Active control for a low-drag Ahmed vehicle model based on steady blowing

An experimental investigation is conducted on the active drag reduction (DR) of an Ahmed body with a rear slant angle of 35°, corresponding to the low-drag regime, using single and combined actuations at the Reynolds number Re = 1.7 × 105. Five different actuations, produced by steady blowing jets, are deployed independently around the edges of the rear slant surface and vertical base, achieving the maximum DR of 1%–9%. An artificial intelligence control system based on ant colony algorithm is used for finding near-optimal control laws of the combined jets. With both DR and control power input considered in the cost function, the maximum DR obtained reaches 18%, though the corresponding control efficiency η (≡ES/EI, where ES and EI are the saved power due to DR and the total input power of the actuations, respectively) is only 0.13. However, η may go up greatly, climbing to 5.8, given a 3% sacrifice of DR. Extensive flow measurements are conducted, with and without control, to understand the flow physics and mechanisms under the control of individual and combined actuations. A linear regression model is established to describe the correlation between the control efficiency and parameters under the combined actuations.