Three-Dimensional Numerical Simulation of the Jet Screech Phenomenon

Abstract

Three-dimensional numerical simulations of the jet screech phenomenon are carried out using the multiple-size-mesh, multiple-time-step, dispersion-relation-preserving scheme. The simulations reproduce all of the experimentally observed characteristic features of the screech tones, including the axisymmetric A 1 and A 2 modes, the flapping/helical B and C modes, and the staging phenomenon. Screech tone frequencies as well as intensities calculated by the numerical simulations are in excellent agreement with experimental measurements. Power spectral analysis of the numerical simulation data provides irrefutable evidence that, whenever two tones are measured in the noise spectrum, it is not because there is a continuous switching from one tone to another, but because the two tones actually coexist simultaneously. A first explanation of why there are two axisymmetric and two flapping/helical screech modes based on two feedback mechanisms is offered. Strong evidence is provided to support the proposed mechanisms.