Generation of negative peak pressures under a separation bubble

Abstract

This paper investigates the generation mechanism of negative peak pressures on a blunt plate under a separation bubble with Large Eddy Simulation (LES). Synchronized sampling of the wind pressures on and velocity fields around the plate is adopted to explore the relation between pressure fluctuations and vortex dynamics. The ordinary pressure fluctuation is found to be induced by high-frequency vortex convection. Formation of a negative peak pressure starts from the vortex head arriving at an observation point and ends up at the vortex tail leaving that location. A negative peak pressure occurs when the vortex core is right beneath/above the observation point. Spectral analysis of the wind pressures and Dynamic Modal Decomposition (DMD) for the velocity fields are combined to detect and visualize the low-frequency motion responsible for extreme pressure fluctuations. A counterpart of the low-frequency dominating component of the wind pressures is found in the velocity modal analysis, which is related to the shedding of an extreme large-scale vortical structure and demonstrates a flapping motion of the shear layer. The present study provides insights to the generation of negative peak pressures and the relation between vortex behaviors and the shear layer movement.