An efficient algorithm for pre-processing of lattice Boltzmann methodbased on STL files

Lattice Boltzmann method (LBM) is a method for computational fluid dynamic simulations. An important pre-processing procedure of LBM is to obtain the information of the types of the lattice so that the solid and fluid areas can be identified. One approach for this is to judge the lattice type based on the solid object model described in the STL file format, followed by a mapping from the STL geometry to the LBM computational model. In order to reconstruct the computational model more efficiently, the present study proposed a fast algorithm for the generation of the computational model. The algorithm finds the point set of the model boundary based on the surface triangles, and then determines the internal and external points of the model according to the boundary points. As the searching starts from the surface triangle, the algorithm significantly reduces the computation cost, saves the computational time and improves the efficiency. The model reconstruction efficiency is compared between the new algorithm and the direct method for a sphere, the NACA0012 airfoil and the CHN-T1 aircraft with different complexity, and the results show that the computational time of the direct method increases rapidly with the increase of geometric complexity, whereas the new algorithm always keeps low computational cost. For example, the direct method takes 11 hours on 120 cores to generate the pre-processing grid for the CHN-T1 model, while the new algorithm takes only 20 seconds on a single core. The new algorithm greatly improves the pre-processing efficiency of LBM for complex geometries. Numerical simulations are performed using the generated grid, and the simulation results further demonstrate the applicability of the new algorithm.