Computational Aeroacoustic Analysis of a Jet Impinging on an Inclined Plate

Speaker: Christoph Brehm, NASA Ames Research Center
February 5, 2015

Presentation

Abstract

The noise generation mechanisms for a supersonic M = 1.8 turbulent jet impinging on an inclined plate are investigated employing a combination of large-eddy simulations, far-field acoustic propagation, and acoustic post-processing techniques within the Launch Ascent and Vehicle Aerodynamics (LAVA) framework. Excellent comparisons with experimental acoustic far-field measurements and pressure measurements on the impingement plane are obtained. Our analysis demonstrates that the two local maxima in the far-field overall sound pressure levels (OASPL) in 75° and 120° observer directions are associated with different noise generation mechanisms. The causality method based on Lighthill’s acoustic analogy is used to link the acoustic noise signature to relevant physical mechanisms in the source region. In the causality approach, we make it a point to differentiate between the application of normalized and un-normalized cross-correlation functions for noise source characterization. Proper orthogonal decomposition (POD) accompanies the results from the causality method. The spectral characteristics of the acoustic signals in the 75° and 120° observer directions can be captured with the most energetic POD modes by choosing proper POD energy norms, in particular based on the disturbance flow energy for 75° and Lighthill’s entropy fluctuation term for 120°.

Biography

Christoph Brehm joined the Science & Technology Corporation (STC) / Applied Modeling and Simulation branch at NASA Ames in 2012. He has been working in the LAVA group with special emphasis on unsteady flows, e.g., launch environment flows, unsteady loads and acoustics. Recently, he started an effort in developing higher-order shock capturing schemes for ILES/LES with the LAVA framework. He received a B.S./M.S. equivalent degree at the University of Stuttgart (Germany) and a Ph.D. at the University of Arizona under the supervision of Professor H.F. Fasel working on active flow control, immersed boundary methods and transition research.

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