Characterization of the flow past real road vehicles with blunt afterbodies

Abstract : The flow past two different road vehicles with blunt afterbodies is studied at a Reynolds number based on the vehicle length of 10 7. The boundary layer thickness and the pressure distribution around the body are characterized. Then, the wake is investigated through static pressure and velocity measurements. Similar properties are obtained for both vehicles, in particular the lowest pressure on the after-body is reported on the lower part of the base. Hot-wire anemometry is also used to depict the dynamics of the flow. The detached shear from the roof behaves as free shear turbulent flows whereas the flow from the underbody rather corresponds to homogeneous shear turbulent flows. In addition, global mode dynamics is reported in the wake of one vehicle and is associated with an antisymmetric coupling of the lateral mixing layers. However, the intensity of this mode is limited and it may not be a contributor to the drag since its maximum of amplitude is downstream the recirculation bubble. Eventually, these results are analyzed to orient future drag reduction control strategies.