Research On Drag Reduction Performance Of Flexible Skin Of Micro Floating Raft Array Based On Penalty Immersion Boundary Method

The ocean supports many major security and development interests,and underwater vehicles are important equipment for safeguarding China’s maritime rights and interests.The endurance and sailing speed are important performance indexes of underwater vehicles,so it is of great strategic significance to reduce the sailing resistance and improve the sailing speed.Among the numerous drag reduction technologies,flexible surface drag reduction is a promising method.In this paper,based on flexible surface drag reduction technology and floating raft vibration reduction technology,a kind of flexible skin for fluid drag reduction is constructed,and the drag reduction performance of the flexible skin is simulated and analyzed based on the penalty immersion boundary method.This paper mainly carries out the following aspects of work:Firstly,according to the large deformation characteristics of the fluid-structure coupling interface of the flexible skin,the penalty immersion boundary method was used as the fluid-structure coupling algorithm of the flexible skin,and the penalty parameters were designed in combination with the numerical stability.The governing equations of fluid-structure interaction of the flexible skin are discretized in time and space,and the Dirac function in the interaction equation is approximated by regularization.Based on the governing equation of discretization,the numerical calculation process of fluid-structure coupling of flexible skin was designed.Secondly,the simulation model of the flexible skin of micro-raft array is established by using the modeling unit in the open source library IBAMR,and the flow of fluid-structure coupling numerical calculation and analysis of the flexible skin is formulated,and a custom solver is created.Combined with the simulation model,the resistance calculation program and the post-processing program were programmed,and the visual analysis tool Visit was configured.The validity of the numerical calculation of fluid-structure coupling based on the penalty immersion boundary method was verified by a case study.Then,according to the simulation model of the flexible skin,the computational domain size,initial conditions,boundary conditions and mesh refinement parameters were set,and the appropriate mesh size and time step were set through independent verification and independent verification.The fluid-structure coupling numerical calculation and data post-processing were carried out for the flexible skin structure.By comparing with the resistance data of the rigid plate,the drag reduction effect of the flexible skin was verified and its drag reduction mechanism was analyzed.Finally,the influence of the flow rate and the structural parameters of the flexible skin on the drag reduction effect is analyzed.The results show that,within the range of numerical simulation,reducing the spacing of micro-floating raft elements and the elastic modulus of the outer wall,and increasing the supporting stiffness ratio and damping coefficient are beneficial to improve the drag reduction performance of the flexible skin.When the flow velocity is1-15 m /s,the drag reduction effect of the flexible skin is improved.When the flow velocity is1-8m /s,the relative drag reduction rate increases with the increase of the flow velocity.When the flow rate is about 8m/s,the relative drag reduction rate reaches the maximum.When the flow rate is between 8 m/s and 15m/s,the relative drag reduction rate decreases with the increase of the flow rate.