Identification of the Mechanism of Low Frequency Pressure Fluctuations Using Vortex Identification Methods

Flow noise is becoming increasingly important in the automotive industry as it significantly influences driving comfort. This is especially true for battery electric vehicles (BEV). Due to the absence of an exhaust system and the advantages in terms of drag coefficients, BEVs customarily possess a very streamlined underbody. Typically, this underbody shape is characterized by a low acoustic interference potential. However, significant pressure fluctuations can be observed for certain vehicle configurations and frequencies below 30 Hz. Initial investigations have shown the relevance of the front wheel spoilers for the existence of the flow phenomenon. Even small geometric modifications can significantly change the development, growth and propagation of the pressure fluctuations. Extensive Particle Image Velocimetry (PIV) measurements in a plane below the underbody of a generic car model were conducted. Until now, the exact and complex mechanism of formation of the flow phenomenon is still largely unknown. Therefore, the PIV experiments aim to investigate the underbody flow in detail. Within this study, the results of the PIV measurements will be analyzed in detail. Therefore, velocity fluctuations and vorticity are investigated first. Since vortex motion plays a significant role in turbulent shear flow, the focus of this investigation is on the identification and analysis of eddies in the underbody flow. For this purpose, different vortex identification methods are first considered. Subsequently, eddies are analyzed using the �� method. Two different underbody configurations are investigated and examined to determine the exact mechanism of origin of the flow phenomenon.