*2.3. Mesh*

The unstructured meshes are constructed in the computational domain. An example mesh of the pipeline is shown in Figure 3. The free triangular grid is constructed the inlet boundary (0.75 *D*). The sweep mesh is adopted because of the long narrow pipe structures and the grid processor along the pipeline to generate the structured quadrangle mesh (generate hexahedron). A boundary layer grid with 25 layers and 1.25 stretch factors is used to discretize the tube in order to ensure adequate analysis of fluid flow and particle erosion behavior near the tube wall.

Three kinds of meshes (as shown in Table 1) are constructed for the present model to test the dependence of the numerical simulation results on the mesh resolution at the same initial boundary conditions and improve the accuracy of the simulation. The variation of the max fluid velocity with the mesh resolution is examined. The results are shown in Table 1. It is found that the differences of the calculated maximum value of fluid velocity among the three meshes are very small. Thus, the first mesh method is used in this paper to reduce the calculation time.

In thin film flow, the shell interface is used to solve the Reynolds equation for flow in narrow structures and the mass and momentum balances are used to formulate with a function across the thickness of the thin structure, which indicates that the thickness does not have to be meshed. This functionality helps avoid meshing problems across the gap and thereby saves computation time.


**Table 1.** Mesh dependence tests.

**Figure 3.** Mesh profile of pipeline.
