The Study And Simulation Of The Behavior Of A Droplet During The Spray/Wall Impingement

The phenomenon of the droplet impacting on a wall widely exists in the nature and engineering practice, such as the whereabouts of the raindrops and the fuel injection. In the engine, the droplet/wall impingement is directly related to the quality of of mixture gas in the cylinder, right after it has a have a significant influence on the combustion and emission processes. The collision between the drople and the wall is a typical free-surface flow problem, the physical mechanism and kinetic behavior of the collision process has a crucial role in the development of spray technology.In this paper, The process and the internal mechanism of the the droplet/wall impingement is discussed, by the summary and the analysis of the phenomenon of a single droplet impacting on a wall. The spreading behavior of a droplet was analyzed in theory. The flow of the adherent region near the contact line was solved, based on the solution, the dynamic contact angle model of the spreading behavior was established. And the model calculations and previous experimental data were compared to verify its reliability, and the various factors that affect droplet spreading behavior was calculated and analyzed, the influence of these factors on the behavior of the spreading was obtained.The mathematical model of a droplet impacting on the wall was established, according to the fluid mechanics equations. Through the open source software-OpenFOAM, using the VOF method and the LES method, the numerical simulation the process of a single droplet hitting the wall was carried out. The flow state of a droplet hitting the wall was analyzed by changing the factors, the droplet properties, wall properties, impact velocity, impact angle and other factors on the morphological changes of the droplet was investigated, futher, further a droplet hitting the wet wall and spherical conditions were simulated and analyzed.The simulation results show that when the droplet hits vertically a plane wall, the flow of the droplet is symmetrical, when there is a certain angle between the direction of droplet velocity and the wall, the flow is asymmetry. The influence of the wall features is mainly characterized by the contact angle, for high wettability wall, the droplet tends to stick on the wall, the droplet easily break up, fracture or rebound. on the non-wetting wall. For the spreading behavior of the droplet on the rough wall, the flow of the droplet was inhibited to a certain extent. The initial impact velocity of the droplet which hits the wall has a great influence on the behavior of the droplet after impacting, the greater the speed, the faster the droplets spread more, the greater the spread length. When the droplet hits the wet wall, the droplet the wall film and wall will interact with each other, two rising liquid curtain were formed, and the flow was affected by the thickness of the liquid film. For the condition of sphere surface, because the sphere exists a certain degree of curvature, it causes the change of the direction of the surface tension. For the different diameter of the droplets hit the wall, the change of the dimensionless spreading thickness and dimensionless spreading diameter over time relationships were analyzed, the results show that in the spreading process spherical diameter increases, the droplet spreading coefficient increases, the time of the droplet reaching the maximum spreading changed for different spherical diameters. Spherical diameter is smaller, the smaller the spread thickness, the smaller the thickness of the smallest spread. When the sphere diameter is small enough, the spreading liquid film will center partial rupture.