Atomization and Sprays, Vol.20, No.8, 721-735, 2010
VISCOELASTIC AIR-BLAST SPRAYS IN A CROSS-FLOW. PART 2: DROPLET VELOCITIES
To better understand spray coating in field conditions, we have examined the effect of a cross-flow on two different air-blast sprays, one comprising water and the other a viscoelastic industrial coating. Using particle image velocimetry, we measured the time-averaged spatial distribution of droplet velocity over a wide range of spray:cross-flow momentum-flux ratios: 134 <= q(ab) <= 1382. For both sprays, increasing the relative momentum-flux of the cross-flow caused the droplet velocity magnitude to decay more rapidly with streamwise distance. Along the deflecting spray centerline, the decay followed jetlike scaling in the near field but wakelike scaling in the far field. The transverse droplet velocity, meanwhile, showed a local maximum in the main spray body, which was always substantially higher than the cross-flow velocity; normalized values of the local maximum increased with gab, reaching as high as 65%. As for differences between the two sprays, the coating droplets were markedly faster than the water droplets because they had lower drag momentum ratios and could thus better preserve their initial momentum. For a similar reason, the water droplets were able to more closely track the carrier airflow, approaching the jet/wakelike velocity scaling earlier than did the coating droplets.