Aeroacoustic formulations for coupling of confined flows with the flow-guiding structure

Two aeroacoustic formulations, namely Lighthill’s wave equation and the Perturbed Convective Wave Equation (PCWE), are applied within the hybrid aeroacoustic approach to compute the propagation of flow-induced sound
in a pipe flow. A low Mach number flow (Ma=0.06) through a diverging and remerging plastic branch pipe is investigated. An analysis of the source terms computed by Large-Eddy Simulation (LES) reveals that the primary acoustic sources occur at flow detachments downstream of the sharp edges of the branch. Spectral results of the wall pressure estimated by the PCWE show good agreement with measurements. In contrast, the spectral peaks due to acoustic resonances are overestimated by Lighthill’s wave equation by at least an order
of magnitude, while correctly reproducing the incompressible pressure field. Overall, the results indicate that the PCWE is better suited for the present flow configuration. By coupling the internal acoustic domain with the surrounding structural domain through appropriate interface conditions, the interaction of the fluid and the structure is simulated. The comparison with results of the non-coupled simulations and the measurement shows that Fluid-Structure Interaction (FSI) must be modeled for accurate results, because the damping of the structure
mitigates the occurring acoustic resonances.