| The research on breakup mechanism of the liquid jet is not only a traditional fluid mechanics problem, but also a topic with great theoretical research value and engineering application background. The liquid sheet formed by impinging jets is a classic method of jet atomization for its simple structure, low cost, good atomization, and has been widely applied to the field of aeronautics and astronautics.For this paper, the breakup progress and characteristic of the liquid sheet were studied under the condition of speed of less than 5.2m/s. High-speed photography was used to investigated the atomization behavior of water, glycerol solution and non-Newtonian power-law gelled fluids which show a shear-thinning behavior, with symmetric and asymmetric impact jet. The sheet characteristic, breakup length, length of liquid film, width of liquid film and aspect ratio were extracted from the optical shadow pictures. The influence on the breakup rule of liquid film of different factors, such as jet impact angle, nozzle diameter, viscosity, pre collision distance, etc, was analyzed.Present results indicate that three breakup patterns of the liquid sheet of symmetric impinging jet is appeared, such as closed rim pattern, open rim pattern, ligament structures. The special open rim pattern for sheets of glycerol solution and Carbopol gel is found which is called fishbone pattern when impact jets are asymmetric. The impact angle of 78°is found to provide well-developed fishbone patterns. It can be got from the images and drop size distribution that the breakup behavior of Carbopol gel film is influenced greater than other kinds of liquid for pre collision distance. The factors influence on water sheet is minimal. For all fluid, length and width of liquid sheet increases along with the increase of speed, and the length-width ratio of liquid sheet is stable value. Only jet impact angle and viscosity can influence on the ratio. The aspect ratio decreases with increase of impact angle. The greater the viscosity is, the bigger the aspect ratio is. Breakup length curves, which move along with the change of Weber number, are corresponding with the breakup patterns. The influence of viscosity on breakup length is greater than nozzle diameter. The breakup length decreases with decreases of the nozzle diameter. Asymmetric impact makes the breakup modes of liquid sheet changes more complex. The comparison between theoretical and experimental breakup length results indicates that the linear instability analysis method can predict the breakup length. Rayleigh instability is relevant to destabilization of the rim of liquid sheet and its periodic atomization namely fishbone pattern, and droplet spacing is about ?8 ?0.5? times the minimum thickness of rim, when the maximum angle of fishbone appears. |
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