Mesh construction algorithm based on TetGen for modeling the external flow around an axisymmetric model

An original algorithm for constructing a computational grid for modeling the external gas-dynamic flow around an axisymmetric model using a TetGen grid generator is described. The algorithm gives opportunity to build unstructured tetrahedral meshes in the space around the model in such a way that the cells near the surface have a shape close to the regular tetrahedrons. On such meshes, the approximation of macroscopic equations is carried out more precisely than on meshes containing tetrahedral cells with small angles. The increased accuracy of the approximation in the boundary layer region can be an important factor in studying the phenomena of flow separation and laminar-turbulent transition. To build such a spatial grid, at the initial stage, a grid is built on the surface of the model. The cells of the surface grid have a shape close to squares. At the second stage, the TetGen generator builds a spatial tetrahedral grid based on the surface grid, using Delaunay triangulation, while introducing additional points near the model surface. These points give opportunity to obtain tetrahedral cells of a fairly regular shape in the boundary layer region. The proposed algorithm is quite versatile and can be used for models of any axisymmetric shape, the profile of which is set as an array of radius values depending on the cross-section. The spatial grid gives opportunity to simulate the external flow for non-zero angles of attack. The paper presents an example of calculating the subsonic flow around the model based on a quasi-gas-dynamic algorithm, which demonstrates the occurrence of a vortex region in the tail section. This region shows the possibility of studying non-stationary flows.