A Hybrid Unstructured Grid Generation Procedure for Boundary Layer and Wake Flow

Abstract

Accurate solution of boundary layer and wake flow require generation of high aspect ratio grids in these regions. A hybrid approach for the efficient generation of inviscid and viscous unstructured grids has been introduced. A novel feature of the current work is its ability to produce boundary layer and wake grids that enables accurate flow solutions in viscous flow regions. The grid generation algorithm starts with a very coarse initial grid. In the inviscid region, isotropic cells of excellent quality are produced using a combination of point insertion and cell subdivision techniques. Simultaneously, a directional grid refinement strategy is used to construct highly stretched triangular cells in viscous regions. First, anisotropic unstructured grids are produced in the stream wise direction. Then, cells close to the solid surface are refined to highly stretched layer of triangles suitable for boundary layer region. Smooth transition between the boundary layer grid and the outer isotropic grid is easily obtained with a user specified cell size and stretch. The accuracy of the current grid generation approach is assessed by laminar and turbulent compressible flow solutions around NACA0012 and RAE2822 airfoils. The results of the numerical flow simulations are compared with published experimental and numerical data. Comparisons point to the ability of the proposed unstructured boundary layer and wake grid generation procedure.