Purpose - To perform 3D unsteady Reynolds Averaged Navier-Stokes (URANS) simulations to predict turbulent flow over bluff body. Design/methodology/ approach - Turbulence closure is achieved through a non-linear k-ε model. This model is incorporated in commercial FLUENT software, through user defined functions (UDF). Findings - The study shows that the present URANS with standard wall functions predicts all the major unsteady phenomena, with a good improvement over other URANS reported so far, which incorporate linear eddy viscosity models. The results are also comparable with those obtained by LES for the same test case. Originality/value - When comparing the computational time required by the present model and by LES, the accuracy achieved is significant and can be used for simulating 3D unsteady complex engineering flows with reasonable success. © Emerald Group Publishing Limited.

S. Vengadesan

Department of Applied Mechanics

J. L. Narasimhan

Computer simulation

Differential equations

Mathematical models

Navier Stokes equations

Reynolds number

Turbulence

Unsteady flow

Computational time

eddy viscosity

EDDY VISCOSITY MODELS

Non-Linear Model

Turbulent flow

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IIT Madras

3D unsteady RANS simulation of turbulent flow over bluff body by non‐linear model

International Journal of Numerical Methods for Heat and Fluid Flow

Numerical simulation of flow past a circular cylinder at sub-critical Reynolds number Re = 3,900 is performed using three-dimensional, unsteady, Reynolds-Averaged Navier-Stokes (URANS) equations. A nonlinear turbulence model based on the k-ε formulation is used to achieve the turbulent closure. The results obtained by the simulations are compared with experimental and previously reported numerical results. The grid used for the present simulation is reasonable, and the accuracy obtained is good considering the computational cost involved in carrying out large-eddy simulations (LES) for the same test case. The test flow is also simulated using standard k-ε model, and the results obtained by the nonlinear k-ε model are found to be better.

Numerical Heat Transfer; Part A: Applications

Three-dimensional simulation of flow past a circular cylinder by nonlinear turbulence model

This paper deals with the CFD predictions of the three dimensional incompressible flow over a wall mounted cubic obstacle placed in fully developed turbulent flow along with the heat transfer calculations. Reynolds number considered in this study is 1870 based on cube height, h and bulk velocity Ub. Our main objective is to find out the appropriate two equation turbulence model for the complex flow structure which involves recirculation, separation and reattachment. We have used standard k-ε, low-Reynolds number k-ε, non-linear k-ε model, standard k-ω and improved k-ω models to solve the closure problem. The non-linear k-ε model and improved k-ω models along with standard models are validated with bench mark problem - flow through a backward facing step (BFS). Results showed that the improved k-ω model is giving overall better predictions of the flow field especially recirculation zone, mean streamwise velocity, and turbulent characteristics when compared to those by standard eddy viscosity models. The non-linear k-ε model is giving better prediction when compared to standard k-ε and low Reynolds number k-ε models. The complex vortex structure around the cube causes large variation in the local convective heat transfer coefficient. The maximum of the heat transfer coefficient occurred in the proximity of the reattachment points and the minimum is found at the recirculation zone. © 2007 Elsevier Ltd. All rights reserved.

International Journal of Heat and Mass Transfer

Performance of two equation turbulence models for prediction of flow and heat transfer over a wall mounted cube

Unsteady 3D Reynolds Averaged Navier-Stokes (URANS) solver is used to simulate the turbulent flow past an isolated prismatic cylinder at Re=37,400. The aspect ratio of height to base width of the body is 5. The turbulence closure is achieved through a non-linear k - ε model. The applicability of this model to predict unsteady forces associated with this flow is examined. The study shows that the present URANS solver with standard wall functions predicts all the major unsteady phenomena showing closer agreement with experiment. This investigation concludes that URANS simulations with the non-linear k - ε model as a turbulence closure provides a promising alternative to LES with view to study flows having complex features.

Wind and Structures, An International Journal

Mean pressure prediction for the case of 3D unsteady turbulent flow past isolated prismatic cylinder

Journal of Wind Engineering and Industrial Aerodynamics

Steady and unsteady RANS simulations of pollutant dispersion around isolated cubical buildings: Effect of large-scale fluctuations on the concentration field

Flow around a high-rise building using steady and unsteady RANS CFD: Effect of large-scale fluctuations on the velocity statistics

3D unsteady RANS simulation of turbulent flow over bluff body by non-linear model

Journal	International Journal of Numerical Methods for Heat and Fluid Flow
ISSN	09615539
Open Access	No