Air–liquid interactions in a pressure-swirl spray

Abstract

The energy transfer between a liquid hollow cone spray and the surrounding air has been studied using both imaging and phase-Doppler techniques. The spray was produced by a pressure-swirl atomizer discharging Jet A-1 fuel at inlet over pressures of p = 0.5, 1.0 and 1.5 MPa into quiescent ambient air. The liquid exits the nozzle as a conical film which thins as it spreads and develops long-and shortwave sinusoidal instabilities with breakup occurring, at the length smaller than that predicted by the inviscid model, to form film fragments and ultimately droplets downstream the spray. The single shot imaging characterised the spray regions of near-nozzle flow, the breakup processes and the developed spray. The phase-Doppler system resolved the three components of velocity and size for the droplet flow as measured on radial profiles for four axial distances from the nozzle exit. A Stokes number, Stk, analysis of the droplets' response times to the airflow timescales showed that droplets < 5 µm followed the airflow faithfully and so were used to estimate the local airflow velocity. This allowed a comparison of both the droplet and airflow fields in terms of their mean and fluctuating velocity components to be made. The formation of the hollow cone spray and the interaction of the fragments and droplets with the air, through viscous drag, induce complex entrained airflows. The airflow was found to be highly anisotropic, fluctuating preferentially in the downstream direction, and spatially varying within three distinct spray regions. The air drag establishes a positive size-velocity correlation of droplets; their Stk reduces with axial distance and increases with droplet size and p; so that Stk ≈ 1 for 20-40 µm droplets and the largest droplets (80-160 µm, Stk > 10) move ballistically. The spatially resolved mean and turbulent kinetic energies of the air and spectra of the droplet velocity fluctuations are detailed in the paper. These findings are relevant to scientists and engineers modelling the complex two-phase flows.

Experimental investigation on spray characteristics of Jet A-1 and alternative aviation fuels

“…For spray analysis, Phase Doppler Particle Analyzer (PDPA) technique is the most commonly used diagnostic tool. Jedelsky et al 6 and Guerrassi & Champoussin 7 with the help of PDPA measurements in atmospheric environments, observed that the droplet Sauter mean diameter (SMD) decreases with the increase of radial distance from the central axis. It is noted that for dense spray, PDPA is doubted to be suitable due to the multi-scattering effect.…”

Numerical Simulation and Experimental Study on Flow Field in a Swirl Nozzle

“…Marchione et al [8][9][10] studied spray characteristics, such as the spray cone angle and the film breakage length, of the external flow field under different spray pressures. Jedelsky et al [11,12] studied the formation of a hollow cone spray and the chang law of the spray cone angle. Xia et al [13] studied spray characteristics and found that the breaking length of the water jet decreases as the gas-liquid ratio in the air increases.…”

Effect of the two-phase hybrid mode of effervescent atomizer on the atomization characteristics

“…The results showed that the spray mean droplets size was reduced by increasing the injection pressure, while a higher effect was pronounced at lower injection pressures. The effect of the pressure on the behavior of droplets was investigated by Liu et al [16], Jedelsky et al [17] and Ge et al [18]. It was concluded that the SMD decreased gradually with the increase in the pressure, and remained constant when the pressure was higher than 20bar.…”

“…It was concluded that the SMD decreased gradually with the increase in the pressure, and remained constant when the pressure was higher than 20bar. Jedelsky et al [17] found that the atomizer structure had a great effect on the atomization quality. Several researchers [19][20][21][22][23] had examined the effect of GLR on the mean droplets size distribution and concluded that the latter remained fairly constant as the GLR changed.…”