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-   -   Inlet fulid splashes (http://www.cfd-online.com/Forums/flow-3d/115947-inlet-fulid-splashes.html)

wusuhong April 10, 2013 02:17

Inlet fulid splashes
 
2 Attachment(s)
I am doing open channel flow simulations, i have a rectangular channel inlet.

I set the inlet boundary condition as shown on the pictureAttachment 20597, it supposed to be a rectangular shape at the inlet, right? However the result is Attachment 20598, the fluid spalashed and the fluid level raised up.

Is there anyone can teell me what is the problem and how to solve it.

thanks very very much!

Jing_min April 10, 2013 08:44

Quote:

Originally Posted by wusuhong (Post 419543)
I am doing open channel flow simulations, i have a rectangular channel inlet.

I set the inlet boundary condition as shown on the pictureAttachment 20597, it supposed to be a rectangular shape at the inlet, right? However the result is Attachment 20598, the fluid spalashed and the fluid level raised up.

Is there anyone can teell me what is the problem and how to solve it.

thanks very very much!

It seems the first picture shows the B.C. at inlet, the left side.
You should use Outflow B.C. at right B.C.

wusuhong April 10, 2013 22:27

Quote:

Originally Posted by Jing_min (Post 419614)
It seems the first picture shows the B.C. at inlet, the left side.
You should use Outflow B.C. at right B.C.

Thanks for your advice, but my in my case, the flow is sub-critical, i can't use Outflow B.C at the right B.C.
And, do you think the outflow B.C would affect the behavior of inflow?

JBurnham April 23, 2013 12:06

That looks like an instability. Make sure that the flat surface of the water profile does not exactly match a grid line. Change the grid so that the free surface is between grid lines: this is only necessary when the free surface is flat for long stretches, normally it can cross grid lines with no problem. Make your exit boundary pressure-type w/ fluid fraction = 1 and the tailwater elevation set as the free surface elevation (Cartesian z coordinates). Also make sure that gravity is in the correct vector: i.e., gz = -9.8. Sometimes people forget that and make gravity point upward. Good luck.

wusuhong April 24, 2013 03:46

Quote:

Originally Posted by JBurnham (Post 422657)
That looks like an instability. Make sure that the flat surface of the water profile does not exactly match a grid line. Change the grid so that the free surface is between grid lines: this is only necessary when the free surface is flat for long stretches, normally it can cross grid lines with no problem. Make your exit boundary pressure-type w/ fluid fraction = 1 and the tailwater elevation set as the free surface elevation (Cartesian z coordinates). Also make sure that gravity is in the correct vector: i.e., gz = -9.8. Sometimes people forget that and make gravity point upward. Good luck.

thanks for your advice.
But i have done all as you just said, and the problem is like this, there must be something i didn't pay attention on. Do you have any other tips for me?

Thanks again.


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