CFD Online Discussion Forums

CFD Online Discussion Forums (
-   FLUENT (
-   -   piston-cylinder UDF (

carno September 16, 2008 02:19

piston-cylinder UDF

I am trying to move the piston in a 2D piston cylinder arrangement with CG_MOTION macro. Piston is moving correctly but the mesh along the cylinder is not changing and the end point of the cylinder is remaining at its original position and creating problem of mesh distortion.

1. Initial position: arrangement look like a rectangle with piston at BDC. 2. After some time the piston moves up and arrangement look like a rectangle with bottom end open and piston at some position in the open rectangle. (cylinder side lengths remain same). This is the problem and the run comes out with negative volume error.

How to resolve this problem?


doki September 16, 2008 08:04

Re: piston-cylinder UDF
I'm wonder if I've understood the problem correctly, but the thing is you have to define the piston walls as All of your bottom edge. Also, you probably should define the cylinder liner as "deforming" in fluent. the negative volume is probably because of a crevice-like portion between the piston and cylinder liner.

carno September 17, 2008 00:30

Re: piston-cylinder UDF
Thanks Doki. After defining the deforming cylinder wall problem got solved.

All times are GMT -4. The time now is 13:27.