A High-Fidelity Transient Fluid-Structure-Interaction Methodology for Evaluation of Rear Bumper Flutter of a Vehicle

The need for fuel efficient and pedestrian safe cars leads to the use of thinner and lighter car exteriors. Interaction of these exterior car components at high speed with an aerodynamic load can lead to undesirable aero-elastic vibration and flutter. Early identification and mitigation of such vibration can bring significant cost and time benefit, by reducing dependence on prototype testing and recalibration of prototype tooling at later stages. The present work demonstrates a transient Fluid-Structure-Interaction based numerical methodology for estimation of aerodynamic-induced flutter of the rear bumper of an SUV. The proposed method performs coupled-high fidelity transient full vehicle aerodynamic Finite Volume based and dynamic rear bumper structural Finite Element based simulations required for flutter estimation. The method has been put through a two-step validation against experimental wind tunnel test data of a prototype car with modified bumper for the specific test-case. The pressure, and the time series data of rear bumper deflection were captured at multiple probe locations from wind tunnel experiments at 140 kmph and 200 kmph. The distribution of pressure on the rear surfaces of the car is well captured by the aerodynamic simulation at both speeds. The deflection amplitude and patterns across multiple probe locations and across the two speeds were reproduced with reasonable accuracy by the methodology. An artificial Rayleigh damping coefficient calibrated against the experimental data is used to capture the overall damping of the rear bumper. The two-step validation against experimental data extracted from a production-ready car demonstrates the accuracy and robustness of the methodology.