Research On Near-Wall Turbulence Characteristics And Drag Reduction Mechanism Of Micro-Floating Raft Array Skin

Since the 1950s,the status of underwater vehicles in national strategic security has become higher and higher,which has put forward higher requirements for their speed and concealment.Therefore,how to improve the resistance and noise reduction performance of underwater vehicles has become a research focus in the field of design and manufacturing.In order to reduce the frictional resistance of the underwater vehicle,this paper combines the floating raft vibration isolation technology and the bionic flexible wall drag reduction technology to construct a new type of micro-floating raft array skin for turbulent drag reduction,and establishes its on-wall The fluid-structure coupling theory model under turbulence excitation,and its drag reduction performance and drag reduction mechanism were studied,which provides a reference for the design and application of drag reduction skins.The main content of this article is:(1)A theoretical model of fluid-structure coupling for the skin of the micro-floating raft array was established.The fluid domain motion control equation was expressed in the form of an incompressible N-S equation.In order to increase the calculation speed and reduce the complexity of turbulence analysis,the pre-solution analysis method was used to reduce the order of the fluid motion control equation.The multi-body dynamics analysis method was used to establish the motion control equation of the structure domain(micro-floating raft array skin),and combined with the boundary conditions of the fluid-solid interface,the fluid-solid coupling model of the system was established.(2)The fluid-solid coupling equation was numerically solved.In order to improve the grid resolution in the near-wall area,spatial discretization was carried out based on the finite difference method and the Chebyshev collocation point method.The partition method was used to numerically solve the fluid-solid coupling equation.First,the arbitrary Lagrangian-Euler method was used to solve the fluid motion control equations.Secondly,the virtual mass and damping method were used to solve the motion control equation of the micro-floating raft array skin.Finally,the sub-iteration and Aitken relaxation method were combined to perform subiteration and coupling iterations on the fluid domain and the structure domain,and parameters such as the velocity and pressure of the flow field are obtained,and the accuracy of the solution method was verified by a calculation example.(3)The effects of structural parameters and flow field parameters on the drag reduction performance of the micro-floating raft array skin were analyzed.Using the relative drag reduction rate as the evaluation index,the change of the drag reduction performance of the micro-floating raft array skin with the flow velocity was studied.The results show that when the flow velocity is in the range of 1m/s-16m/s,the skin of the micro-floating raft array has the drag reduction performance,and the curve of the drag reduction rate with the skin structure parameters at different flow rates is drawn.The research results show that appropriately reducing the thickness of the flexible wall,the elastic modulus and the spacing of the microfloating raft support unit,or increasing the intermediate mass,stiffness ratio,damping coefficient and damping ratio of the micro-floating raft support unit are all beneficial to improve the skin drag reduction.performance,the maximum drag reduction rate can reach 14.33%.(4)The drag reduction mechanism of the micro-floating raft array skin was studied.Using the singular value decomposition method,the near-wall turbulence characteristic parameters(average velocity profile,pulsating velocity,Reynolds stress and turbulence energy spectrum)of the rigid wall,single-layer skin and micro-raft array skin were calculated respectively.The results show that the drag reduction mechanism of the micro-floating raft array skin is as follows:by reducing the strength of the coherent structures in the near-wall region and the interaction between them,the characteristics of the mean flow are changed to achieve drag reduction,so that the mean flow viscous wall region velocity profile is reduced.It increases the thickness of the viscous bottom layer and reduces the flow velocity gradient,thereby reducing the frictional resistance.