Further Analysis of the Blockage Phenomenon during the Testing of Bluff Automotive Bodies in Closed Wall Wind Tunnels – Revised and Updated

The difficulties of testing a bluff automotive body of sufficient scale to match the on-road vehicle Reynolds number in a closed wall wind tunnel has led to many approaches being taken to adjust the resulting data for the inherent interference effects. But it has been impractical if not impossible to experimentally analyze the effects that are occurring on and around the vehicle when these blockage interferences are taking place. The present study is an extension of earlier work by the author and similarly to that study uses the CFD (computational fluid dynamics) analysis of several bodies of differing configurations to examine the interference phenomena in solid wall wind tunnels and the effects that they have on the pressures, forces and force increments experienced by the vehicle model. This is accomplished by executing a series of CFD configurations with varying sized cross sections from 0.2% to 16% blockage enabling an approximation of free air conditions as a reference. The earlier work is extended by using additional body configurations which include reference bodies from the Technical University of Munich, the University of Stuttgart, and Ford Motor Company to complement the simple shapes used in that study along with the use of a SAE Notchback model simple shape and a newly generated Utility Van configuration utilizing chassis components from the Ford GTU pickup. Examination is made of the physical phenomena occurring around the vehicle as the proximity to the walls and ceiling is changed holding the test section aspect ratio and length constant. Static Pressure distortions, skin friction changes, velocity distortions and the distribution of forces on the vehicle body are examined. It is intended that this dataset be used by the SAE Road Vehicle Aerodynamics Forum Committee (RVAC) and the Subsonic Aerodynamic Testing Association combined activity, Commonized Automotive Aerodynamic Test Standards, or CAATS, to evaluate and/or develop wind tunnel blockage techniques for automotive bluff bodies. The report has corrected errors contained in the original paper while revising and updating it.