Difference between volume fraction and pathlines

flow_CH · July 30, 2013, 04:56

Hello friends

I am modeling a chute with a step.
I want to know water is going into the step or not. (you can see step into images)
Which of this show the flowing of water in model?
In iso clip for volume fraction between 0.5 to 1 wee see water is going into step( image number1) but In number 2 image (pathlines) it is not.
I am confused. which is correct.
Thnks

vasava · July 30, 2013, 05:35

You are not seeing the pathlines in that region because of the low velocity of the fluid in that region.

flow_CH · July 30, 2013, 07:08

Quote:

Originally Posted by vasava

You are not seeing the pathlines in that region because of the low velocity of the fluid in that region.

I did not understand. Can you explain more?
I read in fluent user guide: Pathlines are used to visualize the flow of massless particles in the problem domain, so can not display interaction between two phases?
What are the numbers and colors in pathlines?
So you are saying water is going into step?

vasava · July 30, 2013, 07:42

As I understand pathlines are traces of fluid 'particles'. They simply show where the particle have been (in the domain) during the motion of the fluid. If there is a region in your domain where there velocity is extremely low then the tracing would not work i.e. fluent can not draw pathlines in that region. This scenario is often appears in the command window as 'escape particles'.

In your case the velocity in the step region might be extremely low. And this is the reason why you do not see the pathlines although the volume fraction contour show that there is fluid.

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July 30, 2013, 05:35		#2
vasava Senior Member Paritosh Vasava Join Date: Oct 2012 Location: Lappeenranta, Finland Posts: 732 Rep Power: 22	You are not seeing the pathlines in that region because of the low velocity of the fluid in that region.

July 30, 2013, 07:42		#4
vasava Senior Member Paritosh Vasava Join Date: Oct 2012 Location: Lappeenranta, Finland Posts: 732 Rep Power: 22	As I understand pathlines are traces of fluid 'particles'. They simply show where the particle have been (in the domain) during the motion of the fluid. If there is a region in your domain where there velocity is extremely low then the tracing would not work i.e. fluent can not draw pathlines in that region. This scenario is often appears in the command window as 'escape particles'. In your case the velocity in the step region might be extremely low. And this is the reason why you do not see the pathlines although the volume fraction contour show that there is fluid.