Explicit algebraic stress models that are valid for three-dimensional turbulent flows in noninertial frames are systematically derived from a hierarchy of second-order closure models. This represents a generalization of the model derived by Pope who based his analysis on the Launder, Reece, and Rodi model restricted to two-dimensional turbulent flows in an inertial frame. The relationship between the new models and traditional algebraic stress models -- as well as anistropic eddy visosity...

Topics: NASA Technical Reports Server (NTRS), STRESS ANALYSIS, THREE DIMENSIONAL FLOW, TURBULENCE MODELS,...

The prediction of turbulent secondary flows with Reynolds stress models in circular pipes and non-circular ducts is reviewed. Turbulence-driven secondary flows in straight non-circular ducts are considered along with turbulent secondary flows in pipes and ducts that arise from curvature or a system rotation. The physical mechanisms that generate these different kinds of secondary flows are outlined and the level of turbulence closure required to properly compute each type is discussed in...

Topics: DTIC Archive, Speziale, C G, INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON...

The mathematical properties of the pressure-velocity and vorticity-velocity formulations of the equations of viscous flow are compared. It is shown that a vorticity-velocity formulation exists which has the interesting property that non-inertial effects only enter the problem through the implementation of initial and boundary conditions. This valuable characteristic, along with other advantages of the vorticity-velocity approach, are discussed in detail.

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, VELOCITY DISTRIBUTION, VISCOUS...

Direct simulations of homogeneous turbulence have, in recent years, come into widespread use for the evaluation of models for the pressure-strain correlation of turbulence. While work in this area has been beneficial, the increasingly common practice of testing the slow and rapid parts of these models separately in uniformly strained turbulent flows is shown in this paper to be unsound. For such flows, the decomposition of models for the pressure-strain correlation into slow and rapid part is...

Topics: DTIC Archive, Speziale, C G, INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON...

Turbulent channel flow and homogeneous shear flow have served as basic building block flows for the testing and calibration of Reynolds stress models. A direct theoretical connection is made between homogeneous shear flow in equilibrium and the log-layer of fully-developed turbulent channel flow. It is shown that if a second-order closure model is calibrated to yield good equilibrium values for homogeneous shear flow it will also yield good results for the log-layer of channel flow provided...

Topics: NASA Technical Reports Server (NTRS), CHANNEL FLOW, CLOSURE LAW, PREDICTIONS, REYNOLDS STRESS,...

The physical properties of the commonly used second-order closure models are examined theoretically for rotating turbulent flows. Comparisons are made with results which are a rigorous consequence of the Navier-Stokes equations for the problem of a fully-developed turbulent channel flow in a rapidly rotating framework. It is demonstrated that all existing second-order closures yield spurious physical results for this test problem of rotating channel flow. In fact, the results obtained are shown...

Topics: NASA Technical Reports Server (NTRS), CHANNEL FLOW, CLOSURE LAW, NAVIER-STOKES EQUATION, ROTATING...

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,...

A two-equation turbulence model of the K-epsilon type was recently derived by Yakhot and Orszag based on 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 apparent improvements obtained from the RNG K-epsilon model were attributed to the...

Topics: DTIC Archive, Speziale, C G, INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON...

A direct numerical simulation of the decay of initially isotropic turbulence in a rapidly rotating frame was conducted. This 128 x 128 x 128 simulation was completed for a Reynolds number Re sub lambda = 15.3 and a Rossby number Ro sub lambda = 0.07 based on the initial turbulent kinetic energy and Taylor microscale. The numerical results indicate that the turbulence remains essentially isotropic during the major part of the decay (i.e., beyond the point where the turbulent kinetic energy has...

Topics: NASA Technical Reports Server (NTRS), ENERGY TRANSFER, ISOTROPIC TURBULENCE, MATHEMATICAL MODELS,...

A subgrid-scale model recently derived for use in the large-eddy simulation of compressible turbulent flows is examined from a fundamental theoretical and computational standpoint. It is demonstrated that this model, which is applicable only to compressible turbulent flows in the limit of small density fluctuations, correlates somewhat poorly with the results of direct numerical simulations of compressible isotropic turbulence at low Mach numbers. An alternative model, based on Favre-filtered...

Topics: NASA Technical Reports Server (NTRS), COMPRESSIBLE FLOW, SCALE MODELS, TURBULENT FLOW,...

The prediction of turbulent secondary flows, with Reynolds stress models, in circular pipes and non-circular ducts is reviewed. Turbulence-driven secondary flows in straight non-circular ducts are considered along with turbulent secondary flows in pipes and ducts that arise from curvature or a system rotation. The physical mechanisms that generate these different kinds of secondary flows are outlined and the level of turbulence closure required to properly compute each type is discussed in...

Topics: NASA Technical Reports Server (NTRS), DUCTS, K-EPSILON TURBULENCE MODEL, PIPES (TUBES), REYNOLDS...

This paper presents a rational approach to modelling the triple velocity correlations that appear in the transport equations for the Reynolds stresses. All existing models of these correlations have largely been formulated on phenomenological grounds and are defective in one important aspect: they all neglect to allow for the dependence of these correlations on the local gradients of mean velocity. The mathematical necessity for this dependence will be demonstrated in the paper. The present...

Topics: NASA Technical Reports Server (NTRS), CORRELATION, TURBULENCE, VELOCITY, RATIONAL FUNCTIONS,...

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,...

New subgrid-scale models for the large-eddy simulation of compressible turbulent flows are developed based on the Favre-filtered equations of motion for an ideal gas. A compressible generalization of the linear combination of the Smagorinsky model and scale-similarity model (in terms of Favre-filtered fields) is obtained for the subgrid-scale stress tensor. An analogous thermal linear combination model is also developed for the subgrid-scale heat flux vector. The three dimensionless constants...

Topics: NASA Technical Reports Server (NTRS), COMPRESSIBLE FLOW, COMPUTATIONAL GRIDS, SIMULATION, TURBULENT...

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,...

Turbulence models are developed by supplementing the renormalization group (RNG) approach of Yakhot and Orszag with scale expansions for the Reynolds stress and production of dissipation terms. The additional expansion parameter (eta) is the ratio of the turbulent to mean strain time scale. While low-order expansions appear to provide an adequate description of the Reynolds stress, no finite truncation of the expansion for the production of dissipation term in powers of eta suffices - terms of...

Topics: NASA Technical Reports Server (NTRS), FLOW EQUATIONS, RENORMALIZATION GROUP METHODS, SHEAR FLOW,...

The pressure driven, fully-developed turbulent flow of an incompressible viscous fluid in curved ducts of square cross-section is studied numerically by making use of a finite volume method. A nonlinear Kappa - Iota model is used to represent the turbulence. The results for both straight and curved ducts are presented. For the case of fully-developed turbulent flow in straight ducts, the secondary flow is characterized by an eight-vortex structure for which the computed flowfield is shown to be...

Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, DUCT GEOMETRY, FLOW...

New subgrid-scale models for the large-eddy simulation of compressible turbulent flows are developed and tested based on the Favre-filtered equations of motion for an ideal gas. A compressible generalization of the linear combination of the Smagorinsky model and scale-similarity model, in terms of Favre-filtered fields, is obtained for the subgrid-scale stress tensor. An analogous thermal linear combination model is also developed for the subgrid-scale heat flux vector. The two dimensionless...

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

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...

Topics: NASA Technical Reports Server (NTRS), COMPRESSIBLE FLOW, ENERGY DISSIPATION, EQUATIONS OF MOTION,...

Direct numerical simulation data bases for compressible homogeneous shear flow are used to evaluate the performance of recently proposed Reynolds stress closures for compressible turbulence. Three independent pressure-strain models are considered along with a variety of explicit compressible corrections that account for dilatational dissipation and pressure-dilatation effects. The ability of the models to predict both time evolving fields and equilibrium states is systematically tested....

Topics: DTIC Archive, Speziale, C G, INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON...