Detailed Analysis of the Bluff Body Blockage Phenomenon in Closed Wall Wind Tunnels Utilizing CFD

Numerous efforts have been made to adjust the interference effects of solid wall wind tunnels on bluff body forces and moments. Most of these have been based upon a theoretical assumption of the mechanisms that caused the distortion of the wind tunnel data relative to free air conditions; some have been based upon empirical data from wind tunnel testing. But it has been impractical if not impossible to experimentally analyze all of the effects that are actually occurring on and around the vehicle when these blockage interferences are taking place.

The present study uses the CFD analysis of two simple bodies, a fastback shape and a squareback shape, to examine the interference phenomena actually experienced in solid wall wind tunnels and the effects that those phenomena have on the pressures, velocities, and forces on the model. From these observations, conclusions are drawn relative to the type and magnitude of blockage corrections that should be used for testing bluff bodies in closed wall wind tunnels and whether adjustments can even reasonably expect to compensate for the distortions occurring in the flowfield and the data.