背压对敞口型旋流喷嘴液膜特性影响的数值研究

背压对空气物性影响较大，使喷嘴液膜受到的气动力发生大幅变化。采用计算流体力学（Computational Fluid Dynamics，CFD）方法对比3种常见液体工质和3种喷嘴尺寸，研究背压对雾化锥角、液膜厚度、旋流强度、液膜表面自激励不稳定性以及液膜形态的影响。结果表明：雾化锥角随背压增加而减小，其中部分喷嘴当背压达到某定值后，雾化锥角小幅波动；选用正庚烷或正十二烷为工质时，液膜厚度随背压增加而增加，达到一定背压后，3种液体液膜厚度呈小幅波动；旋流强度随背压变化无明显规律性；液膜自激励不稳定性随背压增加而降低；因水的表面张力较大，各雾化参数较为稳定；液膜形态与韦伯数呈明显规律性，背压越小韦伯数越大，液膜形态也更趋近于完美圆锥形；以正十二烷为工质时，其液膜形态在大背压下明显收缩，呈洋葱形，其余工质的液膜形态随背压增加，均逐渐从空心圆锥转变为郁金香形。

Numerical Research on the Effect of Backpressure on Film Characteristics of Open-end Swirl Nozzle

Backpressure obviously influences the physical property of air,resulting in the significant change of the aerodynamics force on film of nozzle.Based on the computational fluid dynamics(CFD),three kinds of common fluid mediums and three kinds of nozzle geometries were compared,and the effect of backpressure on the characteristics of spray cone angle,film thickness,swirl intensity,self excited instability of film surface and film morphology was studied.The results show that spray cone angle decreases with the increase of backpressure.When the backpressure reaches a certain value,low fluctuations of the spray cone angles of a part of nozzles occurs.When n heptane or n dodecane is selected as working medium,the film thickness increases with the increase of backpressure,and low fluctuation of film thickness of three fluids occurs after reaching a certain backpressure.There is no obvious change rule of swirl intensity with backpressure.Self excited instability of film surface decreases with the increase of backpressure.Each spray parameter of water is stable due to the higher surface tension.The film morphology is sensitive to Webber number.The smaller the backpressure is,the larger the Webber number is,and the film morphology is closer to a perfect cone.With the n dodecane as working medium,the film clearly contracts under high backpressure,presenting the onion shape.When the backpressure is growing,the film morphology of water and n heptane gradually transforms from hollow cone to tulip.