Method Research And Application Development On Delaunay Three-dimensional Unstructured Grid Of Ground Heat Exchangers

China is vast in territory with a large number of storage of shallow geothermal resources, ground-source heat pump(GSHP) technology is a new technology for heating and cooling by using shallow geothermal energy, is widely used in engineering practice in recent years. The key point of the research on the technology is to improve the heat transfer model of geothermal heat exchanger(GHE), the heat transfer model is set up mainly with analytical method and numerical method, the range of application of the analytic method is limited, the numerical method is more applicable, we can make use of commercial software or independent programming by numerical method. The heat transfer process of GHE is actually complicated, unsteady coupled heat conduction and groundwater heat advection in the soil, especially for the simulation of the groundwater seepage process is beyond the range of function of the existing commercial software. Therefore, in order to study the problem more specifically, independent programming is inevitable.In computational fluid dynamics programming, meshing quality determines the reliability of the results of numerical calculation. For geometric model of U-type GHE in GSHP, considering the limitation of the structured grid technology for complex geometric model, unstructured grid technology should be adopted. Based on this, this paper studies and realizes the three-dimensional(3D) entity Delaunay unstructured grid generation technology, the purpose of this paper is to provide help for the numerical calculation programming of U-type GHE in GSHP under coupled heat conduction and advection.A set of effective 3D mesh generation algorithm is designed with Fortran language in this paper, the concrete implementation steps and the program design process of the algorithm are described in detail. Then, this paper shows the results of mesh generation which proved the reliability of the algorithm through several typical examples. For the geometric model of GSHP, the author improves the algorithm to adapt to the particularity based on the characteristics of the mode. The improved algorithm uses the relative error to avoid the error problem appeared in the process of calculation, solves the coplanar on insertion point with the cavity boundary, and implements the multi-layer grid which connected with each other but independent, this algorithm has good adaptability and stability.Finally, according to the simplified model of vertical U-type pipe on GSHP, the geometric model of single pipe, double pipe, U-type pipe is built in 3D field in this paper. Unstructured grid division is impled for U-type pipe, backfill soil, soil and other parts based on the improved Delaunay tetrahedral grid generation algorithm, eventually the tetrahedron grid with good quality is obtained, which lays a good foundation for the later numerical calculation and provides theoretical and technical support for practical engineering practice.