Effect of injected longitudinal vorticity on particle dispersion in a swirling, coaxial jet

A passive particle dispersion control technique was investigated in which l ongitudinal vortices were injected into a developing coaxial swirling jet w ith sufficient annular swirl for Pow recirculation to occur. Four vortex ge nerators, separated by 90 degrees and placed along the outside of the annul ar nozzle, injected vorticity opposite in sign to the mean swirl, significa ntly altering the structure of the swirling jet. The injected vorticity com peted with the mean swirl to reduce azimuthal particle Pinging and to disru pt the development of the vortex rings in the outer shear layer. Axial flow visualization showed the formation of axial structures at the forcing freq uency but considerable azimuthal asymmetry. Horizontal cross sections showe d a four-lobed structure which persisted in the natural jet for at least ei ght inner jet diameters. The particle concentration field was measured usin g digital processing of pulsed laser sheer images. Outward radial particle dispersion reduced while inward dispersion toward the jet centerline increa sed indicating that the injected vorticity sufficiently reduced particle Pi nging by large-scale vortices.