Computational analysis of turbulent forced convection in a channel with a triangular prism

Turbulent forced convection in a heated two-dimensional plane channel with a triangular prism is computationally investigated by a cascade of modeling strategies. Reynolds Averaged Numerical Simulations (RANS) and two-dimensional Unsteady RANS (2D URANS) are performed for the Reynolds numbers (Re) 2500, 5000 and 25,000. The Prandtl number is equal to 0.7 in all computations. For Re = 2500 and Re = 5000 three-dimensional URANS (3D URANS) and Large Eddy Simulations (LES) (which are by definition three-dimensional) are also performed. In the RANS and URANS computations, the Shear Stress Transport (SST) model is used as the turbulence model. In LES, the Wall-Adapting Local Eddy-Viscosity (WALE) subgrid-scale model is used. It is predicted that the heat transfer at the channel wall can be augmented by the triangular prism, where the prediction quality depends on the modeling approach used. URANS and LES predict generally much higher Nu values compared to RANS, and, thus, indicate a much stronger heat transfer augmentation by the triangular prism. It is demonstrated that the effect of the unsteady motion of the coherent vortex structures behind the prism, which are mainly responsible for the heat transfer augmentation, cannot be adequately represented by a RANS turbulence model, and an unsteady approach (URANS/LES) is needed for a better prediction. The comparison between 2D URANS and 3D URANS shows, on the other hand, that three-dimensional effects in large scales can also play some role, depending on the Reynolds number, which could rather be evidenced for Re = 2500. The predicted peak time-averaged Nusselt numbers in the downstream region of the prism by LES turn out to be much higher than those of URANS, due to small but intense vortical structures in the wall vicinity, that are resolved by LES. However, further downstream, LES and URANS converge and show a rather similar asymptotic behavior. (C) 2011 Elsevier Masson SAS. All rights reserved.