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October 5, 2011, 00:03 |
Freestream boundary condition
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#1 |
New Member
Lee Yin Jen
Join Date: May 2011
Location: Malaysia
Posts: 10
Rep Power: 15 |
Dear FOAMers,
Hi, I'm pretty new to OpenFOAM and CFD. One question I have is regarding Freestream boundary condition - how exactly does it work? Specifically, I tried to run an external aerodynamics case, using fixedValue for velocity, nut and nuTilda at outer boundary, zeroGradient for pressure at outer boundary; simpleFOAM, S-A turbulence. The results are rather unphysical and diverging. However, following the airfoil example for simpleFoam and using freestream boundary condition, the simulation seems to be more reasonable and without divergence. My question is, how does freestream boundary condition differ from fixed values? Thanks, FOAMers! |
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October 7, 2011, 11:54 |
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#2 |
Member
Frederic Collonval
Join Date: Apr 2009
Location: Technische Universitaet Munich - Lehrstuhl fuer Thermodynamik
Posts: 53
Rep Power: 17 |
Hello Lee,
The freestream BC has the type inletOutlet meaning that it looks locally (for every face of the patch) at the mass flow rate. And if the flow is going outside the boundary will be locally zerogradient, if it is going inside the boundary will be locally fixedValue. The freestreampressure BC is a zeroGradient BC but it fixes the flux on the boundary to be rho*Sf*freestreamValue. Good luck Frederic
__________________
Frederic Collonval Technische Universität München Thermodynamics Dpt. |
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October 8, 2011, 11:37 |
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#3 |
New Member
Lee Yin Jen
Join Date: May 2011
Location: Malaysia
Posts: 10
Rep Power: 15 |
Thanks, Frederic! Think I get the point now...
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December 11, 2012, 12:29 |
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#4 |
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Malik
Join Date: Dec 2012
Location: Austin, USA
Posts: 53
Rep Power: 14 |
Hi,
Thank you for the explanation. If i am right the difference between a freestream BC and a fixedValue BC is that for fixed value there are constraints on each vector of the velocity field, while with freeStream we have a constraint only for the flux. This is why the solution sounds more physical ? |
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December 19, 2012, 22:18 |
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#5 |
New Member
Lee Yin Jen
Join Date: May 2011
Location: Malaysia
Posts: 10
Rep Power: 15 |
Hi, malaboss
Freestream BC is like a hybrid fixedValue and zeroGradient boundary condition. It behaves like a zeroGradient when fluid is flowing out of the boundary face, but behaves like a fixedValue when fluid is not flowing out. So, instead of fixedValue that imposes its constant value regardless of situation, freestream is more flexible, doing whatever is more physically realistic, so to say. |
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October 8, 2014, 08:05 |
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#6 |
Senior Member
Mieszko Młody
Join Date: Mar 2009
Location: POLAND, USA
Posts: 145
Rep Power: 17 |
Hi,
I am using currently freestream BC for the flow in the tunnel (channel). Is it an appropriate BC for such flow ? In short, there is large tunnel (3m in diameter) flow is from left to right (inlet, outlet with freestream BC) but inside the tunnel there is additional small inlet with some mass flow specified. thanks |
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May 5, 2015, 05:00 |
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#7 |
New Member
Join Date: Mar 2015
Location: Brest, France
Posts: 15
Rep Power: 11 |
Hi everyone,
Is it possible to use the freestream BC (to simulate a external hydrodynamic case) in 3D. In this case what is the good boundary condition to use for the frontAndBack ? Thanks for answers |
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June 4, 2015, 09:03 |
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#8 | |
New Member
Join Date: Mar 2015
Location: Brest, France
Posts: 15
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Quote:
Could you explain me what is Sf. In advance, many thanks |
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July 7, 2015, 03:04 |
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#9 |
New Member
Junshin Park
Join Date: Oct 2013
Posts: 6
Rep Power: 13 |
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December 19, 2016, 10:08 |
3D airfoil mesh
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#10 |
New Member
salman sadeghi
Join Date: Dec 2016
Posts: 1
Rep Power: 0 |
Hi everyone, i import .msh file (3D Cgrid mesh for airfoil in gambit) in openfoam and i got this error: {illegal cell label -1 in neighbour addressing for face 0} is it all about boundary condition?
the main question is haw to define that in 3D gambit to not face this error?or is it possible to import just geometry and mesh without boundary and then define it just in openfoam? thanks all of you in advance |
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July 19, 2017, 05:36 |
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#11 | ||
Member
Join Date: Jul 2012
Posts: 66
Rep Power: 14 |
Quote:
Quote:
Thank you both for the explanation. I want to use freestreampressure but combined with having the pressure prescribed as a value: "Prescribed pressure; with allowed in/outflow reversal" Is this possible in OpenFoam? Thanks, PS: more details: It is a wind engineering in-compressible flow simulation. I have a prescribed inlet velocity BC (Fluctuating Inlet). We usually combine this with a zeroGradient Pressure BC on the inlet. I want to have Inlet/Outlet condition on the Top, Sides and Outlet. However, a pressure value should be described on some boundary. Usually we use a fixedValue 0 for pressure. Is there a way to combine this with freestreampressure? |
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August 27, 2018, 01:32 |
regarding difference between freestream and inletoutlet boundary condition
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#12 |
Member
ijaz fazil
Join Date: Apr 2013
Location: Singapore
Posts: 73
Rep Power: 13 |
hi all,
I apologies for reopening this topic after a long time. I have doubt what is the difference between freestream and inletoutlet bC In inletOutlet BC also when the flow is out of the domain it will be zerogradient while the flow is into the domain it is fixed value. Then what is the difference between both condition. |
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March 10, 2019, 05:00 |
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#13 | |
Senior Member
Jianrui Zeng
Join Date: May 2018
Location: China
Posts: 157
Rep Power: 8 |
Quote:
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October 24, 2019, 04:44 |
Inletoutlet also provide same definition
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#14 | |
Member
ijaz fazil
Join Date: Apr 2013
Location: Singapore
Posts: 73
Rep Power: 13 |
Quote:
hi then what is the difference between freestream and inletoutlet because inletoutlet also same definition, when fluid is going out zerogradient while when the fluid is into the domain fixed value. So what is the difference between two? |
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June 5, 2020, 03:54 |
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#15 | |
New Member
Hailong
Join Date: Sep 2019
Posts: 8
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Quote:
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Tags |
boundary condition, freestream, openfoam 2.0.x |
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