Wake Studies of a Model Passenger Car Using PIV

Detailed wake surveys were performed with a 1/8th scale model, hatchback car in a low-speed, wind tunnel. The tests were conducted at a freestream velocity of 20m.s^-1 giving a Reynolds number of 6.0 ×10⁵ based on the model length. PIV was used to obtain cross-flow velocities at four wake survey locations. At one wake position the effect of hatchback geometry was investigated. Using a wake integration technique, lift and induced drag distributions along the model width, total lift and induced drag acting on the model were obtained using flow field data. The induced lift and drag coefficients were found to decrease downstream of the model due to viscous dissipation. A hatchback angle of 30° was found to produce the greatest induced drag. The instantaneous wake structure of hatchback cars was found to be asymmetric and was not adequately described as consisting of counter-rotating C-post vortices, a concept produced by earlier time averaged data obtained elsewhere.