Effects of Bulk Flow Pulsations on Film-Cooled Boundary Layer Structure

Abstract

Experimental results are presented which describe the effects of bulk flow pulsations on film cooled boundary layer structure. The film is produced by a single row of simple angle film cooling holes and 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 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 velocity and streamwise mean vorticity, where x is streamwise distance from the downstream edge of the holes and d is hole diameter. Important changes from the imposed bulk flow pulsations are evident in all measured quantities, especially just downstream of the holes at x/d = 4.5. Here, Maximum Reynolds shear stresses −2u′v ′ /u∞ 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 pulsations is imposed. This causes the shear layer to become more diffused as it is spread over a larger spatial volume.