Numerical simulation of the flow around a simplified vehicle with an upswept aft section

Abstract

An upswept aft section at the underbody in ground effect can improve the aerodynamic downforce of vehicles. In order to clarify the effect of the upswept aft section, a simplified vehicle with the upswept aft section is examined using Large Eddy Simulations. In the present study, four upsweep angles of the upswept aft section, i.e., θ = 0°, 5°, 10° and 15°, are investigated, where 0° corresponds to the original Ahmed body. It is found that the upswept aft section leads to an increase in flow rates through a cross-section between the underbody of the model and the ground. The high flow rate enhances strong negative pressures not only on the upswept aft section but also on a forward part of the underbody. In addition, induced vortexes are generated near both side edges of the upswept aft section. The induced vortex enhances the negative pressure on the upswept aft section close to the side edge because the vortex develops downstream, approximately along the side edge. In this study, the aerodynamic downforce for θ = 10° is the maximum because of the high negative pressure based on the highest flow rate and the strongest induced vortex. Furthermore, the relationship between the induced vortex and an effective cross-sectional area under the upswept aft section is examined and a blockage effect is discussed. Three-dimensional flows, such as the induced vortex and the underbody inflow, are found to increase the effective cross-sectional area because the three-dimensional flow should improve a flow uniformity in the mainstream direction.