The Research On Viscous Flow Calculation Using Unstructured Grids

With the property of efficiency, rapid speed and low cost, computational fluid dynamics methods are paid more attention on and are used more on the aircraft design. How to simulate viscous, rotate and nonlinear true flow field around complex aircraft is the development direction of CFD. The main research of this paper is how to simulate complicated flow by using Navier- Stokes equation. The difficulties of numerical computation are as follows: 1. Mesh generation. 2. Numerical method of N-S equation. 3. Turbulence models. Focusing on these questions, relatively systematic research is given in this paper. The main achievements of work are: 1. A new method for adaptive refinement of unstructured grids is presented. This new adaptive method is different from traditional adaptive methods such as adding point, modiI~ying background grid. Some small triangle units are arranged on the place where mesh needs to be refined, and all the sides of these units are regarded as a part of the initial front. During the advancing process, near the above-mentioned units, the cells are naturally generated from small to large. Numerical examples show the success of the new method. 2. Based on the spring principle of physics, a new method of generating semi- unstructured grids is proposed. At first, inviscid unstructured grids are generated by the advancing front. Then moving the position of cell nodes by the spring principle, a distance of boundary layer thickness is squeezed out near the surface of wall. At last, high aspect ratio structured grids of good quality are created in the boundary layer field. The advantage of this new method is that it can ensure a smooth transition from a viscous highly stretched mesh to an inviscid regular mesh. 3. We extend Jameson cell-center finite volume method to N-S equation ,3D viscous flow numerical simulation is successfully carried out on unstructured grids. 4. The source terms in turbulence equations need to be discretized correctly in order to obtain a stable numerical scheme. In this paper, the recommendation of how to treat the source term is gained by the detailed theoretical analysis done on a kind of source terms. 5. An explicit finite difference scheme is constructed to simulate Baldwin-Barth one-equation turbulence model. By using Von Neumann analysis method, its stability condition is obtained. The result of turbulent simulation is satisfactory.