In this paper we present a method for solving the time-dependent incompressible Euler equations on an adaptive grid. The method is based on a projection formulation in which we first solve convection equations to predict intermediate velocities, and then project these velocities onto a space of approximately divergence-free vector fields. Our treatment of the convection step uses a specialized second-order upwind method for differencing the nonlinear convection terms that provides a robust treatment of these terms suitable for inviscid flow.
Our approach to adaptive refinement uses a nested hierarchy of grids with simultaneous refinement of the grids in both space and time. The integration algorithm on the grid hierarchy is a recursive procedure in which a coarse grid is advanced, fine grids are advanced multiple steps to reach the same time as the coarse grid and the grids are then synchronized. We will describe the integration algorithm in detail, with emphasis on the projection used to enforce the incompressibility constraint. Numerical examples are presented to demonstrate the convergence properties of the method and to illustrate the behavior of the method at the interface between coarse and fine grids. An additional example demonstrates the performance of the method on a more realistic problem.