A high-speed, compressible synthetic jet

The operation of a high-speed, compressible synthetic (zero net mass flux) jet is investigated experimentally using a small (nominally 6.5 cm3) piston/cylinder actuator driven by a variable speed motor. The actuator performance is characterized using phase-locked cavity pressure measurements, particle image velocimetry of the jet flow, and Schlieren flow visualization. Cylinder pressure ratios (relative to the ambient) measured over the experimental limits range as high as 8 and as low as 0.2, during the blowing and suction phases, respectively (producing sonic flow velocities at the orifice during both phases). Owing to compressibility effects, the shapes of the time-periodic pressure curves during the blowing and suction cycles are dissimilar (the suction duration is longer) and there is a clear phase shift between the peak piston displacements and the corresponding pressure extrema. It is shown that the performance is primarily affected by the characteristic velocity (defined by the product of the oper...