CFD Online Discussion Forums

CFD Online Discussion Forums (
-   FLUENT (
-   -   Boundary conditions/solver (

chrisausAUS May 10, 2012 00:23

Boundary conditions/solver

I have to simulate a screw extruder.

I have set up the geometry - I have an inlet and an outlet needle.
I have the inlet as one part, the screw fluid as one part and the needle part.

I meshed within ANSYS workbench. Named the inlet and outlet as well as the screw wall.
I set up: Using laminar flow, defining a new fluid (PCL) with values I found in the literature.
For the cell zone condition I put fluid everywhere. For the screw fluid body I also tick frame rotation with rotation around - y axis with a certain speed.
Boundary conditions: Inlet-pressure 7e5 Pa, outlet-pressure 0 Pa gauge pressure, screw_wall is rotating around - y axis with the same speed as the frame rotation.

Solver is Presto and second order upwind momentum.

Monitors is the convergence turned off.

Then I initialize.
And then run until stable around 4000 iteration steps.

PROBLEMS that I have:
1) it is stable, but in the 10^3 range rather than 10^-4 range.
2) I tried standard/ second as well as standard/first, but the problems remains.
3) I didn't rotate the frame. And the same thing happens (stabilized at around 10^3)
4) If I make the whole extruder out of one part, then I get stabilizing in the 10^-4 to 10^-16 range for standard/second. If I use presto - I get still 10^3 and oscillating like crazy.

That brought me to the thought, that something must be wrong with my parts and their connection maybe.

Please give me some suggestions what I can try out next.


All times are GMT -4. The time now is 08:04.