The present research reports an experimental spray characterization of a generic double-swirl prefilming model aeroengine atomizer,which injects an annular liquid sheet of 0.5 mm thickness at the nozzle exit,sandwiched between an inner and an outer co-rotating swirling air streams.Planar spray measurements are obtained using a non-invasive laser-based Interferometric Laser Imaging Droplet Sizing(ILIDS)technique1,2,which is capable of providing simultaneous planar measurements of droplet size,velocity and number density in the resulting spray.Experiments are reported for a water spray for different axial(Z)and radial(R)locations for different air and water flow conditions.Apart from time-averaged droplet size and velocity measurements,ILIDS allows unique measurements of other important statistical quantities,including droplet-droplet spatial velocity correlation,which is important for evaluation of new modeling approaches for the droplet fluctuating motion,and is presented here for different separation distances between droplets and conditional on droplet size.In addition the extent of droplet clustering for different droplet size classes is presented and the corresponding cluster dimensions quantified,as estimated from the radial distribution function5(RDF)measured conditional on droplet size classes.Finally,measurements of mean and fluctuations of droplet number density for different droplet size classes are reported.The new physical understanding of the spray dynamics and droplet cluster formation in sprays,provided by the novel measured quantities,is discussed.