The structure of an acoustically forced, droplet-laden jet

A detailed characterization of the interaction of a polydisperse spray with large-scale vortical structures in a jet is presented. Phase Doppler interferometry is used to acquire droplet size and velocity information. Planar imaging techniques are applied to document the distribution of droplets and their number density within structures. The presence of large-scale structures results in large local variations of droplet number density. images taken through the cross section of a large-scale structure provide evidence that azimuthal structures contribute to the dispersion of droplets. Size measurements show that, in general, only droplets with Stokes number less than unity are found on the outer edge of vortical structures. However, even for very small droplets (Stokes number < 0.1), a substantial portion of the vortex center is void of droplets. Radial velocity measurements show that droplets have an outward radial velocity on the lending edges and as inward radial velocity on the trailing edges of structures. Axial velocity measurements show complex size-velocity correlations within structures among different droplet size classes. Size-velocity correlations become less distinct across the jet due to the transport of droplets by large-scale vortical structures.