SAE J2071_199406

As a simulation of road driving, wind tunnel testing of full-size vehicles produces certain errors in the aerodynamic forces, aerodynamic moments, and surface pressures.

As a simulation of road driving, wind tunnel testing of full-size vehicles produces certain errors in the aerodynamic forces, aerodynamic moments, and surface pressures. The magnitude of these errors, in general, depends on the following:aFlow qualitybDetermination of the reference dynamic pressurecWind tunnel floor boundary layerdTest section geometry and position of the car within that geometryeShape of the vehiclefBlockage ratio: The ratio of the cross-sectional area of the vehicle to the cross-sectional area of the wind tunnel nozzlegWheel rotationhInternal flow in the modelThe SAE Standards Committee, Open Throat Wind Tunnel Adjustments had as a goal to document the knowledge of the influence of model interference on wind tunnel test results for automotive open jet wind tunnels. This document contains the following information related to this subject:aDesign data of open throat wind tunnelsbA summary of published and unpublished test datacDocumentation and theoretical explanation of various blockage correction procedures for automotive testsdCritical evaluation of blockage correction procedures, especially in relation to other influences, such as test section geometry, position of the car, floor boundary layer, etc.eRecommendation of a calibration procedure to determine the effect of blockage and other influences in each individual wind tunnelAn initial goal of the committee, to recommend a well proven correction procedure for automotive open jet wind tunnels based on blockage theory (Figure 1), could not be established at this time. The reason is that, besides blockage, other factors, such as test section geometry, are at least as influential as pure blockage. As these influential parameters are wind tunnel specific, a general valid adjustment procedure is presently not available.