On the generation and propagation of guided jet waves

Abstract

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Upstream-travelling guided jet waves have been shown to be one of the key elements in many resonance processes underpinned in high-speed jets. Despite its importance, many of its characteristics, including how these waves are generated and how it can travel subsonically, have not been detailed in the literature. In this work, we aim to provide a clarification about the dynamics of this mode. With the aid of an acoustic scattering formulation, we are able to show that the guided-jet mode results from total-internal-reflection and transmission to decaying waves, arising from the shear layer behaving like a hard duct. After total reflection, only discrete streamwise wavenumbers may be supported by the flow, with these wavenumbers dictated by the fact that the standing wave formed inside of the jet must fit between the two shear layers. Close to the sonic line, the transmission of this mode to the outside is maximum, leading to a net-energy flux directed upstream, which dictates the direction of propagation of this mode in the eigenspectrum, providing a clear connection to the better understood soft-duct mode.