Flow characteristics and wake topology of two-seat convertibles

Abstract

This study aims to clarify the flow characteristics and wake structure of convertible vehicles. Numerical simulations are performed to obtain a preliminary visualization, and the potential vortical motion characteristics are investigated by examining the Q-criterion across multiple cross-sections. Comparisons between numerical and experimental results validate the reasonableness of our numerical model. The predominant wake topology of a two-seat convertible is obtained in terms of the location, shape, and spin direction of the vortices. We observe a "nook" vortex that is triggered by the flow acceleration induced by the pressure gradient near the windshield step, provoking undesirable aeroacoustic noise and degrading the cabin comfort. Complicated A-pillar vortex dynamics are revealed, with small vortices that are shed into the cabin and impinge the seats, eventually forming a long tail structure above the back of the vehicle. Moreover, periodic fluctuations of the windshield vortex are induced by the Kelvin-Helmholtz instability, significant impacting the streamwise wake. Ultimately, the combined motion characteristics of the A-pillar and windshield vortices exert undesirable effects on the aeroacoustic noise and drag, suggesting fundamental mechanisms for achieving optimal energy-saving and acoustic convertibles in the future. Based on the wake topology and the vortical generating mechanism, approaches are proposed to reduce the drag and aeroacoustic noise by impeding the flow over the door into the cabin and modifying the shape of windshield step, and lengthening the windshield in stream direction.