Quantification of Energy Transfer Processes in Supersonic Rectangular Screeching Jets*

High-fidelity large-eddy simulation (LES) data of under-expanded rectangular jets are used to analyze energy transfer processes relevant to the generation of high-intensity screech tones. It is believed that interaction between downstream-traveling Kelvin-Helmholtz waves and the shock-cell structure produces an upstream-traveling guided jet mode that is important for sustaining screech. Waves involved in this process can be uniquely identified by frequency and streamwise wavenumber. An energy budget equation for the guided jet mode is derived through spatial filtering of the Navier-Stokes equations and evaluated using LES data. This method allows for identification of spectral energy fluxes across the guided jet mode wavenumber in the physical domain. Source terms involving Kelvin-Helmholtz waves and the shock-cell structure reveal a spatially-distributed energy transfer process to the guided jet mode in the shear layer and jet core. Regions in the jet where the guided jet mode loses significant energy to the slowly-varying mean flow are also identified. The energy equation is simplified by retaining dominant source terms and used to explain the spatial modulation of the guided jet mode amplitude. Stability properties of the guided jet mode are also assessed in this framework.