Response of Liquid Jet to Modulated Crossflow

Abstract

Experimental results on the response of spray formed by the liquid (Jet-A) jet injection into a crossflow (Air) is presented with a special emphasis on its response to the modulating crossflow. The pressure of the chamber is up to 3.5 atm and the corresponding Weber number is up to 510. The spray of a liquid jet for steady and oscillating crossflow is characterized. The flow field at the injector location in the crossflow direction is determined using PIV (Particle Image Velocimetry) for oscillating as well as steady crossflow case. Planar Mie-scattering measurement is used to characterize the response of spray formed under oscillating crossflow and supplementary phase-averaged PDPA measurements are used to understand the response behavior. The global response of spray to the oscillating crossflow is characterized using the planar Mie-scattering imaging. It shows that there exist very little differences in the heights of the maximum-pixel intensity trajectory for the non-oscillating and oscillating crossflow conditions and the trajectory under oscillating crossflow is lower than that of steady crossflow, suggesting the oscillating crossflow affects the atomization (i.e. the oscillating crossflow enhances atomization process, results in smaller droplets and penetrates less transversely). The response of spray to the oscillating crossflow characterized in terms of the spray transfer function (STF) shows that the gain of the STF increases linearly (at least monotonically) as the liquid-air momentum flux ratio increases but does not change as much with respect to the change of the Weber number for a fixed liquid-air momentum flux ratio. This also indicates that the liquid jet atomization under oscillating crossflow is enhanced much more with the increase of liquid-air momentum flux ratio than with the increase of Weber number. The phase-averaged PDPA measurements confirm that the oscillating crossflow indeed enhances the atomization process in that the oscillating crossflow results in relatively greater number of smaller droplets and the mean droplet size.

Experimental and Numerical Characterization of a Liquid Jet Injected into Air Crossflow with Acoustic Forcing

“…Depending on the amplitude and frequency of the air velocity oscillations and the averaged momentum flux ratio q between the two fluids, the liquid jets may cyclically impact the inner or the upper wall of the injection system forming a liquid film which is re-atomized at the edge of the diffuser. Such coupling between the air crossflow and the atomization of a liquid jet was shown by Anderson et al (Anderson, Proscia & Cohen 2001), Song and Lee (Song, Ramasubramanian & Lee 2013) and Sharma and Lee (Sharma & Lee 2018).…”

“…Nevertheless there exist discrepancies concerning the determination of this length in the literature cause by an accurate determination of this location due to high droplets (or ligaments) density around the jet column. and a non-dimensional time scale parameter comparing the breaking time scale of the column introduce by Wu et al ( = 3.07( ⁄ ) 0.53 ) to the oscillating period of the excitation ( = 1⁄ ) Anderson et al (Anderson, Proscia & Cohen 2001), Song and Lee (Song, Ramasubramanian & Lee 2013), Sharman and Lee (Sharma & Lee 2018). For high excitation level and small time scale ratio, large oscillations of the liquid column were observed.…”