Time Averaged and Unsteady Near-Wake Analysis of Cars

From an experimental investigation of a notchback car near-wake, a new topological structure for the wake is proposed. Although experiments were only conducted on notchback vehicles, the topology can be related to other car shapes. The unsteady behavior of the near-wake was investigated. The near-wake frequencies, which can affect ride and steering comfort, were found to be 0.11U∞/x_R and 0.42U∞/x_R (x_R - reattachment length). The lower frequency appears to be a result of large scale vortex shedding (‘hairpin’ vortex) behind the backlight/rear-window. The higher frequency can be attributed to the shear-layer vortices.