Linear-operator-based input-output analysis of a supersonic multi-stream rectangular jet flow

We analyze a supersonic multi-stream rectangular jet flow using the linear-operator-based input-output method. The primary objective is to unravel the fundamental dynamics of perturbations and generate valuable insights for designing flow control strategies to minimize far-field noise and suppress near-field unsteadiness. We conduct a comprehensive resolvent analysis by leveraging a Large Eddy Simulation-derived time-averaged flowfield on the center plane as the base flow. A discounted resolvent analysis is performed over a finite-time window, revealing a reduction in flow response amplification with a higher discounted parameter. Exploring a wide range of frequencies and spanwise wavenumbers, we observe the maximum amplification near the dominant frequency of the flowfield. The leading forcing-response mode is located in different shear layer regions, subject to the combination of frequency and wavenumber. Furthermore, an input-output analysis provides insights into the componentwise amplification of the flow response, considering state variables and spatial restrictions. The streamwise input demonstrates maximum amplification near the dominant frequency and zero spanwise wavenumber across all cases. Intriguingly, a shift in the gain distribution curve is observed, indicating an optimal receptive region switch among shear layers based on input frequency at a specific wavenumber. Further, introducing spatial restrictions at the splitter plate trailing edge (SPTE) in an input yields distinct gain behaviors compared to cases without spatial constraints. The leading 2-D response mode at the dominant frequency resembles Kelvin-Helmholtz instabilities when input is restricted at SPTE. The findings from the resolvent analysis offer valuable guidance for parameter selection in active flow control design.