Conditional analysis of wall pressure fluctuations in plume-induced separated flowfields

The separation process in plume-induced, boundary-layer separated flowfields was found to be unsteady. Two in situ, fast-response pressure transducers were used to make individually and simultaneously sampled wall pressure fluctuation measurements over the intermittent region of separation shock wave motion. A conditional analysis technique was applied to the pressure-time histories, and statistical methods were then used to analyze the period, frequency, and velocity ensembles of the shock motion. The mean frequencies of this motion ranged between 1300 and 1500 Hz over the intermittent region, and the most probable shock wave frequencies occurred between 1 and 4 kHz over this region. The maximum zero-crossing frequency of the shock wave motion was approximately 500-600 kHz. The mean (approximately 3.5% of the freestream velocity) and most probable (approximately 6% of the freestream velocity) shock wave velocities in either direction were found to be essentially constant over the intermittent region. These results are compared to those for shock wave/boundary-layer interactions caused by solid protruberances.