CFD Analysis of Various Automotive Bodies in Linear Static Pressure Gradients

Establishing data adjustments that will give an interference free result for bluff bodies in automotive wind tunnels has been pursued for at least the last 45 years. Recently, the Two-Measurement correction method that yields a wake distortion adjustment for open jet wind tunnels has shown promise of being able to adjust for many of the effects of non-ideal static pressure gradients on bluff automotive bodies. Utilization of this adjustment has shown that a consistent drag results when the vehicle is subjected to the various gradients generated in open jet wind tunnels. What has been lacking is whether this consistent result is independent of the other tunnel interference effects. The studies presented here are intended to fill that gap on the performance of the two-measurement technique. The subject CFD studies are designed to eliminate all wind tunnel interference effects except for the variation of the (linear) static pressure gradient. Zero gradients and linear gradients are generated by tapering the walls of solid wall test sections with a blockage ratio of 0.5%. Under these conditions, the variation in drag coefficient is observed with and without application of simple buoyancy adjustments, Glauert Factor based adjustments, and the two-measurement method adjustments. Conclusions are reached relative to the ability with each of these approaches to achieve interference free results on a range of vehicle body styles both simplified and with a moderate level of production vehicle detail.