Research On Numerical Simulation And Calculation Method Of Fluid-structure Interaction For Thin-walled Structures

Nonlinear dynamic fluid-structure interaction (FSI) is one of the most challenging research issues in academic and engineering fields. A study of the mutual influences between the structure vibration and the flow field by using the state-of-the-art numerical methods is of great significance to avoid the flow-induced resonance of a structure in fluid, and it is quite important to improve the reliability and safety of the structure designs. In this dissertation, a monolithicly coupled model based on the pressure Possion equation (PPE) and a closely coupled model based on the large eddy simulation (LES) solver are presented and verified by several numerical examples. The dissertation is generally outlined into 6 chapters. The main contributions are stated as following.Firstly, a fluid flow and a structure dynamics solvers are constructed, respectively. For the fluid numerical model in the FSI system, a dynamically mixed one-equation subgrid-scale (SGS) model is modeled on the scale-similarity model and Smagorinsky eddy-viscosity model. In the proposed SGS model, the square root of the SGS kinetic energy,(?), is used to obtain the velocity scale for the eddy-viscosity to be applied in the model. The modeled ksgs equation is derived and some of the additional scale-similarity parts are incorporated to compare the ksgs equation with the previous studies. It shows that the suggested model has the capability of capturing the details of the flow structures and the dissipation of the turbulent kinetic energy. Finite volume method (FVM) is used to be discrete of the LES governing equations. The SIMPIEC algorithm is applied to solve of the coupled equation of the velocity and pressure. Tri Diagonal Matrix Algorithm (TDMA) is adopted to solve the algebraic discrete equations. For the structure numerical model in the FSI system, a nonlinear relation between strain and displacement and a linear elastic model are used respectively, and a three dimensional nonlinear finite element model for the structure dynamics is thus constructed. A Newmark-?implicit time integration algorithm is used, and the Newton-Raphson iterative scheme is adopted to solve the algebraic equations.Secondly, a closely coupled approach is constructed based on the LES flow solver. A moving mesh algorithm based on smooth spring analogy is used and a geometrically conservative implicit numerical scheme for the flow computations on the moving mesh is established. A load and motion transfer algorithm with non-matching discrete interface based on the momentum and energy conservation is introduced. It paves a coupling way to use the different solvers for the fluid, the structure and the mesh motion models for the complex nonlinear FSI problems. As an example, the hydro-elasticity vibration of the guide vane of a Francis hydro turbine is simulated. Three different materials for this guide vane are adopted respectively in this working example. The different dynamic behaviors of the fluid and the structure are discussed in detail. The numerical results show the validity of the proposed approach.Thirdly, a monolithic approach based on the fluid pressure Poisson equation (PPE) and predictor-multi-corrector algorithm (PMA) is created to solve the interactions between incompressible viscous fluid and an elastic body. The PPE is derived so as to be consistent with the coupled equations for the FSI system. Based on this approach, the fluid pressure is implicitly derived to satisfy the incompressibility constraint, and the other unknown variables are explicitly derived. In the consistent fluid equation, the momentum and the continuity equations are included in the same fluid domain. A consistent fluid equation is established by the substructure procedure for the structural equation to reduce degrees of freedoms (DOFs) in the structural domain. To demonstrate the performance of the proposed approach, a working example, a beam immersed in the incompressible fluid, is simulated. The results show that the approach developed is a powerful tool in solving the FSI problems of the flexible structures.Finally, we have performed an experiment on the vibration of an elastic thin plane due to being induced by the vortex shedding of the flow through a square body. The fixed square rigid body is submerged in the incompressible fluid and a thin elastic plane is attached to the rigid body in the centre of the downstream face. The pressure sensor that is manufactured by Kulite company, LL-072-25A, was mounted on the surfaces of the elastic plane, and a acceleration sensor provided by DongHua company, DH-201 is embedded in the free end of the elastic plane. The vortices, which separate from the corners of the rigid body, generate a lift force which excites oscillation of the thin elastic plane. Two independent measuring systems, are used in experiment. One is the dynamical test system to pick up the signals from the sensors, and other is of a 3D particle image velocimetry (PIV) to measure the flow fields. The measurements obtain findings on the vibration induced by the vortex shedding and the evolution of the vortex near the vibrating wall surfaces.