INFLUENCE OF PIEZO-DRIVEN SYNTHETIC JET ON WATER SPRAY BEHAVIOR

The opportunity of directly managing the spray formation and its characteristics has gained much interest in the last few years, due to the various active flow control methods available nowadays. In this work particle image velocimetry (PIV) has been applied to investigate the effect of a piezo-driven synthetic jet (SJ) on the droplet velocity distribution of a water spray. Tests were carried out under atmospheric conditions within a chamber test rig, equipped with optical accesses, at two injection pressures, namely, 5 and 10 MPa, exploring the variation of the spray flow field caused by the synthetic jet perturbations. The SJ orifice axis has been placed 45 deg tilted with respect to the water spray axis, and the nozzle body has been moved along its own axis for three different positions. PIV measurements have been averaged on 300 trials. For each operation condition, the actual influence region of the SJ has been evaluated through a T-test algorithm. The synthetic jet locally interacts with the spray, remarkably energizing the region downstream of the impact. The effectiveness of the actuator decreases for higher injection pressures and shorter distances between spray nozzle and SJ orifice. The study has been corroborated by a vorticity field analysis, which is able to identify the influence of coherent vortex structures generated by the air jet, in terms of both droplet momentum and droplet spreading variations.