Effects of stroke and Reynolds number on characteristics of circular synthetic jets

The circular jet flows generated by a piezoelectric disk were studied experimentally. The velocity distributions were measured using a single hot-wire anemometer, and the effects of the oscillatory flow conditions though a circular orifice were examined. The effects of the dimensionless stroke and Reynolds number of the oscillatory flow on the synthetic jet flows were examined. The stroke was the length of the fluid ejected in an oscillatory cycle and non-dimensionalised by the orifice diameter. The mean velocity distributions were examined for a dimensionless stroke range of 0.60-2.40 with a constant Reynolds number (Re) of 2700. The stroke was found to have a remarkable effect on the streamwise variation in the jet centerline velocity and jet width. As the stroke was increased, the starting point of the jet growth was shifted downstream. This change is discussed by examining the instantaneous velocity signals and attributes in relation to the change in the collapse of vortex rings emitted from the orifice. The momentum of the synthetic jet increased sharply above a critical stroke for the jet formation, and seemed to be saturated for strokes longer than the orifice diameter. The flow field was also examined for a Re range of 1900-3000 with a constant dimensionless stroke of 1.02. In the Re range studied, no significant changes in the jet flows were observed.