Wind tunnel blockage corrections: a computational study

Wind tunnel blockage testing has been a wide spread traditional practice in the automobile industry for many years; but the tests conducted have been associated with the so called blockage effects, which arise due to the constrained flow nature inside the wind tunnel test section and over the blockages. These blockage effects need to be corrected in order to comprehend the test results similar to those of the actual road conditions. CFD has emerged as a tool to determine the blockage effects and provide corrections using computational techniques.

In this present study, two such CFD packages, namely PHOENICS and AIRFL03D, are used for determining the wind tunnel blockage effects. The problems taken into consideration are both two dimensional and three dimensional flow cases. The test section domain height is varied so as to produce different blockage ratios, keeping the blockage dimensions constant. A two dimensional free stream case with blockage l/h ratio variation is tested and compared with experimental results. In the other cases, the two packages are compared with each other for pressure and velocity distributions and drag coefficients. A grid independent study was performed for one case. Finally, blockage correction equations are obtained for all the test cases.