Lift and Side Force Corrections for Wind Tunnel Measurements of Ground Vehicles

The limited size of a wind tunnel test section can result in serious errors in the measured results. Therefore corrections for blockage effects are quite commonly used in automotive wind tunnel tests. A second type of test section boundary interaction apart from blockage is a biased flow angle due to lift of the test object. This wind tunnel effect is typically also corrected for in aerospace applications, but not in automotive tests. The reason for this is, that lift corrections are normally negligible for ground vehicles. The general validity of this statement will be demonstrated in this paper. In addition, two special cases will be discussed, where lift corrections are in fact of interest. The first example is the correction of measurements under yawed conditions. The lift correction is transformed into a side force correction in this case. In the second example, the effect of the test section height to width ratio on the lift correction for race cars is studied. From this, design guidelines for the height to width ratio can be derived. In both cases the analysis is based on the classical approach using potential flow theory. In addition, the theoretical results are compared with full scale test data from different wind tunnels.