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-   -   Contours of 2D plotting (http://www.cfd-online.com/Forums/flow-3d/74935-contours-2d-plotting.html)

therockyy April 12, 2010 10:15

Contours of 2D plotting
 
1 Attachment(s)
Hello fellas,

I have a question about the result plotting in 2D.

I've chosen NF value as the contour variable and contour type is colour shaded. The snapshots of the ploted result have white lines indicate the free surface of the fluid (I guess) as showed in the attachments. The blue grids repersent the flow while the red grids are voids. http://picasaweb.google.co.uk/lh/photo/WzFuShttp://picasaweb.google.co.uk/lh/pho...eat=directlink

Since the deep blue grids do not have free surface, if the white line shows the free surface, it should be above the blue grids. This doesn't correspond to the plotting results. However, the white line shows a more realistic free surface of the flow in the attachment which modelled a plunging jet.

So my question is how this white line been plotted? Which data is used to plot the white line of the free surface in 2D?

Cheers!

Yang

http://picasaweb.google.co.uk/lh/pho...eat=directlink

MuxaB April 14, 2010 09:28

Quote:

Originally Posted by therockyy (Post 254322)
Hello fellas,

I have a question about the result plotting in 2D.

I've chosen NF value as the contour variable and contour type is colour shaded. The snapshots of the ploted result have white lines indicate the free surface of the fluid (I guess) as showed in the attachments. The blue grids repersent the flow while the red grids are voids. http://picasaweb.google.co.uk/lh/photo/WzFuShttp://picasaweb.google.co.uk/lh/pho...eat=directlink

Since the deep blue grids do not have free surface, if the white line shows the free surface, it should be above the blue grids. This doesn't correspond to the plotting results. However, the white line shows a more realistic free surface of the flow in the attachment which modelled a plunging jet.

So my question is how this white line been plotted? Which data is used to plot the white line of the free surface in 2D?

Cheers!

Yang

http://picasaweb.google.co.uk/lh/pho...eat=directlink


Yang, the white line is drawn based on the fluid fraction F. It is the contour line of F=0.5 since in the void F=0 and in the fluid bulk it is 1.

therockyy May 5, 2010 06:50

Quote:

Originally Posted by MuxaB (Post 254584)
Yang, the white line is drawn based on the fluid fraction F. It is the contour line of F=0.5 since in the void F=0 and in the fluid bulk it is 1.

Thanks, Michael.

A quick question: Is the free surface plotted in 3D also based on the volume of fraction of the cell?

I just feel confused about the NF value and the fraction of fluid. Can I explain this like that the NF value is the flag to lable the surface cell, but the calculated free surface is plotted by fuid fraction? Is that the concept of the volume of fluid method?

Thanks a lot!

Yang

MuxaB May 5, 2010 11:09

Yang,

You are right, NF is used for labeling free surface cells, while fluid fraction is used for plotting in 2d and 3d. I am not sure the NF flag is part of every VOF method, but it is certainly useful in FLOW-3D.

zandi December 22, 2012 16:04

fluid depth
 
Hi friends,

How we could get results in post processor part for fluid depth (e.g. in a free surface modelling) along the geometery?


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