On the near wake of a simplified heavy vehicle

Particle image velocimetry measurements of the near wake of a simplified generic truck geometry-the Ground Transportation System (GTS)-are presented. The mean flow field is characterised by a vertically asymmetric wake, with a large spanwise vortex in close proximity to the lower part of the base surface. Dominant non-dimensional frequencies of St≈0.08 and St≈0.17 are found, corresponding to a wake pumping mechanism and vortex shedding between the vertical edges of the base. Unsteadiness is largely confined to the top and side shear layers as well as the region downstream of the recirculating wake. In contrast, the lower region of the near wake is shown to remain almost quasi-steady, dominated by the persistent spanwise vortex that has a significant effect on the base pressure distribution. Ground proximity effects were assessed, showing that the wake topology is insensitive to increases in ground clearance, while a number of changes in flow regime were identified as ground clearance was reduced.