An efficient and fast calculation method of wall distance for hybrid-unstructured grids

The wall distance is a parameter which must be specified in solving the Reynolds-Averaged Navier-Stokes equations with turbulence model. In this work, a layer-by-layer fast marching algorithm has been proposed to calculate the minimum distance from a flow field grid cell to the wall, for both structured and hybrid-unstructured meshes. The main principle of the algorithm is to consider the scattered unstructured grids as the form of layer by layer arrangement. Starting from a solid surface and using the stored relationship between adjacent grids, the algorithm searches the spatial grid cell which is the nearest to the surface unit using layer-by-layer diffusion. Each calculation step is effectively limited to the precise wall unit and neighboring wall units, allowing the computational efficiency to be maximally enhanced. Three different aerodynamic configurations are selected to demonstrate the implementation of proposed algorithm. The effectiveness of the method is verified by comparing the computational time and the accuracy of results between the proposed algorithm and the enumeration method. The results show that there is no significant difference between the solution accuracy of the two algorithms. For small and medium-sized meshes, the proposed algorithm can enhance the computational efficiency up to two orders of magnitude. For complex configurations with large mesh size, the calculation efficiency is even higher.