Numerical Investigation Of Droplet Impingement Onto Spherical Surface

The droplet impingement phenomenon is a common phenomenon in real life. Such as spray coating, painting, printing process, casting process, the metal metallurgical industry, the evaporation process in the internal combustion engine, cooling of turbine blade, core cooling of nuclear reactors, spray cooling, plasma spraying, etc. The droplet impingement phenomenon is of importance in the future and will be subject to the attention of relevant personnel and research.In this paper, the numerical simulation method is used to analyze the dynamic behavior of a single droplet impacting on the spherical solid surface. The simulation method tracking interface is CLSVOF (Coupled Level-Set-and-Volume-Of-Fluid) method. This method can not only maintain the conservation of mass and also accurately calculate the curvature of the interface and the normal of interface. The simulations show that this coupling method can get smooth and sharp results and the simulation results is more consistent with the actual images. Compared the simulation and experimental results, the model is verified. Respectively, the droplets with low energy and high energy impact on the spherical solid surface are studied. The main contents are as follows:For the droplet with low energy impacting on the spherical solid surface, the influence of dimensionless Re number, the physical properties of the droplet, the physical properties of the surface on the dynamic behavior of the droplet impacting process is analyzed and qualitative analysis of the droplet spreading coefficient, dimensionless spreading thickness of the liquid film are showed. The results showed that:within the scope of this paper, after droplet impact on the solid, the spreading, rebound, relaxation behavior is observed. In the spread phase, with the increasing of Re number, spreading coefficientdecreases. In the rebound phase, retraction speed decreases, the film thickness increases too fast; Spreading coefficient increases when the droplet velocity increases, the retraction speed increases; With solid spherical diameter increasing, spreading coefficient is slightly larger, retraction speed is larger when solid spherical diameter is small:The influence of coefficient of viscosity of the liquid droplets is obvious when spreading coefficient is near the maximum spreading coefficient and the maximum dimensionless film thickness; surface tension coefficient almost is of no effect on the characteristics of spreading of droplets, the droplet with big surface tension coefficient retraction speed is fast.For the droplet with high energy impacting on the spherical solid surface, the influence of dimensionless Re, We number, the physical properties of the droplet and the physical properties of the surface on the dynamic behavior of the droplet impacting process is analyzed and qualitative analysis of the droplet spreading coefficient, dimensionless spreading thickness of the liquid film are showed. The results showed that:droplet impacting on the solid will spread or splash. With Re number increasing and We number decreasing, spreading coefficient become smaller, non-dimensional film spreading speed become slow; However, with the We number increasing, the reducing trend of thickness is greater than the increasing trend of spreading coefficient; With the curvature ratio increasing, when T=1, spreading coefficient have a tendency to increase, however the variation of the dimensionless spreading film thickness is almost same; With the droplet diameter increasing, spreading coefficient decreases, spreading speed of dimensionless film spreading thickness decreases; with the increase of the droplet velocity, spreading coefficient increases, dimensionless film spreading thickness decreases; The droplet spreading coefficient and the dimensionless film spreading thickness of the liquid almost same with the variation of viscosity coefficient, surface tension coefficient and contact angle; With the increase of Re number, the number of secondary droplets decreases. With the increase of We number, the number of secondary droplets increases. With the curvature increasing, the number of secondary droplets also increased. It showed in the scope of this study, with same We number, increasing Re number inhibit the generation of secondary droplets, increasing We number and curvature promote generation of secondary droplets.