G0500601 Effects of Diffuser for Upper-surface Inclination of Vehicle Models

Abstract

The purpose of the present study is to investigate effects of rear-diffuser for upper-surface inclination in the rear of car models. The Ahmed body with variation of upper-surface inclination angle α in the rear is used as a trial model, where variation of lower-surface inclination angle γ of the rear diffuser is constructed. The wind-tunnel experiments have been carried out with a moving belt to measure the lift and drag coefficients. As the result, 1) at any α, for variation of γ the lift coefficients decrease with minimum value at γ=20° and rapidly increase for γ>20°, and 2) at any γ, the lift coefficients decrease as α is made smaller. Flow visualization by the tuft grid, five-hole Pitot tube, and oil flows suggested the causes of lift reduction for the former that the wind from the lower surface is straightened by the rear diffuser and for the latter that the flow from the upper body interferes with the flow from the lower body.