Experimental and numerical investigation of the flow-induced resonance of slender deep cavities that resemble automotive door gaps

Cavity aeroacoustic noise is relevant for aerospace and automotive industries and widely investigated since the 1950’s. Most investigations so far consider cavities where opening length and width are of similar scale. The present investigation focuses on a less investigated setup, namely cavities that resemble the door gaps of automobiles. These cavities are both slender (width much greater than length or depth) and partially covered. Furthermore they are under influence of a low Mach number flow with a relatively thick boundary layer. Under certain conditions, these gaps can resonate with the flow. The present investigation attempts to reveal the aeroacoustic mechanism of this tonal noise. Also the ability to simulate the resonance behavior using the Lattice Boltzmann method (LBM) is evaluated. Experiments have been conducted on simplified geometries, where hotwire, high speed PIV and microphone measurements have been used. The opening geometry and boundary layer properties have been varied. Using the PIV results, the observed influences of the opening geometry on base mode resonance are explained. With increasing velocity, several resonance modes occur. In order to obtain higher mode shapes, the cavity acoustic response is simulated using LBM and compared with experiment. Using the frequency-filtered simulation pressure field, the higher modes shapes are retrieved. Based on this an analytical model is derived that shows good agreement with the simulations and experimental results. LBM based flow simulations show that the turbulent fluctuation content of the boundary layer is important to correctly simulate the flow induced resonance response. When unsteady fluctuations are implemented in the inlet of the simulation, the cavity excitation shows good resemblance with experiment.