Effects of blowing ratios and lip thicknesses on film cooling for trailing edge cutback with latticework ducts

Abstract

In this study, a trailing edge cutback configuration with latticework ducts is proposed to provide more effective thermal protection for high-pressure turbine blades. Detached eddy simulation, as a LES/RANS hybrid method, is utilized to investigate the film cooling efficiency and turbulent behavior of the trailing edge cutback. The flow dynamics mechanism of cutback film cooling is elucidated by analyzing five blowing ratios (0.2 ∼ 1.25) and four lip thicknesses (0.5 ∼ 2) schemes. Time-averaged results indicate that the counter-intuitive efficiency decline and recovery behavior is identified again. Quantitatively, the area-averaged film cooling efficiency decreases by 14.3 % in the efficiency decline interval and increases by 16.3 % during the recovery interval. The distinct deflection of the swirling coolant jet leads to an efficiency distribution characterized by higher values on the sides and lower values in the center. Moreover, the mixing of the swirling jets and crossflow produces the Asymmetric Counter-rotating vortex pairs and Spiral-vortex system, which exacerbate heat transfer near the wall. At the highest blowing ratio, the excess coolant is forced against the wall by a rotating streamwise vortex system, providing better film coverage. Additionally, the film cooling efficiency of the cutback structure with a lip-to-slot ratio of 2 decays by 27 % as the blowing ratio decreases. The detrimental influence of the lip thickness increase on the film cooling efficiency is considerably mitigated by the swirling jet, especially in the maximum lip thickness.