Numerical Simulation of the Generation of Axisymmetric Mode Jet Screech Tones

Abstract

An imperfectly expanded supersonic jet invariably radiates both broadband noise and discrete frequency sound called screech tones. Screech tonesareknown to begenerated by a feedback loop driven by the large-scaleinstabilitywavesofthejete ow. Insidethejet plumeisa quasiperiodicshockcellstructure.Theinteractionoftheinstability waves and the shock cell structure, as the former propagates through the latter, is responsible for the generation of the tones. Currently, there are formulas that can predict the tone frequency fairly accurately. However, there is no known way to predict the screech tone intensity. In this work, the screech phenomenon of an axisymmetric jet at low supersonic Mach number is reproduced by numerical simulation. The computed mean velocity proe les and the shock cell pressure distribution of the jet are found to be in good agreement with experimental measurements. The same is true with the simulated screech frequency. Calculated screech tone intensity and directivity at selected jet Mach number are reported. The present results demonstrate that numerical simulation using computational aeroacoustic methods offers not only a reliable way to determine the screech tone intensity and directivity but also an opportunity to study the physics and detailed mechanisms of the phenomenon by an entirely new approach.