A Generic Testbody for Low-Frequency Aeroacoustic Buffeting Phenomena

Raising demands towards lightweight design paired with a loss of originally predominant engine noise pose significant challenges for NVH engineers in the automotive industry. Wall thickness reductions particularly emphasize low frequency contributors due to decreasing panel stiffness. From an aeroacoustic point of view, low frequency buffeting ranks among the most frequently encountered issues. The phenomenon typically arises from rooftop or side-window buffeting, structural transmission of hydrodynamic wall pressure fluctuations or, as indicated in this work, through rear vent excitation. A convenient workflow to simulate structure-excited buffeting contains a strongly coupled vibro-acoustic model for structure and interior cavity excited by a spatial pressure distribution obtained from CFD. In the case of rear vent buffeting no validated workflow has been published yet. While approaches have been made to simulate the problem for a real-car geometry, such attempts suffer from tremendous computation costs, meshing effort and lack of flexibility. Additionally, low frequency structural behavior strongly depends on appropriate boundary conditions being subject to manufacturing and mounting tolerances. The goal of this work is to develop, simulate and experimentally validate a generic, easy-to-adjust testbody to test and assess low frequency vibro-aero-acoustic optimization strategies. In the final stage hydrodynamic excitation calculated with EXA Powerflow will be used to excite the coupled FE model and compare with wind channel measurements. As a first contribution, the geometry of the testbody is presented along with a suitable FE model. Structural and airborne transmission mechanisms are analyzed and discussed. Experimental evidence is shown to justify a Helmholtz-resonator mechanism as a simple model for rear vent buffeting. Finally, the different panel contributions subject to artificial loading are evaluated.