hi,

i'm using the fractional scheme to solve the 2d NS eqn. I found that after solving the poisson eqn, sometimes the body will become a sink (ie it seems to be sucking in the flow velocity ) or a source (ie the flow velocity is flowing out).

May I know why this is happening? What is the source of the problem for the above 2 scenario?

Tks!

Is this for incompressible flow?

What do you expect to happen at the body-fluid interface? If you expect zero-flux (or zero normal velocity) at those surfaces, the Poisson equation boundary conditions on those surfaces need to express that.

I don't know "the factional scheme" or how it solves the pressure (Poisson) equation, so that's as far as I can take it.

Maybe someone else can add to this ...

ya, it's for incompressible flow. for stationary body, u=v=0, dp/dn=0. however, I believe there's some error in the implementation of the BC hence resulting in the body changing to a sink or source.

I'm wondering if anybody has experience before and therefore know the cause of it....