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-   -   VOF Model- Volume fraction Contour shows not clear demarcation (http://www.cfd-online.com/Forums/fluent/104379-vof-model-volume-fraction-contour-shows-not-clear-demarcation.html)

Blue July 8, 2012 10:58

VOF Model- Volume fraction Contour shows not clear demarcation
 
Hi,

I am analyzing flow behavior inside a tank. Tank is of rectangular shape and there is velocity inlet(water) at upper side and outlet is at bottom by using VOF model on fluent software. Two phases water and air is considered. Iteration result for 3 seconds shows not a clear demarcation between air and water. All water and air goes mixed up in volume fraction contour. Im using implicit scheme for solution. Another question is for how much time we can run program, as in tutorial and on youtube it shows for few seconds. I want to run it for 600 seconds.

Please reply

Thanks

sicfred July 12, 2012 07:20

Hi!

First of all, I think that your simulation is going to be very very long, try as far as you can to reduce the time of simulation. 10 min of simulation using VOF method will take a lot of time if you want an accurate result.

Second, the best for VOF is the explicit method with geo-recronstuct as the discretization method, the width of the interface between water and air is around on cell; but this will need a small time step (0.001-0.00001, depends how dynamic is your flow) and it is more unstable, the courant number should be less than 2

If you really need to simulate the 600 sec, i think your best shot is use the vof implicit with HRIC Modified, the interface is around 4-3 cells, so you should reduce the size of the mesh much more, but you can use a bigger time step

Blue July 12, 2012 15:22

Thank you :)

shuai_manlou July 13, 2012 07:33

hello sicfred, I have a question, when I choose the 'open channel flow', the scheme changes to implicit automatically, and in which situation should the open channel flow be chosen? Thanks ~

sicfred July 16, 2012 03:58

The open channel flow is to simulate flows like rivers, waves, bump etc. In your case (tank discharge) you don't have to choose the open chanel flow.

Quote:

Originally Posted by shuai_manlou (Post 371288)
hello sicfred, I have a question, when I choose the 'open channel flow', the scheme changes to implicit automatically, and in which situation should the open channel flow be chosen? Thanks ~



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