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Old   March 28, 2014, 07:32
Default understanding compressibleInterDyMFoam
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Hi everyone,

Recently I started using OpenFOAM (v2.3.0). Currently I am trying to model a sloshing tank in 2D (3D will follow later). The need for VOF, body motion and the inclusion of temperature led me to compressibleInterDyMFoam. In fact, I derived my test case from the tutorial multiphase/compressibleInterDyMFoam/ras/sloshingTank2D to which I added 6DoF motion. During my little experiments I came across something I do not fully understand. I'll try to describe it. For the time being, I turned of any motion.

I built a simple tank in blockMesh (square) which is filled up to half with water, the other half is air. To test heating effects, I used setFields to initialize a temperature field (and decreased size to 10 by 10 cm to reduce the problem to manageable time scales). So, within the body of water I assigned a small rectangle with a higher temperature (350 K as opposed to 300 K). I then let the solver do its job and see what happens with the blob of hotter water. Natural convection should ensure it rises, which it does on the square mesh. However, there is something weird going on when I curve the bottom edge (since in the end I want the tank to be circular).

Result on square mesh (after 10s):
Result on curved mesh (after 1.5s):

I tried setting nNonOrthogonalCorrectors to 3, but that did not help. I know the scale of the model is small (for now), but that's because I wanted to see something happening (a blob of hot water in a 1 or 2 meter diameter tank takes a while). Refining the mesh does not seem to alter the flow in a qualitative sense either.

For anyone interested, I added my case files as an attachment.

I am quite new to OpenFOAM, so this might be an incredibly simple problem to solve. But I welcome any suggestions.

One more thing, slightly related. I use the gen6DoF folder which I copied from another test case. What are the requirements on the variable 'label nTimes = ...'. A really dense motion data set seems to influence run time, but not necessarily the flow solution. How dense should the frequency sampling be and on what does it depend? Does it have any effect at all? Should there be a motion input every time step (hard to do when it is variable)?

Sorry for all the questions. I hope someone is able to enlighten me a bit. Thanks in advance.

- Even the slightest curvature causes the effect.
- Filling up the complete domain with water makes the anomaly disappear (simply increasing the water level a bit also has this effect); could it be related to the vibration in the water surface otherwise present when the mesh is curved (given the small scale)?
- Temperature of hot water is beyond boiling (was 400 K), better change that to something more reasonable (350 K).
- A similar effect is observed when the lower boundary is heated (fixed temperature).
- A simple test with increased scale (1 m width instead of 10 cm) produces similar results.

Kind regards,
Attached Files
File Type: gz tank2D.tar.gz (12.9 KB, 1 views)

Last edited by arthurdent; March 28, 2014 at 12:16.
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