret the results they are plotted on a calcomp plotter. Examples of plots of the velocities, the streamlines and the pressure inside a two-dimensional flow divider and an axis-symmetric expansion of a tube are shown for various Reynolds numbers.
Katyal, A. K.; Kaluarachchi, J. J.; Parker, J. C.
1991-05-01
The manual describes a two-dimensional finite element model for coupled multiphase flow and multicomponent transport in planar or radially symmetric vertical sections. Flow and transport of three fluid phases, including water, nonaqueous phase liquid (NAPL), and gas are considered by the program. The program can simulate flow only or coupled flow and transport. The flow module can be used to analyze two phases, water and NAPL, with the gas phase held at constant pressure, or explicit three-phase flow of water, NAPL, and gas at various pressures. The transport module can handle up to five components which partition among water, NAPL, gas and solid phases assuming either local equilibrium or first-order mass transfer. Three phase permeability-saturation-capillary pressure relations are defined by an extension of the van Genuchten model. The governing equations are solved using an efficient upstream-weighted finite element scheme. The required inputs for flow and transport analysis are described. Detailed instructions for creating data files needed to run the program and examples of input and output files are given in appendices.
Fundamental interactions of vortical structures with boundary layers in two-dimensional flows
DEFF Research Database (Denmark)
Coutsias, E.A.; Lynov, Jens-Peter
1991-01-01
in the vorticity-stream function representation for bounded geometries. Fundamental processes connected to vorticity detachment from the boundary layers caused by the proximity of vortical structures are described. These processes include enstrophy enhancement of the main flow during bursting events, and pinning...
Ehlers, E. F.
1974-01-01
A finite difference method for the solution of the transonic flow about a harmonically oscillating wing is presented. The partial differential equation for the unsteady transonic flow was linearized by dividing the flow into separate steady and unsteady perturbation velocity potentials and by assuming small amplitudes of harmonic oscillation. The resulting linear differential equation is of mixed type, being elliptic or hyperbolic whereever the steady flow equation is elliptic or hyperbolic. Central differences were used for all derivatives except at supersonic points where backward differencing was used for the streamwise direction. Detailed formulas and procedures are described in sufficient detail for programming on high speed computers. To test the method, the problem of the oscillating flap on a NACA 64A006 airfoil was programmed. The numerical procedure was found to be stable and convergent even in regions of local supersonic flow with shocks.
Gelfgat, Alexander
2015-01-01
A visualization of three-dimensional incompressible flows by divergence-free quasi-two-dimensional projections of the velocity field on three coordinate planes was recently proposed. The projections were calculated using divergence-free Galerkin bases, which resulted in the whole procedure being complicated and CPU-time consuming. Here we propose an alternative way based on the Chorin projection combined with a SIMPLE-like iteration. The approach proposed is much easier in realization, allows for faster computations, and can be generalized for arbitrary curvilinear orthogonal coordinates. To illustrate the visualization method, examples of flow visualization in cylindrical and spherical coordinates, as well as post-processing of experimental 3D-PTV data are presented.
Rathbun, Wayne
2007-01-01
A method is described for automating the regulation of cold jet flow of a comprehensive two-dimensional gas chromatograph (GCxGC) configured with flame ionization detection. This new capability enables the routine automated separation, identification, and quantitation of hydrocarbon types in petroleum fractions extending into the vacuum gas oil (VGO) range (IBP-540 degrees C). Chromatographic data acquisition software is programmed to precisely change the rate of flow from the cold jet of a nitrogen cooled loop modulator of a GCxGC instrument during sample analysis. This provides for the proper modulation of sample compounds across a wider boiling range. The boiling point distribution of the GCxGC separation is shown to be consistent with high temperature simulated distillation results indicating recovery of higher boiling semi-volatile VGO sample components. GCxGC configured with time-of-flight mass spectrometry is used to determine the molecular identity of individual sample components and boundaries of different molecular types.
Tam, C. K. W.; Burton, D. E.
1984-01-01
An investigation is conducted of the phenomenon of sound generation by spatially growing instability waves in high-speed flows. It is pointed out that this process of noise generation is most effective when the flow is supersonic relative to the ambient speed of sound. The inner and outer asymptotic expansions corresponding to an excited instability wave in a two-dimensional mixing layer and its associated acoustic fields are constructed in terms of the inner and outer spatial variables. In matching the solutions, the intermediate matching principle of Van Dyke and Cole is followed. The validity of the theory is tested by applying it to an axisymmetric supersonic jet and comparing the calculated results with experimental measurements. Very favorable agreements are found both in the calculated instability-wave amplitude distribution (the inner solution) and the near pressure field level contours (the outer solution) in each case.
ANALYSIS OF WATER QUALITY IN SHALLOW LAKES WITH A TWO-DIMENSIONAL FLOW-SEDIMENT MODEL
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The governing equation for sediment pollutions was derived based on the turbulent diffusion of pollutants in shallow lakes. Coupled with shallow water equations, a depth-averaged 2-D flow and water quality model was developed. By means of the conservation law, a proposed differential equation for the change of sediment pollutants was linked to the 2-D equations. Under the framework of the finite volume method, the Osher approximate Riemann solver was employed to solve the equations. An analytical resolution was used to examine the model capabilities. Simulated results matched the exact solutions especially well. As an example, the simulation of CODMn in the Wuli Lake, a part of the Taihu lake, was conducted, which led to reasonable results. This study provides a new approach and a practical tool for the simulation of flow and water quality in shallow lakes.
Unstable manifold computations for the two-dimensional plane Poiseuille flow
Energy Technology Data Exchange (ETDEWEB)
Casas, Pablo S. [Universidad Politecnica de Cataluna, Departamento de Matematica Aplicada I, Barcelona (Spain); Jorba, Angel [Universidad de Barcelona, Departamento de Matematica Aplicada y Analisis, Barcelona (Spain)
2004-11-01
We follow the unstable manifold of periodic and quasi-periodic solutions in time for the Poiseuille problem, using two formulations: holding a constant flux or mean pressure gradient. By means of a numerical integrator of the Navier-Stokes equations, we let the fluid evolve from an initially perturbed unstable solution until the fluid reaches an attracting state. Thus, we detect several connections among different configurations of the flow such as laminar, periodic, quasi-periodic with two or three basic frequencies, and more complex sets that we have not been able to classify. These connections make possible the location of new families of solutions, usually hard to find by means of numerical continuation of curves, and show the richness of the dynamics of the Poiseuille flow. (orig.)
Two-dimensional nonstationary flow of a conducting fluid, induced by a rotating magnetic field
Energy Technology Data Exchange (ETDEWEB)
Kapusta, A.B.
1977-07-01
An examination is made of a full induction problem on the planar movement of a conducting fluid in a rotating magnetic field. The solution to this problem is sought by the method of degradation into Fourier series by harmonics of the rotating field. The initial system of partial differential equations is reduced to the system 2+1 of normal differential equations that bind the amplitudes of function harmonics and electrical vector potential. A solution to the problem for small anti ..omega.. was found with an accuracy up to the second approximation. The unsteadiness of flow was found to be manifested in a form of induced cross-sectional waves, traveling along the stream tubes of this flow at a speed that is equal to the phase velocity of the magnetic field. The appearance of wave effects is explained by considerations of symmetry. 5 references, 1 figure.
Identifying the Flow Physics and Modeling Transient Forces on Two-Dimensional Wings
2016-09-02
becomes smaller relative to the random component of the error (indicated by the size of the confidence ellipse). This means that the modifications to...understanding the dynamics of these unsteady flows, and uses state-of-the-art techniques, both for measuring these phenomena in experiments (using an...art techniques, both for measuring these phenomena in experiments (using an unsteady wind tunnel at IIT), and for analyzing the data and developing
Finite-Difference Lattice Boltzmann Scheme for High-Speed Compressible Flow: Two-Dimensional Case
Gan, Yan-Biao; Xu, Ai-Guo; Zhang, Guang-Cai; Zhang, Ping; Zhang, Lei; Li, Ying-Jun
2008-07-01
Lattice Boltzmann (LB) modeling of high-speed compressible flows has long been attempted by various authors. One common weakness of most of previous models is the instability problem when the Mach number of the flow is large. In this paper we present a finite-difference LB model, which works for flows with flexible ratios of specific heats and a wide range of Mach number, from 0 to 30 or higher. Besides the discrete-velocity-model by Watari [Physica A 382 (2007) 502], a modified Lax Wendroff finite difference scheme and an artificial viscosity are introduced. The combination of the finite-difference scheme and the adding of artificial viscosity must find a balance of numerical stability versus accuracy. The proposed model is validated by recovering results of some well-known benchmark tests: shock tubes and shock reflections. The new model may be used to track shock waves and/or to study the non-equilibrium procedure in the transition between the regular and Mach reflections of shock waves, etc.
Doost, Siamak N; Zhong, Liang; Su, Boyang; Morsi, Yosry S
2016-10-31
The image-based computational fluid dynamics (IB-CFD) technique, as the combination of medical images and the CFD method, is utilized in this research to analyze the left ventricle (LV) hemodynamics. The research primarily aims to propose a semi-automated technique utilizing some freely available and commercial software packages in order to simulate the LV hemodynamics using the IB-CFD technique. In this research, moreover, two different physiological time-resolved 2D models of a patient-specific LV with two different types of aortic and mitral valves, including the orifice-type valves and integrated with rigid leaflets, are adopted to visualize the process of developing intraventricular vortex formation and propagation. The blood flow pattern over the whole cardiac cycle of two models is also compared to investigate the effect of utilizing different valve types in the process of the intraventricular vortex formation. Numerical findings indicate that the model with integrated valves can predict more complex intraventricular flow that can match better the physiological flow pattern in comparison to the orifice-type model.
Investigation of flow separation in a transonic-fan linear cascade using visualization methods
Energy Technology Data Exchange (ETDEWEB)
Lepicovsky, J. [ASRC Aerospace Corporation, NASA GRC, Cleveland, OH (United States)
2008-06-15
An extensive experimental study into the nature of the separated flows on the blade suction surface of modern transonic fans is described in this paper. The study was a subtask of a larger experimental effort focused on blade flutter excited by flow separation in the blade tip region. The tip sections of airfoils on transonic fan blades are designed for precompression and consequently they differ from sections on the rest of the blade. The blade tip section was modeled by a low aspect ratio blade and therefore most of the blade tested was exposed to the secondary flow effects. The aim of this work was to supply reliable data on flow separation on transonic fan blades for validation of future analytical studies. The experimental study focused on two visualization techniques: surface flow visualization using dye oils and schlieren (and shadowgraph) flow visualization. The following key observations were made during the study. For subsonic inlet flow, the flow on the suction surface of the blade was separated over a large portion of the blade, and the separated area increased with increasing inlet Mach number. For the supersonic inlet flow condition, the flow was attached from the leading edge up to the point where a bow shock from the upper neighboring blade imposed on the blade surface. Downstream, there was a separated flow region in which air flowed in the direction opposite the inlet flow. Finally, past the separated flow region, the flow reattached to the blade surface. For subsonic inlet flow, the low cascade solidity resulted in an increased area of separated flow. For supersonic flow conditions, the low solidity resulted in an improvement in flow over the suction surface. (orig.)
Investigation of flow separation in a transonic-fan linear cascade using visualization methods
Lepicovsky, J.
2008-06-01
An extensive experimental study into the nature of the separated flows on the blade suction surface of modern transonic fans is described in this paper. The study was a subtask of a larger experimental effort focused on blade flutter excited by flow separation in the blade tip region. The tip sections of airfoils on transonic fan blades are designed for precompression and consequently they differ from sections on the rest of the blade. The blade tip section was modeled by a low aspect ratio blade and therefore most of the blade tested was exposed to the secondary flow effects. The aim of this work was to supply reliable data on flow separation on transonic fan blades for validation of future analytical studies. The experimental study focused on two visualization techniques: surface flow visualization using dye oils and schlieren (and shadowgraph) flow visualization. The following key observations were made during the study. For subsonic inlet flow, the flow on the suction surface of the blade was separated over a large portion of the blade, and the separated area increased with increasing inlet Mach number. For the supersonic inlet flow condition, the flow was attached from the leading edge up to the point where a bow shock from the upper neighboring blade imposed on the blade surface. Downstream, there was a separated flow region in which air flowed in the direction opposite the inlet flow. Finally, past the separated flow region, the flow reattached to the blade surface. For subsonic inlet flow, the low cascade solidity resulted in an increased area of separated flow. For supersonic flow conditions, the low solidity resulted in an improvement in flow over the suction surface.
Molecular dynamics computations of two dimensional supersonic rarefied gas flow past blunt bodies
Greber, Isaac; Wachman, Harold Y.; Woo, Myeung-Jouh
1991-01-01
This paper presents results of molecular dynamics computations of supersonic flow past a circular cylinder and past a flat plate perpendicular to a supersonic stream. The results are for Mach numbers of approximately 5 and 10, for several Knudsen numbers and several ratios of surface to free stream temperatures. A special feature of the computations is the use of relatively small numbers of particles in the molecular dynamics simulation, and an examination of the adequacy of using small numbers of particles to obtain physically useful results.
Numerical Solutions for Supersonic Flow of an Ideal Gas Around Blunt Two-Dimensional Bodies
Fuller, Franklyn B.
1961-01-01
The method described is an inverse one; the shock shape is chosen and the solution proceeds downstream to a body. Bodies blunter than circular cylinders are readily accessible, and any adiabatic index can be chosen. The lower limit to the free-stream Mach number available in any case is determined by the extent of the subsonic field, which in turn depends upon the body shape. Some discussion of the stability of the numerical processes is given. A set of solutions for flows about circular cylinders at several Mach numbers and several values of the adiabatic index is included.
Directory of Open Access Journals (Sweden)
Mohammad Mehdi Rashidi
2008-01-01
Full Text Available The flow of a viscous incompressible fluid between two parallel plates due to the normal motion of the plates is investigated. The unsteady Navier-Stokes equations are reduced to a nonlinear fourth-order differential equation by using similarity solutions. Homotopy analysis method (HAM is used to solve this nonlinear equation analytically. The convergence of the obtained series solution is carefully analyzed. The validity of our solutions is verified by the numerical results obtained by fourth-order Runge-Kutta.
Statistical theory of reversals in two-dimensional confined turbulent flows
Shukla, Vishwanath; Brachet, Marc
2016-01-01
It is shown that the Truncated Euler Equations, i.e. a finite set of ordinary differential equations for the amplitude of the large-scale modes, can correctly describe the complex transitional dynamics that occur within the turbulent regime of a confined 2D Navier-Stokes flow with bottom friction and a spatially periodic forcing. In particular, the random reversals of the large scale circulation on the turbulent background involve bifurcations of the probability distribution function of the large-scale circulation velocity that are described by the related microcanonical distribution which displays transitions from gaussian to bimodal and broken ergodicity. A minimal 13-mode model reproduces these results.
Molecular dynamics computations of two dimensional supersonic rarefied gas flow past blunt bodies
Greber, Isaac; Wachman, Harold Y.; Woo, Myeung-Jouh
1991-01-01
This paper presents results of molecular dynamics computations of supersonic flow past a circular cylinder and past a flat plate perpendicular to a supersonic stream. The results are for Mach numbers of approximately 5 and 10, for several Knudsen numbers and several ratios of surface to free stream temperatures. A special feature of the computations is the use of relatively small numbers of particles in the molecular dynamics simulation, and an examination of the adequacy of using small numbers of particles to obtain physically useful results.
The orientation field of fibers advected by a two-dimensional chaotic flow
Hejazi, Bardia; Mehlig, Bernhard; Voth, Greg
2016-11-01
We examine the orientation of slender fibers advected by a 2D chaotic flow. The orientation field of these fibers show fascinating structures called scar lines, where they rotate by π over short distances. We use the standard map as a convenient model to represent a time-periodic 2D incompressible fluid flow. To understand the fiber orientation field, we consider the stretching field, given by the eigenvalues and eigenvectors of the Cauchy-Green strain tensors. The eigenvector field is strongly aligned with the fibers over almost the entire field, but develops topological singularities at certain points which do not exist in the advected fiber field. The singularities are points that have experienced zero stretching, and the number of such points increases rapidly with time. A key feature of both the fiber orientation and the eigenvector field are the scar lines. We show that certain scar lines form from fluid elements that are initially stretched in one direction and then stretched in an orthogonal direction to cancel the initial stretching. The scar lines that satisfy this condition contain the singularities of the eigenvector field. These scar lines highlight the major differences between the passive director field and the much more widely studied passive scalar field.
Lefkoff, L.J.; Gorelick, S.M.
1987-01-01
A FORTRAN-77 computer program code that helps solve a variety of aquifer management problems involving the control of groundwater hydraulics. It is intended for use with any standard mathematical programming package that uses Mathematical Programming System input format. The computer program creates the input files to be used by the optimization program. These files contain all the hydrologic information and management objectives needed to solve the management problem. Used in conjunction with a mathematical programming code, the computer program identifies the pumping or recharge strategy that achieves a user 's management objective while maintaining groundwater hydraulic conditions within desired limits. The objective may be linear or quadratic, and may involve the minimization of pumping and recharge rates or of variable pumping costs. The problem may contain constraints on groundwater heads, gradients, and velocities for a complex, transient hydrologic system. Linear superposition of solutions to the transient, two-dimensional groundwater flow equation is used by the computer program in conjunction with the response matrix optimization method. A unit stress is applied at each decision well and transient responses at all control locations are computed using a modified version of the U.S. Geological Survey two dimensional aquifer simulation model. The program also computes discounted cost coefficients for the objective function and accounts for transient aquifer conditions. (Author 's abstract)
Institute of Scientific and Technical Information of China (English)
沈孟育; 刘秋生; 张增产
1996-01-01
An efficient numerical method for calculating the three-dimensional transonic flows in turbomachinery is proposed. Instead of the Euler equation, streamsurface-governing equations are deduced in the generalized von Mises coordinate system to reflect the flow feature in turbomachinery. Its main advantage is that it is easier to specify more reasonable initial values, i.e. initial streamsurface position, thus accelerating the convergence rate of the iteration process. Moreover, to use the generalized von Mises coordinates makes the present method capable of incorporating the calculation of the flow field, design and modification of the blade contour into a unified algorithm. A rotated finite difference scheme for the streamsurface-governing equations is constructed, and a new measure is presented to deal with the double-value problem of the velocity and density caused by the application of the stream functions as coordinates in the transonic flow. Three test cases were considered with the present approach
Statistical mechanics of two-dimensional Euler flows and minimum enstrophy states
Naso, A; Dubrulle, B
2009-01-01
A simplified thermodynamic approach of the incompressible 2D Euler equation is considered based on the conservation of energy, circulation and microscopic enstrophy. Statistical equilibrium states are obtained by maximizing the Miller-Robert-Sommeria (MRS) entropy under these sole constraints. The vorticity fluctuations are Gaussian while the mean flow is characterized by a linear $\\overline{\\omega}-\\psi$ relationship. Furthermore, the maximization of entropy at fixed energy, circulation and microscopic enstrophy is equivalent to the minimization of macroscopic enstrophy at fixed energy and circulation. This provides a justification of the minimum enstrophy principle from statistical mechanics when only the microscopic enstrophy is conserved among the infinite class of Casimir constraints. A new class of relaxation equations towards the statistical equilibrium state is derived. These equations can provide an effective description of the dynamics towards equilibrium or serve as numerical algorithms to determin...
Directory of Open Access Journals (Sweden)
Yuri V. Konovalov
2012-09-01
Full Text Available We present results of basal friction coefficient inversion. The inversion was performed by a 2D flow line model for one of the four fast flowing ice streams on the southern side of the Academy of Sciences Ice Cap in the Komsomolets Island, Severnaya Zemlya archipelago. The input data for the performance of both the forward and the inverse problems included synthetic aperture radar interferometry ice surface velocities, ice surface elevations and ice thicknesses obtained by airborne measurements (all were taken from Dowdeswell et al., 2002. Numerical experiments with: i different sea level shifts; and ii randomly perturbed friction coefficient have been carried out in the forward problem. The impact of sea level changes on vertical distribution of horizontal velocity and on shear stress distribution near the ice front has been investigated in experiments with different sea level shifts. The experiments with randomly perturbed friction coefficient have revealed that the modeled surface velocity is weakly sensitive to the perturbations and, therefore, the inverse problem should be considered ill posed. To mitigate ill posedness of the inverse problem, Tikhonov’s regularization was applied. The regularization parameter was determined from the relation of the discrepancy between observed and modeled velocities to the regularization parameter. The inversion was performed for both linear and non-linear sliding laws. The inverted spatial distributions of the basal friction coefficient are similar for both sliding laws. The similarity between these inverted distributions suggests that the changes in the friction coefficient are accompanied by appropriate water content variations at the glacier base.
Two-dimensional finite volume method for dam-break flow simulation
Institute of Scientific and Technical Information of China (English)
M.ALIPARAST
2009-01-01
A numerical model based upon a second-order upwind cell-center finite volume method on unstructured triangular grids is developed for solving shallow water equations.The assumption of a small depth downstream instead of a dry bed situation changes the wave structure and the propagation speed of the front which leads to incorrect results.The use of Harten-Lax-vau Leer (HLL) allows handling of wet/dry treatment.By usage of the HLL approximate Riemann solver,also it make possible to handle discontinuous solutions.As the assumption of a very small depth downstream of the dam can change the nature of the dam break flow problem which leads to incorrect results,the HLL approximate Riemann solver is used for the computation of inviscid flux functions,which makes it possible to handle discontinuous solutions.A multidimensional slope-limiting technique is applied to achieve second-order spatial accuracy and to prevent spurious oscillations.To alleviate the problems associated with numerical instabilities due to small water depths near a wet/dry boundary,the friction source terms are treated in a fully implicit way.A third-order Runge-Kutta method is used for the time integration of semi-discrete equations.The developed numerical model has been applied to several test cases as well as to real flows.The tests are tested in two cases:oblique hydraulic jump and experimental dam break in converging-diverging flume.Numerical tests proved the robustness and accuracy of the model.The model has been applied for simulation of dam break analysis of Torogh in Irun.And finally the results have been used in preparing EAP (Emergency Action Plan).
Verjus, Romuald; Angilella, Jean-Régis
2016-05-01
Inertial particles are often observed to be trapped, temporarily or permanently, by recirculation cells which are ubiquitous in natural or industrial flows. In the limit of small particle inertia, determining the conditions of trapping is a challenging task, as it requires a large number of numerical simulations or experiments to test various particle sizes or densities. Here, we investigate this phenomenon analytically and numerically in the case of heavy particles (e.g., aerosols) at low Reynolds number, to derive a trapping criterion that can be used both in analytical and numerical velocity fields. The resulting criterion allows one to predict the characteristics of trapped particles as soon as single-phase simulations of the flow are performed. Our analysis is valid for two-dimensional particle-laden flows in the vertical plane, in the limit where the particle inertia, the free-fall terminal velocity, and the flow unsteadiness can be treated as perturbations. The weak unsteadiness of the flow generally induces a chaotic tangle near heteroclinic or homoclinic cycles if any, leading to the apparent diffusion of fluid elements through the boundary of the cell. The critical particle Stokes number Stc below which aerosols also enter and exit the cell in a complex manner has been derived analytically, in terms of the flow characteristics. It involves the nondimensional curvature-weighted integral of the squared velocity of the steady fluid flow along the dividing streamline of the recirculation cell. When the flow is unsteady and St>Stc , a regular motion takes place due to gravity and centrifugal effects, like in the steady case. Particles driven towards the interior of the cell are trapped permanently. In contrast, when the flow is unsteady and St
Energy Technology Data Exchange (ETDEWEB)
Cline, M.C.
1981-08-01
VNAP2 is a computer program for calculating turbulent (as well as laminar and inviscid), steady, and unsteady flow. VNAP2 solves the two-dimensional, time-dependent, compressible Navier-Stokes equations. The turbulence is modeled with either an algebraic mixing-length model, a one-equation model, or the Jones-Launder two-equation model. The geometry may be a single- or a dual-flowing stream. The interior grid points are computed using the unsplit MacCormack scheme. Two options to speed up the calculations for high Reynolds number flows are included. The boundary grid points are computed using a reference-plane-characteristic scheme with the viscous terms treated as source functions. An explicit artificial viscosity is included for shock computations. The fluid is assumed to be a perfect gas. The flow boundaries may be arbitrary curved solid walls, inflow/outflow boundaries, or free-jet envelopes. Typical problems that can be solved concern nozzles, inlets, jet-powered afterbodies, airfoils, and free-jet expansions. The accuracy and efficiency of the program are shown by calculations of several inviscid and turbulent flows. The program and its use are described completely, and six sample cases and a code listing are included.
Experimental investigation of the transonic flow around the leading edge of an eroded fan airfoil
Klinner, Joachim; Hergt, Alexander; Willert, Christian
2014-01-01
The influence of leading edge modification on the time-averaged and instantaneous flow around a fan airfoil is investigated by particle image velocimetry (PIV), schlieren imaging and high-speed shock shadowgraphs in a transonic cascade windtunnel. In addition to a global characterization of the time-averaged flow using PIV, the instantaneous passage shock position was extracted from single-shot PIV measurements by matching the tracer velocity across the normal shock with an exponential fit. T...
Directory of Open Access Journals (Sweden)
Shun Takahashi
2014-01-01
Full Text Available A computational code adopting immersed boundary methods for compressible gas-particle multiphase turbulent flows is developed and validated through two-dimensional numerical experiments. The turbulent flow region is modeled by a second-order pseudo skew-symmetric form with minimum dissipation, while the monotone upstream-centered scheme for conservation laws (MUSCL scheme is employed in the shock region. The present scheme is applied to the flow around a two-dimensional cylinder under various freestream Mach numbers. Compared with the original MUSCL scheme, the minimum dissipation enabled by the pseudo skew-symmetric form significantly improves the resolution of the vortex generated in the wake while retaining the shock capturing ability. In addition, the resulting aerodynamic force is significantly improved. Also, the present scheme is successfully applied to moving two-cylinder problems.
High-speed flow visualization in hypersonic, transonic, and shock tube flows
Kleine, H.; Olivier, H.
2017-02-01
High-speed flow visualisation has played an important role in the investigations conducted at the Stoßwellenlabor of the RWTH Aachen University for many decades. In addition to applying the techniques of high-speed imaging, this laboratory has been actively developing new or enhanced visualisation techniques and approaches such as various schlieren methods or time-resolved Mach-Zehnder interferometry. The investigated high-speed flows are inherently highly transient, with flow Mach numbers ranging from about M = 0.7 to M = 8. The availability of modern high-speed cameras has allowed us to expand the investigations into problems where reduced reproducibility had so far limited the amount of information that could be extracted from a limited number of flow visualisation records. Following a brief historical overview, some examples of recent studies are given, which represent the breadth of applications in which high-speed imaging has been an essential diagnostic tool to uncover the physics of high-speed flows. Applications include the stability of hypersonic corner flows, the establishment of shock wave systems in transonic airfoil flow, and the complexities of the interactions of shock waves with obstacles of various shapes.
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Richard J. Simpson
2006-04-01
Full Text Available This review deals with the application of a new prefractionation tool, free-flow electrophoresis (FFE, for proteomic analysis of colorectal cancer (CRC. CRC is a leading cause of cancer death in the Western world. Early detection is the single most important factor influencing outcome of CRC patients. If identified while the disease is still localized, CRC is treatable. To improve outcomes for CRC patients there is a pressing need to identify biomarkers for early detection (diagnostic markers, prognosis (prognostic indicators, tumour responses (predictive markers and disease recurrence (monitoring markers. Despite recent advances in the use of genomic analysis for risk assessment, in the area of biomarker identification genomic methods alone have yet to produce reliable candidate markers for CRC. For this reason, attention is being directed towards proteomics as a complementary analytical tool for biomarker identification. Here we describe a proteomics separation tool, which uses a combination of continuous FFE, a liquid-based isoelectric focusing technique, in the first dimension, followed by rapid reversed-phase HPLC (1Ã¢Â€Â“6 min/analysis in the second dimension. We have optimized imaging software to present the FFE/RP-HPLC data in a virtual 2D gel-like format. The advantage of this liquid based fractionation system over traditional gel-based fractionation systems is the ability to fractionate large quantity protein samples. Unlike 2D gels, the method is applicable to both high-Mr proteins and small peptides, which are difficult to separate, and in the case of peptides, are not retained in standard 2D gels.
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
Takagi, S.; Og˜uz, H. N.; Zhang, Z.; Prosperetti, A.
2003-05-01
This paper presents a new approach to the direct numerical simulation of particle flows. The basic idea is to use a local analytic representation valid near the particle to "transfer" the no-slip condition from the particle surface to the adjacent grid nodes. In this way the geometric complexity arising from the irregular relation between the particle boundary and the underlying mesh is avoided and fast solvers can be used. The results suggest that the computational effort increases very slowly with the number of particles so that the method is efficient for large-scale simulations. The focus here is on the two-dimensional case (cylindrical particles), but the same procedure, to be developed in forthcoming papers, applies to three dimensions (spherical particles). Several extensions are briefly discussed.
Allen, H Julian; Vincenti, Walter G
1944-01-01
Theoretical tunnel-wall corrections are derived for an airfoil of finite thickness and camber in a two-dimensional-flow wind tunnel. The theory takes account of the effects of the wake of the airfoil and of the compressibility of the fluid, and is based upon the assumption that the chord of the airfoil is small in comparison with the height of the tunnel. Consideration is given to the phenomenon of choking at high speeds and its relation to the tunnel-wall corrections. The theoretical results are compared with the small amount of low-speed experimental data available and the agreement is seen to be satisfactory, even for relatively large values of the chord-height ratio.
Runyan, Harry L; Watkins, Charles E
1953-01-01
This report treats the effect of wind-tunnel walls on the oscillating two-dimensional air forces in a compressible medium. The walls are simulated by the usual method of placing images at appropriate distances above and below the wing. An important result shown is that, for certain conditions of wing frequency, tunnel height, and Mach number, the tunnel and wing may form a resonant system so that the forces on the wing are greatly changed from the condition of no tunnel walls. It is pointed out that similar conditions exist for three-dimensional flow in circular and rectangular tunnels and apparently, within certain Mach number ranges, in tunnels of nonuniform cross section or even in open tunnels or jets.
Directory of Open Access Journals (Sweden)
Wenqiang Zhao
2014-11-01
Full Text Available This work studies the long-time behavior of two-dimensional micropolar fluid flows perturbed by the generalized time derivative of the infinite dimensional Wiener processes. Based on the omega-limit compactness argument as well as some new estimates of solutions, it is proved that the generated random dynamical system admits an H^1-random attractor which is compact in H^1 space and attracts all tempered random subsets of L^2 space in H^1 topology. We also give a general abstract result which shows that the continuity condition and absorption of the associated random dynamical system in H^1 space is not necessary for the existence of random attractor in H^1 space.
Ohsuga, Ken
2011-01-01
We present the detailed global structure of black hole accretion flows and outflows through newly performed two-dimensional radiation-magnetohydrodynamic simulations. By starting from a torus threaded with weak toroidal magnetic fields and by controlling the central density of the initial torus, rho_0, we can reproduce three distinct modes of accretion flow. In model A with the highest central density, an optically and geometrically thick supercritical accretion disk is created. The radiation force greatly exceeds the gravity above the disk surface, thereby driving a strong outflow (or jet). Because of the mild beaming, the apparent (isotropic) photon luminosity is ~22L_E (where L_E is the Eddington luminosity) in the face-on view. Even higher apparent luminosity is feasible if we increase the flow density. In model B with a moderate density, radiative cooling of the accretion flow is so efficient that a standard-type, cold, and geometrically thin disk is formed at radii greater than ~7R_S (where R_S is the S...
Bohling, G.C.; Butler, J.J.
2001-01-01
We have developed a program for inverse analysis of two-dimensional linear or radial groundwater flow problems. The program, 1r2dinv, uses standard finite difference techniques to solve the groundwater flow equation for a horizontal or vertical plane with heterogeneous properties. In radial mode, the program simulates flow to a well in a vertical plane, transforming the radial flow equation into an equivalent problem in Cartesian coordinates. The physical parameters in the model are horizontal or x-direction hydraulic conductivity, anisotropy ratio (vertical to horizontal conductivity in a vertical model, y-direction to x-direction in a horizontal model), and specific storage. The program allows the user to specify arbitrary and independent zonations of these three parameters and also to specify which zonal parameter values are known and which are unknown. The Levenberg-Marquardt algorithm is used to estimate parameters from observed head values. Particularly powerful features of the program are the ability to perform simultaneous analysis of heads from different tests and the inclusion of the wellbore in the radial mode. These capabilities allow the program to be used for analysis of suites of well tests, such as multilevel slug tests or pumping tests in a tomographic format. The combination of information from tests stressing different vertical levels in an aquifer provides the means for accurately estimating vertical variations in conductivity, a factor profoundly influencing contaminant transport in the subsurface. ?? 2001 Elsevier Science Ltd. All rights reserved.
Frankl, F.; Voishel, V.
1943-01-01
In the present report an investigation is made on a flat plate in a two-dimensional compressible flow of the effect of compressibility and heating on the turbulent frictional drag coefficient in the boundary layer of an airfoil or wing radiator. The analysis is based on the Prandtl-Karman theory of the turbulent boundary later and the Stodola-Crocco, theorem on the linear relation between the total energy of the flow and its velocity. Formulas are obtained for the velocity distribution and the frictional drag law in a turbulent boundary later with the compressibility effect and heat transfer taken into account. It is found that with increase of compressibility and temperature at full retardation of the flow (the temperature when the velocity of the flow at a given point is reduced to zero in case of an adiabatic process in the gas) at a constant R (sub x), the frictional drag coefficient C (sub f) decreased, both of these factors acting in the same sense.
Unsteady features of the flow on a bump in transonic environment
Budovsky, A. D.; Sidorenko, A. A.; Polivanov, P. A.; Vishnyakov, O. I.; Maslov, A. A.
2016-10-01
The study deals with experimental investigation of unsteady features of separated flow on a profiled bump in transonic environment. The experiments were conducted in T-325 wind tunnel of ITAM for the following flow conditions: P0 = 1 bar, T0 = 291 K. The base flow around the model was studied by schlieren visualization, steady and unsteady wall pressure measurements and PIV. The experimentally data obtained using PIV are analyzed by Proper Orthogonal Decomposition (POD) technique to investigate the underlying unsteady flow organization, as revealed by the POD eigenmodes. The data obtained show that flow pulsations revealed upstream and downstream of shock wave are correlated and interconnected.
The application of digital particle image velocimetry (DPIV) to transonic flows
Bryanston-Cross, P. J.; Judge, T. R.; Quan, C.; Pugh, G.; Corby, N.
The paper is an extension to earlier PIV work published in Progress in Aerospace Science Vol. 27, pp237-265. 1990. DPIV (Digital Particle Image Velocimetry) measurements have been made at transonic speeds using a new method of both digitally capturing and visualising high speed flow-fields. It has provided a quantitative whole field image of the transonic flow. The area of interest for this test was of the wing/pylon/nacelle/inboard gully region of a 5.7% scale model wing and engine combination. The measurements show velocity and flow angle changes in this region, to a measurement accuracy of 4%, made at an optical stand off distance of 0.5 m.
Experimental results and numerical simulations for transonic flow over the ONERA M4R model
Directory of Open Access Journals (Sweden)
Marius Gabriel COJOCARU
2013-06-01
Full Text Available This paper presents a comparison between experimental results of transonic flow over the ONERA M4R calibration model obtained in the INCAS Trisonic wind tunnel and the numerical results. The first purpose, emphasized in this paper is to compare and validate the computational fluid dynamics (CFD techniques for internal transonic flows and to try to find the most suitable numerical methodology for these flows in both accuracy and computational resources. The second purpose is to develop a general method in experimental data correction and flight Reynolds extrapolation, using numerical simulations for both global and local pressure coefficients, as a replacement for the classical vortex lattices based method. That will be developed in a future paper. Besides the computational work, the periodic wind tunnel calibration is required as a quality insurance operation and a numerical model is developed such that future hardware modifications to be included and their impact to be properly considered.
The efficient solution of transonic wing flow fields
Holst, T. L.; Subramanian, N. R.; Thomas, S. D.
1983-01-01
An evaluation of the transonic-wing-analysis computer code TWING is presented. TWING utilizes a fully implicit, approximate-factorization iteration scheme to solve the full-potential equation in conservative form. A numerical elliptic-solver grid-generation scheme is used to generate the required finite-difference mesh. Several wing configurations have been analyzed, and comparisons of computed results have been made with available experimental data. Results indicate that the code is robust, accurate (when significant viscous effects are not present), and efficient. TWING generally produces solutions an order of magnitude faster than other conservative, full-potential codes using successive-line overrelaxation. The present method is applicable to a wide range of isolated wing configurations, including high-aspect-ratio transport wings and low-aspect-ratio, high-sweep, fighter configurations.
Park, Kyu-Hwan; Son, Jang-Won; Park, Won-Jong; Lee, Sang-Hee; Kim, Ung; Park, Jong-Seon; Shin, Dong-Gu; Kim, Young-Jo; Choi, Jung-Hyun; Houle, Helene; Vannan, Mani A; Hong, Geu-Ru
2013-01-01
This article is the first clinical investigation of the quantitative left atrial (LA) vortex flow by two-dimensional (2-D) transesophageal contrast echocardiography (2-D-TECE) using vector particle image velocimetry (PIV). The aims of this study were to assess the feasibility of LA vortex flow analysis and to characterize and quantify the LA vortex flow in controls and in patients with atrial fibrillation (AF). Thirty-five controls and 30 patients with AF underwent transesophageal contrast echocardiography. The velocity vector was estimated by particle image velocimetry. The morphology and pulsatility of the LA vortex flow were compared between the control and AF groups. In all patients, quantitative LA vortex flow analysis was feasible. In the control group, multiple, pulsatile, compact and elliptical-shaped vortices were seen in the periphery of the LA. These vortices were persistently maintained and vectors were directed toward the atrioventricular inflow. In the AF group, a large, merged, lower pulsatile and round-shaped vortex was observed in the center of the LA. In comparisons of vortex parameters, the relative strength was significantly lower in the AF group (1.624 ± 0.501 vs. 2.105 ± 0.226, p < 0.001). It is feasible to characterize and quantify the LA vortex flow by transesophageal contrast echocardiography in patients with AF, which offers a new method to obtain additional information on LA hemodynamics. The approach has the potential for early detection of the LA dysfunction and in decisions regarding treatment strategy and guiding anticoagulation treatment in patients with AF.
Baskan, O; Speetjens, M F M; Metcalfe, G; Clercx, H J H
2015-10-01
Countless theoretical/numerical studies on transport and mixing in two-dimensional (2D) unsteady flows lean on the assumption that Hamiltonian mechanisms govern the Lagrangian dynamics of passive tracers. However, experimental studies specifically investigating said mechanisms are rare. Moreover, they typically concern local behavior in specific states (usually far away from the integrable state) and generally expose this indirectly by dye visualization. Laboratory experiments explicitly addressing the global Hamiltonian progression of the Lagrangian flow topology entirely from integrable to chaotic state, i.e., the fundamental route to efficient transport by chaotic advection, appear non-existent. This motivates our study on experimental visualization of this progression by direct measurement of Poincaré sections of passive tracer particles in a representative 2D time-periodic flow. This admits (i) accurate replication of the experimental initial conditions, facilitating true one-to-one comparison of simulated and measured behavior, and (ii) direct experimental investigation of the ensuing Lagrangian dynamics. The analysis reveals a close agreement between computations and observations and thus experimentally validates the full global Hamiltonian progression at a great level of detail.
Energy Technology Data Exchange (ETDEWEB)
Baskan, O.; Clercx, H. J. H [Fluid Dynamics Laboratory, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands); Speetjens, M. F. M. [Energy Technology Laboratory, Department of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands); Metcalfe, G. [Commonwealth Scientific and Industrial Research Organisation, Melbourne, Victoria 3190 (Australia); Swinburne University of Technology, Department of Mechanical Engineering, Hawthorn VIC 3122 (Australia)
2015-10-15
Countless theoretical/numerical studies on transport and mixing in two-dimensional (2D) unsteady flows lean on the assumption that Hamiltonian mechanisms govern the Lagrangian dynamics of passive tracers. However, experimental studies specifically investigating said mechanisms are rare. Moreover, they typically concern local behavior in specific states (usually far away from the integrable state) and generally expose this indirectly by dye visualization. Laboratory experiments explicitly addressing the global Hamiltonian progression of the Lagrangian flow topology entirely from integrable to chaotic state, i.e., the fundamental route to efficient transport by chaotic advection, appear non-existent. This motivates our study on experimental visualization of this progression by direct measurement of Poincaré sections of passive tracer particles in a representative 2D time-periodic flow. This admits (i) accurate replication of the experimental initial conditions, facilitating true one-to-one comparison of simulated and measured behavior, and (ii) direct experimental investigation of the ensuing Lagrangian dynamics. The analysis reveals a close agreement between computations and observations and thus experimentally validates the full global Hamiltonian progression at a great level of detail.
Investigation of Three-Dimensional Flow Structure in a Transonic Diffuser by the LIF Method
小野, 大輔; 半田, 太郎; 青木, 俊之; 益田, 光治
2007-01-01
The three-dimensional flow structure induced by normal shock-wave/boundary-layer interaction in a transonic diffuser is investigated by a laser-induced fluorescence (LIF) method. This diagnostic system uses an argon-ion laser as a light source, and target gas is dry nitrogen with iodine seeded as a fluorescence material. The Mach-number distributions in the diffuser are obtained from the measured fluorescence intensity, and the three-dimensional shape of the boundary layers is obtained immedi...
Boufadel, Michel C.; Suidan, Makram T.; Venosa, Albert D.
1999-04-01
We present a formulation for water flow and solute transport in two-dimensional variably saturated media that accounts for the effects of the solute on water density and viscosity. The governing equations are cast in a dimensionless form that depends on six dimensionless groups of parameters. These equations are discretized in space using the Galerkin finite element formulation and integrated in time using the backward Euler scheme with mass lumping. The modified Picard method is used to linearize the water flow equation. The resulting numerical model, the MARUN model, is verified by comparison to published numerical results. It is then used to investigate beach hydraulics at seawater concentration (about 30 g l -1) in the context of nutrients delivery for bioremediation of oil spills on beaches. Numerical simulations that we conducted in a rectangular section of a hypothetical beach revealed that buoyancy in the unsaturated zone is significant in soils that are fine textured, with low anisotropy ratio, and/or exhibiting low physical dispersion. In such situations, application of dissolved nutrients to a contaminated beach in a freshwater solution is superior to their application in a seawater solution. Concentration-engendered viscosity effects were negligible with respect to concentration-engendered density effects for the cases that we considered.
Duddu, Ravindra
2009-05-01
We present a two-dimensional biofilm growth model in a continuum framework using an Eulerian description. A computational technique based on the eXtended Finite Element Method (XFEM) and the level set method is used to simulate the growth of the biofilm. The model considers fluid flow around the biofilm surface, the advection-diffusion and reaction of substrate, variable biomass volume fraction and erosion due to the interfacial shear stress at the biofilm-fluid interface. The key assumptions of the model and the governing equations of transport, biofilm kinetics and biofilm mechanics are presented. Our 2D biofilm growth results are in good agreement with those obtained by Picioreanu et al. (Biotechnol Bioeng 69(5):504-515, 2000). Detachment due to erosion is modeled using two continuous speed functions based on: (a) interfacial shear stress and (b) biofilm height. A relation between the two detachment models in the case of a 1D biofilm is established and simulated biofilm results with detachment in 2D are presented. The stress in the biofilm due to fluid flow is evaluated and higher stresses are observed close to the substratum where the biofilm is attached. © 2008 Wiley Periodicals, Inc.
Directory of Open Access Journals (Sweden)
P. Martini
2004-01-01
Full Text Available The paper presents a numerical model for the simulation of flood waves and suspended sediment transport in a lowland river basin of North Eastern Italy. The two dimensional depth integrated momentum and continuity equations are modified to take into account the bottom irregularities that strongly affect the hydrodynamics in partially dry areas, as for example, in the first stages of an inundation process or in tidal flow. The set of equations are solved with a standard Galerkin finite element method using a semi-implicit numerical scheme where the effects of both the small channel network and the regulation devices on the flood wave propagation are accounted for. Transport of suspended sediment and bed evolution are coupled with the hydrodynamics using an appropriate form of the advection-dispersion equation and Exner's equation. Applications to a case study are presented in which the effects of extreme flooding on the Brenta River (Italy are examined. Urban and rural flood risk areas are identified and the effects of a alleviating action based on a diversion channel flowing into Venice Lagoon are simulated. The results show that this solution strongly reduces the flood risk in the downstream areas and can provide an important source of sediment for the Venice Lagoon. Finally, preliminary results of the sediment dispersion due to currents and waves in the Venice Lagoon are presented.
Effect of the Unsteadiness on the Diffuser Flow in a Transonic Centrifugal Compressor Stage
N. Bulot; I. Trébinjac
2009-01-01
The study is focused on the analysis of the flow structure within the vaned diffuser of a transonic high-pressure centrifugal compressor stage. The analyzed time-dependent flow field comes from unsteady computations of the stage using a 3D Navier-Stokes code with a phase-lagged technique, at an operating point close to the design point. A good comparison with available experimental data allowed the use of CFD for investigating the details of the flow in order to assess the effect of the unste...
Li, Hua; Ma, Gang
2010-08-01
The long-term lateral migration of a two-dimensional elastic capsule in a microchannel is studied numerically in this paper. The numerical method combines a finite volume technique for solving the fluid problem with a front tracking technique for capturing and tracking the capsule membrane. The capsule is modeled as a liquid medium enclosed by a thin membrane which has linear elastic properties. The capsule, whose initial shape is circle and which starts from a near-center position or a near-wall position, experiences tilting and membrane tank-treading, and migrates laterally when moving along the surrounding flow. The lateral migration demonstrates the existence of lift effect of surrounding flow on moving capsule. Before capsule approaches to the microchannel centerline closely, lower membrane dilation modulus and lower viscosity ratio tend to result in faster lateral migration. The initial position also influences the performance behavior of capsule, despite the lateral migration of capsule is a quasisteady process. Small difference in capsule behavior when capsule is not near to the microchannel centerline might lead to significant difference in capsule behavior when capsule approaches closely to the centerline. When capsules are near to microchannel wall, the effect of the wall on capsule behavior might dominate, leading to relatively faster lateral migration. When capsules are not far from microchannel centerline, the effect of the nonlinearity of Poiseuille flow might dominate, resulting in relatively slower lateral movement. When capsules are located closely to the centerline, they behave differently, where the reason still remains poorly understood and it will be one of our future studies. The comparison between the capsule behavior from the present simulation and that by the migration law proposed by Coupier [Phys. Fluids 20, 111702 (2008)] shows that the behavioral agreement for near-wall capsule is better than that for near-center capsule, and the best
Yin, W.-L.
1984-04-01
It is shown that, in the case of non-zero charge density, the class of steady, plane, incompressible, aligned-fluid magnetofluiddynamic flows contains no rotational motions. Therefore, this class of flows is exhausted by the irrotational solutions of Kingston and Power.
Directory of Open Access Journals (Sweden)
Guodong Liu
2013-01-01
Full Text Available Modular pebble-bed nuclear reactor (MPBNR technology is promising due to its attractive features such as high fuel performance and inherent safety. Particle motion of fuel and graphite pebbles is highly associated with the performance of pebbled-bed modular nuclear reactor. To understand the mechanism of pebble’s motion in the reactor, we numerically studied the influence of number ratio of fuel and graphite pebbles, funnel angle of the reactor, height of guide ring on the distribution of pebble position, and velocity by means of discrete element method (DEM in a two-dimensional MPBNR. Velocity distributions at different areas of the reactor as well as mixing characteristics of fuel and graphite pebbles were investigated. Both fuel and graphite pebbles moved downward, and a uniform motion was formed in the column zone, while pebbles motion in the cone zone was accelerated due to the decrease of the cross sectional flow area. The number ratio of fuel and graphite pebbles and the height of guide ring had a minor influence on the velocity distribution of pebbles, while the variation of funnel angle had an obvious impact on the velocity distribution. Simulated results agreed well with the work in the literature.
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
A two-dimensional model of unsteady turbulent flow induced by high-speed elevator system was established in the present study. The research was focused on the instantaneous variation of the aerodynamic force on the car structure during traversing motion of the counter weight in the hoistway. A dynamic meshing method was employed to treat the multi-body motion system to avoid poor distortion of meshes. A comprehensive understanding of this significant aspect was obtained by varying the horizontal gap (δ=0.1m, 0.2m, and 0.3m) between the elevator car and the counter weight, and the moving speed (U0=2m/s, 6m/s, and 10m/s) of the elevator system. A pulsed intensification of the aerodynamic force on the elevator car and subsequent appearance of large valley with negative aerodynamic force were clearly observed in the numerical results. In parameters studied (δ=0.1m, U0=2m/s, 6m/s, 10m/s), the peaked horizontal and vertical forces are respectively 7-11 and 4.3-5.65 times of that when the counter weight is far from the car. These results demonstrated the prominent influence of the traversing counter weight on aerodynamic force on the elevator car, which is of great significance to designers of high-speed elevator system.
Application of a chimera technique to the computation of subsonic and transonic bi-airfoil flows
L.C.Q. Yagua; B. Koren (Barry)
2004-01-01
textabstractThis paper describes the application of a composite overset-grid technique to flow computations around a two-dimensional bi-plane. The flow is described by the steady, 2D, compressible Euler equations of gas dynamics. The discretization method used is a central finite-difference method
Energy Technology Data Exchange (ETDEWEB)
Yoo, Y.Z.; Chmaissem, O.; Kolesnik, S.; Ullah, A.; Lurio, L.B.; Brown, D.E.; Brady, J.; Dabrowski, B.; Kimball, C.W.; Haji-Sheikh, M.; Genis, A.P. (NIU)
2010-12-03
Geometrical anisotropy axes of diverse SrRuO{sub 3} (SRO) films grown by random and directional two-dimensional and step flow modes are determined and their characteristic angular magnetizations are understood in terms of growth mode induced structural effects. Two-dimensional SRO films possess single-crystal-like structural qualities. Angular magnetization measurements show sharp minima and indicate the films easy axis to be in the [310] direction. In contrast, examination of step flow SRO films shows the presence of degenerate multiple in-plane domains and the anisotropy axis in a direction close to [110] even though directional surface steps are clearly visible.
Unsteady flows in a single-stage transonic axial-flow fan stator row
Hathaway, Michael Dale
Detailed measurements of the unsteady velocity field within the stator flow of a transonic axial-flow fan were acquired using a laser anemometer. They were obtained on axisymmetric surfaces located at 10 and 50 percent span from the shroud, with the fan operating at maximum efficiency at design speed. The ensemble-average and variance of the measured velocities are used to identify rotor-wake-generated (deterministic) unsteadiness and turbulence, respectively. Correlations of both deterministic and turbulent velocity fluctuations provide information on the characteristics of unsteady interactions within the stator row. These correlations are derived from the Navier-Stokes equation in a manner similar to deriving the Reynolds stress terms, whereby various averaging operators are used to average the aperiodic, deterministic, and turbulent velocity fluctuations known to be present in multistage turbomachines. The correlations of deterministic and turbulent velocity fluctuations throughout the axial fan stator row are presented. In particular, amplification and attenuation of both types of unsteadiness are shown to occur within the stator blade passage.
Topology Method for Analyses of 3—D Viscous Flow Structure in Transonic Turbomachinery
Institute of Scientific and Technical Information of China (English)
YanhuGuo; BaoguoWang; 等
1997-01-01
A topology method is presented in this paper to reveal flow tructure occurring insie turbomachinery,in which near wall flow structure is revealed by using wall limiting streamilines and space flow feature is revealed by using space streamilines and cross-section streamlines,As an example ,a computational three-dimensional viscous flow field inside a transonic turbine cascade is studied.Through the analysis,the form and evolution of vortex system and the whole process of separation occurring within this cascade are revealed.The application of topology method for analyze flow structure inside turbomachinmery is very important for understanding flow features and mechanism of flow loss even for improving the design of turbomachinery and increasing its efficiency.
Prediction of forces and moments on finned bodies at high angle of attack in transonic flow
Energy Technology Data Exchange (ETDEWEB)
Oberkampf, W. L.
1981-04-01
This report describes a theoretical method for the prediction of fin forces and moments on bodies at high angle of attack in subsonic and transonic flow. The body is assumed to be a circular cylinder with cruciform fins (or wings) of arbitrary planform. The body can have an arbitrary roll (or bank) angle, and each fin can have individual control deflection. The method combines a body vortex flow model and lifting surface theory to predict the normal force distribution over each fin surface. Extensive comparisons are made between theory and experiment for various planform fins. A description of the use of the computer program that implements the method is given.
An analysis of the Circumferential Grooves Casing Treatment for transonic compressor flow
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
The stall mechanism of the NASA Rotor 37 is investigated through the analysis of the critical flow structures near the stall under the transonic condition. The performance of the rotor with Circumferential Grooves Casing Treatment (CGCT) is also studied based on the Reynolds-Averaging Navier-Stokes approach. The study finds that stall margin improvement can be achieved without significant penalty on the efficiency for the two CGCT configurations applied. The effects of circumferential grooves on the critical flow structures are studied through the analysis of the tip leakage mass and momentum transport that further re-veal the CGCT mechanism.
Computational Design and Analysis of a Transonic Natural Laminar Flow Wing for a Wind Tunnel Model
Lynde, Michelle N.; Campbell, Richard L.
2017-01-01
A natural laminar flow (NLF) wind tunnel model has been designed and analyzed for a wind tunnel test in the National Transonic Facility (NTF) at the NASA Langley Research Center. The NLF design method is built into the CDISC design module and uses a Navier-Stokes flow solver, a boundary layer profile solver, and stability analysis and transition prediction software. The NLF design method alters the pressure distribution to support laminar flow on the upper surface of wings with high sweep and flight Reynolds numbers. The method addresses transition due to attachment line contamination/transition, Gortler vortices, and crossflow and Tollmien-Schlichting modal instabilities. The design method is applied to the wing of the Common Research Model (CRM) at transonic flight conditions. Computational analysis predicts significant extents of laminar flow on the wing upper surface, which results in drag savings. A 5.2 percent scale semispan model of the CRM NLF wing will be built and tested in the NTF. This test will aim to validate the NLF design method, as well as characterize the laminar flow testing capabilities in the wind tunnel facility.
Pierzga, M. J.; Wood, J. R.
1984-01-01
An experimental investigation of the three dimensional flow field through a low aspect ratio, transonic, axial flow fan rotor has been conducted using an advanced laser anemometer (LA) system. Laser velocimeter measurements of the rotor flow field at the design operating speed and over a range of through flow conditions are compared to analytical solutions. The numerical technique used herein yields the solution to the full, three dimensional, unsteady Euler equations using an explicit time marching, finite volume approach. The numerical analysis, when coupled with a simplified boundary layer calculation, generally yields good agreement with the experimental data. The test rotor has an aspect ratio of 1.56, a design total pressure ratio of 1.629 and a tip relative Mach number of 1.38. The high spatial resolution of the LA data matrix (9 radial by 30 axial by 50 blade to blade) permits details of the transonic flow field such as shock location, turning distribution and blade loading levels to be investigated and compared to analytical results.
Energy Technology Data Exchange (ETDEWEB)
Eaton, R.R.; Hopkins, P.L.
1992-08-01
LLUVIA-II is a program designed for the efficient solution of two- dimensional transient flow of liquid water through partially saturated, porous media. The code solves Richards equation using the method-of-lines procedure. This document describes the solution procedure employed, input data structure, output, and code verification.
Study of Near-Stall Flow Behavior in a Modern Transonic Fan with Composite Sweep
Hah, Chunill; Shin, Hyoun-Woo
2011-01-01
Detailed flow behavior in a modern transonic fan with a composite sweep is investigated in this paper. Both unsteady Reynolds-averaged Navier-Stokes (URANS) and Large Eddy Simulation (LES) methods are applied to investigate the flow field over a wide operating range. The calculated flow fields are compared with the data from an array of high-frequency response pressure transducers embedded in the fan casing. The current study shows that a relatively fine computational grid is required to resolve the flow field adequately and to calculate the pressure rise across the fan correctly. The calculated flow field shows detailed flow structure near the fan rotor tip region. Due to the introduction of composite sweep toward the rotor tip, the flow structure at the rotor tip is much more stable compared to that of the conventional blade design. The passage shock stays very close to the leading edge at the rotor tip even at the throttle limit. On the other hand, the passage shock becomes stronger and detaches earlier from the blade passage at the radius where the blade sweep is in the opposite direction. The interaction between the tip clearance vortex and the passage shock becomes intense as the fan operates toward the stall limit, and tip clearance vortex breakdown occurs at near-stall operation. URANS calculates the time-averaged flow field fairly well. Details of measured RMS static pressure are not calculated with sufficient accuracy with URANS. On the other hand, LES calculates details of the measured unsteady flow features in the current transonic fan with composite sweep fairly well and reveals the flow mechanism behind the measured unsteady flow field.
Haviland, J. K.
1974-01-01
The results are reported of two unrelated studies. The first was an investigation of the formulation of the equations for non-uniform unsteady flows, by perturbation of an irrotational flow to obtain the linear Green's equation. The resulting integral equation was found to contain a kernel which could be expressed as the solution of the adjoint flow equation, a linear equation for small perturbations, but with non-constant coefficients determined by the steady flow conditions. It is believed that the non-uniform flow effects may prove important in transonic flutter, and that in such cases, the use of doublet type solutions of the wave equation would then prove to be erroneous. The second task covered an initial investigation into the use of the Monte Carlo method for solution of acoustical field problems. Computed results are given for a rectangular room problem, and for a problem involving a circular duct with a source located at the closed end.
Stepped tip gap effects on a transonic axial-flow compressor rotor
Thompson, Donald William
The effects of stepped tip gaps and clearance levels on the performance, flowfield, and stall characteristics of a transonic axial-flow compressor rotor were experimentally and numerically determined. A theory and mechanism for relocation of blockage in the rotor tip region was developed. A two-stage compressor with no inlet guide vanes was tested in a modern transonic compressor research facility. The first-stage rotor was unswept and was tested for an optimum tip clearance with variations in stepped gaps machined into the casing near the aft tip region of the rotor. Nine casing geometries were investigated consisting of three step profiles at each of three clearance levels. For small and intermediate clearances, stepped tip gaps were found to improve pressure ratio, efficiency, and flow range for most operating conditions. At 100% design rotor speed, stepped tip gaps produced a doubling of mass flow range with as much as a 2.0% increase in mass flow and a 1.5% improvement in efficiency. The flowfield characteristics associated with performance improvements were experimentally and numerically analyzed. Stepped tip gaps were found to have no significant effect on the stall characteristics of the rotor; the stability characteristics attributable to tip geometry were determined by the clearance over the forward portion of the rotor blade. This study provides guidelines for engineers to improve compressor performance for an existing design by applying an optimum casing profile.
Pierzga, M. J.; Wood, J. R.
1984-01-01
An experimental investigation of the three-dimensional flow field through a low aspect ratio, transonic, axial flow fan rotor has been conducted, using an advanced laser anemometer (LA) system. Laser velocimeter measurements of the rotor flow field at the design operating speed and over a range of throughflow conditions are compared to analytical solutions. The numerical technique used herein yields the solution to the full, three-dimensional, unsteady Euler equations using an explicit time-marching, finite volume approach. The numerical analysis, when coupled with a simplified boundary layer calculation, generally yields good agreement with the experimental data. The test rotor has an aspect ratio of 1.56, a design total pressure ratio of 1.629 and a tip relative Mach number of 1.38. The high spatial resolution of the LA data matrix (9 radial x 30 axial x 50 blade-to-blade) permits details of the transonic flow field such as shock location, turning distribution, and blade loading levels to be investigated and compared to analytical results.
Transonic flow of moist air around an NACA 0012 airfoil with non-equilibrium condensation
Institute of Scientific and Technical Information of China (English)
LI Liang; SUN Xiuling; FENG Zhenping; LI Guojun
2005-01-01
The classical condensation model of water vapor is coupled with the Euler equations to calculate transonic flows of moist air with non-equilibrium condensation. By means of this model, numerical computations are implemented to investigate the aerodynamic characteristics of an NACA 0012 airfoil in transonic flows of moist air at various angles of attack and relative humidities, and the results are compared with those in dry air flows. For different angles of attack considered at 50 % relative humidity, the lift decreases 30 % -40 %.The pressure drag increases when the angle of attack is smaller than 1.4° and decreases when higher than 1.4°. At zero angle of attack,with the relative humidity rising from zero to 90 %, the pressure drag increases exponentially. At 90 % relative humidity, the pressure drag increases 160 %, and self-oscillation takes place periodically and alternately over the upper and lower surfaces of the airfoil. The oscillation is caused by the interactions of local supersonic flow and heat release in the condensation process.
Wan, Xiaoliang; Yu, Haijun; Weinan, E.
2015-05-01
In this work, we study the nonlinear instability of two-dimensional (2D) wall-bounded shear flows from the large deviation point of view. The main idea is to consider the Navier-Stokes equations perturbed by small noise in force and then examine the noise-induced transitions between the two coexisting stable solutions due to the subcritical bifurcation. When the amplitude of the noise goes to zero, the Freidlin-Wentzell (F-W) theory of large deviations defines the most probable transition path in the phase space, which is the minimizer of the F-W action functional and characterizes the development of the nonlinear instability subject to small random perturbations. Based on such a transition path we can define a critical Reynolds number for the nonlinear instability in the probabilistic sense. Then the action-based stability theory is applied to study the 2D Poiseuille flow in a short channel.
Huizinga, Richard J.
2008-01-01
In cooperation with the Missouri Department of Transportation, the U.S. Geological Survey determined hydrologic and hydraulic parameters for the Gasconade River at the site of a proposed bridge replacement and highway realignment of State Highway 17 near Waynesville, Missouri. Information from a discontinued streamflow-gaging station on the Gasconade River near Waynesville was used to determine streamflow statistics for analysis of the 25-, 50-, 100-, and 500-year floods at the site. Analysis of the streamflow-gaging stations on the Gasconade River upstream and downstream from Waynesville indicate that flood peaks attenuate between the upstream gaging station near Hazelgreen and the Waynesville gaging station, such that the peak discharge observed on the Gasconade River near Waynesville will be equal to or only slightly greater (7 percent or less) than that observed near Hazelgreen. A flood event occurred on the Gasconade River in March 2008, and a flood measurement was obtained near the peak at State Highway 17. The elevation of high-water marks from that event indicated it was the highest measured flood on record with a measured discharge of 95,400 cubic feet per second, and a water-surface elevation of 766.18 feet near the location of the Waynesville gaging station. The measurements obtained for the March flood resulted in a shift of the original stage-discharge relation for the Waynesville gaging station, and the streamflow statistics were modified based on the new data. A two-dimensional hydrodynamic flow model was used to simulate flow conditions on the Gasconade River in the vicinity of State Highway 17. A model was developed that represents existing (2008) conditions on State Highway 17 (the 'model of existing conditions'), and was calibrated to the floods of March 20, 2008, December 4, 1982, and April 14, 1945. Modifications were made to the model of existing conditions to create a model that represents conditions along the same reach of the Gasconade
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.
DEFF Research Database (Denmark)
Sjöholm, Mikael; Angelou, Nikolas; Hansen, Per
2014-01-01
position; all points in space within a cone with a full opening angle of 1208 can be reached from about 8mout to some hundred meters depending on the range resolution required. The first two-dimensional mean wind fields measured in a horizontal plane and in a vertical plane below a hovering search...
Identification of vortices in a transonic compressor flow and the stall process
Institute of Scientific and Technical Information of China (English)
HUANGXu-dong; CHENHai-xin; FUSong; DavidWisler; AspiWadia; G.ScottMcNulty
2007-01-01
A novel vortex identification method for the visualization of the flow field is used for the study of the stall process of a transonic compressor. The parameter η4, which is one of the five invariants formed by the stain rate and vorticity tensors from the theory of modern rational mechanics, is found to have good ability to identify vortex stretching and vortex relaxation/breakdown processes, is introduced here to identify the tip leakage vortices. Compare with former generally used DPH(dynamic pressure head) contour, the new method reveals much more flow details which may advance our understanding of the compressor behaviors. The Vortices details are revealed in both peak efficiency and near stall condition. A possible stall process is also suggested based on the vortices analysis. The tip leakage flow from mid-chord, besides leading edge leakage flow, is also considered to play an important role in the stall process.
Atta, E. H.; Vadyak, J.
An efficient grid interfacing zonal algorithm has been developed for computing the transonic flow field about three-dimensional multicomponent configurations. The algorithm uses the full-potential formulation and the fully-implicit approximate factorization scheme (AF2). The flow field solution is computed using a component adaptive grid approach in which separate grids are employed for the individual components in the multicomponent configuration, where each component grid is optimized for a particular geometry. The component grids are allowed to overlap, and flow field information is transmitted from one grid to another through the overlap region. An overlapped-grid scheme is implemented for a wing and a wing/pylon/nacelle configuration. Numerical results show that the present algorithm is stable, accurate, and can be used effectively to compute the flow field about complex configurations.
Laser anemometer measurements in a transonic axial-flow fan rotor
Strazisar, Anthony J.; Wood, Jerry R.; Hathaway, Michael D.; Suder, Kenneth L.
1989-11-01
Laser anemometer surveys were made of the 3-D flow field in NASA rotor 67, a low aspect ratio transonic axial-flow fan rotor. The test rotor has a tip relative Mach number of 1.38. The flowfield was surveyed at design speed at near peak efficiency and near stall operating conditions. Data is presented in the form of relative Mach number and relative flow angle distributions on surfaces of revolution at nine spanwise locations evenly spaced from hub to tip. At each spanwise location, data was acquired upstream, within, and downstream of the rotor. Aerodynamic performance measurements and detailed rotor blade and annulus geometry are also presented so that the experimental results can be used as a test case for 3-D turbomachinery flow analysis codes.
Laser anemometer measurements in a transonic axial-flow fan rotor
Strazisar, Anthony J.; Wood, Jerry R.; Hathaway, Michael D.; Suder, Kenneth L.
1989-01-01
Laser anemometer surveys were made of the 3-D flow field in NASA rotor 67, a low aspect ratio transonic axial-flow fan rotor. The test rotor has a tip relative Mach number of 1.38. The flowfield was surveyed at design speed at near peak efficiency and near stall operating conditions. Data is presented in the form of relative Mach number and relative flow angle distributions on surfaces of revolution at nine spanwise locations evenly spaced from hub to tip. At each spanwise location, data was acquired upstream, within, and downstream of the rotor. Aerodynamic performance measurements and detailed rotor blade and annulus geometry are also presented so that the experimental results can be used as a test case for 3-D turbomachinery flow analysis codes.
CFD Simulation of Transonic Flow in High-Voltage Circuit Breaker
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Xiangyang Ye
2012-01-01
Full Text Available A high-voltage circuit breaker is an indispensable piece of equipment in the electric transmission and distribution systems. Transonic flow typically occurs inside breaking chamber during the current interruption, which determines the insulating characteristics of gas. Therefore, accurate compressible flow simulations are required to improve the prediction of the breakdown voltages in various test duties of high-voltage circuit breakers. In this work, investigation of the impact of the solvers on the prediction capability of the breakdown voltages in capacitive switching is presented. For this purpose, a number of compressible nozzle flow validation cases have been presented. The investigation is then further extended for a real high-voltage circuit breaker geometry. The correlation between the flow prediction accuracy and the breakdown voltage prediction capability is identified.
Investigation of Three-Dimensional Unsteady Flow Characteristics in Transonic Diffusers
Proshchanka, Dzianis; Yonezawa, Koichi; Tsujimoto, Yoshinobu
Three-dimensional characteristics of unsteady flow in supercritical transonic diffuser are investigated. For various pressure ratios three-dimensional flow containing a normal shock/turbulent boundary layer interaction regions with shockwave and pseudo-shockwaves fluctuating in longitudinal and spanwise directions is observed. Experimental and numerical investigations show details of the flowfield in the vicinity of terminal shock, interaction regions and downstream turbulent unsteady flow. Spectral analysis of pressure fluctuations reveals existence of two characteristic frequencies attributed to the shockwave fluctuation in longitudinal direction for the lower frequency case and acoustic resonance in spanwise direction for the higher one. Vortices appear at each corner in transversal sections modifying the core flow. As a result, size and depth of longitudinal and vertical penetration of separation regions impelled by the terminal shock is either increased or decreased.
Effect of cavity on shock oscillation in transonic flow over RAE2822 supercritical airfoil
Rahman, M. Rizwanur; Labib, Md. Itmam; Hasan, A. B. M. Toufique; Ali, M.; Mitsutake, Y.; Setoguchi, T.
2016-07-01
Transonic flow past a supercritical airfoil is strongly influenced by the interaction of shock wave with boundary layer. This interaction induces unsteady self-sustaining shock wave oscillation, flow instability, drag rise and buffet onset which limit the flight envelop. In the present study, a computational analysis has been carried out to investigate the flow past a supercritical RAE2822 airfoil in transonic speeds. To control the shock wave oscillation, a cavity is introduced on the airfoil surface where shock wave oscillates. Different geometric configurations have been investigated for finding optimum cavity geometry and dimension. Unsteady Reynolds averaged Navier-Stokes equations (RANS) are computed at Mach 0.729 with an angle of attack of 5°. Computed results are well validated with the available experimental data in case of baseline airfoil. However, in case of airfoil with control cavity; it has been observed that the introduction of cavity completely suppresses the unsteady shock wave oscillation. Further, significant drag reduction and successive improvement of aerodynamic performance have been observed in airfoil with shock control cavity.
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Delhaye, D.; Paniagua, G. [von Karman Institute for Fluid Dynamics, Turbomachinery and Propulsion Department, Rhode-Saint-Genese (Belgium); Fernandez Oro, J.M. [Universidad de Oviedo, Area de Mecanica de Fluidos, Gijon (Spain); Denos, R. [European Commission, Directorate General for Research, Brussels (Belgium)
2011-01-15
The paper presents the development and application of a three-sensor wedge probe to measure unsteady aerodynamics in a transonic turbine. CFD has been used to perform a detailed uncertainty analysis related to probe-induced perturbations, in particular the separation zones appearing on the wedge apex. The effects of the Reynolds and Mach numbers are studied using both experimental data together with CFD simulations. The angular range of the probe and linearity of the calibration maps are enhanced with a novel zonal calibration technique, used for the first time in compressible flows. The data reduction methodology is explained and demonstrated with measurements performed in a single-stage high-pressure turbine mounted in the compression tube facility of the von Karman Institute. The turbine was operated at subsonic and transonic pressure ratios (2.4 and 5.1) for a Reynolds number of 10{sup 6}, representative of modern engine conditions. Complete maps of the unsteady flow angle and rotor outlet Mach number are documented. These data allow the study of secondary flows and rotor trailing edge shocks. (orig.)
Delhaye, D.; Paniagua, G.; Fernández Oro, J. M.; Dénos, R.
2011-01-01
The paper presents the development and application of a three-sensor wedge probe to measure unsteady aerodynamics in a transonic turbine. CFD has been used to perform a detailed uncertainty analysis related to probe-induced perturbations, in particular the separation zones appearing on the wedge apex. The effects of the Reynolds and Mach numbers are studied using both experimental data together with CFD simulations. The angular range of the probe and linearity of the calibration maps are enhanced with a novel zonal calibration technique, used for the first time in compressible flows. The data reduction methodology is explained and demonstrated with measurements performed in a single-stage high-pressure turbine mounted in the compression tube facility of the von Karman Institute. The turbine was operated at subsonic and transonic pressure ratios (2.4 and 5.1) for a Reynolds number of 106, representative of modern engine conditions. Complete maps of the unsteady flow angle and rotor outlet Mach number are documented. These data allow the study of secondary flows and rotor trailing edge shocks.
Seidel, B. S.; Matwey, M. D.; Adamczyk, J. J.
1980-01-01
In the present paper, a semi-actuator-disk theory is reviewed that was developed previously for the distorted inflow to a single-stage axial-flow compressor. Flow distortion occurs far upstream; it may be a distortion in stagnation temperature, stagnation pressure, or both. Losses, quasi-steady deviation angles, and reference incidence correlations are included in the analysis, and both subsonic and transonic relative Mach numbers are considered. The theory is compared with measurements made in a transonic fan stage, and a parameter study is carried out to determine the influence of solidity on the attenuation of distortions in stagnation pressure and stagnation temperature.
Pressure drop and thrust predictions for transonic micronozzle flows
Gomez, J.; Groll, R.
2016-02-01
In this paper, the expansion of xenon, argon, krypton, and neon gases through a Laval nozzle is studied experimentally and numerically. The pressurized gases are accelerated through the nozzle into a vacuum chamber in an attempt to simulate the operating conditions of a cold-gas thruster for attitude control of a micro-satellite. The gases are evaluated at several mass flow rates ranging between 0.178 mg/s and 3.568 mg/s. The Re numbers are low (8-256) and the estimated values of Kn number lie between 0.33 and 0.02 (transition and slip-flow regime). Direct Simulation Monte Carlo (DSMC) and continuum-based simulations with a no-slip boundary condition are performed. The DSMC and the experimental results show good agreement in the range Kn > 0.1, while the Navier-Stokes results describe the experimental data more accurately for Kn gas-independent accommodation coefficients. The thrust delivered by the cold-gas thruster and the specific impulse is determined based on the numerical results. Furthermore, an increase of the thickness of the viscous boundary layer through the diffuser of the micronozzle is observed. This results in a shock-less decrease of the Mach number and the flow velocity, which penalizes thrust efficiency. The negative effect of the viscous boundary layer on thrust efficiency can be lowered through higher values of Re and a reduction of the diffuser length.
Allouche, M H; Millet, S; Botton, V; Henry, D; Ben Hadid, H; Rousset, F
2015-12-01
Squire's theorem, which states that the two-dimensional instabilities are more dangerous than the three-dimensional instabilities, is revisited here for a flow down an incline, making use of numerical stability analysis and Squire relationships when available. For flows down inclined planes, one of these Squire relationships involves the slopes of the inclines. This means that the Reynolds number associated with a two-dimensional wave can be shown to be smaller than that for an oblique wave, but this oblique wave being obtained for a larger slope. Physically speaking, this prevents the possibility to directly compare the thresholds at a given slope. The goal of the paper is then to reach a conclusion about the predominance or not of two-dimensional instabilities at a given slope, which is of practical interest for industrial or environmental applications. For a Newtonian fluid, it is shown that, for a given slope, oblique wave instabilities are never the dominant instabilities. Both the Squire relationships and the particular variations of the two-dimensional wave critical curve with regard to the inclination angle are involved in the proof of this result. For a generalized Newtonian fluid, a similar result can only be obtained for a reduced stability problem where some term connected to the perturbation of viscosity is neglected. For the general stability problem, however, no Squire relationships can be derived and the numerical stability results show that the thresholds for oblique waves can be smaller than the thresholds for two-dimensional waves at a given slope, particularly for large obliquity angles and strong shear-thinning behaviors. The conclusion is then completely different in that case: the dominant instability for a generalized Newtonian fluid flowing down an inclined plane with a given slope can be three dimensional.
Ye, Yu; Chiogna, Gabriele; Cirpka, Olaf A.; Grathwohl, Peter; Rolle, Massimo
2015-07-01
In porous media, lateral mass exchange exerts a significant influence on the dilution of solute plumes in quasi steady state. This process is one of the main mechanisms controlling transport of continuously emitted conservative tracers in groundwater and is fundamental for the understanding of many degradation processes. We investigate the effects of high-permeability inclusions on transverse mixing in three-dimensional versus two-dimensional systems by experimental, theoretical, and numerical analyses. Our results show that mixing enhancement strongly depends on the system dimensionality and on the parameterization used to model transverse dispersion. In particular, no enhancement of transverse mixing would occur in three-dimensional media if the local transverse dispersion coefficient was uniform and flow focusing in both transverse directions was identical, which is fundamentally different from the two-dimensional case. However, the velocity and grain size dependence of the transverse dispersion coefficient and the correlation between hydraulic conductivity and grain size lead to prevailing mixing enhancement within the inclusions, regardless of dimensionality. We perform steady state bench-scale experiments with multiple tracers in three-dimensional and quasi two-dimensional flow-through systems at two different velocities (1 and 5 m/d). We quantify transverse mixing by the flux-related dilution index and compare the experimental results with model simulations. The experiments confirm that, although dilution is larger in three-dimensional systems, the enhancement of transverse mixing due to flow focusing is less effective than in two-dimensional systems. The spatial arrangement of the high-permeability inclusions significantly affects the degree of mixing enhancement. We also observe more pronounced compound-specific effects in the dilution of solute plumes in three-dimensional porous media than in two-dimensional ones.
Directory of Open Access Journals (Sweden)
Edris Yousefi Rad
2017-08-01
Full Text Available In the present research, considering the importance of desirable steam turbine design, improvement of numerical modeling of steam two-phase flows in convergent and divergent channels and the blades of transonic steam turbines has been targeted. The first novelty of this research is the innovative use of combined Convective Upstream Pressure Splitting (CUSP and scalar methods to update the flow properties at each calculation point. In other words, each property (density, temperature, pressure and velocity at each calculation point can be computed from either the CUSP or scalar method, depending on the least deviation criterion. For this reason this innovative method is named “hybrid method”. The next novelty of this research is the use of an inverse method alongside the proposed hybrid method to find the amount of the important parameter z in the CUSP method, which is herein referred to as “CUSP’s convergence parameter”. Using a relatively simple computational grid, firstly, five cases with similar conditions to those of the main cases under study in this research with available experimental data were used to obtain the value of z by the Levenberg-Marquardt inverse method. With this innovation, first, an optimum value of z = 2.667 was obtained using the inverse method and then directly used for the main cases considered in the research. Given that the aim is to investigate the two-dimensional, steady state, inviscid and adiabatic modeling of steam nucleating flows in three different nozzle and turbine blade geometries, flow simulation was performed using a relatively simple mesh and the innovative proposed hybrid method (scalar + CUSP, with the desired value of z = 2.667 . A comparison between the results of the hybrid modeling of the three main cases with experimental data showed a very good agreement, even within shock zones, including the condensation shock region, revealing the efficiency of this numerical modeling method innovation
Study of Flow-Field Interactions in a Transonic Compressor using DPIV
Estevadeordal, Jordi; Gogineni, Sivaram; Goss, Larry; Copenhaver, William; Gorrell, Steve; Koch, Peter
1999-11-01
The unsteadiness and spatial structures in a high-through-flow, axial-flow transonic compressor are captured using Digital Particle Image Velocimetry (DPIV). The measurements are made using both single-color and two-color DPIV systems. A special optical probe was designed for laser delivery through the inlet guide vanes (IGVs). Viewing windows on the compressor housing allow optical access. Submicron sized smoke particles are used for seeding the compressor flow and the DPIV system is synchronized with the blade passage. The interactions between the coherent structures from the IGVs with the rotor blades and the bow shock are studied for various configurations. The coherent structures interactions with the potential field of the leading edge of the blades and the shock as a function of the blade position are analyzed for a full blade passage through the wake. Comparisons are made with unsteady numerical simulations.
Phonon spectrum and correlations in a transonic flow of an atomic Bose gas
Michel, Florent
2016-01-01
Motivated by a recent experiment of J.~Steinhauer, we reconsider the properties of the phonons spontaneously emitted in stationary transonic flows. The latter are described by "waterfall" configurations which form a one-parameter family of stable flows. For parameters close to their experimental values, in spite of high gradients near the sonic horizon, the spectrum is accurately planckian in the relevant frequency domain, where the temperature differs from the relativistic prediction by less than $10 \\%$. We then study the density correlations across the sonic horizon and the non-separable character of the final state. We show that the relativistic expressions provide accurate approximations when the initial temperature is not too high. We also show that the phases of the scattering coefficients introduce a finite shift of the location of the correlations which was so far overlooked. This shift is due to the asymmetry of the near-horizon flow, and persists in the dispersion-less regime.
A finite element formulation of Euler equations for the solution of steady transonic flows
Ecer, A.; Akay, H. U.
1982-01-01
The main objective of the considered investigation is related to the development of a relaxation scheme for the analysis of inviscid, rotational, transonic flow problems. To formulate the equations of motion for inviscid flows in a fixed coordinate system, an Eulerian type variational principle is required. The derivation of an Eulerian variational principle which is employed in the finite element formulation is discussed. The presented numerical method describes the mathematical formulation and the application of a numerical process for the direct solution of steady Euler equations. The development of the procedure as an extension of existing potential flow formulations provides the applicability of previous procedures, e.g., proper application of the artificial viscosity for supersonic elements, and the accurate modeling of the shock.
Bogar, T. J.; Sajben, M.
1986-10-01
The propagation of compression pulses in a supercritically operated transonic diffuser was investigated by use of pressure measurements along the top wall of the model. The pulses were generated at the downstream end of the diffuser by the abrupt injection of a secondary flow of air. Two types of waves were observed: (1) an upstream-traveling acoustic wave and (2) a downstream-traveling convective wave which resulted from the impingement of the acoustic wave on the shock. Wave speeds were determined for a range of diffuser pressure ratios including separated, strong-shock flows and fully attached, weak-shock flows. Streamwise distributions of initial and reflected pulse amplitudes were determined for one weak and one strong-shock case over a 3-to-1 range of initial pulse strengths.
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Rio Melvin Aro.T
2015-05-01
Full Text Available Flutter is an unstable oscillation which can lead to destruction. Flutter can occur on fixed surfaces, such as blades, wing or the stabilizer. By self-excited aeroelastic instability, flutter can lead to mechanical or structural failure of aircraft engine blades. The modern engines have been designed with increased pressure ratio and reduced weight in order to improve aerodynamic efficiency, resulting in severe aeroelastic problems. Particularly flutter in axial compressors with transonic flow can be characterized by a number of aerodynamic nonlinear effects such as shock boundary layer interaction, rotating stall, and tip vortex instability. Rotating blades operating under high centrifugal forces may also encounter structural nonlinearities due to friction damping and large deformations. In the future work a standard axial flow compressor blade will be taken for analysis, both Subsonic and Transonic range are taken for analysis. Fluid and Structure are two different domains which will be coupled by full system coupling technique to predict the fluttering effect on the compressor blade. ANSYS is a commercial simulation tool, which will be deployed in this work to perform FSI (Fluid Structure Interaction and FSI coupled Modal to predict the flutter in the compressor blades
High angle of attack aerodynamics subsonic, transonic, and supersonic flows
Rom, Josef
1992-01-01
The aerodynamics of aircraft at high angles of attack is a subject which is being pursued diligently, because the modern agile fighter aircraft and many of the current generation of missiles must perform well at very high incidence, near and beyond stall. However, a comprehensive presentation of the methods and results applicable to the studies of the complex aerodynamics at high angle of attack has not been covered in monographs or textbooks. This book is not the usual textbook in that it goes beyond just presenting the basic theoretical and experimental know-how, since it contains reference material to practical calculation methods and technical and experimental results which can be useful to the practicing aerospace engineers and scientists. It can certainly be used as a text and reference book for graduate courses on subjects related to high angles of attack aerodynamics and for topics related to three-dimensional separation in viscous flow courses. In addition, the book is addressed to the aerodynamicist...
Numerical Investigations of the Benchmark Supercritical Wing in Transonic Flow
Chwalowski, Pawel; Heeg, Jennifer; Biedron, Robert T.
2017-01-01
This paper builds on the computational aeroelastic results published previously and generated in support of the second Aeroelastic Prediction Workshop for the NASA Benchmark Supercritical Wing (BSCW) configuration. The computational results are obtained using FUN3D, an unstructured grid Reynolds-Averaged Navier-Stokes solver developed at the NASA Langley Research Center. The analysis results show the effects of the temporal and spatial resolution, the coupling scheme between the flow and the structural solvers, and the initial excitation conditions on the numerical flutter onset. Depending on the free stream condition and the angle of attack, the above parameters do affect the flutter onset. Two conditions are analyzed: Mach 0.74 with angle of attack 0 and Mach 0.85 with angle of attack 5. The results are presented in the form of the damping values computed from the wing pitch angle response as a function of the dynamic pressure or in the form of dynamic pressure as a function of the Mach number.
Vo, Tony; Pothérat, Alban; Sheard, Gregory J.
2017-03-01
This study considers the linear stability of Poiseuille-Rayleigh-Bénard flows subjected to a transverse magnetic field, to understand the instabilities that arise from the complex interaction between the effects of shear, thermal stratification, and magnetic damping. This fundamental study is motivated in part by the desire to enhance heat transfer in the blanket ducts of nuclear fusion reactors. In pure magnetohydrodynamic flows, the imposed transverse magnetic field causes the flow to become quasi-two-dimensional and exhibit disturbances that are localized to the horizontal walls. However, the vertical temperature stratification in Rayleigh-Bénard flows feature convection cells that occupy the interior region, and therefore the addition of this aspect provides an interesting point for investigation. The linearized governing equations are described by the quasi-two-dimensional model proposed by Sommeria and Moreau [J. Fluid Mech. 118, 507 (1982), 10.1017/S0022112082001177], which incorporates a Hartmann friction term, and the base flows are considered fully developed and one-dimensional. The neutral stability curves for critical Reynolds and Rayleigh numbers, Rec and Rac, respectively, as functions of Hartmann friction parameter H have been obtained over 10-2≤H ≤104 . Asymptotic trends are observed as H →∞ following Rec∝H1 /2 and Rac∝H . The linear stability analysis reveals multiple instabilities which alter the flow both within the Shercliff boundary layers and the interior flow, with structures consistent with features from plane Poiseuille and Rayleigh-Bénard flows.
Subramanian, S. V.; Bozzola, R.
1987-01-01
Numerical solutions of the unsteady Euler equations are obtained using the classical fourth order Runge Kutta time marching scheme. This method is fully explicit and is applied to the governing equations in the finite volume, conservation law form. In order to determine the efficiency of this scheme for solving turbomachinery flows, steady blade-to-blade solutions are obtained for compressor and turbine cascades under subsonic and transonic flow conditions. Computed results are compared with other numerical methods and wind tunnel measurements. The study also focuses on other important numerical aspects influencing the performance of the algorithm and the solution accuracy such as grid types, boundary conditions and artificial viscosity. For this purpose, H, O, and C type computational grids as well as characteristic and extrapolation type boundary conditions are included in solution procedures.
Losses estimation in transonic wet steam flow through linear blade cascade
Dykas, Sławomir; Majkut, Mirosław; Strozik, Michał; Smołka, Krystian
2015-04-01
Experimental investigations of non-equilibrium spontaneous condensation in transonic steam flow were carried out in linear blade cascade. The linear cascade consists of the stator blades of the last stage of low pressure steam turbine. The applied experimental test section is a part of a small scale steam power plant located at Silesian University of Technology in Gliwice. The steam parameters at the test section inlet correspond to the real conditions in low pressure part of 200MWe steam turbine. The losses in the cascade were estimated using measured static pressure and temperature behind the cascade and the total parameters at inlet. The static pressure measurements on the blade surface as well as the Schlieren pictures were used to assess the flow field in linear cascade of steam turbine stator blades.
Subramanian, S. V.; Bozzola, R.
1985-01-01
Numerical solutions of the unsteady Euler equations are obtained using the classical fourth order Runge Kutta time marching scheme. This method is fully explicit and is applied to the governing equations in the finite volume, conservation law form. In order to determine the efficiency of this scheme for solving turbomachinery flows, steady blade-to-blade solutions are obtained for compressor and turbine cascades under subsonic and transonic flow conditions. Computed results are compared with other numerical methods and wind tunnel measurements. The present study also focuses on other important numerical aspects influencing the performance of the algorithm and the solution accuracy such as grid types, boundary conditions, and artificial viscosity. For this purpose, H, O, and C type computational grids as well as characteristic and extrapolation type boundary conditions are included in the solution procedure.
Preliminary results of flow fluctuation measurements in the cryogenic transonic wind tunnel
Zinovyev, V. N.; Lebiga, V. A.; Pak, A. Yu.; Quest, J.
2012-01-01
The detailed information about flow fluctuations structure inside the test section of Pilot of European Transonic Windtunnel (PETW) obtained by means of hot-wire anemometer and fluctuation diagram (FD) method within broad and narrow frequency band is presented. Fluctuation diagrams were derived from an array of hot wire output data measured at different overheating ratio of the probe (not less than 8) at freestream Mach numbers M = 0.2, 0.4, 0.6, 0.7, and 0.8, total temperature T0 = 118 . . . 294.7 K and unit Reynolds numbers Re1 = (5.54 . . . 108.6) · 106 1/m, respectively. Time series of these output signal data were used to obtain information of statistical and correlation features, mode, and spectral composition of flow fluctuations.
The effect of viscosity on steady transonic flow with a nodal solution topology
Owocki, Stanley P.; Zank, Gary P.
1991-01-01
The effect of viscosity on a steady, transonic flow for which the inviscid limit has a nodal solution topology near the critical point is investigated. For the accelerating case, viscous solutions tend to repel each other, so that a very delicate choice of initial conditions is required to prevent them from diverging. Only the two critical solutions extend to arbitrarily large distances into both the subsonic and supersonic flows. For the decelerating case, the solutions tend to attract, and so an entire two-parameter family of solutions now extends over large distances. The general effect of viscosity on the solution degeneracy of a nodal topology is thus to reduce or limit it for the accelerating case and to enhance it for the decelerating case. The astrophysical implications of these findings are addressed.
van der Poel, Erwin P; Ostilla-Mónico, Rodolfo; Verzicco, Roberto; Lohse, Detlef
2014-07-01
The effect of various velocity boundary condition is studied in two-dimensional Rayleigh-Bénard convection. Combinations of no-slip, stress-free, and periodic boundary conditions are used on both the sidewalls and the horizontal plates. For the studied Rayleigh numbers Ra between 10(8) and 10(11) the heat transport is lower for Γ=0.33 than for Γ=1 in case of no-slip sidewalls. This is, surprisingly, the opposite for stress-free sidewalls, where the heat transport increases for a lower aspect ratio. In wider cells the aspect-ratio dependence is observed to disappear for Ra ≥ 10(10). Two distinct flow types with very different dynamics can be seen, mostly dependent on the plate velocity boundary condition, namely roll-like flow and zonal flow, which have a substantial effect on the dynamics and heat transport in the system. The predominantly horizontal zonal flow suppresses heat flux and is observed for stress-free and asymmetric plates. Low aspect-ratio periodic sidewall simulations with a no-slip boundary condition on the plates also exhibit zonal flow. In all the other cases, the flow is roll like. In two-dimensional Rayleigh-Bénard convection, the velocity boundary conditions thus have large implications on both roll-like and zonal flow that have to be taken into consideration before the boundary conditions are imposed.
Numerical Study of Transonic Axial Flow Rotating Cascade Aerodynamics – Part 1: 2D Case
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Irina Carmen ANDREI
2014-06-01
Full Text Available The purpose of this paper is to present a 2D study regarding the numerical simulation of flow within a transonic highly-loaded rotating cascade from an axial compressor. In order to describe an intricate flow pattern of a complex geometry and given specific conditions of cascade’s loading and operation, an appropriate accurate flow model is a must. For such purpose, the Navier-Stokes equations system was used as flow model; from the computational point of view, the mathematical support is completed by a turbulence model. A numerical comparison has been performed for different turbulence models (e.g. KE, KO, Reynolds Stress and Spallart-Allmaras models. The convergence history was monitored in order to focus on the numerical accuracy. The force vector has been reported in order to express the aerodynamics of flow within the rotating cascade at the running regime, in terms of Lift and Drag. The numerical results, expressed by plots of the most relevant flow parameters, have been compared. It comes out that the selecting of complex flow models and appropriate turbulence models, in conjunction with CFD techniques, allows to obtain the best computational accuracy of the numerical results. This paper aims to carry on a 2D study and a prospective 3D will be intended for the same architecture.
Test facility and the available inlet flow condition to transonic radial diffusers
Energy Technology Data Exchange (ETDEWEB)
Hayami, Hiroshi; Senoo, Yasutoshi; Nakashima, Koji; Kawaguchi, Nobumasa
1987-12-28
In order to stabilize the characteristics combined with diffuser(DF) and expand the flow rate range, a transonic centrifugal impeller(B rotor) with backward blade angle of 40deg was made trially. Single characteristic was tested for five rotating speed equal to or less than 19,000 rpm with freon R12. The flow rate range from choke to inducer(ID) stalling for B rotor is 17% of choke flow rate which is comaratively wider than 11% of conventional impeller(R rotor) with forward blade angle. When the flow field of impeller exit, that is, DF inlet is considered, the maximum value of inlet flow angle in a constant rotating speed corresponds to choke condition or maximum flow rate and minimum value corresponds to operating condition of critical flow rate resulting ID spalling speed. Inflow Mach number to DF changes mainly for the impeller rotating speed. It is possible to pursue the experimental work on diffusers in the range of 21deg(max) to 11.6deg(min) inflow angle and up to 1.31 Mach number using the present facility. (9 figs, 4 refs)
High Reynolds number test of a NACA 651-213, a equals 0.5 airfoil at transonic speeds
Burdges, K. P.; Blackwell, J. A., Jr.; Pounds, G. A.
1975-01-01
Wind-Tunnel tests were conducted in the Lockheed-Georgia Company's compressible flow facility to determine the transonic two-dimensional aerodynamic characteristics of a NACA 65 sub 1-213 a = 0.50 airfoil. The results are correlated with data obtained in the NASA-Langley 8-foot transonic pressure tunnel and the NAE high Reynolds number 15x60-inch two-dimensional test facility. The tests were conducted over a Mach number range from 0.60 to 0.80 and an angle of attack range from -1 deg to 8 deg. Reynolds numbers, based on the airfoil chord, were varied.
Energy Technology Data Exchange (ETDEWEB)
Nicklas, M.
2000-11-01
Aero and thermodynamic measurements at the endwall of a turbine nozzle guide vane were carried out. These investigations are the first where the complete blade passage at the endwall in a transonic flow field is analysed for heat transfer and adiabatic film-cooling effectiveness. The aerodynamic measurements identify an intensive interaction between the coolant air and the secondary flow field. Similarly strong variations in heat transfer and film-cooling effectiveness were found. Analysis of the heat transfer measurements indicates that the heat transfer represents an indispensable tool for the evaluation of platform film-cooling design. On the basis of infrared temperature measurements, a procedure for accurate analysis of heat transfer and film-cooling effectiveness in a complex transonic flow field was developed. This measurement technique combines high accuracy with flexibility of application. These investigations have led to design improvements for film-cooling systems at the platform. (orig.) [German] Aero- und thermodynamische Messungen an einer Plattform eines Turbinenleitrads werden beschrieben. Erstmals wird in einem transsonischen Stroemungsfeld die komplette Seitenwand bezueglich des Waermeuebergangs und der adiabaten Filmkuehleffektivitaet untersucht. Die aerodynamischen Messungen zeigen eine intensive Wechselwirkung der Kuehlluft mit dem Sekundaerstroemungsfeld. Daraus resultierend treten starke Aenderungen des Waermeuebergangs und der Filmkuehleffektivitaet auf. Die Resultate der Waermeuebergangsmessungen zeigen, dass der Waermeuebergang eine wichtige Groesse fuer die Bewertung eines Filmkuehldesigns an einer Plattform darstellt. Ein Messverfahren auf der Grundlage von Infrarot-Temperaturmessungen fuer eine genaue Analyse des Waermeuebergangs und der Filmkuehleffektivitaet in den komplexen Verhaeltnissen einer transsonischen Stroemung wurde entwickelt. Mit der verwendeten Messtechnik wird eine hohe Genauigkeit bei der Ermittlung der quantitativen
Chakravarthy, S.
1978-01-01
An efficient, direct finite difference method is presented for computing sound propagation in non-stepped two-dimensional and axisymmetric ducts of arbitrarily varying cross section without mean flow. The method is not restricted by axial variation of acoustic impedance of the duct wall linings. The non-uniform two-dimensional or axisymmetric duct is conformally mapped numerically into a rectangular or cylindrical computational domain using a new procedure based on a method of fast direct solution of the Cauchy-Riemann equations. The resulting Helmholtz equation in the computational domain is separable. The solution to the governing equation and boundary conditions is expressed as a linear combination of fundamental solutions. The fundamental solutions are computed only once for each duct shape by means of the fast direct cyclic reduction method for the discrete solution of separable elliptic equations. Numerical results for several examples are presented to show the applicability and efficiency of the method.
Large Eddy Simulation of Transonic Flow Field in NASA Rotor 37
Hah, Chunill
2009-01-01
The current paper reports on numerical investigations on the flow characteristics in a transonic axial compressor, NASA Rotor 37. The flow field was used previously as a CFD blind test case conducted by American Society of Mechanical Engineers in 1994. Since the CFD blind-test exercise, many numerical studies on the flow field in the NASA Rotor 37 have been reported. Although steady improvements have been reported in both numerical procedure and turbulence closure, it is believed that all the important aspects of the flow field have not been fully explained with numerical studies based on the Reynolds Averaged Navier-Stokes (RANS) solution. Experimental data show large dip in total pressure distribution near the hub at downstream of the rotor at 100% rotor speed. Most original numerical solutions from the blind test exercise did not predict this total pressure deficit correctly. This total pressure deficit at the rotor exit was attributed to a hub corner flow separation by the author. Several subsequent numerical studies with different turbulence closure model also calculated this dip in total pressure rise. Also, several studies attributed this total pressure deficit to a small leakage flow coming from the hub in the test article. As the experimental study cannot be repeated, either explanation cannot be validated. The primary purpose of the current investigation is to investigate the transonic flow field with both RANS and a Large Eddy Simulation (LES). The RANS approach gives similar results presented at the original blind test exercise. Although the RANS calculates higher overall total pressure rise, the total pressure deficit near the hub is calculated correctly. The numerical solution shows that the total pressure deficit is due to a hub corner flow separation. The calculated pressure rise from the LES agrees better with the measured total pressure rise especially near the casing area where the passage shock interacts with the tip clearance vortex and flow
Cunningham, A. M., Jr.
1976-01-01
The feasibility of calculating steady mean flow solutions for nonlinear transonic flow over finite wings with a linear theory aerodynamic computer program is studied. The methodology is based on independent solutions for upper and lower surface pressures that are coupled through the external flow fields. Two approaches for coupling the solutions are investigated which include the diaphragm and the edge singularity method. The final method is a combination of both where a line source along the wing leading edge is used to account for blunt nose airfoil effects; and the upper and lower surface flow fields are coupled through a diaphragm in the plane of the wing. An iterative solution is used to arrive at the nonuniform flow solution for both nonlifting and lifting cases. Final results for a swept tapered wing in subcritical flow show that the method converges in three iterations and gives excellent agreement with experiment at alpha = 0 deg and 2 deg. Recommendations are made for development of a procedure for routine application.
Effect of the Unsteadiness on the Diffuser Flow in a Transonic Centrifugal Compressor Stage
Directory of Open Access Journals (Sweden)
N. Bulot
2009-01-01
Full Text Available The study is focused on the analysis of the flow structure within the vaned diffuser of a transonic high-pressure centrifugal compressor stage. The analyzed time-dependent flow field comes from unsteady computations of the stage using a 3D Navier-Stokes code with a phase-lagged technique, at an operating point close to the design point. A good comparison with available experimental data allowed the use of CFD for investigating the details of the flow in order to assess the effect of the unsteadiness in the diffuser flow development. Applying various data processing techniques, it is shown that the unsteadiness is due to the jet and wake flow structure emerging from the radial impeller and to the pressure waves brought about by the interaction between the vane bow shock wave and the impeller blade. The interaction between the pressure waves and the vane pressure side boundary layer leads to a pulsating behavior of separated bubbles within the diffuser. The pressure waves are similar in shape and strength whatever the blade height. The observed change in the flow field from hub to tip is due to migration of the low momentum fluid contained in the wake toward the pressure side/hub corner.
Evaluation of turbulence models in the PARC code for transonic diffuser flows
Georgiadis, N. J.; Drummond, J. E.; Leonard, B. P.
1994-01-01
Flows through a transonic diffuser were investigated with the PARC code using five turbulence models to determine the effects of turbulence model selection on flow prediction. Three of the turbulence models were algebraic models: Thomas (the standard algebraic turbulence model in PARC), Baldwin-Lomax, and Modified Mixing Length-Thomas (MMLT). The other two models were the low Reynolds number k-epsilon models of Chien and Speziale. Three diffuser flows, referred to as the no-shock, weak-shock, and strong-shock cases, were calculated with each model to conduct the evaluation. Pressure distributions, velocity profiles, locations of shocks, and maximum Mach numbers in the duct were the flow quantities compared. Overall, the Chien k-epsilon model was the most accurate of the five models when considering results obtained for all three cases. However, the MMLT model provided solutions as accurate as the Chien model for the no-shock and the weak-shock cases, at a substantially lower computational cost (measured in CPU time required to obtain converged solutions). The strong shock flow, which included a region of shock-induced flow separation, was only predicted well by the two k-epsilon models.
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.
Numerical Investigation of the Unsteady Flow in a Transonic Compressor with Curved Rotors
Institute of Scientific and Technical Information of China (English)
Mao Mingming; Song Yanping; Wang Zhongqi
2008-01-01
The unsteady 3D flow fields in a single-stage transonic compressor under designed conditions are simulated numerically to inves- tigate the effects of the curved rotors on the stage performance and the aerodynamic interaction between the blade rows. The results show that, compared to the compressor with un-curved rotors, the compressor under scrutiny acquires remarkable increases in efficiency with significantly reduced amplitudes of the time-dependent fluctuation. The amplitude of the pressure fluctuation around the stator leading edge decreases at both endwalls, but increases at the mid-span in the curved rotors. The pressure fluctuation near the stator lead- ing edge, therefore, becomes more uniform in the radial direction of this compressor. Except for the leading edge area, the pressure fluc- tuation amplitude declines remarkably in the tip region of stator surface downstream of the curved rotor, but hardly changes in the mid- dle and at the hub.
Shu, Jian-Jun
2014-01-01
A cold, thin film of liquid impinging on an isothermal hot, horizontal surface has been investigated. An approximate solution for the velocity and temperature distributions in the flow along the horizontal surface is developed, which exploits the hydrodynamic similarity solution for thin film flow. The approximate solution may provide a valuable basis for assessing flow and heat transfer in more complex settings.
Investigation of transonic flow over segmented slotted wind tunnel wall with mass transfer
Bhat, M. K.; Vakili, A. D.; Wu, J. M.
1990-01-01
The flowfield on a segmented multi-slotted wind tunnel wall was studied at transonic speeds by measurements in and near the wall layer using five port cone probes. The slotted wall flowfield was observed to be three-dimensional in nature for a relatively significant distance above the slot. The boundary layer characteristics measured on the single slotted wall were found to be very sensitive to the applied suction through the slot. The perturbation in the velocity components generated due to the flow through the slot decay rapidly in the transverse direction. A vortex-like flow existed on the single slotted wall for natural ventilation but diminished with increased suction flow rate. For flow on a segmented multi-slotted wall, the normal velocity component changes were found to be maximum for measurement points located between the segmented slots atop the active chamber. The lateral influence due to applied suction and blowing, through a compartment, exceeded only slightly that in the downstream direction. Limited upstream influence was observed. Influence coefficients were determined from the data in the least-square sense for blowing and suction applied through one and two compartments. This was found to be an adequate determination of the influence coefficients for the range of mass flows considered.
Effects of the composition on transonic properties of accretion flows around black holes
Chattopadhyay, Indranil
2013-01-01
We study the properties of a steady, multi-species, low angular momentum accretion flow around a Schwarzschild black hole. Each species is described by a relativistic equation of state. We find that the transonic properties depend strongly on the composition of the flow. We find that an electron-positron pair plasma is the least relativistic one. This flow produces only one sonic point very close to the event horizon and does not show multiple critical points for any angular momentum or energy. When the baryons are present, the number of critical points depend on the specific energy content. Since the number of critical points decide whether the flow will have non-linearities or shock waves, our results implies that whether or not standing shocks forms will depend on the flow composition. Thus, for instance, a pure electron-positron pair plasma will never undergo a shock transition, while mixing it with some baryons (common in outflows and jets, for example) as in a completely ionized gas, will have shocks. W...
Al-Maaitah, Ayman A.; Nayfeh, Ali H.; Ragab, Saad A.
1989-01-01
The effect of suction on the stability of compressible flows over backward-facing steps is investigated. Mach numbers up to 0.8 are considered. The results show that continuous suction stabilizes the flow outside the separation bubble, but it destabilizes the flow inside it. Nevertheless, the overall N factor decreases as the suction level increases due to the considerable reduction of the separation bubble. For the same suction flow rate, properly distributed suction strips stabilize the flow more than continuous suction. The size of the separation bubble, and hence its effect on the instability can be considerably reduced by placing strips with high suction velocities in the separation region.
Coupled One and Two Dimensional Model for River Network Flow and Sediment Transport%一二维耦合河网水沙模型研究
Institute of Scientific and Technical Information of China (English)
吕文丽; 张旭
2011-01-01
Based on previous research, a new one and two-dimensional coupled model of river water and sediment was proposed.With reference to the three-level solution for one-dimensional river network water mode, the two-dimensional river section will be generalized to river section within the river network.One and two dimensional coupled river network sediment model will be established with the balance of flow amount and sediment transport.The model sets up the chasing relationship between variables of water level and sediment content at the end and first section to further establish matrix equations of the whole one and two-dimensional river network node water level and sediment content.Though the verification and calculation for generalized river network from Datong to Zhenjiang in the lower reaches of the Yangtze River, it is found that the model is of great practical value.%借鉴河网水流的三级解法,将二维河段概化为河网内部河段,通过河网节点流量和输沙量的平衡,建立一二维耦合河网水沙模型.模型采用全隐式方法建立二维河段以首末断面的水位和含沙量为中间变量的矩阵追赶关系,进而建立整个一二维河网的节点水位及含沙量的矩阵方程组.对方程组的求解,可实现一二维水沙模型的耦合求解.通过对长江下游大通至镇江概化河网的验证计算,表明模型具有很好的实用价值.
Quantitative Relative Comparison of CFD Simulation Uncertainties for a Transonic Diffuser Problem
Hosder, Serhat; Grossman, Bernard; Haftka, Raphael T.; Mason, William H.; Watson, Layne T.
2004-01-01
Different sources of uncertainty in CFD simulations are illustrated by a detailed study of two-dimensional, turbulent, transonic flow in a converging-diverging channel. Runs were performed with the commercial CFD code GASP using different turbulence models, grid levels, and flux-limiters to see the effect of each on the CFD simulation uncertainties. Two flow conditions were studied by changing the exit pressure ratio: the first is a complex case with a strong shock and a separated flow region...
Two-dimensional simulation of Poiseuille-Rayleigh-Bénard flows in binary fluids with Soret effect
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Poiseuille-Rayleigh-Bénard flows in binary fluids with Soret effect are directly simulated by a mixed finite element method.A temperature perturbation is used as an initial disturbed source for the basic parallel flows.The whole spatio-temporal evolution of the binary fluid flows is exhibited:initially only the disturbed mode with the wavenumber k=π is amplified while others are damped.and continuously the amplified mode grows further and the nonlinear effect becomes important;after a nonlinear evolution transition the flow system evolves finally into a periodic right traveling wave.
Triple-deck analysis of transonic high Reynolds number flow through slender channels.
Kluwick, A; Kornfeld, M
2014-07-28
In this work, laminar transonic weakly three-dimensional flows at high Reynolds numbers in slender channels, as found in microsupersonic nozzles and turbomachines of micro-electro-mechanical systems, are considered. The channel height is taken so small that the viscous wall layers forming at the channel walls start to interact strongly rather than weakly with the inviscid core flow and, therefore, the classical boundary layer approach fails. The resulting viscous-inviscid interaction problem is formulated using matched asymptotic expansions and found to be governed by a triple-deck structure. As a consequence, the properties of the predominantly inviscid core region and the viscous wall layers have to be calculated simultaneously in the interaction region. Weakly three-dimensional effects caused by surface roughness, upstream propagating flow perturbations, boundary layer separation as well as bifurcating solutions are discussed. Representative results for subsonic as well as supersonic conditions are presented, and the importance of these flow phenomena in technical applications as, for example, a means to reduce shock losses through the use of deformed geometry is addressed.
Suder, Kenneth L.; Celestina, Mark L.
1995-01-01
Experimental and computational techniques are used to investigate tip clearance flows in a transonic axial compressor rotor at design and part speed conditions. Laser anemometer data acquired in the endwall region are presented for operating conditions near peak efficiency and near stall at 100% design speed and at near peak efficiency at 60% design speed. The role of the passage shock/leakage vortex interaction in generating endwall blockage is discussed. As a result of the shock/vortex interaction at design speed, the radial influence of the tip clearance flow extends to 20 times the physical tip clearance height. At part speed, in the absence of the shock, the radial extent is only 5 times the tip clearance height. Both measurements and analysis indicate that under part-speed operating conditions a second vortex, which does not originate from the tip leakage flow, forms in the endwall region within the blade passage and exits the passage near midpitch. Mixing of the leakage vortex with primary flow downstream of the rotor at both design and part speed conditions is also discussed.
Energy Technology Data Exchange (ETDEWEB)
Suder, K.L. [NASA-Lewis Research Center, Cleveland, OH (United States); Celestina, M.L. [Sverdrup Technology Inc., Cleveland, OH (United States). Lewis Research Center Group
1996-04-01
Experimental and computational techniques are used to investigate tip clearance flows in a transonic axial compressor rotor at design and part-speed conditions. Laser anemometer data acquired in the endwall region are presented for operating conditions near peak efficiency and near stall at 100 percent design speed and at near peak efficiency at 60 percent design speed. The role of the passage shock/leakage vortex interaction at design speed, the radial influence of the tip clearance flow extends to 20 times the physical tip clearance height. At part speed, in the absence of the shock, the radial extent is only five times the tip clearance height. Both measurements and analysis indicate that under part-speed operating conditions a second vortex, which does not originate from the tip leakage flow, forms in the end-wall region within the blade passage and exits the passage near midpitch. Mixing of the leakage vortex with the primary flow downstream of the rotor at both design and part-speed conditions is also discussed.
1955-01-01
8217rinRE-DifMENSONAL HtYPERtSONIC 15.W indicated-flow-separation oin the leewardl side of (lie body for excellent agreemelnt in tlie plano of symmlletry...REIMARKS b~ound~ary layers may, inl like imanner, prove useful il- pie - A mnethod of characteristics employing p)ressure and-flow deigdrednesoa
Directory of Open Access Journals (Sweden)
Cui Michael M.
2005-01-01
Full Text Available To reduce vibration and noise level, the impeller and diffuser blade numbers inside an industrial compressor are typically chosen without common divisors. The shapes of volutes or collectors in these compressors are also not axis-symmetric. When impeller blades pass these asymmetric structures, the flow field in the compressor is time-dependent and three-dimensional. To obtain a fundamental physical understanding of these three-dimensional unsteady flow fields and assess their impact on the compressor performance, the flow field inside the compressors needs to be studied as a whole to include asymmetric and unsteady interaction between the compressor components. In the current study, a unified three-dimensional numerical model was built for a transonic centrifugal compressor including impeller, diffusers, and volute. HFC 134a was used as the working fluid. The thermodynamic and transport properties of the refrigerant gas were modeled by the Martin-Hou equation of state and power laws, respectively. The three-dimensional unsteady flow field was simulated with a Navier-Stokes solver using the k−ϵ turbulent model. The overall performance parameters are obtained by integrating the field quantities. Both the unsteady flow field and the overall performance are analyzed comparatively for each component. The compressor was tested in a water chiller system instrumented to obtain both the overall performance data and local flow-field quantities. The experimental and numerical results agree well. The correlation between the overall compressor performance and local flow-field quantities is defined. The methodology developed and data obtained in these studies can be applied to the centrifugal compressor design and optimization.
Shahriari, S; Kadem, L; Rogers, B D; Hassan, I
2012-11-01
This paper aims to extend the application of smoothed particle hydrodynamics (SPH), a meshfree particle method, to simulate flow inside a model of the heart's left ventricle (LV). This work is considered the first attempt to simulate flow inside a heart cavity using a meshfree particle method. Simulating this kind of flow, characterized by high pulsatility and moderate Reynolds number using SPH is challenging. As a consequence, validation of the computational code using benchmark cases is required prior to simulating the flow inside a model of the LV. In this work, this is accomplished by simulating an unsteady oscillating flow (pressure amplitude: A = 2500 N ∕ m(3) and Womersley number: W(o) = 16) and the steady lid-driven cavity flow (Re = 3200, 5000). The results are compared against analytical solutions and reference data to assess convergence. Then, both benchmark cases are combined and a pulsatile jet in a cavity is simulated and the results are compared with the finite volume method. Here, an approach to deal with inflow and outflow boundary conditions is introduced. Finally, pulsatile inlet flow in a rigid model of the LV is simulated. The results demonstrate the ability of SPH to model complex cardiovascular flows and to track the history of fluid properties. Some interesting features of SPH are also demonstrated in this study, including the relation between particle resolution and sound speed to control compressibility effects and also order of convergence in SPH simulations, which is consistently demonstrated to be between first-order and second-order at the moderate Reynolds numbers investigated.
Energy Technology Data Exchange (ETDEWEB)
Lasseter, T.J.; Karakas, M.
1982-01-01
A simple numerical method has been developed that largely eliminates numerical diffusion errors associated with saturation discontinuities or shocks for two-phase flow in one and two dimensions. The important aspect of the approach is the computation of a variable weighting factor for the interface fractional flow between grid blocks. The approach appears to be generalizable to the multicomponent, multidimensional case including gravity and capilarity. 5 refs.
Phonon spectrum and correlations in a transonic flow of an atomic Bose gas
Michel, Florent; Coupechoux, Jean-François; Parentani, Renaud
2016-10-01
Motivated by a recent experiment of J. Steinhauer, we reconsider the spectrum and the correlations of the phonons spontaneously emitted in stationary transonic flows. The latter are described by "waterfall" configurations which form a one-parameter family of stable flows. For parameters close to their experimental values, in spite of high gradients near the sonic horizon, the spectrum is accurately Planckian in the relevant frequency domain, where the temperature differs from the relativistic prediction by less than 10%. We then study the density correlations across the horizon and the nonseparable character of the final state. We show that the relativistic expressions provide accurate approximations when the initial temperature is not too high. We also show that the phases of the scattering coefficients introduce a finite shift of the location of the correlations which has so far been overlooked. This shift is due to the asymmetry of the flow across the horizon, and persists in the dispersionless regime. Finally we show how the formation of the sonic horizon modifies both local and nonlocal density correlations.
Energy Technology Data Exchange (ETDEWEB)
Katyal, A.K.; Kaluarachchi, J.J.; Parker, J.C.
1991-05-01
The manual describes a two-dimensional finite element model for coupled multiphase flow and multicomponent transport in planar or radially symmetric vertical sections. Flow and transport of three fluid phases, including water, nonaqueous phase liquid (NAPL), and gas are considered by the program. The program can simulate flow only or coupled flow and transport. The flow module can be used to analyze two phases, water and NAPL, with the gas phase held at constant pressure, or explicit three-phase flow of water, NAPL, and gas at various pressures. The transport module can handle up to five components which partition among water, NAPL, gas and solid phases assuming either local equilibrium or first-order mass transfer. Three phase permeability-saturation-capillary pressure relations are defined by an extension of the van Genuchten model. The governing equations are solved using an efficient upstream-weighted finite element scheme. The report describes the required inputs for flow analysis and transport analysis. Time dependent boundary conditions for flow and transport analysis can be handled by the program and are described in the report. Detailed instructions for creating data files needed to run the program and example input and output files are given in appendices.
Transonic Dynamics Tunnel (TDT)
Federal Laboratory Consortium — The Transonic Dynamics Tunnel (TDT) is a continuous flow wind-tunnel facility capable of speeds up to Mach 1.2 at stagnation pressures up to one atmosphere. The TDT...
The shock tube as a device for testing transonic airfoils at high Reynolds numbers
Cook, W. J.; Presley, L. L.; Chapman, G. T.
1978-01-01
A performance analysis of gas-driven shock tubes shows that transonic airfoil flows with chord Reynolds numbers in the range of 100 million can be generated behind the primary shock in a large shock tube. A study of flow over simple airfoils has been carried out at low and intermediate Reynolds numbers to assess the testing technique. Results obtained from schlieren photos and airfoil pressure measurements show that steady transonic flows similar to those observed for the airfoils in wind tunnels can be generated within the available testing time in a shock tube with either properly-contoured test section walls or a properly-designed slotted-wall test section. The study indicates that the shock tube is a useful facility for studying two-dimensional high Reynolds number transonic airfoil flows.
Directory of Open Access Journals (Sweden)
M.N Kherief
2016-01-01
Full Text Available Steady, laminar, natural-convection flow in the presence of a magnetic field in an inclined rectangular enclosure heated from one side and cooled from the adjacent side was considered. The governing equations were solved numerically for the stream function, vorticity and temperature using the finite-volume method for various Grashof and Hartman numbers and inclination angles and magnetic field directions. The results show that the orientation and the strength and direction of the magnetic field have significant effects on the flow and temperature fields. Counterclockwise inclination induces the formation of multiple eddies inside the enclosure significantly affecting the temperature field. Circulation inside the enclosure and therefore the convection become stronger as the Grashof number increases while the magnetic field suppresses the convective flow and the heat transfer rate.
Erpelding, Marion; Sinha, Santanu; Tallakstad, Ken Tore; Hansen, Alex; Flekkøy, Eirik Grude; Måløy, Knut Jørgen
2013-11-01
It is well known that the transient behavior during drainage or imbibition in multiphase flow in porous media strongly depends on the history and initial condition of the system. However, when the steady-state regime is reached and both drainage and imbibition take place at the pore level, the influence of the evolution history and initial preparation is an open question. Here, we present an extensive experimental and numerical work investigating the history dependence of simultaneous steady-state two-phase flow through porous media. Our experimental system consists of a Hele-Shaw cell filled with glass beads which we model numerically by a network of disordered pores transporting two immiscible fluids. From measurements of global pressure evolution, histograms of saturation, and cluster-size distributions, we find that when both phases are flowing through the porous medium, the steady state does not depend on the initial preparation of the system or on the way it has been reached.
Transonic analysis of canted winglets
Rosen, B. S.
1984-01-01
A computational method developed to provide a transonic analysis for upper/lower surface wing-tip mounted winglets is described. Winglets with arbitrary planform, cant and toe angle, and airfoil section can be modeled. The embedded grid approach provides high flow field resolution and the required geometric flexibility. In particular, coupled Cartesian/cylindrical grid systems are used to model the complex geometry presented by canted upper/lower surface winglets. A new rotated difference scheme is introduced in order to maintain the stability of the small-disturbance formulation in the presence of large spanwise velocities. Wing and winglet viscous effects are modeled using a two-dimensional 'strip' boundary layer analysis. Correlations with wind tunnel and flight test data for three transport configurations are included.
2012-05-10
light (Schmelzle, 1994 and Albano , 1994). The kinetic mechanisms were incorporated into the flow field model by introducing the species mass... Albano , M., 1994. Computer Simulation of a Photolytic Reactor to Study the Effects of a Variety of Wavelengths, A Thesis in Environmental Pollution
Takagi, S.; Oguz, H.N.; Zhang, Z.; Prosperetti, A.
2003-01-01
This paper presents a new approach to the direct numerical simulation of particle flows. The basic idea is to use a local analytic representation valid near the particle to “transfer” the no-slip condition from the particle surface to the adjacent grid nodes. In this way the geometric complexity ari
An exploratory study of a finite difference method for calculating unsteady transonic potential flow
Bennett, R. M.; Bland, S. R.
1979-01-01
A method for calculating transonic flow over steady and oscillating airfoils was developed by Isogai. The full potential equation is solved with a semi-implicit, time-marching, finite difference technique. Steady flow solutions are obtained from time asymptotic solutions for a steady airfoil. Corresponding oscillatory solutions are obtained by initiating an oscillation and marching in time for several cycles until a converged periodic solution is achieved. The method is described in general terms and results for the case of an airfoil with an oscillating flap are presented for Mach numbers 0.500 and 0.875. Although satisfactory results are obtained for some reduced frequencies, it is found that the numerical technique generates spurious oscillations in the indicial response functions and in the variation of the aerodynamic coefficients with reduced frequency. These oscillations are examined with a dynamic data reduction method to evaluate their effects and trends with reduced frequency and Mach number. Further development of the numerical method is needed to eliminate these oscillations.
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.
A Model to Predict Stall Inception of Transonic Axial Flow Fan/Compressors
Institute of Scientific and Technical Information of China (English)
SUN Xiaofeng; SUN Dakun; YU Weiwei
2011-01-01
A stall inception model for transonic fan/compressors is presented in this paper.It can be shown that under some assumptions the solution of unsteady flow field consists of pressure wave which propagates upstream or downstream,vortex wave and entropy wave convected with the mean flow speed.By further using the mode-matching technique and applying the conservation law and conditions reflecting the loss characteristics of a compressor in the inlet and outlet of the rotor or stator blade rows,a group of homogeneous equations can be obtained from which the stability equation can be derived.Based on the analysis of the unsteady phenomenon caused by casing treatments,the function of casing treatments has been modeled by a wall impedance condition which has been included in the stability model through the eigenvalues and the corresponding eigenfunctions of the system.Besides,the effect of shock waves in cascade channel on the stability prediction is also considered in the stall inception model.Finally,some numerical analysis and experimental investigation are also conducted with emphasis on the mutual comparison.
Experimental investigation of the transonic flow around the leading edge of an eroded fan airfoil
Klinner, Joachim; Hergt, Alexander; Willert, Christian
2014-09-01
The influence of leading edge modification on the time-averaged and instantaneous flow around a fan airfoil is investigated by particle image velocimetry (PIV), schlieren imaging and high-speed shock shadowgraphs in a transonic cascade windtunnel. In addition to a global characterization of the time-averaged flow using PIV, the instantaneous passage shock position was extracted from single-shot PIV measurements by matching the tracer velocity across the normal shock with an exponential fit. The instantaneous shock positions are assigned to a probability density distribution in order to obtain the average position and the range of fluctuations of the eroded and reference leading edge. The profiles are used to estimate the response time of the particles to the normal shock which was found to be in the sub-microsecond range. Averaged PIV measurements and the probability density of shock position from both geometries are obtained at near stall and choked conditions. In order to extract the frequency range of the shock motion, the shadow of the shock wave was tracked using high-speed shadowgraphy. The paper also provides details on the experimental implementation such as a specifically designed light-sheet probe.
Block, Stephan; Lundgren, Anders; Zhdanov, Vladimir P; Höök, Fredrik
2016-01-01
Biological nanoparticles (BNPs) are of high interest due to their key role in various biological processes and use as biomarkers. BNP size and molecular composition are decisive for their functions, but simultaneous determination of both properties with high accuracy remains challenging, which is a severe limitation. Surface-sensitive microscopy allows one to precisely determine fluorescence or scattering intensity, but not the size of individual BNPs. The latter is better determined by tracking their random motion in bulk, but the limited illumination volume for tracking this motion impedes reliable intensity determination. We here show that attaching BNPs (specifically, vesicles and functionalized gold NPs) to a supported lipid bilayer, subjecting them to a hydrodynamic flow, and tracking their motion via surface-sensitive imaging enable to determine their diffusion coefficients and flow-induced drift velocities and to accurately quantify both BNP size and emission intensity. For vesicles, the high accuracy...
Block, Stephan; Fast, Björn Johansson; Lundgren, Anders; Zhdanov, Vladimir P.; Höök, Fredrik
2016-09-01
Biological nanoparticles (BNPs) are of high interest due to their key role in various biological processes and use as biomarkers. BNP size and composition are decisive for their functions, but simultaneous determination of both properties with high accuracy remains challenging. Optical microscopy allows precise determination of fluorescence/scattering intensity, but not the size of individual BNPs. The latter is better determined by tracking their random motion in bulk, but the limited illumination volume for tracking this motion impedes reliable intensity determination. Here, we show that by attaching BNPs to a supported lipid bilayer, subjecting them to hydrodynamic flows and tracking their motion via surface-sensitive optical imaging enable determination of their diffusion coefficients and flow-induced drifts, from which accurate quantification of both BNP size and emission intensity can be made. For vesicles, the accuracy of this approach is demonstrated by resolving the expected radius-squared dependence of their fluorescence intensity for radii down to 15 nm.
Gai, Ya; Leong, Chia Min; Cai, Wei; Tang, Sindy K. Y.
2016-10-01
When a many-body system is driven away from equilibrium, order can spontaneously emerge in places where disorder might be expected. Here we report an unexpected order in the flow of a concentrated emulsion in a tapered microfluidic channel. The velocity profiles of individual drops in the emulsion show periodic patterns in both space and time. Such periodic patterns appear surprising from both a fluid and a solid mechanics point of view. In particular, when the emulsion is considered as a soft crystal under extrusion, a disordered scenario might be expected based on the stochastic nature of dislocation dynamics in microscopic crystals. However, an orchestrated sequence of dislocation nucleation and migration is observed to give rise to a highly ordered deformation mode. This discovery suggests that nanocrystals can be made to deform more controllably than previously thought. It can also lead to novel flow control and mixing strategies in droplet microfluidics.
Directory of Open Access Journals (Sweden)
Sabet Safa
2016-03-01
Full Text Available In the present study, the fluid flow in a periodic, non-isotropic dual scale porous media consisting of permeable square rods in inline arrangement is analyzed to determine permeability, numerically. The continuity and Navier-Stokes equations are solved to obtain the velocity and pressure distributions in the unit structures of the dual scale porous media for flows within Darcy region. Based on the obtained results, the intrinsic inter and intraparticle permeabilities and the bulk permeability tensor of the dual scale porous media are obtained for different values of inter and intraparticle porosities. The study is performed for interparticle porosities between 0.4 and 0.75 and for intraparticle porosities from 0.2 to 0.8. A correlation based on Kozeny-Carman relationship in terms of inter and intraparticle porosities and permeabilities is proposed to determine the bulk permeability tensor of the dual scale porous media.
Barnwell, R. W.
1981-01-01
The development of a potential-flow/boundary-layer method for calculating subsonic and transonic turbulent flow past airfoils with trailing-edge separation is reported. A moment-of-momentum integral boundary-layer method is used which employs the law-of-the-wall/law-of-the-wake velocity profile and a two-layer eddy-viscosity model and ignores the laminar sublayer. All integrals across the boundary layer are obtained in closed form. Separation is assumed to occur when the shearing-stress velocity vanishes. A closed-form solution is derived for separated-flow regions where the shearing stress is negligible. In the potential-flow method, the exact form of the airfoil boundary condition is used, but it is applied at the chord line rather than the airfoil surface. This allows the accurate computation of flow about airfoils at large angles of attack but permits the use of body-oriented Cartesian computational grids. The governing equation for the perturbation velocity potential contains several terms in addition to the classical small-disturbance terms.
Belfort, Benjamin; Weill, Sylvain; Lehmann, François
2017-07-01
A novel, non-invasive imaging technique is proposed that determines 2D maps of water content in unsaturated porous media. This method directly relates digitally measured intensities to the water content of the porous medium. This method requires the classical image analysis steps, i.e., normalization, filtering, background subtraction, scaling and calibration. The main advantages of this approach are that no calibration experiment is needed, because calibration curve relating water content and reflected light intensities is established during the main monitoring phase of each experiment and that no tracer or dye is injected into the flow tank. The procedure enables effective processing of a large number of photographs and thus produces 2D water content maps at high temporal resolution. A drainage/imbibition experiment in a 2D flow tank with inner dimensions of 40 cm × 14 cm × 6 cm (L × W × D) is carried out to validate the methodology. The accuracy of the proposed approach is assessed using a statistical framework to perform an error analysis and numerical simulations with a state-of-the-art computational code that solves the Richards' equation. Comparison of the cumulative mass leaving and entering the flow tank and water content maps produced by the photographic measurement technique and the numerical simulations demonstrate the efficiency and high accuracy of the proposed method for investigating vadose zone flow processes. Finally, the photometric procedure has been developed expressly for its extension to heterogeneous media. Other processes may be investigated through different laboratory experiments which will serve as benchmark for numerical codes validation.
Energy Technology Data Exchange (ETDEWEB)
Votsish, A.D.
1977-07-01
Results are given for experimental studies of the effect that a cross-sectional magnetic field has on longitudinal and cross-sectional velocity pulsations and the coefficient of their correlation in a homogeneous shear region of averaged flow velocity. An opposite sign change for turbulent friction was obtained as the magnetic field was increased. In this connection an identification was made of an impulse transfer from regions with lower speeds to regions with high speeds. 4 references, 1 figure.
Introduction to transonic aerodynamics
Vos, Roelof
2015-01-01
Written to teach students the nature of transonic flow and its mathematical foundation, this book offers a much-needed introduction to transonic aerodynamics. The authors present a quantitative and qualitative assessment of subsonic, supersonic, and transonic flow around bodies in two and three dimensions. The book reviews the governing equations and explores their applications and limitations as employed in modeling and computational fluid dynamics. Some concepts, such as shock and expansion theory, are examined from a numerical perspective. Others, including shock-boundary-layer interaction, are discussed from a qualitative point of view. The book includes 60 examples and more than 200 practice problems. The authors also offer analytical methods such as Method of Characteristics (MOC) that allow readers to practice with the subject matter. The result is a wealth of insight into transonic flow phenomena and their impact on aircraft design, including compressibility effects, shock and expansion waves, sho...
Glazkov, S. A.; Gorbushin, A. R.; Osipova, S. L.; Semenov, A. V.
2016-10-01
The report describes the results of flow field experimental research in TsAGI T-128 transonic wind tunnel. During the tests Mach number, stagnation pressure, test section wall perforation ratio, angles between the test section panels and mixing chamber flaps varied. Based on the test results one determined corrections to the free-stream Mach number related to the flow speed difference in the model location and in the zone of static pressure measurement on the test section walls, nonuniformity of the longitudinal velocity component in the model location, optimal position of the movable test section elements to provide flow field uniformity in the test section and minimize the test leg drag.
Heat transfer in the flow of a cold, two-dimensional draining sheet over a hot, horizontal cylinder
Shu, Jian-Jun
2014-01-01
The paper considers heat transfer characteristics of thin film flow over a hot horizontal cylinder resulting from a cold vertical sheet of liquid falling onto the surface. The underlying physical features of the developing film thickness, velocity and temperature distributions have been illustrated by numerical solutions of high accuracy for large Reynolds numbers using the modified Keller box method. The solutions for film thickness distribution are good agreement with those obtained using the Pohlhausen integral momentum technique thus providing a basic confirmation of the validity of the results presented.
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.
Numerical Simulation for Two-Phase Water Hammer Flows in Pipe by Quasi-Two-Dimensional Model
Institute of Scientific and Technical Information of China (English)
Tae Uk Jang; Yuebin Wu; Ying Xu; Qiang Sun
2016-01-01
The features of a quasi⁃two⁃dimensional ( quasi⁃2D) model for simulating two⁃phase water hammer flows with vaporous cavity in a pipe are investigated. The quasi⁃2D model with discrete vaporous cavity in the pipe is proposed in this paper. This model uses the quasi⁃2D model for pure liquid zone and one⁃dimensional ( 1D ) discrete vapor cavity model for vaporous cavity zone. The quasi⁃2D model solves two⁃dimensional equations for both axial and radial velocities and 1D equations for both pressure head and discharge by the method of characteristics. The 1D discrete vapor cavity model is used to simulate the vaporous cavity occurred when the pressure in the local pipe is lower than the vapor pressure of the liquid. The proposed model is used to simulate two⁃phase water flows caused by the rapid downstream valve closure in a reservoir⁃pipe⁃valve system. The results obtained by the proposed model are compared with those by the corresponding 1D model and the experimental ones provided by the literature, respectively. The comparison shows that the maximum pressure heads simulated by the proposed model are more accurate than those by the corresponding 1D model.
Johnson, F. T.; Samant, S. S.; Bieterman, M. B.; Melvin, R. G.; Young, D. P.; Bussoletti, J. E.; Hilmes, C. L.
1992-01-01
The TranAir computer program calculates transonic flow about arbitrary configurations at subsonic, transonic, and supersonic freestream Mach numbers. TranAir solves the nonlinear full potential equations subject to a variety of boundary conditions modeling wakes, inlets, exhausts, porous walls, and impermeable surfaces. Regions with different total temperature and pressure can be represented. The user's manual describes how to run the TranAir program and its graphical support programs.
DEFF Research Database (Denmark)
Brix, Lau; Christoffersen, Christian P. V.; Kristiansen, Martin Søndergaard
of the aorta. Methods: 2D phase contrast flow images of the aorta were acquired from a patient with an enlarged pulmonary artery on a Philips Achieva 1.5T CMR system. The cardiac motion was removed from the data set using the Cornelius/Kanade registration algorithm. The time resolved flow data...... promising because it saves time for post-processing. However, the k-means cluster approach is not comprehensive for quantitative flow estimations as it is but seems feasible for a subsequent segmentation algorithm like deformable contours (i.e. snakes). Future work may overcome this manual part and make...
Williams, R. D.; Brasington, J.; Hicks, M.; Measures, R.; Rennie, C. D.; Vericat, D.
2013-09-01
Gravel-bed braided rivers are characterized by shallow, branching flow across low relief, complex, and mobile bed topography. These conditions present a major challenge for the application of higher dimensional hydraulic models, the predictions of which are nevertheless vital to inform flood risk and ecosystem management. This paper demonstrates how high-resolution topographic survey and hydraulic monitoring at a density commensurate with model discretization can be used to advance hydrodynamic simulations in braided rivers. Specifically, we detail applications of the shallow water model, Delft3d, to the Rees River, New Zealand, at two nested scales: a 300 m braid bar unit and a 2.5 km reach. In each case, terrestrial laser scanning was used to parameterize the topographic boundary condition at hitherto unprecedented resolution and accuracy. Dense observations of depth and velocity acquired from a mobile acoustic Doppler current profiler (aDcp), along with low-altitude aerial photography, were then used to create a data-rich framework for model calibration and testing at a range of discharges. Calibration focused on the estimation of spatially uniform roughness and horizontal eddy viscosity, νH, through comparison of predictions with distributed hydraulic data. Results revealed strong sensitivity to νH, which influenced cross-channel velocity and localization of high shear zones. The high-resolution bed topography partially accounts for form resistance, and the recovered roughness was found to scale by 1.2-1.4 D84 grain diameter. Model performance was good for a range of flows, with minimal bias and tight error distributions, suggesting that acceptable predictions can be achieved with spatially uniform roughness and νH.
Tomé, M. F.; Bertoco, J.; Oishi, C. M.; Araujo, M. S. B.; Cruz, D.; Pinho, F. T.; Vynnycky, M.
2016-04-01
This work is concerned with the numerical solution of the K-BKZ integral constitutive equation for two-dimensional time-dependent free surface flows. The numerical method proposed herein is a finite difference technique for simulating flows possessing moving surfaces that can interact with solid walls. The main characteristics of the methodology employed are: the momentum and mass conservation equations are solved by an implicit method; the pressure boundary condition on the free surface is implicitly coupled with the Poisson equation for obtaining the pressure field from mass conservation; a novel scheme for defining the past times t‧ is employed; the Finger tensor is calculated by the deformation fields method and is advanced in time by a second-order Runge-Kutta method. This new technique is verified by solving shear and uniaxial elongational flows. Furthermore, an analytic solution for fully developed channel flow is obtained that is employed in the verification and assessment of convergence with mesh refinement of the numerical solution. For free surface flows, the assessment of convergence with mesh refinement relies on a jet impinging on a rigid surface and a comparison of the simulation of a extrudate swell problem studied by Mitsoulis (2010) [44] was performed. Finally, the new code is used to investigate in detail the jet buckling phenomenon of K-BKZ fluids.
Kreider, Kevin L.; Baumeister, Kenneth J.
1996-01-01
An explicit finite difference real time iteration scheme is developed to study harmonic sound propagation in aircraft engine nacelles. To reduce storage requirements for future large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable for a harmonic monochromatic sound field, a parabolic (in time) approximation is introduced to reduce the order of the governing equation. The analysis begins with a harmonic sound source radiating into a quiescent duct. This fully explicit iteration method then calculates stepwise in time to obtain the 'steady state' harmonic solutions of the acoustic field. For stability, applications of conventional impedance boundary conditions requires coupling to explicit hyperbolic difference equations at the boundary. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.
Characteristic analysis of lock-in for an elastically suspended airfoil in transonic buffet flow
Institute of Scientific and Technical Information of China (English)
Quan Jingge; Zhang Weiwei; Gao Chuanqiang; Ye Zhengyin
2016-01-01
Numerical simulations are performed to study the aeroelastic responses of an elastically suspended airfoil in transonic buffet flow, by coupling the unsteady Reynolds-averaged Navier-Stokes (RANS) equations and structural motion equation. The current work focuses on the char-acteristic analysis of the lock-in phenomenon. Great attentions are paid to studying the frequency range of lock-in and the effects of the three parameters, namely the structural natural frequency, mass ratio and structural damping, on lock-in characteristic of the elastic system in detail. It is found that when the structural natural frequency is close to the buffet frequency, the coupling fre-quency of the elastic system is no longer equal to the buffet frequency, but keeps the same value as the structural natural frequency. The frequency lock-in occurs and stays present until the structural nature frequency is near the double buffet frequency. It means that the lock-in presents within a broad range, of which the lower threshold is near the buffet frequency, while the upper threshold is near the double buffet frequency. Moreover, the frequency range of lock-in is affected by mass ratio and structural damping. The lower the mass ratio and structural damping are, the wider the range of lock-in will be. The upper threshold of lock-in grows with the mass ratio and structural damping decreasing, but the lower threshold always keeps the same.
Numerical calculation of the transonic flow past a swept wing. [FLO 22
Energy Technology Data Exchange (ETDEWEB)
Jameson, A; Caughey, D A
1977-06-01
A numerical method is presented for analyzing the transonic potential flow past a lifting, swept wing. A finite-difference approximation to the full potential equation is solved in a coordinate system which is nearly conformally mapped from the physical space in planes parallel to the symmetry plane, and reduces the wing surface to a portion of one boundary of the computational grid. A coordinate invariant, rotated difference scheme is used, and the difference equations are solved by relaxation. The method is capable of treating wings of arbitrary planform and dihedral, although approximations in treating the tips and vortex sheet make its accuracy suspect for wings of small aspect ratio. Comparisons of calculated results with experimental data are shown for examples of both conventional and supercritical transport wings. Agreement is quite good for both types, but it was found necessary to account for the displacement effect of the boundary layer for the supercritical wing, presumably because of its greater sensitivity to changes in effective geometry.
Filgueira, Marcelo R.; Huang, Yuan; Witt, Klaus; Castells, Cecilia; Carr, Peter W.
2011-01-01
The use of flow splitters between the two dimensions in on-line comprehensive two dimensional liquid chromatography (LC×LC) has not received very much attention in comparison to their use in GC×GC where they are quite common. In principle, splitting the flow after the first dimension column and performing on-line LC×LC on this constant fraction of the first dimension effluent should allow the two dimensions to be optimized almost independently. When there is no flow splitting any change in the first dimension flow rate has an immediate impact on the second dimension. With a flow splitter one could for example double the flow rate into the first dimension column and do a 1:1 flow split without changing the sample loop size or the sampler’s collection time. Of course, the sensitivity would be diminished but this can be partially compensated by use of a larger injection; this will likely only amount to a small price to pay for this increased resolving power and system flexibility. Among other benefits, we found a 2-fold increase in the corrected 2D peak capacity and the number of observed peaks for a 15 min analysis time by using a post first dimension flow splitter. At a fixed analysis time this improvement results primarily from an increase in the gradient time resulting from the reduced system re-equilibration time and to a smaller extent it is due to the increased peak capacity achieved by full optimization of the first dimension. PMID:22017622
Institute of Scientific and Technical Information of China (English)
Cai Qing-Dong; Chen Shi-Yi; Sheng Xiao-Wei
2011-01-01
This paper studies some interesting features of two-dimensional granular shearing flow by using molecular dynamic approach for a specific granular system. The obtained results show that the probability distribution function of velocities of particles is Gaussian at the central part, but diverts from Gaussian distribution nearby the wall. The macroscopic stress along the vertical direction has large fluctuation around a constant value, the non-zero average velocity occurs mainly near the moving wall, which forms a shearing zone. . In the shearing movement, the volume of the granular material behaves in a random manner. The equivalent friction coefficient between moving slab and granular material correlates with the moving speed at low velocity, and approaches constant as the velocity is large enough.
van der Poel, Erwin P; Verzicco, Roberto; Lohse, Detlef
2015-01-01
The effect of various velocity boundary condition is studied in two-dimensional Rayleigh-B\\'enard convection. Combinations of no-slip, stress-free and periodic boundary conditions are used on both the sidewalls and the horizontal plates. For the studied Rayleigh numbers Ra between $10^8$ and $10^{11}$ the heat transport is lower for $\\Gamma = 0.33$ than for $\\Gamma = 1$ in case of no-slip sidewalls. This is surprisingly opposite for stress-free sidewalls, where the heat transport increases for lower aspect-ratio. In wider cells the aspect-ratio dependence is observed to disappear for $\\text{Ra} \\ge 10^{10}$. Two distinct flow types with very different dynamics can be seen, mostly dependent on the plate velocity boundary condition, namely roll-like flow and horizontal zonal flow, which have a substantial effect on the dynamics and heat transport in the system. The predominantly horizontal zonal flow suppresses heat flux and is observed for stress-free and asymmetric plates. Low aspect-ratio periodic sidewall s...
Pavlidis, Mitrofanis
2016-01-01
Purpose. To evaluate comparative aspiration flow performance and also vitrectomy operating time efficiency using a double-cutting open port vitreous cutting system incorporated in a two-dimensional cutting (TDC, DORC International) vitrectome design versus standard vitreous cutter. Methods. In vitro investigations compared aspiration flow rates in artificial vitreous humor at varying cutter speeds and vacuum levels using a TDC vitrectome and a standard vitrectome across different aspiration pump systems. A prospective single-centre clinical study evaluated duration of core vitrectomy in 80 patients with macular pucker undergoing 25-gauge or 27-gauge vitrectomy using either a TDC vitrectome at 16,000 cuts per minute (cpm) or standard single-cut vitrectome, combined with a Valve Timing intelligence (VTi) pump system (EVA, DORC International). Results. Aspiration flow rates remained constant independent of TDC vitrectome cut rate, while flow rates decreased linearly at higher cutter speeds using a classic single-blade vitrectome. Mean duration of core vitrectomy surgeries using a TDC vitreous cutter system was significantly (p < 0.001) shorter than the mean duration of core vitrectomy procedures using a single-cut vitrectome of the same diameter (reduction range, 34%-50%). Conclusion. Vitrectomy surgery performed using a TDC vitrectome was faster than core vitrectomy utilizing a standard single-action vitrectome at similar cut speeds.
Directory of Open Access Journals (Sweden)
Mitrofanis Pavlidis
2016-01-01
Full Text Available Purpose. To evaluate comparative aspiration flow performance and also vitrectomy operating time efficiency using a double-cutting open port vitreous cutting system incorporated in a two-dimensional cutting (TDC, DORC International vitrectome design versus standard vitreous cutter. Methods. In vitro investigations compared aspiration flow rates in artificial vitreous humor at varying cutter speeds and vacuum levels using a TDC vitrectome and a standard vitrectome across different aspiration pump systems. A prospective single-centre clinical study evaluated duration of core vitrectomy in 80 patients with macular pucker undergoing 25-gauge or 27-gauge vitrectomy using either a TDC vitrectome at 16,000 cuts per minute (cpm or standard single-cut vitrectome, combined with a Valve Timing intelligence (VTi pump system (EVA, DORC International. Results. Aspiration flow rates remained constant independent of TDC vitrectome cut rate, while flow rates decreased linearly at higher cutter speeds using a classic single-blade vitrectome. Mean duration of core vitrectomy surgeries using a TDC vitreous cutter system was significantly (p<0.001 shorter than the mean duration of core vitrectomy procedures using a single-cut vitrectome of the same diameter (reduction range, 34%–50%. Conclusion. Vitrectomy surgery performed using a TDC vitrectome was faster than core vitrectomy utilizing a standard single-action vitrectome at similar cut speeds.
Non-linear effects in time-dependent transonic flows: An analysis of analogue black hole stability
Michel, Florent
2015-01-01
We study solutions of the one dimensional Gross-Pitaevskii equation to better understand dynamical instabilities occurring in flowing atomic condensates. Whereas transonic stationary flows can be fully described in simple terms, time dependent flows exhibit a wide variety of behaviors. When the sound speed is crossed once, we observe that flows analogous to black holes obey a kind of "no-hair theorem" since their late time profile is stationary and uniquely fixed by parameters entering the Hamiltonian and conserved quantities. For flows analogous to white holes, at late time one finds a macroscopic undulation in the supersonic side which has either a fixed amplitude, or a widely varying one signaling a quasi periodic emission of solitons on the subsonic side. When considering flows which cross twice the sound speed, we observe various scenarii which can be understood from the above behaviors, and from the hierarchy of the growth rates of the dynamical instabilities characterizing such flows.
Chaparro, Daniel; Fujiwara, Gustavo E. C.; Ting, Eric; Nguyen, Nhan
2016-01-01
The need to rapidly scan large design spaces during conceptual design calls for computationally inexpensive tools such as the vortex lattice method (VLM). Although some VLM tools, such as Vorview have been extended to model fully-supersonic flow, VLM solutions are typically limited to inviscid, subcritical flow regimes. Many transport aircraft operate at transonic speeds, which limits the applicability of VLM for such applications. This paper presents a novel approach to correct three-dimensional VLM through coupling of two-dimensional transonic small disturbance (TSD) solutions along the span of an aircraft wing in order to accurately predict transonic aerodynamic loading and wave drag for transport aircraft. The approach is extended to predict flow separation and capture the attenuation of aerodynamic forces due to boundary layer viscosity by coupling the TSD solver with an integral boundary layer (IBL) model. The modeling framework is applied to the NASA General Transport Model (GTM) integrated with a novel control surface known as the Variable Camber Continuous Trailing Edge Flap (VCCTEF).
Institute of Scientific and Technical Information of China (English)
CAO; Wei
2001-01-01
.0, MNRAS,1992, 256: 349.［25］Hazard, C. , Morton, D. C., Terlevich, R. et al. , Nine new quasi-stellar objects with borad absorption lines, Astrophys.J. , 1984, 282: 33.［26］Osmer, P. S. , Q0353-383: The best case yet for abundance anomalies in quasars, Astrophys. J. , 1980, 237, 666.［27］Hamann, F. , Zuo, L., Tytler, D. , Broad Ne VIII λ774 emission from quasars in the HST-Fos snapshot survey (ABSNAP),Astrophys. J., 1995, 444: L69.［28］Laor, A. , Bahcall, J. N., Jannuzi, B. T. , The ultraviolet emission properties of five low-redshift active galactic unclei at high signal-to-noise ratio and spectral resolution, Astrophys. J., 1994, 420: 110.［29］Barthel, P. D., Tytler, D. R., Thomson, B., Optical spectra of distant radio loud quasars, A&AS, 1990, 82: 339.［30］Schmidt, M., Schneider, D. P., Gunn, J. E., Pc0910 + 5625: An optically selected quasar with a redshift of 4.04, Astro-phys. J., 1987, 321: L7.［31］Adams, M. T., Coleman, G. D., Stockman, H. S. et al., The spectrum of Markarian 132, Astrophys. J., 1978, 228:758.［32］Hammann, F. , Shields, J. C. , Ferland, G. J. et al. , Broad NE VIII lambda 744 emission from the Quasar PG 148 + 549,Astrophys. J., 1995, 454: 688.［33］Baldwin, J. A., McMahon, R., Hazard, C. et al., QSOs with narrow emission lines, Astrophys. J., 1988, 327: 103.［34］Baldwin, J. A. , Burbidge, E. M. , Hazard, C. et al. , A spectroscopic surrvey of 92 QSO candidates, Astrophys. J. ,1973, 185: 739.［35］Baldwin, J. A. , Ferland, G. J. , Korista, K. T., Very high density clumps and out flowing winds in QSO broad-line re-gions, Astrophys. J., 1996, 461: 664.［36］Ferland, G. J., Baldwin, J. A., Korista, K. T., High metal enrichments in luminous quasars, Astrophys. J., 461: 683.［37］Bceker, R. H., Helfand, D. J., White, R. L., The discovery of an X-ray selected radio-loud quasar at z = 3.9 AJ, 1992,104: 531.［38］Schneider, D. P., Lawrence, C. R., Schmide, M. et al., Deep optical and radio observations of the
Directory of Open Access Journals (Sweden)
Y. V. Konovalov
2015-11-01
Full Text Available The prognostic experiments for fast-flowing ice streams on the southern side of the Academy of Sciences Ice Cap in the Komsomolets Island, Severnaya Zemlya archipelago, are implemented in this study. These experiments are based on inversions of basal friction coefficients using a two-dimensional flow-line thermo-coupled model and the Tikhonov's regularization method. The modeled ice temperature distributions in the cross-sections were obtained using the ice surface temperature histories that were inverted previously from the borehole temperature profiles derived at the Academy of Sciences Ice Cap. Input data included InSAR ice surface velocities, ice surface elevations, and ice thicknesses obtained from airborne measurements and the surface mass balance, were adopted from the prior investigations for the implementation of both the forward and inverse problems. The prognostic experiments reveal that both ice mass and ice stream extents decline for the reference time-independent surface mass balance. Specifically, the grounding line retreats (a along the B–B' flow line from ~ 40 to ~ 30 km (the distance from the summit, (b along the C–C' flow line from ~ 43 to ~ 37 km, and (c along the D–D' flow line from ~ 41 to ~ 32 km considering a time period of 500 years and assuming time-independent surface mass balance. Ice flow velocities in the ice streams decrease with time and this trend results in the overall decline of the outgoing ice flux. Generally, the modeled histories are in agreement with observations of sea ice extent and thickness indicating a continual ice decline in the Arctic.
Institute of Scientific and Technical Information of China (English)
Masanori Tanaka; Shigeru Matsuo; Toshiaki Setoguchi; Kenji Kaneko; Heuy-Dong Kim; Shen Yu
2003-01-01
When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released.In the present study, in order to control the transonic flow field with shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock / boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically and experimentally. The result obtained showed that the total pressure loss in the flow fields might be effectively reduced by the suitable combination between non-equilibrium condensation and the position of porous wall.
Sun, Yi; Timofeyev, Ilya
2014-05-01
We employ an efficient list-based kinetic Monte Carlo (KMC) method to study traffic flow models on one-dimensional (1D) and two-dimensional (2D) lattices based on the exclusion principle and Arrhenius microscopic dynamics. This model implements stochastic rules for cars' movements based on the configuration of the traffic ahead of each car. In particular, we compare two different look-ahead rules: one is based on the distance from the car under consideration to the car in front of it, and the other one is based on the density of cars ahead. The 1D numerical results of these two rules suggest different coarse-grained macroscopic limits in the form of integro-differential Burgers equations. The 2D results of both rules exhibit a sharp phase transition from freely flowing to fully jammed, as a function of the initial density of cars. However, the look-ahead rule based on the density of the traffic produces more realistic results. The KMC simulations reported in this paper are compared with those from other well-known traffic flow models and the corresponding empirical results from real traffic.
Zoccali, Mariosimone; Schug, Kevin A; Walsh, Phillip; Smuts, Jonathan; Mondello, Luigi
2017-05-12
The present paper is focused on the use of a vacuum ultraviolet absorption spectrometer (VUV) for gas chromatography (GC), within the context of flow modulated comprehensive two-dimensional gas chromatography (FM GC×GC). The features of the VUV detector were evaluated through the analysis of petrochemical and fatty acids samples. Besides responding in a predictable fashion via Beer's law principles, the detector provides additional spectroscopic information for qualitative analysis. Virtually all chemical species absorb and have unique gas phase absorption features in the 120-240nm wavelength range monitored. The VUV detector can acquire up to 90 full range absorption spectra per second, allowing its coupling with comprehensive two-dimensional gas chromatography. This recent form of detection can address specific limitations related to mass spectrometry (e.g., identification of isobaric and isomeric species with very similar mass spectra or labile chemical compounds), and it is also able to deconvolute co-eluting peaks. Moreover, it is possible to exploit a pseudo-absolute quantitation of analytes based on pre-recorded absorption cross-sections for target analytes, without the need for traditional calibration. Using this and the other features of the detector, particular attention was devoted to the suitability of the FM GC×GC-VUV system toward qualitative and quantitative analysis of bio-diesel fuel and different kinds of fatty acids. Satisfactory results were obtained in terms of tailing factor (1.1), asymmetry factor (1.1), and similarity (average value 97%), for the FAMEs mixtures analysis. Copyright © 2017 Elsevier B.V. All rights reserved.
Czuba, Christiana; Czuba, Jonathan A.; Gendaszek, Andrew S.; Magirl, Christopher S.
2010-01-01
The Cedar River in Washington State originates on the western slope of the Cascade Range and provides the City of Seattle with most of its drinking water, while also supporting a productive salmon habitat. Water-resource managers require detailed information on how best to manage high-flow releases from Chester Morse Lake, a large reservoir on the Cedar River, during periods of heavy precipitation to minimize flooding, while mitigating negative effects on fish populations. Instream flow-management practices include provisions for adaptive management to promote and maintain healthy aquatic habitat in the river system. The current study is designed to understand the linkages between peak flow characteristics, geomorphic processes, riverine habitat, and biological responses. Specifically, two-dimensional hydrodynamic modeling is used to simulate and quantify the effects of the peak-flow magnitude, duration, and frequency on the channel morphology and salmon-spawning habitat. Two study reaches, representative of the typical geomorphic and ecologic characteristics of the Cedar River, were selected for the modeling. Detailed bathymetric data, collected with a real-time kinematic global positioning system and an acoustic Doppler current profiler, were combined with a LiDAR-derived digital elevation model in the overbank area to develop a computational mesh. The model is used to simulate water velocity, benthic shear stress, flood inundation, and morphologic changes in the gravel-bedded river under the current and alternative flood-release strategies. Simulations of morphologic change and salmon-redd scour by floods of differing magnitude and duration enable water-resource managers to incorporate model simulation results into adaptive management of peak flows in the Cedar River. PDF version of a presentation on hydrodynamic modelling in the Cedar River in Washington state. Presented at the American Geophysical Union Fall Meeting 2010.
Barnas, C. R.; Czuba, J. A.; Gendaszek, A. S.; Magirl, C. S.
2010-12-01
The Cedar River in Washington State originates on the western slope of the Cascade Range and provides the City of Seattle with most of its drinking water, while also supporting a productive salmon habitat. Water-resource managers require detailed information on how best to manage high-flow releases from Chester Morse Lake, a large reservoir on the Cedar River, during periods of heavy precipitation to minimize flooding, while mitigating negative effects on fish populations. Instream flow-management practices include provisions for adaptive management to promote and maintain healthy aquatic habitat in the river system. The current study is designed to understand the linkages between peak flow characteristics, geomorphic processes, riverine habitat, and biological responses. Specifically, two-dimensional hydrodynamic modeling is used to simulate and quantify the effects of the peak-flow magnitude, duration, and frequency on the channel morphology and salmon-spawning habitat. Two study reaches, representative of the typical geomorphic and ecologic characteristics of the Cedar River, were selected for the modeling. Detailed bathymetric data, collected with a real-time kinematic global positioning system and an acoustic Doppler current profiler, were combined with a LiDAR-derived digital elevation model in the overbank area to develop a computational mesh. The model is used to simulate water velocity, benthic shear stress, flood inundation, and morphologic changes in the gravel-bedded river under the current and alternative flood-release strategies. Simulations of morphologic change and salmon-redd scour by floods of differing magnitude and duration enable water-resource managers to incorporate model simulation results into adaptive management of peak flows in the Cedar River.
Hall, R. M.; Adcock, J. B.
1981-01-01
The real gas behavior of nitrogen, the gas normally used in transonic cryogenic tunnels, is reported for the following flow processes: isentropic expansion, normal shocks, boundary layers, and interactions between shock waves and boundary layers. The only difference in predicted pressure ratio between nitrogen and an ideal gas which may limit the minimum operating temperature of transonic cryogenic wind tunnels occur at total pressures approaching 9 atm and total temperatures 10 K below the corresponding saturation temperature. These pressure differences approach 1 percent for both isentropic expansions and normal shocks. Alternative cryogenic test gases were also analyzed. Differences between air and an ideal diatomic gas are similar in magnitude to those for nitrogen and should present no difficulty. However, differences for helium and hydrogen are over an order of magnitude greater than those for nitrogen or air. It is concluded that helium and cryogenic hydrogen would not approximate the compressible flow of an ideal diatomic gas.
Directory of Open Access Journals (Sweden)
Hożejowska Sylwia
2014-03-01
Full Text Available The paper presents application of the nodeless Trefftz method to calculate temperature of the heating foil and the insulating glass pane during continuous flow of a refrigerant along a vertical minichannel. Numerical computations refer to an experiment in which the refrigerant (FC-72 enters under controlled pressure and temperature a rectangular minichannel. Initially its temperature is below the boiling point. During the flow it is heated by a heating foil. The thermosensitive liquid crystals allow to obtain twodimensional temperature field in the foil. Since the nodeless Trefftz method has very good performance for providing solutions to such problems, it was chosen as a numerical method to approximate two-dimensional temperature distribution in the protecting glass and the heating foil. Due to known temperature of the refrigerant it was also possible to evaluate the heat transfer coefficient at the foil-refrigerant interface. For expected improvement of the numerical results the nodeless Trefftz method was combined with adjustment calculus. Adjustment calculus allowed to smooth the measurements and to decrease the measurement errors. As in the case of the measurement errors, the error of the heat transfer coefficient decreased.
Energy Technology Data Exchange (ETDEWEB)
Chono, S.; Tsuji, T. [Fukui University, Fukui (Japan). Faculty of Engineering
1995-05-25
Finite difference solutions to the Leslie-Ericksen equations were obtained for flows in two-dimensional L-shaped channels with various contraction ratios of the upstream to downstream channel width. A streamline shift toward the outer wall occurs upstream of the reentrant corner. Such behavior is similar to that of viscoelastic fluids. With increasing contraction ratio, the streamline shift occurs further upstream. The effect of the wall anchoring angle for the director is remarkable; for example, when the anchoring angle along the downstream walls is set to be opposite to the main flow direction, a distortion of streamlines is produced in the corner region and the director moves to the downstream region upside down. At small Ericksen numbers, the orientation angle for the director is varied over a wide area so as to suppress its local deformation. In contrast, when the Ericksen number is large, the director profile in the upstream region is retained close to the corner region where the director turns rapidly to the downstream direction. 7 refs., 9 figs., 1 tab.
Energy Technology Data Exchange (ETDEWEB)
Tomita, Yukio; Ishibashi, Yukio; Saito, Eiji; Saito, Toshio
1988-02-25
For elucidation of the flow behavior of a magnetic fluid as a one-phase fluid, water base ferrofluids were introduced in a two-dimensional channel and the action of a uniform vertical magnetic field axial magnetic field, and both fields inclined at various angles to examine the laminar flow region. The ferrofluids used in the experiment were prepared by dispersing 17.5 weight % of Fe/sub 3/ O/sub 4/ fine particles of about 100A in diameter into ion-exchange water, and adding an anionic sodium oleate to stabilize the dispersion. Under no action of the magnetic fields, ferrofluids having a higher concentration than the above value exhibited plastic fluid. As the direction of the magnetic field acting on the fluid approached the vertical, so the pressure loss was increased. The pipe friction coefficient could be expressed by the empirical formula of which the variables are the ratios of inertia force/viscous force and magnetic force/viscous force, and the inclination of the magnetic poles. (15 figs, 14 refs)
Energy Technology Data Exchange (ETDEWEB)
Fradin, C.
1998-07-01
The prediction of flow structure and performances of an axial transonic compressor requires accurate solvers. Taking into account the complex flow patterns, it is important to validate codes by comparing it with experimental results. It is well understood that the availability of experimental data is fundamentally important for the improvement of the solvers. An axial transonic compressor has been fitted in the ERECA test facility of ONERA. The rotor of this compressor is isolated from stators. This experimental configuration allows to obtain a steady flow into the relative frame linked to the rotor. Due to this fact, experimental tests became easier because the basic phenomena are not hidden by mutual interactions rotor-stator. Measurements have been made in a test section far upstream the rotor, to provide the inlet conditions in the computation domain. Non intrusive and fast response measurement techniques allow to obtain the detailed flow structure in several test sections located in the rotor and far downstream it. All tests were carried out at four operating conditions of the compressor. Results provide good test cases for numerical prediction methods using three-dimensional Navier-Stokes solvers. (author)
Weatherill, W. H.; Ehlers, F. E.
1979-01-01
The design and usage of a pilot program for calculating the pressure distributions over harmonically oscillating airfoils in transonic flow are described. The procedure used is based on separating the velocity potential into steady and unsteady parts and linearizing the resulting unsteady differential equations for small disturbances. The steady velocity potential which must be obtained from some other program, was required for input. The unsteady equation, as solved, is linear with spatially varying coefficients. Since sinusoidal motion was assumed, time was not a variable. The numerical solution was obtained through a finite difference formulation and either a line relaxation or an out of core direct solution method.
Butler, T. D.; Weatherill, W. H.; Sebastian, J. D.; Ehlers, F. E.
1977-01-01
The design and usage of a pilot program using a finite difference method for calculating the pressure distributions over harmonically oscillating wings in transonic flow are discussed. The procedure used is based on separating the velocity potential into steady and unsteady parts and linearizing the resulting unsteady differential equation for small disturbances. The steady velocity potential which must be obtained from some other program, is required for input. The unsteady differential equation is linear, complex in form with spatially varying coefficients. Because sinusoidal motion is assumed, time is not a variable. The numerical solution is obtained through a finite difference formulation and a line relaxation solution method.
Osserman, Robert
2011-01-01
The basic component of several-variable calculus, two-dimensional calculus is vital to mastery of the broader field. This extensive treatment of the subject offers the advantage of a thorough integration of linear algebra and materials, which aids readers in the development of geometric intuition. An introductory chapter presents background information on vectors in the plane, plane curves, and functions of two variables. Subsequent chapters address differentiation, transformations, and integration. Each chapter concludes with problem sets, and answers to selected exercises appear at the end o
Juday, Richard D. (Inventor)
1992-01-01
A two-dimensional vernier scale is disclosed utilizing a cartesian grid on one plate member with a polar grid on an overlying transparent plate member. The polar grid has multiple concentric circles at a fractional spacing of the spacing of the cartesian grid lines. By locating the center of the polar grid on a location on the cartesian grid, interpolation can be made of both the X and Y fractional relationship to the cartesian grid by noting which circles coincide with a cartesian grid line for the X and Y direction.
Modelling flow phenomena in time dependent store release from transonic aircraft
CSIR Research Space (South Africa)
MacLucas, David A
2014-07-01
Full Text Available Computational Fluid Dynamics is routinely used in clearance of stores for carriage and release from aircraft in the transonic range of flight. A well-known validation case is modelled in this study, for which aerodynamic loads have been compared...
Institute of Scientific and Technical Information of China (English)
Gang Guo; Yonggui Yang; Weiqun Yang
2011-01-01
The optimal velocity encoding of phase-contrast magnetic resonance angiography (PC MRA) in measuring cerebral blood flow volume (BFV) ranges from 60 to 80 cm/s. To verify the accuracy of two-dimensional (2D) PC MRA, the present study localized the region of interest at blood vessels of the neck using PC MRA based on three-dimensional time-of-flight sequences, and the velocity encodingwas set to 80 cm/s. Results of the measurements showed that the error rate was 7.0 ± 6.0%in the estimation of BFV in the internal carotid artery, the external carotid artery and the ipsilateralcommon carotid artery. There was no significant difference, and a significant correlation in BFV between internal carotid artery + external carotid artery and ipsilateral common carotid artery. Inaddition, the BFV of the common carotid artery was correlated with that of the ipsilateral internal carotid artery. The main error was attributed to the external carotid artery and its branches. Therefore,after selecting the appropriate scanning parameters and protocols, 2D PC MRA is more accuratein the determination of BFV in the carotid arteries.
Franchina, Flavio Antonio; Machado, Maria Elisabete; Tranchida, Peter Quinto; Zini, Cláudia Alcaraz; Caramão, Elina Bastos; Mondello, Luigi
2015-03-27
The present research is focused on the development of a flow-modulated comprehensive two-dimensional gas chromatography-triple quadrupole mass spectrometry (FM GC × GC-MS/MS) method for the determination of classes of aromatic organic sulphur compounds (benzothiophenes, dibenzothiophenes, and benzonaphthothiophene) in heavy gas oil (HGO). The MS/MS instrument was used to provide both full-scan and multiple-reaction-monitoring (MRM) data. Linear retention index (LRI) ranges were used to define the MRM windows for each chemical class. Calibration solutions (internal standard: 1-fluoronaphthalene) were prepared by using an HGO sample, depleted of S compounds. Calibration information was also derived for the thiophene class (along with MRM and LRI data), even though such constituents were not present in the HGO. Linearity was satisfactory over the analyzed concentration range (1-100 mg/L); intra-day precision for the lowest calibration point was always below 17%. Accuracy was also satisfactory, with a maximum percentage error of 3.5% (absolute value) found among the S classes subjected to (semi-)quantification. The highest limit of quantification was calculated to be 299 μg/L (for the C1-benzothiophene class), while the lowest was 21 μg/L (for the C4-benzothiophene class).
Directory of Open Access Journals (Sweden)
Yonghuai Wang
Full Text Available Coronary slow-flow phenomenon (CSFP is an angiographic diagnosis characterised by a low rate of flow of contrast agent in the normal or near-normal epicardial coronary arteries. Many of the patients with CSFP may experience recurrent acute coronary syndromes. However, current clinical practice tends to underestimate the impact of CSFP due to the yet unknown effect on the cardiac function. This study was performed to evaluate left ventricular (LV and right ventricular (RV diastolic and systolic functions, using two-dimensional (2D longitudinal strain and strain rate, in patients with CSFP, and to determine the relationships between the thrombolysis in myocardial infarction (TIMI frame count (TFC and LV and RV diastolic and systolic functions.Sixty-three patients with CSFP and 45 age- and sex-matched controls without CSFP were enrolled in the study. Diagnosis of CSFP was made by TFC. LV and RV diastolic and systolic functions were assessed by 2D speckle-tracking echocardiography.LV peak early diastolic longitudinal strain rate (LSRe was lower in patients with CSFP than in controls (P = 0.01. LV peak systolic longitudinal strain (LS and LV peak systolic longitudinal strain rate (LSRs were lower in patients with CSFP than in controls (P = 0.004 and P = 0.03, respectively. There was no difference in LV ejection fraction. RV peak early diastolic longitudinal strain rate (RSRe was lower in patients with CSFP than in controls (P = 0.03. There were no differences in RV peak systolic longitudinal strain (RS, RV peak systolic longitudinal strain rate (RSRs, or RV fractional area change among the groups. The mean TFC correlated negatively with LSRe and RSRe in patients with CSFP (r = -0.26, P = 0.04 and r = -0.32, P = 0.01, respectively.LV diastolic and systolic functions were impaired in patients with CSFP. CSFP also affected RV diastolic function, but not RV systolic function.
Allan Brian G.; Owens, Lewis, R.
2006-01-01
This paper will investigate the validation of a NASA developed, Reynolds-averaged Navier-Stokes (RANS) flow solver, OVERFLOW, for a boundary-layer-ingesting (BLI) offset (S-shaped) inlet in transonic flow with passive and active flow control devices as well as the baseline case. Numerical simulations are compared to wind tunnel results of a BLI inlet conducted at the NASA Langley 0.3-Meter Transonic Cryogenic Tunnel. Comparisons of inlet flow distortion, pressure recovery, and inlet wall pressures are performed. The numerical simulations are compared to the BLI inlet data at a freestream Mach number of 0.85 and a Reynolds number of approximately 2 million based on the length of the fan-face diameter. The numerical simulations with and without wind tunnel walls are performed, quantifying effects of the tunnel walls on the BLI inlet flow measurements. The wind tunnel test evaluated several different combinations of jet locations and mass flow rates as well as a vortex generator (VG) vane case. The numerical simulations will be performed on a single jet configuration for varying actuator mass flow rates at a fix inlet mass flow condition. Validation of the numerical simulations for the VG vane case will also be performed for varying inlet mass flow rates. Overall, the numerical simulations were able to predict the baseline circumferential flow distortion, DPCPavg, very well for comparisons made within the designed operating range of the BLI inlet. However the CFD simulations did predict a total pressure recovery that was 0.01 lower than the experiment. Numerical simulations of the baseline inlet flow also showed good agreement with the experimental inlet centerline surface pressures. The vane case showed that the CFD predicted the correct trends in the circumferential distortion for varying inlet mass flow but had a distortion level that was nearly twice as large as the experiment. Comparison to circumferential distortion measurements for a 15 deg clocked 40 probe
Two-dimensional optical spectroscopy
Cho, Minhaeng
2009-01-01
Discusses the principles and applications of two-dimensional vibrational and optical spectroscopy techniques. This book provides an account of basic theory required for an understanding of two-dimensional vibrational and electronic spectroscopy.
Realizability of stationary spherically symmetric transonic accretion
Ray, A K; Ray, Arnab K.
2002-01-01
The spherically symmetric stationary transonic (Bondi) flow is considered a classic example of an accretion flow. This flow, however, is along a separatrix, which is usually not physically realizable. We demonstrate, using a pedagogical example, that it is the dynamics which selects the transonic flow.
Directory of Open Access Journals (Sweden)
Jian Zhou
2016-09-01
Full Text Available Hydraulic fracturing is a useful tool for enhancing rock mass permeability for shale gas development, enhanced geothermal systems, and geological carbon sequestration by the high-pressure injection of a fracturing fluid into tight reservoir rocks. Although significant advances have been made in hydraulic fracturing theory, experiments, and numerical modeling, when it comes to the complexity of geological conditions knowledge is still limited. Mechanisms of fluid injection-induced fracture initiation and propagation should be better understood to take full advantage of hydraulic fracturing. This paper presents the development and application of discrete particle modeling based on two-dimensional particle flow code (PFC2D. Firstly, it is shown that the modeled value of the breakdown pressure for the hydraulic fracturing process is approximately equal to analytically calculated values under varied in situ stress conditions. Furthermore, a series of simulations for hydraulic fracturing in competent rock was performed to examine the influence of the in situ stress ratio, fluid injection rate, and fluid viscosity on the borehole pressure history, the geometry of hydraulic fractures, and the pore-pressure field, respectively. It was found that the hydraulic fractures in an isotropic medium always propagate parallel to the orientation of the maximum principal stress. When a high fluid injection rate is used, higher breakdown pressure is needed for fracture propagation and complex geometries of fractures can develop. When a low viscosity fluid is used, fluid can more easily penetrate from the borehole into the surrounding rock, which causes a reduction of the effective stress and leads to a lower breakdown pressure. Moreover, the geometry of the fractures is not particularly sensitive to the fluid viscosity in the approximate isotropic model.
Bouley, Simon; François, Benjamin; Roger, Michel; Posson, Hélène; Moreau, Stéphane
2017-09-01
The present work deals with the analytical modeling of two aspects of outlet guide vane aeroacoustics in axial-flow fan and compressor rotor-stator stages. The first addressed mechanism is the downstream transmission of rotor noise through the outlet guide vanes, the second one is the sound generation by the impingement of the rotor wakes on the vanes. The elementary prescribed excitation of the stator is an acoustic wave in the first case and a hydrodynamic gust in the second case. The solution for the response of the stator is derived using the same unified approach in both cases, within the scope of a linearized and compressible inviscid theory. It is provided by a mode-matching technique: modal expressions are written in the various sub-domains upstream and downstream of the stator as well as inside the inter-vane channels, and matched according to the conservation laws of fluid dynamics. This quite simple approach is uniformly valid in the whole range of subsonic Mach numbers and frequencies. It is presented for a two-dimensional rectilinear-cascade of zero-staggered flat-plate vanes and completed by the implementation of a Kutta condition. It is then validated in sound generation and transmission test cases by comparing with a previously reported model based on the Wiener-Hopf technique and with reference numerical simulations. Finally it is used to analyze the tonal rotor-stator interaction noise in a typical low-speed fan architecture. The interest of the mode-matching technique is that it could be easily transposed to a three-dimensional annular cascade in cylindrical coordinates in a future work. This makes it an attractive alternative to the classical strip-theory approach.
Weatherill, W. H.; Sebastian, J. D.; Ehlers, F. E.
1978-01-01
Separating the velocity potential into steady and unsteady parts and linearizing the resulting unsteady equations for small disturbances was performed. The steady velocity potential was obtained first from the well known nonlinear equation for steady transonic flow. The unsteady velocity potential was then obtained from a linear differential equation in complex form with spatially varying coefficients. Since sinusoidal motion is assumed, the unsteady equation is independent of time. The results of an investigation into the relaxation-solution-instability problem was discussed. Concepts examined include variations in outer boundary conditions, a coordinate transformation so that the boundary condition at infinity may be applied to the outer boundaries of the finite difference region, and overlapping subregions. The general conclusion was that only a full direct solution in which all unknowns are obtained at the same time will avoid the solution instabilities of relaxation. An analysis of the one-dimensional form of the unsteady transonic equation was studied to evaluate errors between exact and finite difference solutions. Pressure distributions were presented for a low-aspect-ratio clipped delta wing at Mach number of 0.9 and for a moderate-aspect-ratio rectangular wing at a Mach number of 0.875.
Huizinga, Richard J.
2007-01-01
The evaluation of scour at bridges throughout the State of Missouri has been ongoing since 1991, and most of these evaluations have used one-dimensional hydraulic analysis and application of conventional scour depth prediction equations. Occasionally, the complex conditions of a site dictate a more thorough assessment of the stream hydraulics beyond a one-dimensional model. This was the case for structure A-1700, the Interstate 155 bridge crossing the Mississippi River near Caruthersville, Missouri. To assess the complex hydraulics at this site, a two-dimensional hydrodynamic flow model was used to simulate flow conditions on the Mississippi River in the vicinity of the Interstate 155 structure A-1700. The model was used to simulate flow conditions for three discharges: a flood that occurred on April 4, 1975 (the calibration flood), which had a discharge of 1,658,000 cubic feet per second; the 100-year flood, which has a discharge of 1,960,000 cubic feet per second; and the project design flood, which has a discharge of 1,974,000 cubic feet per second. The project design flood was essentially equivalent to the flood that would cause impending overtopping of the mainline levees along the Mississippi River in the vicinity of structure A-1700. Discharge and river-stage readings from the flood of April 4, 1975, were used to calibrate the flow model. The model was then used to simulate the 100-year and project design floods. Hydraulic flow parameters obtained from the three flow simulations were applied to scour depth prediction equations to determine contraction, local pier, and abutment scour depths at structure A-1700. Contraction scour and local pier scour depths computed for the project design discharge generally were the greatest, whereas the depths computed for the calibration flood were the least. The maximum predicted total scour depth (contraction and local pier scour) for the calibration flood was 66.1 feet; for the 100-year flood, the maximum predicted total
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.
Interpolation-based reduced-order modelling for steady transonic flows via manifold learning
DEFF Research Database (Denmark)
Franz, Thomas; Zimmermann, Ralf; Goertz, Stefan
2014-01-01
This paper presents a parametric reduced-order model (ROM) based on manifold learning (ML) for use in steady transonic aerodynamic applications. The main objective of this work is to derive an efficient ROM that exploits the low-dimensional nonlinear solution manifold to ensure an improved...... that has the ability to predict approximate CFD solutions at untried parameter combinations, Isomap is coupled with an interpolation method to capture the variations in parameters like the angle of attack or the Mach number. Furthermore, an approximate local inverse mapping from the reduced...
Adjoint Method and Predictive Control for 1-D Flow in NASA Ames 11-Foot Transonic Wind Tunnel
Nguyen, Nhan; Ardema, Mark
2006-01-01
This paper describes a modeling method and a new optimal control approach to investigate a Mach number control problem for the NASA Ames 11-Foot Transonic Wind Tunnel. The flow in the wind tunnel is modeled by the 1-D unsteady Euler equations whose boundary conditions prescribe a controlling action by a compressor. The boundary control inputs to the compressor are in turn controlled by a drive motor system and an inlet guide vane system whose dynamics are modeled by ordinary differential equations. The resulting Euler equations are thus coupled to the ordinary differential equations via the boundary conditions. Optimality conditions are established by an adjoint method and are used to develop a model predictive linear-quadratic optimal control for regulating the Mach number due to a test model disturbance during a continuous pitch
Moore, R. D.
1982-01-01
The effects of tip clearance on the overall and blade-element performance of an axial-flow transonic fan stage are presented. The 50-centimeter-diameter fan was tested at four tip clearances (nonrotating) from 0.061 to 0.178 centimeter. The calculated radial growth of the blades was 0.040 centimeter at design conditions. The decrease in overall stage performance with increasing clearance is attributed to the loss in rotor performance. For the rotor the effects of clearance on performance parameters extended to about 70 percent of blade span from the tip. The stage still margin based on an assumed operating line decreased from 15.3 to 0 percent as the clearance increased from 0.061 to 0.178 centimeter.
Ghosh, Shubhrangshu; Banik, Prabir
2015-07-01
In this paper, we present a complete work on steady state spherically symmetric Bondi type accretion flow in the presence of cosmological constant (Λ) in both Schwarzschild-de Sitter (SDS) and Schwarzschild anti-de Sitter (SADS) backgrounds considering an isolated supermassive black hole (SMBH), with the inclusion of a simple radiative transfer scheme, in the pseudo-general relativistic paradigm. We do an extensive analysis on the transonic behavior of the Bondi type accretion flow onto the cosmological BHs including a complete analysis of the global parameter space and the stability of flow, and do a complete study of the global family of solutions for a generic polytropic flow. Bondi type accretion flow in SADS background renders multiplicity in its transonic behavior with inner "saddle" type and outer "center" type sonic points, with the transonic solutions forming closed loops or contours. There is always a limiting value for ∣Λ∣ up to which we obtain valid stationary transonic solutions, which correspond to both SDS and SADS geometries; this limiting value moderately increases with the increasing radiative efficiency of the flow, especially correspond to Bondi type accretion flow in SADS background. Repulsive Λ suppresses the Bondi accretion rate by an order of magnitude for relativistic Bondi type accretion flow for a certain range in temperature, and with a marginal increase in the Bondi accretion rate if the corresponding accretion flow occurs in SADS background. However, for a strongly radiative Bondi type accretion flow with high mass accretion rate, the presence of cosmological constant do not much influence the corresponding Bondi accretion rate of the flow. Our analysis show that the relic cosmological constant has a substantial effect on Bondi type accretion flow onto isolated SMBHs and their transonic solutions beyond length-scale of kiloparsecs, especially if the Bondi type accretion occurs onto the host supergiant ellipticals or central
Numerical Computations of Transonic Critical AerodynamicBehavior of a Realistic Artillery Projectile
Directory of Open Access Journals (Sweden)
Ahmed F. M. Kridi
2009-01-01
Full Text Available The determination of aerodynamic coefficients by shell designers is a critical step in the development of any projectile design. Of particular interest is the determination of the aerodynamic coefficients at transonic speeds. It is in this speed regime that the critical aerodynamic behavior occurs and a rapid change in the aerodynamic coefficients is observed. Two-dimensional, transonic, flow field computations over projectiles have been made using Euler equations which were used for solution with no special treatment required. In this work a solution algorithm is based on finite difference MacCormacks technique for solving mixed subsonic-supersonic flow problem. Details of the asymmetrically located shock waves on the projectiles have been determined. Computed surface pressures have been compared with experimental data and are found to be in good agreement. The pitching moment coefficient, determined from the computed flow fields, shows the critical aerodynamic behavior observed in free flights.
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.
Putnam, L. E.; Hodges, J.
1983-01-01
The Langley Research Center of the National Aeronautics and Space Administration and the Royal Aircraft Establishment have undertaken a cooperative program to conduct an assessment of their patched viscous-inviscid interaction methods for predicting the transonic flow over nozzle afterbodies. The assessment was made by comparing the predictions of the two methods with experimental pressure distributions and boattail pressure drag for several convergent circular-arc nozzle configurations. Comparisons of the predictions of the two methods with the experimental data showed that both methods provided good predictions of the flow characteristics of nozzles with attached boundary layer flow. The RAE method also provided reasonable predictions of the pressure distributions and drag for the nozzles investigated that had separated boundary layers. The NASA method provided good predictions of the pressure distribution on separated flow nozzles that had relatively thin boundary layers. However, the NASA method was in poor agreement with experiment for separated nozzles with thick boundary layers due primarily to deficiencies in the method used to predict the separation location.
Energy Technology Data Exchange (ETDEWEB)
Casalis, G.; Robinet, J.Ch. [Office National d`Etudes et de Recherches Aerospatiales (ONERA), 31 - Toulouse (France). Centre d`Etudes et de Recherches
1998-01-01
The purpose of this paper is to give the first results of a linear stability analysis which has been applied to the problem of shock oscillations in a transonic diffuser flow. The mean flow is calculated with a numerical code solving the averaged Navier-Stockes equations, but the proposed stability approach is limited to the core region where the viscous effects can be neglected. In order to validate the present approach, the results are compared with Sahben`s experimental results and those numerically obtained Liou and Coakley. It is the first time that these published results are compared with a simple linear stability analysis. As demonstrated below, the shock motion spectra have been correctly reproduced and the frequencies of 200 Hz and 300 Hz have been clearly obtained for the diffuser lengths of l/h = 13 and l/h 8.6 respectively. As far as stability of the mean flow is concerned, the temporal amplification rate is always negative, the mean flow is therefore linearly stable. Finally, the amplitude and phase of the fluctuating pressure have been compared. The phase of example is in very good agreement with the experimental results. This can prove that at least in some cases, self-sustained shock oscillations can be explained and predicted with an inviscid linear stability analysis. (authors) 11 refs.
Two-dimensional magma-repository interactions
Bokhove, O.
2001-01-01
Two-dimensional simulations of magma-repository interactions reveal that the three phases --a shock tube, shock reflection and amplification, and shock attenuation and decay phase-- in a one-dimensional flow tube model have a precursor. This newly identified phase ``zero'' consists of the impact of
Jeništa, J.; Takana, H.; Nishiyama, H.; Bartlová, M.; Aubrecht, V.; Křenek, P.; Hrabovský, M.; Kavka, T.; Sember, V.; Mašláni, A.
2011-11-01
This paper presents a numerical investigation of characteristics and processes in the worldwide unique type of thermal plasma generator with combined stabilization of arc by argon flow and water vortex, the so-called hybrid-stabilized arc. The arc has been used for spraying of ceramic or metallic particles and for pyrolysis of biomass. The net emission coefficients as well as the partial characteristics methods for radiation losses from the argon-water arc are employed. Calculations for 300-600 A with 22.5-40 standard litres per minute (slm) of argon reveal transition from a transonic plasma flow for 400 A to a supersonic one for 600 A with a maximum Mach number of 1.6 near the exit nozzle of the plasma torch. A comparison with available experimental data near the exit nozzle shows very good agreement for the radial temperature profiles. Radial velocity profiles calculated 2 mm downstream of the nozzle exit show good agreement with the profiles determined from the combination of calculation and experiment (the so-called integrated approach). A recent evaluation of the Mach number from the experimental data for 500 and 600 A confirmed the existence of the supersonic flow regime.
Isaev, Sergey; Baranov, Paul; Popov, Igor; Sudakov, Alexander; Usachov, Alexander
2017-03-01
The modified SST model (2005) is verified using Rodi- Leschziner-Isaev's approach and the multiblock computational technologies are validated in the VP2/3 code on different-structure overlapping grids by comparing the numerical predictions with the experimental data on transonic flow around an NACA0012 airfoil at an angle of attack of 4o for M=0.7 and Re=4×106. It is proved that the aerodynamic characteristics of a thick (20% of the chord) MQ airfoil mounted at an angle of attack of 2o for Re=107 and over the Mach number range 0.3-0.55 are significantly improved because an almost circular small-size (0.12) vortex cell with a defined volumetric flow rate coefficient of 0.007 during slot suction has been located on the upper airfoil section and an intense trapped vortex has been formed in it. A detailed analysis of buffeting within the self-oscillatory regime of flow around the MQ airfoil with a vortex cell has demonstrated the periodic changes in local and integral characteristics; the lift and the aerodynamic efficiency remain quite high, but inferior to the similar characteristics at M=0.55. It is found that the vortex cell at M=0.7 is inactive, and the aerodynamic characteristics of the MQ airfoil with a vortex cell are close to those of a smooth airfoil without a cell.
Goldman, Louis J.
1993-01-01
An advanced laser anemometer (LA) was used to measure the axial and tangential velocity components in an annular cascade of turbine stator vanes operating at transonic flow conditions. The vanes tested were based on a previous redesign of the first-stage stator in a two-stage turbine for a high-bypass-ratio engine. The vanes produced 75 deg of flow turning. Tests were conducted on a 0.771-scale model of the engine-sized stator. The advanced LA fringe system employed an extremely small 50-micron diameter probe volume. Window correction optics were used to ensure that the laser beams did not uncross in passing through the curved optical access port. Experimental LA measurements of velocity and turbulence were obtained at the mean radius upstream of, within, and downstream of the stator vane row at an exit critical velocity ratio of 1.050 at the hub. Static pressures were also measured on the vane surface. The measurements are compared, where possible, with calculations from a three-dimensional inviscid flow analysis. Comparisons were also made with the results obtained previously when these same vanes were tested at the design exit critical velocity ratio of 0.896 at the hub. The data are presented in both graphical and tabulated form so that they can be readily compared against other turbomachinery computations.
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
Taking the distributing calculation of velocity and concentration as an example, the paper established a series of governing equations by the vorticity-stream function method, and dispersed the equations by the finite differencing method. After figuring out the distribution field of velocity, the paper also calculated the concentration distribution in sedimentation tank by using the two-dimensional concentration transport equation. The validity and feasibility of the numerical method was verified through comparing with experimental data. Furthermore, the paper carried out a tentative exploration into the application of numerical simulation of sedimentation tanks.
Kadomtsev−Petviashvili equation for a flow of highly nonisothermal collisionless plasma
Energy Technology Data Exchange (ETDEWEB)
Movsesyants, Yu. B., E-mail: yumovsesyants@gmail.com [All-Russian Electrotechnical Institute (Russian Federation); Rukhadze, A. A., E-mail: rukh@fpl.gpi.ru [Russian Academy of Sciences, Prokhorov General Physics Institute (Russian Federation); Tyuryukanov, P. M. [All-Russian Electrotechnical Institute (Russian Federation)
2016-01-15
It is shown that the equations of two-fluid electrodynamics for a cold ions flow and Boltzmann electrons in the vicinity of the ion-sound point can be reduced to the Kadomtsev−Petviashvili equation. Examples of two-dimensional equilibria with pole singularities obtained by exactly solving the equations are presented. An exact self-similar solution describing a two-dimensional transonic flow and having no pole singularities is found.
Computer program calculates transonic velocities in turbomachines
Katsanis, T.
1971-01-01
Computer program, TSONIC, combines velocity gradient and finite difference methods to obtain numerical solution for ideal, transonic, compressible flow for axial, radial, or mixed flow cascade of turbomachinery blades.
Energy Technology Data Exchange (ETDEWEB)
Handa, T.; Miyazato, Y.; Masuda, M.; Matsuo, K. [Kyushu University, Fukuoka (Japan)
2000-05-25
Mechanism of self-excited shock oscillation in two-dimensional transonic diffuser flow is investigated experimentally. The diffuser used in this work is composed of the fiat top wall and the curved bottom wall. Time-sequence of shock location is recorded by the high speed CCD camera combined with schlieren system, together with simultaneous measurements of static pressure fluctuations along the top wall. The pressure fluctuations at many locations on the side wall are also measured simultaneously. As a result, it is found that disturbances which induce shock oscillation are propagating upstream from downstream portion of the shock wave where the boundary layer behaves unsteadily and the most violently. Furthermore, vortices generated by the shock oscillation are observed to be convected downstream. The shock oscillation is explained to be sustained by the upstream-propagating disturbances and the downstream-convected vortices. (author)
Energy Technology Data Exchange (ETDEWEB)
Wu, Bin; Li, Huiying; Du, Xiaoming; Zhong, Lirong; Yang, Bin; Du, Ping; Gu, Qingbao; Li, Fasheng
2016-02-01
During the process of surfactant enhanced aquifer remediation (SEAR), free phase dense non-aqueous phase liquid (DNAPL) may be mobilized and spread. The understanding of the impact of DNAPL spreading on the SEAR remediation is not sufficient with its positive effect infrequently mentioned. To evaluate the correlation between DNAPL spreading and remediation efficiency, a two-dimensional sandbox apparatus was used to simulate the migration and dissolution process of 1,2-DCA (1,2-dichloroethane) DNAPL in SEAR. Distribution area of DNAPL in the sandbox was determined by digital image analysis and correlated with effluent DNAPL concentration. The results showed that the effluent DNAPL concentration has significant positive linear correlation with the DNAPL distribution area, indicating the mobilization of DNAPL could improve remediation efficiency by enlarging total NAPL-water interfacial area for mass transfer. Meanwhile, the vertical migration of 1,2-DCA was limited within the boundary of aquifer in all experiments, implying that by manipulating injection parameters in SEAR, optimal remediation efficiency can be reached while the risk of DNAPL vertical migration is minimized. This study provides a convenient visible and quantitative method for the optimization of parameters for SEAR project, and an approach of rapid predicting the extent of DNAPL contaminant distribution based on the dissolved DNAPL concentration in the extraction well.
Wu, Bin; Li, Huiying; Du, Xiaoming; Zhong, Lirong; Yang, Bin; Du, Ping; Gu, Qingbao; Li, Fasheng
2016-02-01
During the process of surfactant enhanced aquifer remediation (SEAR), free phase dense non-aqueous phase liquid (DNAPL) may be mobilized and spread. The understanding of the impact of DNAPL spreading on the SEAR remediation is not sufficient with its positive effect infrequently mentioned. To evaluate the correlation between DNAPL spreading and remediation efficiency, a two-dimensional sandbox apparatus was used to simulate the migration and dissolution process of 1,2-DCA (1,2-dichloroethane) DNAPL in SEAR. Distribution area of DNAPL in the sandbox was determined by digital image analysis and correlated with effluent DNAPL concentration. The results showed that the effluent DNAPL concentration has significant positive linear correlation with the DNAPL distribution area, indicating the mobilization of DNAPL could improve remediation efficiency by enlarging total NAPL-water interfacial area for mass transfer. Meanwhile, the vertical migration of 1,2-DCA was limited within the boundary of aquifer in all experiments, implying that by manipulating injection parameters in SEAR, optimal remediation efficiency can be reached while the risk of DNAPL vertical migration is minimized. This study provides a convenient visible and quantitative method for the optimization of parameters for SEAR project, and an approach of rapid predicting the extent of DNAPL contaminant distribution based on the dissolved DNAPL concentration in the extraction well.
Reddy, T. S. R.; Srivastava, R.; Mehmed, Oral
2002-01-01
An aeroelastic analysis system for flutter and forced response analysis of turbomachines based on a two-dimensional linearized unsteady Euler solver has been developed. The ASTROP2 code, an aeroelastic stability analysis program for turbomachinery, was used as a basis for this development. The ASTROP2 code uses strip theory to couple a two dimensional aerodynamic model with a three dimensional structural model. The code was modified to include forced response capability. The formulation was also modified to include aeroelastic analysis with mistuning. A linearized unsteady Euler solver, LINFLX2D is added to model the unsteady aerodynamics in ASTROP2. By calculating the unsteady aerodynamic loads using LINFLX2D, it is possible to include the effects of transonic flow on flutter and forced response in the analysis. The stability is inferred from an eigenvalue analysis. The revised code, ASTROP2-LE for ASTROP2 code using Linearized Euler aerodynamics, is validated by comparing the predictions with those obtained using linear unsteady aerodynamic solutions.
Jump conditions in transonic equilibria
Energy Technology Data Exchange (ETDEWEB)
Guazzotto, L.; Betti, R. [Department of Mechanical Engineering, University of Rochester, Rochester, New York 14627 (United States); Jardin, S. C. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540 (United States)
2013-04-15
In the present paper, the numerical calculation of transonic equilibria, first introduced with the FLOW code in Guazzotto et al.[Phys. Plasmas 11, 604 (2004)], is critically reviewed. In particular, the necessity and effect of imposing explicit jump conditions at the transonic discontinuity are investigated. It is found that 'standard' (low-{beta}, large aspect ratio) transonic equilibria satisfy the correct jump condition with very good approximation even if the jump condition is not explicitly imposed. On the other hand, it is also found that high-{beta}, low aspect ratio equilibria require the correct jump condition to be explicitly imposed. Various numerical approaches are described to modify FLOW to include the jump condition. It is proved that the new methods converge to the correct solution even in extreme cases of very large {beta}, while they agree with the results obtained with the old implementation of FLOW in lower-{beta} equilibria.
Zamuraev, V. P.; Kalinina, A. P.
2017-05-01
Mathematical simulation of the forced vibrations of a surface segment on one side of an aerofoil on the shock wave formed in the transonic flow around it has been performed. The influence of the vibrations of this segment in a wide frequency range on the quantitative and qualitative characteristics of the wave drag and lift of the aerofoil were investigated for the case of maximum amplitude of oscillations of the velocity of movement of the vibrating segment of the aerofoil, close to the velocity of the incident flow. It is shown that an additional lifting force arises in this case.
Institute of Scientific and Technical Information of China (English)
A. Kluwick
2009-01-01
This article is the written version of a lecture given at the Festkolloquium on the occasion of Prof. Dr.-Ing.Dr.techn. E.h. Jurgen Zierep's 80th birthday held at the Universitat Karlsrube, 21 January 2009. It deals with laminar viscous inviscid interactions in transonic narrow channel flows. Special emphasis is placed on the internal structure of pseudo-shocks and properties of nozzle flows. Also, it is shown that the theory, first formulated for perfect gases, can easily be extended to the case of general single phase fluids.
Photographic Study of Obstacle—Induced Disturbations of Transonic Turbine Cascade Flow
Institute of Scientific and Technical Information of China (English)
A.Szumowski; J.Amecke; 等
1998-01-01
In this paper,the cascade flow structures influenced by the position of the obstacle inserted in the downstream flow are presented.The experiments were conducted in a stationary cascade wind tunnel,and the results can not be attributed directly to the real rotor channel flow.Nevertheless,they show qualitatively the very complicated flow pattern in the region of the rotor-stator interaction.They explain the existence of very strong variation of the blade loading and high losses of cascade flow due to the rotor-stator interaction noted by previous authors.
Effect of Nonequilibrium Condensation of Moist Air on Transonic Flow Fields
Institute of Scientific and Technical Information of China (English)
KatsumiShimamoto
2000-01-01
When condensation occurs in a supersonic flow field,the flow in affected by the latent heat released.In the present study,a condensing flow was produced by an expansion of moist air in nozzle with circular bump odels and shock waves occurred in the supersonic parts of the flow fields.The expereimental investigations were carried out to show the effects of initial conditions in the reservoir and nozzle geometries on the shock wave characteristics and the turbulences in the flow fields.Furthermore,in order to clarify the effect of condensation on the flow fields with shock waves,navier-Stokes equations were solved numerically using a 3rd-order MUSCL type TVD finite-difference scheme with a second order fractional step for time integraton,As a result,the effect of condensation on the aspect of flow field has been clarified.
Van den Hove, L E; Meeus, P; Derom, A; Demuynck, H; Verhoef, G E; Vandenberghe, P; Boogaerts, M A
1998-06-01
The distribution of 27 T-, B-, and natural killer-cell subsets in the peripheral blood of 40 patients with multiple myeloma (MM), ten patients with monoclonal gammopathy of undetermined significance (MGUS), and 40 healthy donors was investigated by means of classical univariate statistics and advanced multivariate data-analytical techniques. The latter approach was used to describe, represent, and analyze lymphocyte subset distribution in a two-dimensional correlation biplot, allowing comparison of complex lymphocyte profiles (i.e., compound lymphocyte subset distributions) of individual subjects rather than isolated subset values of selected patient and/or donor groups. The correlation biplot revealed that, in accordance with the univariate statistics, the MM patients were characterized by marked shifts towards CD8+, CD57+, CD62L-, CD(16+56)+, and HLA-DR+ T cells, suggesting in vivo immune activation. The activation profile was most markedly observed in treated MM patients in the advanced disease stage category. The lymphocyte profiles of MGUS patients were heterogeneous, with approximately half of them located in the swarm of MM patients and the other half in the swarm of healthy donors. Although the univariate statistics revealed significant differences between MGUS patients and healthy donors only within the B-cell compartment, the correlation biplot revealed that two MGUS patients clearly had a typical T-cell activation profile similar to that of the MM patients. One MGUS patient with a T-cell activation profile progressed 13 months later to a stage IA MM and required chemotherapy. A marked lymphocyte profile shift in one MM patient was associated with terminal and aggressive disease transformation. Our study illustrates further the practical use of correlation biplots for the detection of aberrant lymphocyte profiles and/or profile shifts in individual patients.
Two-dimensional liquid chromatography
DEFF Research Database (Denmark)
Græsbøll, Rune
of this thesis is on online comprehensive two-dimensional liquid chromatography (online LC×LC) with reverse phase in both dimensions (online RP×RP). Since online RP×RP has not been attempted before within this research group, a significant part of this thesis consists of knowledge and experience gained...
Mantič-Lugo, Vladislav; Gallaire, François
2016-12-01
Selective noise amplifiers are characterized by large linear amplification to external perturbations in a particular frequency range despite their global linear stability. Applying a stochastic forcing with increasing amplitude, the response undergoes a strong nonlinear saturation when compared to the linear estimation. Building upon our previous work, we introduce a predictive model that describes this nonlinear dynamics, and we apply it to a canonical example of selective noise amplifiers: the backward-facing step flow. Rewriting conveniently the stochastic forcing and response in the frequency domain, the model consists in a mean flow equation coupled to the linear response to forcing at each frequency. This coupling is attained by the Reynolds stress, which is constructed by the integral in frequency of the independent responses. We generalize the model for a response to a white noise forcing δ -correlated in space and time restricting the flow dynamics to its most energetic patterns calculated from the optimal harmonic forcing and response of the flow. The model estimates accurately the response saturation when compared to direct numerical simulations, and it correctly approximates the structure of the response and the mean flow modification. It also shows that the response undergoes a selective process governed by the nonlinear gain, which promotes a response structure with an approximately single frequency and wavelength in the whole domain. These results suggest that the mean flow modification by the Reynolds stress is the key nonlinearity in the saturation process of the response to white noise.
Suder, K. L.; Hathaway, M. D.; Okiishi, T. H.; Strazisar, A. J.; Adamczyk, J. J.
1987-01-01
This two-part paper presents laser anemometer measurements of the unsteady velocity field within the stator row of a transonic axial-flow fan. The objective is to provide additional insight into unsteady blade-row interactions within high speed compressors which affect stage efficiency, energy transfer, and other design considerations. Part 1 describes the measurement and analysis techniques used for resolving the unsteady flow field features. The ensemble-average and variance of the measured velocities are used to identify the rotor wake generated and unresolved unsteadiness, respectively. (Rotor wake generated unsteadiness refers to the unsteadiness generated by the rotor wake velocity deficit and the term unresolved unsteadiness refers to all remaining contributions to unsteadiness such as vortex shedding, turbulence, mass flow fluctuations, etc.). A procedure for calculating auto and cross correlations of the rotor wake generated and unresolved unsteady velocity fluctuations is described. These unsteady-velocity correlations have significance since they also result from a decomposition of the Navier-Stokes equations. This decomposition of the Navier-Stokes equations resulting in the velocity correlations used to describe the unsteady velocity field will also be outlined in this paper.
Suder, K. L.; Strazisar, A. J.; Adamczyk, J. J.; Hathaway, M. D.; Okiishi, T. H.
1987-01-01
This two-part paper presents laser anemometer measurements of the unsteady velocity field within the stator row of a transonic axial-flow fan. The objective is to provide additional insight into unsteady blade-row interactions within highspeed compressors which affect stage efficiency, energy transfer, and other design considerations. Part 1 describes the measurement and analysis techniques used for resolving the unsteady flow field features. The ensemble-average and variance of the measured velocities are used to identify the rotor wake generated and unresolved unsteadiness, respectively. (Rotor wake generated unsteadiness refers to the unsteadiness generated by the rotor wake velocity deficit and the term unresolved unsteadiness refers to all remaining contributions to unsteadiness such as vortex shedding, turbulence, mass flow fluctutions, etc.). A procedure for calculating auto and cross correlations of the rotor wake generated and unresolved unsteady velocity fluctuations is described. These unsteady-velocity correlations have significance since they also result from a decomposition of the Navier-Stokes equations. This decomposition of the Navier-Stokes equations resulting in the velocity correlations used to describe the unsteady velocity field will also be outlined in this paper.
Towards two-dimensional search engines
Ermann, Leonardo; Shepelyansky, Dima L
2011-01-01
We study the statistical properties of various directed networks using ranking of their nodes based on the dominant vectors of the Google matrix known as PageRank and CheiRank. On average PageRank orders nodes proportionally to a number of ingoing links, while CheiRank orders nodes proportionally to a number of outgoing links. In this way the ranking of nodes becomes two-dimensional that paves the way for development of two-dimensional search engines of new type. Information flow properties on PageRank-CheiRank plane are analyzed for networks of British, French and Italian Universities, Wikipedia, Linux Kernel, gene regulation and other networks. Methods of spam links control are also analyzed.
Toward two-dimensional search engines
Ermann, L.; Chepelianskii, A. D.; Shepelyansky, D. L.
2012-07-01
We study the statistical properties of various directed networks using ranking of their nodes based on the dominant vectors of the Google matrix known as PageRank and CheiRank. On average PageRank orders nodes proportionally to a number of ingoing links, while CheiRank orders nodes proportionally to a number of outgoing links. In this way, the ranking of nodes becomes two dimensional which paves the way for the development of two-dimensional search engines of a new type. Statistical properties of information flow on the PageRank-CheiRank plane are analyzed for networks of British, French and Italian universities, Wikipedia, Linux Kernel, gene regulation and other networks. A special emphasis is done for British universities networks using the large database publicly available in the UK. Methods of spam links control are also analyzed.
Ultra-Low-Power High-Frequency Micro-Vortex Generators for Transonic Flow Control Project
National Aeronautics and Space Administration — Active flow control to prevent or delay boundary layer separation dramatically improves the performance of air vehicles in critical regions of the flight envelope....
Directory of Open Access Journals (Sweden)
V. Rajesh
2014-08-01
Full Text Available The interaction of free convection with thermal radiation of a viscous incompressible unsteady flow past a vertical plate with ramped wall temperature and mass diffusion is presented here, taking into account the homogeneous chemical reaction of first order. The fluid is gray, absorbing-emitting but non-scattering medium and the Rosseland approximation is used to describe the radiative flux in the energy equation. The dimensionless governing equations are solved using an implicit finite-difference method of the Crank-Nicolson type, which is stable and convergent. The velocity profiles are compared with the available theoretical solution and are found to be in good agreement. Numerical results for the velocity, the temperature, the concentration, the local and average skin friction, the Nusselt number and Sherwood number are shown graphically. This work has wide application in chemical and power engineering and also in the study of vertical air flow into the atmosphere. The present results can be applied to an important class of flows in which the driving force for the flow is provided by combination of the thermal and chemical species diffusion effects.
Lusso, Christelle; Ern, Alexandre; Bouchut, François; Mangeney, Anne; Farin, Maxime; Roche, Olivier
2017-03-01
This work is devoted to numerical modeling and simulation of granular flows relevant to geophysical flows such as avalanches and debris flows. We consider an incompressible viscoplastic fluid, described by a rheology with pressure-dependent yield stress, in a 2D setting with a free surface. We implement a regularization method to deal with the singularity of the rheological law, using a mixed finite element approximation of the momentum and incompressibility equations, and an arbitrary Lagrangian Eulerian (ALE) formulation for the displacement of the domain. The free surface is evolved by taking care of its deposition onto the bottom and of preventing it from folding over itself. Several tests are performed to assess the efficiency of our method. The first test is dedicated to verify its accuracy and cost on a one-dimensional simple shear plug flow. On this configuration we setup rules for the choice of the numerical parameters. The second test aims to compare the results of our numerical method to those predicted by an augmented Lagrangian formulation in the case of the collapse and spreading of a granular column over a horizontal rigid bed. Finally we show the reliability of our method by comparing numerical predictions to data from experiments of granular collapse of both trapezoidal and rectangular columns over horizontal rigid or erodible granular bed made of the same material. We compare the evolution of the free surface, the velocity profiles, and the static-flowing interface. The results show the ability of our method to deal numerically with the front behavior of granular collapses over an erodible bed.
Two dimensional unstable scar statistics.
Energy Technology Data Exchange (ETDEWEB)
Warne, Larry Kevin; Jorgenson, Roy Eberhardt; Kotulski, Joseph Daniel; Lee, Kelvin S. H. (ITT Industries/AES Los Angeles, CA)
2006-12-01
This report examines the localization of time harmonic high frequency modal fields in two dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This paper examines the enhancements for these unstable orbits when the opposing mirrors are both convex and concave. In the latter case the construction includes the treatment of interior foci.
Juday, Richard D.
1992-01-01
Modified vernier scale gives accurate two-dimensional coordinates from maps, drawings, or cathode-ray-tube displays. Movable circular overlay rests on fixed rectangular-grid overlay. Pitch of circles nine-tenths that of grid and, for greatest accuracy, radii of circles large compared with pitch of grid. Scale enables user to interpolate between finest divisions of regularly spaced rule simply by observing which mark on auxiliary vernier rule aligns with mark on primary rule.
Ross, Mark Hamilton
Experimental and computational studies were conducted to study the role of the tip leakage flow in axial compressor stall and the relationship between the tip clearance flow flow field and surge margin extension from circumferential groove casing treatment. The CFD results were used to identify the existence of an interface between the approach ow and the tip-leakage flow. The experiments used a surface streaking visualization method to identify the time-averaged location of this interface as a line of zero axial shear stress at the casing. The axial position of this line, denoted xzs, moved upstream with decreasing ow coefficient in both the experiments and computations. The line was consistently located at the rotor leading edge plane at the stalling flow coefficient, regardless of in flow boundary condition. These results were successfully modeled using a control volume approach that balanced the reverse axial momentum ux of the tip-leakage flow with the momentum flux of the approach fluid. Non-uniform tip clearance measurements demonstrated that movement of the interface upstream of the rotor leading edge plane leads to the generation of short length scale rotating disturbances. Therefore, stall was interpreted as a critical point in the momentum flux balance of the approach ow and the reverse axial momentum flux of the tip-leakage flow. Experimental measurements of surge margin extension from seven CGCT configurations with a fixed groove geometry demonstrated that the contribution of individual grooves in a multi-groove casing to surge margin extension is an (a) additive and (b) linear function of the smooth wall tip clearance axial momentum ux at the location of a each groove. Extending the axial momentum model to include the in uence of a CGCT showed that circumferential grooves reduce the tip leakage flow axial momentum through radial transport. The equivalent force due to a circumferential groove was demonstrated to be related to the smooth wall tip
Institute of Scientific and Technical Information of China (English)
Chai Zhen-Hua; Shi Bao-Chang; Zheng Lin
2006-01-01
By coupling the non-equilibrium extrapolation scheme for boundary condition with the multi-relaxation-time lattice Boltzmann method, this paper finds that the stability of the multi-relaxation-time model can be improved greatly, especially on simulating high Reynolds number (Re) flow. As a discovery, the super-stability analysed by Lallemand and Luo is verified and the complex structure of the cavity flow is also exhibited in our numerical simulation when Re is high enough. To the best knowledge of the authors, the maximum of Re which has been investigated by direct numerical simulation is only around 50 000 in the literature; however, this paper can readily extend the maximum to 1000 000 with the above combination.
Messaris, G. T.; Papastavrou, C. A.; Loukopoulos, V. C.; Karahalios, G. T.
2009-08-01
A new finite-difference method is presented for the numerical solution of the Navier-Stokes equations of motion of a viscous incompressible fluid in two (or three) dimensions and in the primitive-variable formulation. Introducing two auxiliary functions of the coordinate system and considering the form of the initial equation on lines passing through the nodal point (x0, y0) and parallel to the coordinate axes, we can separate it into two parts that are finally reduced to ordinary differential equations, one for each dimension. The final system of linear equations in n-unknowns is solved by an iterative technique and the method converges rapidly giving satisfactory results. For the pressure variable we consider a pressure Poisson equation with suitable Neumann boundary conditions. Numerical results, confirming the accuracy of the proposed method, are presented for configurations of interest, like Poiseuille flow and the flow between two parallel plates with step under the presence of a pressure gradient.
Institute of Scientific and Technical Information of China (English)
杨延强; 易维明; 李志合; 柏雪源; 李永军
2012-01-01
In the cold PIV (particle image velocimetry) system of the laminar entrained flow reactor, the relative position between the camera and the measuring tube was an important condition to ensure accurate test data. To make the PIV operation more convenient, accurate, and fast in the test, two-dimensional PIV automatic control system was designed. And the reliability of the system was tested in the cold simulation equipment of laminar flow furnace, compared with no using two-dimensional PIV automatic control system, the results showed that in different sections of the measuring tube, the particle speed of the axial center achieves a smooth transition, and eliminates the jump change; when collection distance is 350mm and main air flow rate is 1. 5 mVh, the relative error of particle residence time is 9. 218% ; and the operation saves time and effort in the test process. These suggested that the two-dimensional PIV automatic control system could satisfy the cold test of the laminar entrained flow reactor needs, achieve uniform and continuous test, reduce human error and improve the accuracy of test data.%在层流炉冷态粒子图像测速( PIV)系统中,相机与测量管的相对位置是保证试验数据精确的重要条件.为使试验过程中整个PIV系统操作起来更加方便、准确、快捷,设计了二维PIV自动控制系统,并在层流炉冷态模拟装置上对该系统的可靠性进行了试验验证.与没有使用二维PIV自动控制系统之前的试验结果相比:各测量段颗粒的轴向中心速度相互之间的衔接实现了平滑过渡,消除了跳跃性变化；收集距离为350 mm,主气流流量为1.5 m3/h时,层流炉内颗粒停留时间的相对误差为9.218％.说明该二维PIV自动控制系统能够满足层流炉冷态试验需要,实现了均匀、连续拍摄,减少了人为误差,提高了试验数据的准确性.
Mysko, Stephen J.; Chyu, Wei J.; Stortz, Michael W.; Chow, Chuen-Yen
1993-01-01
In this work, the computation of combined external/internal transonic flow on the complex forebody/inlet configuration of the AV-8B Harrier II is performed. The actual aircraft has been measured and its surface and surrounding domain, in which the fuselage and inlet have a common wall, have been described using structured grids. The 'thin-layer' Navier-Stokes equations were used to model the flow along with the Chimera embedded multi-block technique. A fully conservative, alternating direction implicit (ADI), approximately factored, partially fluxsplit algorithm was employed to perform the computation. Comparisons to some experimental wind tunnel data yielded good agreement for flow at zero incidence and angle of attack. The aim of this paper is to provide a methodology or computational tool for the numerical solution of complex external/internal flows.
Stepped Tip Gap Effects on a Transonic Axial-Flow Compressor Rotor
1997-06-01
Along Vortex Trajectory [Extracted from Suder and Celestina [86] ] ........................... 20 Figure 10. Static Pressure of ADLARF Rotor (Peak...Suder and Celestina [86] , Puterbaugh [71] , Puterbaugh and Brendel [72] , Cybyk et al. [24] , and Sellin et al. [81] provide detailed characterization...like flow forming coincident with the smaller secondary normal shock (Figure 4). Suder and Celestina [86] used a Navier-Stokes solver to detail the
Simulations of transonic shock-tube flow with a model micro-cylinder in the driver.
Liu, Yi; Kendall, Mark A F
2007-02-01
A unique hand-held needle-free powder injection system, using a transient shock-tube flow to deliver powder genes and drugs into human skin for a wide range of treatments, has been proposed. In the development of such devices, a strong non-linear phenomenon, possibly shock process instead of unsteady expansion waves, was observed in the driver portion of the shock-tube flow in the presence of a gas micro-cylinder. In this paper, we further investigate effects of a model micro-cylinder in the driver on the gas dynamics of a prototype clinical device numerically. To accurately simulate such complex shock-tube flows, an efficient numerical solver, MIFVS, is extended to incorporate with a transition-modified turbulence model. Comparison with experimental measurements shows that the extended MIFVS accurately predicts pressure traces in both laminar and turbulent regimes. The separation zone due to a strong non-linear process is properly captured via such transition-modified turbulence model. Numerical investigations and discoveries are presented and discussed.
Kardan, Farshid; Cheng, Wai-Chi; Baverel, Olivier; Porté-Agel, Fernando
2016-04-01
Understanding, analyzing and predicting meteorological phenomena related to urban planning and built environment are becoming more essential than ever to architectural and urban projects. Recently, various version of RANS models have been established but more validation cases are required to confirm their capability for wind flows. In the present study, the performance of recently developed RANS models, including the RNG k-ɛ , SST BSL k-ω and SST ⪆mma-Reθ , have been evaluated for the flow past a single block (which represent the idealized architecture scale). For validation purposes, the velocity streamlines and the vertical profiles of the mean velocities and variances were compared with published LES and wind tunnel experiment results. Furthermore, other additional CFD simulations were performed to analyze the impact of regular/irregular mesh structures and grid resolutions based on selected turbulence model in order to analyze the grid independency. Three different grid resolutions (coarse, medium and fine) of Nx × Ny × Nz = 320 × 80 × 320, 160 × 40 × 160 and 80 × 20 × 80 for the computational domain and nx × nz = 26 × 32, 13 × 16 and 6 × 8, which correspond to number of grid points on the block edges, were chosen and tested. It can be concluded that among all simulated RANS models, the SST ⪆mma-Reθ model performed best and agreed fairly well to the LES simulation and experimental results. It can also be concluded that the SST ⪆mma-Reθ model provides a very satisfactory results in terms of grid dependency in the fine and medium grid resolutions in both regular and irregular structure meshes. On the other hand, despite a very good performance of the RNG k-ɛ model in the fine resolution and in the regular structure grids, a disappointing performance of this model in the coarse and medium grid resolutions indicates that the RNG k-ɛ model is highly dependent on grid structure and grid resolution. These quantitative validations are essential
Directory of Open Access Journals (Sweden)
Szymkiewicz Adam
2015-09-01
Full Text Available Flow in unsaturated porous media is commonly described by the Richards equation. This equation is strongly nonlinear due to interrelationships between water pressure head (negative in unsaturated conditions, water content and hydraulic conductivity. The accuracy of numerical solution of the Richards equation often depends on the method used to estimate average hydraulic conductivity between neighbouring nodes or cells of the numerical grid. The present paper discusses application of the computer simulation code VS2DI to three test problems concerning infiltration into an initially dry medium, using various methods for inter-cell conductivity calculation (arithmetic mean, geometric mean and upstream weighting. It is shown that the influence of the averaging method can be very large for coarse grid, but that it diminishes as cell size decreases. Overall, the arithmetic average produced the most reliable results for coarse grids. Moreover, the difference between results obtained with various methods is a convenient indicator of the adequacy of grid refinement.
Szymkiewicz, Adam; Tisler, Witold; Burzyński, Kazimierz
2015-09-01
Flow in unsaturated porous media is commonly described by the Richards equation. This equation is strongly nonlinear due to interrelationships between water pressure head (negative in unsaturated conditions), water content and hydraulic conductivity. The accuracy of numerical solution of the Richards equation often depends on the method used to estimate average hydraulic conductivity between neighbouring nodes or cells of the numerical grid. The present paper discusses application of the computer simulation code VS2DI to three test problems concerning infiltration into an initially dry medium, using various methods for inter-cell conductivity calculation (arithmetic mean, geometric mean and upstream weighting). It is shown that the influence of the averaging method can be very large for coarse grid, but that it diminishes as cell size decreases. Overall, the arithmetic average produced the most reliable results for coarse grids. Moreover, the difference between results obtained with various methods is a convenient indicator of the adequacy of grid refinement.
Two-dimensional liquid chromatography
DEFF Research Database (Denmark)
Græsbøll, Rune
Two-dimensional liquid chromatography has received increasing interest due to the rise in demand for analysis of complex chemical mixtures. Separation of complex mixtures is hard to achieve as a simple consequence of the sheer number of analytes, as these samples might contain hundreds or even...... dimensions. As a consequence of the conclusions made within this thesis, the research group has, for the time being, decided against further development of online LC×LC systems, since it was not deemed ideal for the intended application, the analysis of the polar fraction of oil. Trap-and...
Fuchs, L.; Schmeling, H.
2013-08-01
A key to understand many geodynamic processes is studying the associated large deformation fields. Finite deformation can be measured in the field by using geological strain markers giving the logarithmic strain f = log 10(R), where R is the ellipticity of the strain ellipse. It has been challenging to accurately quantify finite deformation of geodynamic models for inhomogeneous and time-dependent large deformation cases. We present a new formulation invoking a 2-D marker-in-cell approach. Mathematically, one can describe finite deformation by a coordinate transformation to a Lagrangian reference frame. For a known velocity field the deformation gradient tensor, F, can be calculated by integrating the differential equation DtFij = LikFkj, where L is the velocity gradient tensor and Dt the Lagrangian derivative. The tensor F contains all information about the minor and major semi-half axes and orientation of the strain ellipse and the rotation. To integrate the equation centrally in time and space along a particle's path, we use the numerical 2-D finite difference code FDCON in combination with a marker-in-cell approach. For a sufficiently high marker density we can accurately calculate F for any 2-D inhomogeneous and time-dependent creeping flow at any point for a deformation f up to 4. Comparison between the analytical and numerical solution for the finite deformation within a Poiseuille-Couette flow shows an error of less than 2 per cent for a deformation up to f = 1.7. Moreover, we determine the finite deformation and strain partitioning within Rayleigh-Taylor instabilities (RTIs) of different viscosity and layer thickness ratios. These models provide a finite strain complement to the RTI benchmark of van Keken et al. Large finite deformation of up to f = 4 accumulates in RTIs within the stem and near the compositional boundaries. Distinction between different stages of diapirism shows a strong correlation between a maximum occurring deformation of f = 1, 3 and
Bao, Cheng; Bessler, Wolfgang G.
2015-03-01
The state-of-the-art electrochemical impedance spectroscopy (EIS) calculations have not yet started from fully multi-dimensional modeling. For a polymer electrolyte membrane fuel cell (PEMFC) with long flow channel, the impedance plot shows a multi-arc characteristic and some impedance arcs could merge. By using a step excitation/Fourier transform algorithm, an EIS simulation is implemented for the first time based on the full 2D PEMFC model presented in the first part of this work. All the dominant transient behaviors are able to be captured. A novel methodology called 'configuration of system dynamics', which is suitable for any electrochemical system, is then developed to resolve the physical meaning of the impedance spectra. In addition to the high-frequency arc due to charge transfer, the Nyquist plots contain additional medium/low-frequency arcs due to mass transfer in the diffusion layers and along the channel, as well as a low-frequency arc resulting from water transport in the membrane. In some case, the impedance spectra appear partly inductive due to water transport, which demonstrates the complexity of the water management of PEMFCs and the necessity of physics-based calculations.
Hathaway, M. D.; Suder, K. L.; Strazisar, A. J.; Adamczyk, J. J.; Okiishi, T. H.
1987-01-01
Unsteady velocity field measurements made within the stator row of a transonic axial-flow fan are presented. Measurements were obtained at midspan for two different stator blade rows using a laser anemometer. The first stator row consists of double circular-arc airfoils with a solidity of 1.68. The second features controlled-diffusion airfoils with a solidity of 0.85. Both were tested at design-speed peak efficiency conditions. In addition, the controlled-diffusion stator was also tested at near stall conditions. The procedures developed here are used to identify the rotor wake generated and unresolved unsteadiness from the velocity measurements (rotor wake generated unsteadiness refers to the unsteadiness generated by the rotor wake velocity deficit and unresolved unsteadiness refers to all remaining unsteadiness which contributes to the spread in the distribution of velocities such as vortex shedding, turbulence, etc.). Auto and cross correlations of these unsteady velocity fluctuations are presented to show their relative magnitude and spatial distributions. Amplification and attenuation of both rotor wake generated and unresolved unsteadiness are shown to occur within the stator blade passage.
Hathaway, Michael D.
1986-01-01
Measurements of the unsteady velocity field within the stator row of a transonic axial-flow fan were acquired using a laser anemometer. Measurements were obtained on axisymmetric surfaces located at 10 and 50 percent span from the shroud, with the fan operating at maximum efficiency at design speed. The ensemble-average and variance of the measured velocities are used to identify rotor-wake-generated (deterministic) unsteadiness and turbulence, respectively. Correlations of both deterministic and turbulent velocity fluctuations provide information on the characteristics of unsteady interactions within the stator row. These correlations are derived from the Navier-Stokes equation in a manner similar to deriving the Reynolds stress terms, whereby various averaging operators are used to average the aperiodic, deterministic, and turbulent velocity fluctuations which are known to be present in multistage turbomachines. The correlations of deterministic and turbulent velocity fluctuations throughout the axial fan stator row are presented. In particular, amplification and attenuation of both types of unsteadiness are shown to occur within the stator blade passage.
Hathaway, M. D.; Suder, K. L.; Okiishi, T. H.; Strazisar, A. J.; Adamczyk, J. J.
1987-01-01
Unsteady velocity field measurements made within the stator row of a transonic axial-flow fan are presented. Measurements were obtained at midspan for two different stator blade rows using a laser anemometer. The first stator row consists of double circular-arc airfoils with a solidity of 1.68. The second features controlled-diffusion airfoils with a solidity of 0.85. Both were tested at design-speed peak efficiency conditions. In addition, the controlled-diffusion stator was also tested at near stall conditions. The procedures developed here are used to identify the rotor wake generated and unresolved unsteadiness from the velocity measurements (rotor wake generated unsteadiness refers to the unsteadiness generated by the rotor wake velocity deficit and unresolved unsteadiness refers to all remaining unsteadiness which contributes to the spread in the distribution of velocities such as vortex shedding, turbulence, etc.). Auto and cross correlations of these unsteady velocity fluctuations are presented to show their relative magnitude and spatial distributions. Amplification and attenuation of both rotor wake generated and unresolved unsteadiness are shown to occur within the stator blade passage.
Two-dimensional capillary origami
Energy Technology Data Exchange (ETDEWEB)
Brubaker, N.D., E-mail: nbrubaker@math.arizona.edu; Lega, J., E-mail: lega@math.arizona.edu
2016-01-08
We describe a global approach to the problem of capillary origami that captures all unfolded equilibrium configurations in the two-dimensional setting where the drop is not required to fully wet the flexible plate. We provide bifurcation diagrams showing the level of encapsulation of each equilibrium configuration as a function of the volume of liquid that it contains, as well as plots representing the energy of each equilibrium branch. These diagrams indicate at what volume level the liquid drop ceases to be attached to the endpoints of the plate, which depends on the value of the contact angle. As in the case of pinned contact points, three different parameter regimes are identified, one of which predicts instantaneous encapsulation for small initial volumes of liquid. - Highlights: • Full solution set of the two-dimensional capillary origami problem. • Fluid does not necessarily wet the entire plate. • Global energy approach provides exact differential equations satisfied by minimizers. • Bifurcation diagrams highlight three different regimes. • Conditions for spontaneous encapsulation are identified.
Interaction between a shock wave and a turbulent boundary layer in transonic flow
Adamson, T. C., Jr.; Feo, A.
1975-01-01
Interaction between a shock wave and an unseparated turbulent boundary layer is considered. The method of matched asymptotic expansions is used, with solutions valid in the double limit as Reynolds number tends to infinity and Mach number tends to unity. The shock is weak enough that interaction effects can be considered as perturbations to the undisturbed flow; the case considered is that where the sonic line is near the outer edge of the boundary layer. It is shown that, with order estimates for Reynolds stress perturbations, the induced wall pressure distribution can be calculated using only the two outer interaction regions, independent of a specific closure condition and that this solution is in fact a turbulent free interaction solution. A detailed analysis of the inner regions, for which an eddy viscosity model for the Reynolds shear stress is used, provides a description of the variations in velocity, temperature and density near and at the wall.
Transonic Instability in Entrance Part of Mixing Chamber of High-Speed Ejector
Institute of Scientific and Technical Information of China (English)
Vaclav Dvorak; Pavel Safarik
2005-01-01
The paper deals with experimental and numerical study of flow structure in two-dimensional model of supersonic ejector. Schlieren pictures of flow structure were taken, static pressure distributions on side wall were measured and ture were taken, static pressure distributions on side wall were measured and Fluent software to calculate the flow structure in supersonic ejector was used. For certain region of back pressure he terminal shock wave is close to the trailing edge of the primary flow nozzle and a transonic instability occurs. The instability causes the movement of position of boundary layer separation,the structure of shock waves changes and all flow structure oscillates. The movie of these regimes during schlieren experiments was taken and relevant numerical modelling was performed.
Two-dimensional quantum repeaters
Wallnöfer, J.; Zwerger, M.; Muschik, C.; Sangouard, N.; Dür, W.
2016-11-01
The endeavor to develop quantum networks gave rise to a rapidly developing field with far-reaching applications such as secure communication and the realization of distributed computing tasks. This ultimately calls for the creation of flexible multiuser structures that allow for quantum communication between arbitrary pairs of parties in the network and facilitate also multiuser applications. To address this challenge, we propose a two-dimensional quantum repeater architecture to establish long-distance entanglement shared between multiple communication partners in the presence of channel noise and imperfect local control operations. The scheme is based on the creation of self-similar multiqubit entanglement structures at growing scale, where variants of entanglement swapping and multiparty entanglement purification are combined to create high-fidelity entangled states. We show how such networks can be implemented using trapped ions in cavities.
Two-dimensional capillary origami
Brubaker, N. D.; Lega, J.
2016-01-01
We describe a global approach to the problem of capillary origami that captures all unfolded equilibrium configurations in the two-dimensional setting where the drop is not required to fully wet the flexible plate. We provide bifurcation diagrams showing the level of encapsulation of each equilibrium configuration as a function of the volume of liquid that it contains, as well as plots representing the energy of each equilibrium branch. These diagrams indicate at what volume level the liquid drop ceases to be attached to the endpoints of the plate, which depends on the value of the contact angle. As in the case of pinned contact points, three different parameter regimes are identified, one of which predicts instantaneous encapsulation for small initial volumes of liquid.
Two-dimensional cubic convolution.
Reichenbach, Stephen E; Geng, Frank
2003-01-01
The paper develops two-dimensional (2D), nonseparable, piecewise cubic convolution (PCC) for image interpolation. Traditionally, PCC has been implemented based on a one-dimensional (1D) derivation with a separable generalization to two dimensions. However, typical scenes and imaging systems are not separable, so the traditional approach is suboptimal. We develop a closed-form derivation for a two-parameter, 2D PCC kernel with support [-2,2] x [-2,2] that is constrained for continuity, smoothness, symmetry, and flat-field response. Our analyses, using several image models, including Markov random fields, demonstrate that the 2D PCC yields small improvements in interpolation fidelity over the traditional, separable approach. The constraints on the derivation can be relaxed to provide greater flexibility and performance.
沟道二维泥石流运动和冲淤数值模型研究%Two-dimensional numerical model for debris flow motion and gully bed evolution
Institute of Scientific and Technical Information of China (English)
张万顺; 赵琰鑫; 崔鹏; 彭虹; 陈雪娇
2012-01-01
以水沙混合流模型为基础,采用混合流沙量动态变化模式,提出泥石流运动控制方程组,建立适用于模拟泥石流在天然沟道中的运动和冲淤过程的二维数值模型.模型基于水动力学理论、水沙两相混合流理论和宾汉体模型理论,考虑了泥石流运动、泥沙输移、沟床变形、泥石流宾汉体流变特性等主要动力学过程.将模型应用于云南东川蒋家沟实测泥石流过程的模拟研究,结果较好地反映了泥石流运动不连续性的特征和泥石流沟道冲淤随时间演变的实际规律.%A two-dimensional mathematical model of debris flow in natural gully is developed. Based on the hydrodynamic theory, the water-sediments two-phase flow theory and the Bingham rheological theory, the dynamic processes of debris flow movement, sediment transport, bed evolution and rheological properties of the debris flow are considered. The model is applied to simulate debris flow event in Jiangjia Gully, Yunnan Province and predict the flow pattern and bed erosion-deposition processes. The results show the effectiveness of the proposed model.
Effects of Porous Throat on Transonic Diffuser
屋我, 実; 永井, 實; 富田, 教夫; 芳賀, 剛; 宮良, 透; Yaga, Minoru; Nagai, Minoru; Tomita, Norio; Haga, Tsuyoshi; Miyara, Tooru
1995-01-01
The effects of the porous throat on a transonic diffuser were investigated experimentally by wall static pressure measurements and by schlieren optical observations. The porous throat consists of a wall with 126 holes and a cavity underneath it so that the flow around the shock wave can circulate through the porous wall. The results show that no shock wave was observed at 80% of the porous region from the throat and that the pressure fluctuations in the transonic diffuser were greatly reduced...
Classifying Two-dimensional Hyporeductive Triple Algebras
Issa, A Nourou
2010-01-01
Two-dimensional real hyporeductive triple algebras (h.t.a.) are investigated. A classification of such algebras is presented. As a consequence, a classification of two-dimensional real Lie triple algebras (i.e. generalized Lie triple systems) and two-dimensional real Bol algebras is given.
Su, Xiaoru; Shu, Longcang; Chen, Xunhong; Lu, Chengpeng; Wen, Zhonghui
2016-12-01
Interactions between surface waters and groundwater are of great significance for evaluating water resources and protecting ecosystem health. Heat as a tracer method is widely used in determination of the interactive exchange with high precision, low cost and great convenience. The flow in a river-bank cross-section occurs in vertical and lateral directions. In order to depict the flow path and its spatial distribution in bank areas, a genetic algorithm (GA) two-dimensional (2-D) heat-transport nested-loop method for variably saturated sediments, GA-VS2DH, was developed based on Microsoft Visual Basic 6.0. VS2DH was applied to model a 2-D bank-water flow field and GA was used to calibrate the model automatically by minimizing the difference between observed and simulated temperatures in bank areas. A hypothetical model was developed to assess the reliability of GA-VS2DH in inverse modeling in a river-bank system. Some benchmark tests were conducted to recognize the capability of GA-VS2DH. The results indicated that the simulated seepage velocity and parameters associated with GA-VS2DH were acceptable and reliable. Then GA-VS2DH was applied to two field sites in China with different sedimentary materials, to verify the reliability of the method. GA-VS2DH could be applied in interpreting the cross-sectional 2-D water flow field. The estimates of horizontal hydraulic conductivity at the Dawen River and Qinhuai River sites are 1.317 and 0.015 m/day, which correspond to sand and clay sediment in the two sites, respectively.
Su, Xiaoru; Shu, Longcang; Chen, Xunhong; Lu, Chengpeng; Wen, Zhonghui
2016-08-01
Interactions between surface waters and groundwater are of great significance for evaluating water resources and protecting ecosystem health. Heat as a tracer method is widely used in determination of the interactive exchange with high precision, low cost and great convenience. The flow in a river-bank cross-section occurs in vertical and lateral directions. In order to depict the flow path and its spatial distribution in bank areas, a genetic algorithm (GA) two-dimensional (2-D) heat-transport nested-loop method for variably saturated sediments, GA-VS2DH, was developed based on Microsoft Visual Basic 6.0. VS2DH was applied to model a 2-D bank-water flow field and GA was used to calibrate the model automatically by minimizing the difference between observed and simulated temperatures in bank areas. A hypothetical model was developed to assess the reliability of GA-VS2DH in inverse modeling in a river-bank system. Some benchmark tests were conducted to recognize the capability of GA-VS2DH. The results indicated that the simulated seepage velocity and parameters associated with GA-VS2DH were acceptable and reliable. Then GA-VS2DH was applied to two field sites in China with different sedimentary materials, to verify the reliability of the method. GA-VS2DH could be applied in interpreting the cross-sectional 2-D water flow field. The estimates of horizontal hydraulic conductivity at the Dawen River and Qinhuai River sites are 1.317 and 0.015 m/day, which correspond to sand and clay sediment in the two sites, respectively.
Two-dimensional function photonic crystals
Wu, Xiang-Yao; Liu, Xiao-Jing; Liang, Yu
2016-01-01
In this paper, we have firstly proposed two-dimensional function photonic crystals, which the dielectric constants of medium columns are the functions of space coordinates $\\vec{r}$, it is different from the two-dimensional conventional photonic crystals constituting by the medium columns of dielectric constants are constants. We find the band gaps of two-dimensional function photonic crystals are different from the two-dimensional conventional photonic crystals, and when the functions form of dielectric constants are different, the band gaps structure should be changed, which can be designed into the appropriate band gaps structures by the two-dimensional function photonic crystals.
Time integration algorithms for the two-dimensional Euler equations on unstructured meshes
Slack, David C.; Whitaker, D. L.; Walters, Robert W.
1994-06-01
Explicit and implicit time integration algorithms for the two-dimensional Euler equations on unstructured grids are presented. Both cell-centered and cell-vertex finite volume upwind schemes utilizing Roe's approximate Riemann solver are developed. For the cell-vertex scheme, a four-stage Runge-Kutta time integration, a fourstage Runge-Kutta time integration with implicit residual averaging, a point Jacobi method, a symmetric point Gauss-Seidel method and two methods utilizing preconditioned sparse matrix solvers are presented. For the cell-centered scheme, a Runge-Kutta scheme, an implicit tridiagonal relaxation scheme modeled after line Gauss-Seidel, a fully implicit lower-upper (LU) decomposition, and a hybrid scheme utilizing both Runge-Kutta and LU methods are presented. A reverse Cuthill-McKee renumbering scheme is employed for the direct solver to decrease CPU time by reducing the fill of the Jacobian matrix. A comparison of the various time integration schemes is made for both first-order and higher order accurate solutions using several mesh sizes, higher order accuracy is achieved by using multidimensional monotone linear reconstruction procedures. The results obtained for a transonic flow over a circular arc suggest that the preconditioned sparse matrix solvers perform better than the other methods as the number of elements in the mesh increases.
Optimal excitation of two dimensional Holmboe instabilities
Constantinou, Navid C
2010-01-01
Highly stratified shear layers are rendered unstable even at high stratifications by Holmboe instabilities when the density stratification is concentrated in a small region of the shear layer. These instabilities may cause mixing in highly stratified environments. However these instabilities occur in tongues for a limited range of parameters. We perform Generalized Stability analysis of the two dimensional perturbation dynamics of an inviscid Boussinesq stratified shear layer and show that Holmboe instabilities at high Richardson numbers can be excited by their adjoints at amplitudes that are orders of magnitude larger than by introducing initially the unstable mode itself. We also determine the optimal growth that obtains for parameters for which there is no instability. We find that there is potential for large transient growth regardless of whether the background flow is exponentially stable or not and that the characteristic structure of the Holmboe instability asymptotically emerges for parameter values ...
Johnson, D. A.; Rose, W. C.
1976-01-01
Quantitative measurements of the turbulence fluctuations in velocity and mass flux have been obtained in Mach 0.6 and 0.8 turbulent boundary layer and free-shear layer flows by laser velocimetry and hot-wire anemometry techniques. To evaluate the effects of compressibility, these transonic data are compared to available incompressible and supersonic results. Based on some simplifying assumptions, estimates of the rms density fluctuations are made for which error bounds are given. In addition to these fluctuation data, the compressible mean velocity data obtained with the laser velocimeter are presented and compared to pitot tube results. The investigation was conducted in the Ames 6- by 6-Foot Supersonic Wind Tunnel at free-stream Mach numbers of 0.6 and 0.8 for a unit Reynolds number of about 10,000,000 per meter.
Two-dimensional lattice Boltzmann model for magnetohydrodynamics.
Schaffenberger, Werner; Hanslmeier, Arnold
2002-10-01
We present a lattice Boltzmann model for the simulation of two-dimensional magnetohydro dynamic (MHD) flows. The model is an extension of a hydrodynamic lattice Boltzman model with 9 velocities on a square lattice resulting in a model with 17 velocities. Earlier lattice Boltzmann models for two-dimensional MHD used a bidirectional streaming rule. However, the use of such a bidirectional streaming rule is not necessary. In our model, the standard streaming rule is used, allowing smaller viscosities. To control the viscosity and the resistivity independently, a matrix collision operator is used. The model is then applied to the Hartmann flow, giving reasonable results.
A study of test section configuration for shock tube testing of transonic airfoils
Cook, W. J.
1978-01-01
Two methods are investigated for alleviating wall interference effects in a shock tube test section intended for testing two-dimensional transonic airfoils. The first method involves contouring the test section walls to match approximate streamlines in the flow. Contours are matched to each airfoil tested to produce results close to those obtained in a conventional wind tunnel. Data from a previous study and the present study for two different airfoils demonstrate that useful results are obtained in a shock tube using a test section with contoured walls. The second method involves use of a fixed-geometry slotted-wall test section to provide automatic flow compensation for various airfoils. The slotted-wall test section developed exhibited the desired performance characteristics in the approximate Mach number range 0.82 to 0.89, as evidenced by good agreement obtained between shock tube and wind tunnel results for several airfoil flows.
Hadamard States and Two-dimensional Gravity
Salehi, H
2001-01-01
We have used a two-dimensional analog of the Hadamard state-condition to study the local constraints on the two-point function of a linear quantum field conformally coupled to a two-dimensional gravitational background. We develop a dynamical model in which the determination of the state of the quantum field is essentially related to the determination of a conformal frame. A particular conformal frame is then introduced in which a two-dimensional gravitational equation is established.
Topological defects in two-dimensional crystals
Chen, Yong; Qi, Wei-Kai
2008-01-01
By using topological current theory, we study the inner topological structure of the topological defects in two-dimensional (2D) crystal. We find that there are two elementary point defects topological current in two-dimensional crystal, one for dislocations and the other for disclinations. The topological quantization and evolution of topological defects in two-dimensional crystals are discussed. Finally, We compare our theory with Brownian-dynamics simulations in 2D Yukawa systems.
Transonic Experimental Research Facility
Federal Laboratory Consortium — The Transonic Experimental Research Facility evaluates aerodynamics and fluid dynamics of projectiles, smart munitions systems, and sub-munitions dispensing systems;...
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.
KIM, DONG-HYUN; LEE, IN
2000-07-01
A two-degree-of-freedom airfoil with a freeplay non-linearity in the pitch and plunge directions has been analyzed in the transonic and low-supersonic flow region, where aerodynamic non-linearities also exist. The primary purpose of this study is to show aeroelastic characteristics due to freeplay structural non-linearity in the transonic and low-supersonic regions. The unsteady aerodynamic forces on the airfoil were evaluated using two-dimensional unsteady Euler code, and the resulting aeroelastic equations are numerically integrated to obtain the aeroelastic time responses of the airfoil motions and to investigate the dynamic instability. The present model has been considered as a simple aeroelastic model, which is equivalent to the folding fin of an advanced generic missile. From the results of the present study, characteristics of important vibration responses and aeroelastic instabilities can be observed in the transonic and supersonic regions, especially considering the effect of structural non-linearity in the pitch and plunge directions. The regions of limit-cycle oscillation are shown at much lower velocities, especially in the supersonic flow region, than the divergent flutter velocities of the linear structure model. It is also shown that even small freeplay angles can lead to severe dynamic instabilities and dangerous fatigue conditions for the flight vehicle wings and control fins.
Ren, Qiang; Wu, Caisheng; Zhang, Jinlan
2013-08-23
The use of two-dimensional liquid chromatography (2D-LC) for quantification studies presents challenges with respect to repeatability, precision, and robustness. The present study used an on-line stop-flow heart-cutting 2D-LC system to determine 12 chemical constituents in tartary buckwheat. A combination of various stationary phases was developed and bridged using two switch valves as the interface. Hydrophilic interaction chromatography was chosen for separation in the first dimension ((1)D), and mixed mode stationary phases (an amide polar-embedded phase and alkyl-phenyl phase) were used in parallel for separation in the second dimension ((2)D). The mobile phase comprised acetonitrile and water containing 0.03% aqueous phosphoric acid. The sample was separated into two fractions on the (1)D column (HILIC-10 column) using 5% acetonitrile. One fraction, mainly comprising flavonoids, was directly eluted onto the head of (2)D column (Polar Advantage II column) and further separated using a linear gradient of 11-23% acetonitrile. The second fraction, containing phenylpropanoid glycosides, was trapped on the (1)D column. This retained fraction was back-flushed onto the (2)D column (Phenyl-1 column) and separated using a linear gradient of 35-43% acetonitrile. An on-line stop-flow heart-cutting 2D-LC system was successfully developed with column switching and back-flush. This 2D-LC system was validated and was able to simultaneously determine 12 major components in tartary buckwheat: seven flavonoids, four phenylpropanoid glycosides, and N-trans-feruloyltyramine. The system showed good performance with respect to linearity (r>0.996), repeatability (RSD, relative standard deviation<3.4%), intra-day and inter-day precision (RSD<4.6%), recovery (91.2-108%), limit of detection (LOD) (0.05-0.21μg/mL), and limit of quantification (LOQ) (0.10-0.41μg/mL). The on-line stop-flow heart-cutting 2D-LC system offers a potential approach to analyze compounds, which have similar