Cavitation in a Single Hole Nozzle and Mechanism of Liquid Jet Atomization

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The mechanism of cavitation-induced atomization is studied based on high-speed simultaneous visualizations of cavitation in nozzles of pressure atomizers and liquid jet interfaces. Liquid velocity in a two-dimensional nozzle is also measured to investigate the relationship among cavitation, turbulence and atomization. The effects of the change in nozzle geometry on cavitation and the validity of the conventional cavitation numbers as an indicator of flow patterns in nozzles are also examined. A numerical model based on the hybrid integration of an interface tracking method, three kinds of particle tracking methods, an averaging method based on a multi-fluid model, Large Eddy Simulation and a modified Rayleigh-Plesset equation for predicting turbulent cavitating flows in a nozzle and liquid jets is developed, and numerical simulation of a cavitation flow in a nozzle is carried out As a result, the following conclusions are obtained.(1) When cavitation is developed in a nozzle, cavitation clouds are shed and collapse near the exit, which produces strong turbulence. When the trace of the clouds comes out of the nozzle, the strong turbulence induces ligament formation.(2) The thickness of cavitation zone increases with the ratio of the cross-sectional area upstream of the nozzle to that of the nozzle.(3) We can predict the development of cavitation using the cavitation number which accounts for the effects of the flow contraction and frictional pressure drop.(4) The causal relationship between the cloud and the ligament formation holds not only in the two-dimensional nozzle but also in the cylindrical nozzle.(5) Bubble and liquid velocity distributions are well predicted using the proposed model.