Experimental characterization of spray water controlled by a synthetic jet

The paper reports results of an experimental investigation to explore the potential of a synthetic jet (SJ) actuator to control a water spray. Particle Image Velocimetry (PIV) and Phase Doppler Anemometry (PDA) have been applied to characterize, in terms of velocity vector distribution and droplets size, the spray behavior generated by a misting nozzle for humidification under the control of a piezo-element driven synthetic jet. Experiments have been conducted under atmospheric conditions within a chamber test rig equipped with optical accesses, allowing PIV and PDA measurements, and a water misting nozzle driven by a pressure control module. Water has been used as working liquid, investigating the jet action on the water droplets velocity vector distribution and droplets size generated by the nozzle. Tests have been carried out for two injection pressures, namely 5 and 10 MPa. For a certain reference relative position of the SJ orifice, set at 45° with respect to the water nozzle axis, investigation has been performed for three different orifice axial positions and for each operative condition tests have been replicated two-times, with and without the synthetic jet activation. PIV measurements have been taken on 300 realizations and an averaging procedure was applied to provide the velocity vector maps, whereas the number of samples acquired for the PDA tests, performed on different locations, has been set in the order of 105.The two resulting velocity vector maps and the droplets size have been compared and a statistical analysis of the jet effect on the spray velocity magnitude has been carried out. For each operative condition, the influence region of the SJ device on the spray has been computed through a T-Test algorithm. The synthetic jet interacts with the spray locally, energizing the region downstream the impact. The effect of the actuator decreases at higher injection pressures and moving the impact region upwards. Droplets coalescence can be detected along the synthetic jet axis, while no significant variations are observed along the orthogonal direction.