Active flow control using pulsed micro-jets on a full-scale production car

This paper presents experimental flow control results obtained on a full-scale production car in a wind tunnel. The aim of this paper is to demonstrate the feasibility of controlling the separated flow over the rear part of the car by using pulsed micro-jets. Pulsed micro-jets are produced by hybrid actuators mixing both standard and MEMS (Micro Electro Mechanical Systems) technology. Both actuation frequency and injected momentum are studied. Experiments show a small influence on the drag force (less than 1% reduction), but a stronger one on the lift force (up to 9% reduction). Wall pressure coefficients measurements highlight the suppression of the recirculation bubble over the rear window, along with a reinforcement of the longitudinal C-pillars vortices. Spectral measurements in the shear layer above the rear window show that most efficient control frequencies match the shear layer instability frequency, and that the actuation suppresses the energetical contribution associated with the recirculation bubble frequency. Additional measurements demonstrate that a minimum threshold value of the momentum coefficient is needed for the flow actuation to be efficient. This is the first experimental evidence of the efficiency of micro perturbations (380μm thick micro-nozzles) to control flow separation on a full- scale production car. This is a very important step in the perspective of future applications of flow control in automotive industry to improve aerodynamics performances and reduce CO2emissions.