Reducing noise from supersonic jets using linear feedback control informed by resolvent analysis
Murthy, Sandeep Ravikumar
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https://hdl.handle.net/2142/129487
Description
Title
Reducing noise from supersonic jets using linear feedback control informed by resolvent analysis
Author(s)
Murthy, Sandeep Ravikumar
Issue Date
2025-02-17
Director of Research (if dissertation) or Advisor (if thesis)
This thesis tackles the intricate problem of jet noise reduction for supersonic aircraft, with a specific emphasis on mitigating noise generated by coherent structures within their turbulent jets. By combining a physics-based understanding of jet noise with advanced computational methods, we leverage resolvent analysis to investigate the identification and manipulation of noise-generating coherent structures within statistically stationary, chaotic, and nonlinear compressible fluid flows. Through the analysis of optimal forcing and response modes derived from resolvent analysis, we gain critical insights into the dominant frequencies and spatial characteristics of jet noise, informing the development of targeted noise reduction strategies. The thesis then explores the sensitivity of the resolvent operator’s optimal gain to base-flow modifications, providing a rigorous method for optimizing actuator and sensor placement for effective noise control. This optimization process considers the complex interplay between actuator-induced disturbances and the inherent instability mechanisms of the jet flow, ultimately leading to enhanced noise reduction capabilities. Extensive large-eddy simulations (LES) are conducted to validate the theoretical framework and assess the performance of the proposed noise reduction strategies in realistic supersonic jet configurations. These simulations bridge the gap between theoretical analysis and practical application, demonstrating the effectiveness of the developed techniques in achieving significant noise reduction. Despite the extensive application of resolvent analysis to smooth flows, its extension to shockladen flows remains underexplored due to complexities introduced by flow discontinuities. To address this gap, the thesis also develops semi-analytic resolvent solutions for the quasi-one-dimensional Euler and Navier-Stokes equations in a converging–diverging nozzle of arbitrary shape, explicitly incorporating shocks via a Green’s function approach. The objectives are threefold: (1) to derive semi-analytic resolvent solutions for shock-laden base-flows, providing benchmarks for numerical resolvent analyses; (2) to analyze the sensitivity of resolvent solutions to disturbances across flow discontinuities, elucidating the impact of shocks on forcing-response dynamics; and (3) to assess the validity of numerical schemes for computing adjoint and resolvent solutions in the presence of shocks. The findings highlight the significant influence of shocks on flow dynamics and emphasize the necessity of appropriate numerical methods for accurate analysis. This work advances the understanding of shock phenomena in aerodynamic optimization.
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