Convergence angles effect on heat transfer characteristics in a wedged duct with dimples/protrusions

In this study, numerical simulations are performed to investigate the effects of convergence angle on the flow structure, end-wall heat transfer, and friction factor in a wedged duct with dimples/protrusions. The convergence angles are set as 0o, 6.3o, and 12.5o, respectively. The end wall of the wedged duct is arranged with dimples or protrusions in staggered layout. The normalized depth of a dimple/protrusion is set as 0.2. The Reynolds number is between 8,500 and 60,000. Results for the flow field, end-wall heat transfer, and friction factor are considered. The results show that the increase in the convergence angle introduces a pressure gradient pointing from the wedged duct top to the end-wall side. Thus, the flow impingement and flow acceleration are increased, while the flow recirculation is decreased. On the other hand, the secondary edge vortex in the wedged duct with dimples is also increased as the convergence angle increases, which contributes to the heat transfer augmentation. For the wedged duct with protrusions, the increase in the convergence angle enhances the local heat transfer by intensifying the leading edge impingement. However, the flow structure in the duct with protrusions does not change so remarkably as in the dimpled duct. It is also found that the increase in the convergence angle significantly increases the friction factor with moderate heat transfer augmentation. The thermal performance indicates that the large convergence angle reduces the thermal performance remarkably. The value is reduced from 1.7 to 1.35 as the convergence angle increases.