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How do I model a sub-critical flow with FLOW-3D?

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Old   November 8, 2012, 17:31
Default How do I model a sub-critical flow with FLOW-3D?
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abbas bakhtiari
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Hi dear
I want to model a sub-critical flowin FLOW-3D.
When the height of the lower boundary is greater than of the upper boundary the water will enter the downstream boundary of the computational region.
As a result of my assumptions is destroyed.
Please help me
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Old   November 10, 2012, 15:24
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max
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Quote:
Originally Posted by abbaspwut View Post
Hi dear
I want to model a sub-critical flowin FLOW-3D.
When the height of the lower boundary is greater than of the upper boundary the water will enter the downstream boundary of the computational region.
As a result of my assumptions is destroyed.
Please help me
I don't see why the water enters the downstream when height of the downstream boundary is greater than upper boundary?
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Old   November 11, 2012, 05:40
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abbas bakhtiari
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Ask better questions:
Why height of downstream is not more than height of upstream?
if y2>y1 then flow-3d enter water of downstream boundary condition.
y2=height of downstream
y1=height of upstream
i want y2>y1 and flow direction is upstream --> downstream but after Run flow direction is downstream --> upstream

Last edited by abbaspwut; November 11, 2012 at 06:37.
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Old   November 11, 2012, 05:44
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abbas bakhtiari
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Quote:
Originally Posted by abbaspwut View Post
Hi dear
I want to model a sub-critical flowin FLOW-3D.
When the height of the lower boundary is greater than of the upper boundary the water will enter the downstream boundary of the computational region.
As a result of my assumptions is destroyed.
Please help me
Ask better questions:
Why height of downstream is not more than height of upstream?
if y2>y1 then flow-3d enter water of downstream boundary condition.
y2=height of downstream
y1=height of upstream
i want y2>y1 and flow direction is upstream --> downstream but after Run flow direction is downstream --> upstream
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Last edited by abbaspwut; November 11, 2012 at 06:37.
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Old   November 27, 2012, 12:37
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Jeff Burnham
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FLOW-3D is a transient solver. You are using assumptions of steady-state gradually-varied flow. The only way to model this kind of situation is to include the control structure that causes the downstream free surface elevation to be higher than the upstream elevation. That is, you must model the contraction, critical transition structure, or bed elevation change explicitly, instead of assuming that by setting h2 > h1 you can force FLOW-3D to assume that the flow is steady/gradually-varied.
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