Time-averaged three-dimensional flow topology in the wake of a simplified car model using volumetric PIV

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Fuel shortages and air pollution are two major incentives for improving the aerodynamics of vehicles. Reducing wake-induced aerodynamic drag, which is strongly dependent on flow topology, is important for improving fuel consumption rates which directly affect the environment. Therefore, a comprehensive understanding of the baseline flow topology is required to develop targeted drag reduction strategies. In this research, the near wake of a generic ground vehicle, a 25∘ slant Ahmed model at a flow Reynolds number of Re=1.1×106 , is investigated and its flow topology elucidated. The flow field of this canonical bluff body is extremely rich, with complex flow features such as spanwise trailing wake and streamwise C-pillar vortices. The flow is characterized through stereoscopic and tomographic velocity field measurements. The large-scale, horseshoe vortex structures in the trailing wake, conventionally denoted as A- and B-vortices, are found to vary in size and shape along the spanwise direction, which in turn influence the pressure distribution on the rear vertical surface. The longitudinal C-pillar vortices are found to extend far downstream and also influence the trailing wake structures through a complex, three-dimensional interaction. The accuracy and cost of obtaining volumetric information in this complex flow field, by means of volume reconstruction, through Stacked Stereoscopic-Particle Image Velocimetry (PIV) and Tomographic PIV are also investigated.
Experiments in Fluids
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