Experimental Investigation of Low-Frequency Flow Phenomena on the Vehicle Underbody Using Particle Image Velocimetry

The increasing importance of minimizing drag and the absence of an exhaust system result in battery electric vehicles (BEVs) commonly having a very streamlined underbody. Although this shape of underbody is typically characterized by a low acoustic interference potential, significant flow resonance can be observed for certain vehicle configurations and frequencies below 30 Hz. Since the interior of the vehicle can be excited as a Helmholtz resonator, these low-frequency fluctuations result in reduced comfort for the passengers. As preliminary studies have shown, the flow around the front wheel spoilers significantly influences this flow phenomenon. Flow separation occurs at the front-wheel spoilers and at the front wheels. This leads to the generation of vortices which are growing significantly while being transported downstream with the flow. Even small geometric changes to add-on components on the underbody significantly influence both aerodynamics and aeroacoustics. Thus, the goal is to identify the exact origin of the aforementioned low-frequency flow resonances. An understanding of the fluid mechanical mechanisms on the underbody of the vehicle is necessary in order to subsequently develop stable measures that meet both aeroacoustics and aerodynamic requirements. For this purpose, an abstract model was applied which offers the possibility to investigate the flow phenomena independently from a specific car configuration. Particle Image Velocimetry (PIV) was used to measure the flow field underneath the underbody of the abstract vehicle model. The exact experiment setup in the model wind tunnel is presented below. The evaluation of the results includes instantaneous and time-averaged velocity fields as well as velocity fluctuations.