Aerodynamic Effect of Aspect Ratio of Spherical Depressions on the Bonnet of Hatchback Cars 2019-01-5096

Flow separation is one of the primary causes of increase in form drag in vehicles. This phenomenon is also visible in the case of lightweight vehicles moving at high speed, which greatly affects their aerodynamics. Spherical depressions maybe used to delay the flow separation and decrease drag in such vehicles. This study aims for optimization of aspect ratio (AR) of spherical depressions on hatchback cars. Spherical depressions were created on the bonnet of a generalized light vehicle Computer-Aided Design (CAD) model. The diameter of each spherical depression was set constant at 60 mm, and the center-to-center distance between consecutive spherical depressions is fixed at 90 mm. The AR of spherical depressions was taken as the parameter that was varied in each model. ARs 2, 4, 6, and 8 were considered for the current investigation. Three-dimensional (3D) CFD analyses were then performed on each of these models using a validated computational model. Vehicle travel velocities of 22, 24, 26, 28, and 30 m/s, which were nondimensionalized for scaling the results, were considered for analyses, in order to simulate the maximum travel velocity of light vehicles. Various parameters like the coefficient of drag, lift coefficient, and boundary layer separation were studied to investigate the impact of AR of spherical depressions on vehicle aerodynamics. A significant decrease in coefficient of drag was observed as a result of the addition of spherical depressions on the bonnet.