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Old 01-02-2010, 12:01 PM   #1 (permalink)
Rokeby
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Pickup Tail Gate Up or Down... A Scientific Explanation

More info with a scientific basis... is it the last word?

Journal of Wind Engineering and Industrial Aerodynamics
Volume 98, Issue 2, February 2010, Pages 100-112

Experimental study of a pickup truck near wake

Abstract
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
8.5105 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.


From:

ScienceDirect - Journal of Wind Engineering and Industrial Aerodynamics : Experimental study of a pickup truck near wake


Last edited by Rokeby; 01-02-2010 at 12:09 PM..
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