Design And Fabrication Of Discontinuous Slipping Drag Reduction Surface With Flow Field Adaptivity

Drag-reducing surfaces can substantially enhance the speed and survivability of highspeed ships and submarines,providing significant strategic value.These surfaces also yield considerable economic benefits,making them a popular research topic.Various methods have been proposed to construct drag-reducing surfaces,with superhydrophobic-induced sliding surfaces emerging as a simple and effective approach.In recent years,this technique has garnered widespread attention from researchers due to its promising potential and extensive application prospects.While superhydrophobic-induced sliding surfaces effectively reduce underwater resistance,they also present certain challenges.Firstly,the slip effect produced by superhydrophobic surfaces results from the air-liquid interface created by trapped air in surface structures.However,the air layer’s disruption can cause drag-reduction failure under high-speed conditions.Secondly,the sliding effect generated by superhydrophobic surfaces is omnidirectional.While stream-wise sliding contributes to drag reduction,span-wise sliding can compromise the flow’s stability.Inspired by anisotropic sliding surfaces,this paper introduces a novel method for designing drag-reducing surfaces using patterned discontinuous sliding surfaces.The sliding surface reduces interface friction resistance,while the interface difference suppresses transverse flow and enhances flow stability.To validate the performance of the discontinuous sliding surface,the impact on flow characteristics is investigated and analyzed through simulation and experimentation.Furthermore,discontinuous sliding surfaces with flow adaptability are designed and verified.By adjusting the pattern distribution of the discontinuous sliding surface,drag-reduction performance can be further improved,achieving extremely high drag reduction at low-speed domains or stable effects across the full-speed domain.These advancements significantly broaden the application prospects of sliding drag-reducing surfaces.The primary accomplishments include:(1)A novel processing method that combines laser ablation and laser-induced deposition to fabricate hierarchical superhydrophobic surface structures is proposed.The impact of these superhydrophobic structures on drag reduction is thoroughly investigated.Results indicate that the superhydrophobic surface,constructed with hierarchical structures,can generate a more robust slip effect and achieve a higher drag reduction.Additionally,the nanoscale sealed air pockets on the surface create a more resilient gas-liquid interface,which strengthens the stability of the drag reduction effect.(2)A new design for discontinuous sliding drag-reducing surfaces is proposed.The sliding surface reduces interface friction resistance,while the interface difference constructs virtual grooves that inhibit transverse flow and improve flow stability.This discontinuous sliding drag-reducing surface not only enhances the drag reduction effect but also achieves flow control.(3)A 3D simulation analysis model incorporating the slip boundary is established based on the lattice Boltzmann method(LBM).Using this model,the influence of discontinuous sliding surfaces with typical pattern distributions on the flow is clarified.The results demonstrate that the discontinuous sliding surface significantly affects the flow field.When the pattern of the discontinuous sliding surface aligns with the flow direction,it divides the flow field and prevents overall lateral flow,contributing to improved flow stability.In contrast,patterns perpendicular to the flow direction cause periodic disturbances and backflow,damaging the flow’s stability.(4)Discontinuous sliding surfaces with flow adaptability is designed,prepared,and experimentally investigated in this work.Discontinuous sliding surfaces with specific pattern distributions are fabricated by ultrafast laser selective texturing techniques and their drag reduction performance is evaluated through rheological resistance experiments.The results reveal that the discontinuous sliding surfaces exhibit significant flow adaptability,attributable to the relationship between surface pattern distribution and flow direction.By adjusting the surface pattern distribution according to the flow field characteristics at different speeds,an optimized design for drag-reducing surfaces is achieved,providing extremely high drag reduction at low-speed domains or significantly improved stability of drag reduction effects,resulting in full-speed domain drag reduction.These advancements considerably broaden the application prospects of sliding drag-reducing surfaces.