Numerical Study Of Droplet Impact On Microstructure Surface

The phenomenon of droplet impinging on a smooth wall is widely existed in industrial production.There are numerous researches on droplet impinging on a smooth wall by scholars at home and abroad.With the increasingly prominent advantages of microstructure surface,more and more researchers apply it to various fields of engineering practice,including aerospace.Many literatures show that the existence of microstructure has a great influence on the motion and heat transfer characteristics of droplet impinging on the wall.Considering that the heat load of aero-engine bearing cavity is increasing,the lubrication and cooling demand of bearing cavity is also increasing correspondingly.In this paper,the microstructure is combined with the bearing cavity wall of aero-engine to improve the lubrication and cooling of the bearing cavity The three-dimensional numerical simulation of the impact process on the surface of micro column and micro groove was carried out,and the flow characteristics and heat transfer characteristics of the droplet impact on the smooth surface were analyzed.In this paper,a three-dimensional physical model of droplet impact on smooth surface,micro cylinder surface and micro groove surface is established.VOF model is used to capture the two-phase interface in the process of droplet impact.The standard k-ε model is used to simulate the impact process of droplet on different surfaces based on PISO algorithm.The simulation results are compared with the experimental results to verify the accuracy of the model and numerical algorithm.On this basis,the effects of we number,wall contact angle and height factor on the flow and heat transfer characteristics of droplets impacting on smooth surface,micro cylinder surface and micro groove surface were investigated.According to the impact process of droplet on the surface of micro column,the prediction formulas of the maximum spreading factor and the maximum heat transfer coefficient were fitted by using orthogonal experimental design.Compared with smooth surface,we number and wall contact angle have more influence on droplet spreading process when droplets impinge on the surface of micro column.The droplet spreading diameter increases with the increase of we number and height factor,and decreases with the increase of contact angle.For the wall heat transfer characteristics,compared with smooth surface,the height factor has a great influence on the wall heat transfer coefficient,and the wall heat transfer coefficient is larger near the three-phase contact line.The contact angle has the greatest influence on the wall heat transfer coefficient near the three-phase contact point,and the wall heat transfer coefficient near the three-phase contact point decreases with the increase of the contact angle.When the droplet impinges on the surface of the microchannel,the spreading of the droplet and the heat transfer on the surface of the microchannel are anisotropic due to the directivity of the groove structure.For the droplet flow characteristics,compared with smooth surface,the spreading factor perpendicular to the groove direction is the least,and the spreading factor parallel to the groove direction is greater than that of smooth surface;in the directions parallel to and perpendicular to the groove,the spreading diameter increases with the increase of we number;decreases with the increase of contact angle,and the wall hydrophobicity is stronger With the increase of micro height factor,the spreading factor of droplets in the direction perpendicular to the groove decreases,while that in the direction parallel to the groove increases;for the wall heat transfer characteristics,the height factor has a greater influence on the wall heat transfer coefficient than the smooth surface.The change of the wall heat transfer coefficient is mainly reflected in the direction parallel to the groove;the wall heat transfer coefficient near the three-phase contact point in the direction parallel to the groove decreases with the increase of the height factor and the contact angle.According to the process of droplet impacting the surface of micro column,the least square method is used to fit the prediction formula of the maximum spreading diameter of droplet and the maximum heat transfer coefficient of the wall.Among them,the maximum error of the prediction formula for the maximum spreading diameter of droplet is 16.67%,the average error is 12.6%,and the coefficient of determination is 0.97;the maximum error of the prediction formula for the maximum heat transfer coefficient of wall is 0.61%,the average error is 0.45%,and the coefficient of determination is 1.