Typical Interface Mechanical Behavior And Flow Control Of Superhydrophobic Surface

As a typical interface interaction,droplet impact can not only promote combustion and reduce emissions in the combustion chamber,but also corrode and damage the exterior wall surface of the building.Therefore,it is of great significance to effectively control the droplet impact process.Superhydrophobicity is often used to evaluate the solid-liquid interaction,and is considered to be the main technical means to achieve interfacial flow control.In addition,the change of the interfacial flow morphology will also adversely affect the anti-icing properties of the superhydrophobic surface(SHS).Therefore,the physical mechanic of the interface including the both is forme.However,existing researches generally focus on simple bounce characteristics analysis combined with time scale and morphological parameters,and lack in-depth research on mechanical characteristics and energy loss in related processes.For this reason,based on the CFD(Computational Fluid Dynamics)method,this article expounds the interaction mechanism between the both on the macro scale.On the one hand,the anti-icing performance of SHS is evaluated based on quantitative indicators,and the anti-icing mechanism is analyzed from the perspective of interface flow morphology to construct the mapping relationship between the both.On the other hand,the microstructure morphology,wettability distribution law,and external acceleration field are selected for research,and the typical behaviors of interface mechanics are summarized from the perspective of mechanism analysis,so as to achieve effective control of the interface flow morphology.The specific research work and conclusions are as follows:(1)Analysis of the mechanism of the interfacial flow morphology on the antiicing performanceCouple the CLSVOF model and the solidification-melting model to simulate the static icing process and the dynamic impact process.The results show that the static icing time is extended to 220.28%,while the dynamic heat release is reduced to37.687%,which indicate that the SHS has anti-icing properties.Subsequently,the static anti-icing mechanism was analyzed by the vertical height and the solid-liquid contact diameter,and the dynamic anti-icing mechanism was analyzed by spreading diameter,hollow area and contact time.(2)Typical interface mechanical behavior and flow control on the microstructuresThe microstructure morphology(Sample A: convex hull;Sample B: stripes)and impact velocity are selected as independent variables,and the droplet impact process is simulated based on the CLSVOF model.There are four types of rebound due to different impact velocity and various typical mechanical behaviors such as eagle flapping droplet impact dynamics.Finally,the characteristic parameters such as the maximum spreading diameter,the maximum retraction speed and the contact time are selected to discuss the coupling mechanism between the microstructure and the impact velocity.The results show that the lower impact velocity will weaken the influence of the microstructure on the droplet morphology evolution.(3)Typical interface mechanical behavior and flow control on the mixed wetting surfaceBased on the directional migration characteristics of the droplet on the head of the kingfisher,a mixed wettability surface is designed to realize the change of the direction of the droplet movement.The four-stage movement process of spreading,rotation,parabolic movement and horizontal movement are recorded,as well as two rotational movement modes of fixed axis rotation movement and moving axis rotation movement.Taking the centrifugal force and the area of the liquid bridge as the starting point,three methods for regulating the formation of the throwing droplet are proposed,including the contact angle of the non-superhydrophobic side,the wettability arrangement mode,and the impact velocity.In addition,the calculation formula of the horizontal driving force is derived from the gradient wettability and the incompletely symmetrical contraction force,and the accuracy is analyzed based on the momentum theorem,whose error is 6.488%.(4)Typical interface mechanical behavior and flow control on the vibrating surfaceInspired by the rapid desorption characteristics of butterfly wings without support,a rigid surface with sinusoidal motion is taken as an example to explore the impact of droplets under the action of an external acceleration field.Select a variety of morphological parameters and energy loss values to analyze the influence of vibration parameters and impact parameters on morphological evolution and energy loss.The results show that the initial phase angle is the main factor,and its mechanism is affected by the vibration frequency and has nothing to do with the vibration amplitude.The mechanism of impact parameters is basically monotonic.The mechanism of the direction of surface movement and the formation mechanism of the central jet phenomenon are summarized.The results show that the opposite movement of the droplet and the surface will promote the spreading and contraction of the droplet,and the intensity of the central jet phenomenon depends on the movement speed of the surface.