Research On The Anti-wetting Of Aquatic UAV Surface Based On The Wetting Control Behavior Of Kingfisher Interface

Aquatic Unmanned Aerial Vehicle?Aquatic UAV?,which has significant military application prospects,is a new concept amphibious vehicle that can freely pass through the water-gas interface.Generally,the Aquatic UAV needs to complete four key challenges:dry flight,water entry,submerged movement,and water exit,and each mission pose is interrelated.Among these challenges,a series of problems such as flight instability and difficulty in water exit are attributed to rain loads and adhesive water on the surface.It is of academic and engineering application value,that is,performing research on the mechanism of dynamic interface wetting control and the surface anti-wetting technology of the aircraft.Creatures have evolved in nature for hundreds of millions of years that giving innumerable inspirations to human beings.In this dissertation,we have summarized the passive and active wetting control strategies of bionics,explained the dynamic wetting control laws of bionic interfaces,investigated the bionic anti-wetting performance of the surface of Aquatic UAV,and revealed its anti-wetting mechanism via theoretical explanation,experimental analysis,and lattice Boltzmann Method?LBM?numerical simulation method.The contents of the dissertation are as follows:?1?Characterization of kingfisher's surface wettability and qualitative analysis of passive dewetting at the elastic interface.Kingfisher's static wettability and the microstructure of typical feather were characterized by high-speed cameras,static contact angle measuring apparatus,and scanning electron microscopy,respectively.It is found that the differences are reflected in the kingfisher's hydrophobicity and feather microstructures.Kingfisher exhibits a hydrophobic state,and their feathers are anisotropic and hydrophobic.A droplet is impacting a kingfisher's wing feather,which has elasticity,indicating that the feather's elastic potential energy can accelerate the droplet rebound and has a passive dewetting characteristic.An experiment in which a droplet impinged on a kingfisher's wing feather indicates that the elastic potential energy of the feather can accelerate the rebound of the droplet and has a passive dewetting characteristic.The accelerated rebound behavior of the droplet is attributed to the elastic potential energy of the feather,and this dewetting process has a passive characteristic.Thus,the combined effects described above should be avoided during the design and maintenance of the surface of the Aquatic UAV.?2?Quantitative analysis of dynamic wetting behavior of droplet impact on a"viscous"superhydrophobic surface.Four"sticky"superhydrophobic surfaces,including paraffin-copper mesh,zinc foil-CuSO₄·H₂O-CH₃?CH₂?₁₆COOH,and fresh rose petals,were used as target substrates in the experiments.A functional relationship between the degree of adhesion on the"sticky"superhydrophobic surfaces and We was given by experimental comparison,LBM numerical simulation,and construction of intermediate variables.We also find that the degree of asymmetric de-pinning effect is a function of the initial impact velocity v₀ of the droplet.The transient effective non-equilibrium Young's force F_e can cause additional dissipation of the droplet's internal energy.Thus,the droplets tend to adhere to the"sticky"superhydrophobic surfaces at high We.?3?Quantitative analysis of passive dewetting behavior on a superhydrophobic surface with linear elasticity.A spring-superhydrophobic copper mesh device was configured to investigate parameters such as the moving contact line,contact time,the size of the secondary droplet and rebound height of a droplet on"elastic surface"and"rigid surface".The dewetting behavior on the"elastic surface"is quantitatively analyzed when the surface stiffness k=0.0062N/mm by tracing the displacement of the linear elastic superhydrophobic surface and the rebound height of the droplet.We found that the contact time,which is related to the linear elastic surface response time and We,can be increased or decreased,and the mass distribution within the droplet is affected on the linear elastic superhydrophobic surface.Simulations based on the LBM algorithm show that the deformation caused by the droplet on the"elastic surface"can induce the so-called"springboard effect",which can facilitate the separation of solid and liquid,reducing the contact time by 8.5%.?4?Study on active dewetting on an anisotropic superhydrophobic surface.Inspired by the kingfisher's shaking motion in the rain for dewetting,the dewetting behavior?e.g.,stationary,vibration?of the jet impacting on the kingfisher's head was performed comparative analysis.A copper-based anisotropic superhydrophobic surface was fabricated and the above-mentioned bionic dewetting process was quantitatively evaluated by controlling the output frequency of a loudspeaker.We summarized the transient law of the moving contact line and contact time on an anisotropic superhydrophobic surface?opposite phase,same phase,and equilibrium phase?.A simplified mathematical model describing the interaction of a droplet on an anisotropic surface was derived.Superhydrophobic surfaces?same phase?increase contact time?18%?,while opposite phases can significantly reduce contact time?19%?.The velocity field and morphology of the droplet impinging on the same phase and opposite phase surfaces are given.The dewetting behavior of the jet hitting the upper surface of the moving kingfisher has been studied,which is inspired by the kingfisher can fly at high speed and freely change the flight angle in the rain.Conveyor drive—high-speed camera system was designed to analyze the influence of the angle between the surface texture and the velocity vector on the dynamic morphology of the droplet.We found that the asymmetric de-pinning effect induces directional bounce of the droplets and affects the dwell time.The larger the included angle,the more significant the asymmetric pinning effect of the droplets,which can effectively avoid continuous wetting in the same area.?5?Research on anti-wetting performance of Aquatic UAV's surface.Aquatic UAV models with hydrophilic and superhydrophobic anisotropic textured surfaces were fabricated.We conducted experiments to verify the surface wetting control theory in an indoor precipitation system.Finally,the anti-wetting mechanism of the surface of the Aquatic UAV is given.No adherent water was found on the surface of the Aquatic UAV with a superhydrophobic surface,but the continuous and asymmetric high-thickness liquid film was observed on the surface of the Aquatic UAV with a hydrophilic surface.Rain load?equivalent to torque?on superhydrophobic surfaces is 1/8 of that on hydrophilic surfaces when the Aquatic UAV is stationary?passive anti-wetting?.Vibration behavior of the Aquatic UAV with superhydrophobic surface facilitates the solid-liquid separation,and the Aquatic UAV in opposite phases can reduce the contact time?55.5%reduction?.Besides,the vibration of the Aquatic UAV model is driven by a loudspeaker.A stepper motor was used to drive the Aquatic UAV mode through an indoor precipitation area to evaluate its anti-wetting performance in motion.The particle trajectory,liquid velocity field and pressure field inside the droplet,and the directional bounce behavior of the secondary droplet group which induced by the moving surface were analyzed by LBM numerical analysis.The synergistic effect between superhydrophobic surface and motion promotes droplet fragmentation,leading to the directional tumbling behavior of the secondary droplet groups,which can effectively avoid continuous wetting and maintain high kinetic energy in the liquid phase?average speed can be increased by 32%compared to hydrophilic surfaces?.The secondary droplet group can continue to tumble,and the lateral non-equilibrium effect,caused by the high-thickness,asymmetrically adhered water,significantly reduces the aerodynamic penalty.These secondary droplet groups can continue to tumble,and aerodynamic penalties were significantly weakened.