Experimental investigation of the influence of density ratio and vane exit Mach number on platform cooling

Experimental investigation and parametric analysis were carried out to evaluate the influence of coolant to mainstream density ratio (DR) and isentropic exit Mach number (Ma2is) on both thermal and aerodynamic performance of a nozzle vane cascade with platform cooling through slot or discrete cylindrical holes. Measurements were carried out on a 6--vane cascade for a base case scenario, which implied high DR of 1.5, high freestream turbulence intensity of Tu1 = 9.5% and Ma2is = 0.4, while varying the coolant--to--mainstream mass flow rate (MFR) between 0.5% and 1.5%. The impact of reducing DR to 1.0 and increasing Ma2is to 0.68 was assessed, MFR held constant. DR was varied by injecting either air/nitrogen or carbon dioxide as coolant flow, thanks to the pressure sensitive paint (PSP) technique. Lower thermal coverage derived from reduced DR whereas higher Ma2is resulted in enhanced cooling effectiveness over the perforated platform.