Reducing the pressure drag of a D-shaped bluff body using linear feedback control

The pressure drag of blunt bluff bodies is highly relevant in many practical ap- plications, including to the aerodynamic drag of road vehic les. This paper presents theory revealing that a mean drag reduction can be achieved by manip ulating wake flow fluctu- ations. A linear feedback control strategy then exploits th is idea, targeting attenuation of the spatially integrated base (back face) pressure fluctuat ions. Large eddy simulations of the flow over a D-shaped blunt bluff body are used as a test-bed for this control strategy. The flow response to synthetic jet actuation is characterise d using system identification, and controller design is via shaping of the frequency response t o achieve fluctuation attenua- tion. The designed controller successfully attenuates int egrated base pressure fluctuations, increasing the time-averaged pressure on the body base by 38 %. The effect on the flow- field is to push the roll-up of vortices further downstream an d increase the extent of the recirculation bubble. This control approach uses only body -mounted sensing/actuation and input-output model identification, meaning that it could be applied experimentally