Bulk Flow Pulsations and Film Cooling: Flow Structure Just Downstream of the Holes Free

Experimental results are presented which 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 of passing shock waves. Distributions of ensemble-averaged and time-averaged Reynolds stress tensor components are investigated at x / d=4.5 along with distributions of all three mean velocity components, where x is streamwise distance from the downstream edge of the holes and d is hole diameter. Important changes are evident in all measured quantities which must be accounted for in any closure model used to simulate unsteadiness from the relative motion of two adjacent blade rows. 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. The pulsations also produce significant changes to profiles of $u′w′¯/u∞¯2$⁠, $u′2¯/u∞¯2$⁠, $v′2¯/u∞¯2$⁠, and $w′2¯/u∞¯2$ in the film cooled boundary layer, and increase $u¯/u∞¯$ over most of the boundary layer thickness at spanwise locations near the holes.