Shock wave - Film cooling interactions in transonic flows

Interactions between shock waves and film cooling are described as they aff ect magnitudes of local and spanwise-averaged adiabatic film cooling effect iveness distributions. A row of three cylindrical holes is employed. Spanwi se spacing of holes is 4 diameters, and inclination angle is 30 deg. Free-s tream Mach numbers of 0.8 and 1.10-1.12 are used, with coolant to free-stre am density ratios of 1.5-1.6. Shadowgraph images show different shock struc tures as the blowing ratio is changed, and as the condition employed for in jection of film into the cooling holes is altered. Investigated are film pl enum conditions, as well as perpendicular film injection crossflow Mach num bers of 0.15, 0.3, and 0.6. Dramatic changes to local and spanwise-averaged adiabatic film effectiveness distributions are then observed as different shock wave structures develop in the immediate vicinity of the film-cooling holes. Variations are especially evident as the data obtained with a super sonic Mach number are compared to the data obtained with a free-stream Mach number of 0.8. Local and spanwise-ave raged effectiveness magnitudes are g enerally higher when shock waves are present when a film plenum condition ( with zero crossflow Mach number) is utilized. Effectiveness values measured with a supersonic approaching free-stream and shock waves then decrease as the injection crossflow Mach number increases. Such changes are due to alt ered flow separation regions in film holes, different injection velocity di stributions at hole exits, and alterations of static pressures at film hole exits produced by different types of shock wave events.