Applications of EARSM Turbulence Models to Internal Flows

2012 ◽  
Author(s):  
O. Z. Mehdizadeh ◽  
L. Temmerman ◽  
B. Tartinville ◽  
Ch. Hirsch
Keyword(s):  
Reynolds Stress ◽  
High Performance ◽  
Eddy Viscosity ◽  
Computational Cost ◽  
Turbulence Models ◽  
Industrial Applications ◽  
Mean Flow ◽  
Viscosity Models ◽  
Stress Models ◽  
Corner Flows

Turbulence modeling remains an active CFD development front for turbomachinery as well as for general industrial applications. While DNS and even LES still seem out of reach within the typical industrial design cycle due to their high computational cost, RANS-based models remain the workhorse of CFD. Currently, the most widely used models are Linear Eddy-Viscosity Models (LEVM), despite their known limitations for certain flow complexities. Therefore, extending the reliability of eddy-viscosity models to more complex flows without significantly increasing the computational cost can immediately contribute to more reliable CFD results for wider range of applications. This, in turn, can further reduce the need for costly tests and consequently can reduce the product development cost. A promising approach to achieve this goal is using Explicit Algebraic Reynolds Stress Models (EARSM), obtained through a simplification of the full Differential Reynolds Stress Models (DRSM), and can be perceived as an extension of LEVMs by including the non-linear relation between the turbulence stress tensor, the mean-flow gradient and the turbulence scales. These models are thus less demanding than DRSM, yet capable of capturing more complex turbulence features, compared to LEVM, such as anisotropy in the normal stresses. This may be particularly important in corner flows, for instance, in the hub-blade regions or in diffusers. This work explores the application of EARSM models to a double diffuser and a high-performance centrifugal compressor stage (HPCC). The results are compared to available experimental data [1,2] showing the importance of including the anisotropy of turbulence in the model, particularly in presence of turbulent corner flows in a diffuser. Furthermore, the EARSM results are also compared to results from the commonly used SST turbulence model. The CFD comparison includes details of the flow structure in the diffuser, where the most noticeable impact from the use of EARSM turbulence models is expected.

Robust Implicit Multigrid Reynolds-Stress Model Computation of 3-D Turbomachinery Flows

2006 ◽  
Author(s):  
G. A. Gerolymos ◽  
I. Vallet
Keyword(s):  
Reynolds Stress ◽  
Time Integration ◽  
Computational Cost ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Finite Volume Scheme ◽  
Stress Model ◽  
Mean Flow ◽  
Approximate Factorization ◽  
Flow Equations

The purpose of this paper is to present a numerical methodology for the computation of complex 3-D turbomachinery flows using advanced multiequation turbulence closures, including full 7-equation Reynolds-stress transport models. A general frame-work describing the turbulence models and possible future improvements is presented. The flow equations are discretized on structured multiblock grids, using an upwind biased (O[Δx3] MUSCL reconstruction) finite-volume scheme. Time-integration uses a local-dual-time-stepping implicit procedure, with internal subiterations. Computational efficiency is achieved by a specific approximate factorization of the implicit subiterations, designed to minimize the computational cost of the turbulence-transport-equations. Convergence is still accelerated using a mean-flow-multigrid full-approximation-scheme method, where multigrid is applied on the mean-flow-variables only. Speed-ups of a factor 3 are obtained using 3 levels of multigrid (fine + 2 coarser grids). Computational examples are presented using several Reynolds-stress model variants (and also a baseline k–ε model), for various turbomachinery configurations, and compared with available experimental measurements.

High Resolution Overset Structured Grid RANS Simulations of Flow Past a Surface Mounted Cube Using Eddy Viscosity Closure Models

2018 ◽  
Author(s):  
Marc C. Goldbach ◽  
Mesbah Uddin
Keyword(s):  
Eddy Viscosity ◽  
Complex Structure ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Separated Flow ◽  
Industrial Applications ◽  
Separated Flows ◽  
Transitional Flow ◽  
Stream Velocity ◽  
Mean Flow

While Reynolds-averaged simulatons (RAS) have found success in the evaluation of many canonical shear flows, and moderately separated flows, their application to highly separated flows have shown notable deficiencies. This study aims to investigate these deficiencies in the eddy-viscosity formulation of four commonly used turbulence models under separated flow in an attempt to aid in the improved formulation of such models. Analyses are performed on the flow field around a wall mounted cube at a Reynolds number of 40,000 based on the cube height, h, and free stream velocity, U0. While a common occurrence in industrial applications, this type of flow constitutes a complex structure exhibiting a large separated wake region, high anisotropy, and multiple vortex structures. As well, interactions between vortices developed off of different faces of the cube significantly alter the overall flow characteristics, posing a significant challenge for the commonly used industrial turbulence models. Comparison of mean flow characteristics show remarkable agreement between experimental values and turbulence models which are capable of predicting transitional flow. Evaluation of turbulence parameters show the general underestimation of Reynolds stress for transitional models, while fully turbulent models show this value to be overestimated, resulting in completely disparate representations of mean flow structures between the two classes of models (transitional and fully turbulent).

Turbulence Modeling in a Model Combustor

2005 ◽  
Author(s):  
Lei-Yong Jiang ◽  
Ian Campbell
Keyword(s):  
Reynolds Stress ◽  
Eddy Viscosity ◽  
Turbulence Modeling ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Moment Closure ◽  
Superior Performance ◽  
Combustion Model ◽  
Discrete Ordinates ◽  
Viscosity Models

The flow field of a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers was numerically investigated. Solutions obtained from four turbulence models together with a laminar flamelet combustion model, discrete ordinates radiation model and enhanced wall treatment are presented and discussed. The numerical results are compared, in detail, with a comprehensive database obtained from a series of experimental measurements. It is found that the Reynolds stress model (RSM), a second moment closure, illustrates superior performance over three popular two-equation eddy-viscosity models. Although the main flow features are captured by all four turbulence models, only the RSM is able to successfully predict the lengths of both recirculation zones and the turbulence kinetic energy distribution in the combustor chamber. In addition, it provides fairly good predictions for all Reynolds stress components, except for the circumferential normal stress at downstream sections. However, the superiority of the RSM is not so obvious for the temperature and species predictions in comparison with eddy-viscosity models, except for the standard k-ε model. This suggests that coupling between the RSM and combustion models needs to be further improved in order to enhance its applications in practical combustion systems.

Modeling Separation-Induced Transition Using a Non-Linear Three Equation Turbulence Model and a Reynolds Stress Turbulence Model

2010 ◽  
Author(s):  
Zinon Vlahostergios ◽  
Kyros Yakinthos
Keyword(s):  
Transport Equation ◽  
Reynolds Stress ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Viscosity Model ◽  
Transitional Flows ◽  
Eddy Viscosity Model ◽  
Non Linear ◽  
Stress Models

This paper presents an effort to model separation-induced transition on a flat plate with a semi-circular leading edge, by using two advanced turbulence models, the three equation non-linear model k-ε-A2 of Craft et al. [16] and the Reynolds-stress model of Craft [13]. The mechanism of the transition is governed by the different inlet velocity and turbulence intensity conditions, which lead to different recirculation bubbles and different transition onset points for each case. The use of advanced turbulence models in predicting the development of transitional flows has shown, in past studies, good perspectives. The k-ε-A2 model uses an additional transport equation for the A2 Reynolds stress invariant and it is an improvement of Craft et al. [12] non-linear eddy viscosity model. The use of the third transport equation gives improved results in the prediction of the longitudinal Reynolds stress distributions and especially, in flows where transitional phenomena may occur. Although this model is a pure eddy-viscosity model, it borrows many aspects from the more complex Reynolds-stress models. On the other hand, the use of an advanced Reynolds-stress turbulence model, such as the one of Craft [13], can predict many complex flows and there are indications that it can be applied to transitional flows also, since the crucial terms of Reynolds stress generation are computed exactly and normal stress anisotropy is resolved. The model of Craft [13], overcomes the drawbacks of the common used Reynolds-stress models regarding the computation of wall-normal distances and vectors in order to account for wall proximity effects. Instead of these quantities, it employs “normalized turbulence lengthscale gradients” which give the ability to identify the presence of strong inhomogeneity in a flow development, in an easier way. The final results of both turbulence models showed acceptable agreement with the experimental data. In this work it is shown that there is a good potential to model separation-induced transitional flows, with advanced turbulence modeling without any additional use of ad-hoc modifications or additional equations, based on various transition models.

High-Resolution RANS Simulations of Flow Past a Surface-Mounted Cube Using Eddy-Viscosity Closure Models

2019 ◽  
Vol 4 (1) ◽  
Author(s):  
Marc C. Goldbach ◽  
Mesbah Uddin
Keyword(s):  
Eddy Viscosity ◽  
Complex Structure ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Separated Flow ◽  
Industrial Applications ◽  
Separated Flows ◽  
Transitional Flow ◽  
Mean Flow ◽  
Freestream Velocity

Abstract While Reynolds-averaged simulations have found success in the evaluation of many canonical shear flows and moderately separated flows, their application to highly separated flows have shown notable deficiencies. This study aimed to investigate these deficiencies in the eddy-viscosity formulation of four commonly used turbulence models under separated flow in an attempt to aid in the improved formulation of such models. Analyses are performed on the flow field around a wall-mounted cube (WMC) at a Reynolds number of 40,000 based on the cube height, h, and freestream velocity, U0. While a common occurrence in industrial applications, this type of flow constitutes a complex structure exhibiting a large separated wake region, high anisotropy, and multiple vortex structures. As well, interactions between vortices developed off of different faces of the cube significantly alter the overall flow characteristics, posing a significant challenge for the commonly used industrial turbulence models. Comparison of mean flow characteristics show remarkable agreement between experimental values and turbulence models which are capable of predicting transitional flow. Evaluation of turbulence parameters show the general underestimation of Reynolds stress for transitional models, while fully turbulent models show this value to be overestimated, resulting in completely disparate representations of mean flow structures between the two classes of models (transitional and fully turbulent).

Numerical Prediction of Flow in a Nuclear Fuel Bundle With Various Turbulence Models

2002 ◽  
Author(s):  
Wang Kee In ◽  
Dong Seok Oh ◽  
Tae Hyun Chun
Keyword(s):  
Turbulent Flow ◽  
Nuclear Fuel ◽  
Turbulence Models ◽  
Convective Transport ◽  
Stress Model ◽  
Convergence Criteria ◽  
Mean Flow ◽  
Numerical Predictions ◽  
Viscosity Models ◽  
Fuel Bundle

The numerical predictions using the standard and RNG k–ε eddy viscosity models, differential stress model (DSM) and algebraic stress model (ASM) are examined for the turbulent flow in a nuclear fuel bundle with the mixing vane. The hybrid (first-order) and curvature-compensated convective transport (CCCT) schemes were used to examine the effect of the differencing scheme for the convection term. The CCCT scheme was found to more accurately predict the characteristics of turbulent flow in the fuel bundle. There is a negligible difference in the prediction performance between the standard and RNG k-ε models. The calculation using ASM failed in meeting the convergence criteria. DSM appeared to more accurately predict the mean flow velocities as well as the turbulence parameters.

scholarly journals Study on bubble-induced turbulence in pipes and containers with Reynolds-stress models

2022 ◽  
Author(s):  
Yixiang Liao ◽  
Tian Ma
Keyword(s):  
Numerical Simulation ◽  
Reynolds Stress ◽  
Large Scale ◽  
Bubbly Flow ◽  
Reynolds Stress Model ◽  
Viscosity Models ◽  
Stress Components ◽  
Specific Source ◽  
Stress Models ◽  
Made In

AbstractBubbly flow still represents a challenge for large-scale numerical simulation. Among many others, the understanding and modelling of bubble-induced turbulence (BIT) are far from being satisfactory even though continuous efforts have been made. In particular, the buoyancy of the bubbles generally introduces turbulence anisotropy in the flow, which cannot be captured by the standard eddy viscosity models with specific source terms representing BIT. Recently, on the basis of bubble-resolving direct numerical simulation data, a new Reynolds-stress model considering BIT was developed by Ma et al. (J Fluid Mech, 883: A9 (2020)) within the Euler—Euler framework. The objective of the present work is to assess this model and compare its performance with other standard Reynolds-stress models using a systematic test strategy. We select the experimental data in the BIT-dominated range and find that the new model leads to major improvements in the prediction of full Reynolds-stress components.

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.

On Application of Nonlinear k-ε Models for Internal Combustion Engine Flows

2002 ◽  
Vol 124 (3) ◽  
pp. 668-677 ◽  
Author(s):  
G. M. Bianchi ◽  
G. Cantore ◽  
P. Parmeggiani ◽  
V. Michelassi
Keyword(s):  
Internal Combustion Engine ◽  
Eddy Viscosity ◽  
Combustion Engine ◽  
Turbulence Models ◽  
Internal Combustion ◽  
Moment Closure ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Numerical Predictions ◽  
Viscosity Models

The linear k-ε model, in its different formulations, still remains the most widely used turbulence model for the solutions of internal combustion engine (ICE) flows thanks to the use of only two scale-determining transport variables and the simple constitutive relation. This paper discusses the application of nonlinear k-ε turbulence models for internal combustion engine flows. Motivations to nonlinear eddy viscosity models use arise from the consideration that such models combine the simplicity of linear eddy-viscosity models with the predictive properties of second moment closure. In this research the nonlinear k-ε models developed by Speziale in quadratic expansion, and Craft et al. in cubic expansion, have been applied to a practical tumble flow. Comparisons between calculated and measured mean velocity components and turbulence intensity were performed for simple flow structure case. The effects of quadratic and cubic formulations on numerical predictions were investigated too, with particular emphasis on anisotropy and influence of streamline curvature on Reynolds stresses.

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