PDA measurements of droplet size and mass flux in the three-dimensional atomisation region of water jet in air cross-flow

The main objective of this paper is to develop a technique to measure the global droplet properties in the atomisation region of a water jet issuing in a high-speed air cross-flow. Knowledge of these global properties allows comparison of the break-up outcome of geometrically different water nozzles. This is achieved by extending a PDA system to enable measurements in three-dimensional droplet flows. First, the droplet size and the spatial droplet distribution are measured by the PDA method. The global droplet properties are then obtained by using the measured local mass flux as a weighting factor in integrating the local droplet size. To facilitate the measurement of mass flux in three-dimensional flows, the PDA method is extended so that the reference area for the mass flux is derived as a function of both the geometry of the measurement volume and the flow direction. In the present application of three-dimensional droplet flow (a water jet in air cross-flow), a simple method is developed to measure the three velocity components of droplets by means of a two-component PA system. The paper outlines the measurement technique and the procedure of estimating the global droplet size and the global droplet size spectra from local droplet properties and local mass flux.