How Wrong Can a Flow Model Be, and Yet Provide Reasonable Acoustic Predictions?

Speaker: Christophe Schram, von Karman Institute for Fluid Dynamics
July 1, 2014

Presentation

Abstract

In low Mach number applications, aeroacoustic analogies provide an efficient approach to aerodynamic sound prediction, based on the distinction between sound generation and propagation effects. The procedure can be split in two successive steps. Firstly, an adequate flow model is obtained - for example by means of unsteady CFD, providing the aerodynamic quantities from which equivalent acoustic sources can be calculated. In the second step, the sound emitted by the equivalent sources is propagated towards the listener region. While this procedure has been successful in many applications, its numerical implementation remains a difficult task, as seemingly small errors in the flow description can yield very significant errors in the acoustic solution. In this seminar, we will review some of the fundamental assumptions that are involved in two important aeroacoustic analogies, namely Curle's analogy and Vortex Sound Theory, and illustrate through some examples the numerical robustness issues that arise when an inadequate interpretation of the flow data is made. In contrast, it will be shown that aeroacoustical analogies allow using relatively crude flow models through a careful filtering of the non-physical spurious sources of sound.

Biography

Christophe Schram has obtained his Ph.D. degree in aeroacoustics in 2003 for his experimental research conducted at the von Karman Institute for Fluid Dynamics, degree granted by the Eindhoven University of Technology (Netherlands) and Free University of Brussels (Belgium). After a post-doctoral research at the Cambridge University (UK) on thermo-acoustic instabilities in gas turbines, he moved to the company LMS International (Belgium) to lead the numerical aeroacoustic RTD activities for 6 years. He moved then back to VKI as Assistant Professor in aeroacoustics in 2009. Promoted as Associate Professor in 2011, his current fields of interest include the simulation and measurement of flow-induced noise by airframe configurations, ducted ventilation systems and low-speed fans in particular, and the prediction of the aero-acoustic instabilities that arise in complex duct networks or solid propellant boosters.

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