Active flow control with synthetic jets in a station wagon – a CFD study

The reduction of fuel consumption has become one of the main targets in the automotive industry. To achieve this objective, drag reduction plays a major role and one of the techniques that has become attractive in recent years is the use of active flow control (AFC). In the present paper, Computational Fluid Dynamics (CFD) simulations are used to study the application of synthetic jets (SJ) as AFC devices in the flow around a station wagon (SW). The main purpose of this study is to determine the viability of these devices in the overall aerodynamic performance of the vehicle but especially in drag reduction. A baseline case (no actuation) of the simulation of the flow around the SW was initially performed and the drag coefficient was validated with experimental data from a coast-down test. Using the baseline results, two zones for the synthetic jet outlets were defined in the rear part of the SW, one located in the Upper Side (US) and the other in the Lateral Side (LS). Numerical results show that the synthetic jets actuation effectively affects the dynamics of the flow and the near wake, and a reduction of the drag (∼1%) with an increment in the lift (∼20%) was observed with actuation in US. A lift coefficient reduction (∼33%) with a drag increment (∼4%) was also observed with SJ actuating in LS. Nevertheless, due to the high momentum coefficient required by the SJ, a simple estimation of the energy required to operate the SJ shows that it is higher than the energy saved due to the combination of drag reduction and lift increment.