Acoustic resonances and aeroacoustic feedback mechanisms occurring at a deep cavity with an overhanging lip

Abstract

Flow-induced noise effects can significantly influence vehicle passengers’ comfort. Cavities resulting from clearances in the vehicle body represent one of the major source mechanisms of flow-induced sound generation. The objective of this study is to investigate a generic deep cavity with an overhanging lip, mimicking a door gap in a vehicle, that is overflowed by air at two different free stream velocities, $26.8\mathrm{m/s}$ and $50\mathrm{m/s}$. The turbulent boundary layer and the acoustic waves interact with the cavity and form a dominant feedback mechanism. We focus on the details of the compressible turbulent flow structures and their variations concerning velocity and boundary layer thickness. Identification of different tonal modes and the assignment to their sound generation mechanisms can be challenging due to their complex interaction. We conduct a dynamic mode decomposition (DMD) analysis to get a profound insight into it. This method allows us to link the emitted tonal sounds to their origin. In doing so, we assigned previously unknown peaks in the pressure spectrum to their corresponding mechanisms. A particular vortex-edge interaction was found for the lower approaching velocity ($26.8\mathrm{m/s}$), namely an alternating sequence of complete clipping and a subsequent partial escape. The results from this study provide a deeper understanding of the flow-induced noise mechanisms in automotive cavities, offering potential pathways for designing quieter vehicles and thus reducing both passenger and community noise.