Effects of elevated ambient pressure on the disintegration of impinged sheets

Abstract

Numerical simulations that are based on the volume-of-fluid method are performed to study the atomization of impinging jets under the influence of higher steady and oscillating ambient pressures. Both the simulated flow patterns and the statistical features of the droplet size distribution and sheet wave agree well with experimental data from the literature. Then, the instability mechanism of an impinged sheet is explored. The position at which the breakup of the liquid sheet occurs is determined jointly by the velocity distribution of the sheet and aerodynamic effects. Finally, the effects of ambient pressure on the stability of atomization and spray characteristics are discussed in detail. When the ambient pressure is elevated from 0.05 MPa to 0.5 MPa, the sheet’s instability increases as the gas/air density increases. During the above process, the increasing aerodynamic force that is exerted on the liquid sheet increases the impact amplitude values, thereby increasing the spray angle and decreasing the sheet breakup length. However, the breakup of large droplets during secondary atomization is suppressed under high backpressure conditions because of the deceleration of the film’s movement. Additionally, the backpressure oscillation, with the frequency approximating the fundamental frequency of sheet waves, enhances the wave amplitude and the atomization angle, which accelerates the sheet’s breakup and decreases the mean size of the droplets downstream of the impingement point.