Droplet velocity and acceleration measurements in dense sprays by laser flow tagging

The feasibility of liquid-phase velocity measurements in dense sprays by 2D laser-based flow tagging is demonstrated. Velocity measurements in dense s prays are difficult with conventional techniques because of the high number densities of droplets, the optical thickness of the medium, and multiple l ight-scattering effects. The present flow-tagging technique is based on pho sphorescent tracer molecules, which are excited by a grid of pulsed 'write' laser beams. The motion of the tagged droplet groups can be observed by a CCD camera in this way. In addition, multiple consecutive velocity measurem ents are performed by 'droplet-group tracking'. This yields the acceleratio n along the trajectory of individual groups of droplets in unsteady sprays.