Convective heat transfer at the surfaces of a surface-mounted cube in a turbulent boundary layer : LES and RANS simulations

Computational fluid Dynamics (CFD) is increasingly used as a tool for determining the convective heat transfer coefficient (CHTC) at the surfaces of bluff bodies immersed in turbulent flows. Some previous studies on high-resolution CFD simulations of CHTC used the steady Reynolds- Averaged Navier-Stokes RANS approach. However, steady RANS is incapable of capturing the inherently transient behaviour of separation, reattachment and recirculation downstream of the windward surface and of von Karman vortex shedding in the wake. LES on the other hand can provide accurate descriptions of the mean and instantaneous flow field around bluff bodies. Therefore more accurate CHTC simulations should be pursued using LES. To gain insight into the performance of LES compared to steady RANS, this paper presents LES and RANS CFD simulations of the temperature and CHTC distributions at the surfaces of a reduced-scale wall-mounted cubic model measured in turbulent channel flow. The evaluation is based on a grid-sensitivity analysis and on validation with wind-tunnel measurements of surface temperature. The results show that LES can accurately predict the surface temperature distributions of the cube walls. Steady RANS, however, indicates a satisfactory agreement with the experiments only for the windward surface. For the windward and leeward faces, the average deviations of the obtained results by LES with the experiments are 1.4 and 1.3%, respectively. For steady RANS, these deviations are 3.3 and 5.7%. For the top and side faces, where flow separation and reattachment are very complex and intermittent, the deviations are 2.4 and 1.5% for LES, while for steady RANS they increase to 13.1 and 14.9%, respectively. This study is intended to support future CFD studies of CHTC at surfaces of buildings in urban environment.