The effect of fractal orifices on synthetic jets

The effect of fractal orifices on the characteristics and vortex rings of synthetic jets is investigated. Synthetic jets with circular and fractal orifices, as well as a continuous jet with a circular orifice, are measured using two-dimensional particle image velocimetry. The fractal orifice affects the near field and transition region, resulting in smaller jet half-width, volume flow rate, entrainment coefficient, and Reynolds shear stress compared with the circular synthetic jet. Nonetheless, these values are still higher than those of the continuous jet with the same Reynolds number. The vortex rings of the fractal synthetic jets exhibit larger circulation and vortex core diameter, and smaller central vorticity before breakdown, leading to a rapid decrease in circulation and scale during breakdown. After vortex ring breakdown, the vortex scale concentrates around 15 η ( η is the Kolmogorov scale), which is believed to play an important role in the entrainment process.