Analysis of Guided Jet Modes and Energy Transfer in High Aspect Ratio Rectangular Screeching Jets

A detailed study of the guided jet mode involved in screech tone generation for an aspect ratio 4:1 rectangular jet is performed using large-eddy simulation (LES) data generated by Wu et al. (2022). 2D linear stability analysis is performed using cross-sectional mean flow profiles obtained from LES. The dominant flapping Kelvin-Helmholtz wave and guided jet mode are identified through linear theory. The properties of the guided jet modes and the duct modes supported by the jet are analyzed as functions of the downstream location. The flapping guided jet mode is found to be propagative in a narrow region downstream that aligns well with the peak guided jet mode amplitude in LES. Downstream of this region, the flapping guided jet mode and duct mode are evanescent. A velocity variance budget equation is formulated for the guided jet mode and evaluated using LES data. The dynamics of the guided jet mode are found to be well-explained by triadic interactions involving the Kelvin-Helmholtz wave, the shock-cell structure, and the slowly-varying mean jet flow. Source terms are evaluated in physical space, revealing where the guided jet mode gains kinetic energy and where it loses kinetic energy to specific triadic interactions.