Experimental study of a pickup truck near wake

The present study focuses on the aerodynamics of pickup trucks. The flow about a generic pickup truck has been documented experimentally. The main objective is to gain a better understanding of the pickup truck aerodynamics through mean and unsteady pressure measurements as well as detailed flow field measurements using particle image velocimetry (PIV). Of particular interest and complexity are the symmetric and asymmetric separated vortex flows which develop behind the cab and the tailgate. A secondary objective is to obtain a comprehensive experimental data set for validation of computational fluid dynamics (CFD) models. The experiments were conducted at Reynolds numbers in the range of 5-8.5×10⁵ in an open return wind tunnel equipped with two-frame digital PIV system. The mean pressure results of the pickup truck show that the pressure outside the tailgate is higher than inside the tailgate suggesting that the tailgate reduces aerodynamic drag. The root-mean-square (rms) values of pressure fluctuations at the cab back is very low and increases significantly towards the back of the bed and the tailgate top edge. Pressure fluctuation spectra indicate a spectral peak at a Strouhal number of ∼0.07. Velocity field measurements of the near wake flow show a relatively quiet region behind the cab and no recirculating flow region in the symmetry plane behind the tailgate. Instead there is a strong downwash at the symmetry plane behind the tailgate. This downwash is due to the existence of a pair of counter-rotating vortices downstream of the tailgate. The downwash promotes attached flow behind the tailgate, thus resulting in a pressure recovery that reduces drag.