Film cooling over a concave surface through two Staggered rows of compound angle holes

Abstract

Experimental results of film cooling effectiveness over a concave surface with two staggered rows are presented by employing transient liquid crystal thermography. Four different discrete hole configurations are used for the injection of jet flow, including a straight circular hole configuration with a spanwise injection angle (β) of 0° and three forward‐expanded hole configurations with β = 0°, 45° and 90° respectively. In all test models there are two staggered rows of discrete holes with streamwise injection angle (γ ) of 35°. Blowing ratios (M) are 0.5, 1.0, and 2.0. The effects of blowing ratio, hole expanded angle, and injection angle orientation on film cooling performance are investigated. The jet flow with M = 0.5 is fairly uniform along the wall surface. The lift‐off phenomenon can be found in the jet flow with β = 0° for both cases of simple and compound angles at M = 1.0 and also exists among all test cases at M = 2.0 except for β = 90°. The lift‐off effect results in a decrease in both η and h /h0. At β = 0°, the jet flow with a forward‐expanded hole gives higher η and lower h /h0 than a simple angle hole. At a fixed blowing ratio, the jet flow with compound angle holes has lower q /q0 and thus provides better wall protection than that with simple angle holes. In the present study, the compound angle with β = 0° at M = 2.0 provides the best film‐cooling protection over the concave surface among all the test configurations.