Cavitation as a complementary tool for automotive aerodynamics

The wake of a 3D bluff body is studied in a hydrodynamic flow. The high Reynolds number (about 2 x 10(6)) corresponds to the case of a full-scale road vehicle in a wind tunnel. A cavitation technique is proposed to identify the lowest pressure regions. It is found that these regions correspond to the two longitudinal vortices produced at the edges of the rear part of the vehicle. This technique also provides non-intrusive bulk measurements of the pressure minimum. It is found that the pressure coefficient of the longitudinal vortices is equal to C-p=1.67, which underlines their strong contribution to the global drag. We show that cavitation can be a very useful technique to get three-dimensional information which is difficult to obtain through classical wind tunnel measurements.