Simple 2D regular-grid CFD simulation for teaching parallel scaling concepts

This is a simple simulation of an incompressible fluid flowing in a cavity using the 2D Navier-Stokes equation. The fluid flow can either be viscous (finite Reynolds number and vortices in the flow) or non-viscous (no Reynolds number specified and no vortices in the flow).

It is deliberately written to be very simple and easy to understand so it can be used as a teaching example.