Research on Reducing Aerodynamic Drag of the Ahmed Model Using the Passive Flow Control Method

Research using a combined computational fluid dynamics (CFD) simulation method with the SST
$\mathrm{k}-\omega$
turbulence model to passive flow control for reducing aerodynamic drag on the basic Ahmed model 25° (case 1). Passive flow control is achieved by implementing rear air vent holes at the juncture between the rear and side surfaces of the Ahmed model. Three different vent hole cases are created: case 2: 3 holes with a diameter of 20mm, evenly spaced at 60mm intervals; case 3: 3 holes with a diameter of 40mm, evenly spaced at 60mm intervals; case 4: 6 holes with a diameter of 20mm, evenly spaced at 30mm intervals. The simulation results reveal that the vent holes effectively alter the flow of the Ahmed car model, leading to reductions in the aerodynamic drag coefficients by 1.22%, 3.26%, and 2.44% for cases 2, 3, and 4, respectively. Large vent hole diameters yield more significant improvements in reducing aerodynamic drag. However, this may also somewhat compromise the original design of the Ahmed model.