Numerical simulation of jet screech tones

Abstract

Screech tones are discrete frequency sounds radiated from imperfectly expanded supersonic jets. The tones are generated by a feedback loop driven by the large-scale instability waves of the jet flow. In the plume of an imperfectly expanded jet is a quasiperiodic shock cell structure. Screech tones are produced by the interaction of the instability waves and the shock cells as the former passes through the latter. Although the screech phenomenon has been studied over many years, many of its features are still not understood. Presently, there are accurate tone frequency prediction formulas. However, there is no known way to predict tone intensity. In this study, the screech phenomenon is investigated through numerical simulation using CAA methods. The simulation reproduces all the characteristic features of jet screech, including the staging phenomenon. The computed screech frequencies and intensities are found to compare well with experimental measurements. Numerical results on the effects of jet temperature also compare well with experiments. The favorable agreements indicate that numerical simulation is a valuable tool for investigating the jet screech phenomenon. [Work supported by NASA Lewis Research Center Grant NAG 3–2102.]