Effects of Bulk Flow Pulsations on Phase-Averaged and Time-Averaged Film-Cooled Boundary Layer Flow Structure

Abstract

Flow structure in boundary layers film cooled from a single row of round, simple angle holes, and subject to bulk flow pulsations, is investigated, including phase-averaged streamwise velocity variations, and alterations of time-averaged flow structure. The bulk flow pulsations are in the form of sinusoidal variations of velocity and static pressure, and are similar to flow variations produced by potential flow interactions and passing shock waves near turbine surfaces in gas turbine engines. Injection hole length to diameter ratio is 1.6, time-averaged blowing ratio is 0.50, and bulk flow pulsation frequencies range from 0–32 Hz, which gives modified Strouhal numbers from 0–1.02. Profiles of time-averaged flow characteristics and phase-averaged flow characteristics, measured in the spanwise/normal plane at x/d=5 and z/d=0, show that effects of pulsations are larger as imposed pulsation frequency goes up, with the most significant and dramatic changes at a frequency of 32 Hz. Phase shifts of static pressure (and streamwise velocity) waveforms at different boundary layer locations from the wall are especially important. As imposed pulsation frequency varies, this includes changes to the portion of each pulsation phase when the largest influences of static pressure waveform phase-shifting occur. At a frequency of 32 Hz, these phase shifts result in higher instantaneous injectant trajectories, and relatively higher injectant momentum levels throughout a majority of each pulsation period.