Three dimensional inviscid compressible calculations around axial flow turbine blades
Fourmaux, Antoine; Petot, Bertrand
1991-12-01
The application of a three dimensional (3D) method to the prediction of steady inviscid compressible flows in highly loaded stator bladings is presented. The complete set of Euler equations is solved by a finite difference method using a time marching two step Lax-Wendorff algorithm. The treatment of the boundary conditions is based on the use of the characteristic relations. This technique offers a great versatility and allows to prescribe conditions close to the physics of flows encountered in turbomachines. The code was adapted in order to build a 3D design tool able to run in different types of turbine blade geometries. Two types of multidomain structured meshes were tested (H+0+H and H+C). The H+C type of grid was finally choosen for industrial applications. Two applications to turbine nozzles are presented. The first is a low pressure turbine vane with evolutive flow path outer diameter. The results demonstrate the ability to predict flow features that cannot be computed via the classical two dimensional approach. The second is a high pressure inlet guide vane at transonic conditions. The strong radial evolution of pressure distribution and the trailing edge flow pattern are correctly predicted.
Error Representation in Time For Compressible Flow Calculations
Barth, Timothy J.
2010-01-01
Time plays an essential role in most real world fluid mechanics problems, e.g. turbulence, combustion, acoustic noise, moving geometries, blast waves, etc. Time dependent calculations now dominate the computational landscape at the various NASA Research Centers but the accuracy of these computations is often not well understood. In this presentation, we investigate error representation (and error control) for time-periodic problems as a prelude to the investigation of feasibility of error control for stationary statistics and space-time averages. o These statistics and averages (e.g. time-averaged lift and drag forces) are often the output quantities sought by engineers. o For systems such as the Navier-Stokes equations, pointwise error estimates deteriorate rapidly which increasing Reynolds number while statistics and averages may remain well behaved.
Strong, Stuart L.; Meade, Andrew J., Jr.
1992-01-01
Preliminary results are presented of a finite element/finite difference method (semidiscrete Galerkin method) used to calculate compressible boundary layer flow about airfoils, in which the group finite element scheme is applied to the Dorodnitsyn formulation of the boundary layer equations. The semidiscrete Galerkin (SDG) method promises to be fast, accurate and computationally efficient. The SDG method can also be applied to any smoothly connected airfoil shape without modification and possesses the potential capability of calculating boundary layer solutions beyond flow separation. Results are presented for low speed laminar flow past a circular cylinder and past a NACA 0012 airfoil at zero angle of attack at a Mach number of 0.5. Also shown are results for compressible flow past a flat plate for a Mach number range of 0 to 10 and results for incompressible turbulent flow past a flat plate. All numerical solutions assume an attached boundary layer.
A NOVEL SLIGHTLY COMPRESSIBLE MODEL FOR LOW MACH NUMBER PERFECT GAS FLOW CALCULATION
Institute of Scientific and Technical Information of China (English)
邓小刚; 庄逢甘
2002-01-01
By analyzing the characteristics of low Mach number perfect gas flows, a novel Slightly Compressible Model (SCM) for low Mach number perfect gas flows is derived. In view of numerical calculations, this model is proved very efficient,for it is kept within the p-v frame but does not have to satisfy the time consuming divergence-free condition in order to get the incompressible Navier-Stokes equation solutions. Writing the equations in the form of conservation laws, we have derived the characteristic systems which are necessary for numerical calculations. A cellcentered finite-volume method with flux difference upwind-biased schemes is used for the equation solutions and a new Exact Newton Relaxation (ENR) implicit method is developed. Various computed results are presented to validate the present model.Laminar flow solutions over a circular cylinder with wake developing and vortex shedding are presented. Results for inviscid flow over a sphere are compared in excellent agreement with the exact analytic incompressible solution. Three-dimensional viscous flow solutions over sphere and prolate spheroid are also calculated and compared well with experiments and other incompressible solutions. Finally, good convergent performaces are shown for sphere viscous flows.
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.
Armijo C., Javier; Facultad de Química e Ingeniería Química, Universidad Nacional Mayor de San Marcos. Lima, Perú
2014-01-01
We are proposing algoritms to solve problems of flow of an ideal gas in a pipe of constant section. With the compressible flow equations we have determined the pressure and velocity profile for both isothermal and adiabatic flow of air and methane. Se presentan algoritmos para resolver los problemas de flujo de fluidos de gases ideales a través de tubos de sección transversal constante. Con las ecuaciones de flujo compresible se determinan los perfiles de presión y velocidad, en flujo isot...
Shocklets in compressible flows
Institute of Scientific and Technical Information of China (English)
袁湘江; 男俊武; 沈清; 李筠
2013-01-01
The mechanism of shocklets is studied theoretically and numerically for the stationary fluid, uniform compressible flow, and boundary layer flow. The conditions that trigger shock waves for sound wave, weak discontinuity, and Tollmien-Schlichting (T-S) wave in compressible flows are investigated. The relations between the three types of waves and shocklets are further analyzed and discussed. Different stages of the shocklet formation process are simulated. The results show that the three waves in compressible flows will transfer to shocklets only when the initial disturbance amplitudes are greater than the certain threshold values. In compressible boundary layers, the shocklets evolved from T-S wave exist only in a finite region near the surface instead of the whole wavefront.
Introduction to compressible fluid flow
Oosthuizen, Patrick H
2013-01-01
IntroductionThe Equations of Steady One-Dimensional Compressible FlowSome Fundamental Aspects of Compressible FlowOne-Dimensional Isentropic FlowNormal Shock WavesOblique Shock WavesExpansion Waves - Prandtl-Meyer FlowVariable Area FlowsAdiabatic Flow with FrictionFlow with Heat TransferLinearized Analysis of Two-Dimensional Compressible FlowsHypersonic and High-Temperature FlowsHigh-Temperature Gas EffectsLow-Density FlowsBibliographyAppendices
Ockendon, Hilary
2016-01-01
Now in its second edition, this book continues to give readers a broad mathematical basis for modelling and understanding the wide range of wave phenomena encountered in modern applications. New and expanded material includes topics such as elastoplastic waves and waves in plasmas, as well as new exercises. Comprehensive collections of models are used to illustrate the underpinning mathematical methodologies, which include the basic ideas of the relevant partial differential equations, characteristics, ray theory, asymptotic analysis, dispersion, shock waves, and weak solutions. Although the main focus is on compressible fluid flow, the authors show how intimately gasdynamic waves are related to wave phenomena in many other areas of physical science. Special emphasis is placed on the development of physical intuition to supplement and reinforce analytical thinking. Each chapter includes a complete set of carefully prepared exercises, making this a suitable textbook for students in applied mathematics, ...
Vadyak, J.; Hoffman, J. D.
1982-01-01
A computer program was developed which is capable of calculating the flow field in the supersonic portion of a mixed compression aircraft inlet operating at angle of attack. The supersonic core flow is computed using a second-order three dimensional method-of-characteristics algorithm. The bow shock and the internal shock train are treated discretely using a three dimensional shock fitting procedure. The boundary layer flows are computed using a second-order implicit finite difference method. The shock wave-boundary layer interaction is computed using an integral formulation. The general structure of the computer program is discussed, and a brief description of each subroutine is given. All program input parameters are defined, and a brief discussion on interpretation of the output is provided. A number of sample cases, complete with data listings, are provided.
Comments on compressible flow through butterfly valves
Blakenship, John G.
In the flow analysis of process piping systems, it is desirable to treat control valves in the same way as elbow, reducers, expansions, and other pressure loss elements. In a recently reported research program, the compressible flow characteristics of butterfly valves were investigated. Fisher Controls International, Inc., manufacturer of a wide range of control valves, publishes coefficients that can be used to calculate flow characteristics for the full range of valve movement. The use is described of the manufacturer's data to calculate flow parameters as reported by the researchers who investigated compressible flow through butterfly valves. The manufacturer's data produced consistent results and can be used to predict choked flow and the pressure loss for unchoked flow.
Compressibility, turbulence and high speed flow
Gatski, Thomas B
2013-01-01
Compressibility, Turbulence and High Speed Flow introduces the reader to the field of compressible turbulence and compressible turbulent flows across a broad speed range, through a unique complimentary treatment of both the theoretical foundations and the measurement and analysis tools currently used. The book provides the reader with the necessary background and current trends in the theoretical and experimental aspects of compressible turbulent flows and compressible turbulence. Detailed derivations of the pertinent equations describing the motion of such turbulent flows is provided and
Conservative regularization of compressible flow
Krishnaswami, Govind S; Thyagaraja, Anantanarayanan
2015-01-01
Ideal Eulerian flow may develop singularities in vorticity w. Navier-Stokes viscosity provides a dissipative regularization. We find a local, conservative regularization - lambda^2 w times curl(w) of compressible flow and compressible MHD: a three dimensional analogue of the KdV regularization of the one dimensional kinematic wave equation. The regulator lambda is a field subject to the constitutive relation lambda^2 rho = constant. Lambda is like a position-dependent mean-free path. Our regularization preserves Galilean, parity and time-reversal symmetries. We identify locally conserved energy, helicity, linear and angular momenta and boundary conditions ensuring their global conservation. Enstrophy is shown to remain bounded. A swirl velocity field is identified, which transports w/rho and B/rho generalizing the Kelvin-Helmholtz and Alfven theorems. A Hamiltonian and Poisson bracket formulation is given. The regularized equations are used to model a rotating vortex, channel flow, plane flow, a plane vortex ...
Isotropic polarization of compressible flows
Zhu, Jian-Zhou
2015-01-01
The helical absolute equilibrium of a compressible adiabatic flow presents not only the polarization between the two purely helical modes of opposite chiralities but also that between the vortical and acoustic modes, deviating from the equipartition predicted by {\\sc Kraichnan, R. H.} [1955 The Journal of the Acoustical Society of America {\\bf 27}, 438--441.] Due to the existence of the acoustic mode, even if all Fourier modes of one chiral sector in the sharpened Helmholtz decomposition [{\\sc Moses, H. E.} 1971 SIAM ~(Soc. Ind. Appl. Math.) J. Appl. Math. {\\bf 21}, 114--130] are thoroughly truncated, negative temperature and the corresponding large-scale concentration of vortical modes are not allowed, unlike the incompressible case.
Mathematical theory of compressible fluid flow
Von Mises, Richard
2012-01-01
Mathematical Theory of Compressible Fluid Flow covers the conceptual and mathematical aspects of theory of compressible fluid flow. This five-chapter book specifically tackles the role of thermodynamics in the mechanics of compressible fluids. This text begins with a discussion on the general theory of characteristics of compressible fluid with its application. This topic is followed by a presentation of equations delineating the role of thermodynamics in compressible fluid mechanics. The discussion then shifts to the theory of shocks as asymptotic phenomena, which is set within the context of
A PDF closure model for compressible turbulent chemically reacting flows
Kollmann, W.
1992-01-01
The objective of the proposed research project was the analysis of single point closures based on probability density function (pdf) and characteristic functions and the development of a prediction method for the joint velocity-scalar pdf in turbulent reacting flows. Turbulent flows of boundary layer type and stagnation point flows with and without chemical reactions were be calculated as principal applications. Pdf methods for compressible reacting flows were developed and tested in comparison with available experimental data. The research work carried in this project was concentrated on the closure of pdf equations for incompressible and compressible turbulent flows with and without chemical reactions.
Implicit compressible flow solvers on unstructured meshes
Nagaoka, Makoto; Horinouchi, Nariaki
1993-09-01
An implicit solver for compressible flows using Bi-CGSTAB method is proposed. The Euler equations are discretized with the delta-form by the finite volume method on the cell-centered triangular unstructured meshes. The numerical flux is calculated by Roe's upwind scheme. The linearized simultaneous equations with the irregular nonsymmetric sparse matrix are solved by the Bi-CGSTAB method with the preconditioner of incomplete LU factorization. This method is also vectorized by the multi-colored ordering. Although the solver requires more computational memory, it shows faster and more robust convergence than the other conventional methods: three-stage Runge-Kutta method, point Gauss-Seidel method, and Jacobi method for two-dimensional inviscid steady flows.
Characteristics of compressible flow of supercritical kerosene
Institute of Scientific and Technical Information of China (English)
Feng-Quan Zhong; Xue-Jun Fan; Jing Wang; Gong Yu; Jian-Guo Li
2012-01-01
In this paper,compressible flow of aviation kerosene at supercritical conditions has been studied both numerically and experimentally.The thermophysical properties of supercritical kerosene are calculated using a 10-species surrogate based on the principle of extended corresponding states (ECS).Isentropic acceleration of supercritical kerosene to subsonic and supersonic speeds has been analyzed numerically.It has been found that the isentropic relationships of supercritical kerosene are significantly different from those of ideal gases.A two-stage fuel heating and delivery system is used to heat the kerosene up to a temperature of 820 K and pressure of 5.5 MPa with a maximum mass flow rate of 100 g/s.The characteristics of supercritical kerosene flows in a converging-diverging nozzle (Laval nozzle) have been studied experimentally.The results show that stable supersonic flows of kerosene could be established in the temperature range of 730 K-820 K and the measurements in the wall pressure agree with the numerical calculation.
Mathematical theory of compressible fluid flow
von Mises, Richard
2004-01-01
A pioneer in the fields of statistics and probability theory, Richard von Mises (1883-1953) made notable advances in boundary-layer-flow theory and airfoil design. This text on compressible flow, unfinished upon his sudden death, was subsequently completed in accordance with his plans, and von Mises' first three chapters were augmented with a survey of the theory of steady plane flow. Suitable as a text for advanced undergraduate and graduate students - as well as a reference for professionals - Mathematical Theory of Compressible Fluid Flow examines the fundamentals of high-speed flows, with
Near-wall modelling of compressible turbulent flows
So, Ronald M. C.
1990-01-01
Work was carried out to formulate near-wall models for the equations governing the transport of the temperature-variance and its dissipation rate. With these equations properly modeled, a foundation is laid for their extension together with the heat-flux equations to compressible flows. This extension is carried out in a manner similar to that used to extend the incompressible near-wall Reynolds-stress models to compressible flows. The methodology used to accomplish the extension of the near-wall Reynolds-stress models is examined and the actual extension of the models for the Reynolds-stress equations and the near-wall dissipation-rate equation to compressible flows is given. Then the formulation of the near-wall models for the equations governing the transport of the temperature variance and its dissipation rate is discussed. Finally, a sample calculation of a flat plate compressible turbulent boundary-layer flow with adiabatic wall boundary condition and a free-stream Mach number of 2.5 using a two-equation near-wall closure is presented. The results show that the near-wall two-equation closure formulated for compressible flows is quite valid and the calculated properties are in good agreement with measurements. Furthermore, the near-wall behavior of the turbulence statistics and structure parameters is consistent with that found in incompressible flows.
PDF approach for compressible turbulent reacting flows
Hsu, A. T.; Tsai, Y.-L. P.; Raju, M. S.
1993-01-01
The objective of the present work is to develop a probability density function (pdf) turbulence model for compressible reacting flows for use with a CFD flow solver. The probability density function of the species mass fraction and enthalpy are obtained by solving a pdf evolution equation using a Monte Carlo scheme. The pdf solution procedure is coupled with a compressible CFD flow solver which provides the velocity and pressure fields. A modeled pdf equation for compressible flows, capable of capturing shock waves and suitable to the present coupling scheme, is proposed and tested. Convergence of the combined finite-volume Monte Carlo solution procedure is discussed, and an averaging procedure is developed to provide smooth Monte-Carlo solutions to ensure convergence. Two supersonic diffusion flames are studied using the proposed pdf model and the results are compared with experimental data; marked improvements over CFD solutions without pdf are observed. Preliminary applications of pdf to 3D flows are also reported.
Stability of compressible three-dimensional boundary-layer flows
Reed, H. L.; Nayfeh, A. H.
1982-01-01
For compressible three-dimensional flow, the method of multiple scales to formulate the three-dimensional stability problem and determine the partial-differential equations governing variations of the amplitude and complex wavenumbers is used. A method for following one specific wave along its trajectory to ascertain the characteristics of the most unstable disturbance is proposed. Numerical results using the flow over the X-21 wing as calculated from the Kaups-Cebeci code will be presented.
Slip Effects in Compressible Turbulent Channel Flow
Skovorodko, P A
2012-01-01
The direct numerical simulation of compressible fully developed turbulent Couette flow between two parallel plates with equal temperatures moving in opposite directions with some velocity was performed. The algorithm was tested on well known numerical solution for incompressible Poiseuille channel flow and found to provide its well description. The slip effects in studied flow are found to be negligibly small at the values of accommodation coefficients for velocity and temperature of the order of unity. The considerable increase of mean temperature with decreasing the accommodation coefficient for temperature was discovered. The effect may be important in the problems of heat exchange in compressible turbulent boundary layer for some combinations of flowing gas, surface and adsorbing gas.
Slip effects in compressible turbulent channel flow
Skovorodko, P. A.
2012-11-01
The direct numerical simulation of compressible fully developed turbulent Couette flow between two parallel plates with temperature Tw moving with velocities ±Uw was performed. The algorithm was tested on well known numerical solution for incompressible Poiseuille channel flow and found to provide its well description. The slip effects in studied flow are found to be negligibly small at the values of accommodation coefficients αu and αT of the order of unity. The considerable increase of mean temperature with decreasing the accommodation coefficient αT for fixed value of αu = 1 was discovered. The effect may be important in the problems of heat exchange in compressible turbulent boundary layer for some combinations of flowing gas, surface and adsorbing gas.
A compressible near-wall turbulence model for boundary layer calculations
So, R. M. C.; Zhang, H. S.; Lai, Y. G.
1992-01-01
A compressible near-wall two-equation model is derived by relaxing the assumption of dynamical field similarity between compressible and incompressible flows. This requires justifications for extending the incompressible models to compressible flows and the formulation of the turbulent kinetic energy equation in a form similar to its incompressible counterpart. As a result, the compressible dissipation function has to be split into a solenoidal part, which is not sensitive to changes of compressibility indicators, and a dilational part, which is directly affected by these changes. This approach isolates terms with explicit dependence on compressibility so that they can be modeled accordingly. An equation that governs the transport of the solenoidal dissipation rate with additional terms that are explicitly dependent on the compressibility effects is derived similarly. A model with an explicit dependence on the turbulent Mach number is proposed for the dilational dissipation rate. Thus formulated, all near-wall incompressible flow models could be expressed in terms of the solenoidal dissipation rate and straight-forwardly extended to compressible flows. Therefore, the incompressible equations are recovered correctly in the limit of constant density. The two-equation model and the assumption of constant turbulent Prandtl number are used to calculate compressible boundary layers on a flat plate with different wall thermal boundary conditions and free-stream Mach numbers. The calculated results, including the near-wall distributions of turbulence statistics and their limiting behavior, are in good agreement with measurements. In particular, the near-wall asymptotic properties are found to be consistent with incompressible behavior; thus suggesting that turbulent flows in the viscous sublayer are not much affected by compressibility effects.
Theoretical and computational dynamics of a compressible flow
Pai, Shih-I; Luo, Shijun
1991-01-01
An introduction to the theoretical and computational fluid dynamics of a compressible fluid is presented. The general topics addressed include: thermodynamics and physical properties of compressible fluids; 1D flow of an inviscid compressible fluid; shock waves; fundamental equations of the dynamics of a compressible inviscid non-heat-conducting and radiating fluid, method of small perturbations, linearized theory; 2D subsonic steady potential flow; hodograph and rheograph methods, exact solutions of 2D insentropic steady flow equations, 2D steady transonic and hypersonic flows, method of characteristics, linearized theory of 3D potential flow, nonlinear theory of 3D compressibe flow, anisentropic (rotational) flow of inviscid compressible fluid, electromagnetogasdynamics, multiphase flows, flows of a compressible fluid with transport phenomena.
Flow Field Calculations for Afterburner
Institute of Scientific and Technical Information of China (English)
ZhaoJianxing; LiuQuanzhong; 等
1995-01-01
In this paper a calculation procedure for simulating the coimbustion flow in the afterburner with the heat shield,flame stabilizer and the contracting nozzle is described and evaluated by comparison with experimental data.The modified two-equation κ-ε model is employed to consider the turbulence effects,and the κ-ε-g turbulent combustion model is used to determine the reaction rate.To take into accunt the influence of heat radiation on gas temperature distribution,heat flux model is applied to predictions of heat flux distributions,The solution domain spanned the entire region between centerline and afterburner wall ,with the heat shield represented as a blockage to the mesh.The enthalpy equation and wall boundary of the heat shield require special handling for two passages in the afterburner,In order to make the computer program suitable to engineering applications,a subregional scheme is developed for calculating flow fields of complex geometries.The computational grids employed are 100×100 and 333×100(non-uniformly distributed).The numerical results are compared with experimental data,Agreement between predictions and measurements shows that the numerical method and the computational program used in the study are fairly reasonable and appopriate for primary design of the afterburner.
Herzog, J.
1974-01-01
A method of calculating stage parameters and flow distribution of axial turbines is described. The governing equations apply to space between the blade rows and are based on the assumption of rotationally symmetrical, compressible, adiabatic flow conditions. Results are presented for stage design and flow analysis calculations. Theoretical results from the calculation system are compared with experimental data from low pressure steam turbine tests.
Mode Selection in Compressible Active Flow Networks
Forrow, Aden; Woodhouse, Francis G.; Dunkel, Jörn
2017-07-01
Coherent, large-scale dynamics in many nonequilibrium physical, biological, or information transport networks are driven by small-scale local energy input. Here, we introduce and explore an analytically tractable nonlinear model for compressible active flow networks. In contrast to thermally driven systems, we find that active friction selects discrete states with a limited number of oscillation modes activated at distinct fixed amplitudes. Using perturbation theory, we systematically predict the stationary states of noisy networks and find good agreement with a Bayesian state estimation based on a hidden Markov model applied to simulated time series data. Our results suggest that the macroscopic response of active network structures, from actomyosin force networks to cytoplasmic flows, can be dominated by a significantly reduced number of modes, in contrast to energy equipartition in thermal equilibrium. The model is also well suited to study topological sound modes and spectral band gaps in active matter.
Adaptive Lattice Boltzmann Model for Compressible Flows
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
A new lattice Boltzmann model for compressible flows is presented. The main difference from the standard lattice Boltzmann model is that the particle velocities are no longer constant, but vary with the mean velocity and internal energy. The adaptive nature of the particle velocities permits the mean flow to have a high Mach number. The introduction of a particle potential energy makes the model suitable for a perfect gas with arbitrary specific heat ratio. The Navier-Stokes (N-S) equations are derived by the Chapman-Enskog method from the BGK Boltzmann equation. Two kinds of simulations have been carried out on the hexagonal lattice to test the proposed model. One is the Sod shock-tube simulation. The other is a strong shock of Mach number 5.09 diffracting around a corner.
Conjugate Compressible Fluid Flow and Heat Transfer in Ducts
Cross, M. F.
2011-01-01
A computational approach to modeling transient, compressible fluid flow with heat transfer in long, narrow ducts is presented. The primary application of the model is for analyzing fluid flow and heat transfer in solid propellant rocket motor nozzle joints during motor start-up, but the approach is relevant to a wide range of analyses involving rapid pressurization and filling of ducts. Fluid flow is modeled through solution of the spatially one-dimensional, transient Euler equations. Source terms are included in the governing equations to account for the effects of wall friction and heat transfer. The equation solver is fully-implicit, thus providing greater flexibility than an explicit solver. This approach allows for resolution of pressure wave effects on the flow as well as for fast calculation of the steady-state solution when a quasi-steady approach is sufficient. Solution of the one-dimensional Euler equations with source terms significantly reduces computational run times compared to general purpose computational fluid dynamics packages solving the Navier-Stokes equations with resolved boundary layers. In addition, conjugate heat transfer is more readily implemented using the approach described in this paper than with most general purpose computational fluid dynamics packages. The compressible flow code has been integrated with a transient heat transfer solver to analyze heat transfer between the fluid and surrounding structure. Conjugate fluid flow and heat transfer solutions are presented. The author is unaware of any previous work available in the open literature which uses the same approach described in this paper.
Schwarz-based algorithms for compressible flows
Energy Technology Data Exchange (ETDEWEB)
Tidriri, M.D. [ICASE, Hampton, VA (United States)
1996-12-31
To compute steady compressible flows one often uses an implicit discretization approach which leads to a large sparse linear system that must be solved at each time step. In the derivation of this system one often uses a defect-correction procedure, in which the left-hand side of the system is discretized with a lower order approximation than that used for the right-hand side. This is due to storage considerations and computational complexity, and also to the fact that the resulting lower order matrix is better conditioned than the higher order matrix. The resulting schemes are only moderately implicit. In the case of structured, body-fitted grids, the linear system can easily be solved using approximate factorization (AF), which is among the most widely used methods for such grids. However, for unstructured grids, such techniques are no longer valid, and the system is solved using direct or iterative techniques. Because of the prohibitive computational costs and large memory requirements for the solution of compressible flows, iterative methods are preferred. In these defect-correction methods, which are implemented in most CFD computer codes, the mismatch in the right and left hand side operators, together with explicit treatment of the boundary conditions, lead to a severely limited CFL number, which results in a slow convergence to steady state aerodynamic solutions. Many authors have tried to replace explicit boundary conditions with implicit ones. Although they clearly demonstrate that high CFL numbers are possible, the reduction in CPU time is not clear cut.
Subsampling-based compression and flow visualization
Energy Technology Data Exchange (ETDEWEB)
Agranovsky, Alexy; Camp, David; Joy, I; Childs, Hank
2016-01-19
As computational capabilities increasingly outpace disk speeds on leading supercomputers, scientists will, in turn, be increasingly unable to save their simulation data at its native resolution. One solution to this problem is to compress these data sets as they are generated and visualize the compressed results afterwards. We explore this approach, specifically subsampling velocity data and the resulting errors for particle advection-based flow visualization. We compare three techniques: random selection of subsamples, selection at regular locations corresponding to multi-resolution reduction, and introduce a novel technique for informed selection of subsamples. Furthermore, we explore an adaptive system which exchanges the subsampling budget over parallel tasks, to ensure that subsampling occurs at the highest rate in the areas that need it most. We perform supercomputing runs to measure the effectiveness of the selection and adaptation techniques. Overall, we find that adaptation is very effective, and, among selection techniques, our informed selection provides the most accurate results, followed by the multi-resolution selection, and with the worst accuracy coming from random subsamples.
Flux Limiter Lattice Boltzmann for Compressible Flows
Institute of Scientific and Technical Information of China (English)
陈峰; 许爱国; 张广财; 李英骏
2011-01-01
In this paper, a new flux limiter scheme with the splitting technique is successfully incorporated into a multiple-relaxation-time lattice Boltzmann （LB） model for shacked compressible flows. The proposed flux limiter scheme is efficient in decreasing the artificial oscillations and numerical diffusion around the interface. Due to the kinetic nature, some interface problems being difficult to handle at the macroscopic level can be modeled more naturally through the LB method. Numerical simulations for the Richtmyer-Meshkov instability show that with the new model the computed interfaces are smoother and more consistent with physical analysis. The growth rates of bubble and spike present a satisfying agreement with the theoretical predictions and other numerical simulations.
The Compressible Flow Past Various Plane Profiles Near Sonic Velocity
Goethert, B.; Kawalki, K. H.
1949-01-01
In an earlier report UM No.1117 by Gothert,the single-source method was applied to the compressible flow around circles, ellipses, lunes, and around an elongated body of revolution at different Mach numbers and the results compared as far as possible with the calculations by Lamla ad Busemann. Essentially, it was found that with favorable source arrangement the single-source method is in good agreement with the calculations of the same degree of approximation by.Lamla and Busemann. Near sonic velocity the number of steps must be increased considerably in order to sufficiently approximate the adiabatic curve. After exceeding a certain Mach number where local supersonic fields occur already, it was no longer possible, in spite of the substantially increased number of steps, to obtain a systematic solution because the calculation diverged. This result,was interpreted to mean that above this point of divergence the symmetrical type of flow ceases to exist and changes into the unsymmetrical type characterized by compressibility shocks.
A rotational compressible inverse design method for internal flow configurations
Dedoussis, V.; Chaviaropoulos, P.; Papailiou, K. D.
The development of a rotational inviscid compressible inverse design method for two-dimensional internal flow configurations is described. Rotationality is due to an incoming entropy gradient, while total enthalpy is considered to be constant throughout the flowfield. The method is based on the potential function-streamfunction formulation. A novel procedure based on differential geometry arguments is employed to derive the governing equation for velocity by requiring the curvature of the two-dimensional Euclidean space to be zero. The velocity equation solved in conjunction with a transport equation for a thermal drift function provide the flowfield without any geometry feedback. An auxiliary orthogonal computational grid adapted to the solution is employed. Geometry is determined by integrating Frenet equations of the grid lines. Inverse calculation results are compared with results of direct reproduction calculations.
Shi, Jianyong; Qian, Xuede; Liu, Xiaodong; Sun, Long; Liao, Zhiqiang
2016-09-01
The total compression of municipal solid waste (MSW) consists of primary, secondary, and decomposition compressions. It is usually difficult to distinguish between the three parts of compressions. In this study, the odeometer test was used to distinguish between the primary and secondary compressions to determine the primary and secondary compression coefficient. In addition, the ending time of the primary compressions were proposed based on municipal solid waste compression tests in a degradation-inhibited condition by adding vinegar. The amount of the secondary compression occurring in the primary compression stage has a relatively high percentage to either the total compression or the total secondary compression. The relationship between the degradation ratio and time was obtained from the tests independently. Furthermore, a combined compression calculation method of municipal solid waste for all three parts of compressions including considering organics degradation is proposed based on a one-dimensional compression method. The relationship between the methane generation potential L0 of LandGEM model and degradation compression index was also discussed in the paper. A special column compression apparatus system, which can be used to simulate the whole compression process of municipal solid waste in China, was designed. According to the results obtained from 197-day column compression test, the new combined calculation method for municipal solid waste compression was analyzed. The degradation compression is the main part of the compression of MSW in the medium test period.
DNS and scaling law analysis of compressible turbulent channel flow
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Fully developed compressible turbulent channel flow (Ma=0.8,Re=3300) is numerically simulated, and the data base of turbulence is established. The s tatistics such as density_weighted mean velocity and RMS velocity fluctuations i n semi_local coordinates agree well with those from other DNS data. High order s tatistics (skewness and flatness factors) of velocity fluctuations of compressib le turbulence are reported for the first time. Compressibility effects are also discussed. Pressure_dilatation absorbs part of the kinetic energy and makes the streaks of compressible channel flow more smooth. The scaling laws of compressible channel flow are also discussed. The conclusi ons are: (a) Scaling law is found in the center area of the channel. (b) In this area, ESS is also found. (c) When Mach number is not ve ry high, compressibility has little effect on scaling exponents.
Dynamical compressibility of dense granular shear flows
Trulsson, Martin; Bouzid, Mehdi; Claudin, Philippe; Andreotti, Bruno
2012-01-01
It has been conjectured by Bagnold [1] that an assembly of hard non-deformable spheres could behave as a compressible medium when slowly sheared, as the average density of such a system effectively depends on the confining pressure. Here we use discrete element simulations to show the existence of transverse and sagittal waves associated to this dynamical compressibility. For this purpose, we study the resonance of these waves in a linear Couette cell and compare the results with those predic...
Reevaluation of compressible-flow Preston tube calibrations
Allen, J. M.
1977-01-01
Revised zero-pressure-gradient, adiabatic wall skin-friction-balance data covering a Mach number range from 1.6 to 4.6 led to a reevaluation of existing compressible flow Preston tube calibration equations.
Modelling of pressure-strain correlation in compressible turbulent flow
Institute of Scientific and Technical Information of China (English)
Siyuan Huang; Song Fu
2008-01-01
Previous studies carried out in the early 1990s conjectured that the main compressible effects could be associated with the dilatational effects of velocity fluctuation.Later,it was shown that the main compressibility effect came from the reduced pressure-strain term due to reduced pressure fluctuations.Although better understanding of the compressible turbulence is generally achieved with the increased DNS and experimental research effort,there are still some discrepancies among these recent findings.Analysis of the DNS and experimental data suggests that some of the discrepancies are apparent if the compressible effect is related to the turbulent Mach number,Mt.From the comparison of two classes of compressible flow,homogenous shear flow and inhomogeneous shear flow(mixing layer),we found that the effect of compressibility on both classes of shear flow can be characterized in three categories corresponding to three regions of turbulent Mach numbers:the low-Mt,the moderate-Mt and high-Mt regions.In these three regions the effect of compressibility on the growth rate of the turbulent mixing layer thickness is rather different.A simple approach to the reduced pressure-strain effect may not necessarily reduce the mixing-layer growth rate,and may even cause an increase in the growth rate.The present work develops a new second-moment model for the compressible turbulence through the introduction of some blending functions of Mt to account for the compressibility effects on the flow.The model has been successfully applied to the compressible mixing layers.
Studies of compressible shear flows and turbulent drag reduction
Orszag, S. A.
1981-04-01
Compressible shear flows and drag reduction were examined and three methods are addressed: (1) the analytical and numerical aspects of conformal mapping were summarized and a new method for computation of these maps is presented; (2) the computer code SPECFD for solution of the three dimensional time dependent Navier-Stokes equations for compressible flow on the CYBER 203 computer is described; (3) results of two equation turbulence modeling of turbulent flow over wavy walls are presented. A modified Jones-Launder model is used in two dimensional spectral code for flow in general wavy geometries.
Flow calculation of a bulb turbine
Energy Technology Data Exchange (ETDEWEB)
Goede, E.; Pestalozzi, J.
1987-01-01
In recent years remarkable progress has been made in the field of theoretical flow calculation. Studying the relevant literature one might receive the impression that most problems have been solved. But probing more deeply into details one becomes aware that by no means all questions are answered. The report tries to point out what may be expected of the quasi-three-dimensional flow calculation method employed and - much more important - what it must not be expected to accomplish. (orig.)
Vadyak, J.; Hoffman, J. D.; Bishop, A. R.
1978-01-01
The calculation procedure is based on the method of characteristics for steady three-dimensional flow. The bow shock wave and the internal shock wave system were computed using a discrete shock wave fitting procedure. The general structure of the computer program is discussed, and a brief description of each subroutine is given. All program input parameters are defined, and a brief discussion on interpretation of the output is provided. A number of sample cases, complete with data deck listings, are presented.
THE BERNOULLI EQUATION AND COMPRESSIBLE FLOW THEORIES
The incompressible Bernoulli equation is an analytical relationship between pressure, kinetic energy, and potential energy. As perhaps the simplest and most useful statement for describing laminar flow, it buttresses numerous incompressible flow models that have been developed ...
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.
Columbia River flow-time calculations
Energy Technology Data Exchange (ETDEWEB)
Soldat, J.K.
1958-11-21
Re-appraisal of the available data on flow times of the Columbia River between the reactor areas and Pasco was undertaken to permit extrapolation of the flow-time curves to lower river flow rates. Comparisons were made between data collected by the US Corps of Engineers and Regional Monitoring and with the equation for calculation of flow times developed by H.T. Norton. Extrapolation of the Regional Monitoring float study data to a flow of 3 {times} 10{sup 5} gallons per second was accomplished by comparison with the slope of the curve obtained from the US Corps of Engineers data; the latter covered flow times from 100-F Area to Pasco over a range of 3.4 {times} 10{sup 5} gps to 3.7 {times} 10{sup 6} gps. The revised flow-time curves are illustrated in Figures 1 through 6.
Integral representation in the hodograph plane of compressible flow
DEFF Research Database (Denmark)
Hansen, Erik Bent; Hsiao, G.C.
2003-01-01
Compressible flow is considered in the hodograph plane. The linearity of the equation determining the stream function is exploited to derive a representation formula involving boundary data only, and a fundamental solution to the adjoint equation. For subsonic flow, an efficient algorithm for com...
Smoothness monitors for compressible flow computation
Energy Technology Data Exchange (ETDEWEB)
Sjogreen, B; Yee, H C
2008-09-02
In [SY04, YS07] and references cited therein, the authors introduced the concept of employing multiresolution wavelet decomposition of computed flow data as smoothness monitors (flow sensors) to indicate the amount and location of built-in numerical dissipation that can be eliminated or further reduced in shock-capturing schemes. Studies indicated that this approach is able to limit the use of numerical dissipation with improved accuracy compared with standard shock-capturing methods. The studies in [SY04, YS07] were limited to low order multiresolution redundant wavelets with low level supports and low order vanishing moments. The objective of this paper is to expand the previous investigation to include higher order redundant wavelets with larger support and higher order vanishing moments for a wider spectrum of flow type and flow speed applications.
Compressible Turbulent Channel Flows: DNS Results and Modeling
Huang, P. G.; Coleman, G. N.; Bradshaw, P.; Rai, Man Mohan (Technical Monitor)
1994-01-01
The present paper addresses some topical issues in modeling compressible turbulent shear flows. The work is based on direct numerical simulation of two supersonic fully developed channel flows between very cold isothermal walls. Detailed decomposition and analysis of terms appearing in the momentum and energy equations are presented. The simulation results are used to provide insights into differences between conventional time-and Favre-averaging of the mean-flow and turbulent quantities. Study of the turbulence energy budget for the two cases shows that the compressibility effects due to turbulent density and pressure fluctuations are insignificant. In particular, the dilatational dissipation and the mean product of the pressure and dilatation fluctuations are very small, contrary to the results of simulations for sheared homogeneous compressible turbulence and to recent proposals for models for general compressible turbulent flows. This provides a possible explanation of why the Van Driest density-weighted transformation is so successful in correlating compressible boundary layer data. Finally, it is found that the DNS data do not support the strong Reynolds analogy. A more general representation of the analogy is analysed and shown to match the DNS data very well.
Compressibility effects on the flow past a rotating cylinder
Teymourtash, A. R.; Salimipour, S. E.
2017-01-01
In this paper, laminar flow past a rotating circular cylinder placed in a compressible uniform stream is investigated via a two-dimensional numerical simulation and the compressibility effects due to the combination of the free-stream and cylinder rotation on the flow pattern such as forming, shedding, and removing of vortices and also the lift and drag coefficients are studied. The numerical simulation of the flow is based on the discretization of convective fluxes of the unsteady Navier-Stokes equations by second-order Roe's scheme and an explicit finite volume method. Because of the importance of the time dependent parameters in the solution, the second-order time accurate is applied by a dual time stepping approach. In order to validate the operation of a computer program, some results are compared with previous experimental and numerical data. The results of this study show that the effects due to flow compressibility such as normal shock wave caused the interesting variations on the flow around the cylinder even at a free-stream with a low Mach number. At incompressible flow around the rotating cylinder, increasing the speed ratio, α (ratio of the surface speed to free-stream velocity), causes the ongoing increase in the lift coefficient, but in compressible flow for each free-stream Mach number, increasing the speed ratio results in obtaining a limited lift coefficient (a maximum mean lift coefficient). In addition, results from the compressible flow indicate that by increasing the free-stream Mach number, the maximum mean lift coefficient is decreased, while the mean drag coefficient is increased. It is also found that by increasing the Reynolds number at low Mach numbers, the maximum mean lift coefficient and critical speed ratio are decreased and the mean drag coefficient and Strouhal number are increased. However at the higher Mach numbers, these parameters become independent of the Reynolds number.
DEFF Research Database (Denmark)
Andersen, Stig Kildegård; Carlsen, Henrik; Thomsen, Per Grove
2006-01-01
We present an approach for modelling unsteady, primarily one-dimensional, compressible flow. The conservation laws for mass, energy, and momentum are applied to a staggered mesh of control volumes and loss mechanisms are included directly as extra terms. Heat transfer, flow friction......, and multidimensional effects are calculated using empirical correlations. Transformations of the conservation equations into new variables, artificial dissipation for dissipating acoustic phenomena, and an asymmetric interpolation method for minimising numerical diffusion and non physical temperature oscillations...
Investigation of turbulence models with compressibility corrections for hypersonic boundary flows
Directory of Open Access Journals (Sweden)
Han Tang
2015-12-01
Full Text Available The applications of pressure work, pressure-dilatation, and dilatation-dissipation (Sarkar, Zeman, and Wilcox models to hypersonic boundary flows are investigated. The flat plate boundary layer flows of Mach number 5–11 and shock wave/boundary layer interactions of compression corners are simulated numerically. For the flat plate boundary layer flows, original turbulence models overestimate the heat flux with Mach number high up to 10, and compressibility corrections applied to turbulence models lead to a decrease in friction coefficients and heating rates. The pressure work and pressure-dilatation models yield the better results. Among the three dilatation-dissipation models, Sarkar and Wilcox corrections present larger deviations from the experiment measurement, while Zeman correction can achieve acceptable results. For hypersonic compression corner flows, due to the evident increase of turbulence Mach number in separation zone, compressibility corrections make the separation areas larger, thus cannot improve the accuracy of calculated results. It is unreasonable that compressibility corrections take effect in separation zone. Density-corrected model by Catris and Aupoix is suitable for shock wave/boundary layer interaction flows which can improve the simulation accuracy of the peak heating and have a little influence on separation zone.
Environmental flow allocation and statistics calculator
Konrad, Christopher P.
2011-01-01
The Environmental Flow Allocation and Statistics Calculator (EFASC) is a computer program that calculates hydrologic statistics based on a time series of daily streamflow values. EFASC will calculate statistics for daily streamflow in an input file or will generate synthetic daily flow series from an input file based on rules for allocating and protecting streamflow and then calculate statistics for the synthetic time series. The program reads dates and daily streamflow values from input files. The program writes statistics out to a series of worksheets and text files. Multiple sites can be processed in series as one run. EFASC is written in MicrosoftRegistered Visual BasicCopyright for Applications and implemented as a macro in MicrosoftOffice Excel 2007Registered. EFASC is intended as a research tool for users familiar with computer programming. The code for EFASC is provided so that it can be modified for specific applications. All users should review how output statistics are calculated and recognize that the algorithms may not comply with conventions used to calculate streamflow statistics published by the U.S. Geological Survey.
Nonmodal Growth Of Kelvin-Helmholtz Instability In Compressible Flows
Karimi, Mona; Girimaji, Sharath
2016-11-01
Kelvin-helmholtz instability (khi) is central to the vertical mixing in shear flows and is known to be suppressed in compressible flows. To understand the inhibition of mixing under the influence of compressibility, we analyze the linear growth of khi in the short-time limit using initial value analysis. The evolution of perturbations is studied from a nonmodal standpoint. As the underlying suppression mechanism can be understood by considering primarily linear physics, the effect of compressibility on khi is scrutinized by linear analysis. Then its inferences are verified against direct numerical simulations. It has been demonstrated that compressibility forces the dominance of dilatational, rather than shear, dynamics at the interface of two fluids of different velocities. Within the dilatiatonal interface layer, pressure waves cause the velocity perturbation to become oscillatory [karimi and girimaji, 2016]. Thereupon, the focus is to examine the effect of the initial perturbation wavenumber on the formation of this layer and eventually the degree of khi suppression in compressible flows. We demonstrate that the degree of suppression decreases with the increase the wavenumbers of the initial perturbation of dilatational, rather than shear, dynamics at the interface of two fluids of different velocities. Within the dilatiatonal interface layer, pressure waves cause the velocity perturbation to become oscillatory [karimi and girimaji, 2016]. Thereupon, the focus is to examine the effect of the initial perturbation wavenumber on the formation of this layer and eventually the degree of khi suppression in compressible flows. We demonstrate that the degree of suppression decreases with the increase the wavenumbers of the initial perturbation.
A 3-dimensional mass conserving element for compressible flows
Fix, G.; Suri, M.
1985-01-01
A variety of finite element schemes has been used in the numerical approximation of compressible flows particularly in underwater acoustics. In many instances instabilities have been generated due to the lack of mass conservation. Two- and three-dimensional elements are developed which avoid these problems.
Space-time discontinuous Galerkin method for compressible flow
Klaij, C.M.
2006-01-01
The space-time discontinuous Galerkin method allows the simulation of compressible flow in complex aerodynamical applications requiring moving, deforming and locally refined meshes. This thesis contains the space-time discretization of the physical model, a fully explicit solver for the resulting
Gaseous Nitrogen Orifice Mass Flow Calculator
Ritrivi, Charles
2013-01-01
The Gaseous Nitrogen (GN2) Orifice Mass Flow Calculator was used to determine Space Shuttle Orbiter Water Spray Boiler (WSB) GN2 high-pressure tank source depletion rates for various leak scenarios, and the ability of the GN2 consumables to support cooling of Auxiliary Power Unit (APU) lubrication during entry. The data was used to support flight rationale concerning loss of an orbiter APU/hydraulic system and mission work-arounds. The GN2 mass flow-rate calculator standardizes a method for rapid assessment of GN2 mass flow through various orifice sizes for various discharge coefficients, delta pressures, and temperatures. The calculator utilizes a 0.9-lb (0.4 kg) GN2 source regulated to 40 psia (.276 kPa). These parameters correspond to the Space Shuttle WSB GN2 Source and Water Tank Bellows, but can be changed in the spreadsheet to accommodate any system parameters. The calculator can be used to analyze a leak source, leak rate, gas consumables depletion time, and puncture diameter that simulates the measured GN2 system pressure drop.
Tsai, C.; Yeh, G.
2011-12-01
In this investigation, newly proposed constitutive retentions are implemented to a fractional-flow based compressible multiphase-phase flow model. With the new model, a compressible three-phase (water, non-aqueous phase liquid (NAPL) and air) flow problem is simulated. In fractional-flow approaches, the three mass balance equations written in terms of three phase pressures are transformed to those in terms of the total pressure, saturation of water, and saturation of total liquid. These three governing equations are discretized with the Galerkin finite element method (FEM). The resulted matrix equation is solved with Bi-CGSTAB. Several numerical experiments are presented to examine the accuracy and robustness of the proposed model. The results show the presented fractional-flow based multiphase flow model is feasible and yields physically realistic solutions for compressible three-phase flow problems in porous media.
Flow calculation in a bulb turbine
Energy Technology Data Exchange (ETDEWEB)
Goede, E.; Pestalozzi, J.
1987-02-01
In recent years remarkable progress has been made in the field of computational fluid dynamics. Sometimes the impression may arise when reading the relevant literature that most of the problems in this field have already been solved. Upon studying the matter more deeply, however, it is apparent that some questions still remain unanswered. The use of the quasi-3D (Q3D) computational method for calculating the flow in a fuel hydraulic turbine is described.
Study of parameters of a facility generating compressive plasma flows
Leyvi, A. Ya
2017-05-01
The prosperity of plasma technologies stimulates making of a facility generating compressive plasma flows at the South Ural State University. The facility is a compact-geometry magnetoplasma compressor with the following parameters: stored energy up to 15 kJ, voltage of a bank from 3 to 5 kV; nitrogen, air, and other gases can serve as its operating gas. The investigation of parameters of the facility showed the following parameters of compressive plasma flows: impulse duration of up to 120 μs, discharge current of 50-120 kA, speed of plasma flow of 15-30 km/s. By contrast to the available facilities, the parameters of the developed facility can be adjusted in a wide range of voltage from 2 kV to 10 kV, its design permits generating CPF in horizontal and vertical positions.
Compression of flow can reveal overlapping modular organization in networks
Esquivel, Alcides Viamontes
2011-01-01
To better understand the overlapping modular organization of large networks with respect to flow, here we introduce the map equation for overlapping modules. In this information-theoretic framework, we use the correspondence between compression and regularity detection. The generalized map equation measures how well we can compress a description of flow in the network when we partition it into modules with possible overlaps. When we minimize the generalized map equation over overlapping network partitions, we detect modules that capture flow and determine which nodes at the boundaries between modules should be classified in multiple modules and to what degree. With a novel greedy search algorithm, we find that some networks, for example, the neural network of C. Elegans, are best described by modules dominated by hard boundaries, but that others, for example, the sparse road network of California, have a highly overlapping modular organization. To compare our approach with other clustering algorithms, we sugg...
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.
Compressibility Corrections to Closure Approximations for Turbulent Flow Simulations
Energy Technology Data Exchange (ETDEWEB)
Cloutman, L D
2003-02-01
We summarize some modifications to the usual closure approximations for statistical models of turbulence that are necessary for use with compressible fluids at all Mach numbers. We concentrate here on the gradient-flu approximation for the turbulent heat flux, on the buoyancy production of turbulence kinetic energy, and on a modification of the Smagorinsky model to include buoyancy. In all cases, there are pressure gradient terms that do not appear in the incompressible models and are usually omitted in compressible-flow models. Omission of these terms allows unphysical rates of entropy change.
A skin friction law for compressible turbulent flow
Barnwell, Richard W.; Wahls, Richard A.
1989-01-01
An algebraic skin friction law is derived for adiabatic, compressible, equilibrium, turbulent boundary layer flow. An outer solution in terms of the Clauser defect stream function is matched to an inner empirical expression composed of compressible laws of the wall and wake. The modified Crocco temperature-velocity relationship and the Clauser eddy viscousity model are used in the outer solution. The skin friction law pertains for all pressure gradients in the incompressible through supersonic range and for small pressure gradients in the hypersonic range. Excellent comparisons with experiment are obtained in the appropriate parameter ranges. The application to numerical computation is discussed.
Skin blood flow with elastic compressive extravehicular activity space suit.
Tanaka, Kunihiko; Gotoh, Taro M; Morita, Hironobu; Hargens, Alan R
2003-10-01
During extravehicular activity (EVA), current space suits are pressurized with 100% oxygen at approximately 222 mmHg. A tight elastic garment, or mechanical counter pressure (MCP) suit that generates pressure by compression, may have several advantages over current space suit technology. In this study, we investigated local microcirculatory effects produced with negative ambient pressure with an MCP sleeve. The MCP glove and sleeve generated pressures similar to the current space suit. MCP remained constant during negative pressure due to unchanged elasticity of the material. Decreased skin capillary blood flow and temperature during MCP compression was counteracted by greater negative pressure or a smaller pressure differential.
Numerical calculation of turbomachinery cascade flows
Liu, Feng
A numerical method for solving both the Euler and the Reynolds-averaged Navier-Stokes equations for flows in turbomachinery cascades is presented and verified. The method is based on a finite volume method with an explicit multi-stage time-stepping scheme originally developed by Jameson for the Euler equations. Modified discretization schemes, based on Martinelli's work for the second order derivatives in the Navier-Stokes equations, are proposed for both the cell-vertex and the cell-centered schemes. The new schemes avoid a potential discretization problem with kinked meshes. Use of artificial dissipation to stabilize a central difference scheme and capture shocks is discussed. Local time stepping and residual smoothing are used to increase the allowable time steps for stability. A multigrid method is employed to accelerate convergence to steady state. For steady inviscid flows enthalpy damping is also used. The method is capable of handling flows of low Mach number (lower than 0.3), and transonic and supersonic flows. Both laminar and turbulent flows are calculated in solving the Reynolds-averaged equations. The Reynolds number may range from order 1 to 10(exp 7) or even higher as long as enough mesh resolution and a proper turbulence model are provided. The Baldwin-Lomax algebraic turbulence model is used in the current work. An elliptic mesh generator is used to generate H-type meshes for cascades. The cell-centered scheme is programmed in both two- and three-dimensions for the Euler equations. Numerical results included a two-dimensional Hobson cascade, a supersonic wedge cascade and the VKI turbine cascade. The three-dimensional code is used to calculate the flow in a low pressure turbine cascade. Results compare well with experimental data at design conditions. At off-design conditions, the Euler method fails in regions of large separations.
Moortgat, J.; Amooie, M. A.; Soltanian, M. R.
2016-12-01
Problems in hydrogeology and hydrocarbon reservoirs generally involve the transport of solutes in a single solvent phase (e.g., contaminants or dissolved injection gas), or the flow of multiple phases that may or may not exchange mass (e.g., brine, NAPL, oil, gas). Often, flow is viscously and gravitationally unstable due to mobility and density contrasts within a phase or between phases. Such instabilities have been studied in detail for single-phase incompressible fluids and for two-phase immiscible flow, but to a lesser extent for multiphase multicomponent compressible flow. The latter is the subject of this presentation. Robust phase stability analyses and phase split calculations, based on equations of state, determine the mass exchange between phases and the resulting phase behavior, i.e., phase densities, viscosities, and volumes. Higher-order finite element methods and fine grids are used to capture the small-scale onset of flow instabilities. A full matrix of composition dependent coefficients is considered for each Fickian diffusive phase flux. Formation heterogeneity can have a profound impact and is represented by realistic geostatistical models. Qualitatively, fingering in multiphase compositional flow is different from single-phase problems because 1) phase mobilities depend on rock wettability through relative permeabilities, and 2) the initial density and viscosity ratios between phases may change due to species transfer. To quantify mixing rates in different flow regimes and for varying degrees of miscibility and medium heterogeneities, we define the spatial variance, scalar dissipation rate, dilution index, skewness, and kurtosis of the molar density of introduced species. Molar densities, unlike compositions, include compressibility effects. The temporal evolution of these measures shows that, while transport at the small-scale (cm) is described by the classical advection-diffusion-dispersion relations, scaling at the macro-scale (> 10 m) shows
Energy Technology Data Exchange (ETDEWEB)
Rian, Kjell Erik
2003-07-01
In numerical simulations of turbulent reacting compressible flows, artificial boundaries are needed to obtain a finite computational domain when an unbounded physical domain is given. Artificial boundaries which fluids are free to cross are called open boundaries. When calculating such flows, non-physical reflections at the open boundaries may occur. These reflections can pollute the solution severely, leading to inaccurate results, and the generation of spurious fluctuations may even cause the numerical simulation to diverge. Thus, a proper treatment of the open boundaries in numerical simulations of turbulent reacting compressible flows is required to obtain a reliable solution for realistic conditions. A local quasi-one-dimensional characteristic-based open-boundary treatment for the Favre-averaged governing equations for time-dependent three-dimensional multi-component turbulent reacting compressible flow is presented. A k-{epsilon} model for turbulent compressible flow and Magnussen's EDC model for turbulent combustion is included in the analysis. The notion of physical boundary conditions is incorporated in the method, and the conservation equations themselves are applied on the boundaries to complement the set of physical boundary conditions. A two-dimensional finite-difference-based computational fluid dynamics code featuring high-order accurate numerical schemes was developed for the numerical simulations. Transient numerical simulations of the well-known, one-dimensional shock-tube problem, a two-dimensional pressure-tower problem in a decaying turbulence field, and a two-dimensional turbulent reacting compressible flow problem have been performed. Flow- and combustion-generated pressure waves seem to be well treated by the non-reflecting subsonic open-boundary conditions. Limitations of the present open-boundary treatment are demonstrated and discussed. The simple and solid physical basis of the method makes it both favourable and relatively easy to
Viscous and Gravitational Fingering in Multiphase Compositional and Compressible Flow
Moortgat, Joachim
2016-01-01
Viscous and gravitational fingering refer to flow instabilities in porous media that are triggered by adverse mobility or density ratios, respectively. These instabilities have been studied extensively in the past for 1) single-phase flow (e.g., contaminant transport in groundwater, first-contact-miscible displacement of oil by gas in hydrocarbon production), and 2) multi-phase immiscible and incompressible flow (e.g., water-alternating-gas (WAG) injection in oil reservoirs). Fingering in multiphase compositional and compressible flow has received much less attention, perhaps due to its high computational complexity. However, many important subsurface processes involve multiple phases that exchange species. Examples are carbon sequestration in saline aquifers and enhanced oil recovery (EOR) by gas or WAG injection below the minimum miscibility pressure. In multiphase flow, relative permeabilities affect the mobility contrast for a given viscosity ratio. Phase behavior can also change local fluid properties, w...
Discontinuous Galerkin method analysis and applications to compressible flow
Dolejší, Vít
2015-01-01
The subject of the book is the mathematical theory of the discontinuous Galerkin method (DGM), which is a relatively new technique for the numerical solution of partial differential equations. The book is concerned with the DGM developed for elliptic and parabolic equations and its applications to the numerical simulation of compressible flow. It deals with the theoretical as well as practical aspects of the DGM and treats the basic concepts and ideas of the DGM, as well as the latest significant findings and achievements in this area. The main benefit for readers and the book’s uniqueness lie in the fact that it is sufficiently detailed, extensive and mathematically precise, while at the same time providing a comprehensible guide through a wide spectrum of discontinuous Galerkin techniques and a survey of the latest efficient, accurate and robust discontinuous Galerkin schemes for the solution of compressible flow.
Method for Calculation of Steam-Compression Heat Transformers
S. Zditovetckaya; Volodin, V
2012-01-01
The paper considers a method for joint numerical analysis of cycle parameters and heatex-change equipment of steam-compression heat transformer contour that takes into account a non-stationary operational mode and irreversible losses in devices and pipeline contour. The method has been realized in the form of the software package and can be used while making design or selection of a heat transformer with due account of a coolant and actual equipment being included in its structure.The paper p...
Viscous and gravitational fingering in multiphase compositional and compressible flow
Moortgat, Joachim
2016-03-01
Viscous and gravitational fingering refer to flow instabilities in porous media that are triggered by adverse mobility or density ratios, respectively. These instabilities have been studied extensively in the past for (1) single-phase flow (e.g., contaminant transport in groundwater, first-contact-miscible displacement of oil by gas in hydrocarbon production), and (2) multi-phase immiscible and incompressible flow (e.g., water-alternating-gas (WAG) injection in oil reservoirs). Fingering in multiphase compositional and compressible flow has received much less attention, perhaps due to its high computational complexity. However, many important subsurface processes involve multiple phases that exchange species. Examples are carbon sequestration in saline aquifers and enhanced oil recovery (EOR) by gas or WAG injection below the minimum miscibility pressure. In multiphase flow, relative permeabilities affect the mobility contrast for a given viscosity ratio. Phase behavior can also change local fluid properties, which can either enhance or mitigate viscous and gravitational instabilities. This work presents a detailed study of fingering behavior in compositional multiphase flow in two and three dimensions and considers the effects of (1) Fickian diffusion, (2) mechanical dispersion, (3) flow rates, (4) domain size and geometry, (5) formation heterogeneities, (6) gravity, and (7) relative permeabilities. Results show that fingering in compositional multiphase flow is profoundly different from miscible conditions and upscaling techniques used for the latter case are unlikely to be generalizable to the former.
Method for Calculation of Steam-Compression Heat Transformers
Directory of Open Access Journals (Sweden)
S. Zditovetckaya
2012-01-01
Full Text Available The paper considers a method for joint numerical analysis of cycle parameters and heatex-change equipment of steam-compression heat transformer contour that takes into account a non-stationary operational mode and irreversible losses in devices and pipeline contour. The method has been realized in the form of the software package and can be used while making design or selection of a heat transformer with due account of a coolant and actual equipment being included in its structure.The paper presents investigation results revealing influence of pressure loss in an evaporator and a condenser from the side of the coolant caused by a friction and local resistance on power efficiency of the heat transformer which is operating in the mode of refrigerating and heating installation and a thermal pump. Actually obtained operational parameters of the thermal pump in the nominal and off-design operatinal modes depend on the structure of the concrete contour equipment.
Hybrid Explicit Residual Distribution Scheme for Compressible Multiphase Flows
Bacigaluppi, Paola; Abgrall, Rémi; Kaman, Tulin
2017-03-01
The aim of this work is the development of a fully explicit scheme in the framework of time dependent hyperbolic problems with strong interacting discontinuities to retain high order accuracy in the context of compressible multiphase flows. A new methodology is presented to compute compressible two-fluid problems applied to the five equation reduced model given in Kapila et al. (Physics of Fluids 2001). With respect to other contributions in that area, we investigate a method that provides mesh convergence to the exact solutions, where the studied non-conservative system is associated to consistent jump relations. The adopted scheme consists of a coupled predictor-corrector scheme, which follows the concept of residual distributions in Ricchiuto and Abgrall (J. Comp. Physics 2010), with a classical Glimm’s scheme (J. Sci. Stat. Comp. 1982) applied to the area where a shock is occurring. This numerical methodology can be easily extended to unstructured meshes. Test cases on a perfect gas for a two phase compressible flow on a Riemann problem have verified that the approximation converges to its exact solution. The results have been compared with the pure Glimm’s scheme and the expected exact solution, finding a good overlap.
Compressive sampling for energy spectrum estimation of turbulent flows
Adalsteinsson, Gudmundur F
2014-01-01
Recent results from compressive sampling (CS) have demonstrated that accurate reconstruction of sparse signals often requires far fewer samples than suggested by the classical Nyquist--Shannon sampling theorem. Typically, signal reconstruction errors are measured in the $\\ell^2$ norm and the signal is assumed to be sparse, compressible or having a prior distribution. Our spectrum estimation by sparse optimization (SpESO) method uses prior information about isotropic homogeneous turbulent flows with power law energy spectra and applies the methods of CS to 1-D and 2-D turbulence signals to estimate their energy spectra with small logarithmic errors. SpESO is distinct from existing energy spectrum estimation methods which are based on sparse support of the signal in Fourier space. SpESO approximates energy spectra with an order of magnitude fewer samples than needed with Shannon sampling. Our results demonstrate that SpESO performs much better than lumped orthogonal matching pursuit (LOMP), and as well or bette...
Achieving acoustic cloak by using compressible background flow
Zhang, Ruo-Yang; Ge, Mo-Lin
2016-01-01
We propose a scheme of acoustic spherical cloaking by means of background irrotational flow in compressible fluid. The background flow forms a virtual curved spacetime and guides the sound waves bypass the cloaked objects. To satisfy the laws of real fluid, we show that spatially distributed mass source and momentum source are necessary to supply. The propagation of sound waves in this system is studied via both geometric acoustics approximation and full wave approach. The analytic solution of sound fields is obtained for plane wave incidence. The results reveal the effect of phase retardation (or lead) in comparison with the ordinary transformation-acoustic cloak. In addition, the ability of cloaking is also evaluated for unideal background flows by analyzing the scattering cross section.
Achieving acoustic cloak by using compressible background flow
Zhang, Ruo-Yang; Zhao, Qing; Ge, Mo-Lin
2016-08-01
We propose a scheme of acoustic spherical cloaking by means of background irrotational flow in compressible fluid. The background flow forms a virtual curved spacetime and directs the sound waves to bypass the cloaked objects. To satisfy the laws of real fluid, we show that spatially distributed mass source and momentum source are necessary to supply. The propagation of sound waves in this system is studied via both geometric acoustics approximation and full wave approach. The analytic solution of sound fields is obtained for plane wave incidence. The results reveal the effect of phase retardation (or lead) in comparison with the ordinary transformation-acoustic cloak. In addition, the ability of cloaking is also evaluated for unideal background flows by analyzing the scattering cross section. Project supported by the National Natural Science Foundation of China (Grant Nos. 11475088 and 11275024) and the Fund from the Ministry of Science and Technology of China (Grant No. 2013YQ030595-3).
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Between the transformations, witch can transform the compressible wave equation to the incompressible flow, a kind of relativity character can be found, which have the almost equal character as Lorenz time and space relation. This result leads to a new inference: incompressible wave equation with time and space structure of sonic special relativity is only different description of approximate compressible flow. This conclusion can be extended to Euler equation, and arise the interest of "compressible expression" of Maxwell equation. To study the rule of compressibility and thermodynamic character of metastructure field, a try is made by the using KamanTsian virtual gas method, this would give the relation,similar as mass and energy of special relativity theory.At first searching a transformation, witch can transform the compressible wave equation to the incompressible flow, but it is almost equal Lorenz time and space relation, So arrive to the conclusion: incompressible wave equation with approximate Lorentz transformation is only different description of compressible flow. This conclusion is expected be used to Maxwell equation, because its wave equation is also perfectly equal form. To search the rule of electromagnet and gravity field, by the using of Kaman-Tsian virtual gas method, the relation of mass and energy of relativity theory is given.``
Directory of Open Access Journals (Sweden)
Starishko Ivan Nikolaevich
2014-03-01
Full Text Available The proposed calculation method is specific in terms of determining the carrying capacity of eccentrically compressed concrete elements, in contrast to the calculation by error method, as in the existing regulations, where in the result of the calculation is not known what is the limit load the eccentric compression element can withstand. The proposed calculation method, the publication of which is expected in the next issue of the "Vestnik MGSU" the above mentioned shortcomings of the existing calculation methods, as well as the shortcomings listed in this article are eliminated, which results in the higher convergence of theoretical and experimental results of eccentrically compressed concrete elements strength and hence a high reliability of their operation.
Pencil: Finite-difference Code for Compressible Hydrodynamic Flows
Brandenburg, Axel; Dobler, Wolfgang
2010-10-01
The Pencil code is a high-order finite-difference code for compressible hydrodynamic flows with magnetic fields. It is highly modular and can easily be adapted to different types of problems. The code runs efficiently under MPI on massively parallel shared- or distributed-memory computers, like e.g. large Beowulf clusters. The Pencil code is primarily designed to deal with weakly compressible turbulent flows. To achieve good parallelization, explicit (as opposed to compact) finite differences are used. Typical scientific targets include driven MHD turbulence in a periodic box, convection in a slab with non-periodic upper and lower boundaries, a convective star embedded in a fully nonperiodic box, accretion disc turbulence in the shearing sheet approximation, self-gravity, non-local radiation transfer, dust particle evolution with feedback on the gas, etc. A range of artificial viscosity and diffusion schemes can be invoked to deal with supersonic flows. For direct simulations regular viscosity and diffusion is being used. The code is written in well-commented Fortran90.
Self-sustained oscillation for compressible cylindrical cavity flows
Directory of Open Access Journals (Sweden)
Kung-Ming CHUNG
2017-08-01
Full Text Available The presence of a cavity changes the mean and fluctuating pressure distributions. Similarities are observed between a cylindrical cavity and a rectangular cavity for a compressible flow. The type of cavity flow field depends on the diameter-to-depth ratio and the length-to-depth ratio. The feedback loop is responsible for the generation of discrete acoustic tones. In this study, the self-sustained oscillation for a compressible cylindrical cavity flow was investigated experimentally. For open-type cavities, the power spectra show that the strength of resonance depends on the diameter-to-depth ratio (4.43–43.0 and the incoming boundary layer thickness-to-depth ratio (0.72–7.0. The effective streamwise length is used as the characteristic length to estimate the Strouhal number. At higher modes, there is a large deviation from Rossiter’s formula for rectangular cavities. The gradient-based searching method was used to evaluate the values of the empirical parameters. Less phase lag and a lower convection velocity are observed.
Adjoint-based Optimal Flow Control for Compressible DNS
Otero, J Javier; Sandberg, Richard D
2016-01-01
A novel adjoint-based framework oriented to optimal flow control in compressible direct numerical simulations is presented. Also, a new formulation of the adjoint characteristic boundary conditions is introduced, which enhances the stability of the adjoint simulations. The flow configuration chosen as a case study consists of a two dimensional open cavity flow with aspect ratio $L/H=3$ and Reynolds number $Re=5000$. This flow configuration is of particular interest, as the turbulent and chaotic nature of separated flows pushes the adjoint approach to its limit. The target of the flow actuation, defined as cost, is the reduction of the pressure fluctuations at the sensor location. To exploit the advantages of the adjoint method, a large number of control parameters is used. The control consists of an actuating sub-domain where a two-dimensional body force is applied at every point within the sub-volume. This results in a total of $2.256 \\cdot 10^6$ control parameters. The final actuation achieved a successful ...
Computer program for calculating flow parameters and power requirements for cryogenic wind tunnels
Dress, D. A.
1985-01-01
A computer program has been written that performs the flow parameter calculations for cryogenic wind tunnels which use nitrogen as a test gas. The flow parameters calculated include static pressure, static temperature, compressibility factor, ratio of specific heats, dynamic viscosity, total and static density, velocity, dynamic pressure, mass-flow rate, and Reynolds number. Simplifying assumptions have been made so that the calculations of Reynolds number, as well as the other flow parameters can be made on relatively small desktop digital computers. The program, which also includes various power calculations, has been developed to the point where it has become a very useful tool for the users and possible future designers of fan-driven continuous-flow cryogenic wind tunnels.
Coherent structures in compressible free-shear-layer flows
Energy Technology Data Exchange (ETDEWEB)
Aeschliman, D.P.; Baty, R.S. [Sandia National Labs., Albuquerque, NM (United States). Engineering Sciences Center; Kennedy, C.A.; Chen, J.H. [Sandia National Labs., Livermore, CA (United States). Combustion and Physical Sciences Center
1997-08-01
Large scale coherent structures are intrinsic fluid mechanical characteristics of all free-shear flows, from incompressible to compressible, and laminar to fully turbulent. These quasi-periodic fluid structures, eddies of size comparable to the thickness of the shear layer, dominate the mixing process at the free-shear interface. As a result, large scale coherent structures greatly influence the operation and efficiency of many important commercial and defense technologies. Large scale coherent structures have been studied here in a research program that combines a synergistic blend of experiment, direct numerical simulation, and analysis. This report summarizes the work completed for this Sandia Laboratory-Directed Research and Development (LDRD) project.
Simple numerical method for predicting steady compressible flows
Vonlavante, Ernst; Nelson, N. Duane
1986-01-01
A numerical method for solving the isenthalpic form of the governing equations for compressible viscous and inviscid flows was developed. The method was based on the concept of flux vector splitting in its implicit form. The method was tested on several demanding inviscid and viscous configurations. Two different forms of the implicit operator were investigated. The time marching to steady state was accelerated by the implementation of the multigrid procedure. Its various forms very effectively increased the rate of convergence of the present scheme. High quality steady state results were obtained in most of the test cases; these required only short computational times due to the relative efficiency of the basic method.
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.
Viegas, J. R.; Rubesin, M. W.
1983-01-01
To make computer codes for two-dimensional compressible flows more robust and economical, wall functions for these flows, under adiabatic conditions, have been developed and tested. These wall functions have been applied to three two-equation models of turbulence. The tests consist of comparisons of calculated and experimental results for transonic and supersonic flow over a flat plate and for two-dimensional and axisymmetrical transonic shock-wave/boundary-layer interaction flows with and without separation. The calculations are performed with an implicit algorithm that solves the Reynolds-averaged Navier-Stokes equations. It is shown that results obtained agree very well with the data for the complex compressible flows tested, provided criteria for use of the wall functions are followed. The expected savings in cost of the computations and improved robustness of the code were achieved.
Numerical modeling of a compressible multiphase flow through a nozzle
Niedzielska, Urszula; Rabinovitch, Jason; Blanquart, Guillaume
2012-11-01
New thermodynamic cycles developed for more efficient low temperature resource utilization can increase the net power production from geothermal resources and sensible waste heat recovery by 20-40%, compared to the traditional organic Rankine cycle. These improved systems consist of a pump, a liquid heat exchanger, a two-phase turbine, and a condenser. The two-phase turbine is used to extract energy from a high speed multiphase fluid and consists of a nozzle and an axial impulse rotor. In order to model and optimize the fluid flow through this part of the system an analysis of two-phase flow through a specially designed convergent-divergent nozzle has to be conducted. To characterize the flow behavior, a quasi-one-dimensional steady-state model of the multiphase fluid flow through a nozzle has been constructed. A numerical code capturing dense compressible multiphase flow under subsonic and supersonic conditions and the coupling between both liquid and gas phases has been developed. The output of the code delivers data vital for the performance optimization of the two-phase nozzle.
Local conservative regularizations of compressible MHD and neutral flows
Krishnaswami, Govind S; Thyagaraja, Anantanarayanan
2016-01-01
Ideal systems like MHD and Euler flow may develop singularities in vorticity (w = curl v). Viscosity and resistivity provide dissipative regularizations of the singularities. In this paper we propose a minimal, local, conservative, nonlinear, dispersive regularization of compressible flow and ideal MHD, in analogy with the KdV regularization of the 1D kinematic wave equation. This work extends and significantly generalizes earlier work on incompressible Euler and ideal MHD. It involves a micro-scale cutoff length lambda which is a function of density, unlike in the incompressible case. In MHD, it can be taken to be of order the electron collisionless skin depth c/omega_pe. Our regularization preserves the symmetries of the original systems, and with appropriate boundary conditions, leads to associated conservation laws. Energy and enstrophy are subject to a priori bounds determined by initial data in contrast to the unregularized systems. A Hamiltonian and Poisson bracket formulation is developed and applied ...
A Theory of Unstaggered Airfoil Cascades in Compressible Flow
Spurr, Robert A.; Allen, H. Julian
1947-01-01
By use of the methods of thin airfoil theory, which include effects of compressibility, rela.tio^as are developed which permit the rapid determination of the pressure distribution over an unstaggered cascade of airfoils of a given profile, and the determination of the profile shape necessary to yield a given pressure distribution for small chord gap ratios, For incompressible flow the results of the theory are compared with available examples obtained by the more exact method of conformal transformation. Although the theory is developed for small chord/gap ratios, these comparisons show that it may be extended to chord/gap ratios of order unity, at least for low speed flows. Choking of cascades, a phenomenon of particular importance in compressor design, is considered.
On the stability of compressible flow past axisymmetric bodies
Malik, M. R.; Spall, R. E.
1991-01-01
Compressible linear stability theory for axisymmetric flows is presented. The theory is applied to flow past a cylinder and a sharp cone at a Mach number of 5 with adiabatic wall conditions. The effect of transverse curvature and body divergence is studied. It is found that transverse curvature has a stabilizing influence on axisymmetric (first and second mode) disturbances while it has a destabilizing influence on the asymmetric (oblique first mode) disturbances. The body divergence effects are stabilizing for both symmetric and asymmetric disturbances. Comparisons made with the results of planar stability theory show that, for a cylinder, curvature effects become more pronounced with increasing distance along the cylinder. For a sharp cone, these effects become less significant further away from the cone tip since the body radius increases faster than the growth of the boundary layer. The effect of cone angle on stability is also studied.
An interface capturing scheme for modeling atomization in compressible flows
Garrick, Daniel P.; Hagen, Wyatt A.; Regele, Jonathan D.
2017-09-01
The study of atomization in supersonic flow is critical to ensuring reliable ignition of scramjet combustors under startup conditions. Numerical methods incorporating surface tension effects have largely focused on the incompressible regime as most atomization applications occur at low Mach numbers. Simulating surface tension effects in compressible flow requires robust numerical methods that can handle discontinuities caused by both shocks and material interfaces with high density ratios. In this work, a shock and interface capturing scheme is developed that uses the Harten-Lax-van Leer-Contact (HLLC) Riemann solver while a Tangent of Hyperbola for INterface Capturing (THINC) interface reconstruction scheme retains the fluid immiscibility condition in the volume fraction and phasic densities in the context of the five equation model. The approach includes the effects of compressibility, surface tension, and molecular viscosity. One and two-dimensional benchmark problems demonstrate the desirable interface sharpening and conservation properties of the approach. Simulations of secondary atomization of a cylindrical water column after its interaction with a shockwave show good qualitative agreement with experimentally observed behavior. Three-dimensional examples of primary atomization of a liquid jet in a Mach 2 crossflow demonstrate the robustness of the method.
A compressive sensing approach to the calculation of the inverse data space
Khan, Babar Hasan
2012-01-01
Seismic processing in the Inverse Data Space (IDS) has its advantages like the task of removing the multiples simply becomes muting the zero offset and zero time data in the inverse domain. Calculation of the Inverse Data Space by sparse inversion techniques has seen mitigation of some artifacts. We reformulate the problem by taking advantage of some of the developments from the field of Compressive Sensing. The seismic data is compressed at the sensor level by recording projections of the traces. We then process this compressed data directly to estimate the inverse data space. Due to the smaller number of data set we also gain in terms of computational complexity.
Chien Liang, Ru; Che Liu, Cheng; Tsai Liang, Ming; Chen, Jiann Lin
2017-02-01
Dynamic axial compression (DAC) columns are key elements in Simulated Moving Bed, which is a chromatography process in drug industry and chemical engineering. In this study, we apply the computational fluid dynamics (CFD) technique to analyze the flow fields in the DAC column and propose rules for distributor design based on mass conservation in fluid dynamics. Computer aided design (CAD) is used in constructing the numerical 3D modelling for the mesh system. The laminar flow fields with Darcy’s law to model the porous zone are governed by the Navier-Stokes equations and employed to describe the porous flow fields. Experimental works have been conducted as the benchmark for us to choose feasible porous parameters for CFD. Besides, numerical treatments are elaborated to avoid calculation divergence resulting from large source terms. Results show that CFD combined with CAD is a good approach to investigate detailed flow fields in DAC columns and the design for distributors is straightforward.
Columbia River flow-time calculations
Energy Technology Data Exchange (ETDEWEB)
Soldat, J.K.
1962-07-01
An appraisal of available data on flow times in the Columbia River between the reactor areas and Pasco was made to permit extrapolation of the flow-time curves to lower river flow rates. Comparisons were made between data collected by the US Corps of Engineers and environmental monitoring data and with the previously developed equation for flow times. New equations were developed to fit curves over the range (4 to 40) x 10/sup 4/CFS.
Linear Stability Analysis of Compressible Channel Flow with Porous Walls
Rahbari, Iman
2015-01-01
We have investigated the effects of permeable walls, modeled by linear acoustic impedance with zero reactance, on compressible channel flow via linear stability analysis (LSA). Base flow profiles are taken from impermeable isothermal-wall laminar and turbulent channel flow simulations at bulk Reynolds number, $Re_b$= 6900 and Mach numbers, $M_b$ = 0.2, 0.5, 0.85. For a sufficiently high value of permeability, two dominant modes are excited: a bulk pressure mode, causing symmetric expulsion and suction of mass from the porous walls (Mode 0); a standing-wave-like mode, with a pressure node at the centerline (Mode 1). In the case of turbulent mean flow profiles, both modes generate additional Reynolds shear stresses augmenting the (base) turbulent ones, but concentrated in the viscous sublayer region; the trajectories of the two modes in the complex phase velocity space follow each other very closely for values of wall permeability spanning two orders of magnitude, suggesting their coexistence. The transition fr...
Filming the invisible - time-resolved visualization of compressible flows
Kleine, H.
2010-04-01
Essentially all processes in gasdynamics are invisible to the naked eye as they occur in a transparent medium. The task to observe them is further complicated by the fact that most of these processes are also transient, often with characteristic times that are considerably below the threshold of human perception. Both difficulties can be overcome by combining visualization methods that reveal changes in the transparent medium, and high-speed photography techniques that “stop” the motion of the flow. The traditional approach is to reconstruct a transient process from a series of single images, each taken in a different experiment at a different instant. This approach, which is still widely used today, can only be expected to give reliable results when the process is reproducible. Truly time-resolved visualization, which yields a sequence of flow images in a single experiment, has been attempted for more than a century, but many of the developed camera systems were characterized by a high level of complexity and limited quality of the results. Recent advances in digital high-speed photography have changed this situation and have provided the tools to investigate, with relative ease and in sufficient detail, the true development of a transient flow with characteristic time scales down to one microsecond. This paper discusses the potential and the limitations one encounters when using density-sensitive visualization techniques in time-resolved mode. Several examples illustrate how this approach can reveal and explain a number of previously undetected phenomena in a variety of highly transient compressible flows. It is demonstrated that time-resolved visualization offers numerous advantages which normally outweigh its shortcomings, mainly the often-encountered loss in resolution. Apart from the capability to track the location and/or shape of flow features in space and time, adequate time-resolved visualization allows one to observe the development of deliberately
Control volume based modelling of compressible flow in reciprocating machines
DEFF Research Database (Denmark)
Andersen, Stig Kildegård; Thomsen, Per Grove; Carlsen, Henrik
2004-01-01
, and multidimensional effects must be calculated using empirical correlations; correlations for steady state flow can be used as an approximation. A transformation that assumes ideal gas is presented for transforming equations for masses and energies in control volumes into the corresponding pressures and temperatures...
First-principles calculation of the reflectance of shock-compressed xenon
Energy Technology Data Exchange (ETDEWEB)
Norman, G. E.; Saitov, I. M., E-mail: saitovilnur@gmail.com; Stegailov, V. V. [Russian Academy of Sciences, Institute of High Temperatures (Russian Federation)
2015-05-15
Within electron density functional theory (DFT), the reflectance of radiation from shock-compressed xenon plasma is calculated. The dependence of the reflectance on the frequency of the incident radiation and on the plasma density is considered. The Fresnel formula is used. The expression for the longitudinal dielectric tensor in the long-wavelength limit is used to calculate the imaginary part of the dielectric function (DF). The real part of the DF is determined by the Kramers-Kronig transformation. The results are compared with experimental data. An approach is proposed to estimate the plasma frequency in shock-compressed xenon.
Compressible air flow through a collapsing liquid cavity
Gordillo, Stephan Gekle \\and José Manuel
2010-01-01
We present a multiscale approach to simulate the impact of a solid object on a liquid surface: upon impact a thin liquid sheet is thrown upwards all around the rim of the impactor while in its wake a large surface cavity forms. Under the influence of hydrostatic pressure the cavity immediately starts to collapse and eventually closes in a single point from which a thin, needle-like jet is ejected. Existing numerical treatments of liquid impact either consider the surrounding air as an incompressible fluid or neglect air effects altogether. In contrast, our approach couples a boundary-integral method for the liquid with a Roe scheme for the gas domain and is thus able to handle the fully \\emph{compressible} gas stream that is pushed out of the collapsing impact cavity. Taking into account air compressibility is crucial, since, as we show in this work, the impact crater collapses so violently that the air flow through the cavity neck attains supersonic velocities already at cavity diameters larger than 1 mm. Ou...
A Finite Element Method for Simulation of Compressible Cavitating Flows
Shams, Ehsan; Yang, Fan; Zhang, Yu; Sahni, Onkar; Shephard, Mark; Oberai, Assad
2016-11-01
This work focuses on a novel approach for finite element simulations of multi-phase flows which involve evolving interface with phase change. Modeling problems, such as cavitation, requires addressing multiple challenges, including compressibility of the vapor phase, interface physics caused by mass, momentum and energy fluxes. We have developed a mathematically consistent and robust computational approach to address these problems. We use stabilized finite element methods on unstructured meshes to solve for the compressible Navier-Stokes equations. Arbitrary Lagrangian-Eulerian formulation is used to handle the interface motions. Our method uses a mesh adaptation strategy to preserve the quality of the volumetric mesh, while the interface mesh moves along with the interface. The interface jump conditions are accurately represented using a discontinuous Galerkin method on the conservation laws. Condensation and evaporation rates at the interface are thermodynamically modeled to determine the interface velocity. We will present initial results on bubble cavitation the behavior of an attached cavitation zone in a separated boundary layer. We acknowledge the support from Army Research Office (ARO) under ARO Grant W911NF-14-1-0301.
Finite-volume WENO scheme for viscous compressible multicomponent flows
Coralic, Vedran; Colonius, Tim
2014-01-01
We develop a shock- and interface-capturing numerical method that is suitable for the simulation of multicomponent flows governed by the compressible Navier-Stokes equations. The numerical method is high-order accurate in smooth regions of the flow, discretely conserves the mass of each component, as well as the total momentum and energy, and is oscillation-free, i.e. it does not introduce spurious oscillations at the locations of shockwaves and/or material interfaces. The method is of Godunov-type and utilizes a fifth-order, finite-volume, weighted essentially non-oscillatory (WENO) scheme for the spatial reconstruction and a Harten-Lax-van Leer contact (HLLC) approximate Riemann solver to upwind the fluxes. A third-order total variation diminishing (TVD) Runge-Kutta (RK) algorithm is employed to march the solution in time. The derivation is generalized to three dimensions and nonuniform Cartesian grids. A two-point, fourth-order, Gaussian quadrature rule is utilized to build the spatial averages of the reconstructed variables inside the cells, as well as at cell boundaries. The algorithm is therefore fourth-order accurate in space and third-order accurate in time in smooth regions of the flow. We corroborate the properties of our numerical method by considering several challenging one-, two- and three-dimensional test cases, the most complex of which is the asymmetric collapse of an air bubble submerged in a cylindrical water cavity that is embedded in 10% gelatin. PMID:25110358
Lagrangian transported MDF methods for compressible high speed flows
Gerlinger, Peter
2017-06-01
This paper deals with the application of thermochemical Lagrangian MDF (mass density function) methods for compressible sub- and supersonic RANS (Reynolds Averaged Navier-Stokes) simulations. A new approach to treat molecular transport is presented. This technique on the one hand ensures numerical stability of the particle solver in laminar regions of the flow field (e.g. in the viscous sublayer) and on the other hand takes differential diffusion into account. It is shown in a detailed analysis, that the new method correctly predicts first and second-order moments on the basis of conventional modeling approaches. Moreover, a number of challenges for MDF particle methods in high speed flows is discussed, e.g. high cell aspect ratio grids close to solid walls, wall heat transfer, shock resolution, and problems from statistical noise which may cause artificial shock systems in supersonic flows. A Mach 2 supersonic mixing channel with multiple shock reflection and a model rocket combustor simulation demonstrate the eligibility of this technique to practical applications. Both test cases are simulated successfully for the first time with a hybrid finite-volume (FV)/Lagrangian particle solver (PS).
Axisymmetric compressible flow in a rotating cylinder with axial convection
Ungarish, M.; Israeli, M.
1985-05-01
The steady compressible flow of an ideal gas in a rotating annulus with thermally conducting walls is considered for small Rossby number epsilon and Ekman number E and moderate rotational Mach numbers M. Attention is focused on nonlinear effects which show up when sigma and epsilon M-squared are not small (sigma = epsilon/H square root of E, H is the dimensionless height of the container). These effects are not properly predicted by the classical linear perturbation analysis, and are treated here by quasi-linear extensions. The extra work required by these extensions is only the numerical solution of one ordinary differential equation for the pressure. Numerical solutions of the full Navier-Stokes equations in the nonlinear range are presented, and the validity of the present approach is confirmed.
Fluid-plasma interaction in compressible unstable flows
Massa, Luca
2014-11-01
The receptivity of the boundary layer discrete modes to dielectric barrier discharge (DBD) actuation is studied to improve the understanding of the interaction between non-equilibrium plasma and fluid in convectively amplified vortical layers. The momentum transfer induced by a DBD patch at various Reynolds numbers is evaluated using an adaptive mesh refinement computational solver in the Mach number regime 0.8-2.0. The energy of the induced modal perturbation is determined by weighting such a source term with the corresponding adjoint eigenfunctions. Conditions of maximum overlapping between the adjoint and the source term define the regimes of maximum receptivity and the locations of optimal placement of the DBD patch at different Mach and Reynolds numbers. The interaction between non-equilibrium plasma and the jet in cross flow is also being studied to determine the ability of DBD patches to influence mixing in the compressible regime, thus improving flame-holding in plasma assisted ignition and combustion.
Energy Technology Data Exchange (ETDEWEB)
Kuepper, S.
1997-12-01
In this study an analysis method is presented which allows numerical simulation of in situ air sparging coupled with soil vapor extraction. The improved FE-program takes the following phenomena into account: - Two-phase flow of compressible air and incompressible water - convective-dispersive contamination migration with air and water - transfer of volatile components from liquid phase to gas and water phase - sorption of contaminants onto soil - transfer of contaminants between air and water phase - biological processes. By means of back calculations of the results of laboratory experiments made by Eisele (1989) it was shown that with the developed program GWLCOND some of the necessary parameters for the numerical simulation of remedial systems can be determined. (orig./SR) [Deutsch] In dieser Arbeit wird ein Verfahren vorgestellt, mit dem eine numerische Simulation der Drucklufteinblasung und Bodenluftabsaugung durchgefuehrt werden kann. Das weiterentwickelte FE-Programmsystem beinhaltet folgende Ablaeufe: - Zweiphasenstroemung der kompressiblen Luft- und der inkompressiblen Wasserphase - Konvektiv-dispersiver Schadstofftransport mit der Gas- und der Wasserphase - Uebergang fluessiger Schadstoffe in die Gas- und in die Wasserphase - Sorption der Schadstoffe an der Feststoffphase - Uebergang der Schadstoffe zwischen der Gas- und der Wasserphase - Biologischer Abbau. Anhand der Nachrechnung eines Laborversuches von Eisele (1989) wird gezeigt, wie mit dem entwickelten Transportprogramm GWLCOND ein Teil der fuer die numerische Simulation des Sanierungsverfahrens benoetigten Kennwerte ermittelt werden kann. (orig./SR)
Stainback, P. C.; Johnson, C. B.; Basnett, C. B.
1983-01-01
The heat transfer characteristics of a three-wire hot-wire probe operated with a constant temperature anemometer were investigated in the subsonic compressible flow regime. The sensitivity coefficients, with respect to velocity, density and total temperature, were measured and the results were used to calculate the velocity, density, and total temperature fluctuations in the test section of the Langley 0.3-m Transonic Cryogenic Tunnel (TCT). These results were extended to give estimates for fluctuations due to vorticity, sound, and entropy. In addition, attempts were made to determine the major source of disturbances in the 0.3-m TCT.
Aerodynamic control in compressible flow using microwave driven discharges
McAndrew, Brendan
A new aerodynamic control scheme based on heating of the free stream flow is developed. The design, construction, and operation of a unique small scale wind tunnel to perform experiments involving this control scheme is detailed. Free stream heating is achieved by means of microwave driven discharges, and the resulting flow perturbations are used to alter the pressure distribution around a model in the flow. The experimental facility is also designed to allow the injection of an electron beam into the free stream for control of the discharge. Appropriate models for the fluid flow and discharge physics are developed, and comparisons of calculations based on those models are made with experimental results. The calculations have also been used to explore trends in parameters beyond the range possible in the experiments. The results of this work have been (1) the development of an operating facility capable of supporting free stream heat addition experiments in supersonic flow, (2) the development of a compatible instrumented model designed to make lift and drag measurements in a low pressure, high electrical noise environment, (3) a theoretical model to predict the change in breakdown threshold in the presence of an electron beam or other source of ionization, and (4) successful demonstration of aerodynamic control using free stream heat addition.
Control volume based modelling of compressible flow in reciprocating machines
DEFF Research Database (Denmark)
Andersen, Stig Kildegård; Thomsen, Per Grove; Carlsen, Henrik
2004-01-01
conservation laws for mass, energy, and momentum applied to a staggered mesh consisting of two overlapping strings of control volumes. Loss mechanisms can be included directly in the governing equations of models by including them as terms in the conservation laws. Heat transfer, flow friction......, and multidimensional effects must be calculated using empirical correlations; correlations for steady state flow can be used as an approximation. A transformation that assumes ideal gas is presented for transforming equations for masses and energies in control volumes into the corresponding pressures and temperatures...
Pressure Drop Control Using Multiple Orifice System in Compressible Pipe Flows
Institute of Scientific and Technical Information of China (English)
Heuydong Kim; Toshiaki Setoguchi; Shigeru Matsuo; S. R. Raghunathan
2001-01-01
In order to investigate the effectiveness of an orifice system in producing pressure drops and the effect of compressibility on the pressure drop, computations using the mass-averaged implicit Navier-Stokes equations were applied to the axisymmetric pipe flows with the operating pressure ratio from 1.5 to 20.0. The standard k- ε turbulence model was employed to close the governing equations. Numerical calculations were carried out for some combinations of the multiple orifice configurations. The present CFD data showed that the orifice systems,which have been applied to incompressible flow regime to date, could not be used for the high operating pressure ratio flows. The orifice interval did not strongly affect the total pressure drop, but the orifice area ratio more than 2.5 led to relatively high pressure drops. The total pressure drop rapidly increased in the range of the operating pressure ratio from 1.5 to 4.0, but it nearly did not increase when the operating pressure ratio was over 4.0. In the compressible pipe flows through double and triple orifice systems, the total pressure drop was largely due to shock losses.
A high-resolution DNS study of compressible flow past an LPT blade in a cascade
Ranjan, Rajesh; Narasimha, Roddam
2016-01-01
Flow past a low pressure turbine blade in a cascade at $Re \\approx 52000$ and angle of incidence $\\alpha = 45.5^{0}$ is solved using a code developed in-house for solving 3D compressible Navier-Stokes equations. This code, named ANUROOP, has been developed in the finite volume framework using kinetic energy preserving second order central differencing scheme for calculating fluxes, and is compatible with hybrid grids. ANUROOP was verified and validated against several test cases with Mach numbers ranging from 0.1 (Taylor-Green vortex) to 1.5 (compressible turbulent channel flow). The code was found to be robust and stable, and the kinetic energy decay obeys the compressible Navier-Stokes equations. A hybrid grid, with a high resolution hexahedral orthogonal mesh in the boundary layer and unstructured (also hexahedral) elements in the rest of the domain, is used for the turbine blade simulation. Total grid size (160 million) is approximately an order of magnitude higher than in previous simulations for the sam...
Seldam, C.A. ten; Groot, S.R. de
From Jensen's and Gombás' modification of the statistical Thomas-Fermi atom model, a theory for compressed atoms is developed by changing the boundary conditions. Internal kinetic energy and polarizability of argon are calculated as functions of pressure. At 1000 atm. an internal kinetic energy of
A High Resolution Low Dissipation Hybrid Scheme for Compressible Flows
Institute of Scientific and Technical Information of China (English)
YU Jian; YAN Chao; JIANG Zhenhua
2011-01-01
In this paper,an efficient hybrid shock capturing scheme is proposed to obtain accurate results both in the smooth region and around discontinuities for compressible flows.The hybrid algorithm is based on a fifth-order weighted essentially non-oscillatory (WENO) scheme in the finite volume form to solve the smooth part of the flow field,which is coupled with a characteristic-based monotone upstream-centered scheme for conservation laws(MUSCL) to capture discontinuities.The hybrid scheme is intended to combine high resolution of MUSCL scheme and low dissipation of WENO scheme.The two ingredients in this hybrid scheme are switched with an indicator.Three typical indicators are chosen and compared.MUSCL and WENO are both shock capturing schemes making the choice of the indicator parameter less crucial.Several test cases are carried out to investigate hybrid scheme with different indicators in terms of accuracy and efficiency.Numerical results demonstrate that the hybrid scheme in the present work performs well in a broad range of problems.
Directory of Open Access Journals (Sweden)
Wagner Henrik
2011-12-01
Full Text Available Abstract Background Mechanical chest compressions (CCs have been shown capable of maintaining circulation in humans suffering cardiac arrest for extensive periods of time. Reports have documented a visually normalized coronary blood flow during angiography in such cases (TIMI III flow, but it has never been actually measured. Only indirect measurements of the coronary circulation during cardiac arrest with on-going mechanical CCs have been performed previously through measurement of the coronary perfusion pressure (CPP. In this study our aim was to correlate average peak coronary flow velocity (APV to CPP during mechanical CCs. Methods In a closed chest porcine model, cardiac arrest was established through electrically induced ventricular fibrillation (VF in eleven pigs. After one minute, mechanical chest compressions were initiated and then maintained for 10 minutes upon which the pigs were defibrillated. Measurements of coronary blood flow in the left anterior descending artery were made at baseline and during VF with a catheter based Doppler flow fire measuring APV. Furthermore measurements of central (thoracic venous and arterial pressures were also made in order to calculate the theoretical CPP. Results Average peak coronary flow velocity was significantly higher compared to baseline during mechanical chests compressions and this was observed during the entire period of mechanical chest compressions (12 - 39% above baseline. The APV slowly declined during the 10 min period of mechanical chest compressions, but was still higher than baseline at the end of mechanical chest compressions. CPP was simultaneously maintained at > 20 mmHg during the 10 minute episode of cardiac arrest. Conclusion Our study showed good correlation between CPP and APV which was highly significant, during cardiac arrest with on-going mechanical CCs in a closed chest porcine model. In addition APV was even higher during mechanical CCs compared to baseline. Mechanical
Development of an algebraic stress/two-layer model for calculating thrust chamber flow fields
Chen, C. P.; Shang, H. M.; Huang, J.
1993-01-01
Following the consensus of a workshop in Turbulence Modeling for Liquid Rocket Thrust Chambers, the current effort was undertaken to study the effects of second-order closure on the predictions of thermochemical flow fields. To reduce the instability and computational intensity of the full second-order Reynolds Stress Model, an Algebraic Stress Model (ASM) coupled with a two-layer near wall treatment was developed. Various test problems, including the compressible boundary layer with adiabatic and cooled walls, recirculating flows, swirling flows and the entire SSME nozzle flow were studied to assess the performance of the current model. Detailed calculations for the SSME exit wall flow around the nozzle manifold were executed. As to the overall flow predictions, the ASM removes another assumption for appropriate comparison with experimental data, to account for the non-isotropic turbulence effects.
Multigrid Acceleration of Time-Accurate DNS of Compressible Turbulent Flow
Broeze, Jan; Geurts, Bernard; Kuerten, Hans; Streng, Martin
1996-01-01
An efficient scheme for the direct numerical simulation of 3D transitional and developed turbulent flow is presented. Explicit and implicit time integration schemes for the compressible Navier-Stokes equations are compared. The nonlinear system resulting from the implicit time discretization is solved with an iterative method and accelerated by the application of a multigrid technique. Since we use central spatial discretizations and no artificial dissipation is added to the equations, the smoothing method is less effective than in the more traditional use of multigrid in steady-state calculations. Therefore, a special prolongation method is needed in order to obtain an effective multigrid method. This simulation scheme was studied in detail for compressible flow over a flat plate. In the laminar regime and in the first stages of turbulent flow the implicit method provides a speed-up of a factor 2 relative to the explicit method on a relatively coarse grid. At increased resolution this speed-up is enhanced correspondingly.
Finite Element Calculation of the Flexural Stiffness of Corroded RC Eccentric Compressive Members
Institute of Scientific and Technical Information of China (English)
ZHANG Hua; WEI Jun; PAN Qiao; HUANG Ying
2010-01-01
A finite element calculation model of corroded RC eccentric compressive members was build using finite element software ANSYS. The model considers the decline of mechanical properties and the effective section of a corroded steel bar, as well as the deterioration of bond character between corroded reinforcement and concrete. The reliability of the finite element model was evaluated by comparing the results of the finite element calculation with the data from experiments. Based on the finite element analysis results, the influence of corrosion degree, the diameter change of the longitudinal reinforcing bars and the spacing change of stirrups on the flexural stiffness were calculated and analyzed.
Hejranfar, Kazem; Parseh, Kaveh
2017-09-01
The preconditioned characteristic boundary conditions based on the artificial compressibility (AC) method are implemented at artificial boundaries for the solution of two- and three-dimensional incompressible viscous flows in the generalized curvilinear coordinates. The compatibility equations and the corresponding characteristic variables (or the Riemann invariants) are mathematically derived and then applied as suitable boundary conditions in a high-order accurate incompressible flow solver. The spatial discretization of the resulting system of equations is carried out by the fourth-order compact finite-difference (FD) scheme. In the preconditioning applied here, the value of AC parameter in the flow field and also at the far-field boundary is automatically calculated based on the local flow conditions to enhance the robustness and performance of the solution algorithm. The code is fully parallelized using the Concurrency Runtime standard and Parallel Patterns Library (PPL) and its performance on a multi-core CPU is analyzed. The incompressible viscous flows around a 2-D circular cylinder, a 2-D NACA0012 airfoil and also a 3-D wavy cylinder are simulated and the accuracy and performance of the preconditioned characteristic boundary conditions applied at the far-field boundaries are evaluated in comparison to the simplified boundary conditions and the non-preconditioned characteristic boundary conditions. It is indicated that the preconditioned characteristic boundary conditions considerably improve the convergence rate of the solution of incompressible flows compared to the other boundary conditions and the computational costs are significantly decreased.
Through-Flow Calculations in Axial Turbomachinery
1976-10-01
downstzega of the effective throat which is displaced upstream away from its kominal plano flow •_stion. Test data .-n nigh deflection blading tested in...AXIAL PIE ANGs-L;- VrELOC.I- T/Y SI~NG,’ c (,o nd) 2 .959 00 SO~ IS~N1RO iCoWLE tNJ\\\\ NJ\\v ON45l~5INi +U~SWC E.AAINZN5W~N3~6 8Lk5~ P-tO RM~ C -5A
A method for calculating turbulent boundary layers and losses in the flow channels of turbomachines
Schumann, Lawrence F.
1987-01-01
An interactive inviscid core flow-boundary layer method is presented for the calculation of turbomachine channel flows. For this method, a one-dimensional inviscid core flow is assumed. The end-wall and blade surface boundary layers are calculated using an integral entrainment method. The boundary layers are assumed to be collateral and thus are two-dimensional. The boundary layer equations are written in a streamline coordinate system. The streamwise velocity profiles are approximated by power law profiles. Compressibility is accounted for in the streamwise direction but not in the normal direction. Equations are derived for the special cases of conical and two-dimensional rectangular diffusers. For these cases, the assumptions of a one-dimensional core flow and collateral boundary layers are valid. Results using the method are compared with experiment and good quantitative agreement is obtained.
The new high resolution method of Godunov`s type for 3D viscous flow calculations
Energy Technology Data Exchange (ETDEWEB)
Yershov, S.V.; Rusanov, A.V. [Ukranian National Academy of Sciences, Kahrkov (Ukraine)
1996-12-31
The numerical method is suggested for the calculations of the 3D viscous compressible flows described by the thin-layer Reynolds-averaged Navier-Stokes equations. The method is based on the Godunov`s finite-difference scheme and it uses the ENO reconstruction suggested by Harten to achieve the uniformly high-order accuracy. The computational efficiency is provided with the simplified multi grid approach and the implicit step written in {delta} -form. The turbulent effects are simulated with the Baldwin - Lomax turbulence model. The application package FlowER is developed to calculate the 3D turbulent flows within complex-shape channels. The numerical results for the 3D flow around a cylinder and through the complex-shaped channels show the accuracy and the reliability of the suggested method. (author)
Advanced Fluid Reduced Order Models for Compressible Flow.
Energy Technology Data Exchange (ETDEWEB)
Tezaur, Irina Kalashnikova; Fike, Jeffrey A.; Carlberg, Kevin Thomas; Barone, Matthew F.; Maddix, Danielle; Mussoni, Erin E.; Balajewicz, Maciej (UIUC)
2017-09-01
This report summarizes fiscal year (FY) 2017 progress towards developing and implementing within the SPARC in-house finite volume flow solver advanced fluid reduced order models (ROMs) for compressible captive-carriage flow problems of interest to Sandia National Laboratories for the design and qualification of nuclear weapons components. The proposed projection-based model order reduction (MOR) approach, known as the Proper Orthogonal Decomposition (POD)/Least- Squares Petrov-Galerkin (LSPG) method, can substantially reduce the CPU-time requirement for these simulations, thereby enabling advanced analyses such as uncertainty quantification and de- sign optimization. Following a description of the project objectives and FY17 targets, we overview briefly the POD/LSPG approach to model reduction implemented within SPARC . We then study the viability of these ROMs for long-time predictive simulations in the context of a two-dimensional viscous laminar cavity problem, and describe some FY17 enhancements to the proposed model reduction methodology that led to ROMs with improved predictive capabilities. Also described in this report are some FY17 efforts pursued in parallel to the primary objective of determining whether the ROMs in SPARC are viable for the targeted application. These include the implemen- tation and verification of some higher-order finite volume discretization methods within SPARC (towards using the code to study the viability of ROMs on three-dimensional cavity problems) and a novel structure-preserving constrained POD/LSPG formulation that can improve the accuracy of projection-based reduced order models. We conclude the report by summarizing the key takeaways from our FY17 findings, and providing some perspectives for future work.
Local conservative regularizations of compressible magnetohydrodynamic and neutral flows
Krishnaswami, Govind S.; Sachdev, Sonakshi; Thyagaraja, A.
2016-02-01
Ideal systems like magnetohydrodynamics (MHD) and Euler flow may develop singularities in vorticity ( w =∇×v ). Viscosity and resistivity provide dissipative regularizations of the singularities. In this paper, we propose a minimal, local, conservative, nonlinear, dispersive regularization of compressible flow and ideal MHD, in analogy with the KdV regularization of the 1D kinematic wave equation. This work extends and significantly generalizes earlier work on incompressible Euler and ideal MHD. It involves a micro-scale cutoff length λ which is a function of density, unlike in the incompressible case. In MHD, it can be taken to be of order the electron collisionless skin depth c/ωpe. Our regularization preserves the symmetries of the original systems and, with appropriate boundary conditions, leads to associated conservation laws. Energy and enstrophy are subject to a priori bounds determined by initial data in contrast to the unregularized systems. A Hamiltonian and Poisson bracket formulation is developed and applied to generalize the constitutive relation to bound higher moments of vorticity. A "swirl" velocity field is identified, and shown to transport w/ρ and B/ρ, generalizing the Kelvin-Helmholtz and Alfvén theorems. The steady regularized equations are used to model a rotating vortex, MHD pinch, and a plane vortex sheet. The proposed regularization could facilitate numerical simulations of fluid/MHD equations and provide a consistent statistical mechanics of vortices/current filaments in 3D, without blowup of enstrophy. Implications for detailed analyses of fluid and plasma dynamic systems arising from our work are briefly discussed.
Energy-Dependent Octagonal Lattice Boltzmann Modeling for Compressible Flows
Pavlo, Pavol; Vahala, Linda; Vahala, George
2000-10-01
There has been much interest in thermal lattice Boltzmann modeling (TLBM) for compressible flows because of their inherent parallelizeability. Instead of applying CFD techniques to the nonlinear conservation equations, one instead solves a linear BGK kinetic equation. To reduce storage requirements, the velocity space is discretized and lattice geometries are so chosen to minimize the number of degrees of freedom that must be retained in the Chapman-Enskog recovery of the original macroscopic equations. The simplest (and most efficient) TLBM runs at a CFL=1, so that no numerical diffusion or dissipation is introduced. The algorithm involves Lagrangian streaming (shift operator) and purely local operations. Because of the underlying discrete lattice symmetry, the relaxation distributions cannot be Maxwellian and hence the inherent numerical instability problem in TLBM. We are investigating the use of energy-dependent lattices so as to allow simulation of problems of interest in divertor physics, The appeal of TLBM is that it can provide a unified representation for both strongly collisional (‘fluid’) and weakly collisional (‘Monte Carlo’) regimes. Moreover, our TLBM code is more efficiently solved on mulit-PE platforms than the corresponding CFD codes and is readily extended to 3D. MHD can also be handled by TLBM.
Evaluation Study of Pressure-Strain Correlation Models in Compressible Flow
Directory of Open Access Journals (Sweden)
Aicha Hanafi
2016-01-01
Full Text Available This paper is devoted to the second-order closure for compressible turbulent flows with special attention paid to modeling the pressure-strain correlation appearing in the Reynolds stress equation. This term appears as the main one responsible for the changes of the turbulence structures that arise from structural compressibility effects. The structure of the gradient Mach number is similar to that of turbulence, therefore this parameter may be appropriate to study the changes in turbulence structures that arise from structural compressibility effects. Thus, the incompressible model (LRR of the pressure-strain correlation and its corrected form by using the turbulent Mach number, fail to correctly evaluate the compressibility effects at high shear flow. An extension of the widely used incompressible model (LRR on compressible homogeneous shear flow is the major aim of the present work. From this extension the standard coefficients Ci became a function of the compressibility parameters (the turbulent Mach number and the gradient Mach number. Application of the model on compressible homogeneous shear flow by considering various initial conditions shows reasonable agreement with the DNS results of Sarkar. The ability of the models to predict the equilibrium states for the flow in cases A1 and A4 from DNS results of Sarkar is examined, the results appear to be very encouraging. Thus, both parameters Mt and Mg should be used to model significant structural compressibility effects at high-speed shear flow.
Polynomial interpolation methods for viscous flow calculations
Rubin, S. G.; Khosla, P. K.
1977-01-01
Higher-order collocation procedures which result in block-tridiagonal matrix systems are derived from (1) Taylor series expansions and from (2) polynomial interpolation, and the relationships between the two formulations, called respectively Hermite and spline collocation, are investigated. A Hermite block-tridiagonal system for a nonuniform mesh is derived, and the Hermite approach is extended in order to develop a variable-mesh sixth-order block-tridiagonal procedure. It is shown that all results obtained by Hermite development can be recovered by appropriate spline polynomial interpolation. The additional boundary conditions required for these higher-order procedures are also given. Comparative solutions using second-order accurate finite difference and spline and Hermite formulations are presented for the boundary layer on a flat plate, boundary layers with uniform and variable mass transfer, and the viscous incompressible Navier-Stokes equations describing flow in a driven cavity.
Polynomial interpolation methods for viscous flow calculations
Rubin, S. G.; Khosla, P. K.
1977-01-01
Higher-order collocation procedures which result in block-tridiagonal matrix systems are derived from (1) Taylor series expansions and from (2) polynomial interpolation, and the relationships between the two formulations, called respectively Hermite and spline collocation, are investigated. A Hermite block-tridiagonal system for a nonuniform mesh is derived, and the Hermite approach is extended in order to develop a variable-mesh sixth-order block-tridiagonal procedure. It is shown that all results obtained by Hermite development can be recovered by appropriate spline polynomial interpolation. The additional boundary conditions required for these higher-order procedures are also given. Comparative solutions using second-order accurate finite difference and spline and Hermite formulations are presented for the boundary layer on a flat plate, boundary layers with uniform and variable mass transfer, and the viscous incompressible Navier-Stokes equations describing flow in a driven cavity.
Lin, Lin; Ying, Lexing
2016-01-01
Phonon calculations based on first principle electronic structure theory, such as the Kohn-Sham density functional theory, have wide applications in physics, chemistry and material science. The computational cost of first principle phonon calculations typically scales steeply as $\\mathcal{O}(N_e^4)$, where $N_e$ is the number of electrons in the system. In this work, we develop a new method to reduce the computational complexity of computing the full dynamical matrix, and hence the phonon spectrum, to $\\mathcal{O}(N_e^3)$. The key concept for achieving this is to compress the polarizability operator adaptively with respect to the perturbation of the potential due to the change of the atomic configuration. Such adaptively compressed polarizability operator (ACP) allows accurate computation of the phonon spectrum. The reduction of complexity only weakly depends on the size of the band gap, and our method is applicable to insulators as well as semiconductors with small band gaps. We demonstrate the effectiveness...
Chemically reacting supersonic flow calculation using an assumed PDF model
Farshchi, M.
1990-01-01
This work is motivated by the need to develop accurate models for chemically reacting compressible turbulent flow fields that are present in a typical supersonic combustion ramjet (SCRAMJET) engine. In this paper the development of a new assumed probability density function (PDF) reaction model for supersonic turbulent diffusion flames and its implementation into an efficient Navier-Stokes solver are discussed. The application of this model to a supersonic hydrogen-air flame will be considered.
Schmid, L. A.
1977-01-01
The first and second variations are calculated for the irreducible form of Hamilton's Principle that involves the minimum number of dependent variables necessary to describe the kinetmatics and thermodynamics of inviscid, compressible, baroclinic flow in a specified gravitational field. The form of the second variation shows that, in the neighborhood of a stationary point that corresponds to physically stable flow, the action integral is a complex saddle surface in parameter space. There exists a form of Hamilton's Principle for which a direct solution of a flow problem is possible. This second form is related to the first by a Friedrichs transformation of the thermodynamic variables. This introduces an extra dependent variable, but the first and second variations are shown to have direct physical significance, namely they are equal to the free energy of fluctuations about the equilibrium flow that satisfies the equations of motion. If this equilibrium flow is physically stable, and if a very weak second order integral constraint on the correlation between the fluctuations of otherwise independent variables is satisfied, then the second variation of the action integral for this free energy form of Hamilton's Principle is positive-definite, so the action integral is a minimum, and can serve as the basis for a direct trail and error solution. The second order integral constraint states that the unavailable energy must be maximum at equilibrium, i.e. the fluctuations must be so correlated as to produce a second order decrease in the total unavailable energy.
Calculation of the debris flow concentration based on clay content
Institute of Scientific and Technical Information of China (English)
CHEN Ningsheng; CUI Peng; LIU Zhonggang; WEI Fangqiang
2003-01-01
The debris flow clay content has very tremendous influence on its concentration (γC). It is reported that the concentration can be calculated by applying the relative polynomial based on the clay content. Here one polynomial model and one logarithm model to calculate the concentration based on the clay content for both the ordinary debris flow and viscous debris flow are obtained. The result derives from the statistics and analysis of the relationship between the debris flow concentrations and clay content in 45 debris flow sites located in the southwest of China. The models can be applied for the concentration calculation to those debris flows that are impossible to observe. The models are available to calculate the debris flow concentration, the principles of which are in the clay content affecting on the debris flow formation, movement and suspending particle diameter. The mechanism of the relationship of the clay content and concentration is clear and reliable. The debris flow is usually of micro-viscous when the clay content is low (<3%), by analyzing the developing tendency on the basics of the relationship between the clay content and debris flow concentration. Indeed, the less the clay content, the less the concentration for most debris flows. The debris flow tends to become the water rock flow or the hyperconcentrated flow with the clay content decrease. Through statistics it is apt to transform the soil into the viscous debris flow when the clay content of ranges is in 3%-18%. Its concentration increases with the increasing of the clay content when the clay content is between 5% and 10%. But the value decreases with the increasing of the clay content when the clay content is between 10% and 18%. It is apt to transform the soil into the mudflow, when the clay content exceeds 18%. The concentration of the mudflow usually decreases with the increase of the clay content, and this developing tendency reverses to that of the micro-viscous debris flow. There is
Energy Technology Data Exchange (ETDEWEB)
Narayan, A.P. [Univ. of Colorado, Boulder, CO (United States); Rainwater, J.C. [National Institute of Standards and Technology, Boulder, CO (United States); Hanley, H.J.M. [Univ. of Colorado, Boulder, CO (United States)]|[National Institute of Standards and Technology, Boulder, CO (United States)
1995-03-01
A study of the Weissenberg effect (rod climbing in a stirred system) based on nonequilibrium molecular dynamics (NEMD) is reported. Simulation results from a soft-sphere fluid are used to obtain a self-consistent free-surface profile of the fluid of finite compressibility undergoing Couette flow between concentric cylinders. A numerical procedure is then applied to calculate the height profile for a hypothetical fluid with thermophysical properties of the soft-sphere liquid and of a dense colloidal suspension. The height profile calculated is identified with shear thickening and the forms of the viscometric functions. The maximum climb occurs between the cylinders rather than at the inner cylinder.
Predictive simulation of granular flows applied to compressible multiphase flow modeling
Goetsch, Ryan J.; Regele, Jonathan D.
2014-11-01
Multiphase flows have been an active area of research for decades due to their complex nature and occurrence in many engineering applications. However, little information exists about the dense compressible flow regime. Recent experimental work [Wagner et al., Exp. Fluids 52, 1507 (2012)] using a multiphase shock tube has studied gas-solid flows with high solid volume fractions (α = 0 . 2) by measuring shock wave-particle cloud interactions. It is still unclear what occurs at the particle scale inside and behind the particle cloud during this interaction. The objective of this work is to perform direct numerical simulations to understand this phenomena. With this goal in mind, a discrete element method (DEM) solver was developed to predict the properties of a particle cloud formed by gravity driven granular flow through a slit opening. For validation purposes, the results are compared with experimental channel flow data. It is found that the mean velocity profile and mass flow rates correlate well with the experiment, however the fluctuation velocities are significantly under-predicted for both smooth and rough wall cases.
Reattachment heating upstream of short compression ramps in hypersonic flow
Estruch-Samper, David
2016-05-01
Hypersonic shock-wave/boundary-layer interactions with separation induce unsteady thermal loads of particularly high intensity in flow reattachment regions. Building on earlier semi-empirical correlations, the maximum heat transfer rates upstream of short compression ramp obstacles of angles 15° ⩽ θ ⩽ 135° are here discretised based on time-dependent experimental measurements to develop insight into their transient nature (Me = 8.2-12.3, Re_h= 0.17× 105-0.47× 105). Interactions with an incoming laminar boundary layer experience transition at separation, with heat transfer oscillating between laminar and turbulent levels exceeding slightly those in fully turbulent interactions. Peak heat transfer rates are strongly influenced by the stagnation of the flow upon reattachment close ahead of obstacles and increase with ramp angle all the way up to θ =135°, whereby rates well over two orders of magnitude above the undisturbed laminar levels are intermittently measured (q'_max>10^2q_{u,L}). Bearing in mind the varying degrees of strength in the competing effect between the inviscid and viscous terms—namely the square of the hypersonic similarity parameter (Mθ )^2 for strong interactions and the viscous interaction parameter bar{χ } (primarily a function of Re and M)—the two physical factors that appear to most globally encompass the effects of peak heating for blunt ramps (θ ⩾ 45°) are deflection angle and stagnation heat transfer, so that this may be fundamentally expressed as q'_max∝ {q_{o,2D}} θ ^2 with further parameters in turn influencing the interaction to a lesser extent. The dominant effect of deflection angle is restricted to short obstacle heights, where the rapid expansion at the top edge of the obstacle influences the relaxation region just downstream of reattachment and leads to an upstream displacement of the separation front. The extreme heating rates result from the strengthening of the reattaching shear layer with the increase in
Near-wall variable-Prandtl-number turbulence model for compressible flows
Sommer, T. P.; So, R. M. C.; Zhang, H. S.
1993-01-01
A near-wall four-equation turbulence model is developed for the calculation of high-speed compressible turbulent boundary layers. The four equations used are the k-epsilon equations and the theta(exp 2)-epsilon (sub theta) equations. These equations are used to define the turbulent diffusivities for momentum and heat fluxes, thus allowing the assumption of dynamic similarity between momentum and heat transport to be relaxed. The Favre-averaged equations of motion are solved in conjunction with the four transport equations. Calculations are compared with measurements and with another model's predictions where the assumption of the constant turbulent Prandtl number is invoked. Compressible flat plate turbulent boundary layers with both adiabatic and constant temperature wall boundary conditions are considered. Results for the range of low Mach numbers and temperature ratios investigated are essentially the same as those obtained using an identical near-wall k-epsilon model. In general, there are significant improvements in the predictions of mean flow properties at high Mach numbers.
Analytical skin friction and heat transfer formula for compressible internal flows
Dechant, Lawrence J.; Tattar, Marc J.
1994-01-01
An analytic, closed-form friction formula for turbulent, internal, compressible, fully developed flow was derived by extending the incompressible law-of-the-wall relation to compressible cases. The model is capable of analyzing heat transfer as a function of constant surface temperatures and surface roughness as well as analyzing adiabatic conditions. The formula reduces to Prandtl's law of friction for adiabatic, smooth, axisymmetric flow. In addition, the formula reduces to the Colebrook equation for incompressible, adiabatic, axisymmetric flow with various roughnesses. Comparisons with available experiments show that the model averages roughly 12.5 percent error for adiabatic flow and 18.5 percent error for flow involving heat transfer.
Numerical Solution of Compressible Steady Flows around the RAE 2822 Airfoil
Kryštůfek, P.; Kozel, K.
2014-03-01
The article presents results of a numerical solution of subsonic, transonic and supersonic flows described by the system of Navier-Stokes equations in 2D laminar compressible flows around the RAE 2822 airfoil. Authors used FVM multistage Runge-Kutta method to numerically solve the flows around the RAE 2822 airfoil.
Radial flow of slightly compressible fluids: A finite element-finite ...
African Journals Online (AJOL)
Journal of the Nigerian Association of Mathematical Physics ... Open Access DOWNLOAD FULL TEXT Subscription or Fee Access. Radial flow of slightly compressible fluids: A finite element-finite differences approach. JA Akpobi, ED Akpobi ...
MONOTONIC DERIVATIVE CORRECTION FOR CALCULATION OF SUPERSONIC FLOWS WITH SHOCK WAVES
Directory of Open Access Journals (Sweden)
P. V. Bulat
2015-07-01
Full Text Available Subject of Research. Numerical solution methods of gas dynamics problems based on exact and approximate solution of Riemann problem are considered. We have developed an approach to the solution of Euler equations describing flows of inviscid compressible gas based on finite volume method and finite difference schemes of various order of accuracy. Godunov scheme, Kolgan scheme, Roe scheme, Harten scheme and Chakravarthy-Osher scheme are used in calculations (order of accuracy of finite difference schemes varies from 1st to 3rd. Comparison of accuracy and efficiency of various finite difference schemes is demonstrated on the calculation example of inviscid compressible gas flow in Laval nozzle in the case of continuous acceleration of flow in the nozzle and in the case of nozzle shock wave presence. Conclusions about accuracy of various finite difference schemes and time required for calculations are made. Main Results. Comparative analysis of difference schemes for Euler equations integration has been carried out. These schemes are based on accurate and approximate solution for the problem of an arbitrary discontinuity breakdown. Calculation results show that monotonic derivative correction provides numerical solution uniformity in the breakdown neighbourhood. From the one hand, it prevents formation of new points of extremum, providing the monotonicity property, but from the other hand, causes smoothing of existing minimums and maximums and accuracy loss. Practical Relevance. Developed numerical calculation method gives the possibility to perform high accuracy calculations of flows with strong non-stationary shock and detonation waves. At the same time, there are no non-physical solution oscillations on the shock wave front.
Compressible DNS of transitional and turbulent flow in a low pressure turbine cascade
Ranjan, Rajesh; Deshpande, Suresh; Narasimha, Roddam
2015-11-01
Direct numerical simulation (DNS) of flow in a low pressure turbine cascade at high incidence is performed using a new in-house code ANUROOP. This code solves compressible Navier-Stokes equations in conservative form using finite volume technique and uses kinetic-energy consistent scheme for the flux calculations. ANUROOP is capable of handling flow past complex geometries using hybrid grid approach (separate grid topologies for the boundary layer and rest of the blade passage). This approach offers much more control in mesh spacing and distribution compared to elliptic grid technique, which is used in many previous studies. Also, in contrast to previous studies, focus of the current work is mainly on the boundary layer flow. The flow remains laminar on the pressure side of the blade, but separates in the aft region of the suction side leading to transition. Separation bubbles formed at this region are transient in nature and we notice multiple bubbles merging and breaking in time. In the mean flow however, only one bubble is seen. Velocity profiles very near to the leading edge of the suction side suggest strong curvature effect. Higher-order boundary layer theory that includes effect of curvature is found to be necessary to characterize the flow in this region. Also, the grid convergence study reveals interesting aspects of numerics vital for accurate simulation of this kind of complex flows. We would like to thank the Gas Turbine Enabling Technology (GATET) Program for funding this project. We also thank C-DAC, Pune and CSIR-4PI, Bangalore for providing computational resources.
Studies in the Computation of Compressible Viscous Flows.
1987-02-01
singular solutions have been found which may bridge the gap between smooth shock free flow and the flow with embedded shocks. Keywords: Transonic flow; Computational aerodynamics; Viscous inviscid interactions.
The discontinuous Galerkin method for the numerical simulation of compressible viscous flow
Directory of Open Access Journals (Sweden)
Česenek Jan
2014-03-01
Full Text Available In this paper we deal with numerical simulation of the compressible viscous flow. The mathematical model of flow is represented by the system of non-stationary compressible Navier-Stokes equations. This system of equations is discretized by the discontinuous Galerkin finite element method in space and in time using piecewise polynomial discontinuous approximations. We present some numerical experiments to demonstrate the applicability of the method using own-developed code.
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...
Pressure algorithm for elliptic flow calculations with the PDF method
Anand, M. S.; Pope, S. B.; Mongia, H. C.
1991-01-01
An algorithm to determine the mean pressure field for elliptic flow calculations with the probability density function (PDF) method is developed and applied. The PDF method is a most promising approach for the computation of turbulent reacting flows. Previous computations of elliptic flows with the method were in conjunction with conventional finite volume based calculations that provided the mean pressure field. The algorithm developed and described here permits the mean pressure field to be determined within the PDF calculations. The PDF method incorporating the pressure algorithm is applied to the flow past a backward-facing step. The results are in good agreement with data for the reattachment length, mean velocities, and turbulence quantities including triple correlations.
Modeling of Flow Stress of High Titanium Content 6061 Aluminum Alloy Under Hot Compression
Chen, Wei; Guan, Yingping; Wang, Zhenhua
2016-09-01
Hot compression tests were performed on high titanium content 6061 aluminum alloy (AA 6061-Ti) using a Gleeble-3500 thermomechanical testing system at temperatures from 350 to 510 °C with a constant strain rate in the range of 0.001-10 s-1. Three types of flow stress models were established from the experimental stress-strain curves, the correlation coefficient ( R), mean absolute relative error ( MARE), and root mean square deviation ( RMSD) between the predicted data and the experimental data were also calculated. The results show that the Fields-Backofen model, which includes a softening factor, was the simplest mathematical expression with a level of precision appropriate for the numerical simulations. However, the Arrhenius and artificial neural network (ANN) models were also consistent with the experimental results but they are more limited in their application in terms of their accuracy and the mathematical expression of the models.
A procedure for the calculation of flow through axisymmetric ducts
Directory of Open Access Journals (Sweden)
P. S. Heyns
1983-03-01
Full Text Available A procedure for the calculation of flow through axisymmetric ducts as are typically found in turbomachines, is presented. The procedure is based on a streamline curvature method with the governing equations formulated along quasi-orthogonals in the flow field. This formulation allows the procedure to be used for segments of a duct wherein the flow direction is predominantly radial. It is assumed that the flow on specific stream surfaces is isentropic, but normal entropy gradients may exist because of processes which took place upstream of the duct.
On the implicit density based OpenFOAM solver for turbulent compressible flows
Fürst, Jiří
The contribution deals with the development of coupled implicit density based solver for compressible flows in the framework of open source package OpenFOAM. However the standard distribution of OpenFOAM contains several ready-made segregated solvers for compressible flows, the performance of those solvers is rather week in the case of transonic flows. Therefore we extend the work of Shen [15] and we develop an implicit semi-coupled solver. The main flow field variables are updated using lower-upper symmetric Gauss-Seidel method (LU-SGS) whereas the turbulence model variables are updated using implicit Euler method.
On the implicit density based OpenFOAM solver for turbulent compressible flows
Directory of Open Access Journals (Sweden)
Fürst Jiří
2017-01-01
Full Text Available The contribution deals with the development of coupled implicit density based solver for compressible flows in the framework of open source package OpenFOAM. However the standard distribution of OpenFOAM contains several ready-made segregated solvers for compressible flows, the performance of those solvers is rather week in the case of transonic flows. Therefore we extend the work of Shen [15] and we develop an implicit semi-coupled solver. The main flow field variables are updated using lower-upper symmetric Gauss-Seidel method (LU-SGS whereas the turbulence model variables are updated using implicit Euler method.
On the implicit density based OpenFOAM solver for turbulent compressible flows
Fürst, Jiří
2016-11-01
The contribution deals with the development of coupled implicit density based solver for compressible flows in the framework of open source package OpenFOAM. However the standard distribution of OpenFOAM contains several ready-made segregated solvers for compressible flows, the performance of those solvers is rather week in the case of transonic flows. Therefore we extend the work of Shen [15] and we develop an implicit semi-coupled solver. The main flow field variables are updated using lower-upper symmetric Gauss-Seidel method (LU-SGS) whereas the turbulence model variables are updated using implicit Euler method.
Dewaele, Agnès; Torrent, Marc; Loubeyre, Paul; Mezouar, Mohamed
2008-09-01
The ambient temperature equations of state (EoS) of iron, cobalt, nickel, zinc, molybdenum, and silver have been measured by x-ray diffraction. These transition metals were compressed using diamond anvil cells with a helium pressure transmitting medium. The maximum pressure reached during these experiments varied between 65 GPa (for cobalt) and 200 GPa (for iron). This work completes previous measurements on six other metals [Phys. Rev. B 70, 094112 (2004)] to quantify the differences between ab initio calculations and experiment on a large experimental set of transition metals. The compression curves of iron, cobalt, nickel, zinc, molybdenum, silver, platinum, and gold are also calculated ab initio within the density-functional theory (DFT) formalism using the projector augmented-wave (PAW) method and different exchange-correlation functionals (LDA, GGA-PBE, GGA-PBEsol). The difference between PAW and available all-electron calculations is found to be negligible up to very high pressures. The success of each exchange-correlation functional is correlated with the atomic number. For all metals, the bulk modulus becomes overestimated at high pressure. In addition, this extended data set of metals’ EoS enables to reduce further, but marginally, the systematic uncertainty of the high-pressure metrology based on the ruby standard.
Calculating e-flow using UAV and ground monitoring
Zhao, C. S.; Zhang, C. B.; Yang, S. T.; Liu, C. M.; Xiang, H.; Sun, Y.; Yang, Z. Y.; Zhang, Y.; Yu, X. Y.; Shao, N. F.; Yu, Q.
2017-09-01
Intense human activity has led to serious degradation of basin water ecosystems and severe reduction in the river flow available for aquatic biota. As an important water ecosystem index, environmental flows (e-flows) are crucial for maintaining sustainability. However, most e-flow measurement methods involve long cycles, low efficiency, and transdisciplinary expertise. This makes it impossible to rapidly assess river e-flows at basin or larger scales. This study presents a new method to rapidly assessing e-flows coupling UAV and ground monitorings. UAV was firstly used to calculate river-course cross-sections with high-resolution stereoscopic images. A dominance index was then used to identify key fish species. Afterwards a habitat suitability index, along with biodiversity and integrity indices, was used to determine an appropriate flow velocity with full consideration of the fish spawning period. The cross-sections and flow velocity values were then combined into AEHRA, an e-flow assessment method for studying e-flows and supplying-rate. To verify the results from this new method, the widely used Tennant method was employed. The root-mean-square errors of river cross-sections determined by UAV are less than 0.25 m, which constitutes 3-5% water-depth of the river cross-sections. In the study area of Jinan city, the ecological flow velocity (VE) is equal to or greater than 0.11 m/s, and the ecological water depth (HE) is greater than 0.8 m. The river ecosystem is healthy with the minimum e-flow requirements being always met when it is close to large rivers, which is beneficial for the sustainable development of the water ecosystem. In the south river channel of Jinan, the upstream flow mostly meets the minimum e-flow requirements, and the downstream flow always meets the minimum e-flow requirements. The north of Jinan consists predominantly of artificial river channels used for irrigation. Rainfall rarely meets the minimum e-flow and irrigation water requirements
Memory-Assisted Universal Compression of Network Flows
Sardari, Mohsen; Fekri, Faramarz
2012-01-01
Recently, the existence of considerable amount of redundancy in the Internet traffic has stimulated the deployment of several redundancy elimination techniques within the network. These techniques are often based on either packet-level Redundancy Elimination (RE) or Content-Centric Networking (CCN). However, these techniques cannot exploit sub-packet redundancies. Further, other alternative techniques such as the end-to-end universal compression solutions would not perform well either over the Internet traffic, as such techniques require infinite length traffic to effectively remove redundancy. This paper proposes a memory-assisted universal compression technique that holds a significant promise for reducing the amount of traffic in the networks. The proposed work is based on the observation that if a source is to be compressed and sent over a network, the associated universal code entails a substantial overhead in transmission due to finite length traffic. However, intermediate nodes can learn the source sta...
Directory of Open Access Journals (Sweden)
Isaev Veniamin
2016-01-01
Full Text Available Calculation of compressed footings settlement is one of the most vital tasks of soil mechanics. The calculation method of layer-by-layer addition, which recommended by current regulations and used in structural engineering practice, is most suitable for determining the settlement of foundations with an area of less than 50 m2. The authors prove that it’s possible to apply the one-dimensional problem of soils compression seal theory to the calculation of the settlement of large foundation plates. The proposed method of determining the settlement of large foundation plates makes the calculations simpler. There are examples of comparable calculations using the existing and proposed methods.
A Riemann problem based method for solving compressible and incompressible flows
Lu, Haitian; Zhu, Jun; Wang, Chunwu; Wang, Donghong; Zhao, Ning
2017-02-01
A Riemann problem based method for solving two-medium flow including compressible and incompressible regions is presented. The material interface is advanced by front tracking method and the material interface boundary conditions are defined by modified ghost fluid method. A coupled compressible and incompressible Riemann problem constructed in the normal direction of the material interface is proposed to predict the interfacial states. With the ghost fluid states, the compressible and incompressible flows are solved by discontinuous Galerkin method. An incompressible discontinuous Galerkin method with nonuniform time step is also deduced. For shock wave formed in compressible flow, the numerical errors for the ghost fluid method in earlier works are analyzed and discussed in the numerical examples. It shows that the proposed method can provide reasonable results including shock wave location.
Simulation of inviscid compressible multi-phase flow with condensation
Kelleners, P.H.
2003-01-01
Condensation of vapours in rapid expansions of compressible gases is investigated. In the case of high temperature gradients the condensation will start at conditions well away from thermodynamic equilibrium of the fluid. In those cases homogeneous condensation is dominant over heterogeneous
Energy Technology Data Exchange (ETDEWEB)
Fechter, Stefan, E-mail: stefan.fechter@iag.uni-stuttgart.de [Institut für Aerodynamik und Gasdynamik, Universität Stuttgart, Pfaffenwaldring 21, 70569 Stuttgart (Germany); Munz, Claus-Dieter, E-mail: munz@iag.uni-stuttgart.de [Institut für Aerodynamik und Gasdynamik, Universität Stuttgart, Pfaffenwaldring 21, 70569 Stuttgart (Germany); Rohde, Christian, E-mail: Christian.Rohde@mathematik.uni-stuttgart.de [Institut für Angewandte Analysis und Numerische Simulation, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart (Germany); Zeiler, Christoph, E-mail: Christoph.Zeiler@mathematik.uni-stuttgart.de [Institut für Angewandte Analysis und Numerische Simulation, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart (Germany)
2017-05-01
The numerical approximation of non-isothermal liquid–vapor flow within the compressible regime is a difficult task because complex physical effects at the phase interfaces can govern the global flow behavior. We present a sharp interface approach which treats the interface as a shock-wave like discontinuity. Any mixing of fluid phases is avoided by using the flow solver in the bulk regions only, and a ghost-fluid approach close to the interface. The coupling states for the numerical solution in the bulk regions are determined by the solution of local two-phase Riemann problems across the interface. The Riemann solution accounts for the relevant physics by enforcing appropriate jump conditions at the phase boundary. A wide variety of interface effects can be handled in a thermodynamically consistent way. This includes surface tension or mass/energy transfer by phase transition. Moreover, the local normal speed of the interface, which is needed to calculate the time evolution of the interface, is given by the Riemann solution. The interface tracking itself is based on a level-set method. The focus in this paper is the description of the two-phase Riemann solver and its usage within the sharp interface approach. One-dimensional problems are selected to validate the approach. Finally, the three-dimensional simulation of a wobbling droplet and a shock droplet interaction in two dimensions are shown. In both problems phase transition and surface tension determine the global bulk behavior.
Fechter, Stefan; Munz, Claus-Dieter; Rohde, Christian; Zeiler, Christoph
2017-05-01
The numerical approximation of non-isothermal liquid-vapor flow within the compressible regime is a difficult task because complex physical effects at the phase interfaces can govern the global flow behavior. We present a sharp interface approach which treats the interface as a shock-wave like discontinuity. Any mixing of fluid phases is avoided by using the flow solver in the bulk regions only, and a ghost-fluid approach close to the interface. The coupling states for the numerical solution in the bulk regions are determined by the solution of local two-phase Riemann problems across the interface. The Riemann solution accounts for the relevant physics by enforcing appropriate jump conditions at the phase boundary. A wide variety of interface effects can be handled in a thermodynamically consistent way. This includes surface tension or mass/energy transfer by phase transition. Moreover, the local normal speed of the interface, which is needed to calculate the time evolution of the interface, is given by the Riemann solution. The interface tracking itself is based on a level-set method. The focus in this paper is the description of the two-phase Riemann solver and its usage within the sharp interface approach. One-dimensional problems are selected to validate the approach. Finally, the three-dimensional simulation of a wobbling droplet and a shock droplet interaction in two dimensions are shown. In both problems phase transition and surface tension determine the global bulk behavior.
Local and global stability analysis of compressible channel flow over wall impedance
Rahbari, Iman; Scalo, Carlo
2016-11-01
The stability properties of compressible channel flow over porous walls is investigated via Local (LSA) and Global Stability Analysis (GSA) for laminar and turbulent base flows at Reb = 6900 and Mb = 0 . 85 , 1 . 5 , 3 . 5 . Linearized Navier-Stokes equations are discretized via a sixth-order fully collocated Padé scheme leading to a Generalized Eigenvalue Problem (GEVP) solved using a parallel sparse eigenvalue solver based on the shift-invert Arnoldi method. The adopted discretization guarantees spectral-like spatial resolution. Fully sparsity of the system is retained via implicit calculation of the numerical derivatives ensuring computational efficiency on multi-processor platforms. The global eigen-spectrum exhibits various sets of modes grouped by streamwise wave-numbers, which are captured via LSA, as well as global acoustic modes. Consistently with the findings of C. Scalo et al., two unstable local modes are found for sufficiently high wall permeability: one standing-wave-like and one representing a bulk pressure mode, both generating additional Reynolds shear stresses concentrated in the viscous sublayer region. Stability properties of the flow over non-modal streamwise impedance distributions are also discussed.
Energy Technology Data Exchange (ETDEWEB)
Berry, R. A. [Idaho National Lab. (INL), Idaho Falls, ID (United States)
2017-08-14
In the literature, the abundance of pipe network junction models, as well as inclusion of dissipative losses between connected pipes with loss coefficients, has been treated using the incompressible flow assumption of constant density. This approach is fundamentally, physically wrong for compressible flow with density change. This report introduces a mathematical modeling approach for general junctions in piping network systems for which the transient flows are compressible and single-phase. The junction could be as simple as a 1-pipe input and 1-pipe output with differing pipe cross-sectional areas for which a dissipative loss is necessary, or it could include an active component, between an inlet pipe and an outlet pipe, such as a pump or turbine. In this report, discussion will be limited to the former. A more general branching junction connecting an arbitrary number of pipes with transient, 1-D compressible single-phase flows is also presented. These models will be developed in a manner consistent with the use of a general equation of state like, for example, the recent Spline-Based Table Look-up method [1] for incorporating the IAPWS-95 formulation [2] to give accurate and efficient calculations for properties for water and steam with RELAP-7 [3].
Numerical Calculation of Interaction Between Plane Jet and Subsonic Flow
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V. O. Moskalenko
2016-01-01
Full Text Available The paper makes numerical calculation of interaction between plane jet and subsonic flow. Its aim is to determine the jet trajectory, velocity profiles, distribution of pressure coefficient on the plate surface at different jet angles, namely ωj=45°; 90°; 105° and at low blowing strengths ( ≤1.5 as well as a to make comparison with the experimental data of other authors.To simulate a two-dimensional jet in the subsonic flow the software package “CAD SolidWorks Flow Simulation” has been used. Initially, the test task was solved with its calculation results compared with experimental ones [6.8] in order to improve the convergence; the size of the computational domain and a computational grid within the k-ε turbulence model were selected. As a result of the calculation, were identified and analysed the pressure values, jet trajectories, and velocity profiles. In the graphs the solid lines show calculation results, and dots represent experimental data.From the calculation results it is seen that, with increasing intensity of the reduced mass flow ¯q in the above range, the change of the jet pressure coefficient p¯ distribution behind a slotted nozzle is almost linear and significant. Before the nozzle, with increasing ¯q the pressure coefficient increases slightly.Analysis of results has shown that blowing of jets with ωj>90ω, provides a greater perturbation of the subsonic flow. Thus, the jet penetrates into the flow deeper, forms a dead region of the greater length, and more significantly redistributes the pressure coefficient on the surface of the plate.The calculation results are in good compliance with the experimental data both for the jet axis and for the pressure coefficient distribution on the plate surface. The research results can be used in the designing the jet control of aircrafts.
Nonequilibrium flow calculations for the hydrogen constricted arc
Scott, R. K.; Incropera, F. P.
1973-01-01
A nonequilibrium flow model has been formulated and solved numerically for conditions in an atomic hydrogen cascade arc. Solutions show that although thermal nonequilibrium effects are minor, the departure from chemical equilibrium is significant. Comparisons with results obtained from an equilibrium flow model reveal the deficiencies associated with such a model and parametric calculations reveal the effect of current, pressure, and radius on arc behavior.
Omori, S.; Gross, K. W.
1973-01-01
The turbulent kinetic energy equation is coupled with boundary layer equations to solve the characteristics of compressible turbulent boundary layers with mass injection and combustion. The Reynolds stress is related to the turbulent kinetic energy using the Prandtl-Wieghardt formulation. When a lean mixture of hydrogen and nitrogen is injected through a porous plate into the subsonic turbulent boundary layer of air flow and ignited by external means, the turbulent kinetic energy increases twice as much as that of noncombusting flow with the same mass injection rate of nitrogen. The magnitudes of eddy viscosity between combusting and noncombusting flows with injection, however, are almost the same due to temperature effects, while the distributions are different. The velocity profiles are significantly affected by combustion. If pure hydrogen as a transpiration coolant is injected into a rocket nozzle boundary layer flow of combustion products, the temperature drops significantly across the boundary layer due to the high heat capacity of hydrogen. At a certain distance from the wall hydrogen reacts with the combustion products, liberating an extensive amount of heat.
Computer solutions of Wu's equations for compressible flow through turbomachines
Smith, D. J. L.
1974-01-01
Two computers programs, known as Matrix Through-Flow and Matrix Blade-To-Blade, for analyzing the meridional and blade-to-blade flow patterns are described. The numerical solutions are obtained by finite difference approximations to the governing Poisson-type differential equations for the stream function. Solutions for several turbomachines, giving flow patterns and velocity distributions, are included.
A physical five-equation model for compressible two-fluid flow, and its numerical treatment
Kreeft, J.J.; Koren, B.
2009-01-01
A novel five-equation model for inviscid, non-heat-conducting, compressible two-fluid flow is derived, together with an appropriate numerical method. The model uses flow equations based on conservation laws and exchange laws only. The two fluids exchange momentum and energy, for which source terms a
Fluctuation diagrams for hot-wire anemometry in subsonic compressible flows
Stainback, P. C.; Nagabushana, K. A.
1991-01-01
The concept of using 'fluctuation diagrams' for describing basic fluctuations in compressible flows was reported by Kovasznay in the 1950's. The application of this technique, for the most part, was restricted to supersonic flows. Recently, Zinovev and Lebiga published reports where they considered the fluctuation diagrams in subsonic compressible flows. For the above studies, the velocity and density sensitivities of the heated wires were equal. However, there are considerable data, much taken in the 1950's, which indicate that under some conditions the velocity and density sensitivities are not equal in subsonic compressible flows. Therefore, possible fluctuation diagrams are described for the cases where the velocity and density sensitivities are equal and the more general cases where they are unequal.
The role of hand calculations in ground water flow modeling.
Haitjema, Henk
2006-01-01
Most ground water modeling courses focus on the use of computer models and pay little or no attention to traditional analytic solutions to ground water flow problems. This shift in education seems logical. Why waste time to learn about the method of images, or why study analytic solutions to one-dimensional or radial flow problems? Computer models solve much more realistic problems and offer sophisticated graphical output, such as contour plots of potentiometric levels and ground water path lines. However, analytic solutions to elementary ground water flow problems do have something to offer over computer models: insight. For instance, an analytic one-dimensional or radial flow solution, in terms of a mathematical expression, may reveal which parameters affect the success of calibrating a computer model and what to expect when changing parameter values. Similarly, solutions for periodic forcing of one-dimensional or radial flow systems have resulted in a simple decision criterion to assess whether or not transient flow modeling is needed. Basic water balance calculations may offer a useful check on computer-generated capture zones for wellhead protection or aquifer remediation. An easily calculated "characteristic leakage length" provides critical insight into surface water and ground water interactions and flow in multi-aquifer systems. The list goes on. Familiarity with elementary analytic solutions and the capability of performing some simple hand calculations can promote appropriate (computer) modeling techniques, avoids unnecessary complexity, improves reliability, and is likely to save time and money. Training in basic hand calculations should be an important part of the curriculum of ground water modeling courses.
Pressure, density, temperature and entropy fluctuations in compressible turbulent plane channel flow
Gerolymos, G A
2013-01-01
We investigate the fluctuations of thermodynamic state-variables in compressible aerodynamic wall-turbulence, using results of direct numerical simulation (DNS) of compressible turbulent plane channel flow. The basic transport equations governing the behaviour of thermodynamic variables (density, pressure, temperature and entropy) are reviewed and used to derive the exact transport equations for the variances and fluxes (transport by the fluctuating velocity field) of the thermodynamic fluctuations. The scaling with Reynolds and Mach number of compressible turbulent plane channel flow is discussed. Correlation coefficients and higher-order statistics of the thermodynamic fluctuations are examined. Finally, detailed budgets of the transport equations for the variances and fluxes of the thermodynamic variables from a well-resolved DNS are analysed. Implications of these results both to the understanding of the thermodynamic interactions in compressible wall-turbulence and to possible improvements in statistical...
Numerical calculation of periodic viscous flow through a circular hole
Notomi, T.; Namba, M.
1992-08-01
Periodic viscous flows through a circular hole driven by fluctuating far field pressure are studied numerically. The time dependent incompressible Navier-Stokes equations formulated with orthogonal curvilinear co-ordinates are solved by using a finite difference method. The flow patterns and acoustic impedance of the circular hole are investigated for various combinations of the pressure/viscous force ratio, frequency and hole edge thickness. Numerical calculations revealed some interesting facts, as follows. First, the flow patterns are classified into three regimes by fluctuating pressure amplitude and frequency: flows with no laminar separation (high-frequency-low-pressure range), flows with attached separation bubble (intermediate frequency and pressure range) and flows with detached vortex rings (low-frequency-high-pressure range). Second, the flow resistance of the circular hole is proportional to the acoustic particle velocity but independent of the viscosity of the fluid, and almost invariant with the frequency for the low-frequency-high-pressure range. On the other hand, for the high-frequency-low-pressure range, the flow resistance is independent of the periodic pressure amplitude and varies directly with the 2/3 power of the frequency. Finally, the predicted circular hole impedance is in good agreement with the experimental data for the orifice impedance of Ingard and Ising.
Compressive Loads on the Lumbar Spine During Lifting: 4D WATBAK versus Inverse Dynamics Calculations
Directory of Open Access Journals (Sweden)
M. H. Cole
2005-01-01
Full Text Available Numerous two- and three-dimensional biomechanical models exist for the purpose of assessing the stresses placed on the lumbar spine during the performance of a manual material handling task. More recently, researchers have utilised their knowledge to develop specific computer-based models that can be applied in an occupational setting; an example of which is 4D WATBAK. The model used by 4D WATBAK bases its predications on static calculations and it is assumed that these static loads reasonably depict the actual dynamic loads acting on the lumbar spine. Consequently, it was the purpose of this research to assess the agreement between the static predictions made by 4D WATBAK and those from a comparable dynamic model. Six individuals were asked to perform a series of five lifting tasks, which ranged from lifting 2.5 kg to 22.5 kg and were designed to replicate the lifting component of the Work Capacity Assessment Test used within Australia. A single perpendicularly placed video camera was used to film each performance in the sagittal plane. The resultant two-dimensional kinematic data were input into the 4D WATBAK software and a dynamic biomechanical model to quantify the compression forces acting at the L4/L5 intervertebral joint. Results of this study indicated that as the mass of the load increased from 2.5 kg to 22.5 kg, the static compression forces calculated by 4D WATBAK became increasingly less than those calculated using the dynamic model (mean difference ranged from 22.0% for 2.5 kg to 42.9% for 22.5 kg. This study suggested that, for research purposes, a validated three-dimensional dynamic model should be employed when a task becomes complex and when a more accurate indication of spinal compression or shear force is required. Additionally, although it is clear that 4D WATBAK is particularly suited to industrial applications, it is suggested that the limitations of such modelling tools be carefully considered when task-risk and employee
Numerical Solution of Inviscid Compressible Steady Flows around the RAE 2822 Airfoil
Kryštůfek, P.; Kozel, K.
2015-05-01
The article presents results of a numerical solution of subsonic, transonic and supersonic flows described by the system of Euler equations in 2D compressible flows around the RAE 2822 airfoil. Authors used FVM multistage Runge-Kutta method to numerically solve the flows around the RAE 2822 airfoil. The results are compared with the solution using the software Ansys Fluent 15.0.7.
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.
Free-surface modelling technology for compressible and violent flows
CSIR Research Space (South Africa)
Heyns, Johan A
2011-06-01
Full Text Available of bench-marked test cases FCSCF is compared to a state-of-the-art higher-resolution scheme. II.B. Evaluation of FCSCF FCSCF is evaluated by applying it to a number of benchmark problems presented in literature. To asses the increased accuracy.... In line with the above a new weakly compressible formulation for the volume-of-fluid free-surface mod- elling approach is presented, where after it is evaluated by considering various bench-marked test cases. 9 of 16 American Institute of Aeronautics...
On Exact Solutions of Rarefaction-Rarefaction Interactions in Compressible Isentropic Flow
Jenssen, Helge Kristian
2016-12-01
Consider the interaction of two centered rarefaction waves in one-dimensional, compressible gas flow with pressure function p(ρ )=a^2ρ ^γ with γ >1 . The classic hodograph approach of Riemann provides linear 2nd order equations for the time and space variables t, x as functions of the Riemann invariants r, s within the interaction region. It is well known that t(r, s) can be given explicitly in terms of the hypergeometric function. We present a direct calculation (based on works by Darboux and Martin) of this formula, and show how the same approach provides an explicit formula for x(r, s) in terms of Appell functions (two-variable hypergeometric functions). Motivated by the issue of vacuum and total variation estimates for 1-d Euler flows, we then use the explicit t-solution to monitor the density field and its spatial variation in interactions of two centered rarefaction waves. It is found that the variation is always non-monotone, and that there is an overall increase in density variation if and only if γ >3 . We show that infinite duration of the interaction is characterized by approach toward vacuum in the interaction region, and that this occurs if and only if the Riemann problem defined by the extreme initial states generates a vacuum. Finally, it is verified that the minimal density in such interactions decays at rate O(1)/t.
Application of Gridless Method to Simulation of Compressible Multi-Material Flows
Institute of Scientific and Technical Information of China (English)
Liang Wang; Houqian Xu; Wei Wu; Rui Xue
2015-01-01
The least⁃square gridless method was extended to simulate the compressible multi⁃material flows. The algorithm was accomplished to solve the Arbitrary Lagrange⁃Euler ( ALE ) formulation. The local least⁃square curve fits was adopted to approximate the spatial derivatives of a point on the base of the points in its circular support domain, and the basis function was linear. The HLLC ( Harten⁃Lax⁃van Leer⁃Contact) scheme was used to calculate the inviscid flux. On the material interfaces, the gridless points were endued with a dual definition corresponding to different materials. The moving velocity of the interface points was updated by solving the Riemann problem. The interface boundary condition was built by using the Ghost Fluid Method ( GFM ) . Computations were performed for several one and two dimensional typical examples. The numerical results show that the interface and the shock wave are well captured, which proves the effectiveness of gridless method in dealing with multi⁃material flow problems.
Chang, Chih-Hao; Liou, Meng-Sing
2007-07-01
In this paper, we propose a new approach to compute compressible multifluid equations. Firstly, a single-pressure compressible multifluid model based on the stratified flow model is proposed. The stratified flow model, which defines different fluids in separated regions, is shown to be amenable to the finite volume method. We can apply the conservation law to each subregion and obtain a set of balance equations . Secondly, the AUSM + scheme, which is originally designed for the compressible gas flow, is extended to solve compressible liquid flows. By introducing additional dissipation terms into the numerical flux, the new scheme, called AUSM +-up, can be applied to both liquid and gas flows. Thirdly, the contribution to the numerical flux due to interactions between different phases is taken into account and solved by the exact Riemann solver. We will show that the proposed approach yields an accurate and robust method for computing compressible multiphase flows involving discontinuities, such as shock waves and fluid interfaces. Several one-dimensional test problems are used to demonstrate the capability of our method, including the Ransom's water faucet problem and the air-water shock tube problem. Finally, several two dimensional problems will show the capability to capture enormous details and complicated wave patterns in flows having large disparities in the fluid density and velocities, such as interactions between water shock wave and air bubble, between air shock wave and water column(s), and underwater explosion. However, conservative form is lost in these balance equations when considering each individual phase; in fact, the interactions that exist simultaneously in both phases manifest themselves as nonconservative terms.
Large scale steam flow test: Pressure drop data and calculated pressure loss coefficients
Energy Technology Data Exchange (ETDEWEB)
Meadows, J.B.; Spears, J.R.; Feder, A.R.; Moore, B.P.; Young, C.E. [Bettis Atomic Power Lab., Pittsburgh, PA (United States)
1993-12-01
This report presents the result of large scale steam flow testing, 3 million to 7 million lbs/hr., conducted at approximate steam qualities of 25, 45, 70 and 100 percent (dry, saturated). It is concluded from the test data that reasonable estimates of piping component pressure loss coefficients for single phase flow in complex piping geometries can be calculated using available engineering literature. This includes the effects of nearby upstream and downstream components, compressibility, and internal obstructions, such as splitters, and ladder rungs on individual piping components. Despite expected uncertainties in the data resulting from the complexity of the piping geometry and two-phase flow, the test data support the conclusion that the predicted dry steam K-factors are accurate and provide useful insight into the effect of entrained liquid on the flow resistance. The K-factors calculated from the wet steam test data were compared to two-phase K-factors based on the Martinelli-Nelson pressure drop correlations. This comparison supports the concept of a two-phase multiplier for estimating the resistance of piping with liquid entrained into the flow. The test data in general appears to be reasonably consistent with the shape of a curve based on the Martinelli-Nelson correlation over the tested range of steam quality.
Directory of Open Access Journals (Sweden)
Tahmina Akhter
2014-01-01
Full Text Available The flow of a compressible fluid with slip through a cylinder with an asymmetric local constriction has been considered both numerically, as well as analytically. For the numerical work, a particle-based method whose dynamics is governed by the multiparticle collision (MPC rule has been used together with a generalized boundary condition that allows for slip at the wall. Since it is well known that an MPC system corresponds to an ideal gas and behaves like a compressible, viscous flow on average, an approximate analytical solution has been derived from the compressible Navier–Stokes equations of motion coupled to an ideal gas equation of state using the Karman–Pohlhausen method. The constriction is assumed to have a polynomial form, and the location of maximum constriction is varied throughout the constricted portion of the cylinder. Results for centerline densities and centerline velocities have been compared for various Reynolds numbers, Mach numbers, wall slip values and flow geometries.
A meshless method for compressible flows with the HLLC Riemann solver
Ma, Z H; Qian, L
2014-01-01
The HLLC Riemann solver, which resolves both the shock waves and contact discontinuities, is popular to the computational fluid dynamics community studying compressible flow problems with mesh methods. Although it was reported to be used in meshless methods, the crucial information and procedure to realise this scheme within the framework of meshless methods were not clarified fully. Moreover, the capability of the meshless HLLC solver to deal with compressible liquid flows is not completely clear yet as very few related studies have been reported. Therefore, a comprehensive investigation of a dimensional non-split HLLC Riemann solver for the least-square meshless method is carried out in this study. The stiffened gas equation of state is adopted to capacitate the proposed method to deal with single-phase gases and/or liquids effectively, whilst direct applying the perfect gas equation of state for compressible liquid flows might encounter great difficulties in correlating the state variables. The spatial der...
Application of Lossless Data Compression Techniques to Radio Astronomy Data flows
Natusch, Tim
2014-01-01
The modern practice of Radio Astronomy is characterized by extremes of data volume and rates, principally because of the direct relationship between the signal to noise ratio that can be achieved and the need to Nyquist sample the RF bandwidth necessary by way of support. The transport of these data flows is costly. By examining the statistical nature of typical data flows and applying well known techniques from the field of Information Theory the following work shows that lossless compression of typical radio astronomy data flows is in theory possible. The key parameter in determining the degree of compression possible is the standard deviation of the data. The practical application of compression could prove beneficial in reducing the costs of data transport and (arguably) storage for new generation instruments such as the Square Kilometer Array.
Flow and Performance Calculations of Axial Compressor near Stall Margin
Hwang, Yoojun; Kang, Shin-Hyoung
2010-06-01
Three-dimensional flows through a Low Speed Research Axial Compressor were numerically conducted in order to estimate the performance through unsteady and steady-state simulations. The first stage with the inlet guide vane was investigated at the design point to confirm that the rotor blade induced periodicity exists. Special attention was paid to the flow near the stall condition to inspect the flow behavior in the vicinity of the stall margin. The performance predicted under the steady-state assumption is in good agreement with the measured data. However, the steady-state calculations induce more blockage through the blade passage. Flow separations on the blade surface and end-walls are reduced when unsteady simulation is conducted. The negative jet due to the wake of the rotor blade periodically distorts the boundary layer on the surface of the stator blade and improves the performance of the compressor in terms of the pressure rise. The advantage of the unsteadiness increases as the flow rate reduces. In addition, the rotor tip leakage flow is forced downstream by the unsteadiness. Consequently, the behavior contributes to extending the range of operation by preventing the leakage flow from proceeding upstream near the stall margin.
An implicit numerical model for multicomponent compressible two-phase flow in porous media
Zidane, Ali; Firoozabadi, Abbas
2015-11-01
We introduce a new implicit approach to model multicomponent compressible two-phase flow in porous media with species transfer between the phases. In the implicit discretization of the species transport equation in our formulation we calculate for the first time the derivative of the molar concentration of component i in phase α (cα, i) with respect to the total molar concentration (ci) under the conditions of a constant volume V and temperature T. The species transport equation is discretized by the finite volume (FV) method. The fluxes are calculated based on powerful features of the mixed finite element (MFE) method which provides the pressure at grid-cell interfaces in addition to the pressure at the grid-cell center. The efficiency of the proposed model is demonstrated by comparing our results with three existing implicit compositional models. Our algorithm has low numerical dispersion despite the fact it is based on first-order space discretization. The proposed algorithm is very robust.
Research on flow stress of spray formed 70Si30Al ahoy under hot compression deformation
Institute of Scientific and Technical Information of China (English)
WEI Yanguang; XIONG Baiqing; ZHANG Yong'an; LIU Hongwei; ZHU Baohong; WANG feng
2006-01-01
The flow stress of spray formed 70Si30Al alloy was studied by hot compression on a Gleeble-1500 test machine.The experimental results indicated that the flow stress depends on the strain rate and the deformation temperature. The flow stress increases with an increase in strain rate at a given deformation temperature. The flow stress decreases with the deformation temperature increasing at a given strain rate. The relational expression among the flow stress, the strain rate, and the deformation temperature satisfies the Arrhenius equation. The deformation activation energy of 70Si30Al alloy during hot deformation is 866.27 kJ/mol from the Arrhenius equation.
Nonlinear stability of non-stationary cross-flow vortices in compressible boundary layers
Gajjar, J. S. B.
1995-01-01
The nonlinear evolution of long wavelength non-stationary cross-flow vortices in a compressible boundary layer is investigated and the work extends that of Gajjar (1994) to flows involving multiple critical layers. The basic flow profile considered in this paper is that appropriate for a fully three-dimensional boundary layer with O(1) Mach number and with wall heating or cooling. The governing equations for the evolution of the cross-flow vortex are obtained and some special cases are discussed. One special case includes linear theory where exact analytic expressions for the growth rate of the vortices are obtained. Another special case is a generalization of the Bassom & Gajjar (1988) results for neutral waves to compressible flows. The viscous correction to the growth rate is derived and it is shown how the unsteady nonlinear critical layer structure merges with that for a Haberman type of viscous critical layer.
Lymphoedema management with the LymphFlow Advance pneumatic compression pump.
Lee, Natalie; Wigg, Jane; Pugh, Stacy; Barclay, Janet; Moore, Hayley
2016-10-01
There are many intermittent pneumatic compression devices available for use in the management and adjunct treatment of lymphatic, venous and arterial disease. This article discusses the development of a new advanced pneumatic compression device, the LymphFlow Advance, which can perform focussed treatment on the lymphoedematous area using a variety of different cycles. Case studies with therapist and patient feedback are used to demonstrate the use of the LymphFlow Advance in the lymphoedema clinic, with a discussion of the evidence to underpin recommended treatment regimes.
Development of an app for compressible flow “App4Comp”
Adam Alberdi, Andrés; Gámez Montero, Pedro Javier
2015-01-01
In this paper is discussed the development and operation of a new Android App made through Google’s platform App Inventor 2. This App is focused on solving classic problems related to compressible flow, dealing with the typical cases seen in the subject of Fluid Mechanics of a degree in Aeronautics. It is downloadable from [1], or through the QR code at the end of this paper. The main objective of this project was to bring in a new, useful app about compressible flow to the market, but als...
An Improved Ghost-cell Immersed Boundary Method for Compressible Inviscid Flow Simulations
Chi, Cheng
2015-05-01
This study presents an improved ghost-cell immersed boundary approach to represent a solid body in compressible flow simulations. In contrast to the commonly used approaches, in the present work ghost cells are mirrored through the boundary described using a level-set method to farther image points, incorporating a higher-order extra/interpolation scheme for the ghost cell values. In addition, a shock sensor is in- troduced to deal with image points near the discontinuities in the flow field. Adaptive mesh refinement (AMR) is used to improve the representation of the geometry efficiently. The improved ghost-cell method is validated against five test cases: (a) double Mach reflections on a ramp, (b) supersonic flows in a wind tunnel with a forward- facing step, (c) supersonic flows over a circular cylinder, (d) smooth Prandtl-Meyer expansion flows, and (e) steady shock-induced combustion over a wedge. It is demonstrated that the improved ghost-cell method can reach the accuracy of second order in L1 norm and higher than first order in L∞ norm. Direct comparisons against the cut-cell method demonstrate that the improved ghost-cell method is almost equally accurate with better efficiency for boundary representation in high-fidelity compressible flow simulations. Implementation of the improved ghost-cell method in reacting Euler flows further validates its general applicability for compressible flow simulations.
Community detection by label propagation with compression of flow
Han, Jihui; Li, Wei; Su, Zhu; Zhao, Longfeng; Deng, Weibing
2016-12-01
The label propagation algorithm (LPA) has been proved to be a fast and effective method for detecting communities in large complex networks. However, its performance is subject to the non-stable and trivial solutions of the problem. In this paper, we propose a modified label propagation algorithm LPAf to efficiently detect community structures in networks. Instead of the majority voting rule of the basic LPA, LPAf updates the label of a node by considering the compression of a description of random walks on a network. A multi-step greedy agglomerative strategy is employed to enable LPAf to escape the local optimum. Furthermore, an incomplete update condition is also adopted to speed up the convergence. Experimental results on both synthetic and real-world networks confirm the effectiveness of our algorithm.
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.
AbuAlSaud, Moataz
2012-07-01
The purpose of this thesis is to solve unsteady two-dimensional compressible Navier-Stokes equations for a moving mesh using implicit explicit (IMEX) Runge- Kutta scheme. The moving mesh is implemented in the equations using Arbitrary Lagrangian Eulerian (ALE) formulation. The inviscid part of the equation is explicitly solved using second-order Godunov method, whereas the viscous part is calculated implicitly. We simulate subsonic compressible flow over static NACA-0012 airfoil at different angle of attacks. Finally, the moving mesh is examined via oscillating the airfoil between angle of attack = 0 and = 20 harmonically. It is observed that the numerical solution matches the experimental and numerical results in the literature to within 20%.
Shouman, A. R.; Garcia, C. E.
1971-01-01
An analytical solution for the compressible one-dimensional flow in convergent and divergent ducts with friction is obtained. It is found that a nondimensional parameter, N, can be formed using the friction factor, duct half-angle and the ratio of specific heats of the gas. Seven flow regimes are describable with the solution, based on certain bounds on the magnitude of N. The regimes are discussed and corollary data are presented graphically.
Equations and simulations for multiphase compressible gas-dust flows
Oran, Elaine; Houim, Ryan
2014-11-01
Dust-gas multiphase flows are important in physical scenarios such as dust explosions in coal mines, asteroid impact disturbing lunar regolith, and soft aircraft landings dispersing desert or beach sand. In these cases, the gas flow regime can range from highly subsonic and nearly incompressible to supersonic and shock-laden flow, the grain packing can range from fully packed to completely dispersed, and both the gas and the dust can range from chemically inert to highly exothermic. To cover the necessary parameter range in a single model, we solve coupled sets of Navier-Stokes equations describing the background gas and the dust. As an example, a reactive-dust explosion that results in a type of shock-flame complex is described and discussed. Sponsored by the University of Maryland through Minta Martin Endowment Funds in the Department of Aerospace Engineering, and through the Glenn L. Martin Institute Chaired Professorship at the A. James Clark School of Engineering.
A calculation procedure for viscous flow in turbomachines, volume 1
Khalil, I.; Tabakoff, W.
1979-01-01
A method for analyzing the nonadiabatic viscous flow through turbomachine rotors is presented. The field analysis is based upon the numerical integration of the full incompressible stream function vorticity form of the Navier-Stokes equations, together with the energy equation, over the rotor blade-to-blade stream channels. The numerical code used to solve the governing equations employs a nonorthogonal boundary fitted coordinate system that suits the most complicated blade geometries. A numerical scheme is used to carry out the necessary integration of the elliptic governing equations. The flow characteristics within the rotor of a radial inflow turbine are investigated over a wide range of operating conditions. The calculated results are compared to existing experimental data. The flow in a radial compressor is analyzed in order to study the behavior of viscous flow in diffusing cascades. The results are compared qualitatively to known experimental trends. The solution obtained provides insight into the flow phenomena in this type of turbomachine. It is concluded that the method of analysis is quite general and gives a good representation of the actual flow behavior within turbomachine passages.
Calculation of the dynamic air flow resistivity of fibre materials
DEFF Research Database (Denmark)
Tarnow, Viggo
1997-01-01
The acoustic attenuation of acoustic fiber materials is mainly determined by the dynamic resistivity to an oscillating air flow. The dynamic resistance is calculated for a model with geometry close to the geometry of real fibre material. The model constists of parallel cylinders placed randomly. ......-consistent procedure gives the same results as the more complicated procedure based on average over Voronoi cells. Graphs of the dynamic resistivity versus frequency are given for fiber densities and diameters typical for acoustic fiber materials.......The acoustic attenuation of acoustic fiber materials is mainly determined by the dynamic resistivity to an oscillating air flow. The dynamic resistance is calculated for a model with geometry close to the geometry of real fibre material. The model constists of parallel cylinders placed randomly...
Energy Technology Data Exchange (ETDEWEB)
Poojitganont, T.; Berg, H.P.; Izweik, H.T. [Brandenburg Univ. of Technology Cottbus, Cottbus (Germany)
2009-07-01
As a result of continuously increasing oil prices, automotive industries are looking for alternative power sources for their automobiles. An excellent solution is the hybrid system. However due to the additional weight of its batteries, this causes the total weight of the car to increase. This higher battery weight can be compensated by reducing the weight of the engine. A rotary engine, such as the Wankel rotary engine, has a more attractive power to weight ratio than the normal reciprocating engine. The rotary engine can be treated and evaluated with respect to performance characteristics as a displacement type, four-stroke internal combustion engine, one-cycle similar to the reciprocating engine. For any combustion engine to reach the maximum power output, the mixture formation inside the engine should be considered. The flow phenomenon inside the engine is a key parameter which involves the mixture formation mechanism. This paper investigated the spray characteristic from the injector and the flow phenomena inside the combustion chamber. Its behaviours were studied using computational fluid dynamics simulation. The simulation setup was described in detail, with reference to meshes; initial condition; and boundary condition. Verification of the calculation was also presented. A comparison of the temperature during compression stroke from the analytical calculation and the adiabetic system simulation were also illustrated. Simulation results showed that the speed of the engine provides a proportional effect on the magnitude of air velocity inside the engine, whereas the circulation region can be expanded by increasing the intake pressure during the intake stroke. 9 refs., 1 tab., 13 figs.
Stress Analysis and Calculation of Flow Interruption Capability Test Loop
Institute of Scientific and Technical Information of China (English)
FENG; Bo; QI; Xiao-guang; CHENG; Dao-xi
2012-01-01
<正>A stress-analysis and calculation has been done for the flow interruption capability test loop (Fig. 1). In the design condition, the test loop is operated on 350 ℃ and 20MPa. By reasonably simplifying and modeling, a stress-analysis program named Triflex was used to analyze the piping stress and optimize the piping supports, which meet the compliance. The work will provide the necessary basis for the construction of the loop and operation security.
Design of a lube oil reservoir by using flow calculations
Energy Technology Data Exchange (ETDEWEB)
Rinkinen, J.; Alfthan, A. [Institute of Hydraulics and Automation IHA, Tampere University of Technology, Tampere (Finland)] Suominen, J. [Institute of Energy and Process Engineering, Tampere University of Technology, Tampere (Finland); Airaksinen, A.; Antila, K. [R and D Engineer Safematic Oy, Muurame (Finland)
1997-12-31
The volume of usual oil reservoir for lubrication oil systems is designed by the traditional rule of thumb so that the total oil volume is theoretically changed in every 30 minutes by rated pumping capacity. This is commonly used settling time for air, water and particles to separate by gravity from the oil returning of the bearings. This leads to rather big volumes of lube oil reservoirs, which are sometimes difficult to situate in different applications. In this presentation traditionally sized lube oil reservoir (8 m{sup 3}) is modelled in rectangular coordinates and laminar oil flow is calculated by using FLUENT software that is based on finite difference method. The results of calculation are velocity and temperature fields inside the reservoir. The velocity field is used to visualize different particle paths through the reservoir. Particles that are studied by the model are air bubbles and water droplets. The interest of the study has been to define the size of the air bubbles that are released and the size of the water droplets that are separated in the reservoir. The velocity field is also used to calculate the modelled circulating time of the oil volume which is then compared with the theoretical circulating time that is obtained from the rated pump flow. These results have been used for designing a new lube oil reservoir. This reservoir has also been modelled and optimized by the aid of flow calculations. The best shape of the designed reservoir is constructed in real size for empirical measurements. Some results of the oil flow measurements are shown. (orig.) 7 refs.
Compressible Turbulent Flow Numerical Simulations of Tip Vortex Cavitation
Khatami, F.; Weide, van der E.T.A.; Hoeijmakers, H.W.M.
2015-01-01
For an elliptic Arndt’s hydrofoil numerical simulations of vortex cavitation are presented. An equilibrium cavitation model is employed. This single-fluid model assumes local thermodynamic and mechanical equilibrium in the mixture region of the flow, is employed. Furthermore, for characterizing the
Hot-Wire Probe for Compressible Subsonic Flow
Stainback, P. C.; Johnson, C. B.; Basnett, C. B.
1985-01-01
Probe measures velocity, density, and total temperature fluctuations. Three-wire probe used with each wire operating at different overheat ratio. Technique extendable into transonic and low supersonic flow regimes without difficulty except for those problems usually associated with lengthy calibration and possible wire breaking.
Nonequilibrium thermohydrodynamic effects on the Rayleigh-Taylor instability in compressible flows
Lai, Huilin; Xu, Aiguo; Zhang, Guangcai; Gan, Yanbiao; Ying, Yangjun; Succi, Sauro
2016-08-01
The effects of compressibility on Rayleigh-Taylor instability (RTI) are investigated by inspecting the interplay between thermodynamic and hydrodynamic nonequilibrium phenomena (TNE, HNE, respectively) via a discrete Boltzmann model. Two effective approaches are presented, one tracking the evolution of the local TNE effects and the other focusing on the evolution of the mean temperature of the fluid, to track the complex interfaces separating the bubble and the spike regions of the flow. It is found that both the compressibility effects and the global TNE intensity show opposite trends in the initial and the later stages of the RTI. Compressibility delays the initial stage of RTI and accelerates the later stage. Meanwhile, the TNE characteristics are generally enhanced by the compressibility, especially in the later stage. The global or mean thermodynamic nonequilibrium indicators provide physical criteria to discriminate between the two stages of the RTI.
Spectral Element Method for the Simulation of Unsteady Compressible Flows
Diosady, Laslo Tibor; Murman, Scott M.
2013-01-01
This work uses a discontinuous-Galerkin spectral-element method (DGSEM) to solve the compressible Navier-Stokes equations [1{3]. The inviscid ux is computed using the approximate Riemann solver of Roe [4]. The viscous fluxes are computed using the second form of Bassi and Rebay (BR2) [5] in a manner consistent with the spectral-element approximation. The method of lines with the classical 4th-order explicit Runge-Kutta scheme is used for time integration. Results for polynomial orders up to p = 15 (16th order) are presented. The code is parallelized using the Message Passing Interface (MPI). The computations presented in this work are performed using the Sandy Bridge nodes of the NASA Pleiades supercomputer at NASA Ames Research Center. Each Sandy Bridge node consists of 2 eight-core Intel Xeon E5-2670 processors with a clock speed of 2.6Ghz and 2GB per core memory. On a Sandy Bridge node the Tau Benchmark [6] runs in a time of 7.6s.
1D compressible flow with temperature dependent transport coefficients
Jenssen, Helge Kristian
2009-01-01
We establish existence of global-in-time weak solutions to the one dimensional, compressible Navier-Stokes system for a viscous and heat conducting ideal polytropic gas (pressure $p=K\\theta/\\tau$, internal energy $e=c_v \\theta$), when the viscosity $\\mu$ is constant and the heat conductivity $\\kappa$ depends on the temperature $\\theta$ according to $\\kappa(\\theta) = \\bar \\kappa \\theta^\\beta$, with $0\\leq\\beta<{3/2}$. This choice of degenerate transport coefficients is motivated by the kinetic theory of gasses. Approximate solutions are generated by a semi-discrete finite element scheme. We first formulate sufficient conditions that guarantee convergence to a weak solution. The convergence proof relies on weak compactness and convexity, and it applies to the more general constitutive relations $\\mu(\\theta) = \\bar \\mu \\theta^\\alpha$, $\\kappa(\\theta) = \\bar \\kappa \\theta^\\beta$, with $\\alpha\\geq 0$, $0 \\leq \\beta < 2$ ($\\bar \\mu, \\bar \\kappa$ constants). We then verify the sufficient conditions in the case...
Symmetries of the Euler compressible flow equations for general equation of state
Energy Technology Data Exchange (ETDEWEB)
Boyd, Zachary M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Ramsey, Scott D. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Baty, Roy S. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-10-15
The Euler compressible flow equations exhibit different Lie symmetries depending on the equation of state (EOS) of the medium in which the flow occurs. This means that, in general, different types of similarity solution will be available in different flow media. We present a comprehensive classification of all EOS’s to which the Euler equations apply, based on the Lie symmetries admitted by the corresponding flow equations, restricting to the case of 1-D planar, cylindrical, or spherical geometry. The results are conveniently summarized in tables. This analysis also clarifies past work by Axford and Ovsiannikov on symmetry classification.
A Numerical Study of Methods for Moist Atmospheric Flows: Compressible Equations
Duarte, Max; Balakrishnan, Kaushik; Bell, John B; Romps, David M
2013-01-01
We investigate different numerical techniques for evolving moist atmospheric flows within a fully compressible framework. In the standard numerical approach, the choice of variables is motivated by those that remain invariant in dry adiabatic flow, phase transitions are treated as an external energy source, and the physically-irrelevant fast acoustic modes are decoupled during the numerical integration. For the purposes of this study, we consider the compressible Euler equations in terms of the primitive thermodynamic variables, namely density, momentum, and total energy of moist air, without any special numerical treatment of the fast acoustic dynamics. This allows us to incorporate consistent moist thermodynamic properties throughout the numerical solution, and to thoroughly investigate both the standard two-step splitting approach for moist atmospheric flows as well as a fully coupled technique based on the use of variables that are conserved in moist flows, i.e. total energy of moist air and total water c...
Flow Instability and Its Control in Compression Systems
Institute of Scientific and Technical Information of China (English)
Jingyi Chen
2003-01-01
This paper reviews the development in the research of flow instability and its control over the recent ten or more years. This development was largely stimulated by the novel idea of active control of the aerodynamic instability in compressors. Three topics are covered in the paper, which appeared as the major themes towards the goal of stability enhancement. The first topic is the pre-stall behavior of rotating stall, which plays a vital role in designing the control scheme and discovering the convenient route to find the causal factors of flow disturbances potentially leading to stall. The second topic is the mechanism of blade passage flow during stall and its inception, which is the basic knowledge needed to manipulate the blade design for the stability improvement and eventually to predict the unsteady performance of the compressor system. The third topic is the recent trend of the control strategy based on the learning of active vs. passive methods. To introduce to the discussion of these topics, a brief description of the history of the recent development is given at the beginning of the paper. In discussing each topic, future works are also highlighted to enhance the further development of this long-standing problem in turbomachinery research and application.
Compressible Flow Produced by Distributed Sources of Mass: An Exact Solution
Clarke, J.F.
1987-01-01
The paper considers the case of a one-dimensional isentropic unsteady compressible flow that is driven entirely by a distribution of sources in the left-hand half space of an unbounded domain. The right-hand half-space contains no sources, so that source-strength drops discontinuously to zero as one crosses from left to right-hand space. Exact solutions are obtained for those parts of the flow that remain isentropic.
Numerical simulation of compressible Navier-Stokes flow in a double throat nozzle
Scott, James N.; Visbal, Miguel R.
The flow through a double-throat nozzle is computed using the complete time-dependent compressible Navier-Stokes equations. The computations were performed by using an existing working code with no special modifications for this particular application. The computations were performed on a Cyber 845 computer and a CRAY XMP-48 computer using three different grid sizes.
Applications of Taylor-Galerkin finite element method to compressible internal flow problems
Sohn, Jeong L.; Kim, Yongmo; Chung, T. J.
1989-01-01
A two-step Taylor-Galerkin finite element method with Lapidus' artificial viscosity scheme is applied to several test cases for internal compressible inviscid flow problems. Investigations for the effect of supersonic/subsonic inlet and outlet boundary conditions on computational results are particularly emphasized.
Prediction of mean flow data for adiabatic 2-D compressible turbulent boundary layers
Motallebi, F.
1997-01-01
This book presents a method for the prediction of mean flow data (i.e. skin friction, velocity profile and shape parameter) for adiabatic two-dimensional compressible turbulent boundary layers at zero pressure gradient. The transformed law of the wall, law of the lake, the van Driest model for the
Prediction of mean flow data for adiabatic 2-D compressible turbulent boundary layers
Motallebi, F.
1997-01-01
This book presents a method for the prediction of mean flow data (i.e. skin friction, velocity profile and shape parameter) for adiabatic two-dimensional compressible turbulent boundary layers at zero pressure gradient. The transformed law of the wall, law of the lake, the van Driest model for the c
Comparison of high order algorithms in Aerosol and Aghora for compressible flows
Directory of Open Access Journals (Sweden)
Mbengoue D. A.
2013-12-01
Full Text Available This article summarizes the work done within the Colargol project during CEMRACS 2012. The aim of this project is to compare the implementations of high order finite element methods for compressible flows that have been developed at ONERA and at INRIA for about one year, within the Aghora and Aerosol libraries.
Computational turbulent stress closure for large-eddy simulation of compressible flow
van der Bos, F.; Geurts, Bernardus J.
2006-01-01
This paper studies the computation of stress tensors for turbulent compressible flow for purposes of subgrid modeling for LES (large eddy simulation) methods in an effort to provide a model closure. The method uses and compares a variety of filters and special decomposition methods on the velocity
Simulation techniques for spatially evolving instabilities in compressible flow over a flat plate
Wasistho, B.; Geurts, B.J.; Kuerten, J.G.M.
1997-01-01
In this paper we present numerical techniques suitable for a direct numerical simulation in the spatial setting. We demonstrate the application to the simulation of compressible flat plate flow instabilities. We compare second and fourth order accurate spatial discretization schemes in combination w
Global smooth flows for compressible Navier-Stokes-Maxwell equations
Xu, Jiang; Cao, Hongmei
2016-08-01
Umeda et al. (Jpn J Appl Math 1:435-457, 1984) considered a rather general class of symmetric hyperbolic-parabolic systems: A0zt+sum_{j=1}nAjz_{xj}+Lz=sum_{j,k=1}nB^{jk}z_{xjxk} and showed optimal decay rates with certain dissipative assumptions. In their results, the dissipation matrices {L} and {B^{jk}(j,k=1,ldots,n)} are both assumed to be real symmetric. So far there are no general results in case that {L} and {B^{jk}} are not necessarily symmetric, which is left open now. In this paper, we investigate compressible Navier-Stokes-Maxwell (N-S-M) equations arising in plasmas physics, which is a concrete example of hyperbolic-parabolic composite systems with non-symmetric dissipation. It is observed that the Cauchy problem for N-S-M equations admits the dissipative mechanism of regularity-loss type. Consequently, extra higher regularity is usually needed to obtain the optimal decay rate of {L1({mathbb{R}}^3)}-{L^2({mathbb{R}}^3)} type, in comparison with that for the global-in-time existence of smooth solutions. In this paper, we obtain the minimal decay regularity of global smooth solutions to N-S-M equations, with aid of {L^p({mathbb{R}}^n)}-{Lq({mathbb{R}}^n)}-{Lr({mathbb{R}}^n)} estimates. It is worth noting that the relation between decay derivative orders and the regularity index of initial data is firstly found in the optimal decay estimates.
Groundwater flow modelling under ice sheet conditions. Scoping calculations
Energy Technology Data Exchange (ETDEWEB)
Jaquet, O.; Namar, R. (In2Earth Modelling Ltd (Switzerland)); Jansson, P. (Dept. of Physical Geography and Quaternary Geology, Stockholm Univ., Stockholm (Sweden))
2010-10-15
The potential impact of long-term climate changes has to be evaluated with respect to repository performance and safety. In particular, glacial periods of advancing and retreating ice sheet and prolonged permafrost conditions are likely to occur over the repository site. The growth and decay of ice sheets and the associated distribution of permafrost will affect the groundwater flow field and its composition. As large changes may take place, the understanding of groundwater flow patterns in connection to glaciations is an important issue for the geological disposal at long term. During a glacial period, the performance of the repository could be weakened by some of the following conditions and associated processes: - Maximum pressure at repository depth (canister failure). - Maximum permafrost depth (canister failure, buffer function). - Concentration of groundwater oxygen (canister corrosion). - Groundwater salinity (buffer stability). - Glacially induced earthquakes (canister failure). Therefore, the GAP project aims at understanding key hydrogeological issues as well as answering specific questions: - Regional groundwater flow system under ice sheet conditions. - Flow and infiltration conditions at the ice sheet bed. - Penetration depth of glacial meltwater into the bedrock. - Water chemical composition at repository depth in presence of glacial effects. - Role of the taliks, located in front of the ice sheet, likely to act as potential discharge zones of deep groundwater flow. - Influence of permafrost distribution on the groundwater flow system in relation to build-up and thawing periods. - Consequences of glacially induced earthquakes on the groundwater flow system. Some answers will be provided by the field data and investigations; the integration of the information and the dynamic characterisation of the key processes will be obtained using numerical modelling. Since most of the data are not yet available, some scoping calculations are performed using the
Numerical model of compressible gas flow in soil pollution control
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
Based on the theory of fluid dynamics in porous media, a numerical model of gas flow in unsaturated zone is developed with the consideration of gas density change due to variation of air pressure. This model is characterized of its wider range of availability. The accuracy of this numerical model is analyzed through comparison with modeling results by previous model with presumption of little pressure variation and the validity of this numerical model is shown. Thus it provides basis for the designing and management of landfill gas control system or soil vapor ex.action system in soil pollution control.
The New Performance Calculation Method of Fouled Axial Flow Compressor
Directory of Open Access Journals (Sweden)
Huadong Yang
2014-01-01
Full Text Available Fouling is the most important performance degradation factor, so it is necessary to accurately predict the effect of fouling on engine performance. In the previous research, it is very difficult to accurately model the fouled axial flow compressor. This paper develops a new performance calculation method of fouled multistage axial flow compressor based on experiment result and operating data. For multistage compressor, the whole compressor is decomposed into two sections. The first section includes the first 50% stages which reflect the fouling level, and the second section includes the last 50% stages which are viewed as the clean stage because of less deposits. In this model, the performance of the first section is obtained by combining scaling law method and linear progression model with traditional stage stacking method; simultaneously ambient conditions and engine configurations are considered. On the other hand, the performance of the second section is calculated by averaged infinitesimal stage method which is based on Reynolds’ law of similarity. Finally, the model is successfully applied to predict the 8-stage axial flow compressor and 16-stage LM2500-30 compressor. The change of thermodynamic parameters such as pressure ratio, efficiency with the operating time, and stage number is analyzed in detail.
The new performance calculation method of fouled axial flow compressor.
Yang, Huadong; Xu, Hong
2014-01-01
Fouling is the most important performance degradation factor, so it is necessary to accurately predict the effect of fouling on engine performance. In the previous research, it is very difficult to accurately model the fouled axial flow compressor. This paper develops a new performance calculation method of fouled multistage axial flow compressor based on experiment result and operating data. For multistage compressor, the whole compressor is decomposed into two sections. The first section includes the first 50% stages which reflect the fouling level, and the second section includes the last 50% stages which are viewed as the clean stage because of less deposits. In this model, the performance of the first section is obtained by combining scaling law method and linear progression model with traditional stage stacking method; simultaneously ambient conditions and engine configurations are considered. On the other hand, the performance of the second section is calculated by averaged infinitesimal stage method which is based on Reynolds' law of similarity. Finally, the model is successfully applied to predict the 8-stage axial flow compressor and 16-stage LM2500-30 compressor. The change of thermodynamic parameters such as pressure ratio, efficiency with the operating time, and stage number is analyzed in detail.
Lift and drag in three-dimensional steady viscous and compressible flow
Liu, Luoqin; Kang, Linlin; Wu, Jiezhi
2016-01-01
In a recent paper, Liu, Zhu & Wu (2015, J. Fluid Mech. 784: 304; LZW for short) present a far-field theory for the aerodynamic force experienced by a body in a two-dimensional, viscous, compressible and steady flow. In this companion theoretical paper we do the same for three-dimensional flow. By a rigorous fundamental solution method of the linearized Navier-Stokes equations, we not only improve the far-field force formula for incompressible flow originally derived by Goldstein in 1931 and summarized by Milne-Thomson in 1968, both being far from complete, to its perfect final form, but also prove that this final form holds universally true in a wide range of compressible flow, from subsonic to supersonic flows. We call this result the unified force theorem (UF theorem for short) and state it as a theorem, which is exactly the counterpart of the two-dimensional compressible Joukowski-Filon theorem obtained by LZW. Thus, the steady lift and drag are always exactly determined by the values of vector circula...
Tsuji, Takuya; Yokomine, Takehiko; Shimizu, Akihiko
2002-11-01
We have been engaged in the development of multi-scale adaptive simulation technique for incompressible turbulent flow. This is designed as that important scale components in the flow field are detected automatically by lifting wavelet and solved selectively. In conventional incompressible scheme, it is very common to solve Poisson equation of pressure to meet the divergence free constraints of incompressible flow. It may be not impossible to solve the Poisson eq. in the adaptive way, but this is very troublesome because it requires generation of control volume at each time step. We gave an eye on weakly compressible model proposed by Bao(2001). This model was derived from zero Mach limit asymptotic analysis of compressible Navier-Stokes eq. and does not need to solve the Poisson eq. at all. But it is relatively new and it requires demonstration study before the combination with the adaptation by wavelet. In present study, 2-D and 3-D Backstep flow were selected as test problems and applicability to turbulent flow is verified in detail. Besides, combination of adaptation by wavelet with weakly compressible model towards the adaptive turbulence simulation is discussed.
Toward compressed DMD: spectral analysis of fluid flows using sub-Nyquist-rate PIV data
Tu, Jonathan H; Kutz, J Nathan; Shang, Jessica K
2014-01-01
Dynamic mode decomposition (DMD) is a powerful and increasingly popular tool for performing spectral analysis of fluid flows. However, it requires data that satisfy the Nyquist-Shannon sampling criterion. In many fluid flow experiments, such data are impossible to capture. We propose a new approach that combines ideas from DMD and compressed sensing. Given a vector-valued signal, we take measurements randomly in time (at a sub-Nyquist rate) and project the data onto a low-dimensional subspace. We then use compressed sensing to identify the dominant frequencies in the signal and their corresponding modes. We demonstrate this method using two examples, analyzing both an artificially constructed test dataset and particle image velocimetry data collected from the flow past a cylinder. In each case, our method correctly identifies the characteristic frequencies and oscillatory modes dominating the signal, proving the proposed method to be a capable tool for spectral analysis using sub-Nyquist-rate sampling.
Calculation of Thomson scattering spectral fits for interpenetrating flows
Swadling, G. F.; Lebedev, S. V.; Harvey-Thompson, A. J.; Rozmus, W.; Burdiak, G. C.; Suttle, L.; Patankar, S.; Smith, R. A.; Bennett, M.; Hall, G. N.; Suzuki-Vidal, F.; Yuan, J.
2014-12-01
Collective mode optical Thomson scattering has been used to investigate the interactions of radially convergent ablation flows in Tungsten wire arrays. These experiments were carried out at the Magpie pulsed power facility at Imperial College, London. Analysis of the scattered spectra has provided direct evidence of ablation stream interpenetration on the array axis, and has also revealed a previously unobserved axial deflection of the ablation streams towards the anode as they approach the axis. It is has been suggested that this deflection is caused by the presence of a static magnetic field, advected with the ablation streams, stagnated and accrued around the axis. Analysis of the Thomson scattering spectra involved the calculation and fitting of the multi-component, non-relativistic, Maxwellian spectral density function S (k, ω). The method used to calculate the fits of the data are discussed in detail.
Calculation of Thomson scattering spectral fits for interpenetrating flows
Energy Technology Data Exchange (ETDEWEB)
Swadling, G. F., E-mail: george.swadling@imperial.ac.uk; Lebedev, S. V., E-mail: george.swadling@imperial.ac.uk; Burdiak, G. C.; Suttle, L.; Patankar, S.; Smith, R. A.; Bennett, M.; Suzuki-Vidal, F. [Blackett Laboratory, Imperial College, London SW7 2BW (United Kingdom); Harvey-Thompson, A. J. [Sandia National Laboratories, PO Box 5800, Albuquerque, New Mexico 87185-1193 (United States); Rozmus, W. [Department of Physics, University of Alberta, Edmonton, Alberta T6G 2JI (Canada); Hall, G. N. [Blackett Laboratory, Imperial College, London, United Kingdom SW7 2BW and Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (United States); Yuan, J. [Key Laboratory of Pulsed Power, Institute of Fluid Physics, CAE, Mianyang 621900 (China)
2014-12-15
Collective mode optical Thomson scattering has been used to investigate the interactions of radially convergent ablation flows in Tungsten wire arrays. These experiments were carried out at the Magpie pulsed power facility at Imperial College, London. Analysis of the scattered spectra has provided direct evidence of ablation stream interpenetration on the array axis, and has also revealed a previously unobserved axial deflection of the ablation streams towards the anode as they approach the axis. It is has been suggested that this deflection is caused by the presence of a static magnetic field, advected with the ablation streams, stagnated and accrued around the axis. Analysis of the Thomson scattering spectra involved the calculation and fitting of the multi-component, non-relativistic, Maxwellian spectral density function S (k, ω). The method used to calculate the fits of the data are discussed in detail.
Two Phase Compressible Flow Fields in One Dimensional and Eulerian Grid Framework
Lee, Sungsu; Park, Chan Wook
2008-11-01
Numerical investigation for two phase compressible flow fields of air-water in one dimensional tube are performed in the fixed Eulerian grid framework. Using an equation of states of Tait's type for a multiphase cell, the two phase compressible flow is modeled as equivalent single phase which is discretized using the Roe`s approximate Riemann solver, while the phase interface is captured via volume fractions of each phase. The most common problem found in the computational approaches in compressible multiphase flow is occurrence of the pressure oscillation at the phase interface. In order to suppress that phenomenon, tried are two approaches; a passive advection of volume fraction and a direct pressure relaxation with the compressible form of volume fraction equation. The results show that the direct pressure equalizing method suppresses pressure oscillation successfully and generates sharp discontinuities, transmitting and reflecting acoustic waves naturally at the phase interface. This work was supported by a research fund granted from Agency for Defense Development, South Korea
Uniqueness of weak solutions of the Navier-Stokes equations of compressible flow
Ariane Piovezan Entringer
2009-01-01
Resumo: Este trabalho consiste de uma exposição detalhada do resultado provado no artigo Uniqueness of Weak Solutions of the Navier-Stokes Equations of Multidimensional, Compressible Flow de D. Hoff (SIAM J. Math. Anal - 2006) sobre a unicidade de solução fraca e a dependência contínua da solução fraca nos dados iniciais para as equações de Navier-Stokes para fluídos compressíveis...Observação: O resumo, na integra, podera ser visualizado no texto completo da tese digital Abstract: Uniquen...
Shornikov, A; Wolf, A
2014-01-01
We present design and commissioning results of a forced flow cooling system utilizing neon at 30 K. The cryogen is pumped through the system by a room-temperature compression stage. To decouple the cold zone from the compression stage a recuperating counterflow tube-in-tube heat exchanger is used. Commissioning demonstrated successful condensation of neon and transfer of up to 30 W cooling power to the load at 30 K using only 30 g of the cryogen circulating in the system at pressures below 170 kPa.
Yang, L. M.; Shu, C.; Wang, Y.; Sun, Y.
2016-08-01
The sphere function-based gas kinetic scheme (GKS), which was presented by Shu and his coworkers [23] for simulation of inviscid compressible flows, is extended to simulate 3D viscous incompressible and compressible flows in this work. Firstly, we use certain discrete points to represent the spherical surface in the phase velocity space. Then, integrals along the spherical surface for conservation forms of moments, which are needed to recover 3D Navier-Stokes equations, are approximated by integral quadrature. The basic requirement is that these conservation forms of moments can be exactly satisfied by weighted summation of distribution functions at discrete points. It was found that the integral quadrature by eight discrete points on the spherical surface, which forms the D3Q8 discrete velocity model, can exactly match the integral. In this way, the conservative variables and numerical fluxes can be computed by weighted summation of distribution functions at eight discrete points. That is, the application of complicated formulations resultant from integrals can be replaced by a simple solution process. Several numerical examples including laminar flat plate boundary layer, 3D lid-driven cavity flow, steady flow through a 90° bending square duct, transonic flow around DPW-W1 wing and supersonic flow around NACA0012 airfoil are chosen to validate the proposed scheme. Numerical results demonstrate that the present scheme can provide reasonable numerical results for 3D viscous flows.
Computer modeling of flow and transport interactions for compressible Navier-Stokes equations
Rahman, Mohamed Mizanur
A unified numerical algorithm to simulate viscous flow with heat transfer over a wide range of Mach number and Reynolds number is developed. The governing equations used to model the numerical simulations are the 2-D compressible viscous Navier-Stokes equations. The numerical procedure is based on MacCormack's explicit 'predictor corrector' time dependent finite difference scheme. For an explicit scheme, a great number of iterations is required to get a converged steady solution because of a small time step. Vectorizing and parallelizing the code greatly alleviates this problem by reducing the total job running time manifold. The numerical algorithm, thus developed, is used to simulate such demanding and interacting flow problems as convection heat transfer in a cavity flow heat transfer enhancement by eddy-promoters, laminar/turbulent shock boundary layer interactions and unsteady shock boundary layer interactions over a compression corner. A detailed analysis of all important flow features that characterize such flows and the mechanisms that are involved, is performed for each individual case. The flow physics are discussed and new insights are provided. Results are compared with experimental data where available and the empirical relations between different flow properties or parameters are either established or verified where possible. Apart from these, some algorithm related questions, such as grid sensitivity, boundary conditions, convergence criteria, effects of artificial viscosity and the numerical stability are investigated.
Suppression mechanism of Kelvin-Helmholtz instability in compressible fluid flows.
Karimi, Mona; Girimaji, Sharath S
2016-04-01
The transformative influence of compressibility on the Kelvin-Helmholtz instability (KHI) at the interface between two fluid streams of different velocities is explicated. When the velocity difference is small (subsonic), shear effects dominate the interface flow dynamics causing monotonic roll-up of vorticity and mixing between the two streams leading to the KHI. We find that at supersonic speed differentials, compressibility forces the dominance of dilatational (acoustic) rather than shear dynamics at the interface. Within this dilatational interface layer, traveling pressure waves cause the velocity perturbations to become oscillatory. We demonstrate that the oscillatory fluid motion reverses vortex roll-up and segregates the two streams leading to KHI suppression. Analysis and illustrations of the compressibility-induced suppression mechanism are presented.
Klimachkov, D. A.; Petrosyan, A. S.
2016-09-01
Shallow water magnetohydrodynamic (MHD) theory describing incompressible flows of plasma is generalized to the case of compressible flows. A system of MHD equations is obtained that describes the flow of a thin layer of compressible rotating plasma in a gravitational field in the shallow water approximation. The system of quasilinear hyperbolic equations obtained admits a complete simple wave analysis and a solution to the initial discontinuity decay problem in the simplest version of nonrotating flows. In the new equations, sound waves are filtered out, and the dependence of density on pressure on large scales is taken into account that describes static compressibility phenomena. In the equations obtained, the mass conservation law is formulated for a variable that nontrivially depends on the shape of the lower boundary, the characteristic vertical scale of the flow, and the scale of heights at which the variation of density becomes significant. A simple wave theory is developed for the system of equations obtained. All self-similar discontinuous solutions and all continuous centered self-similar solutions of the system are obtained. The initial discontinuity decay problem is solved explicitly for compressible MHD equations in the shallow water approximation. It is shown that there exist five different configurations that provide a solution to the initial discontinuity decay problem. For each configuration, conditions are found that are necessary and sufficient for its implementation. Differences between incompressible and compressible cases are analyzed. In spite of the formal similarity between the solutions in the classical case of MHD flows of an incompressible and compressible fluids, the nonlinear dynamics described by the solutions are essentially different due to the difference in the expressions for the squared propagation velocity of weak perturbations. In addition, the solutions obtained describe new physical phenomena related to the dependence of the
Nonaffine deformation under compression and decompression of a flow-stabilized solid
Ortiz, Carlos P.; Riehn, Robert; Daniels, Karen E.
2016-08-01
Understanding the particle-scale transition from elastic deformation to plastic flow is central to making predictions about the bulk material properties and response of disordered materials. To address this issue, we perform experiments on flow-stabilized solids composed of micron-scale spheres within a microfluidic channel, in a regime where particle inertia is negligible. Each solid heap exists within a stress field imposed by the flow, and we track the positions of particles in response to single impulses of fluid-driven compression or decompression. We find that the resulting deformation field is well-decomposed into an affine field, with a constant strain profile throughout the solid, and a non-affine field. The magnitude of this non-affine response decays with the distance from the free surface in the long-time limit, suggesting that the distance from jamming plays a significant role in controlling the length scale of plastic flow. Finally, we observe that compressive pulses create more rearrangements than decompressive pulses, an effect that we quantify using the D\\text{min}2 statistic for non-affine motion. Unexpectedly, the time scale for the compression response is shorter than for decompression at the same strain (but unequal pressure), providing insight into the coupling between deformation and cage-breaking.
On the unsteady inviscid force on cylinders and spheres in subcritical compressible flow.
Parmar, M; Haselbacher, A; Balachandar, S
2008-06-28
The unsteady inviscid force on cylinders and spheres in subcritical compressible flow is investigated. In the limit of incompressible flow, the unsteady inviscid force on a cylinder or sphere is the so-called added-mass force that is proportional to the product of the mass displaced by the body and the instantaneous acceleration. In compressible flow, the finite acoustic propagation speed means that the unsteady inviscid force arising from an instantaneously applied constant acceleration develops gradually and reaches steady values only for non-dimensional times c(infinity)t/R approximately >10, where c(infinity) is the freestream speed of sound and R is the radius of the cylinder or sphere. In this limit, an effective added-mass coefficient may be defined. The main conclusion of our study is that the freestream Mach number has a pronounced effect on both the peak value of the unsteady force and the effective added-mass coefficient. At a freestream Mach number of 0.5, the effective added-mass coefficient is about twice as large as the incompressible value for the sphere. Coupled with an impulsive acceleration, the unsteady inviscid force in compressible flow can be more than four times larger than that predicted from incompressible theory. Furthermore, the effect of the ratio of specific heats on the unsteady force becomes more pronounced as the Mach number increases.
Ensemble Averaged Probability Density Function (APDF) for Compressible Turbulent Reacting Flows
Shih, Tsan-Hsing; Liu, Nan-Suey
2012-01-01
In this paper, we present a concept of the averaged probability density function (APDF) for studying compressible turbulent reacting flows. The APDF is defined as an ensemble average of the fine grained probability density function (FG-PDF) with a mass density weighting. It can be used to exactly deduce the mass density weighted, ensemble averaged turbulent mean variables. The transport equation for APDF can be derived in two ways. One is the traditional way that starts from the transport equation of FG-PDF, in which the compressible Navier- Stokes equations are embedded. The resulting transport equation of APDF is then in a traditional form that contains conditional means of all terms from the right hand side of the Navier-Stokes equations except for the chemical reaction term. These conditional means are new unknown quantities that need to be modeled. Another way of deriving the transport equation of APDF is to start directly from the ensemble averaged Navier-Stokes equations. The resulting transport equation of APDF derived from this approach appears in a closed form without any need for additional modeling. The methodology of ensemble averaging presented in this paper can be extended to other averaging procedures: for example, the Reynolds time averaging for statistically steady flow and the Reynolds spatial averaging for statistically homogeneous flow. It can also be extended to a time or spatial filtering procedure to construct the filtered density function (FDF) for the large eddy simulation (LES) of compressible turbulent reacting flows.
Efficiency of energy separation at compressible gas flow in a planar duct
Makarov, M. S.; Makarova, S. N.
2014-12-01
The method of energy separation in a high-speed flow proposed by A.I. Leontyev is investigated numerically. The adiabatic compressible gas flow (of a helium-xenon mixture) with a low Prandtl number in a planar narrow duct and a flow with heat exchange in a duct partitioned by a heat-conducting wall are analysed. The temperature recovery factor on the adiabatic wall, degree of cooling the low-speed flow part, temperature efficiency, and the adiabatic efficiency in a duct with heat exchange are estimated. The data are obtained for the first time, which make it possible to compare the efficiency of energy separation in a high-speed flow with the efficiency of similar processes in vortex tubes and other setups of gas-dynamic energy separation.
Directory of Open Access Journals (Sweden)
Yusuke Mizuno
2015-01-01
Full Text Available This study is devoted to investigating a flow around a stationary or moving sphere by using direct numerical simulation with immersed boundary method (IBM for the three-dimensional compressible Navier-Stokes equations. A hybrid scheme developed to solve both shocks and turbulent flows is employed to solve the flow around a sphere in the equally spaced Cartesian mesh. Drag coefficients of the spheres are compared with reliable values obtained from highly accurate boundary-fitted coordinate (BFC flow solver to clarify the applicability of the present method. As a result, good agreement was obtained between the present results and those from the BFC flow solver. Moreover, the effectiveness of the hybrid scheme was demonstrated to capture the wake structure of a sphere. Both advantages and disadvantages of the simple IBM were investigated in detail.
An improved ghost-cell immersed boundary method for compressible flow simulations
Chi, Cheng
2016-05-20
This study presents an improved ghost-cell immersed boundary approach to represent a solid body in compressible flow simulations. In contrast to the commonly used approaches, in the present work ghost cells are mirrored through the boundary described using a level-set method to farther image points, incorporating a higher-order extra/interpolation scheme for the ghost cell values. A sensor is introduced to deal with image points near the discontinuities in the flow field. Adaptive mesh refinement (AMR) is used to improve the representation of the geometry efficiently in the Cartesian grid system. The improved ghost-cell method is validated against four test cases: (a) double Mach reflections on a ramp, (b) smooth Prandtl-Meyer expansion flows, (c) supersonic flows in a wind tunnel with a forward-facing step, and (d) supersonic flows over a circular cylinder. It is demonstrated that the improved ghost-cell method can reach the accuracy of second order in L1 norm and higher than first order in L∞ norm. Direct comparisons against the cut-cell method demonstrate that the improved ghost-cell method is almost equally accurate with better efficiency for boundary representation in high-fidelity compressible flow simulations. Copyright © 2016 John Wiley & Sons, Ltd.
Directory of Open Access Journals (Sweden)
Česenek Jan
2016-01-01
Full Text Available In this article we deal with numerical simulation of the non-stationary compressible turbulent flow. Compressible turbulent flow is described by the Reynolds-Averaged Navier-Stokes (RANS equations. This RANS system is equipped with two-equation k-omega turbulence model. These two systems of equations are solved separately. Discretization of the RANS system is carried out by the space-time discontinuous Galerkin method which is based on piecewise polynomial discontinuous approximation of the sought solution in space and in time. Discretization of the two-equation k-omega turbulence model is carried out by the implicit finite volume method, which is based on piecewise constant approximation of the sought solution. We present some numerical experiments to demonstrate the applicability of the method using own-developed code.
Well-posed continuum equations for granular flow with compressibility and μ(I)-rheology
Schaeffer, D. G.; Shearer, M.; Gray, J. M. N. T.
2017-01-01
Continuum modelling of granular flow has been plagued with the issue of ill-posed dynamic equations for a long time. Equations for incompressible, two-dimensional flow based on the Coulomb friction law are ill-posed regardless of the deformation, whereas the rate-dependent μ(I)-rheology is ill-posed when the non-dimensional inertial number I is too high or too low. Here, incorporating ideas from critical-state soil mechanics, we derive conditions for well-posedness of partial differential equations that combine compressibility with I-dependent rheology. When the I-dependence comes from a specific friction coefficient μ(I), our results show that, with compressibility, the equations are well-posed for all deformation rates provided that μ(I) satisfies certain minimal, physically natural, inequalities. PMID:28588402
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
Adaptive Delaunay triangulation is combined with the cell-centered upwinding algorithm to analyze inviscid high-speed compressible flow problems. The multidimensional dissipation scheme was developed and included in the upwinding algorithm for unstructured triangular meshes to improve the computed shock wave resolution. The solution accuracy is further improved by coupling an error estimation procedure to a remeshing algorithm that generates small elements in regions with large change of solution gradients, and at the same time, larger elements in other regions. The proposed scheme is further extended to achieve higher-order spatial and temporal solution accuracy. Efficiency of the combined procedure is evaluated by analyzing supersonic shocks and shock propagation behaviors for both the steady and unsteady high-speed compressible flows.
Well-posed continuum equations for granular flow with compressibility and $\\mu(I)$-rheology
Barker, T; Shearer, M; Gray, J M N T
2016-01-01
Continuum modelling of granular flow has been plagued with the issue of ill-posed equations for a long time. Equations for incompressible, two-dimensional flow based on the Coulomb friction law are ill-posed regardless of the deformation, whereas the rate-dependent $\\mu(I)$-rheology is ill-posed when the non-dimensional strain-rate $I$ is too high or too low. Here, incorporating ideas from Critical-State Soil Mechanics, we derive conditions for well-posedness of PDEs that combine compressibility with $I$-dependent rheology. When the $I$-dependence comes from a specific friction coefficient $\\mu(I)$, our results show that, with compressibility, the equations are well-posed for all deformation rates provided that $\\mu(I)$ satisfies certain minimal, physically natural, inequalities.
Bie, Qunyi; Cui, Haibo; Wang, Qiru; Yao, Zheng-An
2017-10-01
The Cauchy problem for the compressible flow of nematic liquid crystals in the framework of critical spaces is considered. We first establish the existence and uniqueness of global solutions provided that the initial data are close to some equilibrium states. This result improves the work by Hu and Wu (SIAM J Math Anal 45(5):2678-2699, 2013) through relaxing the regularity requirement of the initial data in terms of the director field. Based on the global existence, we then consider the incompressible limit problem for ill prepared initial data. We prove that as the Mach number tends to zero, the global solution to the compressible flow of liquid crystals converges to the solution to the corresponding incompressible model in some function spaces. Moreover, the accurate converge rates are obtained.
Mohammadyari, Parvin; Faghihi, Reza; Mosleh-Shirazi, Mohammad Amin; Lotfi, Mehrzad; Rahim Hematiyan, Mohammad; Koontz, Craig; Meigooni, Ali S.
2015-12-01
Compression is a technique to immobilize the target or improve the dose distribution within the treatment volume during different irradiation techniques such as AccuBoost® brachytherapy. However, there is no systematic method for determination of dose distribution for uncompressed tissue after irradiation under compression. In this study, the mechanical behavior of breast tissue between compressed and uncompressed states was investigated. With that, a novel method was developed to determine the dose distribution in uncompressed tissue after irradiation of compressed breast tissue. Dosimetry was performed using two different methods, namely, Monte Carlo simulations using the MCNP5 code and measurements using thermoluminescent dosimeters (TLD). The displacement of the breast elements was simulated using a finite element model and calculated using ABAQUS software. From these results, the 3D dose distribution in uncompressed tissue was determined. The geometry of the model was constructed from magnetic resonance images of six different women volunteers. The mechanical properties were modeled by using the Mooney-Rivlin hyperelastic material model. Experimental dosimetry was performed by placing the TLD chips into the polyvinyl alcohol breast equivalent phantom. The results determined that the nodal displacements, due to the gravitational force and the 60 Newton compression forces (with 43% contraction in the loading direction and 37% expansion in the orthogonal direction) were determined. Finally, a comparison of the experimental data and the simulated data showed agreement within 11.5% ± 5.9%.
A parallel and matrix free framework for global stability analysis of compressible flows
Henze, O; Sesterhenn, J
2015-01-01
An numerical iterative framework for global modal stability analysis of compressible flows using a parallel environment is presented. The framework uses a matrix-free implementation to allow computations of large scale problems. Various methods are tested with regard to convergence acceleration of the framework. The methods consist of a spectral Cayley transformation used to select desired Eigenvalues from a large spectrum, an improved linear solver and a parallel block-Jacobi preconditioning scheme.
Integrated LTCC Pressure/Flow/Temperature Multisensor for Compressed Air Diagnostics†
Nicolas Craquelin; Aurélie Barras; Peter Ryser; Grégoire Boutinard-Rouelle; Yannick Fournier; Thomas Maeder
2010-01-01
We present a multisensor designed for industrial compressed air diagnostics and combining the measurement of pressure, flow, and temperature, integrated with the corresponding signal conditioning electronics in a single low-temperature co-fired ceramic (LTCC) package. The developed sensor may be soldered onto an integrated electro-fluidic platform by using standard surface mount device (SMD) technology, e.g., as a standard electronic component would be on a printed circuit board, obviating th...
UNIFIED COMPUTATION OF FLOW WITH COMPRESSIBLE AND INCOMPRESSIBLE FLUID BASED ON ROE'S SCHEME
Institute of Scientific and Technical Information of China (English)
HUANG Dian-gui
2006-01-01
A unified numerical scheme for the solutions of the compressible and incompressible Navier-Stokes equations is investigated based on a time-derivative preconditioning algorithm. The primitive variables are pressure, velocities and temperature. The time integration scheme is used in conjunction with a finite volume discretization. The preconditioning is coupled with a high order implicit upwind scheme based on the definition of a Roe's type matrix. Computational capabilities are demonstrated through computations of high Mach number, middle Mach number, very low Mach number, and incompressible flow. It has also been demonstrated that the discontinuous surface in flow field can be captured for the implementation Roe's scheme.
Barnett, Mark
This investigation is concerned with calculating strong viscous-inviscid interactions in two-dimensional laminar supersonic flows with and without separation. The equations solved are the so-called parabolized Navier-Stokes equations. The streamwise pressure gradient term is written as a combination of a forward and a backward difference to provide a path for upstream propogation of information. Global iteration is employed to repeatedly update the solution from an initial guess until convergence is achieved. Interacting boundary layer theory is discussed in order to provide some essential background information for the development of the present calculation technique. The numerical scheme used is an alternating direction explicit (ADE) procedure which is adapted from the Saul'yev method. This technique is chosen as an alternative to the more difficult to program multigrid strategy used by other investigators and the slower converging Gauss-Seidel method. Separated flows are computed using the ADE method. Only small or moderate separation bubbles are considered. This restriction permits simple approximations to the convective terms in reversed flow regions without introducing severe error since the reversed flow velocities are small. Results are presented for a number of geometries including compression ramps and humps on flat plates with separation. The present results are compared with those obtained by other investigators using the full Navier-Stokes equations and interacting boundary layer theory. Comparisons were found to be qualitatively good. The quantitative comparisons varied, however mesh refinement studies indicated that the parabolized Navier-Stokes solutions tended towards second-order accurate full Navier-Stokes solutions as well as interacting boundary layer solutions for which mesh refinement studies were also executed.
Dixon, G. V.; Barringer, S. R.; Gray, C. E.; Leatherman, A. D.
1975-01-01
Computer programs and resulting tabulations are presented of pipeline length-to-diameter ratios as a function of Mach number and pressure ratios for compressible flow. The tabulations are applicable to air, nitrogen, oxygen, and hydrogen for compressible isothermal flow with friction and compressible adiabatic flow with friction. Also included are equations for the determination of weight flow. The tabulations presented cover a wider range of Mach numbers for choked, adiabatic flow than available from commonly used engineering literature. Additional information presented, but which is not available from this literature, is unchoked, adiabatic flow over a wide range of Mach numbers, and choked and unchoked, isothermal flow for a wide range of Mach numbers.
Structure and flow calculation of cake layer on microfiltration membranes
Institute of Scientific and Technical Information of China (English)
Yadong Yu; Zhen Yang; Yuanyuan Duan
2017-01-01
Submerged membrane bioreactors (SMBR) are widely used in wastewater treatment.The permeability of a membrane declines rapidly because of the formation of a cake layer on the membrane surface.In this paper,a multiple staining protocol was conducted to probe the four major foulants in the cake layer formed on a filtration membrane.Fluorescent images of the foulants were obtained using a confocal laser scanning microscope (CLSM).The three dimensional structure of the cake layer was reconstructed,and the internal flow was calculated using computational fluid dynamics (CFD).Simulation results agreed well with the experimental data on the permeability of the cake layer during filtration and showed better accuracy than the calculation by Kozeny-Carman method.β-D-Glucopyranose polysaccharides and proteins are the two main foulants with relatively large volume fractions,while α-D-glucopyranose polysaccharides and nucleic acids have relatively large specific surface areas.The fast growth of β-D-glucopyranose polysaccharides in the volume fraction is mainly responsible for the increase in cake volume fraction and the decrease in permeability.The specific area,or the aggregation/dispersion of foulants,is less important to its permeability compared to its volume fraction.
Propagation of Shock on NREL Phase VI Wind Turbine Airfoil under Compressible Flow
Directory of Open Access Journals (Sweden)
Mohammad A. Hossain
2013-01-01
Full Text Available The work is focused on numeric analysis of compressible flow around National Renewable Energy Laboratory (NREL phase VI wind turbine blade airfoil S809. Although wind turbine airfoils are low Reynolds number airfoils, a reasonable investigation of compressible flow under extreme condition might be helpful. A subsonic flow (mach no. M=0.8 has been considered for this analysis and the impacts of this flow under seven different angles of attack have been determined. The results show that shock takes place just after the mid span at the top surface and just before the mid span at the bottom surface at zero angle of attack. Slowly the shock waves translate their positions as angle of attack increases. A relative translation of the shock waves in upper and lower face of the airfoil are presented. Variation of Turbulent viscosity ratio and surface Y+ have also been determined. A k-ω SST turbulent model is considered and the commercial CFD code ANSYS FLUENT is used to find the pressure coefficient (Cp as well as the lift (CL and drag coefficients (CD. A graphical comparison of shock propagation has been shown with different angle of attack. Flow separation and stream function are also determined.
Sin, Irina; Lagneau, Vincent; Corvisier, Jérôme
2017-02-01
This work aims to incorporate compressible multiphase flow into the conventional reactive transport framework using an operator splitting approach. This new approach would allow us to retain the general paradigm of the flow module independent of the geochemical processes and to model complex multiphase chemical systems, conserving the versatile structure of conventional reactive transport. The phase flow formulation is employed to minimize the number of mass conservation nonlinear equations arising from the flow module. Applying appropriate equations of state facilitated precise descriptions of the compressible multicomponent phases, their thermodynamic properties and relevant fluxes. The proposed flow coupling method was implemented in the reactive transport software HYTEC. The entire framework preserves its flexibility for further numerical developments. The verification of the coupling was achieved by modeling a problem with a self-similar solution. The simulation of a 2D CO2-injection problem demonstrates the pertinent physical results and computational efficiency of this method. The coupling method was employed for modeling injection of acid gas mixture in carbonated reservoir.
Flow stress and tribology size effects in scaled down cylinder compression
Institute of Scientific and Technical Information of China (English)
GUO Bin; GONG Feng; WANG Chun-ju; SHAN De-bin
2009-01-01
Microforming is an effective method to manufacture small metal parts. However, macro forming can not be transferred to microforming directly because of size effects. Flow stress and tribology size effects were studied. Scaled down copper T2 cylinder compression was carried out with the lubrication of castor oil and without lubrication. The results show that the flow stress decreases with decreasing the initial specimen diameter in both lubrication conditions, and the flow stress decreases by 30 MPa with the initial specimen diameter decreasing from 8 mm to 1 mm. The friction factor increases obviously with decreasing the initial specimen diameter in the case of lubricating with castor oil, and the friction factor increases by 0.11 with the initial specimen diameter decreasing from 8mm to 1mm. However, the tribology size effect is not found in the case without lubrication. The reasons of the flow stress and tribology size effects were also discussed.
Amplification, attenuation, and dispersion of sound in inhomogeneous flows. [of compressible gas
Kentzer, C. P.
1975-01-01
First order effects of gradients in nonuniform potential flows of a compressible gas are included in a dispersion relation for sound waves. Three nondimensional numbers, the ratio of the change in the kinetic energy in one wavelength to the thermal energy of the gas, the ratio of the change in the total energy in one wavelength to the thermal energy, and the ratio of the dilatation frequency (the rate of expansion per unit volume) to the acoustic frequency, play the dominant role permitting the separation of the effects of flow gradients into isotropic and anisotropic effects. Dispersion and attenuation (or amplification) of sound are proportional to the wavelength for small wavelength and depend on the direction of wave propagation relative to flow gradients. Modification of ray acoustics for the effects of flow gradients is suggested and conditions for amplification and attenuation of sound are discussed.
Near Continuum Velocity and Temperature Coupled Compressible Boundary Layer Flow over a Flat Plate
He, Xin; Cai, Chunpei
2017-04-01
The problem of a compressible gas flows over a flat plate with the velocity-slip and temperature-jump boundary conditions are being studied. The standard single- shooting method is applied to obtain the exact solutions for velocity and temperature profiles when the momentum and energy equations are weakly coupled. A double-shooting method is applied if these two equations are closely coupled. If the temperature affects the velocity directly, more significant velocity slip happens at locations closer to the plate's leading edge, and inflections on the velocity profiles appear, indicating flows may become unstable. As a consequence, the temperature-jump and velocity-slip boundary conditions may trigger earlier flow transitions from a laminar to a turbulent flow state.
A finite-volume HLLC-based scheme for compressible interfacial flows with surface tension
Energy Technology Data Exchange (ETDEWEB)
Garrick, Daniel P. [Department of Aerospace Engineering, Iowa State University, Ames, IA (United States); Owkes, Mark [Department of Mechanical and Industrial Engineering, Montana State University, Bozeman, MT (United States); Regele, Jonathan D., E-mail: jregele@iastate.edu [Department of Aerospace Engineering, Iowa State University, Ames, IA (United States)
2017-06-15
Shock waves are often used in experiments to create a shear flow across liquid droplets to study secondary atomization. Similar behavior occurs inside of supersonic combustors (scramjets) under startup conditions, but it is challenging to study these conditions experimentally. In order to investigate this phenomenon further, a numerical approach is developed to simulate compressible multiphase flows under the effects of surface tension forces. The flow field is solved via the compressible multicomponent Euler equations (i.e., the five equation model) discretized with the finite volume method on a uniform Cartesian grid. The solver utilizes a total variation diminishing (TVD) third-order Runge–Kutta method for time-marching and second order TVD spatial reconstruction. Surface tension is incorporated using the Continuum Surface Force (CSF) model. Fluxes are upwinded with a modified Harten–Lax–van Leer Contact (HLLC) approximate Riemann solver. An interface compression scheme is employed to counter numerical diffusion of the interface. The present work includes modifications to both the HLLC solver and the interface compression scheme to account for capillary force terms and the associated pressure jump across the gas–liquid interface. A simple method for numerically computing the interface curvature is developed and an acoustic scaling of the surface tension coefficient is proposed for the non-dimensionalization of the model. The model captures the surface tension induced pressure jump exactly if the exact curvature is known and is further verified with an oscillating elliptical droplet and Mach 1.47 and 3 shock-droplet interaction problems. The general characteristics of secondary atomization at a range of Weber numbers are also captured in a series of simulations.
A finite-volume HLLC-based scheme for compressible interfacial flows with surface tension
Garrick, Daniel P.; Owkes, Mark; Regele, Jonathan D.
2017-06-01
Shock waves are often used in experiments to create a shear flow across liquid droplets to study secondary atomization. Similar behavior occurs inside of supersonic combustors (scramjets) under startup conditions, but it is challenging to study these conditions experimentally. In order to investigate this phenomenon further, a numerical approach is developed to simulate compressible multiphase flows under the effects of surface tension forces. The flow field is solved via the compressible multicomponent Euler equations (i.e., the five equation model) discretized with the finite volume method on a uniform Cartesian grid. The solver utilizes a total variation diminishing (TVD) third-order Runge-Kutta method for time-marching and second order TVD spatial reconstruction. Surface tension is incorporated using the Continuum Surface Force (CSF) model. Fluxes are upwinded with a modified Harten-Lax-van Leer Contact (HLLC) approximate Riemann solver. An interface compression scheme is employed to counter numerical diffusion of the interface. The present work includes modifications to both the HLLC solver and the interface compression scheme to account for capillary force terms and the associated pressure jump across the gas-liquid interface. A simple method for numerically computing the interface curvature is developed and an acoustic scaling of the surface tension coefficient is proposed for the non-dimensionalization of the model. The model captures the surface tension induced pressure jump exactly if the exact curvature is known and is further verified with an oscillating elliptical droplet and Mach 1.47 and 3 shock-droplet interaction problems. The general characteristics of secondary atomization at a range of Weber numbers are also captured in a series of simulations.
Energy Technology Data Exchange (ETDEWEB)
Rusanov, A.V.; Yershov, S.V. [Institute of Mechanical Engineering Problems of National Academy of Sciences of Ukraine Kharkov (Ukraine)
1997-12-31
The numerical method is suggested for the calculation of the 3D periodically unsteady viscous cascade flow evoked by the aerodynamics interaction of blade rows. Such flow is described by the thin-layer Reynolds-averaged unsteady Navier-Stokes equations. The turbulent effects are simulated with the modified Baldwin-Lomax turbulence model. The problem statement allows to consider an unsteady flow through either a single turbo-machine stage or a multi stage turbomachine. The sliding mesh techniques and the time-space non-oscillatory square interpolation are used in axial spacings to calculate the flow in a computational domain that contains the reciprocally moving elements. The gasdynamical equations are integrated numerically with the implicit quasi-monotonous Godunov`s type ENO scheme of the second or third order of accuracy. The suggested numerical method is incorporated in the FlowER code developed by authors for calculations of the 3D viscous compressible flows through multi stage turbomachines. The numerical results are presented for unsteady turbine stage throughflows. The method suggested is shown to simulate qualitatively properly the main unsteady cascade effects in particular the periodically blade loadings, the propagation of stator wakes through rotor blade passage and the unsteady temperature flowfields for stages with cooled stator blades. (author) 21 refs.
Three-dimensional supersonic flow around double compression ramp with finite span
Lee, H. S.; Lee, J. H.; Park, G.; Park, S. H.; Byun, Y. H.
2017-01-01
Three-dimensional flows of Mach number 3 around a double-compression ramp with finite span have been investigated numerically. Shadowgraph visualisation images obtained in a supersonic wind tunnel are used for comparison. A three-dimensional Reynolds-averaged Navier-Stokes solver was used to obtain steady numerical solutions. Two-dimensional numerical results are also compared. Four different cases were studied: two different second ramp angles of 30° and 45° in configurations with and without sidewalls, respectively. Results showed that there is a leakage of mass and momentum fluxes heading outwards in the spanwise direction for three-dimensional cases without sidewalls. The leakage changed the flow characteristics of the shock-induced boundary layer and resulted in the discrepancy between the experimental data and two-dimensional numerical results. It is found that suppressing the flow leakage by attaching the sidewalls enhances the two-dimensionality of the experimental data for the double-compression ramp flow.
A Simple and Efficient Diffuse Interface Method for Compressible Two-Phase Flows
Energy Technology Data Exchange (ETDEWEB)
Ray A. Berry; Richard Saurel; Fabien Petitpas
2009-05-01
In nuclear reactor safety and optimization there are key issues that rely on in-depth understanding of basic two-phase flow phenomena with heat and mass transfer. For many reasons, to be discussed, there is growing interest in the application of two-phase flow models to provide diffuse, but nevertheless resolved, simulation of interfaces between two immiscible compressible fluids – diffuse interface method (DIM). Because of its ability to dynamically create interfaces and to solve interfaces separating pure media and mixtures for DNS-like (Direct Numerical Simulation) simulations of interfacial flows, we examine the construction of a simple, robust, fast, and accurate numerical formulation for the 5-equation Kapila et al. [1] reduced two-phase model. Though apparently simple, the Kapila et al. model contains a volume fraction differential transport equation containing a nonlinear, non-conservative term which poses serious computational challenges. To circumvent the difficulties encountered with the single velocity and single pressure Kapila et al. [1] multiphase flow model, a 6-equation relaxation hyperbolic model is built to solve interface problems with compressible fluids. In this approach, pressure non-equilibrium is first restored, followed by a relaxation to an asymptotic solution which is convergent to the solutions of the Kapila et al. reduced model. The apparent complexity introduced with this extended hyperbolic model actually leads to considerable simplifications regarding numerical resolution, and the various ingredients used by this method are general enough to consider future extensions to problems involving complex physics.
A pseudo-compressible variational multiscale solver for turbulent incompressible flows
Yang, Liang; Badia, Santiago; Codina, Ramon
2016-12-01
In this work, we design an explicit time-stepping solver for the simulation of the incompressible turbulent flow through the combination of VMS methods and artificial compressibility. We evaluate the effect of the artificial compressibility on the accuracy of the explicit formulation for under-resolved LES simulations. A set of benchmarks have been solved, e.g., the 3D Taylor-Green vortex problem in turbulent regimes. The resulting method is proven to be an effective alternative to implicit methods in some application ranges (in terms of problem size and computational resources), providing comparable results with very low memory requirements. As an example, with the explicit approach, we are able to solve accurately the Taylor-Green vortex benchmark in a fine mesh with 512^3 cells on a 12 cores 64 GB ram machine.
Kadatskiy, M. A.; Khishchenko, K. V.
2016-11-01
Quantum-statistical calculations of shock compressibility of iron are performed. Electronic part of thermodynamic functions is calculated in the framework of three quantum-statistical approaches: the Thomas-Fermi, the Thomas-Fermi with quantum and exchange corrections and the Hartree-Fock-Slater models. The influence of ionic part of thermodynamic functions is taken into account separately with using three models: the ideal gas, the one-component plasma and the charged hard spheres models. The results of calculations are presented in the pressure range from 1 to 107 GPa for samples with initially densities 7.85, 4.31 and 2.27 g/cm3. Calculated Hugoniots are compared with available experimental data.
Observation of dual-mode, Kelvin-Helmholtz instability vortex merger in a compressible flow
Wan, W. C.; Malamud, G.; Shimony, A.; Di Stefano, C. A.; Trantham, M. R.; Klein, S. R.; Shvarts, D.; Drake, R. P.; Kuranz, C. C.
2017-05-01
We report the first observations of Kelvin-Helmholtz vortices evolving from well-characterized, dual-mode initial conditions in a steady, supersonic flow. The results provide the first measurements of the instability's vortex merger rate and supplement data on the inhibition of the instability's growth rate in a compressible flow. These experimental data were obtained by sustaining a shockwave over a foam-plastic interface with a precision-machined seed perturbation. This technique produced a strong shear layer between two plasmas at high-energy-density conditions. The system was diagnosed using x-ray radiography and was well-reproduced using hydrodynamic simulations. Experimental measurements imply that we observed the anticipated vortex merger rate and growth inhibition for supersonic shear flow.
Flow Stress Behavior and Processing Map of Al-Cu-Mg-Ag Alloy during Hot Compression
Institute of Scientific and Technical Information of China (English)
YANG Sheng; YI Danqing; ZHANG Hong; YAO Sujuan
2008-01-01
The hot deformation behavior of Al-Cu-Mg-Ag was studied by isothermal hot compression tests in the temperature range of 573-773 K and strain rate range of 0.001-1 s-1 on a Gleeble 1500 D thermal mechanical simulator. The results show the flow stress of Al-Cu-Mg-Ag alloy increases with strain rate and decreases after a peak value, indicating dynamic recovery and recrystallization. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate and temperature, the flow stress equation is estimated to illustrate the relation of strain rate and stress and temperature during high temperature deformation process. The processing maps exhibit two domains as optimum fields for hot deformation at different strains, including the high strain rate domain in 623-773 K and the low strain rate domain in 573-673 K.
Modesti, Davide
2016-01-01
We develop a semi-implicit algorithm for time-accurate simulation of the compressible Navier-Stokes equations, with special reference to wall-bounded flows. The method is based on linearization of the partial convective fluxes associated with acoustic waves, in such a way to suppress, or at least mitigate the acoustic time step limitation. Together with replacement of the total energy equation with the entropy transport equation, this approach avoids the inversion of block-banded matrices involved in classical methods, which is replaced by less demanding inversion of standard banded matrices. The method is extended to deal with implicit integration of viscous terms and to multiple space dimensions through approximate factorization, and used as a building block of third-order Runge-Kutta time stepping scheme. Numerical experiments are carried out for isotropic turbulence, plane channel flow, and flow in a square duct. All available data support higher computational efficiency than existing methods, and saving ...
Large eddy simulation of compressible turbulent channel flow with spanwise wall oscillation
Institute of Scientific and Technical Information of China (English)
FANG Jian; LU LiPeng; SHAO Liang
2009-01-01
The influences of the modification of turbulent coherent structures on temperature field and heat transfer in turbulent channel flow are studied using large eddy simulation (LES) of compressible tur-bulent channel flows with spanwise wall oscillation (SWO). The reliability of the LES on such problems is proved by the comparisons of the drag reduction data with those of other researches. The high con-sistency of coherent velocity structures and temperature structures is found based on the analyses of the turbulent flow field. When the coherent velocity structures are suppressed, the transportations of momentum and heat are reduced simultaneously, demonstrating the same trend. This shows that the turbulent coherent structures have the same effects on the transportations of momentum and heat. The averaged wall heat flux can be reduced with appropriate oscillating parameters.
A multiscale method for compressible liquid-vapor flow with surface tension*
Directory of Open Access Journals (Sweden)
Jaegle Felix
2013-01-01
Full Text Available Discontinuous Galerkin methods have become a powerful tool for approximating the solution of compressible flow problems. Their direct use for two-phase flow problems with phase transformation is not straightforward because this type of flows requires a detailed tracking of the phase front. We consider the fronts in this contribution as sharp interfaces and propose a novel multiscale approach. It combines an efficient high-order Discontinuous Galerkin solver for the computation in the bulk phases on the macro-scale with the use of a generalized Riemann solver on the micro-scale. The Riemann solver takes into account the effects of moderate surface tension via the curvature of the sharp interface as well as phase transformation. First numerical experiments in three space dimensions underline the overall performance of the method.
Modeling the Plasma Flow in the Inner Heliosheath with a Spatially Varying Compression Ratio
Nicolaou, G.; Livadiotis, G.
2017-03-01
We examine a semi-analytical non-magnetic model of the termination shock location previously developed by Exarhos & Moussas. In their study, the plasma flow beyond the shock is considered incompressible and irrotational, thus the flow potential is analytically derived from the Laplace equation. Here we examine the characteristics of the downstream flow in the heliosheath in order to resolve several inconsistencies existing in the Exarhos & Moussas model. In particular, the model is modified in order to be consistent with the Rankine-Hugoniot jump conditions and the geometry of the termination shock. It is shown that a shock compression ratio varying along the latitude can lead to physically correct results. We describe the new model and present several simplified examples for a nearly spherical, strong termination shock. Under those simplifications, the upstream plasma is nearly adiabatic for large (˜100 AU) heliosheath thickness.
Large eddy simulation of compressible turbulent channel flow with spanwise wall oscillation
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The influences of the modification of turbulent coherent structures on temperature field and heat transfer in turbulent channel flow are studied using large eddy simulation(LES) of compressible turbulent channel flows with spanwise wall oscillation(SWO).The reliability of the LES on such problems is proved by the comparisons of the drag reduction data with those of other researches.The high consistency of coherent velocity structures and temperature structures is found based on the analyses of the turbulent flow field.When the coherent velocity structures are suppressed,the transportations of momentum and heat are reduced simultaneously,demonstrating the same trend.This shows that the turbulent coherent structures have the same effects on the transportations of momentum and heat.The averaged wall heat flux can be reduced with appropriate oscillating parameters.
Energy Technology Data Exchange (ETDEWEB)
Zhou, Fei [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Nielson, Weston [Univ. of California, Los Angeles, CA (United States); Xia, Yi [Univ. of California, Los Angeles, CA (United States); Ozoliņš, Vidvuds [Univ. of California, Los Angeles, CA (United States)
2014-10-01
First-principles prediction of lattice thermal conductivity κ_{L} of strongly anharmonic crystals is a long-standing challenge in solid-state physics. Making use of recent advances in information science, we propose a systematic and rigorous approach to this problem, compressive sensing lattice dynamics. Compressive sensing is used to select the physically important terms in the lattice dynamics model and determine their values in one shot. Nonintuitively, high accuracy is achieved when the model is trained on first-principles forces in quasirandom atomic configurations. The method is demonstrated for Si, NaCl, and Cu_{12}Sb_{4}S_{13}, an earth-abundant thermoelectric with strong phonon-phonon interactions that limit the room-temperature κ_{L} to values near the amorphous limit.
Zhou, Fei; Nielson, Weston; Xia, Yi; Ozoliņš, Vidvuds
2014-10-31
First-principles prediction of lattice thermal conductivity κ(L) of strongly anharmonic crystals is a long-standing challenge in solid-state physics. Making use of recent advances in information science, we propose a systematic and rigorous approach to this problem, compressive sensing lattice dynamics. Compressive sensing is used to select the physically important terms in the lattice dynamics model and determine their values in one shot. Nonintuitively, high accuracy is achieved when the model is trained on first-principles forces in quasirandom atomic configurations. The method is demonstrated for Si, NaCl, and Cu(12)Sb(4)S(13), an earth-abundant thermoelectric with strong phonon-phonon interactions that limit the room-temperature κ(L) to values near the amorphous limit.
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.
Stickel, J J; Fotopoulos, A
2001-01-01
Pressure drop across chromatography beds employing soft or semirigid media can be a significant problem in the operation of large-scale preparative chromatography columns. The shape or aspect ratio (length/diameter) of a packed bed has a significant effect on column pressure drop due to wall effects, which can result in unexpectedly high pressures in manufacturing. Two types of agarose-based media were packed in chromatography columns at various column aspect ratios, during which pressure drop, bed height, and flow rate were carefully monitored. Compression of the packed beds with increasing flow velocities was observed. An empirical model was developed to correlate pressure drop with the aspect ratio of the packed beds and the superficial velocity. Modeling employed the Blake-Kozeny equation in which empirical relationships were used to predict bed porosity as a function of aspect ratio and flow velocity. Model predictions were in good agreement with observed pressure drops of industrial scale chromatography columns. A protocol was developed to predict compression in industrial chromatography applications by a few laboratory experiments. The protocol is shown to be useful in the development of chromatographic methods and sizing of preparative columns.
Keshet, Uri
2016-01-01
Compressible flows around blunt objects have diverse applications, but current analytic treatments are inaccurate and limited to narrow parameter regimes. We show that the gas-dynamic flow in front of an axisymmetric blunt body is accurately derived analytically using a low order expansion of the perpendicular gradients in terms of the parallel velocity. This reproduces both subsonic and supersonic flows measured and simulated for a sphere, including the transonic regime and the bow shock properties. Some astrophysical implications are outlined, in particular for planets in the solar wind and for clumps and bubbles in the intergalactic medium. The bow shock standoff distance normalized by the obstacle curvature is $\\sim 2/(3g)$ in the strong shock limit, where $g$ is the compression ratio. For a subsonic Mach number $M$ approaching unity, the thickness $\\delta$ of an initially weak, draped magnetic layer is a few times larger than in the incompressible limit, with amplification $\\sim ({1+1.3M^{2.6}})/({3\\delt...
Schneider, T.; Botta, N.; Geratz, K. J.; Klein, R.
1999-11-01
When attempting to compute unsteady, variable density flows at very small or zero Mach number using a standard finite volume compressible flow solver one faces at least the following difficulties: (i) Spatial pressure variations vanish as the Mach number M→0, but they do affect the velocity field at leading order; (ii) the resulting spatial homogeneity of the leading order pressure implies an elliptic divergence constraint for the energy flux; (iii) violations of this constraint crucially affect the transport of mass, preventing a code to properly advect even a constant density distribution. We overcome these difficulties through a new algorithm for constructing numerical fluxes in the context of multi-dimensional finite volume methods in conservation form. The construction of numerical fluxes involves: (1) An explicit upwind step yielding predictions for the nonlinear convective flux components. (2) A first correction step that introduces pressure gradients which guarantee compliance of the convective fluxes with a divergence constraint. This step requires the solution of a first Poisson-type equation. (3) A second projection step which provides the yet unknown (non-convective) pressure contribution to the total flux of momentum. This second projection requires the solution of another Poisson-type equation and yields the cell centered velocity field at the new time. This velocity field exactly satisfies a divergence constraint consistent with the asymptotic limit. Step (1) can be done by any standard finite volume compressible flow solver. The input to steps (2) and (3) involves solely the fluxes from step (1) and is independent of how these were obtained. Thus, our approach allows any such solver to be extended to compute variable density incompressible flows.
Computation of compressible flows with high density ratio and pressure ratio
Institute of Scientific and Technical Information of China (English)
CHEN Rong-san
2008-01-01
The WENO method, RKDG method, RKDG method with original ghost fluid method, and RKDG method with modified ghost fluid method are applied to single-medium and two-medium air-air, air-liquid compressible flows with high density and pressure ratios. We also provide a numerical comparison and analysis for the above methods. Numerical results show that, compared with the other methods, the RKDG method with modified ghost fluid method can obtain high resolution results and the correct position of the shock, and the computed solutions are converged to the physical solutions as the mesh is refined.
Integrated LTCC Pressure/Flow/Temperature Multisensor for Compressed Air Diagnostics†
Fournier, Yannick; Maeder, Thomas; Boutinard-Rouelle, Grégoire; Barras, Aurélie; Craquelin, Nicolas; Ryser, Peter
2010-01-01
We present a multisensor designed for industrial compressed air diagnostics and combining the measurement of pressure, flow, and temperature, integrated with the corresponding signal conditioning electronics in a single low-temperature co-fired ceramic (LTCC) package. The developed sensor may be soldered onto an integrated electro-fluidic platform by using standard surface mount device (SMD) technology, e.g., as a standard electronic component would be on a printed circuit board, obviating the need for both wires and tubes and thus paving the road towards low-cost integrated electro-fluidic systems. Several performance aspects of this device are presented and discussed, together with electronics design issues. PMID:22163518
Integrated LTCC pressure/flow/temperature multisensor for compressed air diagnostics.
Fournier, Yannick; Maeder, Thomas; Boutinard-Rouelle, Grégoire; Barras, Aurélie; Craquelin, Nicolas; Ryser, Peter
2010-01-01
We present a multisensor designed for industrial compressed air diagnostics and combining the measurement of pressure, flow, and temperature, integrated with the corresponding signal conditioning electronics in a single low-temperature co-fired ceramic (LTCC) package. The developed sensor may be soldered onto an integrated electro-fluidic platform by using standard surface mount device (SMD) technology, e.g., as a standard electronic component would be on a printed circuit board, obviating the need for both wires and tubes and thus paving the road towards low-cost integrated electro-fluidic systems. Several performance aspects of this device are presented and discussed, together with electronics design issues.
Federrath, Christoph; Schober, Jennifer; Banerjee, Robi; Klessen, Ralf S; Schleicher, Dominik R G; 10.1103/PhysRevLett.107.114504
2011-01-01
We study the growth rate and saturation level of the turbulent dynamo in magnetohydrodynamical simulations of turbulence, driven with solenoidal (divergence-free) or compressive (curl-free) forcing. For models with Mach numbers ranging from 0.02 to 20, we find significantly different magnetic field geometries, amplification rates, and saturation levels, decreasing strongly at the transition from subsonic to supersonic flows, due to the development of shocks. Both extreme types of turbulent forcing drive the dynamo, but solenoidal forcing is more efficient, because it produces more vorticity.
A model and numerical method for compressible flows with capillary effects
Schmidmayer, Kevin; Petitpas, Fabien; Daniel, Eric; Favrie, Nicolas; Gavrilyuk, Sergey
2017-04-01
A new model for interface problems with capillary effects in compressible fluids is presented together with a specific numerical method to treat capillary flows and pressure waves propagation. This new multiphase model is in agreement with physical principles of conservation and respects the second law of thermodynamics. A new numerical method is also proposed where the global system of equations is split into several submodels. Each submodel is hyperbolic or weakly hyperbolic and can be solved with an adequate numerical method. This method is tested and validated thanks to comparisons with analytical solutions (Laplace law) and with experimental results on droplet breakup induced by a shock wave.
A Functional Equation Governing the Motion of a Compressible Fluid Flow
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The fundamental problem of the statistical dynamics of a turbulent flow, formulated in terms of characteristic functionals, has already been pointed out in the work of E. Hopf. In his work he deduced a functional equation governing the evolution of the characteristic functional of a turbulent velocity field in an incompressible field. In this paper we present a derivation of a dynamical equation governing the evolution of the characteristic functional of a turbulent velocity field in a compressible field. However, the characteristic functional equations we derived are governing the motions of an ideal gas and van der Waals gas.
Variational Formulation of 1-D Unsteady Compressible Flow in a Deforming Tube
Institute of Scientific and Technical Information of China (English)
Gaolian Liu; Yi Tao; Yingxue Liu
2003-01-01
The variational principles for 1-D unsteady compressible flow in a deforming tube derived in a previous paper are improved essentially by reconstructing the initial/final-integral terms according to a new method suggested in a recent paper. As a result, the inherent shortcoming of variational principles of being unable to admit physically rational initial/final-value conditions in initial/boundary-value problems is successfully eliminated. Thus, a new theoretical basis for the time-space finite-element analysis is provided.
Institute of Scientific and Technical Information of China (English)
甘延标; 许爱国; 张广财; 李英骏
2011-01-01
We further develop the lattice Boltzmann （LB） model [Physica A 382 （2007） 502] for compressible flows from two aspects. Firstly, we modify the Bhatnagar Gross Krook （BGK） collision term in the LB equation, which makes the model suitable for simulating flows with different Prandtl numbers. Secondly, the flux limiter finite difference （FLFD） scheme is employed to calculate the convection term of the LB equation, which makes the unphysical oscillations at discontinuities be effectively suppressed and the numerical dissipations be significantly diminished. The proposed model is validated by recovering results of some well-known benchmarks, including （i） The thermal Couette flow; （ii） One- and two-dlmenslonal FLiemann problems. Good agreements are obtained between LB results and the exact ones or previously reported solutions. The flexibility, together with the high accuracy of the new model, endows the proposed model considerable potential for tracking some long-standing problems and for investigating nonlinear nonequilibrium complex systems.
The Effect of Water Compressibility on a Rigid Body Movement in Two Phase Flow
Park, Chan Wook; Kim, Hak Sun; Lee, Sungsu
2008-11-01
The motion of a rigid body in a tube full of water-filled, initiated by a sudden release of highly pressurized air is simulated presuming the flow field as a two dimensional one. The effects of water compressibility on the body movement are investigated, comparing results based on the Fluent VOF model where water is treated as an incompressible medium with those from the presently developed VOF scheme. The present model considers compressibility of both air and water. The Fluent results show that the body moves farther and at higher speeds than the present ones. As time proceeds, the relative difference of speed and displacement between the two results drops substantially, after acoustic waves in water traverse and return the full length of the tube several times. To estimate instantaneous accelerations, however, requires implementation of the water compressibility effect as discrepancies between them do not decrease even after several pressure wave cycles. This work was supported by a research fund granted from Agency for Defense Development, South Korea.
CALCULATION ON TWO-PHASE FLOW TRANSIENTS AND THEIR EXPERIMENTAL RESEARCH
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
From basic equations of gas-liquid, solid-liquid, solid-gas two-phase flow, the calculating method on flowtransients of two-phase flow is developed by means of characteristic method. As one example, a gas-liquid flow transientis calculated and it agrees well with the experimental result. It is shown that the method is satisfactory for engineeringdemand.
A Gas-Kinetic Scheme For The Simulation Of Compressible Turbulent Flows
Righi, Marcello
2013-01-01
A gas-kinetic scheme for the continuum regime is applied to the simulation of turbu- lent compressible flow, by replacing the molecular relaxation time with a turbulent relaxation time in the BGK model. The turbulence dynamics is modelled on the basis of a standard, linear two-equation turbulence model. The hydrodynamic limit of the resulting turbulence model is linear in smooth flow and non-linear in the presence of stronger flow gradients. The non-linear correction terms in the numerical flux are weighed as a function of "rarefaction" - referred to turbulence dynamics and not to molecular dynamics, i.e. measured by the ratio of turbulence to mean flow scales of motion. Even though no assumptions on the nature of the turbulence have been made and a linear two-equation turbulence model is used, the turbulence gas-kinetic scheme seems able to correct the turbulent stress tensor in an effective way; on the basis of a number of turbulence modelling benchmark flow cases, characterized by strong shock - boundary l...
Effect of intermolecular potential on compressible Couette flow in slip and transitional regimes
Weaver, Andrew B.; Venkattraman, A.; Alexeenko, Alina A.
2014-10-01
The effect of intermolecular potentials on compressible, planar flow in slip and transitional regimes is investigated using the direct simulation Monte Carlo method. Two intermolecular interaction models, the variable hard sphere (VHS) and the Lennard-Jones (LJ) models, are first compared for subsonic and supersonic Couette flows of argon at temperatures of 40, 273, and 1,000 K, and then for Couette flows in the transitional regime ranging from Knudsen numbers (Kn) of 0.0051 to 1. The binary scattering model for elastic scattering using the Lennard-Jones (LJ) intermolecular potential proposed recently [A. Venkattraman and A. Alexeenko, "Binary scattering model for Lennard-Jones potential: Transport coefficients and collision integrals for non-equilibrium gas flow simulations," Phys. Fluids 24, 027101 (2012)] is shown to accurately reproduce both the theoretical collision frequency in an equilibrium gas as well as the theoretical viscosity variation with temperature. The use of a repulsive-attractive instead of a purely repulsive potential is found to be most important in the continuum and slip regimes as well as in flows with large temperature variations. Differences in shear stress of up to 28% between the VHS and LJ models is observed at Kn=0.0051 and is attributed to differences in collision frequencies, ultimately affecting velocity gradients at the wall. For Kn=1 where the Knudsen layer expands the entire domain, the effect of the larger collision frequency in the LJ model relative to VHS diminishes, and a 7% difference in shear stress is observed.
Transmission of sound through nonuniform circular ducts with compressible mean flows
Nayfeh, A. H.; Shaker, B. S.; Kaiser, J. E.
1980-01-01
An acoustic theory is developed to determine the sound transmission and attenuation through an infinite hard-walled or lined circular duct carrying compressible, sheared mean flows and having a variable cross section. The theory is applicable to large as well as small axial variations, as long as the mean flow does not separate. The technique is based on solving for the envelopes of the quasi-parallel acoustic modes that exist in the duct instead of solving for the actual wave, thereby reducing the computation time and the round-off error encountered in purely numerical techniques. A number of test cases that demonstrate the flexibility of the program are included. Convergence of the transmission coefficients and the acoustic pressure profiles with an increasing number of modes is illustrated.
Extension of the pressure correction method to zero-Mach number compressible flows
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
In the present paper,the classical pressure correction method was extended into low Mach number compressible flow regime by integrating equation of state into SIMPLE algorithm.The self-developed code based on this algorithm was applied to predicting the lid-driven cavity flow and shock tube prob-lems,and the results showed good agreement with benchmark solutions and the Mach number can reach the magnitude of as low as 10-5.The attenuation of sound waves in viscous medium was then simulated.The results agree well with the analytical solutions given by theoretical acoustics.This demonstrated that the present method could also be implemented in acoustics field simulation,which is crucial for thermoacoustic simulation.
Extension of the pressure correction method to zero-Mach number compressible flows
Institute of Scientific and Technical Information of China (English)
HE YaLing; HUANG Jing; TAO YuBing; TAO WenQuan
2009-01-01
In the present paper, the classical pressure correction method was extended into low Mach number compressible flow regime by integrating equation of state into SIMPLE algorithm. The self-developed code based on this algorithm was applied to predicting the lid-driven cavity flow and shock tube prob-lems, and the results showed good agreement with benchmark solutions and the Mach number can reach the magnitude of as low as 10-5. The attenuation of sound waves in viscous medium was then simulated. The results agree well with the analytical solutions given by theoretical acoustics. This demonstrated that the present method could also be implemented in acoustics field simulation, which is crucial for thermoacoustic simulation.
Simulation of Free Surface Compressible Flows Via a Two Fluid Model
Dias, Frederic; Ghidaglia, Jean-Michel
2008-01-01
The purpose of this communication is to discuss the simulation of a free surface compressible flow between two fluids, typically air and water. We use a two fluid model with the same velocity, pressure and temperature for both phases. In such a numerical model, the free surface becomes a thin three dimensional zone. The present method has at least three advantages: (i) the free-surface treatment is completely implicit; (ii) it can naturally handle wave breaking and other topological changes in the flow; (iii) one can easily vary the Equation of States (EOS) of each fluid (in principle, one can even consider tabulated EOS). Moreover, our model is unconditionally hyperbolic for reasonable EOS.
An adaptive semi-implicit scheme for simulations of unsteady viscous compressible flows
Steinthorsson, Erlendur; Modiano, David; Crutchfield, William Y.; Bell, John B.; Colella, Phillip
1995-11-01
A numerical scheme for simulation of unsteady, viscous, compressible flows is considered. The scheme employs an explicit discretization of the inviscid terms of the Navier-Stokes equations and an implicit discretization of the viscous terms. The discretization is second order accurate in both space and time. Under appropriate assumptions, the implicit system of equations can be decoupled into two linear systems of reduced rank. These are solved efficiently using a Gauss-Seidel method with multigrid convergence acceleration. When coupled with a solution-adaptive mesh refinement technique, the hybrid explicit-implicit scheme provides an effective methodology for accurate simulations of unsteady viscous flows. The methodology is demonstrated for both body-fitted structured grids and for rectangular (Cartesian) grids.
Brown-Dymkoski, Eric; Kasimov, Nurlybek; Vasilyev, Oleg V.
2014-04-01
In order to introduce solid obstacles into flows, several different methods are used, including volume penalization methods which prescribe appropriate boundary conditions by applying local forcing to the constitutive equations. One well known method is Brinkman penalization, which models solid obstacles as porous media. While it has been adapted for compressible, incompressible, viscous and inviscid flows, it is limited in the types of boundary conditions that it imposes, as are most volume penalization methods. Typically, approaches are limited to Dirichlet boundary conditions. In this paper, Brinkman penalization is extended for generalized Neumann and Robin boundary conditions by introducing hyperbolic penalization terms with characteristics pointing inward on solid obstacles. This Characteristic-Based Volume Penalization (CBVP) method is a comprehensive approach to conditions on immersed boundaries, providing for homogeneous and inhomogeneous Dirichlet, Neumann, and Robin boundary conditions on hyperbolic and parabolic equations. This CBVP method can be used to impose boundary conditions for both integrated and non-integrated variables in a systematic manner that parallels the prescription of exact boundary conditions. Furthermore, the method does not depend upon a physical model, as with porous media approach for Brinkman penalization, and is therefore flexible for various physical regimes and general evolutionary equations. Here, the method is applied to scalar diffusion and to direct numerical simulation of compressible, viscous flows. With the Navier-Stokes equations, both homogeneous and inhomogeneous Neumann boundary conditions are demonstrated through external flow around an adiabatic and heated cylinder. Theoretical and numerical examination shows that the error from penalized Neumann and Robin boundary conditions can be rigorously controlled through an a priori penalization parameter η. The error on a transient boundary is found to converge as O
NONLINEAR PERTURBATION METHOD FOR CALCULATING AXISYMMETRIC CAVITATIONAL FLOWS
Directory of Open Access Journals (Sweden)
Vasyl Buivol
2013-12-01
Full Text Available A mathematical model of a cavity under the influence of perturbations of various origins is evaluated. The model is based on hydrodynamics of flows with free boundaries and the theory of small perturbations. Specific analysis is provided for cavitational flows behind cones
HIGH-ORDER I-STABLE CENTERED DIFFERENCE SCHEMES FOR VISCOUS COMPRESSIBLE FLOWS
Institute of Scientific and Technical Information of China (English)
Weizhu Bao; Shi Jin
2003-01-01
In this paper we present high-order I-stable centered difference schemes for the numer-ical simulation of viscous compressible flows. Here I-stability refers to time discretizationswhose linear stability regions contain part of the imaginary axis. This class of schemeshas a numerical stability independent of the cell-Reynolds number Rc, thus allows one tosimulate high Reynolds number flows with relatively larger Rc, or coarser grids for a fixedRc. On the other hand, Rc cannot be arbitrarily large if one tries to obtain adequatenumerical resolution of the viscous behavior. We investigate the behavior of high-orderI-stable schemes for Burgers' equation and the compressible Navier-Stokes equations. Wedemonstrate that, for the second order scheme, Rc ≤ 3 is an appropriate constraint for nu-merical resolution of the viscous profile, while for the fourth-order schemes the constraintcan be relaxed to Rc ≤ 6. Our study indicates that the fourth order scheme is preferable:better accuracy, higher resolution, and larger cell-Reynolds numbers.
The semi-discrete Galerkin finite element modelling of compressible viscous flow past an airfoil
Meade, Andrew J., Jr.
1992-01-01
A method is developed to solve the two-dimensional, steady, compressible, turbulent boundary-layer equations and is coupled to an existing Euler solver for attached transonic airfoil analysis problems. The boundary-layer formulation utilizes the semi-discrete Galerkin (SDG) method to model the spatial variable normal to the surface with linear finite elements and the time-like variable with finite differences. A Dorodnitsyn transformed system of equations is used to bound the infinite spatial domain thereby permitting the use of a uniform finite element grid which provides high resolution near the wall and automatically follows boundary-layer growth. The second-order accurate Crank-Nicholson scheme is applied along with a linearization method to take advantage of the parabolic nature of the boundary-layer equations and generate a non-iterative marching routine. The SDG code can be applied to any smoothly-connected airfoil shape without modification and can be coupled to any inviscid flow solver. In this analysis, a direct viscous-inviscid interaction is accomplished between the Euler and boundary-layer codes, through the application of a transpiration velocity boundary condition. Results are presented for compressible turbulent flow past NACA 0012 and RAE 2822 airfoils at various freestream Mach numbers, Reynolds numbers, and angles of attack. All results show good agreement with experiment, and the coupled code proved to be a computationally-efficient and accurate airfoil analysis tool.
Progress Towards a Cartesian Cut-Cell Method for Viscous Compressible Flow
Berger, Marsha; Aftosmis, Michael J.
2011-01-01
The proposed paper reports advances in developing a method for high Reynolds number compressible viscous flow simulations using a Cartesian cut-cell method with embedded boundaries. This preliminary work focuses on accuracy of the discretization near solid wall boundaries. A model problem is used to investigate the accuracy of various difference stencils for second derivatives and to guide development of the discretization of the viscous terms in the Navier-Stokes equations. Near walls, quadratic reconstruction in the wall-normal direction is used to mitigate mesh irregularity and yields smooth skin friction distributions along the body. Multigrid performance is demonstrated using second-order coarse grid operators combined with second-order restriction and prolongation operators. Preliminary verification and validation for the method is demonstrated using flat-plate and airfoil examples at compressible Mach numbers. Simulations of flow on laminar and turbulent flat plates show skin friction and velocity profiles compared with those from boundary-layer theory. Airfoil simulations are performed at laminar and turbulent Reynolds numbers with results compared to both other simulations and experimental data
Multi-core/GPU accelerated multi-resolution simulations of compressible flows
Hejazialhosseini, Babak; Rossinelli, Diego; Koumoutsakos, Petros
2010-11-01
We develop a multi-resolution solver for single and multi-phase compressible flow simulations by coupling average interpolating wavelets and local time stepping schemes with high order finite volume schemes. Wavelets allow for high compression rates and explicit control over the error in adaptive representation of the flow field, but their efficient parallel implementation is hindered by the use of traditional data parallel models. In this work we demonstrate that this methodology can be implemented so that it can benefit from the processing power of emerging hybrid multicore and multi-GPU architectures. This is achieved by exploiting task-based parallelism paradigm and the concept of wavelet blocks combined with OpenCL and Intel Threading Building Blocks. The solver is able to handle high resolution jumps and benefits from adaptive time integration using local time stepping schemes as implemented on heterogeneous multi-core/GPU architectures. We demonstrate the accuracy of our method and the performance of our solver on different architectures for 2D simulations of shock-bubble interaction and Richtmeyer-Meshkov instability.
Laser driven supersonic flow over a compressible foam surface on the Nike lasera)
Harding, E. C.; Drake, R. P.; Aglitskiy, Y.; Plewa, T.; Velikovich, A. L.; Gillespie, R. S.; Weaver, J. L.; Visco, A.; Grosskopf, M. J.; Ditmar, J. R.
2010-05-01
A laser driven millimeter-scale target was used to generate a supersonic shear layer in an attempt to create a Kelvin-Helmholtz (KH) unstable interface in a high-energy-density (HED) plasma. The KH instability is a fundamental fluid instability that remains unexplored in HED plasmas, which are relevant to the inertial confinement fusion and astrophysical environments. In the experiment presented here the Nike laser [S. P. Obenschain et al., Phys. Plasmas 3, 2098 (1996)] was used to create and drive Al plasma over a rippled foam surface. In response to the supersonic Al flow (Mach=2.6±1.1) shocks should form in the Al flow near the perturbations. The experimental data were used to infer the existence and location of these shocks. In addition, the interface perturbations show growth that has possible contributions from both KH and Richtmyer-Meshkov instabilities. Since compressible shear layers exhibit smaller growth, it is important to use the KH growth rate derived from the compressible dispersion relation.
Non-isothermal, compressible gas flow for the simulation of an enhanced gas recovery application
DEFF Research Database (Denmark)
Böttcher, N.; Singh, Ashok; Kolditz, O.
2012-01-01
In this work, we present a framework for numerical modeling of CO 2 injection into porous media for enhanced gas recovery (EGR) from depleted reservoirs. Physically, we have to deal with non-isothermal, compressible gas flows resulting in a system of coupled non-linear PDEs. We describe the mathe......In this work, we present a framework for numerical modeling of CO 2 injection into porous media for enhanced gas recovery (EGR) from depleted reservoirs. Physically, we have to deal with non-isothermal, compressible gas flows resulting in a system of coupled non-linear PDEs. We describe...... the mathematical framework for the underlying balance equations as well as the equations of state for mixing gases. We use an object-oriented finite element method implemented in C++. The numerical model has been tested against an analytical solution for a simplified problem and then applied to CO 2 injection...... into a real reservoir. Numerical modeling allows to investigate physical phenomena and to predict reservoir pressures as well as temperatures depending on injection scenarios and is therefore a useful tool for applied numerical analysis. © 2011 Elsevier B.V. All rights reserved....
Flow Curve Analysis of 17-4 PH Stainless Steel under Hot Compression Test
Mirzadeh, Hamed; Najafizadeh, Abbas; Moazeny, Mohammad
2009-12-01
The hot compression behavior of a 17-4 PH stainless steel (AISI 630) has been investigated at temperatures of 950 °C to 1150 °C and strain rates of 10-3 to 10 s-1. Glass powder in the Rastegaev reservoirs of the specimen was used as a lubricant material. A step-by-step procedure for data analysis in the hot compression test was given. The work hardening rate analysis was performed to reveal if dynamic recrystallization (DRX) occurred. Many samples exhibited typical DRX stress-strain curves with a single peak stress followed by a gradual fall toward the steady-state stress. At low Zener-Hollomon ( Z) parameter, this material showed a new DRX flow behavior, which was called multiple transient steady state (MTSS). At high Z, as a result of adiabatic deformation heating, a drop in flow stress was observed. The general constitutive equations were used to determine the hot working constants of this material. Moreover, after a critical discussion, the deformation activation energy of 17-4 PH stainless steel was determined as 337 kJ/mol.
Numerically stable fluid–structure interactions between compressible flow and solid structures
Grétarsson, Jón Tómas
2011-04-01
We propose a novel method to implicitly two-way couple Eulerian compressible flow to volumetric Lagrangian solids. The method works for both deformable and rigid solids and for arbitrary equations of state. The method exploits the formulation of [11] which solves compressible fluid in a semi-implicit manner, solving for the advection part explicitly and then correcting the intermediate state to time tn+1 using an implicit pressure, obtained by solving a modified Poisson system. Similar to previous fluid-structure interaction methods, we apply pressure forces to the solid and enforce a velocity boundary condition on the fluid in order to satisfy a no-slip constraint. Unlike previous methods, however, we apply these coupled interactions implicitly by adding the constraint to the pressure system and combining it with any implicit solid forces in order to obtain a strongly coupled, symmetric indefinite system (similar to [17], which only handles incompressible flow). We also show that, under a few reasonable assumptions, this system can be made symmetric positive-definite by following the methodology of [16]. Because our method handles the fluid-structure interactions implicitly, we avoid introducing any new time step restrictions and obtain stable results even for high density-to-mass ratios, where explicit methods struggle or fail. We exactly conserve momentum and kinetic energy (thermal fluid-structure interactions are not considered) at the fluid-structure interface, and hence naturally handle highly non-linear phenomenon such as shocks, contacts and rarefactions. © 2011 Elsevier Inc.
Modeling compressible multiphase flows with dispersed particles in both dense and dilute regimes
McGrath, T.; St. Clair, J.; Balachandar, S.
2017-06-01
Many important explosives and energetics applications involve multiphase formulations employing dispersed particles. While considerable progress has been made toward developing mathematical models and computational methodologies for these flows, significant challenges remain. In this work, we apply a mathematical model for compressible multiphase flows with dispersed particles to existing shock and explosive dispersal problems from the literature. The model is cast in an Eulerian framework, treats all phases as compressible, is hyperbolic, and satisfies the second law of thermodynamics. It directly applies the continuous-phase pressure gradient as a forcing function for particle acceleration and thereby retains relaxed characteristics for the dispersed particle phase that remove the constituent material sound velocity from the eigenvalues. This is consistent with the expected characteristics of dispersed particle phases and can significantly improve the stable time-step size for explicit methods. The model is applied to test cases involving the shock and explosive dispersal of solid particles and compared to data from the literature. Computed results compare well with experimental measurements, providing confidence in the model and computational methods applied.
A calculation procedure for viscous flow in turbomachines, volume 2
Khalil, J.; Tabakoff, W.
1980-01-01
Turbulent flow within turbomachines having arbitrary blade geometries is examined. Effects of turbulence are modeled using two equations, one expressing the development of the turbulence kinetic energy and the other its dissipation rate. To account for complicated blade geometries, the flow equations are formulated in terms of a nonorthogonal boundary fitted coordinate system. The analysis is applied to a radial inflow turbine. The solution obtained indicates the severity of the complex interaction mechanism that occurs between the different flow regimes (i.e., boundary layers, recirculating eddies, separation zones, etc.). Comparison with nonviscous flow solutions tend to justify strongly the inadequacy of using the latter with standard boundary layer techniques to obtain viscous flow details within turbomachine rotors. Capabilities and limitations of the present method of analysis are discussed.
CFD Calculations of the Flow Around a Wind Turbine Nacelle
Energy Technology Data Exchange (ETDEWEB)
Varela, J.; Bercebal, D. [Ciemat, Madrid (Spain)
2000-07-01
The purpose of this work is to identify the influence of a MADE AE30 wind turbine nacelle on the site calibration anemometer placed on the upper back of the nacelle by means of flow simulations around the nacelle using FLUENT, a Commercial Computational Fluid Dynamics code (CFD), which provides modeling capabilities for the simulation of wide range laminar and turbulent fluid flow problems. Different 2D and 3D simulations were accomplished in order to estimate the effects of the complex geometry on the flow behavior. The speed up and braking values of the air flow at the anemometer position are presented for different flow conditions. Finally some conclusions about the accuracy of results are mentioned. (Author) 5 refs.
Energy Technology Data Exchange (ETDEWEB)
McMahan, A K
2005-03-30
This paper reports calculations for compressed Ce (4f{sup 1}), Pr (4f{sup 2}), and Nd (4f{sup 3}) using a combination of the local-density approximation (LDA) and dynamical mean field theory (DMFT), or LDA+DMFT. The 4f moment, spectra, and the total energy among other properties are examined as functions of volume and atomic number for an assumed face-centered cubic (fcc) structure. These materials are seen to be strongly localized at ambient pressure and for compressions up through the experimentally observed fcc phases ({gamma} phase for Ce), in the sense of having fully formed Hund's rules moments and little 4f spectral weight at the Fermi level. Subsequent compression for all three lanthanides brings about significant deviation of the moments from their Hund's rules values, a growing Kondo resonance at the fermi level, an associated softening in the total energy, and quenching of the spin orbit since the Kondo resonance is of mixed spin-orbit character while the lower Hubbard band is predominantly j = 5/2. while the most dramatic changes for Ce occur within the two-phase region of the {gamma}-{alpha} volume collapse transition, as found in earlier work, those for Pr and Nd occur within the volume range of the experimentally observed distorted fcc (dfcc) phase, which is therefore seen here as transitional and not part of the localized trivalent lanthanide sequence. The experimentally observed collapse to the {alpha}-U structure in Pr occurs only on further compression, and no such collapse is found in Nd. These lanthanides start closer to the localized limit for increasing atomic number, and so the theoretical signatures noted above are also offset to smaller volume as well, which is possibly related to the measured systematics of the size of the volume collapse being 15%, 9%, and none for Ce, Pr, and Nd, respectively.
Energy Technology Data Exchange (ETDEWEB)
R. A. Berry; R. Saurel; F. Petitpas; E. Daniel; O. Le Metayer; S. Gavrilyuk; N. Dovetta
2008-10-01
In nuclear reactor safety and optimization there are key issues that rely on in-depth understanding of basic two-phase flow phenomena with heat and mass transfer. Within the context of multiphase flows, two bubble-dynamic phenomena – boiling (heterogeneous) and flashing or cavitation (homogeneous boiling), with bubble collapse, are technologically very important to nuclear reactor systems. The main difference between boiling and flashing is that bubble growth (and collapse) in boiling is inhibited by limitations on the heat transfer at the interface, whereas bubble growth (and collapse) in flashing is limited primarily by inertial effects in the surrounding liquid. The flashing process tends to be far more explosive (and implosive), and is more violent and damaging (at least in the near term) than the bubble dynamics of boiling. However, other problematic phenomena, such as crud deposition, appear to be intimately connecting with the boiling process. In reality, these two processes share many details.
Turbulent Compressible Convection with Rotation. 2; Mean Flows and Differential Rotation
Brummell, Nicholas H.; Hurlburt, Neal E.; Toomre, Juri
1998-01-01
The effects of rotation on turbulent, compressible convection within stellar envelopes are studied through three-dimensional numerical simulations conducted within a local f-plane model. This work seeks to understand the types of differential rotation that can be established in convective envelopes of stars like the Sun, for which recent helioseismic observations suggest an angular velocity profile with depth and latitude at variance with many theoretical predictions. This paper analyzes the mechanisms that are responsible for the mean (horizontally averaged) zonal and meridional flows that are produced by convection influenced by Coriolis forces. The compressible convection is considered for a range of Rayleigh, Taylor, and Prandtl (and thus Rossby) numbers encompassing both laminar and turbulent flow conditions under weak and strong rotational constraints. When the nonlinearities are moderate, the effects of rotation on the resulting laminar cellular convection leads to distinctive tilts of the cell boundaries away from the vertical. These yield correlations between vertical and horizontal motions that generate Reynolds stresses that can drive mean flows, interpretable as differential rotation and meridional circulations. Under more vigorous forcing, the resulting turbulent convection involves complicated and contorted fluid particle trajectories, with few clear correlations between vertical and horizontal motions, punctuated by an evolving and intricate downflow network that can extend over much of the depth of the layer. Within such networks are some coherent structures of vortical downflow that tend to align with the rotation axis. These yield a novel turbulent alignment mechanism, distinct from the laminar tilting of cellular boundaries, that can provide the principal correlated motions and thus Reynolds stresses and subsequently mean flows. The emergence of such coherent structures that can persist amidst more random motions is a characteristic of turbulence
A power flow solvability identification and calculation algorithm
Energy Technology Data Exchange (ETDEWEB)
Echavarren, F.M.; Lobato, E.; Rouco, L. [School of Engineering of Universidad Pontificia Comillas, C/Alberto Aguilera 23, 28015 Madrid (Spain)
2006-01-15
This paper presents a continuation and optimization based algorithm to detect power flow unsolvability. In addition, the algorithm obtains the power flow solution, if it exists, no matter how ill-conditioned the power system is. The proposed algorithm is based on the parameterization of the distance from the starting point to the real power flow to be solved, using a convergence margin. The performance of the algorithm is illustrated considering an highly loaded scenario of the operation of the Spanish power system. (author)
Peng, Naifu; Yang, Yue
2016-11-01
We investigate the evolution of vortex-surface fields (VSFs) in viscous compressible Taylor-Green flows. The VSF is applied to the direct numerical simulation of the Taylor-Green flows at a range of Mach numbers from Ma = 0 . 6 to Ma = 2 . 2 for characterizing the Mach-number effects on evolving vortical structures. We find that the dilatation and baroclinic force strongly influence the geometry of vortex surfaces and the energy dissipation rate in the transitional stage. The vortex tubes in compressible flows are less curved than those in incompressible flows, and the maximum dissipation rate occurs earlier in high-Mach-number flows perhaps owing to the conversion of kinetic energy into heat. Moreover, the relations between the evolutionary geometry of vortical structures and flow statistics are discussed. This work has been supported in part by the National Natural Science Foundation of China (Grant Nos. 11522215 and 11521091), and the Thousand Young Talents Program of China.
Luxa, Martin; Příhoda, Jaromír; Šimurda, David; Straka, Petr; Synáč, Jaroslav
2016-04-01
The contribution deals with the experimental and numerical investigation of compressible flow through the tip-section turbine blade cascade with the blade 54″ long. Experimental investigations by means of optical (interferometry and schlieren method) and pneumatic measurements provide more information about the behaviour and nature of basic phenomena occurring in the profile cascade flow field. The numerical simulation was carried out by means of the EARSM turbulence model according to Hellsten [5] completed by the bypass transition model with the algebraic equation for the intermittency coefficient proposed by Straka and Příhoda [6] and implemented into the in-house numerical code. The investigation was focused particularly on the effect of shock waves on the shear layer development including the laminar/turbulent transition. Interactions of shock waves with shear layers on both sides of the blade result usually in the transition in attached and/ or separated flow and so to the considerable impact to the flow structure and energy losses in the blade cascade.
Thermodynamic bounds for existence of normal shock in compressible fluid flow in pipes
Directory of Open Access Journals (Sweden)
SERGIO COLLE
Full Text Available Abstract The present paper is concerned with the thermodynamic theory of the normal shock in compressible fluid flow in pipes, in the lights of the pioneering works of Lord Rayleigh and G. Fanno. The theory of normal shock in pipes is currently presented in terms of the Rayleigh and Fanno curves, which are shown to cross each other in two points, one corresponding to a subsonic flow and the other corresponding to a supersonic flow. It is proposed in this paper a novel differential identity, which relates the energy flux density, the linear momentum flux density, and the entropy, for constant mass flow density. The identity so obtained is used to establish a theorem, which shows that Rayleigh and Fanno curves become tangent to each other at a single sonic point. At the sonic point the entropy reaches a maximum, either as a function of the pressure and the energy density flux or as a function of the pressure and the linear momentum density flux. A Second Law analysis is also presented, which is fully independent of the Second Law analysis based on the Rankine-Hugoniot adiabatic carried out by Landau and Lifshitz (1959.
Canonical fluid thermodynamics. [variational principles of stability for compressible adiabatic flow
Schmid, L. A.
1974-01-01
The space-time integral of the thermodynamic pressure plays in a certain sense the role of the thermodynamic potential for compressible adiabatic flow. The stability criterion can be converted into a variational minimum principle by requiring the molar free-enthalpy and temperature to be generalized velocities. In the fluid context, the definition of proper-time differentiation involves the fluid velocity expressed in terms of three particle identity parameters. The pressure function is then converted into a functional which is the Lagrangian density of the variational principle. Being also a minimum principle, the variational principle provides a means for comparing the relative stability of different flows. For boundary conditions with a high degree of symmetry, as in the case of a uniformly expanding spherical gas box, the most stable flow is a rectilinear flow for which the world-trajectory of each particle is a straight line. Since the behavior of the interior of a freely expanding cosmic cloud may be expected to be similar to that of the fluid in the spherical box of gas, this suggests that the cosmic principle is a consequence of the laws of thermodynamics, rather than just an ad hoc postulate.
Thermodynamic bounds for existence of normal shock in compressible fluid flow in pipes.
Colle, Sergio
2017-01-01
The present paper is concerned with the thermodynamic theory of the normal shock in compressible fluid flow in pipes, in the lights of the pioneering works of Lord Rayleigh and G. Fanno. The theory of normal shock in pipes is currently presented in terms of the Rayleigh and Fanno curves, which are shown to cross each other in two points, one corresponding to a subsonic flow and the other corresponding to a supersonic flow. It is proposed in this paper a novel differential identity, which relates the energy flux density, the linear momentum flux density, and the entropy, for constant mass flow density. The identity so obtained is used to establish a theorem, which shows that Rayleigh and Fanno curves become tangent to each other at a single sonic point. At the sonic point the entropy reaches a maximum, either as a function of the pressure and the energy density flux or as a function of the pressure and the linear momentum density flux. A Second Law analysis is also presented, which is fully independent of the Second Law analysis based on the Rankine-Hugoniot adiabatic carried out by Landau and Lifshitz (1959).
A wave-envelope of sound propagation in nonuniform circular ducts with compressible mean flows
Nayfeh, A. H.; Kaiser, J. E.; Shaker, B. S.
1979-01-01
An acoustic theory is developed to determine the sound transmission and attenuation through an infinite, hard-walled or lined circular duct carrying compressible, sheared, mean flows and having a variable cross section. The theory is applicable to large as well as small axial variations, as long as the mean flow does not separate. The technique is based on solving for the envelopes of the quasi-parallel acoustic modes that exist in the duct instead of solving for the actual wave, thereby reducing the computation time and the round-off error encountered in purely numerical techniques. The solution recovers the solution based on the method of multiple scales for slowly varying duct geometry. A computer program was developed based on the wave-envelope analysis for general mean flows. Results are presented for the reflection and transmission coefficients as well as the acoustic pressure distributions for a number of conditions: both straight and variable area ducts with and without liners and mean flows from very low to high subsonic speeds are considered.
Neutral stability calculations for boundary-layer flows
Nayfeh, A. H.; Padhye, A.
1980-01-01
An analysis is presented of the parallel neutral stability of three-dimensional incompressible, isothermal boundary-layer flows. A Taylor-series expansion of the dispersion relation is used to derive the general eigenvalues. These equations are functions of the complex group velocity. These relations are verified by numerical results obtained for two- and three-dimensional disturbances in two- and three-dimensional flows.
Theoretical calculation of the shock compression properties of liquid H2 + D2 mixtures
Institute of Scientific and Technical Information of China (English)
陈其峰; 蔡灵仓; 陈栋泉; 经福谦
1999-01-01
Based on liquid variational perturbation theory with quantum mechanics correction, the effective exp-6 potential is adopted to compute the shock Hugoniot of liquid H2+D2 mixtures at different molar rations. An examination of the confidence of the above computation is performed by comparing experiments and calculations, in which similar calculation procedure used for H2+D2 is adopted for H2 and D2 each, since no experimental data are available to conduct this kind of comparison. Good agreement in both comparisons is found. This fact may look as if an indirect positive verification of calculation procedure was used here at least in the pressure and temperature domain covered by the experimental data of H2 and D2 used for comparison, numerically nearly up to 20 GPa and 104 K.
Institute of Scientific and Technical Information of China (English)
Ke TANG; Juan YU; Tao JIN; Zhi-hua GAN
2013-01-01
Compression and expansion of a working gas due to the pressure oscillation of an oscillating flow can lead to a temperature variation of the working gas,which will affect the heat transfer in the oscillating flow.This study focuses on the impact of the compression-expansion effect,indicated by the pressure ratio,on the heat transfer in a finned heat exchanger under practical operating conditions of the ambient-temperature heat exchangers in Stirling-type pulse tube refrigerators.The experimental results summarized as the Nusselt number are presented for analysis.An increase in the pressure ratio can result in a marked rise in the Nussclt number,which indicates that the compression-expansion effect should be considered in characterizing the heat transfer of the oscillating flow,especially in the cases with a higher Valensi number and a lower maximum Reynolds number.
Navier-Stokes flow field analysis of compressible flow in a high pressure safety relief valve
Vu, Bruce; Wang, Ten-See; Shih, Ming-Hsin; Soni, Bharat
1993-12-01
The objective of this study is to investigate the complex three-dimensional flowfield of an oxygen safety pressure relieve valve during an incident, with a computational fluid dynamic (CFD) analysis. Specifically, the analysis will provide a flow pattern that would lead to the expansion of the eventual erosion pattern of the hardware, so as to combine it with other findings to piece together a most likely scenario for the investigation. The CFD model is a pressure based solver. An adaptive upwind difference scheme is employed for the spatial discretization, and a predictor, multiple corrector method is used for the velocity-pressure coupling. The computational result indicated vortices formation near the opening of the valve which matched the erosion pattern of the damaged hardware.
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.
An eddy viscosity calculation method for a turbulent duct flow
Antonia, R. A.; Bisset, D. K.; Kim, J.
1991-01-01
The mean velocity profile across a fully developed turbulent duct flow is obtained from an eddy viscosity relation combined with an empirical outer region wake function. Results are in good agreement with experiments and with direct numerical simulations in the same flow at two Reynolds numbers. In particular, the near-wall trend of the Reynolds shear stress and its variation with Reynolds number are similar to those of the simulations. The eddy viscosity method is more accurate than previous mixing length or implicit function methods.
Development of a Water Based, Critical Flow, Non-Vapor Compression cooling Cycle
Energy Technology Data Exchange (ETDEWEB)
Hosni, Mohammad H.
2014-03-30
Expansion of a high-pressure liquid refrigerant through the use of a thermostatic expansion valve or other device is commonplace in vapor-compression cycles to regulate the quality and flow rate of the refrigerant entering the evaporator. In vapor-compression systems, as the condensed refrigerant undergoes this expansion, its pressure and temperature drop, and part of the liquid evaporates. We (researchers at Kansas State University) are developing a cooling cycle that instead pumps a high-pressure refrigerant through a supersonic converging-diverging nozzle. As the liquid refrigerant passes through the nozzle, its velocity reaches supersonic (or critical-flow) conditions, substantially decreasing the refrigerant’s pressure. This sharp pressure change vaporizes some of the refrigerant and absorbs heat from the surrounding conditions during this phase change. Due to the design of the nozzle, a shockwave trips the supersonic two-phase refrigerant back to the starting conditions, condensing the remaining vapor. The critical-flow refrigeration cycle would provide space cooling, similar to a chiller, by running a secondary fluid such as water or glycol over one or more nozzles. Rather than utilizing a compressor to raise the pressure of the refrigerant, as in a vapor-cycle system, the critical-flow cycle utilizes a high-pressure pump to drive refrigerant liquid through the cooling cycle. Additionally, the design of the nozzle can be tailored for a given refrigerant, such that environmentally benign substances can act as the working fluid. This refrigeration cycle is still in early-stage development with prototype development several years away. The complex multi-phase flow at supersonic conditions presents numerous challenges to fully understanding and modeling the cycle. With the support of DOE and venture-capital investors, initial research was conducted at PAX Streamline, and later, at Caitin. We (researchers at Kansas State University) have continued development
Flow calculations for Yucca Mountain groundwater travel time (GWTT-95)
Energy Technology Data Exchange (ETDEWEB)
Altman, S.J.; Arnold, B.W.; Barnard, R.W.; Barr, G.E.; Ho, C.K.; McKenna, S.A.; Eaton, R.R.
1996-09-01
In 1983, high-level radioactive waste repository performance requirements related to groundwater travel time were defined by NRC subsystem regulation 10 CFR 60.113. Although DOE is not presently attempting to demonstrate compliance with that regulation, understanding of the prevalence of fast paths in the groundwater flow system remains a critical element of any safety analyses for a potential repository system at Yucca Mountain, Nevada. Therefore, this analysis was performed to allow comparison of fast-path flow against the criteria set forth in the regulation. Models developed to describe the conditions for initiation, propagation, and sustainability of rapid groundwater movement in both the unsaturated and saturated zones will form part of the technical basis for total- system analyses to assess site viability and site licensability. One of the most significant findings is that the fastest travel times in both unsaturated and saturated zones are in the southern portion of the potential repository, so it is recommended that site characterization studies concentrate on this area. Results support the assumptions regarding the importance of an appropriate conceptual model of groundwater flow and the incorporation of heterogeneous material properties into the analyses. Groundwater travel times are sensitive to variation/uncertainty in hydrologic parameters and in infiltration flux at upper boundary of the problem domain. Simulated travel times are also sensitive to poorly constrained parameters of the interaction between flow in fractures and in the matrix.
Homogenization of immiscible compressible two-phase flow in double porosity media
Directory of Open Access Journals (Sweden)
Latifa Ait Mahiout
2016-02-01
Full Text Available A double porosity model of multidimensional immiscible compressible two-phase flow in fractured reservoirs is derived by the mathematical theory of homogenization. Special attention is paid to developing a general approach to incorporating compressibility of both phases. The model is written in terms of the phase formulation, i.e. the saturation of one phase and the pressure of the second phase are primary unknowns. This formulation leads to a coupled system consisting of a doubly nonlinear degenerate parabolic equation for the pressure and a doubly nonlinear degenerate parabolic diffusion-convection equation for the saturation, subject to appropriate boundary and initial conditions. The major difficulties related to this model are in the doubly nonlinear degenerate structure of the equations, as well as in the coupling in the system. Furthermore, a new nonlinearity appears in the temporal term of the saturation equation. The aim of this paper is to extend the results of [9] to this more general case. With the help of a new compactness result and uniform a priori bounds for the modulus of continuity with respect to the space and time variables, we provide a rigorous mathematical derivation of the upscaled model by means of the two-scale convergence and the dilatation technique.
A near-wall two-equation model for compressible turbulent flows
Zhang, H. S.; So, R. M. C.; Speziale, C. G.; Lai, Y. G.
1992-01-01
A near-wall two-equation turbulence model of the k-epsilon type is developed for the description of high-speed compressible flows. The Favre-averaged equations of motion are solved in conjunction with modeled transport equations for the turbulent kinetic energy and solenoidal dissipation wherein a variable density extension of the asymptotically consistent near-wall model of So and co-workers is supplemented with new dilatational models. The resulting compressible two-equation model is tested in the supersonic flat plate boundary layer - with an adiabatic wall and with wall cooling - for Mach numbers as large as 10. Direct comparisons of the predictions of the new model with raw experimental data and with results from the K-omega model indicate that it performs well for a wide range of Mach numbers. The surprising finding is that the Morkovin hypothesis, where turbulent dilatational terms are neglected, works well at high Mach numbers, provided that the near wall model is asymptotically consistent. Instances where the model predictions deviate from the experiments appear to be attributable to the assumption of constant turbulent Prandtl number - a deficiency that will be addressed in a future paper.
On the convergence of the weakly compressible sharp-interface method for two-phase flows
Schranner, Felix S.; Hu, Xiangyu; Adams, Nikolaus A.
2016-11-01
A weakly compressible sharp-interface framework for two-phase flows is presented. Special emphasis is on investigating its convergence properties. For this purpose a well-defined set of benchmark configurations is introduced. These may serve as future references for the verification of sharp-interface methods. Global mass and momentum conservation is ensured by the conservative sharp-interface method. Viscous and capillary stresses are considered directly at the interface. A low-dissipation weakly compressible Roe Riemann solver, in combination with a 5th-order WENO scheme, leads to high spatial accuracy. A wavelet-based adaptive multi-resolution approach permits to combine computational efficiency with physical consistency. The first test configuration is a Rayleigh-Taylor instability at moderate Reynolds number and infinite Eötvös number. A second group of benchmark cases are isolated air bubbles rising in water at high Eötvös numbers, and low to high Reynolds numbers. With these test cases, three distinct types of complex interface evolution, which are typical for a wide range of industrial applications, are realized.
Energy Technology Data Exchange (ETDEWEB)
Gorman, Jhana; Hales, Jason Dean; Corona, Edmundo
2010-05-01
This report considers the calculation of the quasi-static nonlinear response of rectangular flat plates and tubes of rectangular cross-section subjected to compressive loads using quadrilateralshell finite element models. The principal objective is to assess the effect that the shell drilling stiffness parameter has on the calculated results. The calculated collapse load of elastic-plastic tubes of rectangular cross-section is of particular interest here. The drilling stiffness factor specifies the amount of artificial stiffness that is given to the shell element drilling Degree of freedom (rotation normal to the plane of the element). The element formulation has no stiffness for this degree of freedom, and this can lead to numerical difficulties. The results indicate that in the problems considered it is necessary to add a small amount of drilling tiffness to obtain converged results when using both implicit quasi-statics or explicit dynamics methods. The report concludes with a parametric study of the imperfection sensitivity of the calculated responses of the elastic-plastic tubes with rectangular cross-section.
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.
GPU computing of compressible flow problems by a meshless method with space-filling curves
Ma, Z. H.; Wang, H.; Pu, S. H.
2014-04-01
A graphic processing unit (GPU) implementation of a meshless method for solving compressible flow problems is presented in this paper. Least-square fit is used to discretize the spatial derivatives of Euler equations and an upwind scheme is applied to estimate the flux terms. The compute unified device architecture (CUDA) C programming model is employed to efficiently and flexibly port the meshless solver from CPU to GPU. Considering the data locality of randomly distributed points, space-filling curves are adopted to re-number the points in order to improve the memory performance. Detailed evaluations are firstly carried out to assess the accuracy and conservation property of the underlying numerical method. Then the GPU accelerated flow solver is used to solve external steady flows over aerodynamic configurations. Representative results are validated through extensive comparisons with the experimental, finite volume or other available reference solutions. Performance analysis reveals that the running time cost of simulations is significantly reduced while impressive (more than an order of magnitude) speedups are achieved.
Discrete unified gas kinetic scheme for all Knudsen number flows: II. Compressible case
Guo, Zhaoli; Xu, Kun
2014-01-01
This paper is a continuation of our earlier work [Z.L. Guo {\\it et al.}, Phys. Rev. E {\\bf 88}, 033305 (2013)] where a multiscale numerical scheme based on kinetic model was developed for low speed isothermal flows with arbitrary Knudsen numbers. In this work, a discrete unified gas-kinetic scheme (DUGKS) for compressible flows with the consideration of heat transfer and shock discontinuity is developed based on the Shakhov model with an adjustable Prandtl number. The method is an explicit finite-volume scheme where the transport and collision processes are coupled in the evaluation of the fluxes at cell interfaces, so that the nice asymptotic preserving (AP) property is retained, such that the time step is limited only by the CFL number, the distribution function at cell interface recovers to the Chapman-Enskog one in the continuum limit while reduces to that of free-transport for free-molecular flow, and the time and spatial accuracy is of second-order accuracy in smooth region. These features make the DUGK...
A ghost fluid method for sharp interface simulations of compressible multiphase flows
Energy Technology Data Exchange (ETDEWEB)
Majidi, Sahand; Afshari, Asghar [University of Tehran, Teheran (Iran, Islamic Republic of)
2016-04-15
A ghost fluid based computational tool is developed to study a wide range of compressible multiphase flows involving strong shocks and contact discontinuities while accounting for surface tension, viscous stresses and gravitational forces. The solver utilizes constrained reinitialization method to predict the interface configuration at each time step. Surface tension effect is handled via an exact interface Riemann problem solver. Interfacial viscous stresses are approximated by considering continuous velocity and viscous stress across the interface. To assess the performance of the solver several benchmark problems are considered: One-dimensional gas-water shock tube problem, shock-bubble interaction, air cavity collapse in water, underwater explosion, Rayleigh-Taylor Instability, and ellipsoidal drop oscillations. Results obtained from the numerical simulations indicate that the numerical methodology performs reasonably well in predicting flow features and exhibit a very good agreement with prior experimental and numerical observations. To further examine the accuracy of the developed ghost fluid solver, the obtained results are compared to those by a conventional diffuse interface solver. The comparison shows the capability of our ghost fluid method in reproducing the experimentally observed flow characteristics while revealing more details regarding topological changes of the interface.
Institute of Scientific and Technical Information of China (English)
G.S. Fu; W.Z. Chen; K.W. Qian
2005-01-01
The behavior of flow stress of Al sheets used for pressure can prepared by different melt-treatment during plastic deformation at elevated temperature was studied by isothermal compression testusing Gleeble1500 dynamic hot-simulation testing machine. The results show that the A1 sheets possess the remarkable characteristic of steady state flow stress when they are deformed in the temperature range of 350-500℃ at strain rates within the range of 0.01-10.0s-1. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate, and an Arrhenius relationship with the temperature, which implies that the process of plastic deformation at elevated temperature for this material is thermally activated. Compared with the Al pieces prepared by no or conventional melt-treatment, hot deformation activation energy of Al sheets prepared by high-efficient melt-treatment is the smallest (Q = 168.0kJ/mol), which reveals that the hot working formability of this material is very better, and has directly to do with the effective improvement of its metallurgical quality.
Institute of Scientific and Technical Information of China (English)
Ravindranadh BOBBILI; B. RAMAKRISHNA; V. MADHU; A.K. GOGIA
2015-01-01
An artificial neural network (ANN) constitutive model and JohnsoneCook (JeC) model were developed for 7017 aluminium alloy based on high strain rate data generated from split Hopkinson pressure bar (SHPB) experiments at various temperatures. A neural network configuration consists of both training and validation, which is effectively employed to predict flow stress. Temperature, strain rate and strain are considered as inputs, whereas flow stress is taken as output of the neural network. A comparative study on JohnsoneCook (JeC) model and neural network model was performed. It was observed that the developed neural network model could predict flow stress under various strain rates and tem-peratures. The experimental stressestrain data obtained from high strain rate compression tests using SHPB over a range of temperatures (25?e300 ?C), strains (0.05e0.3) and strain rates (1500e4500 s?1) were employed to formulate JeC model to predict the flow stress behaviour of 7017 aluminium alloy under high strain rate loading. The JeC model and the back-propagation ANN model were developed to predict the flow stress of 7017 aluminium alloy under high strain rates, and their predictability was evaluated in terms of correlation coefficient (R) and average absolute relative error (AARE). R and AARE for the J-C model are found to be 0.8461 and 10.624%, respectively, while R and AARE for the ANN model are 0.9995 and 2.58%, respectively. The predictions of ANN model are observed to be in consistent with the experimental data for all strain rates and temperatures.
Yan, Xiaopeng; Lv, Yi; Ma, Feng; Ma, Jia; Wang, Haohua; Wang, Shanpei; Li, Dichen; Liu, Yaxiong; Jia, Shenli; Shi, Zongqian; Luo, Ruixue
2014-03-01
A new system of blood flow block for control of bleeding in abdominal operation is composed of an abdominal magnetic blocking unit, an abdominal external electromagnet unit and other non-magnetic operation instrument. The abdominal external electromagnetic unit is placed in advance in the operation bed. The abdominal magnetic blocking unit can be placed directly on the ventral of the large vessels when need to blocking the abdominal large vessels during the operation. According to the non-contact suction characteristics of magnetic materials, the two magnetic units will attract each other and compression the vessels. Using this system for vascular occlusion does not need clear exposure and without separating vessel. There is the advantage of rapid, accurate and reliable for the system.
Review of Fluorescence-Based Velocimetry Techniques to Study High-Speed Compressible Flows
Bathel, Brett F.; Johansen, Criag; Inman, Jennifer A.; Jones, Stephen B.; Danehy, Paul M.
2013-01-01
This paper reviews five laser-induced fluorescence-based velocimetry techniques that have been used to study high-speed compressible flows at NASA Langley Research Center. The techniques discussed in this paper include nitric oxide (NO) molecular tagging velocimetry (MTV), nitrogen dioxide photodissociation (NO2-to-NO) MTV, and NO and atomic oxygen (O-atom) Doppler-shift-based velocimetry. Measurements of both single-component and two-component velocity have been performed using these techniques. This paper details the specific application and experiment for which each technique has been used, the facility in which the experiment was performed, the experimental setup, sample results, and a discussion of the lessons learned from each experiment.
Fernandez, Pablo; Roca, Xevi; Peraire, Jaime
2016-01-01
We present a high-order implicit large-eddy simulation (ILES) approach for simulating transitional turbulent flows. The approach consists of an Interior Embedded Discontinuous Galerkin (IEDG) method for the discretization of the compressible Navier-Stokes equations and a parallel preconditioned Newton-GMRES solver for the resulting nonlinear system of equations. The IEDG method arises from the marriage of the Embedded Discontinuous Galerkin (EDG) method and the Hybridizable Discontinuous Galerkin (HDG) method. As such, the IEDG method inherits the advantages of both the EDG method and the HDG method to make itself well-suited for turbulence simulations. We propose a minimal residual Newton algorithm for solving the nonlinear system arising from the IEDG discretization of the Navier-Stokes equations. The preconditioned GMRES algorithm is based on a restricted additive Schwarz (RAS) preconditioner in conjunction with a block incomplete LU factorization at the subdomain level. The proposed approach is applied to...
Wan, Ling; Wang, Tao
2017-06-01
We consider the Navier-Stokes equations for compressible heat-conducting ideal polytropic gases in a bounded annular domain when the viscosity and thermal conductivity coefficients are general smooth functions of temperature. A global-in-time, spherically or cylindrically symmetric, classical solution to the initial boundary value problem is shown to exist uniquely and converge exponentially to the constant state as the time tends to infinity under certain assumptions on the initial data and the adiabatic exponent γ. The initial data can be large if γ is sufficiently close to 1. These results are of Nishida-Smoller type and extend the work (Liu et al. (2014) [16]) restricted to the one-dimensional flows.
A Low-Dissipation Technique for Computing Dense Granular Compressible Flows with Shock Waves
Houim, Ryan W
2013-01-01
A low-dissipation numerical method was developed for solving kinetic theory-based granular multiphase models with volume fractions ranging from very dilute to very dense in highly compressible flows containing shock waves. The proposed numerical method takes advantage of particle incompressibility and allows computation of gas-phase and granular-phase hyperbolic fluxes to be decoupled while treating non-conservative terms consistent with their physical meaning. The technique converges under grid refinement even with very high volume fraction granular interfaces and is compatible with high-order numerical algorithms. The method can advect sharp granular interfaces that coincide with multi-species gaseous contacts without violating the pressure non-disturbing conditions. The method also reproduces features from multiphase shock tube problems, granular shocks, transmission angles of compaction waves, and shock wave and dust layer interactions. The proposed scheme is relatively straight-forward to implement and c...
Timofeev, Evgeny; Norouzi, Farhang
2016-06-01
The motivation for using hybrid, explicit-implicit, schemes rather than fully implicit or explicit methods for some unsteady high-speed compressible flows with shocks is firstly discussed. A number of such schemes proposed in the past are briefly overviewed. A recently proposed hybridization approach is then introduced and used for the development of a hybrid, explicit-implicit, TVD (Total Variation Diminishing) scheme of the second order in space and time on smooth solutions in both, explicit and implicit, modes for the linear advection equation. Further generalizations of this finite-volume method for the Burgers, Euler and Navier-Stokes equations discretized on unstructured grids are mentioned in the concluding remarks.
An Embedded Ghost-Fluid Method for Compressible Flow in Complex Geometry
Al-Marouf, M.
2016-06-03
We present an embedded ghost-fluid method for numerical solutions of the compressible Navier Stokes (CNS) equations in arbitrary complex domains. The PDE multidimensional extrapolation approach of Aslam [1] is used to reconstruct the solution in the ghost-fluid regions and impose boundary conditions at the fluid-solid interface. The CNS equations are numerically solved by the second order multidimensional upwind method of Colella [2] and Saltzman [3]. Block-structured adaptive mesh refinement implemented under the Chombo framework is utilized to reduce the computational cost while keeping high-resolution mesh around the embedded boundary and regions of high gradient solutions. Numerical examples with different Reynolds numbers for low and high Mach number flow will be presented. We compare our simulation results with other reported experimental and computational results. The significance and advantages of our implementation, which revolve around balancing between the solution accuracy and implementation difficulties, are briefly discussed as well. © 2016 Trans Tech Publications.
Integrated LTCC Pressure/Flow/Temperature Multisensor for Compressed Air Diagnostics†
Directory of Open Access Journals (Sweden)
Nicolas Craquelin
2010-12-01
Full Text Available We present a multisensor designed for industrial compressed air diagnostics and combining the measurement of pressure, flow, and temperature, integrated with the corresponding signal conditioning electronics in a single low-temperature co-fired ceramic (LTCC package. The developed sensor may be soldered onto an integrated electro-fluidic platform by using standard surface mount device (SMD technology, e.g., as a standard electronic component would be on a printed circuit board, obviating the need for both wires and tubes and thus paving the road towards low-cost integrated electro-fluidic systems. Several performance aspects of this device are presented and discussed, together with electronics design issues.
Calculating the respiratory flow velocity fluctuations in pericardial diseases.
Siniorakis, Eftychios; Arvanitakis, Spyridon; Zarreas, Elias; Barlagiannis, Dimitris; Skandalakis, Nikos; Karidis, Constantinos
2010-11-01
An excessive respiratory fluctuation (RTFV) in transmitral early diastolic velocity E is a pivotal Doppler echocardiographic sign of haemodynamic compromise, in constrictive pericardial diseases. RTFV is expressed as a percentage and 25% is considered a threshold value. Unfortunately there is no unanimity in calculating RTFV. Sometimes it is expressed as a percentage of expiratory E velocity, while others of inspiratory E velocity. This disparity has led to gross misinterpretations in medical literature. Here we emphasize the importance of a rational procedure calculating RTFV and we propose the appropriate mathematical model.
Numerical Investigation of Vortex Generator Flow Control for External-Compression Supersonic Inlets
Baydar, Ezgihan
Vortex generators (VGs) within external-compression supersonic inlets for Mach 1.6 were investigated to determine their ability to increase total pressure recovery and reduce total pressure distortion. Ramp and vane-type VGs were studied. The geometric factors of interest included height, length, spacing, angle-of-incidence, and positions upstream and downstream of the inlet terminal shock. The flow through the inlet was simulated numerically through the solution of the steady-state, Reynolds-averaged Navier-Stokes equations on multi-block, structured grids using the Wind-US flow solver. The inlet performance was characterized by the inlet total pressure recovery and the radial and circumferential total pressure distortion indices at the engine face. Previous research of downstream VGs in the low-boom supersonic inlet demonstrated improvement in radial distortion up to 24% while my work on external-compression supersonic inlets improved radial distortion up to 86%, which is significant. The design of experiments and statistical analysis methods were applied to quantify the effect of the geometric factors of VGs and search for optimal VG arrays. From the analysis, VG angle-of-incidence and VG height were the most influential factors in increasing total pressure recovery and reducing distortion. The study on the two-dimensional external-compression inlet determined which passive flow control devices, such as counter-rotating vanes or ramps, reduce high distortion levels and improve the health of the boundary layer, relative to the baseline. Downstream vanes demonstrate up to 21% improvement in boundary layer health and 86% improvement in radial distortion. Upstream vanes demonstrated up to 3% improvement in boundary layer health and 9% improvement in radial distortion. Ramps showed no improvement in boundary layer health and radial distortion. Micro-VGs were preferred for their reduced viscous drag and improvement in total pressure recovery at the AIP. Although
Badie, R.; Jonker, J.B.; Braembussche, van den R.A.
1994-01-01
In this paper we present a finite-element-based methode for the calculation of the unsteady potential flow in rotor/stator configurations. A numerical algorithm was developed to calculate the two-dimensional flow through a centrifugal volute pump, taking into account the width variation of the volut
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.
Calculation of turbulent reactive flows in general orthogonal coordinates
Lai, M. K. Y.
1992-02-01
The mathematical and numerical methodology for an extended and enhanced version of the TURCOM computer code, called TURCOM-BFC, is presented. This code solves the conservation equations of multi-component chemically reactive and turbulent flows in general curvilinear orthogonal coordinates. The k-epsilon turbulence submodel is used. Flame chemistry assumes a number of species and chemical reactions. The latter are subdivided into finite-rate reaction steps and a one-step irreversible reaction, whose rate is controlled by a combination of mixing and global kinetics. Both the SIMPLE and PISO algorithms are implemented to solve the system of equations. The capability of TURCOM-BFC is tested and demonstrated by predicting 3-dimensional combustion flow inside a reaction furnace, where both polar-cylindrical and bipolar coordinates are used.
40 CFR 1065.640 - Flow meter calibration calculations.
2010-07-01
....013 V rev = 0.03166 m3/rev (2) PDP slip correction factor, Ks (s/rev): ER13JY05.065 Example: f nPDP... judgment. Note that the equation for the flow coefficient, C f, is based on the ideal gas assumption that... follows: ER13JY05.067 Where: C d = Discharge coefficient, as determined in paragraph (c)(1) of...
Mclean, J. D.; Randall, J. L.
1979-01-01
A system of computer programs for calculating three dimensional transonic flow over wings, including details of the three dimensional viscous boundary layer flow, was developed. The flow is calculated in two overlapping regions: an outer potential flow region, and a boundary layer region in which the first order, three dimensional boundary layer equations are numerically solved. A consistent matching of the two solutions is achieved iteratively, thus taking into account viscous-inviscid interaction. For the inviscid outer flow calculations, the Jameson-Caughey transonic wing program FLO 27 is used, and the boundary layer calculations are performed by a finite difference boundary layer prediction program. Interface programs provide communication between the two basic flow analysis programs. Computed results are presented for the NASA F8 research wing, both with and without distributed surface suction.
Directory of Open Access Journals (Sweden)
Masafumi Nozoe
2016-01-01
Full Text Available Background: Manual chest wall compression (CWC during expiration is a technique for removing airway secretions in patients with respiratory disorders. However, there have been no reports about the physiological effects of CWC in patients with chronic obstructive pulmonary disease (COPD. Objective: To compare the effects of CWC on expiratory flow rates in patients with COPD and asymptomatic controls. Method: Fourteen subjects were recruited from among patients with COPD who were receiving pulmonary rehabilitation at the University Hospital (COPD group. Fourteen age-matched healthy subjects were also consecutively recruited from the local community (Healthy control group. Airflow and lung volume changes were measured continuously with the subjects lying in supine position during 1 minute of quiet breathing (QB and during 1 minute of CWC by a physical therapist. Results: During CWC, both the COPD group and the healthy control group showed significantly higher peak expiratory flow rates (PEFRs than during QB (mean difference for COPD group 0.14 L/sec, 95% confidence interval (CI 0.04 to 0.24, p<0.01, mean difference for healthy control group 0.39 L/sec, 95% CI 0.25 to 0.57, p<0.01. In the between-group comparisons, PEFR was significantly higher in the healthy control group than in the COPD group (-0.25 L/sec, 95% CI -0.43 to -0.07, p<0.01. However, the expiratory flow rates at the lung volume at the PEFR during QB and at 50% and 25% of tidal volume during QB increased in the healthy control group (mean difference for healthy control group 0.31 L/sec, 95% CI 0.15 to 0.47, p<0.01: 0.31 L/sec, 95% CI 0.15 to 0.47, p<0.01: 0.27 L/sec, 95% CI 0.13 to 0.41, p<0.01, respectively but not in the COPD group (0.05 L/sec, 95% CI -0.01 to 0.12: -0.01 L/sec, 95% CI -0.11 to 0.08: 0.02 L/sec, 95% CI -0.05 to 0.90 with the application of CWC. Conclusion: The effects of chest wall compression on expiratory flow rates was different between COPD patients and
Numerical Calculation of the Three-Dimensional Swirling Flow Inside the Centrifugal Pump Volutes
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E. Cezmi Nursen
2003-01-01
Full Text Available The flow inside the volute of a centrifugal pump is threedimensional and, depending upon the position of the inlet relative to the cross-section center line, a single or double swirling flow occurs. The purpose of this study was the calculation of the three-dimensional swirling flow inside the centrifugal pump volute.
National Research Council Canada - National Science Library
Liushuai CAO; Jun ZHU; Guanghui ZENG
2016-01-01
.... In a collaborative exercise, the authors performed calculations on the bare hull DRAPA SUBOFF submarine to investigate the capability of viscous-flow solvers to predict the forces and moments as well...
Directory of Open Access Journals (Sweden)
K. Majidi
2000-01-01
Full Text Available The flow field in volute and circular casings interacting with a centrifugal impeller is obtained by numerical analysis. In the present study, effects of the volute and circular casings on the flow pattern have been investigated by successively combining a volute casing and a circular casing with a single centrifugal impeller. The numerical calculations are carried out with a multiple frame of reference to predict the flow field inside the entire impeller and casings. The impeller flow field is solved in a rotating frame and the flow field in the casings in a stationary frame. The static pressure and velocity in the casing and impeller, and the static pressures and secondary velocity vectors at several cross-sectional planes of the casings are calculated. The calculations show that the curvature of the casings creates pressure gradients that cause vortices at cross-sectional planes of the casings.
Multigrid diagonal implicit solutions for compressible turbulent flows and their evaluation
Varma, Rama Rajaraja
A numerical scheme to solve the two dimensional Navier-Stokes equations is developed and applied to several compressible turbulent flows over airfoils. A method for evaluating the quality of these solutions is then developed and illustrated with representative examples. The distinguishing features of the numerical scheme are its implicitness for improving stability, the diagonalization of the matrices in the implicit operator for computational efficiency, and the implementation within a multigrid procedure for convergence acceleration. A finite volume approximation is used for spatial discretization of the governing equations to handle complicated geometries. Artificial dissipation is added in the form of an adaptive blend of second and fourth differences of the solution to maintain robustness and stability. The viscous terms are treated explicitly to maintain the diagonal form. Results of simulations of viscous transonic flows past airfoils are presented. The computed flow field quantities are compared with those from other computations and experiments to confirm the accuracy of the method. Comparisons of convergence rates are made to demonstrate the efficiency of the method. In solutions to the Navier-Stokes equations it is important that the added numerical dissipation does not overwhelm the real viscous dissipation. In order to verify this, it is necessary to be able to estimate quantitatively the effect of numerical dissipation. A method for estimating the integrated effect of numerical dissipation on solutions to the Navier-Stokes equations is developed in this dissertation. The method is based on integration of the momentum equations and the computation of corrections due to numerical dissipation to the drag integral. These corrections can then be considered as estimates of the error due to dissipation. Solutions to the Navier-Stokes equations for laminar and turbulent flows over airfoils are used to illustrate the method. The errors due to numerical
Finite-time Lyapunov exponent-based analysis for compressible flows
González, D. R.; Speth, R. L.; Gaitonde, D. V.; Lewis, M. J.
2016-08-01
The finite-time Lyapunov exponent (FTLE) technique has shown substantial success in analyzing incompressible flows by capturing the dynamics of coherent structures. Recent applications include river and ocean flow patterns, respiratory tract dynamics, and bio-inspired propulsors. In the present work, we extend FTLE to the compressible flow regime so that coherent structures, which travel at convective speeds, can be associated with waves traveling at acoustic speeds. This is particularly helpful in the study of jet acoustics. We first show that with a suitable choice of integration time interval, FTLE can extract wave dynamics from the velocity field. The integration time thus acts as a pseudo-filter separating coherent structures from waves. Results are confirmed by examining forward and backward FTLE coefficients for several simple, well-known acoustic fields. Next, we use this analysis to identify events associated with intermittency in jet noise pressure probe data. Although intermittent events are known to be dominant causes of jet noise, their direct source in the turbulent jet flow has remained unexplained. To this end, a Large-Eddy Simulation of a Mach 0.9 jet is subjected to FTLE to simultaneously examine, and thus expose, the causal relationship between coherent structures and the corresponding acoustic waves. Results show that intermittent events are associated with entrainment in the initial roll up region and emissive events downstream of the potential-core collapse. Instantaneous acoustic disturbances are observed to be primarily induced near the collapse of the potential core and continue propagating towards the far-field at the experimentally observed, approximately 30° angle relative to the jet axis.
Finite-time Lyapunov exponent-based analysis for compressible flows.
González, D R; Speth, R L; Gaitonde, D V; Lewis, M J
2016-08-01
The finite-time Lyapunov exponent (FTLE) technique has shown substantial success in analyzing incompressible flows by capturing the dynamics of coherent structures. Recent applications include river and ocean flow patterns, respiratory tract dynamics, and bio-inspired propulsors. In the present work, we extend FTLE to the compressible flow regime so that coherent structures, which travel at convective speeds, can be associated with waves traveling at acoustic speeds. This is particularly helpful in the study of jet acoustics. We first show that with a suitable choice of integration time interval, FTLE can extract wave dynamics from the velocity field. The integration time thus acts as a pseudo-filter separating coherent structures from waves. Results are confirmed by examining forward and backward FTLE coefficients for several simple, well-known acoustic fields. Next, we use this analysis to identify events associated with intermittency in jet noise pressure probe data. Although intermittent events are known to be dominant causes of jet noise, their direct source in the turbulent jet flow has remained unexplained. To this end, a Large-Eddy Simulation of a Mach 0.9 jet is subjected to FTLE to simultaneously examine, and thus expose, the causal relationship between coherent structures and the corresponding acoustic waves. Results show that intermittent events are associated with entrainment in the initial roll up region and emissive events downstream of the potential-core collapse. Instantaneous acoustic disturbances are observed to be primarily induced near the collapse of the potential core and continue propagating towards the far-field at the experimentally observed, approximately 30° angle relative to the jet axis.
Spanwise effects on instabilities of compressible flow over a long rectangular cavity
Sun, Y.; Taira, K.; Cattafesta, L. N.; Ukeiley, L. S.
2016-11-01
The stability properties of two-dimensional (2D) and three-dimensional (3D) compressible flows over a rectangular cavity with length-to-depth ratio of L/D=6 are analyzed at a free-stream Mach number of M_∞ =0.6 and depth-based Reynolds number of Re_D=502 . In this study, we closely examine the influence of three-dimensionality on the wake mode that has been reported to exhibit high-amplitude fluctuations from the formation and ejection of large-scale spanwise vortices. Direct numerical simulation (DNS) and bi-global stability analysis are utilized to study the stability characteristics of the wake mode. Using the bi-global stability analysis with the time-averaged flow as the base state, we capture the global stability properties of the wake mode at a spanwise wavenumber of β =0 . To uncover spanwise effects on the 2D wake mode, 3D DNS are performed with cavity width-to-depth ratio of W/D=1 and 2. We find that the 2D wake mode is not present in the 3D cavity flow with W/D=2 , in which spanwise structures are observed near the rear region of the cavity. These 3D instabilities are further investigated via bi-global stability analysis for spanwise wavelengths of λ /D=0.5{-}2.0 to reveal the eigenspectra of the 3D eigenmodes. Based on the findings of 2D and 3D global stability analysis, we conclude that the absence of the wake mode in 3D rectangular cavity flows is due to the release of kinetic energy from the spanwise vortices to the streamwise vortical structures that develops from the spanwise instabilities.
A multilevel approximate projections for incompressible flow calculations
Energy Technology Data Exchange (ETDEWEB)
Howell, L.H. [Lawrence Livermore National Lab., CA (United States)
1994-12-31
An adaptive-mesh projection algorithm for unsteady, variable-density, incompressible flow at high Reynolds number has been developed in the Applied Mathematics Group at LLNL. A grid-based refinement scheme combines the theoretical efficiencies of adaptive methods with the computational advantages of uniform grids, while a second-order Godunov method provides a robust and accurate treatment of advection in the presence of discontinuities without excessive dissipation. This paper focuses on the work of the present author concerning the approximate projection itself, which involves the numerical inversion of the operator {del} {center_dot} (1/{rho}){del} on various subsets of the adaptive grid hierarchy.
Axisymmetric and 3D calculations of melt flow during VCz growth
Bänsch, E.; Davis, D.; Langmach, H.; Miller, W.; Rehse, U.; Reinhardt, G.; Uhle, M.
2004-05-01
Axisymmetric and 3D calculations of melt flow have been performed for a configuration used at the vapour-pressure-controlled Czochalski growth of GaAs single crystals. Thermal boundary conditions were adapted from a global simulation of the temperature field. The axisymmetric calculations with the code NAVIER confirmed the ones previously perfomed with FIDAP TM. The 3D calculations showed that the flow exhibits an asymmetric transient behaviour beyond a certain critical Reynolds number.
Calculation of transonic flow in a linear cascade
Donovan, L. F.
1984-01-01
Turbomachinery blade designs are becoming more aggressive in order to achieve higher loading and greater range. New analysis tools are required to cope with these heavily loaded blades that may operate with a thin separated region near the trailing edge on the suction surface. An existing, viscous airfoil code was adapted to cascade conditions in an attempt to provide this capability. Comparisons with recently obtained data show that calculated and experimental surface Mach numbers were in good agreement but loss coefficients and outlet air angles were not. Previously announced in STAR as N84-24539
Modeling and Simulation of Radiative Compressible Flows in Aerodynamic Heating Arc-Jet Facility
Bensassi, Khalil; Laguna, Alejandro A.; Lani, Andrea; Mansour, Nagi N.
2016-01-01
Numerical simulations of an arc heated flow inside NASA's 20 [MW] Aerodynamics heating facility (AHF) are performed in order to investigate the three-dimensional swirling flow and the current distribution inside the wind tunnel. The plasma is considered in Local Thermodynamics Equilibrium(LTE) and is composed of Air-Argon gas mixture. The governing equations are the Navier-Stokes equations that include source terms corresponding to Joule heating and radiative cooling. The former is obtained by solving an electric potential equation, while the latter is calculated using an innovative massively parallel ray-tracing algorithm. The fully coupled system is closed by the thermodynamics relations and transport properties which are obtained from Chapman-Enskog method. A novel strategy was developed in order to enable the flow solver and the radiation calculation to be preformed independently and simultaneously using a different number of processors. Drastic reduction in the computational cost was achieved using this strategy. Details on the numerical methods used for space discretization, time integration and ray-tracing algorithm will be presented. The effect of the radiative cooling on the dynamics of the flow will be investigated. The complete set of equations were implemented within the COOLFluiD Framework. Fig. 1 shows the geometry of the Anode and part of the constrictor of the Aerodynamics heating facility (AHF). Fig. 2 shows the velocity field distribution along (x-y) plane and the streamline in (z-y) plane.
Central upwind scheme for a compressible two-phase flow model.
Directory of Open Access Journals (Sweden)
Munshoor Ahmed
Full Text Available In this article, a compressible two-phase reduced five-equation flow model is numerically investigated. The model is non-conservative and the governing equations consist of two equations describing the conservation of mass, one for overall momentum and one for total energy. The fifth equation is the energy equation for one of the two phases and it includes source term on the right-hand side which represents the energy exchange between two fluids in the form of mechanical and thermodynamical work. For the numerical approximation of the model a high resolution central upwind scheme is implemented. This is a non-oscillatory upwind biased finite volume scheme which does not require a Riemann solver at each time step. Few numerical case studies of two-phase flows are presented. For validation and comparison, the same model is also solved by using kinetic flux-vector splitting (KFVS and staggered central schemes. It was found that central upwind scheme produces comparable results to the KFVS scheme.
Large scale dynamics in a turbulent compressible rotor/stator cavity flow at high Reynolds number
Lachize, C.; Verhille, G.; Le Gal, P.
2016-08-01
This paper reports an experimental investigation of a turbulent flow confined within a rotor/stator cavity of aspect ratio close to unity at high Reynolds number. The experiments have been driven by changing both the rotation rate of the disk and the thermodynamical properties of the working fluid. This fluid is sulfur hexafluoride (SF6) whose physical properties are adjusted by imposing the operating temperature and the absolute pressure in a pressurized vessel, especially near the critical point of SF6 reached for T c = 45.58 ◦C, P c = 37.55 bar. This original set-up allows to obtain Reynolds numbers as high as 2 × 107 together with compressibility effects as the Mach number can reach 0.5. Pressure measurements reveal that the resulting fully turbulent flow shows both a direct and an inverse cascade as observed in rotating turbulence and in accordance with Kraichnan conjecture for 2D-turbulence. The spectra are however dominated by low-frequency peaks, which are subharmonics of the rotating disk frequency, involving large scale structures at small azimuthal wavenumbers. These modes appear for a Reynolds number around 105 and experience a transition at a critical Reynolds number Re c ≈ 106. Moreover they show an unexpected nonlinear behavior that we understand with the help of a low dimensional amplitude equations.
Numerical analysis of a non equilibrium two-component two-compressible flow in porous media
Saad, Bilal Mohammed
2013-09-01
We propose and analyze a finite volume scheme to simulate a non equilibrium two components (water and hydrogen) two phase flow (liquid and gas) model. In this model, the assumption of local mass non equilibrium is ensured and thus the velocity of the mass exchange between dissolved hydrogen and hydrogen in the gas phase is supposed finite. The proposed finite volume scheme is fully implicit in time together with a phase-by-phase upwind approach in space and it is discretize the equations in their general form with gravity and capillary terms We show that the proposed scheme satisfies the maximum principle for the saturation and the concentration of the dissolved hydrogen. We establish stability results on the velocity of each phase and on the discrete gradient of the concentration. We show the convergence of a subsequence to a weak solution of the continuous equations as the size of the discretization tends to zero. At our knowledge, this is the first convergence result of finite volume scheme in the case of two component two phase compressible flow in several space dimensions.
CFD Simulations of the IHF Arc-Jet Flow: Compression-Pad/Separation Bolt Wedge Tests
Gokcen, Tahir; Skokova, Kristina A.
2017-01-01
This paper reports computational analyses in support of two wedge tests in a high enthalpy arc-jet facility at NASA Ames Research Center. These tests were conducted using two different wedge models, each placed in a free jet downstream of a corresponding different conical nozzle in the Ames 60-MW Interaction Heating Facility. Panel test articles included a metallic separation bolt imbedded in the compression-pad and heat shield materials, resulting in a circular protuberance over a flat plate. As part of the test calibration runs, surface pressure and heat flux measurements on water-cooled calibration plates integrated with the wedge models were also obtained. Surface heating distributions on the test articles as well as arc-jet test environment parameters for each test configuration are obtained through computational fluid dynamics simulations, consistent with the facility and calibration measurements. The present analysis comprises simulations of the non-equilibrium flow field in the facility nozzle, test box, and flow field over test articles, and comparisons with the measured calibration data.
3D reconstruction of a compressible flow by synchronized multi-camera BOS
Nicolas, F.; Donjat, D.; Léon, O.; Le Besnerais, G.; Champagnat, F.; Micheli, F.
2017-05-01
This paper investigates the application of a 3D density reconstruction from a limited number of background-oriented schlieren (BOS) images as recently proposed in Nicolas et al. (Exp Fluids 57(1):1-21, 2016), to the case of compressible flows, such as underexpanded jets. First, an optimization of a 2D BOS setup is conducted to mitigate the intense local blurs observed in raw BOS images and caused by strong density gradients present in the jets. It is demonstrated that a careful choice of experimental conditions enables one to obtain sharp deviation fields from 2D BOS images. Second, a 3DBOS experimental bench involving 12 synchronized cameras is specifically designed for the present study. It is shown that the 3DBOS method can provide physically consistent 3D reconstructions of instantaneous and mean density fields for various underexpanded jet flows issued into quiescent air. Finally, an analysis of the density structure of a moderately underexpanded jet is conducted through phase-averaging, highlighting the development of a large-scale coherent structure associated with a jet shear layer instability.
A versatile embedded boundary adaptive mesh method for compressible flow in complex geometry
Al-Marouf, M.
2017-02-25
We present an embedded ghost-fluid method for numerical solutions of the compressible Navier Stokes (CNS) equations in arbitrary complex domains. A PDE multidimensional extrapolation approach is used to reconstruct the solution in the ghost-fluid regions and imposing boundary conditions on the fluid-solid interface, coupled with a multi-dimensional algebraic interpolation for freshly cleared cells. The CNS equations are numerically solved by the second order multidimensional upwind method. Block-structured adaptive mesh refinement, implemented with the Chombo framework, is utilized to reduce the computational cost while keeping high resolution mesh around the embedded boundary and regions of high gradient solutions. The versatility of the method is demonstrated via several numerical examples, in both static and moving geometry, ranging from low Mach number nearly incompressible flows to supersonic flows. Our simulation results are extensively verified against other numerical results and validated against available experimental results where applicable. The significance and advantages of our implementation, which revolve around balancing between the solution accuracy and implementation difficulties, are briefly discussed as well.
Numerical Study of Water Production from Compressible Moist-Air Flow
Directory of Open Access Journals (Sweden)
sabah hamidi
2016-01-01
Full Text Available In this research a numerical study of water production from compressible moist-air flow by condensing of the vapor component of the atmospheric air through a converging-diverging nozzle is performed. The atmospheric air can be sucked by a vacuum compressor. The geographical conditions represent a hot and humid region, for example Bandar Abbas, Iran, with coordinates, 270 11 ’ N and 560 16’ E and summer climate conditions of about 40℃and relative humidity above 80%. Parametric studies are performed for the atmospheric-air temperature between, 40℃ to 50℃, and relative humidity between49.6% to 100.%. For these ranges of operating conditions and a nozzle with the area ratio of 1.17, the liquid mass flow rates falls in the range 0.272 to 0.376 kg/s. The results show that, the energy consumed by the compressor for production 1 kg of water will be 1.279 kWh. The price of 1 kWh is 372 Rials, therefore the price for the production of 1 kg liquid water will be 475.8 Rials, therefore, the scheme is economically suitable.
Directory of Open Access Journals (Sweden)
Chen Mingtao
2011-01-01
Full Text Available Abstract This article is concerned with global strong solutions of the micro-polar, compressible flow with density-dependent viscosity coefficients in one-dimensional bounded intervals. The important point in this article is that the initial density may vanish in an open subset.
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.
Calculation of shocks in oil reservoir modeling and porous flow
Energy Technology Data Exchange (ETDEWEB)
Concus, P.
1982-03-01
For many enhanced recovery methods propagating fronts arise that may be steep or discontinuous. One example is the waterflooding of a petroleum reservoir, in which there is forced out residual oil that remains after outflow by decompression has declined. In this paper high-resolution numerical methods to solve porous flow problems having propagating discontinuities are discussed. The random choice method can track solution discontinuities sharply and accurately for one space dimension. The first phase of this study adapted this method for solving the Buckley-Leverett equation for immiscible displacement in one space dimension. Extensions to more than one space dimension for the random choice method were carried out subsequently by means of fractional splitting. Because inaccuracies could be introduced for some problems at dicontinuity fronts propagating obliquely to the splitting directions, efforts are currently being directed at investigating alternatives for multidimensional cases.
Kundalkar, Deepak; Singh, Rajkumar; Tewari, Asim
2017-07-01
Friction plays an important role in high-temperature deformation process. Friction affects local displacement field in the tool-workpiece interface region, thus affecting the overall material flow. Under high-temperature compression, macro-indicators like bulge radius and load displacement curves are not sensitive enough to distinguish subtle differences between various friction models. Hence, a new approach to match the experimental Lagrangian flow field with flow field obtained from FE simulation is proposed. For this uniaxial barreling, compression tests at constant temperature were conducted on Gleeble thermo-mechanical simulator. The compression tests were conducted at different strain, strain rate and friction conditions. Finite element simulations employing various friction models and parameters were performed for matching the experimental conditions. Experimental Lagrangian flow fields were obtained from the grain flow lines observed on high-resolution larger area micrographs of the specimen. It was observed that all the investigated friction models provided equally good fit with the macro-experimental indicators (bulge radius and load displacement curves). However, Coulomb friction model was the only friction model that provided the closest fit with the experimentally obtained Lagrangian flow fields. Coulomb friction model provided the best agreement between experimental and numerical simulation for both lubricated and non-lubricated conditions using friction coefficients μ = 0.2993 and μ = 0.3895, respectively.
Garrick, I E; Kaplan, Carl
1944-01-01
The differential equation of Chaplygin's jet problem is utilized to give a systematic development of particular solutions of the hodograph flow equations, which extends the treatment of Chaplygin into the supersonic range and completes the set of particular solutions. The particular solutions serve to place on a reasonable basis the use of velocity correction formulas for the comparison of incompressible and compressible flows. It is shown that the geometric-mean type of velocity correction formula introduced in part I has significance as an over-all type of approximation in the subsonic range. A brief review of general conditions limiting the potential flow of an adiabatic compressible fluid is given and application is made to the particular solutions, yielding conditions for the existence of singular loci in the supersonic range. The combining of particular solutions in accordance with prescribed boundary flow conditions is not treated in the present paper.
Garrick, I. E.; Kaplan, Carl
1944-01-01
The differential equation of Chaplygin's jet problem is utilized to give a systematic development of particular solutions of the hodograph flow equations, which extends the treatment of Chaplygin into the supersonic range and completes the set of particular solutions. The particular solutions serve to place on a reasonable basis the use of velocity correction formulas for the comparison of incompressible and compressible flows. It is shown that the geometric-mean type of velocity correction formula introduced in part I has significance as an over-all type of approximation in the subsonic range. A brief review of general conditions limiting the potential flow of an adiabatic compressible fluid is given and application is made to the particular solutions, yielding conditions for the existence of singular loci in the supersonic range. The combining of particular solutions in accordance with prescribed boundary flow conditions is not treated in the present paper.
Institute of Scientific and Technical Information of China (English)
Ling Li; Ming-Shun Yuan
2011-01-01
In this paper the effects of hydrophobic wall on skin-friction drag in the channel flow are investigated through large eddy simulation on the basis of weaklycompressible flow equations with the MacCormack's scheme on collocated mesh in the FVM framework. The slip length model is adopted to describe the behavior of the slip velocities in the streamwise and spanwise directions at the interface between the hydrophobic wall and turbulent channel flow. Simulation results are presented by analyzing flow behaviors over hydrophobic wall with the Smagorinky subgrid-scale model and a dynamic model on computational meshes of different resolutions. Comparison and analysis are made on the distributions of timeaveraged velocity, velocity fluctuations, Reynolds stress as well as the skin-friction drag. Excellent agreement between the present study and previous results demonstrates the accuracy of the simple classical second-order scheme in representing turbulent vertox near hydrophobic wall. In addition, the relation of drag reduction efficiency versus time-averaged slip velocity is established. It is also found that the decrease of velocity gradient in the close wall region is responsible for the drag reduction. Considering its advantages of high calculation precision and efficiency, the present method has good prospect in its application to practical projects.
Energy Technology Data Exchange (ETDEWEB)
Kobus, C.J.; Wedekind, G.L.; Bhatt, B.L.
2000-02-01
An equivalent single-tube model concept was extended to predict the frequency-response characteristics of multitube two-phase condensing flow systems, complete with the ability to predict the influence of compressibility and thermal and flow distribution asymmetry. The predictive capability of the equivalent single-tube model was verified experimentally with extensive data that encompassed a three-order-of-magnitude range of frequencies, and a wide range of operating parameters.
A Semi-Hydrostatic Theory of Gravity-Dominated Compressible Flow
Dubos, T.; Voitus, F.
2014-12-01
Compressible Euler equations support the propagation of acoustic waves. Although much progress has been achieved towards efficient and accurate solutions to the resulting numerical difficulties, it can still be desirable to identify "unified" equations of motion that would not support acoustic waves while retaining accuracy at large and small scales. Even if such equations are eventually not chosen as the basis of a numerical model, they may help identifying the independent degrees of freedom of the atmospheric flow to be modeled and how the dependent fields are related to the independent fields. From Hamilton's least action principle (HP), "semi-hydrostatic" compressible equations of motion with density diagnosed from potential temperature through hydrostatic balance are derived. Energy, potential vorticity and momentum are conserved. Slaving density to potential temperature suppresses the degrees of freedom supporting the propagation of acoustic waves and results in a sound-proof system. Scale analysis and linear normal modes analysis for an isothermal state of rest suggest that the semy-hydrostatic system is accurate from hydrostatic to non-hydrostatic scales, except for deep internal gravity waves (Figure : decimal logarithm of relative error of the frequency of internal normal modes of a non-rotating isothermal atmosphere as a function of horizontal and vertical wavenumbers k,m normalized by the scale height H). Especially the Lamb wave and long Rossby waves are not distorted, unlike with anelastic or pseudo-incompressible systems. Compared to similar equations derived by Arakawa and Konor (2009), the semi-hydrostatic system possesses an additional term in the horizontal momentum budget. This term is an apparent force resulting from the vertical coordinate not being the actual height of an air parcel, but its hydrostatic height, i.e. the hypothetical height it would have after the atmospheric column it belongs to has reached hydrostatic balance through
Multi-scale Modeling of Compressible Single-phase Flow in Porous Media using Molecular Simulation
Saad, Ahmed Mohamed
2016-05-01
In this study, an efficient coupling between Monte Carlo (MC) molecular simulation and Darcy-scale flow in porous media is presented. The cell-centered finite difference method with a non-uniform rectangular mesh were used to discretize the simulation domain and solve the governing equations. To speed up the MC simulations, we implemented a recently developed scheme that quickly generates MC Markov chains out of pre-computed ones, based on the reweighting and reconstruction algorithm. This method astonishingly reduces the required computational time by MC simulations from hours to seconds. In addition, the reweighting and reconstruction scheme, which was originally designed to work with the LJ potential model, is extended to work with a potential model that accounts for the molecular quadrupole moment of fluids with non-spherical molecules such as CO2. The potential model was used to simulate the thermodynamic equilibrium properties for single-phase and two-phase systems using the canonical ensemble and the Gibbs ensemble, respectively. Comparing the simulation results with the experimental data showed that the implemented model has an excellent fit outperforming the standard LJ model. To demonstrate the strength of the proposed coupling in terms of computational time efficiency and numerical accuracy in fluid properties, various numerical experiments covering different compressible single-phase flow scenarios were conducted. The novelty in the introduced scheme is in allowing an efficient coupling of the molecular scale and Darcy scale in reservoir simulators. This leads to an accurate description of the thermodynamic behavior of the simulated reservoir fluids; consequently enhancing the confidence in the flow predictions in porous media.
Development of a three dimensional compressible flow calibration facility for thermal anemometry
Morrison, Evan Samson Sprung
Measurements of unsteady, three-dimensional turbomachinery flowfields are needed to improve the computational models in predictive tools used in the design process of new turbomachines. Hot-wire anemometers, which offer a high frequency response for a relatively low cost, are one of the most common methods for investigating turbulent flows. Triple-wire sensors provide a means of obtaining simultaneous measurements of all three velocity components but require a significantly more complicated calibration scheme than single-wire sensors. In addition, the heat transfer from a hot-wire is dependent not only on the flow velocity but also the temperature and density, which must be accounted for through calibration and correction factors. To enable triple-wire hot-wire measurements in the Purdue 3-Stage Axial Compressor Facility, a new compressible flow calibration facility has been developed which can position the probe through a range of pitch and yaw angles and provide a means to derive temperature and density correction factors specific to each probe. A lookup table method is used to convert the voltage signals back to velocities and angles. The calibration facility can reach velocities in excess of 500 ft/s, temperatures up to 155°F and densities up to 0.090 lbm/ft3. The velocity is accurate to within 3.5 ft/s, temperature control accurate to within 1°F and density to within 5.5x10-5 lbm/ft3. A triple-wire fiber-film probe was used to validate the calibration method, and was able to resolve the three-dimensional flowfield downstream of a rotor.
Turbulent Flow Physics and Noise in High Reynolds Number Compressible Jets
Glauser, Mark
2016-11-01
In this talk I will present a snapshot of our ongoing research in high Reynolds number turbulent compressible jets. The high speed axisymmetric jet work (Mach 0.6 - 1.1) has been jointly performed with Spectral Energies LLC through AFRL support and involves 10 kHz and large window PIV data extracted from the near field jet plume, simultaneously sampled with near field pressure and far field noise. We have learned from the simultaneously sampled 10 kHz PIV near field plume and far field noise data, using POD/OID and Wavelet filtering, that there are certain "loud" velocity modes that have low averaged turbulent kinetic energy content but strongly correlate with the far field noise. From the large window PIV data obtained at Mach 1.0 and 1.1, specific POD modes were found to contain important physics of the problem. For example, the large-scale structure of the jet, shock-related fluctuations, and turbulent mixing regions of the flow were isolated through POD. By computing cross correlations, particular POD modes were found to be related to particular noise spectra. I will conclude with a description of our complex nozzle work which uses the multi-stream supersonic single expansion rectangular nozzle (SERN) recently installed in our large anechoic chamber at SU. This work is funded from both AFOSR (joint with OSU with a primary focus on flow physics) and Spectral Energies LLC (via AFRL funds with a focus on noise). Particular emphasis will be on insight gained into this complex 3D flow field (and its relationship to the far field noise) from applications of POD, Wavelet filtering and DMD to various numerical (LES) and experimental (PIV, high speed schlieren, near and far field pressure) data sets, at a core nozzle Mach number of 1.6 and a second stream Mach number of 1.0.
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Using the T63L16 analysis data with the resolution of 1.875╳1.875 degree of latitude and longitude obtained from National Meteorological Center (NMC) and the real central position information of tropical cyclone (referred to as TC hereafter) numbered by NMC, the basic environmental geostrophic flow at 126 time levels of 25 TCs in 1996 are calculated. The vertical distribution features of the flows are analyzed. Besides, the deviation of real TC tracks from the flows (referred as steering deviation hereafter, namely, the deviation between the real central position of TC and the position calculated according to the steering flow) is also investigated. The result shows that the steering deviation would be different if the domain used to calculate the steering flow is different. The present paper obtains the optimum domain size to calculate the steering flow. It is found that the steering deviation is related to the velocity of steering flow and the initial latitude and intensity of TC itself, and that TC motion has relationship with the vertical shear structure of environmental geostrophic flow. The result also shows that the optimum steering flow is the deep-layer averaged basic flow from 1000 hPa to 200 hPa. Having the knowledge of these principle and features would help make accurate forecast of TC motion.
Calculation of the Instream Ecological Flow of the Wei River Based on Hydrological Variation
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Shengzhi Huang
2014-01-01
Full Text Available It is of great significance for the watershed management department to reasonably allocate water resources and ensure the sustainable development of river ecosystems. The greatly important issue is to accurately calculate instream ecological flow. In order to precisely compute instream ecological flow, flow variation is taken into account in this study. Moreover, the heuristic segmentation algorithm that is suitable to detect the mutation points of flow series is employed to identify the change points. Besides, based on the law of tolerance and ecological adaptation theory, the maximum instream ecological flow is calculated, which is the highest frequency of the monthly flow based on the GEV distribution and very suitable for healthy development of the river ecosystems. Furthermore, in order to guarantee the sustainable development of river ecosystems under some bad circumstances, minimum instream ecological flow is calculated by a modified Tennant method which is improved by replacing the average flow with the highest frequency of flow. Since the modified Tennant method is more suitable to reflect the law of flow, it has physical significance, and the calculation results are more reasonable.
Energy Technology Data Exchange (ETDEWEB)
Park, S.R. [Inha University, Inchon (Korea); Kim, Y.J.; Kim, T.W. [Doowon Technical College, Ansung (Korea)
1999-12-01
This paper presents a quasi-three-dimensional calculation method considered a spanwise mixing effect in a diagonal flow impeller. The effect of this spanwise mixing caused by spanwise distribution of blade loading is evaluated by a secondary flow theory. In order to verify the validity of this method, it is applied to the analysis of a diagonal flow fan designed under a vortex type of constant circumferential velocity and that of a free vortex. The comparison of the calculated result with experimental data shows a good agreement except the regions near the casing where the flow field is affected by the tip leakage flow. (author). 18 refs., 10 figs.
Chen, Yang M; Wu, Qiang; Geng, Hua Y; Yan, Xiao Z; Wang, Yi X; Wang, Zi W
2016-01-01
High pressure and high temperature properties of AB (A = $^6$Li, $^7$Li; B = H, D, T) are investigated with first-principles method comprehensively. It is found that the H$^{-}$ sublattice features in the low-pressure electronic structure near the Fermi level of LiH are shifted to that dominated by the Li$^{+}$ sublattice in compression. The lattice dynamics is studied in quasi-harmonic approximation, from which the phonon contribution to the free energy and the isotopic effects are accurately modelled with the aid of a parameterized double-Debye model. The obtained equation of state (EOS) matches perfectly with available static experimental data. The calculated principal Hugoniot is also in accordance with that derived from shock wave experiments. Using the calculated principal Hugoniot and the previous theoretical melting curve, we predict a shock melting point at 56 GPa and 1923 K. In order to establish the phase diagram for LiH, the phase boundaries between the B1 and B2 solid phases are explored. The B1-...
Three-dimensional hypersonic rarefied flow calculations using direct simulation Monte Carlo method
Celenligil, M. Cevdet; Moss, James N.
1993-01-01
A summary of three-dimensional simulations on the hypersonic rarefied flows in an effort to understand the highly nonequilibrium flows about space vehicles entering the Earth's atmosphere for a realistic estimation of the aerothermal loads is presented. Calculations are performed using the direct simulation Monte Carlo method with a five-species reacting gas model, which accounts for rotational and vibrational internal energies. Results are obtained for the external flows about various bodies in the transitional flow regime. For the cases considered, convective heating, flowfield structure and overall aerodynamic coefficients are presented and comparisons are made with the available experimental data. The agreement between the calculated and measured results are very good.
Turbulent Compressible Convection with Rotation. Part 1; Flow Structure and Evolution
Brummell, Nicholas H.; Hurlburt, Neal E.; Toomre, Juri
1996-01-01
The effects of Coriolis forces on compressible convection are studied using three-dimensional numerical simulations carried out within a local modified f-plane model. The physics is simplified by considering a perfect gas occupying a rectilinear domain placed tangentially to a rotating sphere at various latitudes, through which a destabilizing heat flux is driven. The resulting convection is considered for a range of Rayleigh, Taylor, and Prandtl (and thus Rossby) numbers, evaluating conditions where the influence of rotation is both weak and strong. Given the computational demands of these high-resolution simulations, the parameter space is explored sparsely to ascertain the differences between laminar and turbulent rotating convection. The first paper in this series examines the effects of rotation on the flow structure within the convection, its evolution, and some consequences for mixing. Subsequent papers consider the large-scale mean shear flows that are generated by the convection, and the effects of rotation on the convective energetics and transport properties. It is found here that the structure of rotating turbulent convection is similar to earlier nonrotating studies, with a laminar, cellular surface network disguising a fully turbulent interior punctuated by vertically coherent structures. However, the temporal signature of the surface flows is modified by inertial motions to yield new cellular evolution patterns and an overall increase in the mobility of the network. The turbulent convection contains vortex tubes of many scales, including large-scale coherent structures spanning the full vertical extent of the domain involving multiple density scale heights. Remarkably, such structures align with the rotation vector via the influence of Coriolis forces on turbulent motions, in contrast with the zonal tilting of streamlines found in laminar flows. Such novel turbulent mechanisms alter the correlations which drive mean shearing flows and affect the
Pre-test CFD Calculations for a Bypass Flow Standard Problem
Energy Technology Data Exchange (ETDEWEB)
Rich Johnson
2011-11-01
The bypass flow in a prismatic high temperature gas-cooled reactor (HTGR) is the flow that occurs between adjacent graphite blocks. Gaps exist between blocks due to variances in their manufacture and installation and because of the expansion and shrinkage of the blocks from heating and irradiation. Although the temperature of fuel compacts and graphite is sensitive to the presence of bypass flow, there is great uncertainty in the level and effects of the bypass flow. The Next Generation Nuclear Plant (NGNP) program at the Idaho National Laboratory has undertaken to produce experimental data of isothermal bypass flow between three adjacent graphite blocks. These data are intended to provide validation for computational fluid dynamic (CFD) analyses of the bypass flow. Such validation data sets are called Standard Problems in the nuclear safety analysis field. Details of the experimental apparatus as well as several pre-test calculations of the bypass flow are provided. Pre-test calculations are useful in examining the nature of the flow and to see if there are any problems associated with the flow and its measurement. The apparatus is designed to be able to provide three different gap widths in the vertical direction (the direction of the normal coolant flow) and two gap widths in the horizontal direction. It is expected that the vertical bypass flow will range from laminar to transitional to turbulent flow for the different gap widths that will be available.
Energy Technology Data Exchange (ETDEWEB)
Held, E.D. [Univ. of Wisconsin, Madison, WI (United States). Center for Plasma Theory and Computation; Leboeuf, J.N.; Carreras, B.A. [Oak Ridge National Lab., TN (United States). Fusion Energy Div.
1998-07-01
The linear and nonlinear stability of a nonmonotonic q profile is examined using a reduced set of magnetohydrodynamic (MHD) equations with an equilibrium, sheared toroidal flow. The reversed shear profile is shown to be unstable to a rich variety of resistive MHD modes including pressure-driven instabilities and tearing instabilities possessing a tearing/interchange character at low Lundquist number, S, and taking on a double/triple tearing structure at high S. Linear calculations show that the destabilizing effect of toroidal velocity shear on tearing modes is enhanced at finite pressure seen previously for tearing modes at high S. Nonlinear calculations show the generation of a large, m = 1, n = 0, Reynolds-stress-driven poloidal flow in the absence of significant flow damping. Calculations in which the poloidal flow was heavily damped show that sub-Alfvenic, sheared toroidal flows have a minimal effect on weakly-coupled, localized instabilities.
NUMERICAL CALCULATION OF SOLID-LIQUID TWO PHASE FLOW BETWEEN STAY VANES IN HYDRAULIC TURBINE
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
In this paper, an energy equation of silt-laden water flow is educed based on the energy equation of continuum fluid flow. The dissipation functions of liquid phase and solid phase are presented respectively. Then the extremity law of energy dissipation rate is introduced for the research of the silt-laden water flow and a new mathematical model is developed. The corresponding procedure based on the finite difference method (FDM) is developed to calculate the two phase flow in hydraulic turbine. The method is applied to analyze the silt-laden water flow between stay vanes, and the numerical results are in good agreement with the experimental ones.
Direct numerical simulation of a compressible multiphase flow through the fast Eulerian approach
Cerminara, Matteo; Ongaro, Tomaso Esposti; Salvetti, Maria Vittoria
2014-01-01
Our work is motivated by the analysis of ash plume dynamics, arising in the study of volcanic eruptions. Such phenomena are characterized by large Reynolds number (exceeding $10^7$) and a large number of polydispersed particles~[1]. Thus, the choice of the methodology to be used is straightforward: we need LES of a multiphase gas-particles flow. Since the simulation of the behavior of a large number of dispersed particles is very difficult with Lagrangian methods, we model the particles as a continuum, Eulerian fluid (dust), by using reduced models involving two fluids, as proposed in Ref.~[2,3,4]. Moreover, we need a robust numerical scheme to simultaneously treat compressibility, buoyancy effects and turbulent dispersal dynamics. We analyze the turbulence properties of such models in a homogeneous and isotropic setting, with the aim of formulating a LES model. In particular, we examine the development of freely decaying homogeneous and isotropic turbulence in subsonic regime (the r.m.s. Mach number either 0...
On the modelling of compressible inviscid flow problems using AUSM schemes
Directory of Open Access Journals (Sweden)
Hajžman M.
2007-11-01
Full Text Available During last decades, upwind schemes have become a popular method in the field of computational fluid dynamics. Although they are only first order accurate, AUSM (Advection Upstream Splitting Method schemes proved to be well suited for modelling of compressible flows due to their robustness and ability of capturing shock discontinuities. In this paper, we review the composition of the AUSM flux-vector splitting scheme and its improved version noted AUSM+, proposed by Liou, for the solution of the Euler equations. Mach number splitting functions operating with values from adjacent cells are used to determine numerical convective fluxes and pressure splitting is used for the evaluation of numerical pressure fluxes. Both versions of the AUSM scheme are applied for solving some test problems such as one-dimensional shock tube problem and three dimensional GAMM channel. Features of the schemes are discussed in comparison with some explicit central schemes of the first order accuracy (Lax-Friedrichs and of the second order accuracy (MacCormack.
Ramsey, Scott; Baty, Roy
2015-11-01
This work considers the group invariance properties of the inviscid compressible flow equations (Euler equations) under the assumptions of one-dimensional symmetry and a modified Tait equation of state (EOS) closure model. When written in terms of an adiabatic bulk modulus, a transformed version of these equations is found to be identical to that for an ideal gas EOS. As a result, the Lie group invariance structure of these equations - and their subsequent reduction to a lower-order system - is identical to the published results for the ideal gas case. Following the reduction of the Euler equations to a system of ordinary differential equations, a variety of elementary closed-form solutions are derived. These solutions are then used in conjunction with the Rankine-Hugoniot conditions to construct discontinuous shock wave and free surface solutions that are analogous to the classical Noh, Sedov, Guderley, and Hunter similarity solutions of the Euler equations for an ideal gas EOS. The versions of these problems for the modified Tait EOS are found to be semi-analytic in that a transcendental root extraction (and in some cases numerical integration of ordinary differential equations) enables solution of the relevant equations.
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Ahmed M. Elsayed
2013-01-01
Full Text Available Film cooling is vital to gas turbine blades to protect them from high temperatures and hence high thermal stresses. In the current work, optimization of film cooling parameters on a flat plate is investigated numerically. The effect of film cooling parameters such as inlet velocity direction, lateral and forward diffusion angles, blowing ratio, and streamwise angle on the cooling effectiveness is studied, and optimum cooling parameters are selected. The numerical simulation of the coolant flow through flat plate hole system is carried out using the “CFDRC package” coupled with the optimization algorithm “simplex” to maximize overall film cooling effectiveness. Unstructured finite volume technique is used to solve the steady, three-dimensional and compressible Navier-Stokes equations. The results are compared with the published numerical and experimental data of a cylindrically round-simple hole, and the results show good agreement. In addition, the results indicate that the average overall film cooling effectiveness is enhanced by decreasing the streamwise angle for high blowing ratio and by increasing the lateral and forward diffusion angles. Optimum geometry of the cooling hole on a flat plate is determined. In addition, numerical simulations of film cooling on actual turbine blade are performed using the flat plate optimal hole geometry.
Generalized adjoint consistent treatment of wall boundary conditions for compressible flows
Hartmann, Ralf; Leicht, Tobias
2015-11-01
In this article, we revisit the adjoint consistency analysis of Discontinuous Galerkin discretizations of the compressible Euler and Navier-Stokes equations with application to the Reynolds-averaged Navier-Stokes and k- ω turbulence equations. Here, particular emphasis is laid on the discretization of wall boundary conditions. While previously only one specific combination of discretizations of wall boundary conditions and of aerodynamic force coefficients has been shown to give an adjoint consistent discretization, in this article we generalize this analysis and provide a discretization of the force coefficients for any consistent discretization of wall boundary conditions. Furthermore, we demonstrate that a related evaluation of the cp- and cf-distributions is required. The freedom gained in choosing the discretization of boundary conditions without loosing adjoint consistency is used to devise a new adjoint consistent discretization including numerical fluxes on the wall boundary which is more robust than the adjoint consistent discretization known up to now. While this work is presented in the framework of Discontinuous Galerkin discretizations, the insight gained is also applicable to (and thus valuable for) other discretization schemes. In particular, the discretization of integral quantities, like the drag, lift and moment coefficients, as well as the discretization of local quantities at the wall like surface pressure and skin friction should follow as closely as possible the discretization of the flow equations and boundary conditions at the wall boundary.
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.
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.
A finite point method for adaptive-three-dimensional compressible flow calculations
Ortega, Enrique; Oñate Ibáñez de Navarra, Eugenio; Idelsohn Barg, Sergio Rodolfo
2009-01-01
Electronic version of an article published as "International journal for numerical methods in fluids", vol. 60, no 9, 2009, p. 937-971. DOI:10.1002/fld.1892 The finite point method (FPM) is a meshless technique, which is based on both, a weighted least-squares numerical approximation on local clouds of points and a collocation technique which allows obtaining the discrete system of equations. The research work we present is part of a broader investigation into the capabilities of the FPM...
Viscous-flow calculations for KVLCC2 in deep and shallow water
Toxopeus, S.L.
2011-01-01
In the SIMMAN 2008 workshop, the capability of CFD tools to predict the flow around manoeuvring ships has been investigated. It was decided to continue this effort but to extend the work to the flow around ships in shallow water. In this paper, CFD calculations for the KLVCC2 are presented. The aim
Viscous-flow calculations for KVLCC2 in deep and shallow water
Toxopeus, S.L.
2011-01-01
In the SIMMAN 2008 workshop, the capability of CFD tools to predict the flow around manoeuvring ships has been investigated. It was decided to continue this effort but to extend the work to the flow around ships in shallow water. In this paper, CFD calculations for the KLVCC2 are presented. The aim
FINITE DIFFERENCE METHOD FOR CALCULATING OF THE GAS FLOW IN A SUBSONIC GAS EJECTOR
Directory of Open Access Journals (Sweden)
Kostjantin Kapitanchuk
2015-12-01
Full Text Available Describe analysis of eddy viscosity actual mathematical models for numerical simulation a reversal gas flow in subsonic gas ejector. Considered advantages and disadvantages each of it. Proposed use method of finite elements for provides viscous gas flow calculation of gas ejectors.
Directory of Open Access Journals (Sweden)
Shan Yang
2016-01-01
Full Text Available Power flow calculation and short circuit calculation are the basis of theoretical research for distribution network with inverter based distributed generation. The similarity of equivalent model for inverter based distributed generation during normal and fault conditions of distribution network and the differences between power flow and short circuit calculation are analyzed in this paper. Then an integrated power flow and short circuit calculation method for distribution network with inverter based distributed generation is proposed. The proposed method let the inverter based distributed generation be equivalent to Iθ bus, which makes it suitable to calculate the power flow of distribution network with a current limited inverter based distributed generation. And the low voltage ride through capability of inverter based distributed generation can be considered as well in this paper. Finally, some tests of power flow and short circuit current calculation are performed on a 33-bus distribution network. The calculated results from the proposed method in this paper are contrasted with those by the traditional method and the simulation method, whose results have verified the effectiveness of the integrated method suggested in this paper.
Dynamic relaxation processes in compressible multiphase flows. Application to evaporation phenomena
Directory of Open Access Journals (Sweden)
Le Métayer O.
2013-07-01
Full Text Available Phase changes and heat exchanges are examples of physical processes appearing in many industrial applications involving multiphase compressible flows. Their knowledge is of fundamental importance to reproduce correctly the resulting effects in simulation tools. A fine description of the flow topology is thus required to obtain the interfacial area between phases. This one is responsible for the dynamics and the kinetics of heat and mass transfer when evaporation or condensation occurs. Unfortunately this exchange area cannot be obtained easily and accurately especially when complex mixtures (drops, bubbles, pockets of very different sizes appear inside the transient medium. The natural way to solve this specific trouble consists in using a thin grid to capture interfaces at all spatial scales. But this possibility needs huge computing resources and can be hardly used when considering physical systems of large dimensions. A realistic method is to consider instantaneous exchanges between phases by the way of additional source terms in a full non-equilibrium multiphase flow model [2,15,17]. In this one each phase obeys its own equation of state and has its own set of equations and variables (pressure, temperature, velocity, energy, entropy,.... When enabling the relaxation source terms the multiphase mixture instantaneously tends towards a mechanical or thermodynamic equilibrium state at each point of the flow. This strategy allows to mark the boundaries of the real flow behavior and to magnify the dominant physical effects (heat exchanges, evaporation, drag,... inside the medium. A description of the various relaxation processes is given in the paper. Les changements de phase et les transferts de chaleur sont des exemples de phénomènes physiques présents dans de nombreuses applications industrielles faisant intervenir des écoulements compressibles multiphasiques. La connaissance des mécanismes associés est primordiale afin de reproduire
40 CFR 1065.642 - SSV, CFV, and PDP molar flow rate calculations.
2010-07-01
... 40 Protection of Environment 32 2010-07-01 2010-07-01 false SSV, CFV, and PDP molar flow rate calculations. 1065.642 Section 1065.642 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Calculations and Data Requirements § 1065.642...
Lan, C. Edward
1985-01-01
A computer program based on the Quasi-Vortex-Lattice Method of Lan is presented for calculating longitudinal and lateral-directional aerodynamic characteristics of nonplanar wing-body combination. The method is based on the assumption of inviscid subsonic flow. Both attached and vortex-separated flows are treated. For the vortex-separated flow, the calculation is based on the method of suction analogy. The effect of vortex breakdown is accounted for by an empirical method. A summary of the theoretical method, program capabilities, input format, output variables and program job control set-up are described. Three test cases are presented as guides for potential users of the code.
Finite element calculations of viscoelastic fluid flow in a spinning and nutating cylinder
Rosenblat, S.; Gooding, A.; Engleman, M. S.
1986-12-01
An investigation has been performed of the flow of a non-Newtonian liquid in a spinning and nutating cylinder. An approximate analysis has been effected on the assumption that the ratio of coning rate to spin rate is small and applied to the case of a cylinder of infinite length. A numerical calculation has been performed for the actual flow of two specified non-Newtonian liquids, using the finite element code FIDAP. Results are presented in both graphical and tabular form showing flow fields and calculated values of the despin moment for ranges of parameters. The question of appropriate representation of the liquid's non-Newtonian behavior is discussed.
A Computer Program to Calculate the Supersonic Flow over a Solid Cone in Air or Water.
1984-06-01
ix air or water. The rain objective is to calculate the ccne semi-vertei angle given prescribed initial ccndi- tions. The program is written in...tc the motion of the metal jet frcm an explczive shaped-charge fired underwater. A tiical result for supersonic flow over a ccne in water is as follcws...the ccne semi-vertex angle is calculated to be 7.23 degrees. Gene rally, pressures invclved in water flow are much larger than for air flow, and the
Directory of Open Access Journals (Sweden)
Guoqiang Wang
2014-01-01
Full Text Available Effect of anisotropy in compression is studied on hot rolling of AZ31 magnesium alloy with a three-dimensional constitutive model based on the quadratic Hill48 yield criterion and nonassociated flow rule (non-AFR. The constitutive model is characterized by compressive tests of AZ31 billets since plastic deformations of materials are mostly caused by compression during rolling processes. The characterized plasticity model is implemented into ABAQUS/Explicit as a user-defined material subroutine (VUMAT based on semi-implicit backward Euler's method. The subroutine is employed to simulate square-bar rolling processes. The simulation results are compared with rolled specimens and those predicted by the von Mises and the Hill48 yield function under AFR. Moreover, strip rolling is also simulated for AZ31 with the Hill48 yield function under non-AFR. The strip rolling simulation demonstrates that the lateral spread generated by the non-AFR model is in good agreement with experimental data. These comparisons between simulation and experiments validate that the proposed Hill48 yield function under non-AFR provides satisfactory description of plastic deformation behavior in hot rolling for AZ31 alloys in case that the anisotropic parameters in the Hill48 yield function and the non-associated flow rule are calibrated by the compressive experimental results.
Naftal', M. M.; Baranenko, V. I.; Gulina, O. M.
2014-06-01
The results obtained from calculations of flow accelerated corrosion of equipment and pipelines operating at nuclear power plants constructed on the basis of PWR, VVER, and RBMK reactors carried out using the EKI-02 and EKI-03 software tools are presented. It is shown that the calculation error does not exceed its value indicated in the qualification certificates for these software tools. It is pointed out that calculations aimed at predicting the service life of pipelines and efficient surveillance of flow accelerated corrosion wear are hardly possible without using the above-mentioned software tools.
Mohammed, H. E. Abu-Sei'leek
2011-01-01
A non-relativistic microscopic mean field theory of finite nuclei is investigated where the nucleus is described as a collection of nucleons and delta resonances. The ground state properties of 90Zr nucleus have been investigated at equilibrium and large amplitude compression using a realistic effective baryon-baryon Hamiltonian based on Reid Soft Core (RSC) potential. The sensitivity of the ground state properties is studied, such as binding energy, nuclear radius, radial density distribution, and single particle energies to the degree of compression. It is found that the most of increasing in the nuclear energy generated under compression is used to create the massive Δ particles. For 90Zr nucleus under compression at 2.5 times density of the normal nuclear density, the excited nucleons to Δ's are increased sharply up to 14% of the total number of constituents. This result is consistent with the values extracted from relativistic heavy-ion collisions. The single particle energy levels are calculated and their behaviors under compression are examined too. A good agreement between results with effective Hamiltonian and the phenomenological shell model for the low lying single-particle spectra is obtained. A considerable reduction in compressibility for the nucleus, and softening of the equation of state with the inclusion of the Δ's in the nuclear dynamics are suggested by the results.
Degani, D.
1984-01-01
A numerical algorithm that is second-order accurate in time has been developed for the conjugated problem of a separated, compressible flow field and a conductive solid body. The full two-dimensional time-dependent Navier-Stokes equations are coupled with the time-dependent energy equation for the solid body and are solved simultaneously. using implicit algorithms. The energy equation for the solid body may include arbitrarily distributed heat sources. The algorithm has been exmined for the case of two-dimensional supersonic compression-corner interaction, with a heat source embedded in the wall in the vicinity of the separation bubble and the attached boundary layer. The effect of the heat source on the flow field is studied for steady and transient cases.
PSFC: a Pathway Signal Flow Calculator App for Cytoscape [version 2; referees: 2 approved
Directory of Open Access Journals (Sweden)
Lilit Nersisyan
2017-04-01
Full Text Available Cell signaling pathways are sequences of biochemical reactions that propagate an input signal, such as a hormone binding to a cell-surface receptor, into the cell to trigger a reactive process. Assessment of pathway activities is crucial for determining which pathways play roles in disease versus normal conditions. To date various pathway flow/perturbation assessment tools are available, however they are constrained to specific algorithms and specific data types. There are no accepted standards for evaluation of pathway activities or simulation of flow propagation events in pathways, and the results of different software are difficult to compare. Here we present Pathway Signal Flow Calculator (PSFC, a Cytoscape app for calculation of a pathway signal flow based on the pathway topology and node input data. The app provides a rich framework for customization of different signal flow algorithms to allow users to apply various approaches within a single computational framework.
PSFC: a Pathway Signal Flow Calculator App for Cytoscape [version 1; referees: 2 approved
Directory of Open Access Journals (Sweden)
Lilit Nersisyan
2015-08-01
Full Text Available Cell signaling pathways are sequences of biochemical reactions that propagate an input signal, such as a hormone binding to a cell-surface receptor, into the cell to trigger a reactive process. Assessment of pathway activities is crucial for determining which pathways play roles in disease versus normal conditions. To date various pathway flow/perturbation assessment tools are available, however they are constrained to specific algorithms and specific data types. There are no accepted standards for evaluation of pathway activities or simulation of flow propagation events in pathways, and the results of different software are difficult to compare. Here we present Pathway Signal Flow Calculator (PSFC, a Cytoscape app for calculation of a pathway signal flow based on the pathway topology and node input data. The app provides a rich framework for customization of different signal flow algorithms to allow users to apply various approaches within a single computational framework.
Michalek, Arthur J.; Iatridis, James C.
2011-01-01
Extensive experimental work on the effects of penetrating annular injuries indicated that large injuries impact axial compressive properties of small animal intervertebral discs, yet there is some disagreement regarding the sensitivity of mechanical tests to small injury sizes. In order to understand the mechanism of injury size sensitivity, this study proposed a simple one dimensional model coupling elastic deformations in the annulus with fluid flow into and out of the nucleus through both ...
Institute of Scientific and Technical Information of China (English)
刘法贵; 孔德兴
2004-01-01
By means of maximum principle for nonlinear hyperbolic systems,the results given by HSIAO Ling and D.Serre was improved for Cauchy problem of compressible adiabatic flow through porous media,and a complete result on the global existence and the blow-up phenomena of classical solutions of these systems.These results show that the dissipation is strong enough to preserve the smoothness of 'small ' solution.
CALCULATION OF SPLITTING VANES AND INNER FLOW ANALYSIS FOR CENTRIFUGAL PUMP IMPELLER
Institute of Scientific and Technical Information of China (English)
Pan Zhongyong; Yuan Shouqi; Li Hong; Cao Weidong
2004-01-01
The calculation method for vane numbers is obtained on the intention that it should have no back flow area in the flow passage of centrifugal passage.Then a criterion that the design of splitting vanes of centrifugal compound impeller should ensure that the back flow area ratio be the minimum is proposed.On the basis of the criterion, the slippery theory is used as one of CFD methods to analyze the inner flow field of the impeller of various kinds of splitting vanes design, therefore, the optimized design of splitting vanes is obtained and which agrees with that of some testing results.
Analysis of High Order Difference Methods for Multiscale Complex Compressible Flows
Sjoegreen, Bjoern; Yee, H. C.; Tang, Harry (Technical Monitor)
2002-01-01
Accurate numerical simulations of complex multiscale compressible viscous flows, especially high speed turbulence combustion and acoustics, demand high order schemes with adaptive numerical dissipation controls. Standard high resolution shock-capturing methods are too dissipative to capture the small scales and/or long-time wave propagations without extreme grid refinements and small time steps. An integrated approach for the control of numerical dissipation in high order schemes with incremental studies was initiated. Here we further refine the analysis on, and improve the understanding of the adaptive numerical dissipation control strategy. Basically, the development of these schemes focuses on high order nondissipative schemes and takes advantage of the progress that has been made for the last 30 years in numerical methods for conservation laws, such as techniques for imposing boundary conditions, techniques for stability at shock waves, and techniques for stable and accurate long-time integration. We concentrate on high order centered spatial discretizations and a fourth-order Runge-Kutta temporal discretizations as the base scheme. Near the bound-aries, the base scheme has stable boundary difference operators. To further enhance stability, the split form of the inviscid flux derivatives is frequently used for smooth flow problems. To enhance nonlinear stability, linear high order numerical dissipations are employed away from discontinuities, and nonlinear filters are employed after each time step in order to suppress spurious oscillations near discontinuities to minimize the smearing of turbulent fluctuations. Although these schemes are built from many components, each of which is well-known, it is not entirely obvious how the different components be best connected. For example, the nonlinear filter could instead have been built into the spatial discretization, so that it would have been activated at each stage in the Runge-Kutta time stepping. We could think
Saikia, Bijaylakshmi; Ramachandran, Ashwin; Sinha, Krishnendu; Govindarajan, Rama
2017-02-01
Accurate prediction of laminar to turbulent transition in compressible flows is a challenging task, as it can be affected by a combination of factors. Compressibility causes large variations in thermodynamic as well as transport properties of a gas, which in turn are known to affect flow stability. We study the stratification of individual transport properties and their combined behavior. We also examine the effect of a change in the magnitude of viscosity and conductivity on flow stability. The Couette flow of a perfect gas is our model problem and both modal and non-modal analyses are carried out. We notice a large destabilizing role of the increase in the conductivity value and a dramatic stabilizing effect of mean viscosity stratification, over a range of free-stream Mach number, Reynolds number, Prandtl number, and disturbance wavenumber. In the combined case, viscosity stratification plays a dominant role. We find this to be the case for finite-time transient growth in the parameter regime below linear instability as well as asymptotically at large time. A budget of the transient growth energy amplification is also shown to identify the effects of transport properties on the constituents of perturbation energy. The extensive results presented in this paper, we believe should motivate those studying more realistic flows to examine how these contrasting effects of stratification come together.
Directory of Open Access Journals (Sweden)
Chen Hsiang-Ho
2006-12-01
Full Text Available Abstract Background Metastatic diseases and infections frequently involve the spine. This is the result of seeding of the vertebral body by tumor cells or bacteria delivered by venous blood from Batson's plexus, which is hypothesized to enter the vertebral body via the epidural veins. Isolated spinal segments deform significantly at the bony end plate when under compression. This deformation could cause a volume change of the vertebral body and may be accompanied by retrograde flow of venous blood. To date, this process has not been investigated quantitatively. The purpose of this study was to determine the volume changes of the vertebral body and basivertebral vein for a vertebral body under compression. Methods A three-dimensional finite element mesh model of the L4 segment with both adjacent discs was modified from a 3-D computed tomography scan image. An octagon representing the basivertebral vein was introduced into the center of the vertebral body in the model. Four compressive orientations (1500 N were applied on the top disc. The volume change of the vertebral body model and the basivertebral vein were then computed. Results The volume change of the vertebral body was about 0.1 cm3 (16.3% of the basivertebral vein for the four loading conditions. The maximum cross-sectional area reductions of the basivertebral vein and volume reduction were 1.54% and 1.02%, for uniform compression. Conclusion Our study quantified the small but significant volume change of a modeled vertebral body and cross-sectional areas and that of the basivertebral vein, due to the inward bulging of the end plate under compression. This volume change could initiate the reverse flow of blood from the epidural venous system and cause seeding of tumors or bacterial cells.
Energy Technology Data Exchange (ETDEWEB)
Bright, Ido; Lin, Guang; Kutz, Nathan
2013-12-05
Compressive sensing is used to determine the flow characteristics around a cylinder (Reynolds number and pressure/flow field) from a sparse number of pressure measurements on the cylinder. Using a supervised machine learning strategy, library elements encoding the dimensionally reduced dynamics are computed for various Reynolds numbers. Convex L1 optimization is then used with a limited number of pressure measurements on the cylinder to reconstruct, or decode, the full pressure field and the resulting flow field around the cylinder. Aside from the highly turbulent regime (large Reynolds number) where only the Reynolds number can be identified, accurate reconstruction of the pressure field and Reynolds number is achieved. The proposed data-driven strategy thus achieves encoding of the fluid dynamics using the L2 norm, and robust decoding (flow field reconstruction) using the sparsity promoting L1 norm.
Calculation of watershed flow concentration based on the grid drop concept
Directory of Open Access Journals (Sweden)
Rui Xiaofang
2008-03-01
Full Text Available The grid drop concept is introduced and used to develop a micromechanism-based methodology for calculating watershed flow concentration. The flow path and distance traveled by a grid drop to the outlet of the watershed are obtained using a digital elevation model (DEM. Regarding the slope as an uneven carpet through which the grid drop passes, a formula for overland flow velocity differing from Manning’s formula for stream flow as well as Darcy's formula for pore flow is proposed. Compared with the commonly used unit hydrograph and isochronal methods, this new methodology has outstanding advantages in that it considers the influences of the slope velocity field and the heterogeneity of spatial distribution of rainfall on the flow concentration process, and includes only one parameter that needs to be calibrated. This method can also be effectively applied to the prediction of hydrologic processes in un-gauged basins.
Calculation of watershed flow concentration based on the grid drop concept
Institute of Scientific and Technical Information of China (English)
Rui Xiaofang; Yu Mei; Liu Fanggui; Gong Xinglong
2008-01-01
The grid drop concept is introduced and used to develop a micromechanism-based methodology for calculating watershed flow concentration. The flow path and distance traveled by a grid drop to the outlet of the watershed are obtained using a digital elevation model (DEM). Regarding the slope as an uneven carpet through which the grid drop passes, a formula for overland flow velocity differing from Manning's formula for stream flow as well as Darcy's formula for pore flow is proposed. Compared with the commonly used unit hydrograph and isochronal methods, this new methodology has outstanding advantages in that it considers the influences of the slope velocity field and the heterogeneity of spatial distribution of rainfall on the flow concentration process, and includes only one parameter that needs to be calibrated. This method can also be effectively applied to the prediction of hydrologic processes in un-gauged basins.
VOF Calculations of Countercurrent Gas-Liquid Flow in a PWR Hot Leg
Directory of Open Access Journals (Sweden)
M. Murase
2012-01-01
Full Text Available We improved the computational grid and schemes in the VOF (volume of fluid method with the standard − turbulent model in our previous study to evaluate CCFL (countercurrent flow limitation characteristics in a full-scale PWR hot leg (750 mm diameter, and the calculated CCFL characteristics agreed well with the UPTF data at 1.5 MPa. In this paper, therefore, to evaluate applicability of the VOF method to different fluid properties and a different scale, we did numerical simulations for full-scale air-water conditions and the 1/15-scale air-water tests (50 mm diameter, respectively. The results calculated for full-scale conditions agreed well with CCFL data and showed that CCFL characteristics in the Wallis diagram were mitigated under 1.5 MPa steam-water conditions comparing with air-water flows. However, the results calculated for the 1/15-scale air-water tests greatly underestimated the falling water flow rates in calculations with the standard − turbulent model, but agreed well with the CCFL data in calculations with a laminar flow model. This indicated that suitable calculation models and conditions should be selected to get good agreement with data for each scale.
NEW METHOD FOR IMPROVED CALCULATIONS OF UNSTEADY COMPLEX FLOWS IN LARGE ARTERIES
Institute of Scientific and Technical Information of China (English)
A. Cheer; Harry A. Dwyer; T. Kim
2011-01-01
Using an improved computational fluid dynamics (CFD) method developed for highly unsteady three-dimensional flows,numerical simulations for oscillating flow cycles and detailed unsteady simulations of the flow and forces on the aortic vessels at the iliac bifurcation,for both healthy and diseased patients,are analyzed.Improvements in computational efficiency and acceleration in convergence are achieved by calculating both an unsteady pressure gradient which is due to fluid acceleration and a good global pressure field correction based on mass flow for the pressure Poisson equation.Applications of the enhanced method to oscillatory flow in curved pipes yield an order of magnitude increase in speed and efficiency,thus allowing the study of more complex flow problems such as flow through the mammalian abdominal aorta at the iliac arteries bifurcation.To analyze the large forces which can exist on stent graft of patients with abdominal aortic aneurysm (AAA) disease,a complete derivation of the force equations is presented.The accelerated numerical algorithm and the force equations derived are used to calculate flow and forces for two individuals whose geometry is obtained from CT data and whose respective blood pressure measurements are obtained experimentally.Although the use of endovascular stent grafts in diseased patients can alter vessel geometries,the physical characteristics of stents are still very different when compared to native blood vessels of healthy subjects.The geometry for the AAA stent graph patient studied in this investigation induced flows that resulted in large forces that are primarily caused by the blood pressure.These forces are also directly related to the flow cross-sectional area and the angle of the iliac arteries relative to the main descending aorta.Furthermore,the fluid flow is significantly disturbed in the diseased patient with large flow recirculation and stagnant regions which are not present for healthy subjects.
Directory of Open Access Journals (Sweden)
Coquel Frédéric
2013-07-01
Full Text Available We give in this paper a short review of some recent achievements within the framework of multiphase flow modeling. We focus first on a class of compressible two-phase flow models, detailing closure laws and their main properties. Next we briefly summarize some attempts to model two-phase flows in a porous region, and also a class of compressible three-phase flow models. Some of the main difficulties arising in the numerical simulation of solutions of these complex and highly non-linear systems of PDEs are then discussed, and we eventually show some numerical results when tackling two-phase flows with mass transfer. Nous présentons dans cet article quelques résultats récents concernant la modélisation et la simulation numérique des écoulements multiphasiques. Nous nous concentrons tout d’abord sur une classe de modèles diphasiques compressibles, en détaillant les lois de fermeture et les principales propriétés du sytème. Nous résumons ensuite brièvement les propositions de modélisation d’écoulements diphasiques en milieu poreux et d’écoulements triphasiques. Quelques difficultés apparaissant dans la simulation numérique de ces modèles sont présentées, et des résultats récents comportant un transfert de masse entre phases sont finalement décrits.
Xia, Yidong
a computer program. By using an AD tool, the manpower can be significantly reduced for deriving the flux Jacobians, which can be quite complicated, tedious, and error-prone if done by hand or symbolic arithmetic software, depending on the complexity of the numerical flux scheme. In addition, the workload for code maintenance can also be largely reduced in case the underlying flux scheme is updated. The approximate system of linear equations arising from the Newton linearization is solved by the general minimum residual (GMRES) algorithm with lower-upper symmetric gauss-seidel (LUSGS) preconditioning. This GMRES+LU-SGS linear solver is the most robust and efficient for implicit time integration of the discretized Navier-Stokes equations when the AD-based flux Jacobians are provided other than the other two approaches. The developed HWENO(P1P2) method is used to compute a variety of well-documented compressible inviscid and viscous flow test cases on 3D hybrid grids, including some standard benchmark test cases such as the Sod shock tube, flow past a circular cylinder, and laminar flow past a at plate. The computed solutions are compared with either analytical solutions or experimental data, if available to assess the accuracy of the HWENO(P 1P2) method. Numerical results demonstrate that the HWENO(P 1P2) method is able to not only enhance the accuracy of the underlying HWENO(P1) method, but also ensure the linear and non-linear stability at the presence of strong discontinuities. An extensive study of grid convergence analysis on various types of elements: tetrahedron, prism, hexahedron, and hybrid prism/hexahedron, for a number of test cases indicates that the developed HWENO(P1P2) method is able to achieve the designed third-order accuracy of spatial convergence for smooth inviscid flows: one order higher than the underlying second-order DG(P1) method without significant increase in computing costs and storage requirements. The performance of the the developed
Huang, C Y; Mow, V C; Ateshian, G A
2001-10-01
articular cartilage, under stress-relaxation and dynamic loading, can be achieved when properly taking into account both flow-dependent and flow-independent viscoelasticity effects, as well as tension-compression nonlinearity.
Intermittency and universality in fully-developed inviscid and weakly-compressible turbulent flows
Benzi, R; Biferale, L Luca; Fisher, RT; Kadanoff, LP; Lamb, DQ; Toschi, F Federico
2008-01-01
We performed high resolution numerical simulations of homogenous and isotropic compressible turbulence, with an average 3D Mach number close to 0.3. We study the statistical properties of intermittency for velocity, density and entropy. For the velocity field, which is the primary quantity that can be compared to the isotropic incompressible case, we find no statistical differences in its behavior in the inertial range due either to the slight compressibility or to the different dissipative m...
RESEARCH ON METHOD TO CALCULATE VELOCITIES OF SOLID PHASE AND LIQUID PHASE IN DEBRIS FLOW
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
Velocities of solid phase and liquid phase in debris flow are one key problem to research on impact and abrasion mechanism of banks and control structures under action of debris flow. Debris flow was simplified as two-phase liquid composed of solid phase with the same diameter particles and liquid phase with the same mechanical features. Assume debris flow was one-dimension two-phase liquid moving to one direction,then general equations of velocities of solid phase and liquid phase were founded in twophase theory. Methods to calculate average pressures, volume forces and surface forces of debris flow control volume were established. Specially, surface forces were ascertained using Bingham's rheology equation of liquid phase and Bagnold's testing results about interaction between particles of solid phase. Proportional coefficient of velocities between liquid phase and solid phase was put forward, meanwhile, divergent coefficient between theoretical velocity and real velocity of solid phase was provided too. To state succinctly before, method to calculate velocities of solid phase and liquid phase was obtained through solution to general equations. The method is suitable for both viscous debris flow and thin debris flow. Additionally, velocities every phase can be identified through analyzing deposits in-situ after occurring of debris flow. It is obvious from engineering case the result in the method is consistent to that in real-time field observation.
Measurement and calculations of laminar flow in a ninety degree bifurcation.
Liepsch, D; Moravec, S; Rastogi, A K; Vlachos, N S
1982-01-01
Measurements and numericaL calculations of laminar flow in a plane 90 degrees bifurcation are presented. The corresponding two-dimensional steady flow Navier-Stokes equations solved by a finite-difference procedure employing pressure and velocity as dependent variables. The influence of Reynolds number and mass flow ratio on the velocity field, streamlines, local shear stress and pressure drop are quantified and shown to be substantial. The circulation patterns and shear stresses are examined in view of available data regarding the formation of atherotic plaques in the human circulatory system. The calculated velocity profiles are compared with measurements obtained with laser Doppler anemometry and the agreement is shown to be satisfactory. Calculations outside the range of measurements which are of value to biomechanics are also presented.
Reynolds shear stress and heat flux calculations in a fully developed turbulent duct flow
Antonia, R. A.; Kim, J.
1991-01-01
The use of a modified form of the Van Driest mixing length for a fully developed turbulent channel flow leads to mean velocity and Reynolds stress distributions that are in close agreement with data obtained either from experiments or direct numerical simulations. The calculations are then extended to a nonisothermal flow by assuming a constant turbulent Prandtl number, the value of which depends on the molecular Prandtl number. Calculated distributions of mean temperature and lateral heat flux are in reasonable agreement with the simulations. The extension of the calculations to higher Reynolds numbers provides some idea of the Reynolds number required for scaling on wall variables to apply in the inner region of the flow.
Mynard, Jonathan; Penny, Daniel J; Smolich, Joseph J
2008-12-05
Local reflection coefficients (R) provide important insights into the influence of wave reflection on vascular haemodynamics. Using the relatively new time-domain method of wave intensity analysis, R has been calculated as the ratio of the peak intensities (R(PI)) or areas (R(CI)) of incident and reflected waves, or as the ratio of the changes in pressure caused by these waves (R(DeltaP)). While these methods have not yet been compared, it is likely that elastic non-linearities present in large arteries will lead to changes in the size of waves as they propagate and thus errors in the calculation of R(PI) and R(CI). To test this proposition, R(PI), R(CI) and R(DeltaP) were calculated in a non-linear computer model of a single vessel with various degrees of elastic non-linearity, determined by wave speed and pulse amplitude (DeltaP(+)), and a terminal admittance to produce reflections. Results obtained from this model demonstrated that under linear flow conditions (i.e. as DeltaP(+)-->0), R(DeltaP) is equivalent to the square-root of R(PI) and R(CI) (denoted by R(PI)(p) and R(CI)(p)). However for non-linear flow, pressure-increasing (compression) waves undergo amplification while pressure-reducing (expansion) waves undergo attenuation as they propagate. Consequently, significant errors related to the degree of elastic non-linearity arise in R(PI) and R(CI), and also R(PI)(p) and R(CI)(p), with greater errors associated with larger reflections. Conversely, R(Delta)(P) is unaffected by the degree of non-linearity and is thus more accurate than R(PI) and R(CI).
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
Optimal power flow calculation for power system with UPFC considering load rate equalization
Liu, Jiankun; Chen, Jing; Zhang, Qingsong
2017-06-01
Unified power flow controller (UPFC) device can change system electrical quantity (such as voltage, impedance, phase angle, etc.) rapidly and flexibly under the premise of maintain security, stability and reliability of power system, thus can improve the transmission power and transmission line utilization, so as to enhance the power supply capacity of the power grid. Based on a thorough study of the steady-state model of UPFC, taking load rate equalization as objective function, the optimal power flow model is established with UPFC, and simplified interior point method is used to solve it. Finally, optimal power flow of 24 continuous sections actual data is calculated on a typical day of Nanjing network. The results show that the optimal power flow calculation with UPFC can optimize the load rate equalization on the basis of eliminating line overload, improving the voltage level of local power network.
Convection Heat Transfer and Flow Calculations Suitable for Electric Machines Thermal Models
Cavagnino, Andrea
2008-01-01
This paper deals with the formulations used to predict convection cooling and flow in electric machines. Empirical dimensionless analysis formulations are used to calculate convection heat transfer. The particular formulation used is selected to match the geometry of the surface under consideration and the cooling type used. Flow network analysis, which is used to study the ventilation inside the machine, is also presented. In order to focus the discussion using examples, a commercial softwar...
Propulsion and Energetics Panel Working Group 12 on through Flow Calculations in Axial Turbomachines
1981-10-01
form: of" z•G* (2 (M1 - Micr) + 1) cr = critical where again the double prime denotes the corrected value. 3. For off-design operation a parabolic... prime importance, but frequently very difficult, to determine what simplifications are made in each method. Whether a specific through-flow method is...unsteady through-flow calculations Erdos , Alzner and McNally (1977) have developed a time- dependent, inviscid computation system with capability in
Briesemeister, A.; Zhai, K.; Anderson, D. T.; Anderson, F. S. B.; Talmadge, J. N.
2013-01-01
Intrinsic flow velocities of up to ˜20 km s-1 have been measured using charge exchange recombination spectroscopy (CHERS) in the quasi-helically symmetric HSX stellarator and are compared with the neoclassical values calculated using an updated version (Lore 2010 Measurement and Transport Modeling with Momentum Conservation of an Electron Internal Transport Barrier in HSX (Madison, WI: University of Wisconsin); Lore et al 2010 Phys. Plasmas 17 056101) of the PENTA code (Spong 2005 Phys. Plasmas. 12 056114). PENTA uses the monoenergetic transport coefficients calculated by the drift kinetic equation solver code (Hirshman et al 1986 Phys. Fluids 29 2951; van Rij and Hirshman 1989 Phys. Fluids B 1 563), but corrects for momentum conservation. In the outer half of the plasma good agreement is seen between the measured parallel flow profile and the calculated neoclassical values when momentum correction is included. The flow velocity in HSX is underpredicted by an order of magnitude when this momentum correction is not applied. The parallel flow is calculated to be approximately equal for the majority hydrogen ions and the C6+ ions used for the CHERS measurements. The pressure gradient of the protons is the primary drive of the calculated parallel flow for a significant portion of the outer half of the plasma. The values of the radial electric field calculated with and without momentum correction were similar, but both were smaller than the measured values in the outer half of the plasma. Differences between the measured and predicted radial electric field are possibly a result of uncertainty in the composition of the ion population and sensitivity of the ion flux calculation to resonances in the radial electric field.
A modified calculation model for groundwater flowing to horizontal seepage wells
Indian Academy of Sciences (India)
Wei Wang; Peng Chen; Qingqing Zheng; Xinyu Zheng; Kunming Lu
2013-04-01
The simulation models for groundwater flowing to horizontal seepage wells proposed by Wang and Zhang (2007) are based on the theory of coupled seepage-pipe flow model which treats the well pipe as a highly permeable medium. However, the limitations of the existing model were found during applications. Specifically, a high-resolution grid is required to depict the complex structure of horizontal seepage wells; the permeability of the screen or wall material of radiating bores is usually neglected; and the irregularly distributed radiating bores cannot be accurately simulated. A modified calculation model of groundwater flowing to a horizontal seepage well is introduced in this paper. The exchange flow between well pipe and aquifer couples the turbulent flow inside the horizontal seepage well with laminar flow in the aquifer. The modified calculation model can reliably calculate the pumpage of a real horizontal seepage well. The characteristics of radiating bores, including the diameter, the permeability of screen material and irregular distribution of radiating bores, can be accurately depicted using the modified model that simulates the scenario in which several horizontal seepage wells work together.
Lee, Jeffrey M.
1999-01-01
This study establishes a consistent set of differential equations for use in describing the steady secondary flows generated by periodic compression and expansion of an ideal gas in pulse tubes. Also considered is heat transfer between the gas and the tube wall of finite thickness. A small-amplitude series expansion solution in the inverse Strouhal number is proposed for the two-dimensional axisymmetric mass, momentum and energy equations. The anelastic approach applies when shock and acoustic energies are small compared with the energy needed to compress and expand the gas. An analytic solution to the ordered series is obtained in the strong temperature limit where the zeroth-order temperature is constant. The solution shows steady velocities increase linearly for small Valensi number and can be of order I for large Valensi number. A conversion of steady work flow to heat flow occurs whenever temperature, velocity or phase angle gradients are present. Steady enthalpy flow is reduced by heat transfer and is scaled by the Prandtl times Valensi numbers. Particle velocities from a smoke-wire experiment were compared with predictions for the basic and orifice pulse tube configurations. The theory accurately predicted the observed steady streaming.
On calculation of a steam-water flow in a geothermal well
Shulyupin, A. N.; Chermoshentseva, A. A.
2013-08-01
Approaches to calculation of a steam-water flow in a geothermal well are considered. For hydraulic applications, a WELL-4 model of a steam-water well is developed. Data obtained using this model are compared with experimental data and also with calculations by similar models including the well-known HOLA model. The capacity of the A-2 well in the Mutnovskoe flash-steam field (Kamchatka half-island, Russia) after planned reconstruction is predicted.
A new approach for thermal performance calculation of cross-flow heat exchangers
Energy Technology Data Exchange (ETDEWEB)
Navarro, H.A. [Universidade Estadual Paulista, Rio Claro (Brazil). Dpto. de Estatistica; Cabezas-Gomez, L. [Universidade de Sao Paulo, Sao Carlos (Brazil). Dpto. de Engenharia Mecanica
2005-08-01
A new numerical methodology for thermal performance calculation in cross-flow heat exchangers is developed. Effectiveness-number of transfer units ({epsilon}-NTU) data for several standard and complex flow arrangements are obtained using this methodology. The results are validated through comparison with analytical solutions for one-pass cross-flow heat exchangers with one to four rows and with approximate series solution for an unmixed-unmixed heat exchanger, obtaining in all cases very small errors. New effectiveness data for some complex configurations are provided. (author)
CALCULATION OF THERMAL AND SALINE TURBULENT FLOW BY k-ε MODEL
Institute of Scientific and Technical Information of China (English)
Hu Zhen-hong; Shen Yong-ming; Zheng Yong-hong; Liu Cai-guang
2003-01-01
Based on the N-S equation, taking the character of thermal and saline stratified flow into account, and considering the effects of buoyancy on turbulence, the k-ε model of thermal and saline stratified flow is established.Density stratified flow with both the vertical temperature gradient and the vertical salinity gradient is simulated numerically, in which turbulent terms are calculated by the k-ε turbulent model.The distributions of velocity, temperature and salinity are given in this paper.The feature of stratification and turbulence is described correctly by the model.The computational results agree well with the experimental data.
The calculation of mechanical energy loss for incompressible steady pipe flow of homogeneous fluid
Institute of Scientific and Technical Information of China (English)
刘士和; 薛娇; 范敏
2013-01-01
The calculation of the mechanical energy loss is one of the fundamental problems in the field of Hydraulics and Enginee- ring Fluid Mechanics. However, for a non-uniform flow the relation between the mechanical energy loss in a volume of fluid and the kinematical and dynamical characteristics of the flow field is not clearly established. In this paper a new mechanical energy equation for the incompressible steady non-uniform pipe flow of homogeneous fluid is derived, which includes the variation of the mean tur- bulent kinetic energy, and the formula for the calculation of the mechanical energy transformation loss for the non-uniform flow bet- ween two cross sections is obtained based on this equation. This formula can be simplified to the Darcy-Weisbach formula for the uniform flow as widely used in Hydraulics. Furthermore, the contributions of the mechanical energy loss relative to the time avera- ged velocity gradient and the dissipation of the turbulent kinetic energy in the turbulent uniform pipe flow are discussed, and the con- tributions of the mechanical energy loss in the viscous sublayer, the buffer layer and the region above the buffer layer for the turbu- lent uniform flow are also analyzed.
Energy Technology Data Exchange (ETDEWEB)
Blanchard, M., E-mail: mathieu.blanchard@ladhyx.polytechnique.fr [LadHyX, CNRS and Ecole Polytechnique, 91128 Palaiseau (France); Schuller, T. [CNRS, UPR 288, Laboratoire d’Energétique Moléculaire et Macroscopique Combustion (EM2C), Grande Voie des Vignes, 92290 Châtenay-Malabry (France); Centrale-Supélec, Grande Voie des Vignes, 92290 Châtenay-Malabry (France); Sipp, D. [ONERA-DAFE, 8 rue des Vertugadins, 92190 Meudon (France); Schmid, P. J. [Department of Mathematics, Imperial College London, London SW7 2AZ (United Kingdom)
2015-04-15
The response of a laminar premixed methane-air flame subjected to flow perturbations around a steady state is examined experimentally and using a linearized compressible Navier-Stokes solver with a one-step chemistry mechanism to describe combustion. The unperturbed flame takes an M-shape stabilized both by a central bluff body and by the external rim of a cylindrical nozzle. This base flow is computed by a nonlinear direct simulation of the steady reacting flow, and the flame topology is shown to qualitatively correspond to experiments conducted under comparable conditions. The flame is then subjected to acoustic disturbances produced at different locations in the numerical domain, and its response is examined using the linearized solver. This linear numerical model then allows the componentwise investigation of the effects of flow disturbances on unsteady combustion and the feedback from the flame on the unsteady flow field. It is shown that a wrinkled reaction layer produces hydrodynamic disturbances in the fresh reactant flow field that superimpose on the acoustic field. This phenomenon, observed in several experiments, is fully interpreted here. The additional perturbations convected by the mean flow stem from the feedback of the perturbed flame sheet dynamics onto the flow field by a mechanism similar to that of a perturbed vortex sheet. The different regimes where this mechanism prevails are investigated by examining the phase and group velocities of flow disturbances along an axis oriented along the main direction of the flow in the fresh reactant flow field. It is shown that this mechanism dominates the low-frequency response of the wrinkled shape taken by the flame and, in particular, that it fully determines the dynamics of the flame tip from where the bulk of noise is radiated.
Numerical calculations of mass transfer flow in semi-detached binary systems. [of stars
Edwards, D. A.; Pringle, J. E.
1987-01-01
The details of the mass transfer flow near the inner Lagrangian point in a semidetached binary system are numerically calculated. A polytropic equation of state with n = 3/2 is used. The dependence of the mass transfer rate on the degree to which the star overfills its Roche lobe is calculated, and good agreement with previous analytic estimates is found. The variation of mass transfer rate which occurs if the binary system has a small eccentricity is calculated and is used to cast doubt on the model for superhumps in dwarf novae proposed by Papaloizou and Pringle (1979).
Institute of Scientific and Technical Information of China (English)
Shuqing HAO; Hongwei HUANG; Kun YIN
2007-01-01
By simplifying the characters in the air reverse circulation bit interior fluid field, the authors used air dynamics and fluid mechanics to calculate the air distribution in the bit and obtained an equation of flow distribution with a unique resolution. This study will provide help for making certain the bit parameters of the bit structure effectively and study the air reverse circulation bit interior fluid field character deeply.
Method of calculation of a thermolysis and friction of a turbulent disperse flow in nozzles
Kovalnogov, Vladislav N.; Fedorov, Ruslan V.; Boyarkin, Mikhail S.
2017-07-01
The mathematical model and method of calculation of exchange processes in boundary layer of a carrying agent of a dispersible flow in nozzles which are adequately reflecting intensive aero mechanical and thermal influences of the condensed elements in the conditions of their directed cross movement in boundary layer and also effects of a laminarization of a current in a gradient stream.
DEFF Research Database (Denmark)
Kanno, I; Lassen, N A
1979-01-01
Two methods are described for calculation of regional cerebral blood flow from completed tomographic data of radioactive inert gas distribution in a slice of brain tissue. It is assumed that the tomographic picture gives the average inert gas concentration in each pixel over data collection periods...
DEFF Research Database (Denmark)
Celsis, P; Goldman, T; Henriksen, L
1981-01-01
to avoid loss of information in brain areas with low flow rates. It is based on linearizing and scaling the early isotope distribution picture (recorded from 0 to 2 min) in rCBF units of ml/100 g/min. This is done by calculating the time constant ki for pixels with high count rate using the entire sequence...
An explicit Lagrangian finite element method for free-surface weakly compressible flows
Cremonesi, Massimiliano; Meduri, Simone; Perego, Umberto; Frangi, Attilio
2017-07-01
In the present work, an explicit finite element approach to the solution of the Lagrangian formulation of the Navier-Stokes equations for weakly compressible fluids or fluid-like materials is investigated. The introduction of a small amount of compressibility is shown to allow for the formulation of a fast and robust explicit solver based on a particle finite element method. Newtonian and Non-Newtonian Bingham laws are considered. A barotropic equation of state completes the model relating pressure and density fields. The approach has been validated through comparison with experimental tests and numerical simulations of free surface fluid problems involving water and water-soil mixtures.
Intermittency and universality in fully developed inviscid and weakly compressible turbulent flows.
Benzi, Roberto; Biferale, Luca; Fisher, Robert T; Kadanoff, Leo P; Lamb, Donald Q; Toschi, Federico
2008-06-13
We perform high-resolution numerical simulations of homogenous and isotropic compressible turbulence, with an average 3D Mach number close to 0.3. We study the statistical properties of intermittency for velocity, density, and entropy. For the velocity field, which is the only quantity that can be compared to the isotropic incompressible case, we find no statistical differences in its behavior in the inertial range due either to the slight compressibility or to the different dissipative mechanism. For the density field, we find evidence of "frontlike" structures, although no shocks are produced by the simulation.
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.
Power flow model/calculation for power systems with multiple FACTS controllers
Energy Technology Data Exchange (ETDEWEB)
Radman, Ghadir; Raje, Reshma S. [Center for Energy Systems Research, Tennessee Technological University, P.O. Box 5004, Cookeville, Tennessee-38505 (United States)
2007-10-15
This paper presents a new procedure for steady state power flow calculation of power systems with multiple flexible AC transmission system (FACTS) controllers. The focus of this paper is to show how the conventional power flow calculation method can systematically be modified to include multiple FACTS controllers. Newton-Raphson method of iterative solution is used for power flow equations in polar coordinate. The impacts of FACTS controllers on power flow is accommodated by adding new entries and modifying some existing entries in the linearized Jacobian equation of the same system with no FACTS controllers. Three major FACTS controllers (STATic synchronous COMpensator (STATCOM), static synchronous series compensator (SSSC), and unified power flow controller (UPFC)) are studied in this paper. STATCOM is modeled in voltage control mode. SSSC controls the active power of the link to which it is connected. The UPFC controls the active and the reactive power flow of the link while maintaining a constant voltage at one of the buses. The modeling approach presented in this paper is tested on the 9-bus western system coordinating council (WSCC) power system and implemented using MATLAB software package. The numerical results show the robust convergence of the presented procedure. (author)
Model-based calculating tool for pollen-mediated gene flow frequencies in plants.
Lei, Wang; Bao-Rong, Lu
2016-12-30
The potential social-economic and environmental impacts caused by transgene flow from genetically engineered (GE) crops have stimulated worldwide biosafety concerns. To determine transgene flow frequencies resulted from pollination is the first critical step for assessing such impacts, in addition to the determination of transgene expression and fitness in crop-wild hybrid descendants. Two methods are commonly used to estimate pollen-mediated gene flow (PMGF) frequencies: field experimenting and mathematical modeling. Field experiments can provide relatively accurate results but are time/resource consuming. Modeling offers an effective complement for PMGF experimental assessment. However, many published models describe PMGF by mathematical equations and are practically not easy to use. To increase the application of PMGF modeling for the estimation of transgene flow, we established a tool to calculate PMGF frequencies based on a quasi-mechanistic PMGF model for wind-pollination species. This tool includes a calculating program displayed by an easy-operating interface. PMGF frequencies of different plant species can be quickly calculated under different environmental conditions by including a number of biological and wind speed parameters that can be measured in the fields/laboratories or obtained from published data. The tool is freely available in the public domain (http://ecology.fudan.edu.cn/userfiles/cn/files/Tool_Manual.zip). Case studies including rice, wheat, and maize demonstrated similar results between the calculated frequencies based on this tool and those from published PMGF data. This PMGF calculating tool will provide useful information for assessing and monitoring social-economic and environmental impacts caused by transgene flow from GE crops. This tool can also be applied to determine the isolation distances between GE and non-GE crops in a coexistence agro-ecosystem, and to ensure the purity of certified seeds by setting proper isolation distances
Henry de Frahan, Marc T.; Varadan, Sreenivas; Johnsen, Eric
2015-01-01
Although the Discontinuous Galerkin (DG) method has seen widespread use for compressible flow problems in a single fluid with constant material properties, it has yet to be implemented in a consistent fashion for compressible multiphase flows with shocks and interfaces. Specifically, it is challenging to design a scheme that meets the following requirements: conservation, high-order accuracy in smooth regions and non-oscillatory behavior at discontinuities (in particular, material interfaces). Following the interface-capturing approach of Abgrall [1], we model flows of multiple fluid components or phases using a single equation of state with variable material properties; discontinuities in these properties correspond to interfaces. To represent compressible phenomena in solids, liquids, and gases, we present our analysis for equations of state belonging to the Mie-Grüneisen family. Within the DG framework, we propose a conservative, high-order accurate, and non-oscillatory limiting procedure, verified with simple multifluid and multiphase problems. We show analytically that two key elements are required to prevent spurious pressure oscillations at interfaces and maintain conservation: (i) the transport equation(s) describing the material properties must be solved in a non-conservative weak form, and (ii) the suitable variables must be limited (density, momentum, pressure, and appropriate properties entering the equation of state), coupled with a consistent reconstruction of the energy. Further, we introduce a physics-based discontinuity sensor to apply limiting in a solution-adaptive fashion. We verify this approach with one- and two-dimensional problems with shocks and interfaces, including high pressure and density ratios, for fluids obeying different equations of state to illustrate the robustness and versatility of the method. The algorithm is implemented on parallel graphics processing units (GPU) to achieve high speedup.
Hafez, M.; Soliman, M.; White, S.
1992-01-01
A new formulation (including the choice of variables, their non-dimensionalization, and the form of the artificial viscosity) is proposed for the numerical solution of the full Navier-Stokes equations for compressible and incompressible flows with heat transfer. With the present approach, the same code can be used for constant as well as variable density flows. The changes of the density due to pressure and temperature variations are identified and it is shown that the low Mach number approximation is a special case. At zero Mach number, the density changes due to the temperature variation are accounted for, mainly through a body force term in the momentum equation. It is also shown that the Boussinesq approximation of the buoyancy effects in an incompressible flow is a special case. To demonstrate the new capability, three examples are tested. Flows in driven cavities with adiabatic and isothermal walls are simulated with the same code as well as incompressible and supersonic flows over a wall with and without a groove. Finally, viscous flow simulations of an oblique shock reflection from a flat plate are shown to be in good agreement with the solutions available in literature.
CSIR Research Space (South Africa)
Malan, AG
2011-08-01
Full Text Available This work is concerned with the development of an artificial compressibility version of the characteristicbased split (CBS) method proposed by Zienkiewicz and Codina (Int. J. Numer. Meth. Fluids 1995; 20:869–885). The technique is applied...
Energy Technology Data Exchange (ETDEWEB)
Smith, G.C.; Wiles, L.E.; Loscutoff, W.V.
1979-02-01
A detailed description of the method of analysis and the results obtained for an investigation of the hydrodynamic and thermodynamic response of a model of a dry porous media reservoir used for compressed air energy storage (CAES) is presented. Results were obtained from a one-dimensional simulation of the cycling of heated air to and from a radial flow field surrounding a single well in a porous rock. It was assumed that the performance of the bulk of the reservoir could be characterized by the performance of a single well.
Kweon, Jae Ryong
2016-09-01
In this paper, when the initial density has a jump across an interior curve in a bounded domain, we show unique existence, piecewise regularity and jump discontinuity dynamics for the density and the velocity vector governed by the Navier-Stokes equations of compressible viscous barotropic flows. A critical difficulty is in controlling the gradient of the pressure across the jump curve. This is resolved by constructing a vector function associated with the pressure jump value on the convecting curve and extending it to the whole domain.
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.
Muralidharan, Balaji; Menon, Suresh
2016-09-01
A new adaptive finite volume conservative cut-cell method that is third-order accurate for simulation of compressible viscous flows is presented. A high-order reconstruction approach using cell centered piecewise polynomial approximation of flow quantities, developed in the past for body-fitted grids, is now extended to the Cartesian based cut-cell method. It is shown that the presence of cut-cells of very low volume results in numerical oscillations in the flow solution near the embedded boundaries when standard small cell treatment techniques are employed. A novel cell clustering approach for polynomial reconstruction in the vicinity of the small cells is proposed and is shown to achieve smooth representation of flow field quantities and their derivatives on immersed interfaces. It is further shown through numerical examples that the proposed clustering method achieves the design order of accuracy and is fairly insensitive to the cluster size. Results are presented for canonical flow past a single cylinder and a sphere at different flow Reynolds numbers to verify the accuracy of the scheme. Investigations are then performed for flow over two staggered cylinders and the results are compared with prior data for the same configuration. All the simulations are carried out with both quadratic and cubic reconstruction, and the results indicate a clear improvement with the cubic reconstruction. The new cut-cell approach with cell clustering is able to predict accurate results even at relatively low resolutions. The ability of the high-order cut-cell method in handling sharp geometrical corners and narrow gaps is also demonstrated using various examples. Finally, three-dimensional flow interactions between a pair of spheres in cross flow is investigated using the proposed cut-cell scheme. The results are shown to be in excellent agreement with past studies, which employed body-fitted grids for studying this complex case.
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.
Hu, Zeming; Chen, Xuechun; Wu, Yulin
The block-implicit finite-difference method is used to calculate 3D incompressible turbulent flows in the body-fitted coordinate system. In the numerical discretization the hybrid difference scheme is used to treat Reynolds-averaged Navier-Stokes equations. The iterative solution of velocities and pressure on the flow field is obtained by solving simultaneously the Reynolds-averaged N-S equations and continuity equation for each cell. In the iterative process the Gauss-Seidel method is used to solve nonlinear algebraic equations. The turbulent flow is simulated by the k-epsilon turbulence modeling in conjunction with Reynolds equations. The turbulent flow of a curved duct with square cross sections is treated in detail.
A Unified View of Global Instability of Compressible Flow over Open Cavities
2006-03-28
predict instability in Hagen- Poiseuille (pipe) flow , aggravated by the erroneous predictions of BiGlobal theory of stability of pressure-gradient driven... flow in a square duct (Tatsumi and Yoshimura 1990) and wall-bounded Couette flow . It thus becomes of interest, before investing efforts in the... Couette flow at φ = π / 2 which is (erroneously predicted by BiGlobal analysis to be) stable. The introduction of a third velocity component by the lid
Deklunder, G; Goullard, L; Lecroart, J L; Foulard, M; Houdas, Y
1990-05-19
Measuring blood flow in arteriovenous fistulae in patients under chronic dialysis is of interest to evaluate the repercussions of the fistula on the heart. The apparently simplest method is direct measurement of the mean blood flow velocity by the pulsed doppler technique and ot the cross-section area by ultrasonography, the product of these two values being the blood flow rate. Another method has been proposed, which consists of measuring the cardiac output before and after compression of the fistula, the difference between the two values being supposed to represent the blood flow rate in the fistula. A comparative study of these two methods was conducted in 17 patients aged from 2 to 21 years (mean: 14 years). The direct method gave a figure of 475 ml.min-1.m-2 (SD = 240), while the figure obtained with the indirect method was 471 ml.min-1.m-2 (SD = 227); the difference was statistically not significant. In terms of concept, however, the indirect method is open to much more severe criticism than the direct method, and whenever possible the latter should be preferred when measuring blood flow in arteriovenous fistulae.
Mckenzie, R. L.; Logan, P.
1986-01-01
A hot-wire anemometer and a new nonintrusive laser-induced fluorescence (LIF) technique are used to survey a Mach 2 turbulent boundary layer. The hot-wire anemometer's ability to accurately measure mass flux, temperature, and density fluctuations in a compressible flow is examined by comparing its results with those obtained using LIF. Several methods of hot-wire calibration are used, and the uncertainties in their measurements of various fluctuating flow parameters are determined. The results show that although a hot-wire operated at high overheat can measure mass flux fluctuations, temperature and density fluctuations are not determined accurately from such measurements. However, a hot-wire operated at multiple overheats can be used to measure static and total temperature fluctuations. The presence of pressure fluctuations and their correlation with density can prevent the use of hot-wire data to determine density fluctuations.
Directory of Open Access Journals (Sweden)
Adam B. Sefkow
2008-07-01
Full Text Available Large-space-scale and long-time-scale plasma flow simulations are executed in order to study the spatial and temporal evolution of plasma parameters for two types of plasma sources used in the neutralized drift compression experiment (NDCX. The results help assess the charge neutralization conditions for ion beam compression experiments and can be employed in more sophisticated simulations, which previously neglected the dynamical evolution of the plasma. Three-dimensional simulations of a filtered cathodic-arc plasma source show the coupling efficiency of the plasma flow from the source to the drift region depends on geometrical factors. The nonuniform magnetic topology complicates the well-known general analytical considerations for evaluating guiding-center drifts, and particle-in-cell simulations provide a self-consistent evaluation of the physics in an otherwise challenging scenario. Plasma flow profiles of a ferroelectric plasma source demonstrate that the densities required for longitudinal compression experiments involving ion beams are provided over the drift length, and are in good agreement with measurements. Simulations involving azimuthally asymmetric plasma creation conditions show that symmetric profiles are nevertheless achieved at the time of peak on-axis plasma density. Also, the ferroelectric plasma expands upstream on the thermal expansion time scale, and therefore avoids the possibility of penetration into the acceleration gap and transport sections, where partial neutralization would increase the beam emittance. Future experiments on NDCX will investigate the transverse focusing of an axially compressing intense charge bunch to a sub-mm spot size with coincident focal planes using a strong final-focus solenoid. In order to fill a multi-tesla solenoid with the necessary high-density plasma for beam charge neutralization, the simulations predict that supersonically injected plasma from the low-field region will penetrate and
定常可压缩泡状流动激波的数值仿真%Numerical study on the shocks in the steady compressible bubbly flows
Institute of Scientific and Technical Information of China (English)
陈红兵
2012-01-01
The simulation method on the compressible bubbly flows was investigated accompanied with the numerical cases of the transonic flows around a hydrofoil being calculated with the air volume fraction takes 0.5 in the incoming flows. The numerical experiments give that the velocity inlet could be employed as the infinite or inlet boundary conditions in the bubbly flows as long as the mach number of the air phase is smaller than 0.1. Calculations show that the disturbance because of the hydrofoil in the subsonic incoming flows propagates upstream, therefore, the inlet boundary must be set sufficiently far from the hydrofoil, and that a detached bow like shock wave occurs before the hydrofoil in the supersonic incoming flow, the disturbance from the hydrofoil could not propagate across the shock wave, and that the air volume fraction on the upstream of the shock wave is much larger than its downstream value. The result on the bubbly shock wave derived here approximately accords the relation of dynamic shock wave in the bubbly flow.%探讨了可压缩泡状流动的计算机仿真方法,计算了水翼在气相体积分数为0.5的来流中的跨声速流动.数值试验表明,当泡状流中气相本身为小亚声速流动或气相马赫数小于0.1时,则速度入口边界可用于泡状流的无穷远或入口边界条件.计算表明,亚声速泡状来流的下游扰动会向上游传播,从而需要将入口边界远离水翼；而超声速泡状来流在水翼前端形成弓形脱体压缩激波,下游扰动向上游的传播不超过波阵面.激波上游的气体体积分数大于其下游的值.正激波的上下游流动计算结果基本满足泡状流动力激波的激波关系.
Bircher, Pascal; Liniger, Hanspeter; Prasuhn, Volker
2016-04-01
Soil erosion is a well-known challenge both from a global perspective and in Switzerland, and it is assessed and discussed in many projects (e.g. national or European erosion risk maps). Meaningful assessment of soil erosion requires models that adequately reflect surface water flows. Various studies have attempted to achieve better modelling results by including multiple flow algorithms in the topographic length and slope factor (LS-factor) of the Revised Universal Soil Loss Equation (RUSLE). The choice of multiple flow algorithms is wide, and many of them have been implemented in programs or tools like Saga-Gis, GrassGis, ArcGIS, ArcView, Taudem, and others. This study compares six different multiple flow algorithms with the aim of identifying a suitable approach to calculating the LS factor for a new soil erosion risk map of Switzerland. The comparison of multiple flow algorithms is part of a broader project to model soil erosion for the entire agriculturally used area in Switzerland and to renew and optimize the current erosion risk map of Switzerland (ERM2). The ERM2 was calculated in 2009, using a high resolution digital elevation model (2 m) and a multiple flow algorithm in ArcView. This map has provided the basis for enforcing soil protection regulations since 2010 and has proved its worth in practice, but it has become outdated (new basic data are now available, e.g. data on land use change, a new rainfall erosivity map, a new digital elevation model, etc.) and is no longer user friendly (ArcView). In a first step towards its renewal, a new data set from the Swiss Federal Office of Topography (Swisstopo) was used to generate the agricultural area based on the existing field block map. A field block is an area consisting of farmland, pastures, and meadows which is bounded by hydrological borders such as streets, forests, villages, surface waters, etc. In our study, we compared the six multiple flow algorithms with the LS factor calculation approach used in
Directory of Open Access Journals (Sweden)
Liushuai CAO
2016-01-01
Full Text Available To estimate the maneuverability of a submarine at the early design stage, an accurate evaluation of the hydrodynamic coefficients is important. In a collaborative exercise, the authors performed calculations on the bare hull DRAPA SUBOFF submarine to investigate the capability of viscous-flow solvers to predict the forces and moments as well as flow field around the body. A typical simulation program was performed for both the steady drift tests and rotating arm tests. The same grid topology based on multi-block mesh strategy was used to discretize the computational domain. A procedure designated drift sweep was implemented to automatically increment the drift angle during the simulation of steady drift tests. The rotating coordinate system was adopted to perform the simulation of rotating arm tests. The Coriolis force and centrifugal force due to the computation in a rotating frame of reference were treated explicitly and added to momentum equations as source terms. Lastly, the computed forces and moment as a function of angles of drift in both conditions are compared with experimental results and literature values. They always show the correct trend. Flow field quantities including pressure coefficients and vorticity and axial velocity contours are also visualized to vividly describe the evolution of flow motions along the hull.
Statistical fluctuations in Monte Carlo calculations. [for solution of rarefied flow problems
Boyd, I. D.; Stark, J. P. W.
1989-01-01
The time counter and modified Nanbu simulation techniques are analyzed, with emphasis placed on the convergence of the calculations to a steady macroscopic state. Such variables as translational and rotational temperature, and flow velocity, sampled at several points in the flowfield, are considered. Both macroscopic averages and molecular distribution functions are analyzed. The calculation of inelastic collisions, in which transfer of energy between translational and internal energy modes is performed, is achieved through the use of the Larsen-Borgnakke phenomenological model. It is noted that, with reference to translational temperature, the time counter method shows less statistical scatter than that found with the modified Nanbu simulation technique.
AEROFROSH: a shock condition calculator for multi-component fuel aerosol-laden flows
Campbell, M. F.; Haylett, D. R.; Davidson, D. F.; Hanson, R. K.
2016-07-01
This article introduces an algorithm that determines the thermodynamic conditions behind incident and reflected shocks in aerosol-laden flows. Importantly, the algorithm accounts for the effects of droplet evaporation on post-shock properties. Additionally, this article describes an algorithm for resolving the effects of multiple-component-fuel droplets. This article presents the solution methodology and compares the results to those of another similar shock calculator. It also provides examples to show the impact of droplets on post-shock properties and the impact that multi-component fuel droplets have on shock experimental parameters. Finally, this paper presents a detailed uncertainty analysis of this algorithm's calculations given typical experimental uncertainties.
A three-dimensional turbulent compressible flow model for ejector and fluted mixers
Rushmore, W. L.; Zelazny, S. W.
1978-01-01
A three dimensional finite element computer code was developed to analyze ejector and axisymmetric fluted mixer systems whose flow fields are not significantly influenced by streamwise diffusion effects. A two equation turbulence model was used to make comparisons between theory and data for various flow fields which are components of the ejector system, i.e., (1) turbulent boundary layer in a duct; (2) rectangular nozzle (free jet); (3) axisymmetric nozzle (free jet); (4) hypermixing nozzle (free jet); and (5) plane wall jet. Likewise, comparisons of the code with analytical results and/or other numerical solutions were made for components of the axisymmetric fluted mixer system. These included: (1) developing pipe flow; (2) developing flow in an annular pipe; (3) developing flow in an axisymmetric pipe with conical center body and no fluting and (4) developing fluted pipe flow. Finally, two demonstration cases are presented which show the code's ability to analyze both the ejector and axisymmetric fluted mixers.
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.
Flow induced noise calculations for non-axially distributed hydrophones in towed arrays
Institute of Scientific and Technical Information of China (English)
WANG Bin; TANG Weilin; FAN Jun
2009-01-01
Two improvements are put forward on the analyses of flow induced noise in towed arrays. First, the differences between Corcos/Carpenter pressure fluctuation models have been discussed at length, as well as flow induced noise calculated with these two models. Second, flow induced noise received by the finite hydrophones distributed non-axially is discussed and the relevant power spectrum is deduced. The results show that there are some disparities between the wavenumber spectrums and the responses of flow induced noise of these two models. Flow induced noise is closely related with the tow speed, the tube radius and the off-axis distance. The numerical analyses with Carpenter model indicate that the power spectrum of flow induced noise will increase 24 dB approximately with the tow speed doubled, decrease with the radius of the tube, and increase with the off-axis distance. The tube radius and the off-axis distance have greater influence on the high-frequency components than on the low-frequency components.
Bayesian inference in mass flow simulations - from back calculation to prediction
Kofler, Andreas; Fischer, Jan-Thomas; Hellweger, Valentin; Huber, Andreas; Mergili, Martin; Pudasaini, Shiva; Fellin, Wolfgang; Oberguggenberger, Michael
2017-04-01
Mass flow simulations are an integral part of hazard assessment. Determining the hazard potential requires a multidisciplinary approach, including different scientific fields such as geomorphology, meteorology, physics, civil engineering and mathematics. An important task in snow avalanche simulation is to predict process intensities (runout, flow velocity and depth, ...). The application of probabilistic methods allows one to develop a comprehensive simulation concept, ranging from back to forward calculation and finally to prediction of mass flow events. In this context optimized parameter sets for the used simulation model or intensities of the modeled mass flow process (e.g. runout distances) are represented by probability distributions. Existing deterministic flow models, in particular with respect to snow avalanche dynamics, contain several parameters (e.g. friction). Some of these parameters are more conceptual than physical and their direct measurement in the field is hardly possible. Hence, parameters have to be optimized by matching simulation results to field observations. This inverse problem can be solved by a Bayesian approach (Markov chain Monte Carlo). The optimization process yields parameter distributions, that can be utilized for probabilistic reconstruction and prediction of avalanche events. Arising challenges include the limited amount of observations, correlations appearing in model parameters or observed avalanche characteristics (e.g. velocity and runout) and the accurate handling of ensemble simulations, always taking into account the related uncertainties. Here we present an operational Bayesian simulation framework with r.avaflow, the open source GIS simulation model for granular avalanches and debris flows.
A semi-direct solver for compressible three-dimensional rotational flow
Chang, S.-C.; Adamczyk, J. J.
1983-01-01
An iterative procedure is presented for solving steady inviscid 3-D subsonic rotational flow problems. The procedure combines concepts from classical secondary flow theory with an extension to 3-D of a novel semi-direct Cauchy-Riemann solver. It is developed for generalized coordinates and can be exercised using standard finite difference procedures. The stability criterion of the iterative procedure is discussed along with its ability to capture the evolution of inviscid secondary flow in a turning channel.
A semi-direct solver for compressible 3-dimensional rotational flow
Chang, S. C.; Adamczyk, J. J.
1983-01-01
An iterative procedure is presented for solving steady inviscid 3-D subsonic rotational flow problems. The procedure combines concepts from classical secondary flow theory with an extension to 3-D of a novel semi-direct Cauchy-Riemann solver. It is developed for generalized coordinates and can be exercised using standard finite difference procedures. The stability criterion of the iterative procedure is discussed along with its ability to capture the evolution of inviscid secondary flow in a turning channel.
A comparison of calibration techniques for hot-wires operated in subsonic compressible slip flows
Jones, Gregory S.; Stainback, P. C.; Nagabushana, K. A.
1992-01-01
This paper focuses on the correlation of constant temperature anemometer voltages to velocity, density, and total temperature in the transonic slip flow regime. Three different calibration schemes were evaluated. The ultimate use of these hot-wire calibrations is to obtain fluctuations in the flow variables. Without the appropriate mean flow sensitivities of the heated wire, the measurements of these fluctuations cannot be accurately determined.
Three-dimensional flow calculations of axial compressors and turbines using CFD techniques.
Jesuino Takachi Tomita
2009-01-01
With the advent of powerful computer hardware, Computational Fluid Dynamics (CFD) has been vastly used by researches and scientists to investigate flow behavior and its properties. The cost of CFD simulation is very small compared to the experimental arsenal as test facilities and wind-tunnels. In the last years many CFD commercial packages were developed and some of them possess prominence in industry and academia. However, some specific CFD calculations are particular cases and sometimes ne...
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Based on the time-averaging equations and a modified engineering turbulence model, the mold filling and solidification processes of castings are approximately described. The algorithm for the control equations is briefly introduced, and some problems and improvement methods for the traditional method are also presented. Both calculation and tests proved that, comparing with the laminar fluid flow and heat transfer, the simulation results by using the turbulence model are closer to the real mold filling and solidification processes of castings.
Advanced numerical methods for three dimensional two-phase flow calculations
Energy Technology Data Exchange (ETDEWEB)
Toumi, I. [Laboratoire d`Etudes Thermiques des Reacteurs, Gif sur Yvette (France); Caruge, D. [Institut de Protection et de Surete Nucleaire, Fontenay aux Roses (France)
1997-07-01
This paper is devoted to new numerical methods developed for both one and three dimensional two-phase flow calculations. These methods are finite volume numerical methods and are based on the use of Approximate Riemann Solvers concepts to define convective fluxes versus mean cell quantities. The first part of the paper presents the numerical method for a one dimensional hyperbolic two-fluid model including differential terms as added mass and interface pressure. This numerical solution scheme makes use of the Riemann problem solution to define backward and forward differencing to approximate spatial derivatives. The construction of this approximate Riemann solver uses an extension of Roe`s method that has been successfully used to solve gas dynamic equations. As far as the two-fluid model is hyperbolic, this numerical method seems very efficient for the numerical solution of two-phase flow problems. The scheme was applied both to shock tube problems and to standard tests for two-fluid computer codes. The second part describes the numerical method in the three dimensional case. The authors discuss also some improvements performed to obtain a fully implicit solution method that provides fast running steady state calculations. Such a scheme is not implemented in a thermal-hydraulic computer code devoted to 3-D steady-state and transient computations. Some results obtained for Pressurised Water Reactors concerning upper plenum calculations and a steady state flow in the core with rod bow effect evaluation are presented. In practice these new numerical methods have proved to be stable on non staggered grids and capable of generating accurate non oscillating solutions for two-phase flow calculations.
A New Parallel Algorithm in Power Flow Calculation: Dynamic Asynchronous Parallel Algorithm
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
Based on the general methods in power flow calculation of power system and onconceptions and classifications of parallel algorithm, a new approach named DynamicAsynchronous Parallel Algorithm that applies to the online analysis and real-time dispatching and controlling of large-scale power network was put forward in this paper. Its performances of high speed and dynamic following have been verified on IEEE-14 bus system.
Calculation of three-dimensional supersonic flow of a gas past a cube
Barausov, D. I.; Drobyshevskii, E. M.
1991-09-01
Flow of a nonviscous gas near the front face of a cube is investigated numerically using a second-order MacCormack scheme. Calculations are performed on a 40 x 32 x 32 grid using Godunov's finite difference scheme. The drag coefficient of a cube moving in air at Mach 20 is estimated at 1.7-1.8. The results of the study are relevant to the development of electrodynamic rail-gun launchers.
An Improved Method for Calculating Paleoheat Flow from Vitrinite Reflectance Profiles
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Based on the models developed by Lerche et al. (1984) and Pang et al. (1993), an improved model for calculating paleoheat flow into basins is investigated. The new model is an optimization problem with the state variables governed by a thermal conduction equation. A genetic algorithm is used to solve the highly nonlinear optimization problem. As an application, the model is applied to the research into the history of heat flow in the Pearl River Mouth basin located in the South China Sea. The numerical analysis shows that the simulation results are in good agreement with the measured data and indicates that the basin may have undergone three rifting and thermal events. It is also demonstrated that a high R. gradient reflects a response to high paleoheat flow during the early, rapid subsidence stage,while a Iow Ro gradient is a result of the thermal decay during the thermal subsidence because of thermal contraction of a cooling lithosphere.
A steady-state solver and stability calculator for nonlinear internal wave flows
Viner, Kevin C.; Epifanio, Craig C.; Doyle, James D.
2013-10-01
A steady solver and stability calculator is presented for the problem of nonlinear internal gravity waves forced by topography. Steady-state solutions are obtained using Newton's method, as applied to a finite-difference discretization in terrain-following coordinates. The iteration is initialized using a boundary-inflation scheme, in which the nonlinearity of the flow is gradually increased over the first few Newton steps. The resulting method is shown to be robust over the full range of nonhydrostatic and rotating parameter space. Examples are given for both nonhydrostatic and rotating flows, as well as flows with realistic upstream shear and static stability profiles. With a modest extension, the solver also allows for a linear stability analysis of the steady-state wave fields. Unstable modes are computed using a shifted-inverse method, combined with a parameter-space search over a set of realistic target values. An example is given showing resonant instability in a nonhydrostatic mountain wave.
Directory of Open Access Journals (Sweden)
Dun Lin
2017-01-01
Full Text Available Gas turbines are important energy-converting equipment in many industries. The flow inside gas turbines is very complicated and the knowledge about the flow loss mechanism is critical to the advanced design. The current design system heavily relies on empirical formulas or Reynolds Averaged Navier–Stokes (RANS, which faces big challenges in dealing with highly unsteady complex flow and accurately predicting flow losses. Further improving the efficiency needs more insights into the loss generation in gas turbines. Conventional Unsteady Reynolds Averaged Simulation (URANS methods have defects in modeling multi-frequency, multi-length, highly unsteady flow, especially when mixing or separation occurs, while Direct Numerical Simulation (DNS and Large Eddy Simulation (LES are too costly for the high-Reynolds number flow. In this work, the Delayed Detached Eddy Simulation (DDES method is used with a low-dissipation numerical scheme to capture the detailed flow structures of the complicated flow in a high pressure turbine guide vane. DDES accurately predicts the wake vortex behavior and produces much more details than RANS and URANS. The experimental findings of the wake vortex length characteristics, which RANS and URANS fail to predict, are successfully captured by DDES. Accurate flow simulation builds up a solid foundation for accurate losses prediction. Based on the detailed DDES results, loss analysis in terms of entropy generation rate is conducted from two aspects. The first aspect is to apportion losses by its physical resources: viscous irreversibility and heat transfer irreversibility. The viscous irreversibility is found to be much stronger than the heat transfer irreversibility in the flow. The second aspect is weighing the contributions of steady effects and unsteady effects. Losses due to unsteady effects account for a large part of total losses. Effects of unsteadiness should not be neglected in the flow physics study and design
MODELING AND CALCULATION OF FLOW AMPLIFIER PARAMETERS IN STEERING OF HEAVY TRUCKS
Directory of Open Access Journals (Sweden)
V. P. Avtushko
2008-01-01
Full Text Available The paper analyzes prospects pertaining to development of methods for dynamic calculation of monitoring hydraulic units with various types of relations. Calculated diagram of steering hydraulic drive with flow amplifier and turning cylinder has been given in the paper and its dynamic model has been developed. A hydraulic drive is considered as a system with lumped parameters. It is supposed that properties of working fluid are unchangeable during transient process; leakages and cavitations do not occur; fluid can be pressed; resistance of service drain line is taken into account. Model has been developed with due account of resistance of manifolds and internal channels of flow amplifier, hydrodynamic forces, that influence on amplifier control valves, and friction forces of movable elements. Multi-variant dynamic calculation has been done and some results of the investigations are presented in the paper. The paper also contains analysis that shows influence of various design and component parameters of flow amplifier on the drive dynamics.
Liu, Shun; Xu, Jinglei; Yu, Kaikai
2017-06-01
This paper proposes an improved approach for extraction of pressure fields from velocity data, such as obtained by particle image velocimetry (PIV), especially for steady compressible flows with strong shocks. The principle of this approach is derived from Navier-Stokes equations, assuming adiabatic condition and neglecting viscosity of flow field boundaries measured by PIV. The computing method is based on MacCormack's technique in computational fluid dynamics. Thus, this approach is called the MacCormack method. Moreover, the MacCormack method is compared with several approaches proposed in previous literature, including the isentropic method, the spatial integration and the Poisson method. The effects of velocity error level and PIV spatial resolution on these approaches are also quantified by using artificial velocity data containing shock waves. The results demonstrate that the MacCormack method has higher reconstruction accuracy than other approaches, and its advantages become more remarkable with shock strengthening. Furthermore, the performance of the MacCormack method is also validated by using synthetic PIV images with an oblique shock wave, confirming the feasibility and advantage of this approach in real PIV experiments. This work is highly significant for the studies on aerospace engineering, especially the outer flow fields of supersonic aircraft and the internal flow fields of ramjets.
Yuan, Ruifeng
2016-01-01
An immersed-boundary (IB) method is proposed and applied in the gas-kinetic BGK scheme to simulate incompressible/compressible viscous flow with stationary/moving boundary. In present method the ghost-cell technique is adopted to fulfill the boundary condition on the immersed boundary. A novel idea "local boundary determination" is put forward to identify the ghost cells, each of which may have several different ghost-cell constructions corresponding to different boundary segments, thus eliminating the singularity of the ghost cell. Furthermore, the so-called "fresh-cell" problem when implementing the IB method in moving-boundary simulation is resolved by a simple extrapolation in time. The method is firstly applied in the gas-kinetic BGK scheme to simulate the Taylor-Couette flow, where the second-order spatial accuracy of the method is validated and the "super-convergence" of the BGK scheme is observed. Then the test cases of supersonic flow around a stationary cylinder, incompressible flow around an oscill...
Computer modeling of the vapor compression cycle with constant flow area expansion device
Domanski, P.; Didion, D.
1983-05-01
An analysis of the vapor compression cycle and the main components of an air source heat pump during steady state operator was performed with emphasis on fundamental phenomena taking place between key locations in the refrigerant system. The basis of the general heat pump model formulation is the logic which links the analytical models of heat pump components together in a format requiring an iterative solution of refrigerant pressure, enthalpy and mass balances. The modeling effort emphasis was on the local thermodynamic phenomena which were described by fundamental heat transfer equations and equation of state relationships among material properties.
CALCULATION OF VISCOUS FLOW AROUND CIRCULAR CYLINDER WITH THREE-DIMENSIONAL NUMERICAL SIMULATION
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Three-dimensional numerical simulation of a uniform incompressible viscous flow around a stationary circular cylinder was conducted. The CFX-4 software was used to calculate the hydrodynamic characteristics of the flow and the finite volume method for incompressible Navier-Stokes equations was employed in the program. The simulation of the flow was performed for Re=103 and Re=104 respectively within the sub-critical region. In order to overcome numerical instability for the high Reynolds number flows, a quadratic upwind scheme was incorporated for the Navier-Stokes equations. The periodicity boundary condition was used at the ends of the cylinder. It was found that the evolution of the lift and drag coefficients in each plane along the cylinder span is different. Comparison between the predicted results based on the three-dimensional and the two-dimensional analysis was also given. It is concluded that at the high Reynolds number the effect of three-dimensionality of the flow around the circular cylinder is remarkable, and in addition hydrodynamic coefficients with of 3-D simulation are less than those given by 2-D simulation.
Computational Analysis of the Compressible Flow Driven by a Piston in a Ballistic Range
Institute of Scientific and Technical Information of China (English)
G. Rajesh; R. Mishra; H. G. Kang; H. D. Kim
2007-01-01
The ballistic range has long been employed in a variety of engineering fields such as high-velocity impact engineering, projectile aerodynamics and aeroballistics, since it can create an extremely high-pressure state in very short time. Since the operation of the ballistic range includes many complicated phenomena, each process should be understood in detail for the performance enhancement of the device. One of the main processes which have significant influence on the device performance is the compression process of the driver gas. Most of the studies available in this field hardly discuss this phenomenon in detail and thus lack a proper understanding of its effect on the whole system performance. In the present study, a computational analysis has been made to investigate the fluid dynamic aspects of the compression process in the pump tube of a ballistic range and to assess how it affects the performance of the ballistic range, The results obtained are validated with the available experimental data. In order to evaluate the system performance, several performance parameters are defined. Effect of a shock tube added in between the pump tube and launch tube on the performance of the ballistic range is also studied analytically. Performance of the ballistic range could be significantly improved by the proper selection of the pump tube and high-pressure tube parameters and the addition of the shock tube.
Simakov, N. N.
2016-12-01
An early drag crisis can occur at high turbulence of incoming gas flow to a sphere. To study the influence of a crisis on heat transfer from a sphere to gas, a numerical experiment was carried out in which the free gas flow around a sphere with a temperature lower than the sphere temperature was simulated for two cases. The flow was laminar in the first case and highly turbulent in the second case. To take into account turbulence, the kinematic coefficient of turbulent viscosity with a value, which is much higher (up to 2000 times) than that for physical viscosity, was introduced. The results of calculations show that the early drag crisis occurs at Reynolds numbers of about 100 and results in considerable (by four to seven times) decrease in the hydrodynamic force and sphere drag coefficient C d . The early drag crisis is also accompanied by the crisis of heat transfer from a sphere to gas with a decrease in Nusselt numbers Nu by three to six times.
Kawahara, Mutsuto
2016-01-01
This book focuses on the finite element method in fluid flows. It is targeted at researchers, from those just starting out up to practitioners with some experience. Part I is devoted to the beginners who are already familiar with elementary calculus. Precise concepts of the finite element method remitted in the field of analysis of fluid flow are stated, starting with spring structures, which are most suitable to show the concepts of superposition/assembling. Pipeline system and potential flow sections show the linear problem. The advection–diffusion section presents the time-dependent problem; mixed interpolation is explained using creeping flows, and elementary computer programs by FORTRAN are included. Part II provides information on recent computational methods and their applications to practical problems. Theories of Streamline-Upwind/Petrov–Galerkin (SUPG) formulation, characteristic formulation, and Arbitrary Lagrangian–Eulerian (ALE) formulation and others are presented with practical results so...
3D Simulations of a Pyroclastic Surge as an Example of a Compressible Suspension Flow
National Research Council Canada - National Science Library
ISHIMINE, Yasuhiro
2004-01-01
.... As a conspicuous example of such a flow, we present three-dimensional numerical simulations of a pyroclastic surge, which spreads laterally over the ground surface during some volcanic eruptions...
Numerical Simulation of Muzzle Flow Field Based on Calculation of Combustion Productions in Bore
Institute of Scientific and Technical Information of China (English)
Liang Wang∗,Houqian Xu,Wei Wu; Rui Xue
2015-01-01
To improve the accuracy of numerical simulation of muzzle chemical flow field, and study the gunpowder combustion productions, the muzzle flow field is simulated coupled with the calculation of combustion productions in bore. The calculation in bore uses the gibbs free⁃energy minimization method and the classical interior ballistics model. The simulation of the muzzle flow field employs the multi⁃component ALE ( Arbitrary Lagrange⁃Euler ) equations. Computations are performed for a 12�7 mm gun. From 2�48 ms to 3�14 ms, the projectile moves in the gun barrel. CO and H2 O masses decrease by 3�37% and 6�51%, and H2 and CO2 masses increase by 11�11% and 10�58%. The changes conform to the fact that the water⁃gas equilibrium reaction of all reactions plays a dominant role in this phase. After the projectile leaves the barrel, the masses of H2 and CO decrease, and the masses of H2 O and CO2 increase. When it moves to 80d away from the muzzle, the decreases are 12�75% and 8�05%, and the increases are 12�76% and 36�26%, which tallies with the existence of muzzle flame. Further, CO and H2 burn more and more fiercely with the muzzle pressure pg increasing, and burn more and more weakly with the altitude rising. When two projectiles launch in series, the combustion of the second projectile muzzle flow field is fiercer than the first projectile. Analysis results have shown that the proposed method is effective for simulating the muzzle flow filed.
Energy Technology Data Exchange (ETDEWEB)
Costa, Gustavo Koury
2004-11-15
Although incompressible fluid flows can be regarded as a particular case of a general problem, numerical methods and the mathematical formulation aimed to solve compressible and incompressible flows have their own peculiarities, in such a way, that it is generally not possible to attain both regimes with a single approach. In this work, we start from a typically compressible formulation, slightly modified to make use of pressure variables and, through augmenting the stabilising parameters, we end up with a simplified model which is able to deal with a wide range of flow regimes, from supersonic to low speed gas flows. The resulting methodology is flexible enough to allow for the simulation of liquid flows as well. Examples using conservative and pressure variables are shown and the results are compared to those published in the literature, in order to validate the method. (author)
Semianalytical calculation of the zonal-flow oscillation frequency in stellarators
Monreal, Pedro; Sánchez, Edilberto; Calvo, Iván; Bustos, Andrés; Parra, Félix I.; Mishchenko, Alexey; Könies, Axel; Kleiber, Ralf
2017-06-01
Due to their capability to reduce turbulent transport in magnetized plasmas, understanding the dynamics of zonal flows is an important problem in the fusion program. Since the pioneering work by Rosenbluth and Hinton in axisymmetric tokamaks, it is known that studying the linear and collisionless relaxation of zonal flow perturbations gives valuable information and physical insight. Recently, the problem has been investigated in stellarators and it has been found that in these devices the relaxation process exhibits a characteristic feature: a damped oscillation. The frequency of this oscillation might be a relevant parameter in the regulation of turbulent transport, and therefore its efficient and accurate calculation is important. Although an analytical expression can be derived for the frequency, its numerical evaluation is not simple and has not been exploited systematically so far. Here, a numerical method for its evaluation is considered, and the results are compared with those obtained by calculating the frequency from gyrokinetic simulations. This ‘semianalytical’ approach for the determination of the zonal-flow frequency is revealed to be accurate and faster than the one based on gyrokinetic simulations.
Blocking of Snow/Water Slurry Flow in Pipeline Caused by Compression-Strengthening of Snow Column
Directory of Open Access Journals (Sweden)
Masataka Shirakashi
2014-01-01
Full Text Available In earlier works by the present authors, two systems for sustainable energy were proposed: (i a system for urban snow removal in winter and storage for air conditioning in summer, applied to Nagaoka City, which suffers heavy snow fall every winter, and (ii a district cooling system utilizing latent heat of ice to reduce the size of storage reservoir and transportation pipeline system. In these systems, the hydraulic conveying of snow or ice through pump-and-pipeline is the key technique to be developed, since characteristics of snow (ice/ water slurry is largely different from those of conventional non-cohesive solid particle slurries. In this study, the blocking of pipeline of snow/water slurry is investigated experimentally. While the blocking of conventional slurry occurs due to deposition of heavy particles at low flow velocity or arching of large rigid particles, that of snow/water slurry is caused by a compressed plug of snow formed due to cohesive nature of snow particles. This is because the strength of snow plug formed at a high resistance piping element, such as an orifice, becomes higher when the compression velocity is lower, resulting in a solid-like plug filling the whole channel upstream the element.
Engelder, Terry; Peacock, David C. P.
2001-02-01
Alpine inversion in the Bristol Channel Basin includes reverse-reactivated normal faults with hanging wall buttress anticlines. At Lilstock Beach, joint sets in Lower Jurassic limestone beds cluster about the trend of the hinge of the Lilstock buttress anticline. In horizontal and gently north-dipping beds, J3 joints ( 295-285° strike) are rare, while other joint sets indicate an anticlockwise sequence of development. In the steeper south-dipping beds, J3 joints are the most frequent in the vicinity of the reverse-reactivated normal fault responsible for the anticline. The J3 joints strike parallel to the fold hinge, and their poles tilt to the south when bedding is restored to horizontal. This southward tilt aims at the direction of σ 1 for Alpine inversion. Finite-element analysis is used to explain the southward tilt of J3 joints that propagate under a local σ 3 in the direction of σ 1 for Alpine inversion. Tilted principal stresses are characteristic of limestone-shale sequences that are sheared during parallel (flexural-flow) folding. Shear tractions on the dipping beds generate a tensile stress in the stiffer limestone beds even when remote principal stresses are compressive. This situation favors the paradoxical opening of joints in the direction of the regional maximum horizontal stress. We conclude that J3 joints propagated during the Alpine compression caused the growth of the Lilstock buttress anticline.
Michalek, Arthur J; Iatridis, James C
2011-08-01
Extensive experimental work on the effects of penetrating annular injuries indicated that large injuries impact axial compressive properties of small animal intervertebral discs, yet there is some disagreement regarding the sensitivity of mechanical tests to small injury sizes. In order to understand the mechanism of injury size sensitivity, this study proposed a simple one dimensional model coupling elastic deformations in the annulus with fluid flow into and out of the nucleus through both porous boundaries and through a penetrating annular injury. The model was evaluated numerically in dynamic compression with parameters obtained by fitting the solution to experimental stress-relaxation data. The model predicted low sensitivity of mechanical changes to injury diameter at both small and large sizes (as measured by low and high ratios of injury diameter to annulus thickness), with a narrow range of high sensitivity in between. The size at which axial mechanics were most sensitive to injury size (i.e., critical injury size) increased with loading frequency. This study provides a quantitative hypothetical model of how penetrating annulus fibrosus injuries in discs with a gelatinous nucleus pulposus may alter disc mechanics by changing nucleus pulposus fluid pressurization through introduction of a new fluid transport pathway though the annulus. This model also explains how puncture-induced biomechanical changes depend on both injury size and test protocol.
A convergent mixed method for the Stokes approximation of viscous compressible flow
Karlsen, Kenneth
2009-01-01
We propose a mixed finite element method for the motion of a strongly viscous, ideal, and isentropic gas. At the boundary we impose a Navier-slip condition such that the velocity equation can be posed in mixed form with the vorticity as an auxiliary variable. In this formulation we design a finite element method, where the velocity and vorticity is approximated with the div- and curl- conforming Nedelec elements, respectively, of the first order and first kind. The mixed scheme is coupled to a standard piecewise constant upwind discontinuous Galerkin discretization of the continuity equation. For the time discretization, implicit Euler time stepping is used. Our main result is that the numerical solution converges to a weak solution as the discretization parameters go to zero. The convergence analysis is inspired by the continuous analysis of Feireisl and Lions for the compressible Navier-Stokes equations. Tools used in the analysis include an equation for the effective viscous flux and various renormalizatio...
Two-dimensional lattice Boltzmann model for compressible flows with high Mach number
Gan, Yanbiao; Xu, Aiguo; Zhang, Guangcai; Yu, Xijun; Li, Yingjun
2008-03-01
In this paper we present an improved lattice Boltzmann model for compressible Navier-Stokes system with high Mach number. The model is composed of three components: (i) the discrete-velocity-model by M. Watari and M. Tsutahara [Phys. Rev. E 67 (2003) 036306], (ii) a modified Lax-Wendroff finite difference scheme where reasonable dissipation and dispersion are naturally included, (iii) artificial viscosity. The improved model is convenient to compromise the high accuracy and stability. The included dispersion term can effectively reduce the numerical oscillation at discontinuity. The added artificial viscosity helps the scheme to satisfy the von Neumann stability condition. Shock tubes and shock reflections are used to validate the new scheme. In our numerical tests the Mach numbers are successfully increased up to 20 or higher. The flexibility of the new model makes it suitable for tracking shock waves with high accuracy and for investigating nonlinear nonequilibrium complex systems.