[samarth]

Hi everyone,

I am a new user of OpenFOAM and am facing some problems in using OF.

I'm trying to run 3-dimensional poiseuille flow. I'm using icoFOAM. However the solution that I got after about a day that the code ran for is mostly noise (I think). The diameter of the channel is 2 cm, the length is 400 cm.

My questions are :
1) I have to use a very small step size. I calculated it and it should be around 0.05 but I have to use a step size of about 0.005, otherwise the solution blows up (residuals increase by orders of magnitude, of about 7 or 8). Can any one tell me why?

2) Is there any way to output the density. I know that I'm using an incompressible solver but I still want to see the density to check the solution.

3) The solution that I'm getting now is mostly noise. I set the inlet velocity as 1 m/s and after the code ran for about a day I took velocity profiles close to the entrance. The maximum velocity at the entrance is about 0.007 m/s (about 1000 times smaller than what I set as the inlet velocity). Any suggestions?

4) Also, while setting the boundary conditions (Under fields in FoamX),for U and p, the internal field value was set as 0. This changed to non-uniform as the solution progressed. Can someone please tell me what internal field value means and what should I set as the value for it initially. And why does it change to non-uniform as the solution progresses?

I am posting a sample of the runtime output in case it helps.

Time = 8.524

Courant Number mean: 8.41347e-06 max: 9.01006e-05
DILUPBiCG: Solving for Ux, Initial residual = 0.00111436, Final residual = 3.55223e-06, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.00495135, Final residual = 2.97364e-07, No Iterations 2
DILUPBiCG: Solving for Uz, Initial residual = 0.00488221, Final residual = 3.02446e-07, No Iterations 2
DICPCG: Solving for p, Initial residual = 0.00727199, Final residual = 8.52667e-07, No Iterations 751
time step continuity errors : sum local = 2.29261e-14, global = -2.05372e-15, cumulative = -3.99418e-09
DICPCG: Solving for p, Initial residual = 0.00283887, Final residual = 9.52671e-07, No Iterations 544
time step continuity errors : sum local = 2.5485e-14, global = 3.18756e-17, cumulative = -3.99418e-09
ExecutionTime = 2951.51 s ClockTime = 2996 s

Any help given will be greatly appreciated.