Basic Poiseuille flow simulation question

Ashish

Hi experts,

My question is very basic. I am running a simulation for Poiseuille flow in a pipe (Laminar; incompressible flow) using ADINA. I model the pipe in 3D. Pipe is long enough (Dia 4mm and lenght 60mm).

For BC : at one end I give constant velocity (inlet) and at the other 0.0 pressure. The velocity distribution becomes parabolic as it should be. But the value of peak velocity is not what I expected from Poiseuille's flow V(r)=Vmax(R^2-r^2). Same about pressure drop.

Likewise if I just give Pressure BCs at both ends, velocity distribution is parabolic but not what poisullie's eqn predicts for Vmax?

I am not familiar with computational aspects of CFD but I think I am missing something very basic. I have varried mesh size etc.?

Thanks.

Ashish