Abstract: IN order to control the aerodynamic force and noise of ground vehciels, unsteady flows in the wake of three-dimensional (3D) vehicles with different rear slant angles (0°, 25° and 35°) were experimentally studied with fluid dynamics, spectrum and correlation analysis for data processing, using hot wire anemometry. Two frequencies measured in the wake of 0° model are resulted from the unsteady flow emanating from the recirculation bubbles in the flow direction and the side direction respectively. Four frequencies detected for the 25° model are ascribed to C-pillar vortex, dynamics attachment flow on the rear slant, the structures emanating from recirculation bubbles in flow direction and resonance effect. Three frequencies captured for 35° model are connected to the structures emanating from the recirculation bubbles in flow direction and C-pillar vortex. The differences are significant among different models. Flow separation position, flow on the rear slant, C-pillar vortex are all different for different slant angle, which explains the physical meaning for each unsteady flow, the quantity and spatial distribution of dominant frequency.

Key words: vehicle engineering, unsteady flow, wake, vortex shedding, flow separation