Surface flow and aerodynamic drag of Ahmed body with deflectors

•Flow on the slant surface, force and pressure are analyzed for Ahmed body with deflectors.•At the deflection angle above −5°, total drag, flow fields, and pressure distribution on the slant change suddenly.•Maximum drag reduction obtains at 8%, lift almost cancels out at deflection angles above 0°.•Flow on the slant is fully separated with D-shape attachment line for deflection angles above −5°.•The pressure drag acting on the slant reaches around 40% of the total drag of the model. This study investigated the surface flow and the aerodynamic characteristics of a 7/10 scale Ahmed model equipped with deflectors at several angles. The experiments were conducted at Reynolds number of 2.45 × 105 based on the model height. A global luminescent oil film skin-friction measurement technique was applied for the flow fields on the slant and base surfaces. The aerodynamic forces of the model were measured to understand the effect of the deflection angle on the aerodynamic characteristics. The pressure was measured and pressure drags acting on the slant and base surfaces were also calculated. The results showed that the drag and lift of the model suddenly dropped at the deflection angle above −5°. The pressure distribution on the slant and base surfaces became flat with a maximum drag reduction of 8% for the model with a deflection angle of 0°. The skin-friction measurement indicated that the drag reduction was connected to the breakdown of the separation bubble and longitudinal vortices on the slant. At the fully separated flow state, the skin-friction results illustrated two small vortices and a counter-clockwise vortex on the slant. Additionally, the wake vortices shifted from horizontal to vertical structures. The relation among the flow fields on the slant surface, flow on the symmetric plan, pressure distribution, and drag was illustrated for the model with different deflection angles.