Active flow control analysis at the rear of an SUV

This paper aims to present an experimental investigation of an active flow control solution mounted at rear of a sport utility vehicle (SUV) with the objective of drag reduction, thanks to a selection of flow control parameters leading to a pressure increase on the tailgate.

A flow control design of experiments was conducted with a pulsed jet system mounted on the top and sides of the rear window of the vehicle. The wall pressure, instantaneous velocity and drag were measured with this prototype in a wind tunnel. A dynamic modal decomposition (DMD) analysis of the pressure enables to describe the pressure fluctuations. Fluid dynamic computations show relation between pressure and velocity fields.

Measurements with this prototype in the wind tunnel revealed small improvements in drag for the best flow control configurations. This small benefit is because of the core of the upper span wise vortex further away from the rear window than the lower span wise vortex. These small improvements in drag were confirmed with pressure measurements on the rear window and tailgate. The DMD analysis of the surface pressure showed a low frequency pendulum oscillation on the lower area of the tailgate, linked with low velocity frequencies in the shear layers near the tailgate.

Experimental and numerical results show interest to increase pressure at bottom of the rear end of this SUV prototype. The dynamic description of the wall pressure shows importance of flow control solutions reducing pressure fluctuations at low frequencies in the lower area of the tailgate.