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

Film cooling and heat transfer measurements on a cylinder model have been c onducted using the transient thermochromic liquid crystal technique. Three showerhead cooling configurations adapted to leading edge film cooling of g as turbine blades were directly compared: "classical" cylindrical holes ver sus two types of shaped hole exits. The experiments were carried out in a:f ree jet test facility at two different flow conditions, Mach numbers M = 0. 14 and M = 0.26 yielding Reynolds numbers based on the cylinder diameter of 8.6e4 and 1.55e5, respectively. All experiments were done at a mainstream turbulence level of Tu = 7 percent with an integral length scale of L-x = 9 .1 mm (M = 0.141, or L-x = 10.5 mm (M = 0.26), respectively. Foreign gas in jection (CO2) 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 s hown, including surface distributions of film cooling effectiveness and loc al heal transfer coefficients. Additionally, hear transfer and heat load au gmentation due to injection with respect to the uncooled cylinder are repor ted. For a given cooling gas consumption, the laid-back shaped hole exits l ead to a clear enhancement of the cooling performance compared to cylindric al exits, whereas laterally expanded holes give only slight performance enh ancement.