Numerical Evaluation on Effects of Upstream Sand-Dune-Shaped Ramp and Backward Coolant Injection on Heat Transfer

Abstract

Numerical simulations are performed for the forward and backward injection film cooling with the presence of upstream ramp under three typical blowing ratios of 0.5, 1.0 and 1.5. Totally nine film cooling configurations are taken into considerations in the current study, where two ramps (straight-wedge-shaped ramp (SWR) and sand-dune-shaped ramp (SDR)), two coolant injection modes (forward injection (FW) and backward injection (BW)), and two film-hole shapes (cylindrical hole (CH) and fan-shaped hole (FH)) are involved. From the current study, the effects of coolant injection scheme and upstream ramp on the film cooling performance are evaluated in the viewing of the heat transfer. Based on the numerical results, it is demonstrated that a wide high net heat flux reduction (NHFR) zone is created in the forward injection cases at M(the blowing ratio)=0.5, but it is shrunk or disappeared rapidly at M=1.5, except the FH-FW-SDR case. While for the backward injection case, two high heat flux reduction zones are generated around the hole exit where the separate bubbles locate, and it remains even at M=1.5. Among the current cases, the FH-FW-SDR is demonstrated to be the best one for achieving the highest NHFR under the all three blowing ratios. With regard to the coolant injection scheme, its influence on heat transfer coefficient is more complicated, tightly associated with the blowing ratio, film-hole shape and the upstream ramp.