pimpleDyMFoam
 

Hello,

I'm new openFoam user. I choose to do CFD simulations with dynamic mesh for my thesis work. I've some experience with fluent/gambit. OpenFoam left a big impression on me after the few classes with prof. Hrvoje Jasak at my university. So now I decide to use it.

I'm using the movingCone tutorial as my guide, because it is very similar. Here are my problems:

blockMeshDict - I changed the geometry and the mesh. In paraFoam it looks fine. Patch left is wall, yes? I need it to become atmosphere, how to fix it?

dynamicMeshDict - Don't understand this part “diffusivity directional ( 1 200 0 )”. Its smth with the cone distance/speed? The cone distance travel should be 40 mm, with constant speed of 0.002 m/s.

controlDict - endTime I should put here the time, that the cone is moving? (20 sec)
deltaT I calculate it for Co=1. (2.5e-05)
maxCo In the tutorial its Co=0.2. Should I put here “Co=1”, because deltaT is calculated for Co=1?

Where I can put the wall roughness or material?


Thanks,
Stefan

Hi Stefan!
The movement of the boundary points is propagated into the other/interior points by diffusion. “diffusivity directional ( 1 200 0 )” defines the diffusion coefficients for the three directions (x, y, z). Try for example “diffusivity directional ( 1 1 0 )” and observe the moving mesh.

I'm not sure about the settings for deltaT end maxCo. The actual Co number depends on the meshsize and the actual speed of characteristics. If you fix deltaT you should take care of the resulting Co number: It must not exceed 1 during the whole simulation. I assume that OpenFOAM will control deltaT (when adjustTimeStep yes; in the controlDict) such that the maximum Co number will be smaller than maxCo.

Concerning your blockMeshDict: What exactly means "I need it to become atmosphere"? In the case directory you can modify boundary conditions for each patch. Just edit the approriate files 0/U 0/p and so on.

Hi Markus

1. I just run the movingCone tutorial, with different set up in dynamicMeshDict.
- diffusivity directional ( 1 200 0 ) => default
- diffusivity directional ( 1 1 0 ) => bad mesh
- diffusivity directional ( 200 1 0 ) => worse than (1 1 0)
- diffusivity directional ( 1 400 0) => the mash is same as (1 200 0) but the results are different
How U know the proper set up? Can U calculate the numbers, U know by experience, or it's trial and error?

2. blockMeshDict. Patch left, should be open to the atmosphere (1 bar).

3. controlDict. I'm positive that my problem is here. When run pimpleDyMFoam, Co is higher than 1. The thing is that the gap is just 0.04 mm, so there is big difference in the speed between the cells. But I calculate the deltaT, for Co=1 in the smallest cell with max speed. Don't know where is my mistake.

Maybe I ask dump questions :D but U'll forgive me, I'm new here

Thanks,
Stefan

request for dynamic mesh help
 

hi
I have to model a cavity (which upper vortex(the lid of it) oscillate vertically) with dynamic mesh modeling in fluent
i don't know how to create mesh, define moving zone in fluent and i don't know hot to model a very simple dynamic mesh problem in fluent
can any body help me?
could you send me some guide lines or some tutorials about it?
i need the tutorial that model cylinder-piston with dynamic mesh.
my email is :sharifi.fatemeh@gmail.com


please answer me
i need it very urgently

thank you very much

Hi!
Tomorrow I'll load up a simple case: pump with moving piston and put a link in http://www.cfd-online.com/Forums/ope...erdymfoam.html