The predominant effect of stroke length on velocity profiles at the exit of axisymmetric synthetic jet actuators

This paper addresses the effect of stroke length on velocity profiles at the exit of axisymmetric synthetic jet actuators. An actuator with a “short-orifice” nozzle geometry was studied (the length of the sharp-edged orifice nozzle being always shorter than the stroke length). The investigation was carried out using hot-wire experiments and numerical approaches in the range of the Reynolds number from 400 to 5600 and a dimensionless stroke length from 1.5 to 86 (i.e. the Stokes number was from 16 to 102). To quantify the velocity profiles at the actuator exit, the ratio of the two characteristic velocities was used. The former one was evaluated as the time- and spatially-averaged orifice velocity and the latter as the time-mean centerline velocity. It was found that this average-to-centerline velocity ratio depends mainly on the dimensionless stroke length, with a minor dependence on the Reynolds number. An approximation function of this predominant relationship has been proposed. The results of both experimental and numerical approaches are in reasonable agreement showing variation of average-to-centerline velocity ratio in the range of 0.7-1.3.