[FMDenaro]

Originally Posted by TurbJet

I kind of figured this out. 1st case will be Poiseuille flow and it follows the parabola profile. But for 2nd case, it's not Poiseuill flow, the velocity profile will not be parabola. It has much larger gradient at near wall region to balance the pressure gradient, so the entire velocity field is smaller than the 1st case.

I think this solution has not really reached a convergence to steady state. If it does not converge that should confirm a bug in setting the BC.

PS: are you using a small Re number?

[TurbJet]

Originally Posted by FMDenaro

I think this solution has not really reached a convergence to steady state. If it does not converge that should confirm a bug in setting the BC.

PS: are you using a small Re number?

Actually, fixed total pressure at the inlet will give a different velocity profile. So it seems we cannot simply compare with Poiseuille solution.

[FMDenaro]

Originally Posted by TurbJet

Actually, fixed total pressure at the inlet will give a different velocity profile. So it seems we cannot simply compare with Poiseuille solution.

At the steady state the solution has a constant velocity along x, therefore (p0_inl=p_inl + k_inl) and (p0_out=p_out + k_out) being k_out=k_inl should provide the same pressure difference.