Session Ca - Turbulent Jets & Wakes.
ORAL session, Sunday, November 23
301, Moscone Center
Previous investigations of pulsed turbulent transverse jets have reported an increase in penetration with pulsing frequency. The present experiments study the combined effect of pulsing frequency, duty cycle and ratio of mean jet velocity to crossflow velocity in the penetration and flame length of the transverse jet. Experiments are conducted in a water tunnel with a circular jet issuing from a submerged flat plate. A solenoid valve allows for the full modulation of the jet in the range of 0.5 to 5 Hz with duty cycles of 1/2, 1/4 and 1/8. The velocity ratios are roughly 5 and 10. Flow visualization is achieved by premixing fluorescent dye into the jet fluid and measurements are taken directly from video photography over a downstream distance of up to 50 jet diameters. Initial experiments showed a slight increase in penetration with frequency up to about 3 Hz. At duty cycles of 1/4 and 1/8, distinct vortex rings are observed to penetrate into the crossflow at high speeds. The penetration of these rings is higher than the corresponding steady jet. The location of the first interaction between successive turbulent puffs shifts upstream with increasing frequency. The interaction between puffs tends to reduce the penetration compared to that of the vortex rings. Chemically reactive jets are employed to examine the influence of the aforementioned parameters on mixing and flame length.