V形面喷涂成膜数值模拟

Numerical Simulation of Film Formation on V-shaped Surface by Spraying

目的建立V形面喷涂成膜仿真模型,深入研究V形面喷涂成膜特性,为优化喷涂喷枪轨迹及获取理想涂膜提供理论支撑。方法采用欧拉-欧拉方法建立包含喷雾流场模型和喷雾沉积模型的V形面喷涂成膜模型,结合动态自适应加密技术和SIMPLE算法,求解分析喷雾流场规律和涂膜厚度分布特性及形成机理,开展喷涂实验验证所建模型及成膜特性的正确性。结果随着Z轴距离的增大,喷雾流场横向雾形由椭圆形变为长条状,纵向雾形在长轴方向上近壁面时与平面喷涂差别较大。相较平面喷涂,外壁喷涂喷雾覆盖范围广,内壁喷涂结果相反,且喷雾横向扩展程度与Z轴坐标值均呈线性关系。V形面内外壁喷涂涂膜均呈椭圆形,且膜厚均沿径向递减。外壁喷涂涂膜光环宽度最大,涂膜厚度值普遍低于平面喷涂;内壁喷涂涂膜光环宽度最窄,短轴方向涂膜厚度值普遍高于平面喷涂。随着V形面角度变大,涂膜中心厚度不断增加。涂膜厚度值在短轴方向均呈单峰分布,而在长轴方向上,外壁喷涂涂膜厚度均呈双峰分布,内壁喷涂涂膜厚度分布随角度变化有差异。结论建立的喷涂成膜模型用于V形面喷涂成膜过程仿真是有效的,V形面较大地改变了喷涂过程中的喷雾流场特性和涂膜厚度分布特性。

The work aims to establish a computational fluid dynamic(CFD)simulation model for in-depth research of film-forming characteristics on V-shaped surface by spraying,in order to provide theoretical support for optimizing the trajectory of the spray gun and obtaining an ideal film.The mathematical model of film formation was established by the Euler-Euler method to solve the over-simplification problem of the empirical model and the limitations of the Euler-Lagrange method,and the unstructured grids and adaptive-mesh refinement were adopted to discretize the computational domain.The model established was solved with the SIMPLE algorithm of the phase solver based on pressure and spray experiments were conducted to verify the correctness of the model.By analyzing the results of the numerical simulations,the spray flow field characteristics and film thickness distribution law of spraying the V-shaped surface were obtained.The effect of the V shape on the spray flow field in the long axis direction was greater than that on the spray flow field in the short axis direction.Compared with the spray flow field of the plane spraying,the horizontal shape of the spraying flow field of the V-shaped surface was almost the same except that of the inner wall surface spraying was significantly different when the Z-axis distance was 140 mm.With the increase of the Z-coordinate value,the horizontal spraying shape changed from the ellipse to the long strip.The longitudinal shape of the spray flow field was quite different when it was close to the wall in the long-axis direction.Their tail shapes in the order of plane spraying,outer wall spraying and inner wall spraying were in a straight line,an inverted V shape,and a V shape,respectively.The spraying coverage of the outer wall was wider,and that of the inner wall was narrower.Besides,the horizontal expansion degree of the spraying had a linear relationship with the value of coordinate Z.The film shapes on the inner and outer walls of the V-shaped surface were all elliptical,and their thickness decreased along the radial direction.The film on the outer wall had the larger halo width than that on the plane,yet with a generally lower thickness.The film on the inner wall was just the opposite.As the angle of the V-shaped surface became larger,the thickness of the film center increased continuously.The thickness distribution of the film in the short axis direction was single-peak,while the thickness distribution of the film on the outer wall in the long axis direction was double-peak,and that of film on the inner wall varied with the angle.It is concluded that the film-forming model on sprayed V-shaped surface and film-forming characteristics obtained are correct,and the V-shaped surface greatly changes the characteristics of the spray flow field and the film during the air spraying process.Film-forming numerical simulation on sprayed V-shaped surface is of great theoretical and practical significance for revealing the film-forming characteristics of spraying complex free-form surfaces with large curvature,optimizing the spray gun trajectory and improving the film quality,etc.