Effect of Combination Yaw Angle Variation and Base Bleeding for Tractor-Trailer Drag Reduction through Experimental Investigation and CFD

Abstract This study focuses on the effect of variations in yaw angle and base bleeding configuration on the reduction of tractor-trailer drag. Detailed experimental and CFD investigations are introduced. Crosswind is used to simulate the yawed flow conditions. Three bleeding hole settings are arranged in the tractor base area. Experiments and CFD are done using 1:32 scale model, after validating the results of the CFD extended to a full-scale model. In the CFD investigation, the structure and rotation of the flow around the tractor-trailer and the gap area are examined. Experimental investigations was Carried out in an open jet wind tunnel. The results showed that when the yaw angle is greater than 3 a drag reduction is clearly observed. At the yaw angle of 12 ° maximum drag reduction occurs in the form of drag coefficient is 19%, 21% and 23% for bleeding coefficient of 0.04, 0.05 and 0.06. Through the results of CFD predictions, the effects of bleed increase entrainment flow in the gap and reduce the wake area on the leeward side of the trailer and consequently produce a significant reduction in drag. This result is caused by a large flow separation zone that forms along the underside of the trailer when there is no bleeding which increases vehicle drag. The appropriate bleeding area of the tractor base is an alternative that allows in reducing the drag in the tractor- trailer gap.