Coupling Computation Of The Flow Field And Large Deformation Membrane Structure Stratosphere Airships

The stratospheric airship, as a typical nearspace aircraft, has bright prospect in its application to civil aviation and national defense. Thus, it has in recent years drawn extensive attention in many countries. For the stratosphere airship envelop, membrane structure is adopted. The membrane with the characteristic of low rigid as a whole is taken as a flexible structure. The interaction between the nonlinear large deformation of membrane and the flow field around is a rather complicated fluid-structure coupling problem. To understand accurately the mechanical properties of the membrane and to optimize its utility in engineering, the key is to find out the mutual influence of the structure and the flow around. In this paper, the mathematical model of the coupling of the three-dimensional fluid flow and the large deformation of membrane structure is established. The fluid-structure coupling interaction is simulated using the computational codes developed by the author. By analyzing the interactions of membrane and flow field, the aeroelasticity of the airship is detailed. Later on, all the results are adopted in the focused study of the stratosphere airship in the trimmed state.The main contents are as follows:Firstly, in the study, the mathematical models and the numerical solvers of the coupling computation of three-dimensional fluid flow and the large deformation of membrane are established respectively. For the three-dimensional flow solver, the control equation is based on continuity equation and Reynolds-Averged Navier-Stokes equations, while the standard K ?εtwo model and LL-Low Reynolds modified model are introduced for simulating the turbulence. The pressure correction method SIMPLE, which is based on the finite volume method, is proposed for the numerical simulation of the fluid flow. The approach of SIP is adopted as the interactive solver of the equations. For the analysis of the flexible deformation of large deflection of membrane, the mathematical model lies on the nonlinear geometric relationship, the constitutive relationship, and the equilibrium equations of membrane structure. For the numerical simulation of membrane deformation, the nonlinear finite element method is employed. To ensure the computation accuracy of large deformation, the updated Lagrange Formulation is adopted and the nonlinear equations solver is based on the Newton-Raphson method.Secondly, by establishing the close coupled computation solution for the analysis of membrane in three-dimensional flow, the problems of grids deformation and interface information exchanges in the fluid-structure coupling computation have been solved. The structural flow grids in fairly complex bodies are generated with the method of blocks structure grids, and the method of the transfinite interpolation is utilized for the automatic generation of the fluid grids. Thus, the grid deformation at flow boundary in the coupling interaction computation is smoothly dealt with. Meanwhile, the thin plate spline (TPS) method is adopted for the exchange of information between the fluid and structure models.Thirdly, the computational codes of coupled computation are programmed. The program modules of fluid analysis, structure analysis, grid generation, and interface information exchange technique are integrated. The validity and the accuracy of the computation program are evaluated by current theories and experiments. It provides a useful tool for structures analysis and engineering design.Fourthly, with the fluid-structure coupling approach, the aeroelasticity of the stratosphere airship in the trimmed condition is specialized in this paper. Different computation models and flow conditions are compared to discuss the aeroelasticity of the bare hull and the hull-fin configuration, respectively. The changes of aeroelastic parameters, differences of pressure distribution, and deflection distribution of all the models are analyzed so as to fully understand the aeroelasticity of the flexible airship. The influences of the areoelasticity of airship on aeroelastic parameters, pressure distribution, and structure deformation are specially detailed under the conditions of different inflow angles, inflow velocities, lengths of airships, material rigidity, and differential pressurization in the trimmed state. All the results are helpful for establishing the numerical computation and analysis tool for the design of the stratosphere airship in terms of aerodynamics, dynamics, structure, and control system.