Conditional Sampling Analysis of Acoustic Phenomena from a Supersonic Jet Impinging on an Inclined Flat Plate

Acoustic waves generated from an impingement of the exhaust jet on the flame deflector is one of the causes of the payload vibration during the liftoff of a launch vehicle. To understand this acoustic phenomenon, the authors conducted experiments using a correctly expanded jet impinging on an inclined flat plate, and observed an acoustic wave propagating from the jet impingement region in a direction approximately perpendicular to the plate. The results of the wavelet analysis indicated that this acoustic phenomenon occurs intermittently. In this study, a flow phenomenon related to this intermittent acoustic phenomenon is extracted from schlieren visualization movies and wall surface pressure signals using a conditional sampling analysis. The extracted flow phenomenon is similar to the Mach wave of a free jet. With the nozzle-plate distance at which the OASPL of this acoustic phenomenon is the maximum, the flow phenomenon extracted is also similar, but some minor differences appear. These differences are expected to be a key to understand the change in OASPL when varying the nozzle-plate distance.