Characterization of synthetic jet actuation with application to Ahmed body wake
Résumé
The active flow control by synthetic jet is applied on a road vehicle wake flow. Experiments have been conducted in a wind tunnel. Experimental model is an Ahmed body scaled at 0.7 of the original Ahmed model mounted on aerodynamic balance. Static pressure measurements, wall visualization and PIV as well as hot wire techniques have been used. Synthetic jet actuator has been developed by using electromechanical analogy with the help of the Lumped Element Modeling. It is based on piezoelectric membrane. Its aerodynamic performances have been characterized experimentally. The dynamical response to the membrane power signal (frequency and voltage) is compared to the reduced model (LEM) of the synthetic jet used to scale the actuator. Spatial and temporal evolution of the jet is compared to the existing results and their operating regimes are validated to be used for the control. The flow downstream from the Ahmed body without control is described. The topology of the longitudinal vortices of the wake and their evolution with the Reynolds number is examined. Spectral analysis is also performed. For different Reynolds numbers, the aerodynamic efficiency of the drag control is analyzed varying synthetic jet parameters: momentum coefficient, reduced jet frequency and jet position. The study with respect to C variation allows for characterizing the mean topology of the controlled flow. The spectral analysis leads to identify the developed instabilities. With a rear window tilted at 25◦, drag reductions of 8.5% (Re = 1.2 × 106) and of 6.5% (Re = 1.2 × 106) are reached. The control allows to reattach dynamically the rear window separation and to balance the torus vortex structure at the base.