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Both the unsteady aerodynamics force and base pressure distributions are investigated for four model cars in real flow conditions. The low pass cut-off frequency of the measurements is about 5 Hz which is sufficient to consider the global fluctuations of drag, lift and side forces. The drag fluctuations are very low, they never exceed 1% of the mean drag. A clear correlation is found with the base pressure distribution fluctuations. It is found that the regions of smallest pressure fluctuations on the vehicle base are the most correlated to the drag fluctuations or in other words, the regions of largest pressure fluctuations on the base are not associated with the drag fluctuations. Sideslip effect is studied, and one of the models presented a clear bistable behaviour on the lift creating huge fluctuations as investigated in the academic experiment of Grandemange et al. (2013b).

The flows past two different road vehicles with blunt after-bodies are studied at Reynolds numbers 107. The boundary layer thickness and the pressure distribution around the body are characterised. 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 afterbody 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 its maximum of amplitude is downstream of the recirculation bubble; therefore it may not be a contributor to the drag. Eventually, these results are analysed to orient future drag reduction control strategies.