Research On Drag Reduction Performance Of Flexible Skin Based On Immersed Boundary Method

Laying the flexible skin on the surface of the underwater vehicle can significantly reduce its fluid resistance,which is the main measure to improve the speed of navigation and increase the endurance time.In this paper,based on the flexible surface drag reduction technology and vibration control theory,a flexible skin structure for fluid drag reduction is constructed and its detailed design is completed.At the same time,the fluid structure coupling control equation,numerical discretization and numerical calculation based on the immersed boundary method are completed,and the drag reduction performance of the flexible skin is simulated and analyzed.This paper mainly carries out the following work:Firstly,the structural design of flexible skin is completed.In order to reduce the fluid resistance,a double-layer flexible skin structure is constructed based on the flexible surface drag reduction technology and vibration control theory,which is composed of the outer flexible wall and the inner elastic support.The outer flexible wall plays the role of drag reduction while fixing the inner elastic support,and the parameter design is completed based on the flexible surface drag reduction technology;the inner elastic support is a distributed double-layer vibration isolation system,which is used to suppress the turbulence fluctuation,and the parameter design is completed based on the vibration control theory and stability theory.Secondly,the governing equations and numerical discretization based on the immersed boundary method are completed.Due to the complexity of flexible skin structure and its large deformation,the immersion boundary method is introduced.Based on the N-S equation,the coupled equations of fluid and flexible skin immersed boundary are obtained.The Cartesian grid and curvilinear grid are used for spatial discretization of convective and solid domains respectively,and the second-order Runge Kutta method is used for temporal discretization.Based on the fluid structure coupled control equation and the numerical discrete method,the numerical algorithm flow of the flexible skin based on the immersed boundary method is completed.Then,the numerical calculation of fluid structure coupling based on the immersed boundary method is completed.Based on the control equation and numerical discretization of the immersed boundary method,the numerical calculation of fluid structure coupling based on the immersed boundary method is completed by MATLAB,including the process of modeling,boundary constraint,simulation parameter setting and simulation calculation.The post-processing process is completed by paraview and MATLAB,and the effectiveness of the numerical calculation of fluid structure coupling is verified by the flow around the cylinder.Finally,the drag reduction performance of the flexible skin is verified and the influence of various parameters on the drag reduction performance is analyzed.The simulation of flexible skin is carried out by numerical calculation of fluid structure coupling based on immersed boundary method.Through the calculation of resistance coefficient and relative drag reduction rate,it is verified that the flexible skin has good drag reduction effect compared with the rigid plate,and the influence of the design parameters of the flexible skin on its drag reduction performance is analyzed.The results show that in the range of numerical calculation,the drag reduction effect of the flexible skin is enhanced with the increase of the thickness of the flexible wall,the decrease of the elastic modulus,the decrease of the spring stiffness,the increase of the damping coefficient,the increase of the intermediate mass and the increase of the distribution distance of the elastic support.