flow depth in channel

mahdi1 · May 6, 2013, 14:46

Hello dears,

In a part of my project, I need to simulate a channel with horizontal slope.
For inlet, I chose volume flow rate with a fluid height. Also , I considered a length for this channel to reach developed flow. As you can see in attached picture, flow depth is less than fluid height that I had considered in inlet boundary condition.

I want to simulate flow in a channel with horizontal slope (Also with a desired flow depth in channel).

I would be thankful if some one could help me.

Regards,

Andy Chen · May 7, 2013, 03:47

What did you set up at downstream condition?

mahdi1 · May 7, 2013, 05:50

Quote:

Originally Posted by Andy Chen

What did you set up at downstream condition?

Hello Andy

I have tested both cases of Continuative and outflow for downstream.

Do you have an advise?

Regards,

elephant · May 13, 2013, 16:29

Your case is a channel that I assume is flowing under subcritical flow, and the water elevation is influenced by hydrostatic pressure downstream. This downstream hydrostatic pressure is caused by some sort of physical boundary such as a reservoir of constant depth or a flow control structure (eg. weir).

In order to model this, you need to set a hydrostatic pressure at your downstream boundary. If you just model it as free outflow or continuative, the water level will drop to the hydraulic grade line, based on the slope and friction of the surface. This is what you are seeing in the output you have posted.

mahdi1 · May 13, 2013, 16:44

Quote:

Originally Posted by elephant

Your case is a channel that I assume is flowing under subcritical flow, and the water elevation is influenced by hydrostatic pressure downstream. This downstream hydrostatic pressure is caused by some sort of physical boundary such as a reservoir of constant depth or a flow control structure (eg. weir).

In order to model this, you need to set a hydrostatic pressure at your downstream boundary. If you just model it as free outflow or continuative, the water level will drop to the hydraulic grade line, based on the slope and friction of the surface. This is what you are seeing in the output you have posted.

Hi elephant

Thanks

wusuhong · May 30, 2013, 06:28

Set downstream as 'Pressure' boundary condition with the same fluid height as you set in the upstream boudary condition.

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May 7, 2013, 03:47		#2
Andy Chen Member Yi-Lang Chen Join Date: May 2009 Posts: 58 Rep Power: 17	What did you set up at downstream condition?

May 13, 2013, 16:29		#4
elephant New Member Join Date: Jul 2012 Posts: 2 Rep Power: 0	Your case is a channel that I assume is flowing under subcritical flow, and the water elevation is influenced by hydrostatic pressure downstream. This downstream hydrostatic pressure is caused by some sort of physical boundary such as a reservoir of constant depth or a flow control structure (eg. weir). In order to model this, you need to set a hydrostatic pressure at your downstream boundary. If you just model it as free outflow or continuative, the water level will drop to the hydraulic grade line, based on the slope and friction of the surface. This is what you are seeing in the output you have posted.

May 30, 2013, 06:28		#6
wusuhong New Member wusuhong Join Date: Jan 2013 Location: Singapore Posts: 8 Rep Power: 13	Set downstream as 'Pressure' boundary condition with the same fluid height as you set in the upstream boudary condition.