Research On Density Control Technology Of Surface Mesh Generation Based On Global Size Field

The aerodynamic design of aircraft shape is based on computational fluid dynamics(CFD).Meshing is the key step of CFD technology,which determines the success or failure of subsequent numerical calculation.Grid density distribution is an important index to determine the quality of grid generation.However,The traditional grid density control method depends on a large number of human interaction,which is tedious and error-prone,and it is also one of the bottlenecks of automatic grid generation.Therefore,the research on automatic grid density distribution control method is very important.Boundary discretization is the key to grid density control.at present,the commonly used unstructured grid generation methods take the initial distribution of boundary discretization as input,and then generate the grid step by step.Therefore,boundary discretization is a key step to successfully determine the size and distribution of the grid within the model.In this paper,a series of studies on the density control technology of unstructured grid have been carried out.The main research work is as follows:(1)The method of unstructured grid generation is studied.At present,the commonly used methods are advancing front method and Delaunay triangulation method,both of which have their advantages and disadvantages.On the other hand,the advancing front-Delaunay coupling method can combine the advantages of the two methods to generate a better quality grid.(2)The grid density control technology is studied.At present,the main control methods of grid density are size-based control method,calculation adaptive method and geometric adaptive method.Aiming at geometric adaptation,a set of surface mesh generation density control framework based on global size field is developed,which mainly includes parameter calculation of size field,uniform boundary discretization,adaptive boundary discretization based on multi-boundary,boundary coordination algorithm and so on.Among them,the adaptive boundary discretization method based on multi-boundary is an improvement of the traditional boundary discretization method based on single boundary.Through the improvement,this method has better adaptability to complex models.Through examples,it is proved that the framework can effectively control the density of grid distribution,and there is a certain engineering application.(3)In order to further improve the flexibility of grid density control,a density control method based on distributed density function is proposed.Its core is to realize the flexible control of grid density through the establishment of continuous distribution density function curve and the flexible control of the curve.(4)Using the geometric kernel of the unstructured version of NNW-Gridstar software,the unstructured surface grid generation module is developed by C++ language.In order to verify the feasibility and engineering application of the method proposed in this paper,through several aircraft models,after grid generation and density control,through a series of unstructured grid quality indicators,the grid quality is analyzed.