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The flow conditions in a closed test section wind tunnel are not the same as in freestream due in part to the constraints imposed by the wind tunnel walls. Boundary correction methods can be applied to wind tunnel results to estimate the effects of wind tunnel wall constraints. One such scheme, the two-variable method, which is a measurement based scheme used to estimate a particular class of wind tunnel wall constraints known as solid and wake blockage, is described herein. The Glenn L. Martin Wind Tunnel (GLMWT) has implemented the two-variable method and has applied it previously for large models in a variety of applications, primarily in the evaluation of yacht’s offwind sail performance. This paper describes the application of the two-variable method to simplified fastback style three-dimensional automobile shapes at zero yaw angle. Models ranged in size from 2.75% to 5.53% of the tunnel’s cross-sectional area.

The work presented here is a further step in a continuing effort by the authors to study and document the aerodynamic effect of varying aspect ratio, ground clearance, and underbody roughness for basic rectangular shapes with radiused edges in ground effect. Previous papers by the authors have presented extensive wake data for a range of aspect ratios and underbody roughness conditions. Force and moment data have been published for various aspect ratios, underbody roughness, and ground clearance. In this paper, additional wake data showing the effects of variation in ground clearance is presented. The focus of this paper is on analyses to make progress toward a rational correlation between body characteristics, the forces, and the measured wake properties. A parametric analysis is presented linking the effects of the parameters varied in the study to the changes in the aerodynamic forces and moments. Results show correlations between the wake flows and the force results.