[wusuhong]

I am doing open channel flow simulations, i have a rectangular channel inlet.

I set the inlet boundary condition as shown on the pictureinlet boundary condition.jpg, it supposed to be a rectangular shape at the inlet, right? However the result is inlet 3D image.jpg, 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]

Originally Posted by wusuhong

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]

Originally Posted by Jing_min

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]

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]

Originally Posted by JBurnham

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.