PIV Measurements of the Cross-Flow Velocity Field in the Near Wake of a Generic Pickup Truck

The cross-flow field (flow in planes normal to the direction of motion) in the near wake of a generic pickup truck is investigated experimentally using Particle Image Velocimetry (PIV). The PIV measurements of the velocity field normal to the free-stream direction are carried out at four stream-wise locations behind the cab and the tailgate. The PIV data are processed to obtain the instantaneous velocity field, the mean and the turbulence properties of the flow. The instantaneous results in the near wake of the cab show various vortical structures. The mean velocity data shows that the flow moves from the sides toward the center of the bed near the tailgate. The velocity data in the near wake of the tailgate shows a pair of counter-rotating vortices that induces a downwash velocity field at the symmetry plane. This downwash promotes an attached flow behind the tailgate, thus generating a pressure recovery which leads to reductions in the total drag.