Elevated Mainstream Mach Number Effects on Shaped Gas Turbine Film Cooling Holes

Abstract Compressible flow fields associated with engine realistic high-speed conditions can have a significant impact on the performance of shaped film cooling holes in gas turbines. Such flow fields are dependent upon a variety of parameters, notably the stagnation temperature ratio, an analog to the density ratio, and the mainstream Mach number. In previous high-speed computations using 7-7-7 shaped hole geometry, cases with a higher stagnation temperature ratio performed significantly worse than those with a lower stagnation temperature ratio, at the same blowing ratios. The same computational work, in addition to a preliminary experimental study, demonstrated that 7-7-7 cases with elevated mainstream Mach numbers perform significantly worse than those with low mainstream Mach number. In the present study, experiments were performed with 7-7-7 shaped film cooling holes across a wide range of conditions. The stagnation temperature ratio was varied from 0.6 to 0.8, and the mainstream Mach number was varied from 0.15 to 0.50. The results confirmed that the stagnation temperature ratio has a significant impact on the performance at high speeds, with higher performance occurring at a lower stagnation temperature ratio, or by proxy higher density ratio. Furthermore, cases with an elevated mainstream Mach number performed significantly worse than those with low mainstream Mach number. For all cases, performance was scaled with both blowing ratio and pressure ratio, and the implications of such scaling are discussed.