Investigation of detailed film cooling effectiveness and heat transfer distributions on a gas turbine airfoil

In the present study film cooling effectiveness and heat transfer were syst ematically investigated on a tur bine NGV airfoil employing the transient l iquid crystal technique and a multiple regression procedure. Tests were con ducted in a linear cascade at exit Reynolds numbers of 0.52e6, 1.02e6 and 1 .45e6 and exit Mach numbers of 0.33, 0.62 and 0.8, at two mainstream turbul ence intensities of 5.5 and 10 percent. The film cooling geometry consisted of a single compound angle row an the pressure side (PS), and a single or a double row on the suction side (SS). Foreign gas injection was used to ob tain a density ratio of approximately 1.65, while air injection yielded a d ensity ratio of unity. Tests were conducted for blowing ratios of 0.25 to 2 .3 on the SS, and 0.55 to 7.3 on the PS. In general film cooling injection into a laminar BL showed considerably higher effectiveness in the near-hole region, as compared to a turbulent BL. While mainstream turbulence had onl y a weak influence on SS cooling, higher effectiveness was noted on the PS at high turbulence due to increased lateral spreading of the coolant. Effec ts of,mainstream Mach and Reynolds number were attributed to changes of the BL thickness and flow acceleration. Higher density coolant yielded higher effectiveness on both SS and PS, whereas heat transfer ratios were increase d on the SS and decreased on the PS. Comparison of the single and double ro w cooling configurations on the SS revealed a better film cooling performan ce of the double row due to an improved film coverage and delayed jet separ ation.