EFFECTS OF BULK FLOW PULSATIONS ON FILM-COOLED BOUNDARY-LAYER STRUCTURE

Experimental results are presented which describe the effects of bulk flow pulsations on film cooled boundary layer structure. The film is p roduced by a single row of simple angle film cooling holes and the pul sations are in the form of sinusoidal variations of static pressure an d streamwise velocity. Such pulsations are important in turbine studie s because: (i) static pressure pulsations result in significant period ic variations of film cooling flow rates, coverage, and trajectories, and (ii) static pressure pulsations occur near blade surfaces in opera ting engines from passing shock waves and potential flow interactions between moving blade rows. Distributions of ensemble-averaged and time -averaged Reynolds stress tensor components are presented for x/d of 4 .5, 9.8, 16.4, and 24.1 along with distributions of streamwise mean ve locity and streamwise mean vorticity, where x is streamwise distance f rom the downstream edge of the holes and d is hole diameter. Important changes from the imposed bulk flow pulsations are evident in all meas ured quantities, especially just downstream of the holes at x/d = 4.5. Here, maximum Reynolds shear stresses -2<(u'v')over bar>/<(u(infinity ))over bar>(2) are reduced by the pulsations in regions containing the largest film concentrations. This is because the shear layer produced by the injectant oscillates its position as each pulsation is imposed . This causes the shear layer to become more diffused as it is spread over a larger spatial volume.