High-Fidelity Modeling and Prediction of Hood Buffeting of Trailing Automobiles

The importance of fluid-structure interaction (FSI) is of increasing concern in automotive design criteria as automobile hoods become lighter and thinner. This work focuses on computational simulation and analysis of automobile hoods under unsteady aerodynamic loads encountered at typical highway conditions while trailing another vehicle. These driving conditions can cause significant hood vibrations due to the unsteady loads caused by the vortex shedding from the leading vehicle. The study is carried out using coupled computational fluid dynamics (CFD) and computational structural dynamics (CSD) codes. The main goal of this work is to characterize the importance of fluid modeling fidelity to hood buffeting response by comparing fluid and structural responses using both Reynolds-Averaged Navier-Stokes (RANS) and detached eddy simulation (DES) approaches. Results are presented for a sedan trailing another sedan. Comparisons between RANS and DES emphasize the importance of turbulence modeling fidelity in order to capture the unsteadiness of the flow and the vibration response of the hood. These comparisons include analysis of the lift forces, pressure loads on the hood, power spectral density (PSD) analysis of the flow in the region between the two vehicles, and displacement at discrete points on the hood. As expected, DES predicts higher frequency content and significantly higher turbulence levels than RANS. The hood response is found to be sensitive to these characteristics. The increased levels of turbulence result in up to 40-60% higher maximum peak-to-peak deformation and the excitation of a torsional mode of the trailing vehicle hood.