Experimental studies of the influence of parameters on axisymmetric synthetic jets

This paper studies the influences of two dimensionless parameters, the Reynolds number and dimensionless stroke, on an axisymmetric synthetic jet by using flow visualization and particle image velocimetry (PIV) techniques. The flow visualization results and the relevant analyses, such as the formation and state of the vortex ring, the time-averaged streamwise velocity and kinetic energy of the fluctuating motion, etc., are provided. It was found that the Reynolds number does not influence the formation location of vortex rings; however, with increasing Reynolds number, the vortex rings go through the laminar–turbulent transition and tend to lose stability, leading to breakdown. In addition, the similarity of the jet kinetic energy distribution of fluctuating motion can be reached in a short distance downstream from the orifice, and the characteristics of conventional turbulent jets also appear as the Reynolds number is increased to a certain value. The dimensionless stroke strongly influences the formation and development of vortex rings. Furthermore, the experimental investigations on an axisymmetric synthetic jet actuated by a novel actuator signal, proposed by Zhang and Wang [16], are implemented in the present paper, and the ‘actual efficient stroke’ concept is introduced.