Active Flow Control of the Unsteady Wake behind a Square-Back Road Vehicle using Synthetic Jets

Road transportationis particularly one of thesignificant contributorsto greenhouse gasemissions, a dominantcause of global warming.To lessen fuel consumption and greenhouse gas emission, aerodynamic drag reduction of road vehicles is one of the viable techniques. The aim of the present study is to investigate the effectiveness of active flow control by means of synthetic jet actuators to reduce aerodynamic drag of a simplified truck model (a square-back Ahmed body). Numerical simulations of a three-dimensional unsteady airflow over a square-back Ahmed body were performed at the Reynolds number, based on the height of the Ahmed body and the free-stream velocity, of 33,000 using OpenFOAM.Synthetic jet actuators were placed at the rear end of the Ahmed body to alter the unsteady wake due to boundary layer separation. Three different synthetic jet actuator configurations (left-right, top-bottom, and all sides)were compared. Synthetic jet actuator’s parameters, amplitude and frequency, were also varied. Aerodynamic coefficients, power spectral density of the lift coefficient, time-averaged velocity streamlines, cross-stream turbulence velocity fluctuations, and coherent vortical structures in the unsteady wake were examined. For unforced flow, the drag coefficient (Cd) of the squared-back Ahmed body agrees well with the literature value. For controlled flow, the results demonstrate that the greatest drag coefficient reduction of approximately 2.52% can be achieved with a base pressure recovery of about 9%, using the left-right synthetic jet actuator configuration. On the other hand, the drag coefficients of the Ahmed body increase for thetop-bottom and four-sided jet actuator configurations. This finding highlights the importance of synthetic jet actuator configurations. Further improvement on synthetic jet actuator’s parameters and configurations is needed to obtain a better drag reduction.