Structure of the Continuous Liquid Jet Core during Coaxial Air-Blast Atomisation

Abstract

This paper investigates the structure of the continuous liquid jet of a coaxial air-blast atomiser over a range of Weber numbers 60-1040, Reynolds numbers of liquid jet 5400-21700 and air to liquid momentum ratios of the two streams of 1.7-335. A novel optical technique, based on internal illumination of the liquid jet through the jet nozzle by a laser pulse, which excites a fluorescing dye introduced in the atomizing liquid, was used to obtain instantaneous measurements of the breakup length and the three dimensional location of the liquid core of the continuous liquid jet. The latter was achieved by simultaneously imaging the liquid jet from two directions normal to each other. Such measurements are usually prevented by droplets surrounding the liquid jet at the dense spray near the nozzle exit. The measurements showed that the break-up length of the liquid jet scaled well with the air to liquid momentum ratio. The standard deviation of the temporal fluctuations of the break-up length was around 10% of the mean breakup length for each considered flow condition. The instantaneous jet surface does not develop axi-symmetric wave structures but the time-averaged liquid jet is axi-symmetric around the nozzle axis, while the maximum deflection of the liquid jet occurs close to the breaking point.

Experimental and Mathematical Tools to Predict Droplet Size and Velocity Distribution for a Two-Fluid Nozzle

“…(u g /u l ) −b , for which a and b, depending on the feed properties, were in the range of 0.0001-0.0003 and 0.7-0.9, respectively. This is in agreement with the well-known power law dependency of SMD in other experimental works [36,37].…”

Flapping instability of a liquid jet

“…As pointed at in Eroglu et al (1991) [7], the motion of the liquid jet exhibits in this regime a flapping motion. The same instability, either termed flapping or helicoidal instability, is observed in subsequent studies involving the atomization of a liquid jet, but is not studied as such [2,5,[8][9][10][11][12]. Juniper & Candel (2003) [10], who observe it when liquid injection is recessed, suggest it is a wake instability.…”

Influence of steady and oscillating swirl on the near-field spray characteristics in a two-fluid coaxial atomizer

“…Despite this comment, and comments about the time-dependent, pulsating, nature of sprays [Chigier and Farago, 1992], average values have been predominantly reported in recent investigations. Even when using an advanced measurement method, [Charalampous et al, 2009] showed fluctuations of the order of 10% around the mean. Recently, [Kumar and Sahu, 2018] used series of instantaneous measurements of the liquid core length to derived the mean and standard deviation values, but also to report distributions that better characterize its variations.…”