Experimental Study of showerhead cooling on a cylinder comparing several configurations using cylindrical and shaped holes

Abstract

Film cooling and heat transfer measurements on a cylinder model have been conducted using the transient thennochromic liquid crystal technique. Three showerhead cooling configurations adapted to leading edge film cooling of gas turbine blades were directly compared : 'classical' cylindrical holes versus two types of shaped hole exits. The experiments were carried out in a free jet test facility at two different flow conditions, Mach numbers M=0.14 and M4.26, yielding Reynolds numbers based on the cylinder diameter of 8.6e4 and 1.556, respectively. All experiments were done at a main stream turbulence level of Tu=7% with an integral lengthscale of L x =9.1mm (M=0.14), or L x =10.5mm (M=0.26) respectively. Foreign gas injection (CO 2) was used yielding an engine-near density ratio of 1.6, with blowing ratios ranging from 0.6 to 1.5. Detailed experimental results are shown, including surface distribution of film, cooling effectiveness and local heat transfer coefficients. Additionally, heat transfer and heat load augmentation due to injection with respect to the uncooled cylinder are reported. For a given cooling gas consumption the laid-back shaped hole exits lead to a clear enhancement of the cooling performance compared to cylindrical exits, whereas laterally expanded holes give only slight performance enhancement.