Flow control of wingtip vortices through synthetic jets

The effectiveness of synthetic jet actuation on the wingtip vortices produced by an unswept, low aspect ratio, rectangular wing at a chord Reynolds number of 8.16×104 is experimentally investigated. The synthetic jet is operated at different actuation frequencies and amplitudes in order to investigate five different control cases characterized by different momentum coefficients and dimensionless frequencies, for a comprehensive parametric study. In particular, the instability frequencies (known as Crow and Widnall) characterizing the wingtip vortex dissipation, are chosen among the tested synthetic jet actuation frequencies. A phase-locked stereoscopic particle image velocimetry is employed to analyze the development of the wingtip vortices in the near wake at a distance from the wing trailing edge of 3 chord lengths. The time-averaged results suggest that the synthetic jet actuation greatly affects the wingtip vorticity distribution causing an outward diffusion which increases with the actuation frequency, with a maximum reduction of 46% on the peak value. On the other hand, when the synthetic jet is operated at the Crow instability frequency, the wingtip induced velocity shows its maximum decrease equal to 29% with respect to the baseline case. The phase-averaged analysis reveals a clear relation between the synthetic jet blowing and suction phases and the periodic variation of the vortices features. In correspondence to the blowing phase, the wingtip vortices undergo a huge diffusion and they are characterized by a larger diameter, higher circulation, and lower induced velocity. These findings confirm that this synthetic jet control configuration can represent a useful device to promote the vortex dissipation and reduce the wake vortex hazard.