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Massflow or average velocity boundary condition |
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November 18, 2011, 10:55 |
Massflow or average velocity boundary condition
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#1 |
New Member
Jan Willem Krijger
Join Date: May 2010
Posts: 8
Rep Power: 16 |
Hello
I'm trying to simulate a pipeflow with 2 inflow boundary conditions and 1 outflow boundary condition using simpleFoam. I tried using a fixedValue boundary condition for the velocity at the outflow. But the simulation didn't converged and I got disturbances at the outflow. Which is expected because the flow is not uniform when it approaches the outflow boundary. I would like to define the velocity with zeroGradient at the inflow and the massflow or average velocity at the outflow. And the pressure with fixedValue at the inflow and zeroGradient at the outflow. How can I set the massflow or the average velocity at the outflow boundary? Any suggestions are appreciated!! |
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November 18, 2011, 15:33 |
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#2 | |
Assistant Moderator
Bernhard Gschaider
Join Date: Mar 2009
Posts: 4,225
Rep Power: 51 |
Quote:
If I had to do such a thing I'd use groovyBC (basically using an expression for the value like "U*mfTarget/mfCurrent" - the two mfs being specified/calculated). Note that probably to get this stable you'll have to make it a bit more complicated: at least some kind of underrelaxation to avoid trouble during the startup-phase and you'll have to decide whether you allow backflow (because that would be accelerated by the scaling too). And of course there is the general problem of specifying the massflow at the outlet .... |
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November 18, 2011, 20:20 |
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#3 |
Senior Member
Wouter van der Meer
Join Date: May 2009
Location: Elahuizen, Netherlands
Posts: 203
Rep Power: 18 |
hello,
If you have two inlets and one outlet. I think the best thing to do is set the two inlet velocities (fixed value). Calculate the velocities from the ratio of flows through the inlet and the area of the inlets by hand and let simpleFoam calculate the outlet flow, what being an incompressible steady state should result in the asked for massflow. hope this helps Wouter |
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November 21, 2011, 05:05 |
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#4 | ||
New Member
Jan Willem Krijger
Join Date: May 2010
Posts: 8
Rep Power: 16 |
Thank you both for your reply!
Ansys CFX does have a massflow boundary condition, could be a very nice addition to OPENFOAM! Quote:
Quote:
Of course you could iterate between inlet velocities to end up with a similar pressure at both inlets. |
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November 21, 2011, 13:50 |
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#5 |
Senior Member
Wouter van der Meer
Join Date: May 2009
Location: Elahuizen, Netherlands
Posts: 203
Rep Power: 18 |
hello Jan Willem,
Maybe you can use my suggestion as a stable start for the simulation with groovyBC Best Wouter |
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August 10, 2016, 06:16 |
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#6 |
Senior Member
Anton Kidess
Join Date: May 2009
Location: Germany
Posts: 1,377
Rep Power: 30 |
I think the fixedMean boundary condition works nicely for such a case.
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September 27, 2016, 16:09 |
Conservation of momentum
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#7 |
New Member
Rizvi
Join Date: Sep 2016
Posts: 3
Rep Power: 10 |
Hello i am trying to solve the same problem in Ansys fluent , how do i check if momentum is conserved?
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