Bulk flow pulsations and film cooling : Flow structure just downstream of the holes

Experimental results are presented that describe the effects of bulk flow pulsations on film cooling from a single row of simple angle film cooling holes. The pulsations are in the form of sinusoidal variations of static pressure and streamwise velocity. Such pulsations are important in turbine studies because: (i) Static pressure pulsations result in significant periodic variations of film cooling flow rates, coverage, and trajectories, and (ii) static pressure pulsations occur near blade surfaces in operating engines from potential flow interactions between moving blade rows and from families ofpassing shock waves. Distributions of ensemble-averaged and time-averaged Reynolds stress tensor components are investigated just downstream of the holes along with distributions of all three mean velocity components. Important changes are evident in all measured quantities. In particular, maximum Reynolds shear stresses -2u'v'/u∞ 2 are lower in regions containing the largest film concentrations because the strong shear layer produced by the injectant is more three dimensional, larger in extent, and oscillates its position from the wall with time.