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Old   September 17, 2003, 03:11
Default VOF problem
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Jarrod Sinclair
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Hi,

I am using the VOF model with Star-CD v3150A.020 for a water/air simulation in a 10cm X 10cm 2D domain with grid size of 0.2cm. I am implementing a sloshing effect by oscillating the gravity vector from -45deg to 45deg (period 0.3s) using SORMOM.F. After about ~2 seconds, a layer of "misting" (10% water concentration) develops on top of the water surface, and does not decay. Therefore the interface is not clearly defined anymore. Due to the scale I am not using surface tension. Also, the time-step used is keeping the mean Courant number well below 1. The same effect is seen with a finer grid of 0.1cm cells, and also for some other VOF problems I am studying.

Has anyone ever seen this problem before? Are there any techniques to minimize this misting? Can the VOF concentration be modified on an adhoc basis using SORSCA.F?

Thanks.
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Old   September 17, 2003, 17:34
Default Re: VOF problem
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allan
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I did a similar analysis and didn't have any problems. Are you using mars or ud?

allan
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Old   September 17, 2003, 19:56
Default Re: VOF problem
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Jarrod Sinclair
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Thanks Allan,

I am using MARS for both momentum (blend=0.5) and for VOF (blend=1.0). Are there any other Star-CD settings that are important for this VOF problem; e.g. amount of subcycling, etc?

I can email you a better problem description (brief report) if you like.
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Old   September 18, 2003, 02:15
Default Re: VOF problem
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allan
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yes, send the email. In the meantime, try setting relatation on pressure and vof to 0.8. You could also try ud instead of mars, just to see if the problem dissapears

allan
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Old   September 19, 2003, 07:50
Default Re: VOF problem
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4xF
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I do not agree with allan that you should use UD instead of MARS. I would, from my personal experience, that you always use as much higher order scheme for momentum instead of CD. Els e you get with VOF really crap results. Another important thing to be taken into account is that you need to have a fine mesh where the interface deforms so that you may capture breaking waves that will certainly occur. I do not think that you will capture these effects on a 50x50 mesh.
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Old   September 19, 2003, 13:36
Default Re: VOF problem
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allan
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yes, ud is not as accurate as mars, but it is more robust, if the grid cannot be solved with ud then it is likely to be a grid problem. I agree with you that a fine mesh is required.

allan
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