Flow calculation of moving body on Cartesian grid by using new cell-merging method

Flow simulation around a moving body is a challenging problem, especially when there is more than one body moving relative to each other, To tackle this problem, a Cartesian grid is used in this paper, where its non-body-fitted property allows the grid to stay stationary while the bodies move across it. As a result, it requires only local grid modification in the vicinity of body surface, which may lead to a significant saving of computational cost. On the other hand, the body-fitted grids such as structured and tetrahedral-based unstructured grids move with the body; thus global grid modification is necessary during the movement. In the present study we devised a new implementation procedure for an existing two-dimensional cell-merging method to overcome the problem of conservation regarding gas dynamic properties, a problem caused by body movement across a grid. The present method may have a better potential for extension to 3D. It is based on our previous algorithm developed for a 3D unstructured Cartesian grid and was successfully applied to several test cases in this study. In particular, the efficiency of the method is greatly improved by employing a tree-based data structure to reduce the time to find body panels during computation of the cell's geometrical properties.