interFoam - Volume of Fluid

Fool · March 5, 2019, 10:21

Hello everybody,

I have a short and probably quite simple question about the presentation of the results of interFoam in Paraview.

So there are two phases, air and water. To view only the water in Paraview, I use the clip function in conjunction with scalar and set the alpha value to 0.5. What I haven't quite understood yet is what this value stands for? Does this mean that all cells containing at least 50% water are displayed?
In simulations with a finer grid, areas were also displayed in which there was no water according to the coarser grid.
Or is this a clear indication that my grid is too coarse?

Unfortunately, I have not yet found an answer that I can understand.

Thanks a lot.
Dave

santiagomarquezd · March 6, 2019, 10:26

Hello, there is an intrinsic uncertainty in VOF regarding the interface. In cells with 0 < alpha < 1 the cell is not completely filled of water and you don't know which is the shape of the interface and its position. So, yes, the system shows you the cells with at least 0.5 of water. When you refine the solution can change since the NS equation are non-linear.

Regards.

Fool · April 12, 2019, 11:32

what I don't quite understand is:
after using the clip function with 0.5 for alpha.water and then marking the cells and exporting them as a CSV file, alpha.water will display values from 0.14 to 0.69. Shouldn't the values all be between 0.5 and 1.0 if only cells with alpha.water values above 0.5 are displayed?

March 5, 2019, 10:21	interFoam - Volume of Fluid	#1
Fool New Member David Join Date: Oct 2018 Posts: 27 Rep Power: 8	Hello everybody, I have a short and probably quite simple question about the presentation of the results of interFoam in Paraview. So there are two phases, air and water. To view only the water in Paraview, I use the clip function in conjunction with scalar and set the alpha value to 0.5. What I haven't quite understood yet is what this value stands for? Does this mean that all cells containing at least 50% water are displayed? In simulations with a finer grid, areas were also displayed in which there was no water according to the coarser grid. Or is this a clear indication that my grid is too coarse? Unfortunately, I have not yet found an answer that I can understand. Thanks a lot. Dave

March 6, 2019, 10:26		#2
santiagomarquezd Senior Member Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 452 Rep Power: 24	Hello, there is an intrinsic uncertainty in VOF regarding the interface. In cells with 0 < alpha < 1 the cell is not completely filled of water and you don't know which is the shape of the interface and its position. So, yes, the system shows you the cells with at least 0.5 of water. When you refine the solution can change since the NS equation are non-linear. Regards. Fool likes this. __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Research Scientist Research Center for Computational Methods (CIMEC) - CONICET/UNL Tel: 54-342-4511594 Int. 7032 Colectora Ruta Nac. 168 / Paraje El Pozo (3000) Santa Fe - Argentina. http://www.cimec.org.ar

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April 12, 2019, 11:32		#3
Fool New Member David Join Date: Oct 2018 Posts: 27 Rep Power: 8	what I don't quite understand is: after using the clip function with 0.5 for alpha.water and then marking the cells and exporting them as a CSV file, alpha.water will display values from 0.14 to 0.69. Shouldn't the values all be between 0.5 and 1.0 if only cells with alpha.water values above 0.5 are displayed?