Reverse flow region associated to a heat transfer in a turbulent wall jet

A numerical study is performed in order to investigate the effects of the inlet flow structure on the flow and heat transfer characteristics in the reattachment zone downstream a backward facing step. Indeed, two inlet flow configurations are considered: a turbulent wall jet (WJ) which presents a particular structure with two sources of turbulence production (one is due to the shear flow related to the inner layer with small scale eddies and another one corresponds to the free shear jet flow with entrainment of large turbulence scales) and a standard channel flow (CF). The numerical approach is based on two-scale energy-flux model coupled with a full Reynolds stress closure valid at low turbulence Reynolds numbers. To calculate the turbulent heat-flux vector, we considered two models: a Single Gradient Diffusion Hypothesis (SGDH) and a Generalized Gradient Diffusion Hypothesis under a fixed heat flux boundary condition. Numerical predictions for the CF configuration are compared with experimental data of Vogel and Eaton (1985). So the present study would contribute emphasizing the role of the large eddies in the outer flow on the convective heat transfer in the recirculation zone. (C) 2014 Elsevier Masson SAS. All rights reserved.