Effect of an Add-On Device on the Aerodynamic Characteristics of a 3-Dimensional Ahmed Body

This study investigated the effect of add-on-device (side-view mirrors) on the aerodynamic characteristics of a 3-Dimensional Ahmed body using both numerical and experimental methods. It aims at controlling aerodynamic drag on vehicles by determining the optimum mirror position for a simplified vehicle geometry known as Ahmed body model. The rear slant angle of 25 ° has been used as a benchmark. The geometry is generated in ANSYS ’14 design modeler with a single domain of air created surrounding the model after subtracting it from the air enclosure. The turbulent flows around the 3D Ahmed body model was solved using the realizable k-epsilon model with non-equilibrium wall function for near wall treatment with an inlet velocity of 40 m/s. For geometrical optimization, the following were used: distance between the attachment plate and the mirror ranges from 5-20 mm in an increment of 5 mm; height of the mirror foot ranges from 3-9 mm in an increment of 2 mm and the angle of inclination of the foot between -10 ° to +10 ° in an increment of 5 ° . The small scale prototype of Ahmed body was produced from a Prusa-i3 12 volts 3D printer. This was tested in a wind tunnel to determine the aerodynamic forces (drag and lift). The validation was done by comparing the small scale numerical modeling results with the experimental results obtained from the wind tunnel. The results from this study show that the position of the side-view mirror contributes to drag on the entire vehicle. Minimum drag coefficient CD = 0.3022 and the corresponding lift coefficient CL = 0.3410 was obtained at mirror position 20 mm foot length, 5 mm foot height and 10 ° angle of inclination. This position added 6% to the drag coefficient of the Ahmed body 25 ° model. The study concluded that the position of the side mirror contributes a significant effect when it comes to drag on the entire vehicle.