For point located in the far field, the pressure spectrum generated by a flow over a rectangular cavity in wake mode is shown. A comparisson is made between different hybrid CAA-methodologies.

The image below shows the pressure spectrum in a point inside the expansion chamber.

• polygon: 1st Rossiter mode
• squares: acoustic resonances of the expansion chamber
• circle: tailpipe resonances

The phenomenon of flow-induced noise radiation in cavities has a broad range of aerospace and automotive applications. The noise spectrum of cavity noise contains both broadband components, introduced by the turbulence in the shear layer, and tonal components due to a periodical vortex shedding at the cavity leading edge or a feedback coupling between the flow field and the acoustic field.

The research in cavity flow noise application is focused on the numerical identification of the flow-induced oscillation modes and on an evaluation of different hybrid methodologies to predict the acoustic radiation into the far-field.

• Cavity Shear Mode, evolution of vorticity (4.7MB)
• Cavity Wake Mode, evolution of vorticity (5.4MB)

• APE driven by pressure boundary conditions, evolution of acoustic pressure (11.2MB)
• APE driven by equivalent sources based on vortex sound theory, evolution of acoustic pressure (13.1MB)

In exhaust ducts, expansion chambers are commonly installed to attenuate the noise emitted by e.g. IC engines and compressors. The energy of this engine noise is concentrated around the harmonics of the engine firing frequency. Their contribution is dominant for low to medium engine speeds due to the relative inefficiency of aerodynamically generated noise sources at low Mach number. When the engine speed increases, flow noise effects become more important and can even become the dominant source of exhaust noise. In this framework, expansion chambers can even become flow-excited sound generators rather than silencers.

Therefore, the purpose of the ongoing research, is to numerically predict and gain more insight in the internally generated broadband and tonal flow noise sources in expansion chambers. Tonal noise components can either be generated by a flow-acoustic feedback-loop inside the expansion chamber or by an excitation of chamber and tailpipe acoustic modes. Broadband components are maily generated by the turbulence inside the shear layers.

• 2D Expansion chamber (M=0.5, Re=2500), evolution of vorticity (8.2MB)
• 3D Square Muffler (M=0.5, Re=1000), vorticity contours colored with streamwise velocity (1.6MB)

Aeolian tones, generated by the Von Karman vortex street in the wake of an cylinder, occur in many practical applications. Some examples include the flow around an automotive roof carrier, a rear view mirror, antennas,... The problem of aerodynamic noise, generated by a flow around a cylinder is a well-studied problem and reference solutions are available.

For this purpose, this application is used for research involving validation of different propagation equations and coupling strategies. This problem is also used to investigate the accuracy of the source region modelling (boundary conditions, numerical schemes, subgrid-scale modelling,...) on the final acoustic results.

• Flow around square cilinder (M=0.5, Re=200), evolution of vorticity (1.2MB)
• Flow around square cilinder (M=0.5, Re=200), evolution of pressure (5.6MB)