EFFECT OF A CROSS-FLOW AT THE ENTRANCE TO A FILM-COOLING HOLE

Understanding the complex flow of jets issuing into a crossflow from a n inclined hole that has a short length-to-diameter ratio is relevant for film-cooling applications on gas turbine blades. In particular thi s 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 h ole exit remaining fixed, only the flow velocity in the channel at the hole entrance was varied. The Mach number at the hole entrance was va ried between 0 < Ma(c) < 0.5, while the Mach number at the hole exit r emained constant at Ma(infinity) = 0.25. The velocity ratio and densit y ratio of the jet were unify giving a blowing ratio and momentum flux ratio also of unity. The single, scaled-lip film-cooling hole was inc lined at 30 deg with respect to the mainstream and had a hole length-t o-diameter ratio of L/D = 6. Flowfield measurements were made inside t he 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 s how that for entrance crossflow Mach numbers of Ma(c) = 0 and 0.5, a s eparation region occurs on the leeward and windward side of the coolin g hole entrances, respectively. As a result of this separation region, the cooling jet exits in a skewed manner with very high turbulence le vels.