Effects of bulk flow pulsations on phase-averaged and time-averaged film-cooled boundary layer flow structure

Flow structure in boundary layers film cooled from a single row of round, s imple angle holes, and subject to bulk flow pulsations, is investigated, in cluding phase-averaged streamwise velocity variations, and alterations of t ime-averaged flow structure. The bulk flow pulsations are in the form of si nusoidal variations of velocity and static pressure, and arc similar to flo w variations produced by potential flow interactions and passing shock wave s near turbine surfaces in gas turbine engines. Injection hole length to di ameter ratio is 1.6, time-averaged blowing ratio is 0.50, and bulk flow pul sation frequencies range from 0-32 Hz, which gives modified Strouhal number s from 0-1.02. Profiles of 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 fre quency goes up, with the most significant and dramatic changes at a frequen cy of 32 Hz. Phase shifts of static pressure (and streamwise velocity) wave forms at different boundary layer locations from the wall are especially im portant. As imposed pulsation frequency varies, this includes changes to th e portion of each pulsation phase when the largest influences of static pre ssure waveform phase-shifting occur. At a frequency of 32 Hz, these phase s hifts result in higher instantaneous injectant trajectories, and relatively higher injectant momentum levels throughout a majority of each Pulsation p eriod.