Moving Boundary for Piston Dynamics

March 27, 2007, 10:19

Hi CFX users!

I am trying to simulate dynamic characteristics of simple piston. This model is composed of only 3 surfaces, top, bottom, and side, resulting in 1 volume. When the moving part, bottom surface, moves upward, the inside gas will be compressed. Here, I'd like to solve this problem by using transient analysis.

To solve this problem, I set the wall velocity in wall boundary condition on the bottom surface. I, however, cannot get the result. Of course, there is no movement of the bottom surface. I have a warning as follows:

Initial conditions have been defined both globally and for Domain 'Air'. The values defined on the domain will be used by the flow solver.

Do I need to do something for this simple (?) simulation?

Thanks,

Se-Hee

March 27, 2007, 10:41

Dear Se-Hee,

If the domain is deforming, you must active MESH MOTION; otherwise, the domain remains fixed..

Did you do that?

Then, you must setup the MESH MOTION at the bottom boundary..

Check the tutorial for mesh motion..

Opaque.

March 27, 2007, 10:19	Moving Boundary for Piston Dynamics	#1
Se-Hee Guest Posts: n/a	Hi CFX users! I am trying to simulate dynamic characteristics of simple piston. This model is composed of only 3 surfaces, top, bottom, and side, resulting in 1 volume. When the moving part, bottom surface, moves upward, the inside gas will be compressed. Here, I'd like to solve this problem by using transient analysis. To solve this problem, I set the wall velocity in wall boundary condition on the bottom surface. I, however, cannot get the result. Of course, there is no movement of the bottom surface. I have a warning as follows: Initial conditions have been defined both globally and for Domain 'Air'. The values defined on the domain will be used by the flow solver. Do I need to do something for this simple (?) simulation? Thanks, Se-Hee

March 27, 2007, 10:41	Re: Moving Boundary for Piston Dynamics	#2
opaque Guest Posts: n/a	Dear Se-Hee, If the domain is deforming, you must active MESH MOTION; otherwise, the domain remains fixed.. Did you do that? Then, you must setup the MESH MOTION at the bottom boundary.. Check the tutorial for mesh motion.. Opaque.

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