Development of Lift and Drag Corrections for Open Jet Wind Tunnel Tests for an Extended Range of Vehicle Shapes 2003-01-0934

Wind Tunnel 8 of the Driveability Test Facility (DTF), which achieved full operational status in 2001, is designed to provide full powertrain, aerodynamic, and aero-acoustic test capabilities for automotive product development. In order for it to be fully integrated into product testing, the Ford product engineering community needed to correlate the facility. The major objective of the correlation is quantitative aerodynamic correlation, which will be achieved when aerodynamic coefficients measured in Wind Tunnel 8 can be understood in the context of aerodynamic measurements obtained in other wind tunnels that Ford has used for product testing.

The motivation for this study is the aerodynamic interference that is present in all wind tunnels. Aerodynamic interference is the deviation between the true result—which is difficult to determine—and the actual result obtained from the wind tunnel. Because interference effects give rise to errors in wind tunnel simulation, they are an impediment to aerodynamic correlation of any new wind tunnel. Correction methods for interference effects have been most thoroughly investigated for solid wall test sections. For open jet test sections, which have traditionally been the choice of the European automotive community for aerodynamic testing, interference effects are less understood. Only in recent years have open jet test sections been used for automotive aerodynamic testing in North America. The cumulative result is that open jet aerodynamic interference is not as well understood as closed wall test section interference.

In this work, open jet experiments were carried out in a 1/11-scale model of the open jet DTF Wind Tunnel 8 test leg. To maximize the applicability of the work, the experiments were carried out for an ensemble of models representative of the full range of vehicle shapes and blockages to be tested in DTF Wind Tunnel 8. Reference data were obtained by testing the same models in Sverdrup's sub-scale adaptive wall wind tunnel, using the same force balance as employed in the open jet experiments. The adaptive wall test section has been shown to be free of aerodynamic interference for vehicle blockages approaching 30%, so the adaptive wall results were adopted as error free reference data. This paper summarizes the experiments performed and the process by which the correction equations were obtained. The final results indicate that:

1. 1.
   Vehicle blockage and the vehicle's location in the test section are important variables for correcting aerodynamic drag interference errors.
2. 2.
   Increasing vehicle size (especially height) increases interference on lift measurements.