Hello,

I am a CFD newbie and am attempting to model incompressible 2D flow in a cylinder with SIMPLE and a staggered grid. I have two rather basic questions:

1) How do you handle the no-slip condition at the wall with a staggered grid? Do you interpolate?

2) What is an appropriate velocity BC at the outlet for a specified pressure drop across the cylinder? Obviously I cannot specify the velocity itself, but what do I do with those outer grid points?

Thank you in advance for your help - Katherine Daru

Hi, Katherine,

1) How do you handle the no-slip condition at the wall with a staggered grid? Do you interpolate?

1a): By using the no-slip condition in calculating the momentum flux through the wall when we derive the finite-difference equation for the near-wall nodes.

1b) Yes, in a sense.

2) What is an appropriate velocity BC at the outlet for a specified pressure drop across the cylinder?

For example, du/dx=0. Mathematically, you can even prescribe u (as far as continuity is satisfied) but du/dx=0 is more realistic.

It is not that easy to specify the pressure drop. Specyfying the flow rate is more convenient.

Rgds, S.