W. De Roeck, Hybrid methodologies for the computational aeroacoustic analysis of confined, subsonic flows, 2007

Abstract

This work aims at the development of numerical methods for the analysis of noise generation and propagation in confined subsonic flows. The adopted approach is a hybrid aero-acoustics prediction technique which decomposes the computational domain in two different subdomains: a source region, where an aerodynamic flow field is generating noise and an acoustic domain, where acoustic waves are propagated in the presence of a mean flow. The coupling between both regions is elaborated using equivalent source term formulations or through aero-acoustic boundary conditions. This dissertation focuses mainly on the propagation of acoustic waves in a moving medium and the ability of the coupling techniques to predict accurately tonal aerodynamic noise phenomena.

The linearized Euler equations and an irrotational variant, the Acoustic Perturbation Equations are the main propagation equations. They are discretized using high-order finite-difference techniques with low dispersion and dissipation errors, which are through the different coupling strategies, linked with a finite volume Large Eddy Simulation solver, specially designed for aeroacoustic applications. A validation of both the propagation equations and the different coupling techniques is carried out for a number of aero-acoustic benchmark problems, including the aero-acoustic study of a simple expansion chamber. It is shown that, especially for confined subsonic flow applications, a distinction between aerodynamic and acoustic fluctuating variables is needed and a new aerodynamic/acoustic filtering technique is developed. In this way, a general numerical technique is developed and validated which allows to study in an accurate way both the aerodynamic noise generating mechanisms and the propagation of acoustic waves in a non-quiescent medium for subsonic confined flow applications.

Order Code

Code: 07D10