Structural Parameters and Prediction of Adverse Pressure Gradient Turbulent Flows: An Improved k-ε Model

1995 ◽  
Vol 117 (3) ◽  
pp. 424-432 ◽  
Author(s):  
G. Chukkapalli ◽  
O¨. F. Turan
Keyword(s):  
Pressure Gradient ◽  
Turbulent Flows ◽  
Reynolds Stress ◽  
Eddy Viscosity ◽  
Structural Parameters ◽  
Adverse Pressure Gradient ◽  
Reynolds Stress Model ◽  
Model Representation ◽  
Stress Model ◽  
Kinetic Diffusion

A modified k-ε model is proposed to predict complex, adverse pressure gradient, turbulent diffuser flows. The need for an eddy viscosity is eliminated by using three structural parameters. A fuller treatment of the rate of kinetic diffusion terms is incorporated with a Reynolds stress model representation. A thorough evaluation is given of the three structural parameters in three decreasing and one increasing adverse pressure gradient diffuser flows leading to a three-layer representation. The results indicate the need for better modeling of the ε-equation.

Improved Prediction of Turbomachinery Flows Using Near-Wall Reynolds-Stress Model

2001 ◽  
Vol 124 (1) ◽  
pp. 86-99 ◽  
Author(s):  
G. A. Gerolymos ◽  
J. Neubauer ◽  
V. C. Sharma ◽  
I. Vallet
Keyword(s):  
Experimental Data ◽  
Turbulent Flows ◽  
Reynolds Stress ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Flow Equations ◽  
Near Wall

In this paper an assessment of the improvement in the prediction of complex turbomachinery flows using a new near-wall Reynolds-stress model is attempted. The turbulence closure used is a near-wall low-turbulence-Reynolds-number Reynolds-stress model, that is independent of the distance-from-the-wall and of the normal-to-the-wall direction. The model takes into account the Coriolis redistribution effect on the Reynolds-stresses. The five mean flow equations and the seven turbulence model equations are solved using an implicit coupled OΔx3 upwind-biased solver. Results are compared with experimental data for three turbomachinery configurations: the NTUA high subsonic annular cascade, the NASA_37 rotor, and the RWTH 1 1/2 stage turbine. A detailed analysis of the flowfield is given. It is seen that the new model that takes into account the Reynolds-stress anisotropy substantially improves the agreement with experimental data, particularily for flows with large separation, while being only 30 percent more expensive than the k−ε model (thanks to an efficient implicit implementation). It is believed that further work on advanced turbulence models will substantially enhance the predictive capability of complex turbulent flows in turbomachinery.

scholarly journals Rotating Flow and Heat Transfer in Cylindrical Cavities With Radial Inflow

2012 ◽  
Author(s):  
B. G. Vinod Kumar ◽  
John W. Chew ◽  
Nicholas J. Hills
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Stress ◽  
Integral Method ◽  
Eddy Viscosity ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Rotating Disc ◽  
Flow And Heat Transfer ◽  
Viscosity Models

Design and optimization of an efficient internal air system of a gas turbine requires thorough understanding of the flow and heat transfer in rotating disc cavities. The present study is devoted to numerical modelling of flow and heat transfer in a cylindrical cavity with radial inflow and comparison with the available experimental data. The simulations are carried out with axi-symmetric and 3-D sector models for various inlet swirl and rotational Reynolds numbers upto 2.1×106. The pressure coefficients and Nusselt numbers are compared with the available experimental data and integral method solutions. Two popular eddy viscosity models, the Spalart-Allmaras and the k-ε, and a Reynolds stress model have been used. For cases with particularly strong vortex behaviour the eddy viscosity models show some shortcomings with the Spalart-Allmaras model giving slightly better results than the k-ε model. Use of the Reynolds stress model improved the agreement with measurements for such cases. The integral method results are also found to agree well with the measurements.

Development and Application of an Anisotropic Two-Equation Model for Flows With Swirl and Curvature

2003 ◽  
Author(s):  
Xiaohua Wang ◽  
Siva Thangam
Keyword(s):  
Energy Spectrum ◽  
Turbulent Flows ◽  
Reynolds Stress ◽  
Scaling Laws ◽  
Reynolds Stress Model ◽  
Equation Model ◽  
Stress Model ◽  
Generalized Model

An anisotropic two-equation Reynolds-stress model is developed by modeling the energy spectrum and through invariance based scaling. In this approach the effect of rotation is used to modify the energy spectrum, while the influence of swirl is modeled based on scaling laws. The resulting generalized model is validated for benchmark turbulent flows with swirl and curvature.

Performance Evaluation of a Non-Linear Explicit Algebraic Reynolds Stress Model for Surface Mounted Obstacles

2020 ◽  
Author(s):  
Benjamin H. Taylor ◽  
Tausif Jamal ◽  
D. Keith Walters
Keyword(s):  
Reynolds Stress ◽  
Eddy Viscosity ◽  
Numerical Data ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Rans Model ◽  
Non Linear ◽  
Additional Strain ◽  
Dynamic Hybrid ◽  
Algebraic Reynolds Stress Model

Abstract The presence of complex vortical structures, unsteady wakes, separated shear layers, and streamline curvature pose considerable challenges for traditional linear Eddy-Viscosity (LEV) models. Since Non-Linear Eddy Viscosity Models (NEV) models contain additional strain-rate and vorticity relationships, they can provide a better description for flows with Reynolds stress anisotropy and can be considered to be suitable alternatives to traditional EVMs in some cases. In this study, performance of a Non-Linear Explicit Algebraic Reynolds Stress Model (NEARSM) to accurately resolve flow over a surface mounted cube and a 3D axisymmetric hill is evaluated against existing experimental and numerical studies. Numerical simulations were performed using the SST k-ω RANS model, SST k-ω-NEARSM, SST-Multiscale LES model, and two variants of the Dynamic Hybrid RANS-LES (DHRL) model that include the SST k-ω and the SST k-ω-NEARSM as the RANS models. Results indicate that the SST k-ω RANS model fails to accurately predict the flowfield in the separated wake region and although the SST-NEARSM and SST-Multiscale LES models provide an improved description of the flow, they suffer from incorrect RANS-LES transition caused by Modeled Stress Depletion (MSD) and sensitivity to changes in grid resolution. The SST-DHRL and the SST-NEARSM-DHRL variants provide the best agreement to experimental and numerical data.

Investigation of an Algebraic Reynolds Stress Model for Simulation of Wall-Bounded Turbulent Flows With and Without Buoyancy Effects

2020 ◽  
Author(s):  
Tausif Jamal ◽  
D. Keith Walters
Keyword(s):  
Heat Flux ◽  
Turbulent Flows ◽  
Reynolds Stress ◽  
Nuclear Reactor ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Reynolds Analogy ◽  
Suitable Alternative ◽  
Rans Models ◽  
Algebraic Reynolds Stress Model

Abstract Complex turbulent flows such as those encountered in nuclear reactor cooling systems pose considerable challenges for computational fluid dynamics (CFD) simulation using traditional Reynolds-averaged Navier-Stokes (RANS) models based on the linear eddy-viscosity modeling (LEVM) framework. One particular difficulty is the use of low Prandtl number (Pr) fluids such as liquid metal coolants, which considerably alters the fluctuating thermal field and violates the Reynolds analogy upon which turbulent heat flux modeling in LEVMs is based. Although previous studies have shown that Reynolds Stress Models (RSM) offer some improvements over traditional LEVMs for flows containing complex inter-component interaction and Reynolds stress anisotropy, the added complexity, increased computational requirements, and the lack of robustness introduced by traditional RSMs do not always result in an overall improvement. This study evaluates the performance of a newly proposed Algebraic Reynolds Stress Model (ARSM) including an Algebraic Heat Flux Model (AHFM) against two industry standard RANS models, standard k-ε and realizable k-ε model, for a set of canonical test cases relevant to nuclear reactor cooling applications. Numerical simulations using the spectral element code Nek5000 are performed for fully developed channel flows with varying values of Reynolds number (Re) and Pr, both with and without the effects of buoyancy. Results are compared to Direct Numerical Simulation (DNS) data in terms of the velocity and thermal statistics. For all cases investigated, the ARSM model consistently outperforms the other RANS models in this study and it is concluded that the new ARSM model can be a suitable alternative to traditional LEVMs for complex turbulent flows without significant penalty to efficiency and robustness that are commonly associated with traditional RSMs.

Development and Application of a Two-Scale Non-Linear Reynolds Stress Turbulence Model

2007 ◽  
Author(s):  
S. Y. Jaw ◽  
R. R. Hwang
Keyword(s):  
Turbulent Flows ◽  
Reynolds Stress ◽  
Turbulence Model ◽  
Dissipation Rate ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Turbulence Scale ◽  
Non Linear ◽  
Algebraic Reynolds Stress Model ◽  
Near Wall

To improve the prediction of turbulent flows, a two-scale, non-linear Reynolds stress turbulence model is proposed in this study. It is known that for the near-wall low-Reynolds number turbulent flows, the Kolmogorov turbulence scale, based on the fluid kinematic viscosity and dissipation rate of turbulent kinetic energy (ν,ε), is the dominant turbulence scale, hence it is adopted to address the viscous effects and the rapid increase of dissipation rate in the near wall region. As a wall is approached, the turbulence scale transits smoothly from turbulent kinetic energy based (k, ε) scale to (ν,ε) scale. The damping functions of the low-Reynolds number models can thus be simplified and the near-wall turbulence characteristics, such as the ε distribution, are correctly reproduced. Furthermore, to improve the prediction of the anisotropic Reynolds stresses for complex flows, a nonlinear algebraic Reynolds stress model is incorporated. The same turbulence scales are adopted in the nonlinear algebraic Reynolds stress model. The developed two-scale non-linear Reynolds stress model is first calibrated with the DNS budgets of two-dimensional channel flows, and then applied to predict the separation flow behind a backward facing step. It is found that the proposed two-scale nonlinear Reynolds stress turbulence model is capable of providing satisfactory results without increasing much computation efforts or causing numerical stability problems.

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