Grid Quality and Resolution Effects for Aerodynamic Modeling of Ram-Air Parachutes

Abstract

This work provides an overview of the grid quality and resolution effects on the aerodynamic modeling of ram-air parachute canopies. The computational-fluid-dynamics simulations of this work were performed using the Cobalt flow solver, which is a three-dimensional code, but it was run in a two-dimensional mode for canopy sections with open and closed inlets. Previous simulation results of these geometries showed that grid independence is achieved for the closed and open airfoils with grids containing around half a million and 2 million cells, respectively. Previous grids were either hybrid with prismatic layers near the walls or multiblock structured using algebraic grid generators. The results presented in this work show that grid independence of both geometries can be achieved with much coarser grids. These grids, however, were generated with good smoothness, wall orthogonality, and skewness qualities. The results show that the grid quality value is mainly related to the grid smoothness and does not depend on the grid skewness or the wall orthogonality. Although a smooth grid improves the quality value, and therefore the solution convergence, it does not always lead to an accurate solution. For example, the unstructured grids with anisotropic cells near the wall have very good grid quality; however, they have the worst accuracy among all grids considered because of the poor skewness at the walls. The results also showed that, in comparison to the closed inlets, the open geometry solutions are less sensitive to the initial grid spacing and number of constant spacing layers at the outside airfoil walls. Finally, the open inlet solutions do not change with the inside airfoil grid resolution and type.