Study On Synchronous Fluctuation Of Disturbance Waves Between Porous Flexible Skin And Fluid Boundary Layer Of Micro Floating Raft Array

With the increasing demand of underwater vehicles for drag reduction,flexible surface fluid drag reduction technology has attracted extensive attention,but the commonly used flexible skin has a series of defects,which greatly restricts the development of this technology.In this paper,taking dolphin flexible skin as the prototype and combined with the floating raft structure commonly used in the field of vibration isolation,a micro floating raft array porous flexible skin is designed.The skin is composed of porous flexible wall and micro floating raft damping unit.The synchronous fluctuation drag reduction mechanism between the porous flexible skin and the disturbance wave of fluid boundary layer is studied,The drag reduction performance of porous flexible skin is analyzed by the shear stress under synchronous fluctuation.This article mainly carried out the following work:(1)The synchronous wave characteristic equation of the porous flexible skin and the disturbance wave of the fluid boundary layer is established.First,the physical model of the porous flexible skin of the micro-floating raft array is constructed;then,the wave control equation of the porous flexible skin is established based on the viscoelastic theory and the fluid wave theory,and the boundary between the porous flexible skin and the inner and outer fluids is established at the same time Mechanics and displacement boundary conditions are combined to form a synchronous wave characteristic equation.(2)The simultaneous fluctuation conditions of the porous flexible skin and the disturbance wave of the fluid boundary layer are determined.First,the frequency and wave speed at different wave numbers are obtained by solving the stability characteristic equation;Then,the different wave numbers and their corresponding frequencies and wave speeds are substituted into the synchronous wave characteristic equation to determine whether the wave constant has a solution.The results show that:only when the distorted wave speed c1,the irrotational wave speed c2 and the perturbed wave speed c3 satisfy c1<c3<c2,the wave constant is solvable,which means that only when c1<c3<c2,the porous flexible skin is attached to the fluid Layer disturbance waves can produce synchronous fluctuations.(3)The influence of the structural parameters of the porous flexible skin on the synchronous fluctuation is analyzed.First,by solving the stability characteristic equation,the characteristic roots of the wave velocity under different structural parameters and Reynolds numbers are obtained,and then the Reynolds number range for realizing the synchronous wave is obtained from the synchronous wave condition;Then,the orthogonal test method is used to obtain the wave speed characteristic root for realizing the synchronous wave optimal parameters,and the significant influence of structural parameters on synchronous fluctuations is studied.The results show that appropriately increasing the spacing l,stiffness ratio γ,damping ratio ε,mass ratio β and permeability coefficient a expands the range of Reynolds number that produces synchronous fluctuations,and the optimal structural parameters are:l=0.8,γ=16,ε=10,β=4,a=0.004,the order of the magnitude of the significant influence on the synchronization fluctuation is:.l>γ>ε>β>a.(4)The influence of porous flexible skin structure parameters on drag reduction performance is studied.The effect of different structural parameters on the drag reduction performance of the skin was studied by analyzing the surface shear stress of the skin.The results show that:appropriately increasing the parameters such as l,γ and ε reduces the shear stress.The changing trend of shear stress with structural parameters is consistent with the changing trend of synchronous fluctuations with structural parameters.This shows that adjusting structural parameters may be achieved by expanding the Reynolds number range that produces synchronous fluctuations to obtain better drag reduction effects,and in the optimal structure Under the parameters,the shear stress of the porous flexible skin is reduced by about 7.9%compared with that of the single-layer flexible skin.