New Noise Component of Supersonic Jets: Laboratory Jets to High-Performance Aircraft

High-performance aircraft operate at high jet speed and temperature when the afterburner is on. The jet speed and temperature ratio are significantly higher than most laboratory facilities. At these high-speed and high-temperature conditions, compressibility effects become important. It is, therefore, possible that high-performance aircraft could emit a new noise component that has not been observed before. In the case of laboratory jets, turbulent mixing noise is generated by the shearing motion of the jet flow. The details of the process are discussed in this paper and others. In addition, this paper reports the identification of a new noise component from high-performance aircraft. This new noise component contains a significant fraction of infrasound. Infrasound at high intensity could lead to body cavity resonance. It becomes a health hazard. How this noise component is related to the early experimental observations of Mach wave radiation from shock-tube-generated jets, first reported by Oertel, and subsequent analysis based on the Euler equation by Tam and Hu are examined. The existence of the new noise component, which is the dominant component at an inlet angle larger than 140 deg, is confirmed by spectral data, directivity data, and as-measured sound pulse data.