A Correction Method to Estimate Wake Effects for Aerodynamic Performance Metrics

Wake effects modify the aerodynamic performance of a road vehicle when driving in traffic. Analysis of wind-tunnel measurements conducted in flows with wake characteristics, using a traffic-wake-simulation system, suggests that conventional uniform-wind performance coefficients can be scaled, using wake-flow-field information, to predict the influence of wake effects. This paper presents a flow-field-averaging method that estimates a dynamic-pressure correction and yaw-angle correction for application to uniform-wind data, to account for changes in performance due to wake effects. This first-order method is shown to provide reasonably-good accuracy when reverse correcting the wind-tunnel wake-effects measurements. Drag-coefficient data for light-duty-vehicle models, which showed wake effects exceeding 20%, were corrected to within 5% of uniform-wind values, while data for heavy-duty-vehicle models, which showed wake effects exceeding 15%, were corrected to within 2% of uniform-wind values. However, despite the good agreement, the reverse-corrected surface-pressure coefficients showed significant deviations from the uniform-flow/isolated-body results, with some coefficient differences exceeding ±0.15, demonstrating that wake effects are more complex than just a nominal change in effective dynamic pressure and yaw angle.