Visualization and acoustic-triggered conditional sampling analysis of acoustic phenomena with screech-tone of an over-expanded supersonic jet

Abstract

In the liftoff of launch vehicles and supersonic aircrafts, jet noise is required to be reduced because it causes various problems. To reduce the influence of jet noise, it is significant to clarify the source location and the direction of propagation as well as the spectrum of each acoustic phenomenon. For this purpose, the authors have proposed the acoustic-triggered conditional sampling analysis to obtain acoustic information from high-speed schlieren movies. In the authors’ previous studies, this method was applied to correctly and under expanded jets, and the broadband phenomena were clarified, such as Mach wave radiation and shock associated noise. In this study, this method was applied to an over-expanded jet, in which screech tone is observed in addition to the broadband acoustic phenomena. First, it was found that the broadband phenomena and screech tone could be observed separately by this method with choosing the microphone location for trigger detection. Then, two screech tone noises of different frequencies are observed, and it was clarified that they are propagating to different directions from different source locations. Also, the acoustic phenomenon generated by impingement of the same over-expanded jet on an inclined flat plate will be discussed.In the liftoff of launch vehicles and supersonic aircrafts, jet noise is required to be reduced because it causes various problems. To reduce the influence of jet noise, it is significant to clarify the source location and the direction of propagation as well as the spectrum of each acoustic phenomenon. For this purpose, the authors have proposed the acoustic-triggered conditional sampling analysis to obtain acoustic information from high-speed schlieren movies. In the authors’ previous studies, this method was applied to correctly and under expanded jets, and the broadband phenomena were clarified, such as Mach wave radiation and shock associated noise. In this study, this method was applied to an over-expanded jet, in which screech tone is observed in addition to the broadband acoustic phenomena. First, it was found that the broadband phenomena and screech tone could be observed separately by this method with choosing the microphone location for trigger detection. Then, two screech tone noises of differ...