1.西南大学工程技术学院;2.重庆市北碚区天生路2号西南大学工程技术学院;3.重庆大学航空航天学院
O359
国家自然科学基金(Grant Nos.12172070 and 12102071)和重庆市科技局直通车项目(No. CSTB2022BSXM-JCX0086)
1.College of Engineering and Technology, Southwest University;2.College of Aerospace Engineering, Chongqing University
The National Natural Science Foundation of China (Grant Nos.12172070 and 12102071) and Chongqing Doctoral Through Train Program (No. CSTB2022BSXM-JCX0086)
表面活性剂可以降低流体界面的表面张力，显著改变固体表面的润湿特性，在工业生产中被广泛使用。为探究载表面活性剂液滴在固体表面上的运动特性，基于Cahn-Hilliard相场格子玻尔兹曼方法，引入由实验得出的考虑三相接触线移动速度的Yokoi动态接触角模型，建立了一种考虑可溶性表面活性剂流动的移动接触线模型。根据控制方程独立开发计算程序，并采用并行化处理提高了计算效率。在此基础上研究了线性剪切作用下液滴的动态过程，分析了有效毛细数Cae和固体表面润湿性对纯净液滴和载表面活性剂液滴变形的影响规律。结果表明：有效毛细数Cae增大会促进液滴变形，当其增大到一定程度时液滴会产生破裂，载表面活性剂液滴相对于纯净液滴有更大的变形量和移动速度。当液滴附着于亲水性固体表面时，在相同剪切作用下，载活性剂液滴相对于纯净液滴有更长的相对弧长和相对润湿长度；且液滴在亲水表面比其在中性表面变形的相对弧长和相对润湿长度值亦更大。而当液滴附着于疏水性固体表面时，液滴则会在剪切作用下脱离固体表面；在相同的毛细数下，载表面活性剂液滴相对于纯净液滴先脱离固体表面且移动速度更快。研究结果表明可溶性表面活性剂的存在会对液滴剪切运动和变形产生较大影响，其可以促进液滴的变形，增大液滴的移动速度。本文的数值方法可用于计算载有可溶性活性剂液滴的移动接触线问题。
Surfactants can reduce the surface tension of fluid interfaces and significantly alter the wetting properties of solid surfaces, making them widely used in industrial production. In order to investigate the motion characteristics of surfactant-laden droplets on solid surfaces, a mixed model incorporating soluble surfactant flow and contact line dynamics was established based on the Cahn-Hilliard phase field lattice Boltzmann method, and the Yokoi dynamic contact angle model considering the speed of three-phase contact line movement obtained from experiments. A computational program was independently developed based on the governing equations, and parallel processing was used to improve computational efficiency. Subsequently, the dynamic process of droplets under linear shear was studied, and the influence of the effective capillary number (Cae) and the solid surface wettability on the deformation of clean droplets and surfactant-laden droplets was analyzed. The results show that the increase of the effective capillary number Cae promotes droplet deformation, but when it reaches a certain value, the droplet will rupture. While, surfactant-laden droplets exhibit the greater deformation and the movement speed compared to pure droplets. When droplets are attached to hydrophilic solid surfaces, they are further elongated under shear, exhibiting longer relative arc length and relative wetting length compared to neutral surfaces, while surfactant-laden droplets have longer relative arc length and relative wetting length compared to pure droplets. However, when droplets are attached to hydrophobic solid surfaces, they will detach from the solid surface under shear, and surfactant-laden droplets detach earlier than pure droplets. The research results indicate that the presence of soluble surfactants has a significant impact on the shear motion of droplets, promoting droplet deformation and increasing droplet movement speed. The numerical methods used in this study can be applied to calculate the moving contact line problem of droplets with soluble surfactants.
