[startingcfd]

So I've written an unsteady finite element solver.

Now I want to test the code by running an unsteady flow simulation (INCOMPRESSIBLE) over a cylinder.

I want to see the evolution of the trailing backflow region then the von karman vortex street.

The problem: I'm having trouble setting the boundary conditions.

Basically I want a uniform inlet flow that slowly impinges upon the cylinder, but I'm thinking a propagating wave front isn't possible in incompressible flow.

So my questions:

How do I ensure conservation of mass (perhaps by setting outflow)? So let's say I do set the outflow to ensure continuity, this then means the flow has already gone past the cylinder and I can't simulate the evolution of the backflow region behind the cylinder (backflow is the steady state solution at low Re).

And related to the above, can I see the flow phenomena evolve even with an incompressible flow?

[startingcfd]

Bump

Anyone have an answer?