奶牛喷淋降温水滴形态特性的数值模拟

Study on morphological characteristics of sprayed water drop by numerical simulation

为研究奶牛喷淋降温过程中的水滴形态特性,以及水滴撞击壁面过程中的铺展系数与水滴喷淋速度和接触角之间的关系问题,采用CLSVOF数值模拟方法,对单个水滴与固体壁面撞击过程进行三维数值模拟。首先根据Yokoi的试验对本研究数值模型的准确性进行验证,然后根据本研究试验测试数据建立数值模型,同时结合韦伯数(We)、雷诺数(Re)及系数K对数值模型进行分析验证。研究了水滴粒径分别在0.5和0.8mm条件下:当速度分别以1、2和3m/s,平均接触角为120°时水滴撞击固体壁面时的形态变化;当接触角分别为90°、120°和140°,速度为1m/s时水滴撞击固体壁面时的形态变化。结果表明:随液滴直径和撞击速度的增加,液滴撞击壁面后主要有振荡、反弹、破碎和飞溅这4种典型运动形态;随着水滴速度的增大,水滴铺展速度加快,最大铺展直径与铺展系数增大;随着接触角增大,水滴最大铺展直径减小,最大铺展系数值减小。

In order to study the droplet morphological characteristics of cow during the spray cooling process,and the relationship between spread coefficient and droplet spraying velocity and contact angle in the process of water drop hitting the wall,a three-dimensional numerical simulation of the collision between a single droplet and the solid wall was carried out by using the CLSVOF numerical simulation method.First of all,based on the experimental test reported by Yokoi,this study verified the accuracy of the numerical model in this study.Then,based on the experimental data,a numerical model was established.Combined with Weber number（We）,Reynolds number（Re）and coefficient K,the numerical model is validated.Morphological changes during the process of water droplets hitting solid wall were studied at 2 droplet diameter of 0.5 and 0.8 mm：Firstly,the velocity of 1,2 and 3 m/s,the average contact angle of 120°respectively;Secondly,the contact angles of 90°,120°and 140°,the velocity of 1 m/s respectively.The results showed that：With the increase of droplet diameter and impact velocity,there were 4 typical forms of motion after the droplet hitting wall including oscillation,bounce,breaking,splashing;With the increase of water droplet velocity,the spreading velocity of water droplets accelerated,the maximum spreading diameter and spread coefficient increased at the same time;With the increase of contact angle,the maximum spreading diameter of water droplets decreased and the maximum spreading coefficient decreased.