Effect of a crossflow at the entrance to a film-cooling hole

Understanding the complex flow of jets issuing into a crossflow from an inclined hole that has a short length-to-diameter ratio is relevant for film-cooling applications on gas turbine blades. In particular, this experimental study focused on the effect of different velocities in a coflowing channel at the cooling hole entrance. Flows on both sides of the cooling hole (entrance and exit) were parallel and in the same direction. With the blowing ratio and the mainstream velocity at the hole exit remaining fixed, only the flow velocity in the channel at the hole entrance was varied. The Mach number at the hole entrance was varied between 0 < Ma_c< 0.5, while the Mach number at the hole exit remained constant at Ma_∞= 0.25. The velocity ratio and density ratio of the jet were unity giving a blowing ratio and momentum flux ratio also of unity. The single, scaled’up film-cooling hole was inclined at 30 deg with respect to the mainstream and had a hole length-to-diameter ratio of L/D = 6. Flowfield measurements were made inside the hole, at the hole inlet and exit, and in the near-hole region where the jet interacted with the crossflow at the hole exit. The results show that for entrance crossflow Mach numbers of Ma_c= 0 and 0.5, a separation region occurs on the leeward and windward side of the cooling hole entrances, respectively. As a result of this separation region, the cooling jet exits in a skewed manner with very high turbulence levels.