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215

Jul 23, 2010
07/10

by
Kulikovskii, A. G

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No Abstract Available

Topics: REATTACHED FLOW, SUPERSONIC FLOW, TWO DIMENSIONAL FLOW, BACKWARD FACING STEPS, BOUNDARY LAYERS,...

A single grid local mode analysis is used to predict the smoothing properties of numerical schemes for solving the Navier-Stokes equations with factorization based on Stone's Strongly Implicit Method. Four difference approximations for the convection terms are considered, namely, hybrid, central, second-order upwind, and third-order upwind. Smoothing factors from the analysis are compared with practical convergence factors in a multigrid method for flow over a backward facing step and it is...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, MULTIGRID METHODS, NAVIER-STOKES...

536
536

Jul 23, 2010
07/10

by
Fleischman, G. L.; Peck, S. J.; Tanzer, H. J

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The feasibility of fabricating and processing moderate temperature range vapor chamber type heat pipes in a low mass honeycomb panel configuration for highly efficient radiator fins for potential use on the space station was investigated. A variety of honeycomb panel facesheet and core-ribbon wick concepts were evaluated within constraints dictated by existing manufacturing technology and equipment. Concepts evaluated include type of material, material and panel thickness, wick type and...

Topics: K-EPSILON TURBULENCE MODEL, MATHEMATICAL MODELS, NUMERICAL ANALYSIS, TURBULENT BOUNDARY LAYER,...

173
173

Jul 12, 2010
07/10

by
Katow, M. S.; Khan, I.; Williams, W. F

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Using a Cassegrainian geometry, the 64-meter antenna with its distorted paraboloidal reflecting surface is forced to produce a uniform phase wavefront by a pathlength-compensating subreflector. First, the computed distortion vectors at the joints or nodes of the main reflector structure supporting the surface panels are best fitted to a paraboloid. Second, the resulting residual distortion errors are used to determine a compensating subreflector surface by ray tracing using geometric optics...

Topics: BACKWARD FACING STEPS, INCOMPRESSIBLE FLOW, REATTACHED FLOW, TURBULENT FLOW, EQUATIONS OF MOTION,...

203
203

Jul 21, 2010
07/10

by
NON

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An agreement between the government of the Federal Republic of Germany and the government of the Union of Soviet Socialist Republics concerning scientific technical cooperation is disclosed. The parties to the treaty agree to promote scientific and technical cooperation on a basis of equality, reciprocity and mutual advantage.

Topics: BACKWARD FACING STEPS, VORTEX SHEDDING, CIRCULAR CYLINDERS, COMPUTER PROGRAMS, INCOMPRESSIBLE FLOW,...

This progress report covers the grant period from March until the end of January 1993. Extensive data reduction and analysis of single and two-point measurements for a backward-facing experiment were performed. Pertinent results are presented in two conference papers which are appended to this report. The titles of the papers are as follows: (1) 'Two-point correlation measurements in a recovering turbulent boundary layer'; and (2) 'An experimental study on the recovery of a turbulent boundary...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, REATTACHED FLOW, SEPARATED FLOW,...

348
348

May 23, 2011
05/11

by
Iek, Chanthy; Boldman, Donald R.; Ibrahim, Mouni

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A time-marching Navier-Stokes code called PARC3D was used to study the three-dimensional viscous flow associated with an advanced ducted propeller (ADP) subsonic inlet at takeoff operating conditions. At a freestream Mach number of 0.2, experimental data of the ADP inlet model indicated that the flow on the cowl windward lip remained attached at an angle of attack of 25 deg became unstable at 29 deg and separated at 30 deg. An experimental through-flow test study (without propeller) using...

Topics: TURBULENT BOUNDARY LAYER, QUADRANTS, VELOCITY DISTRIBUTION, TIME DEPENDENCE, CORRELATION, BACKWARD...

The NCC code was validated for a case involving staged transverse injection into Mach 2 flow behind a rearward facing step. Comparisons with experimental data and with solutions from the FPVortex code was then used to perform computations to study fuel-air mixing for the combustor of a candidate rocket based combined cycle engine geometry. Comparisons with a one-dimensional analysis and a three-dimensional code (VULCAN) were performed to assess the qualitative and quantitative performance of...

Topics: NASA Technical Reports Server (NTRS), INJECTION, COMBUSTION CHAMBERS, BACKWARD FACING STEPS,...

289
289

May 27, 2011
05/11

by
RHEINBOLDT, WERNE

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ALMOST ALL SOLUTIONS, SO FAR KNOWN, OF THE PROBLEM OF EXACT CALCULATION OF THE VELOCITY DISTRIBUTION IN A BOUNDARY LAYER UNDER THE INFLUENCE OF CONTINUOUS SUCTION PERTAIN TO THE CLASS OF ''SIMILAR'' SOLUTIONS. ONE DEALS, THEREFORE, WITH INDIVIDUAL PARTICULAR INTEGRALS OF THE BOUNDARY-LAYER EQUATIONS UNDER SPECIAL BOUNDARY CONDITIONS. COMPILATIONS MAY BE FOUND, FOR INSTANCE, IN H. SCHLICHTING OR E. J. WATSON. IF ONE DISREGARDS THE REPORTS USING THE SO-CALLED POHLHAUSEN METHODS, THUS NOT YIELDING...

Topics: BOUNDARY LAYER TRANSITION, ANGLE OF ATTACK, FORWARD FACING STEPS, PHOTOGRAPHS, VORTICES, TURBULENT...

There are inherent uncertainties and errors associated with using Computational Fluid Dynamics (CFD) to predict the flow field and there is no standard method for evaluating uncertainty in the CFD community. This paper describes an approach to -validate the . uncertainty in using CFD. The method will use the state of the art uncertainty analysis applying different turbulence niodels and draw conclusions on which models provide the least uncertainty and which models most accurately predict the...

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, FLOW DISTRIBUTION, UNCERTAIN...

A study is made to improve the predictions of Reynolds stresses in backward facing step flows, through modifications of the pressure-strain correlation. The mean-strain term of the pressure-strain correlation is formulated only in terms of nonisotropic turbulence in order to take the severe nonisotropic effect caused by a separating flow. This model is compared with other models and results are verified with experimental results.

Topics: NASA Technical Reports Server (NTRS), MODELS, PRESSURE RATIO, REYNOLDS STRESS, STRESS-STRAIN...

Topics considered include: New approach to turbulence modeling; Second moment closure analysis of the backstep flow database; Prediction of the backflow and recovery regions in the backward facing step at various Reynolds numbers; Turbulent flame propagation in partially premixed flames; Ensemble averaged dynamic modeling. Also included a study of the turbulence structures of wall-bounded shear flows; Simulation and modeling of the elliptic streamline flow.

Topics: NASA Technical Reports Server (NTRS), CONFERENCES, TURBULENCE MODELS, SHEAR FLOW, PREMIXED FLAMES,...

The sizes and arrangement of the wind tunnel used for the experimentation are described. The specifications for the cold-wire anemometers, hot-wire anemometers, cold-wire rakes, and miniature 3-wire probe are proveded. The results of the experiment are briefly discussed.

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, BOUNDARY LAYER FLOW, CIRCUITS,...

This viewgraph presentation discusses the following: introduction to CFD Research Corporation; experiences with two-equation models - models used, numerical difficulties, validation and applications, and strengths and weaknesses; and answers to three questions posed by the workshop organizing committee - what are your customers telling you, what are you doing in-house, and how can NASA-CMOTT (Center for Modeling of Turbulence and Transition) help.

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, K-EPSILON TURBULENCE MODEL,...

Reynolds stress closure models based on the recursion renormalization group theory are developed for the prediction of turbulent separated flows. The proposed model uses a finite wavenumber truncation scheme to account for the spectral distribution of energy. In particular, the model incorporates effects of both local and nonlocal interactions. The nonlocal interactions are shown to yield a contribution identical to that from the epsilon-renormalization group (RNG), while the local interactions...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, RENORMALIZATION GROUP METHODS,...

A numerical study of incompressible turbulent separated flows is carried out by using two-equation turbulence models of the K-epsilon type. On the basis of realizability analysis, a new formulation of the eddy-viscosity is proposed which ensures the positiveness of turbulent normal stresses - a realizability condition that most existing two-equation turbulence models are unable to satisfy. The present model is applied to calculate two backward-facing step flows. Calculations with the standard...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, COMPUTATIONAL FLUID DYNAMICS,...

238
238

Aug 1, 2010
08/10

by
Mankbadi, Reda R

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Here, numerical results are computed from an asymptotic near-resonance triad analysis. The analysis considers a resonant triad of instability waves consisting of a plane fundamental wave and a pair of symmetrical oblique subharmonic waves. The relevant scaling ensures that nonlinearity is confined to a distinct critical layer. The analysis is first used to form a composite solution that accounts for both the flow divergence and nonlinear effects. It is shown that the backreaction on the plane...

Topics: ALGORITHMS, COMPUTATIONAL FLUID DYNAMICS, COMPUTER PROGRAMS, FLOW DISTRIBUTION, FLOW VISUALIZATION,...

This viewgraph presentation provides a brief review of two-equation eddy-viscosity models (TEM's) from the perspective of applied CFD. It provides objective assessment of both well-known and newer models, compares model predictions from various TEM's with experiments, identifies sources of modeling error and gives historical perspective of their effects on model performance and assessment, and recommends directions for future research on TEM's.

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, EDDY VISCOSITY, TURBULENCE...

For a computational flow simulation tool to be useful in a design environment, it must be very robust and efficient. To develop such a tool for incompressible flow applications, a number of different implicit schemes are compared for several two-dimensional flow problems in the current study. The schemes include Point-Jacobi relaxation, Gauss-Seidel line relaxation, incomplete lower-upper decomposition, and the generalized minimum residual method preconditioned with each of the three other...

Topics: NASA Technical Reports Server (NTRS), INCOMPRESSIBLE FLOW, NAVIER-STOKES EQUATION, COMPUTATIONAL...

The Streamline-Upwind Petrov-Galerkin (SUPG) finite element simulations of compressible flows is presented. The topics include: 1) Introduction; 2) SUPG Galerkin Finite Element Methods; 3) Applications; and 4) Bibliography.

Topics: NASA Technical Reports Server (NTRS), FINITE ELEMENT METHOD, GALERKIN METHOD, SIMULATION,...

A two-equation turbulence model of the K-epsilon type was recently derived by using Renormalization Group (RNG) methods. It was later reported that this RNG based model yields substantially better predictions than the standard K-epsilon model for turbulent flow over a backward facing step - a standard test case used to benchmark the performance of turbulence models in separated flows. The improvements obtained from the RNG K-epsilon model were attributed to the better treatment of near wall...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, K-EPSILON TURBULENCE MODEL,...

The purpose of the study is the evaluation of the numerical accuracy of FIDAP (Fluid Dynamics Analysis Package). Accordingly, four test problems in laminar and turbulent incompressible flows are selected and the computational results of these problems compared with other numerical solutions and/or experimental data. These problems include: (1) 2-D laminar flow inside a wall-driven cavity; (2) 2-D laminar flow over a backward-facing step; (3) 2-D turbulent flow over a backward-facing step; and...

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, FINITE ELEMENT METHOD,...

The primary objective of the Center for Turbulence Research (CTR) is to stimulate and produce advances in physical understanding of turbulence, in turbulence modeling and simulation, and in turbulence control. Topics addressed include: fundamental modeling of turbulence; turbulence structure and control; transition and turbulence in high-speed compressible flows; and turbulent reacting flows.

Topics: NASA Technical Reports Server (NTRS), BOUNDARY LAYER CONTROL, COMPUTERIZED SIMULATION, FLOW...

A four-equation model of turbulence is applied to the numerical simulation of flows with massive separation induced by a sudden expansion. The model constants are a function of the flow parameters, and two different formulations for these functions are tested. The results are compared with experimental data for a high Reynolds-number case and with experimental and DNS data for a low Reynolds-number case. The computations prove that the recovery region downstream of the massive separation is...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, FLOW CHARACTERISTICS, MATHEMATICAL...

The near-wall viscous and buffer regions of wall-bounded flows generally require a large expenditure of computational resources to be resolved adequately, even in large-eddy simulation (LES). Often as much as 50% of the grid points in a computational domain are devoted to these regions. The dense grids that this implies also generally require small time steps for numerical stability and/or accuracy. It is commonly assumed that the inner wall layers are near equilibrium, so that the standard...

Topics: NASA Technical Reports Server (NTRS), BOUNDARY CONDITIONS, WALL FLOW, VORTICES, NUMERICAL FLOW...

The effect of acoustic excitation on a class of separated flows with a transitional boundary layer at the point of separation is considered. Experimental results on the flow over airfoils, a two-dimensional backward-facing step, and through large angle conical diffusers are presented. In all cases, the separated flow undergoes large amplitude fluctuations, much of the energy being concentrated at unusually low frequencies. In each case, an appropriate high frequency acoustic excitation is found...

Topics: NASA Technical Reports Server (NTRS), ACOUSTIC EXCITATION, AERODYNAMIC STALLING, AIRFOILS, BACKWARD...

A general turbulent constitutive relation is directly applied to propose a new Reynolds stress algebraic equation model. In the development of this model, the constraints based on rapid distortion theory and realizability (i.e. the positivity of the normal Reynolds stresses and the Schwarz' inequality between turbulent velocity correlations) are imposed. Model coefficients are calibrated using well-studied basic flows such as homogeneous shear flow and the surface flow in the inertial sublayer....

Topics: NASA Technical Reports Server (NTRS), FLOW EQUATIONS, REYNOLDS STRESS, TURBULENCE MODELS, TURBULENT...

Previously the theoretical development leading to the dynamic localization model (DLM) for large-eddy simulation (LES) was presented. The method has been successfully applied to isotropic turbulence, channel flow, and the flow over a backward-facing step. Here we apply the model to the computation of the temporally developing place wake. The two main objectives of this project are: (1) Use the model to perform an LES of a time developing plane wake and compare the results with direction...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, CHANNEL FLOW, DYNAMIC MODELS, EDDY...

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235

May 23, 2011
05/11

by
Nagy, Andrew F.; Cravens, Thomas E.; Waite, H. J., Jr

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Our understanding of planetary ionospheres made some progress during the last four years. Most of this progress was due to new and/or improved theoretical models, although some new data were also obtained by direct and remote sensing observations. The very basic processes such as ionization, chemical transformations and diffusive as well as convective transports are analogous in all ionospheres; the major differences are the result of factors such as different neutral atmospheres, intrinsic...

Topics: SEPARATED FLOW, TWO DIMENSIONAL BOUNDARY LAYER, TURBULENT BOUNDARY LAYER, FLOW VELOCITY, TURBULENT...

We report preliminary results obtained from the large eddy simulation of a backward facing step at a Reynolds number of 5100. The numerical platform is based on a high order Legendre spectral element spatial discretization and a least squares time integration scheme. A non-reflective outflow boundary condition is in place to minimize the effect of downstream influence. Smagorinsky model with Van Driest near wall damping is used for sub-grid scale modeling. Comparisons of mean velocity profiles...

Topics: NASA Technical Reports Server (NTRS), SIMULATION, BACKWARD FACING STEPS, FLOW CHARACTERISTICS,...

Velocity-pressure integrated and consistent penalty finite element computations of high Reynolds number, laminar flows are presented. In both of the methods, the pressure has been interpolated using linear shape functions for a triangular element. The triangular element is contained inside the bi-quadratic isoparametric element. It has been reported previously that the pressure interpolation method, when used in the velocity-pressure integrated method, yielded accurate computational results for...

Topics: NASA Technical Reports Server (NTRS), FINITE ELEMENT METHOD, HIGH REYNOLDS NUMBER, LAMINAR FLOW,...

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...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, COMPUTATIONAL FLUID DYNAMICS, PRESSURE...

An extended kappa-epsilon turbulence model is proposed and tested with successful results. An improved transport equation for the rate of dissipation of the turbulent kinetic energy, epsilon, is proposed. The proposed model gives more effective response to the energy production rate than does the standard kappa-epsilon turbulence model. An extra time scale of the production range is included in the dissipation rate equation. This enables the present model to perform equally well for several...

Topics: NASA Technical Reports Server (NTRS), K-EPSILON TURBULENCE MODEL, MATHEMATICAL MODELS, NUMERICAL...

The objectives of this study are as follows: (1) to conduct a direct numerical simulation of turbulent backward facing step flow using inflow and outflow conditions; and (2) to provide data in the form of Reynolds stress budgets for Reynolds averaged modeling. The report presents the basic statistical data and comparisons with the concurrent experiments of Jovic and Driver and budgets of turbulent kinetic energy.

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, FINITE DIFFERENCE THEORY, GRID...

A technique for improving the numerical predictions of turbulent flows with the effect of streamline curvature is developed. Separated flows, the flow in a curved duct, and swirling flows are examples of flow fields where streamline curvature plays a dominant role. A comprehensive literature review on the effect of streamline curvature was conducted. New algebraic formulations for the eddy viscosity incorporating the kappa-epsilon turbulence model are proposed to account for various effects of...

Topics: NASA Technical Reports Server (NTRS), DUCTED FLOW, EDDY VISCOSITY, FLOW DISTRIBUTION, K-EPSILON...

An efficient diagonal scheme implemented in an overset mesh framework has permitted the analysis of geometrically complex cavity flows via the Reynolds averaged Navier-Stokes equations. Use of rapid hyperbolic and algebraic grid methods has allowed simple specification of critical turbulent regions with an algebraic turbulence model. Comparisons between numerical and experimental results are made in two dimensions for the following problems: a backward-facing step; a resonating cavity; and two...

Topics: NASA Technical Reports Server (NTRS), CAVITIES, CAVITY FLOW, SHEAR LAYERS, SOFIA (AIRBORNE...

Two-dimensional incompressible turbulent flow in a channel with a backward-facing step was studied numerically by Chorin's Random Vortex Method (RVM), an algorithm capable of tracing the action of elementary turbulent eddies and their cumulative effects without imposing any restrictions upon their motions. The step occurs in one side of a channel with otherwise flat, parallel walls; its height equals 1/3, 1/4 or 1/5 the width of the channel downstream. The main objective was to investigate the...

Topics: NASA Technical Reports Server (NTRS), INCOMPRESSIBLE FLOW, TURBULENT FLOW, TWO DIMENSIONAL FLOW,...

A velocity-pressure integrated, mixed interpolation, Galerkin finite element method for the Navier-Stokes equations is presented. In the method, the velocity variables are interpolated using complete quadratic shape functions, and the pressure is interpolated using linear shape functions which are defined on a triangular element for the two-dimensional case and on a tetrahedral element for the three-dimensional case. The triangular element and the tetrahedral element are contained inside the...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, FINITE ELEMENT METHOD, HIGH REYNOLDS...

Topics include: upper stage engine key requirements and design drivers; Calspan "stage 1" results, He slot injection into hypersonic flow (air); test articles for shock generator diagram, slot injector details, and instrumentation positions; test conditions; modeling approach; 2-d grid used for film cooling simulations of test article; heat flux profiles from 2-d flat plate simulations (run #4); heat flux profiles from 2-d backward facing step simulations (run #43); isometric sketch...

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, LIQUID PROPELLANT ROCKET...

Turbulent backward-facing step flow was examined using four low turbulent Reynolds number k-epsilon models and one standard high Reynolds number technique. A tunnel configuration of 1:9 (step height: exit tunnel height) was used. The models tested include: the original Jones and Launder; Chien; Launder and Sharma; and the recent Shih and Lumley formulation. The experimental reference of Driver and Seegmiller was used to make detailed comparisons between reattachment length, velocity, pressure,...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, K-EPSILON TURBULENCE MODEL, LOW...

The flow field about a backward facing step was investigated to determine the characteristics of particle sampling bias in the various flow phenomena. The investigation used the calculation of the velocity:data rate correlation coefficient as a measure of statistical dependence and thus the degree of velocity bias. While the investigation found negligible dependence within the free stream region, increased dependence was found within the boundary and shear layers. Full classic correction...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, FLOW DISTRIBUTION, SHEAR FLOW,...

A computer code for calculating the flow field and flame propagation in a turbulent combustion tunnel is described. The model used in the analysis is the random vortex model, which allows the turbulent field to evolve as a fundamental solution to the Navier-Stokes equations without averaging or closure modeling. The program was used to study the flow field in a model combustor, formed by a rearward-facing step in a channel, in terms of the vorticity field, the turbulent shear stresses, the...

Topics: NASA Technical Reports Server (NTRS), COMBUSTIBLE FLOW, FLAME PROPAGATION, TURBULENT FLOW, TWO...

A numerical method for computing incompressible turbulent flows is presented. The method is tested by calculating laminar recirculating flows and is applied in conjunction with a modified Kappa-epsilon model to compute the flow over a backward-facing step. In the laminar regime, the computational results are in good agreement with the experimental data. The turbulent flow study shows that the reattachment length is underpredicted by the standard Kappa-epsilon model. The addition of a term to...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, INCOMPRESSIBLE FLOW, REATTACHED FLOW,...

A model for the effects of rotation on turbulence is proposed and tested. These effects which influence mainly the rate of turbulence decay are modeled in a modified turbulent energy dissipation rate equation that has explicit dependence on the mean rotation rate. An appropriate definition of the rotation rate derived from critical point theory and based on the invariants of the deformation tensor is proposed. The modeled dissipation rate equation is numerically well behaved and can be used in...

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, K-EPSILON TURBULENCE MODEL,...

Presented here is an algorithm for solving the multidimensional unsteady Navier-Stokes equations for compressible flows. It is based on a diagonally-dominant approximate factorization procedure. The factorization error and the timewise linearization error associated with this procedure are reduced by performing Newton-type inner iterations at each time step. The inviscid fluxes are evaluated by the fourth-order central differencing scheme amended with a numerical dissipation directly...

Topics: NASA Technical Reports Server (NTRS), ALGORITHMS, BACKWARD FACING STEPS, CONVECTION, FACTORIZATION,...

255
255

Jun 12, 2011
06/11

by
Greenhall, C. A.; Riley, W. J

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This work gives an algorithm for computing the degrees of freedom of estimators of Allan and Hadamard variances, including their modified versions. A consistent approach is used throughout.

Topics: PARTICLE IMAGE VELOCIMETRY, CROSS FLOW, BOUNDARY LAYER THICKNESS, ROOT-MEAN-SQUARE ERRORS, WALL...

The primary objective of the Center for Modelling of Turbulence and Transition (CMOTT) is to further the understanding of turbulence theory for engineering applications. One important foundation is the establishment of a data base encompassing the multitude of existing models as well as newly proposed ideas. The research effort described is a precursor to an extended survey of two equation turbulence models in the presence of a separated shear layer. Recently, several authors have examined the...

Topics: NASA Technical Reports Server (NTRS), COMPRESSIBLE BOUNDARY LAYER, FLOW DISTRIBUTION, MATHEMATICAL...

The ability of two-equation models to accurately predict separated flows is analyzed from a combined theoretical and computational standpoint. Turbulent flow past a backward facing step is chosen as a test case in an effort to resolve the variety of conflicting results that were published during the past decade concerning the performance of two-equation models. It is found that the errors in the reported predictions of the k-epsilon model have two major origins: (1) numerical problems arising...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, COMPUTATIONAL FLUID DYNAMICS,...

The problem of turbulent flow past a backward facing step is important in many technological applications and has been used as a standard test case to evaluate the performance of turbulence models in the prediction of separated flows. It is well known that the commonly used kappa-epsilon (and K-l) models of turbulence yield inaccurate predictions for the reattachment points in this problem. By an analysis of the mean vorticity transport equation, it will be argued that the intrinsically...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, K-EPSILON TURBULENCE MODEL, MODELS,...

Separation and reattachment of turbulent shear layers is observed in many important engineering applications, yet it is poorly understood. This has motivated many studies on understanding and predicting the processes of separation and reattachment of turbulent shear layers. Both of the situations in which separation is induced by adverse pressure gradient, or by discontinuities of geometry, have attracted attention of turbulence model developers. Formulation of turbulence closure models to...

Topics: NASA Technical Reports Server (NTRS), BACKWARD FACING STEPS, BOUNDARY LAYERS, COMPUTATIONAL FLUID...