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 sprays are difficult with conventional techniques because of the high number densities of droplets, the optical thickness of the medium, and multiple light-scattering effects. The present flow-tagging technique is based on phosphorescent 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 measurements are performed by ‘droplet-group tracking’. This yields the acceleration along the trajectory of individual groups of droplets in unsteady sprays. Received: 5 June 2000 / Revised version: 28 July 2000 / Published online: 6 September 2000