Input-Output Analysis of High-Speed Turbulent Jet Noise

Speaker: Jinah Jeun, Center for Turbulence Research, Stanford University
March 28, 2019

Presentation

Abstract

In this talk we investigate amplifying behavior of small perturbations about Reynolds-averaged Navier-Stokes solutions of high-speed turbulent jets using input-output (I/O) analysis. Inspired by control theory in electrical engineering, our method examines how input forcing (jet turbulence) leads to output noise. Singular value decomposition of the resolvent of the linearized Navier-Stokes equations forms an orthonormal set of I/O mode pairs, sorted in descending order by the magnitude of the corresponding singular values. In this way we find that the input modes capture coherent structures in the near-field of turbulent jets. The optimal input modes correspond to wavepackets represented by asymmetric pseudo-Gaussian envelope functions at a given forcing frequency. These wavepackets remain similar in shape over a range of frequencies for St > 0.5. While the optimal mode is a wavepacket, sub-optimal modes represent decoherence of the optimal input mode. Furthermore, by projecting high-fidelity large eddy simulation (LES) data onto the basis of input modes, we find that input modes do indeed capture the acoustically relevant dynamics in the jet. The far-field acoustics predicted by the LES are recovered using only few numbers of I/O modes.

Biography

Jinah Jeun is a Postdoctoral Fellow at the Center for Turbulence Research (CTR) at Stanford University. Before joining the CTR, she was a Postdoctoral Associate in the Department of Aerospace Engineering and Mechanics at the University of Minnesota. She received her B.S. in Aerospace Engineering from Korea Advanced Institute of Science and Technology (KAIST); her M.S. in Mechanical Engineering from the University of California, Los Angeles; and her Ph.D. in Aerospace Engineering and Mechanics from the University of Minnesota in 2018 under the supervision of Professor Joseph W. Nichols. Jeun’s research interests are in the areas of computational aeroacoustics, hydrodynamic instability, and reduced-order modeling.

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