Numerical simulation of the unsteady flow past a cavity and application to the sunroof buffeting

Abstract

Coupling between vortex shedding over automotive sunroof and acoustic resonance of the passenger compartment can induce strong self-sustained oscillations of the flow. The maximum amplitude oscillation occurs when the frequency of an aerodynamic instability matches the resonance frequency of the vehicle. A detailed study of the phenomenon shows that aerodynamic coupling also participates to the self-sustained oscillation when the flow characteristics lead to aerodynamic frequencies outside the matching frequency range. For the numerical prediction of the sunroof buffeting, both coupling mechanisms have to be computed. A CFD solver based on Lattice Boltzmann Method has been tested on simple bidimensional cases and the results have been compared to experimental data. Although a frequency shift of the successive stages of oscillation is observed, the simulation of the aerodynamic feedback loop is achieved. The deviation from experimental measurements is mainly due to the damping influence of the eddy viscosity model. The propagation of a pressure pulse and the acoustic response of a Helmholtz-like cavity have been simulated. The results show very good agreement with theory and numerical simulation performed with Boundary Element Method. Finally, the response of the bidimensional Helmholtz-like cavity under grazing flow has been investigated. Maximum amplitude of oscillation and frequency lock-on are observed at the