| A new version of numerical method of fluid dynamics named immersed boundary method (IBM) is presented, which is based on the Cartesian grid system for solving the interaction between flexible or rigid structure with large deformation and viscous fluid. When dealing with the complex geometric boundary, unsteady moving boundary and fluid-solid interaction problems, compared with traditional numerical method of fluid dynamics, these are many advantages in immersed boundary method. For example, when the rigid body has large movement, it would be a potential challenge for the ordinary FSI method based on the dynamic gird technique. The problems of the grid’s genneration, skewness and the updating often arise. But the immersed boundary method use Cartesian grid doesn’t need to update the grids, and this shows huge advantages in the calculation including large movement. What’s more, immersed boundary method also has the advantages of simple algorithm, easy programming, and grid togeneration, convenience in parallel computation, and handling with boundary highly computational efficiency and so on. In the treatment of flexible and rigid structure, work is underway to develop the IBM based on the energy function or finite element discretization. the researchers proposed direct-forcing IBM, the virtual boundary method, and so on. In addition, it is also the development of IBM can simulate the high Reynolds number, and the IBM combining with large eddy simulation method or Lattice Boltzmann Method. This greatly expanded the scope of application of the IBM.Due to the shape of turbine flow channel and the complexity of water movement. Guide vane is an important component, which regulates the speed of flow into the rotor circulation. The hydraulic performance of the guide vane has a direct influence on the flow pattern inside the runner and thus affects the efficiency and stability of the turbine. According to type of HLA551-LJ-43francis turbine in laboratory, model of double cascades are established. By using finite element IBM combined with feedback force method simulated double cascades, which is an important component in hydraulic turbine. And finally meaningful results are gained. This will be of certain reference value for a better understanding of guide apparatus dynamic mechanics. There are seven chapters altogether, and the main content are list below:(1) Example of stationary cylinders in flow and rotating circular cylinder in flow are given to verify the feasibility of the feedback-forcing IBM to solve rigid flow and moving boundary problem.(2) The flow around tandem cascade of Francis turbine based on the feedback force IBM is studied here. Through numerical calculation, flow field distribution and the non-uniformity indexes about pressure and velocity are obtained.(3) Through the rotating cylinder the reliability of feedback force IBM is verified. The swirl of guide vane of hydro-turbine in water, the dynamical flow characteristics is gained, and the evolution of vortex is also shown.(4) Preliminary discussion about drag reduction of turbine guide vanes are brought up. In the case of18degree, using hybrid finite finite element IBM combined with traditional feedback force method, numerical simulation about guide vanes with three method are given: blow flow method; manufacturing vortex method; flexible surface method. Comparative analysis in vortex shedding, lift and drag force are proposed to see the difference about drag reduction forms. |
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