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June 28, 2011, 22:19 |
chtMultiRegionSimpleFoam Boundary Conditions
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#1 | ||
New Member
Miguel Suarez
Join Date: Aug 2010
Location: El Paso Texas
Posts: 28
Rep Power: 15 |
I am using Openfoam 1.7 chtMultiRegionSimpleFoam solver and I'm trying to get the same results as in Fluent. However, I'm getting different results (Pressure and Velocity).
My case is as follows: Straight duct with a constant temperature bottom wall. the area of the inlet is 4x10-6 m^2. Reynolds no of 2000 (laminar flow). length of pipe is .25 m The following are my boundary conditions Quote:
Quote:
fixedValue zeroGradient inletOutlet etc I have not tried freeStreamPressure because i Dont know if it applies in this case Any help is greatly appreciated!!!! PLEASE HELP!!!!!!!! Miguel |
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June 30, 2011, 17:27 |
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#2 |
New Member
Jean El-Hajal
Join Date: Jun 2010
Location: Ulm
Posts: 16
Rep Power: 15 |
Hi Miguel,
is there a big difference in the results calculated with Fluent and OpenFoam ? could you give us some figures or graph. Could you post your case ? so we can have a look at it. Jean |
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July 1, 2011, 13:54 |
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#3 |
New Member
Miguel Suarez
Join Date: Aug 2010
Location: El Paso Texas
Posts: 28
Rep Power: 15 |
Jean,
the difference in the pressure and velocities between Fluent and OpenFOAM are pretty significant. as you can see in the pictures, Fluent has an outlet velocity of approx 13 m/s, however, Openfoam has a velocity of < 2.5 m/s. Obviously there is an issue with my boundary conditions that I have not been able to solve. Any help is greatly appreciated. I attached my case (B.C., fv, etc). Thank you. |
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July 4, 2011, 16:17 |
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#4 |
New Member
Jean El-Hajal
Join Date: Jun 2010
Location: Ulm
Posts: 16
Rep Power: 15 |
Hi Miguel,
Try to change the boundary condition in 0/p_rgh like that: inlet { type zeroGradient; } outlet { type fixedValue; value uniform 1.0e5; } Also the temperature are in Kelvin, check the temperature value !!! jean |
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July 5, 2011, 16:26 |
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#5 | ||
New Member
Miguel Suarez
Join Date: Aug 2010
Location: El Paso Texas
Posts: 28
Rep Power: 15 |
j
Quote:
Quote:
regarding the Temperature... i made sure that the units were Kelvin. as soon as I have consistent results with fluent I will post my case and my results Thank you so much for your help. Miguel |
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July 26, 2011, 04:30 |
pressure outlet bc on chtMultiRegionSimpleFoam OF 1.6-x
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#6 |
Senior Member
maddalena
Join Date: Mar 2009
Posts: 436
Rep Power: 23 |
Hello all,
I am running a chtMultiRegionSimpleFoam case on OF 1.6-x. The geometry is quite simple: a pipe flow with air, used to cool some warm surrounding solids. BC is more or less standard, however I have some doubt about the pressure outlet BC. I used: - inlet: U fixedValue, p buoyantPressure; - outlet: U zeroGradient; p fixedValue; as made on the chtMultiRegionSimpleFoam tutorial, but I have high continuity errors: Code:
time step continuity errors : sum local = 0.2007526, global = 0.004036046, cumulative = 0.220919 mad |
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July 26, 2011, 13:17 |
Pressure Outlet bc on OF 1.7-x
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#7 |
New Member
Miguel Suarez
Join Date: Aug 2010
Location: El Paso Texas
Posts: 28
Rep Power: 15 |
Mad,
I have used the following boundary conditions for my pressure and velocity: -inlet: U flowRateInletVelocity, p_rgh mixed (with value fraction = .5) -outlet: U inletOutlet (or fluxCorrectedVelocity), p_rgh mixed (with value fraction = .5) I have confirmed my results with FLUENT when my flow was laminar, but when i have turbulent flow, my results differ a little than FLUENT. They are not completely off, about 5 - 10 %. I recommend that you look at http://www.cfd-online.com/Forums/ope...-no-catch.html by m.nichols19. he has a pretty detailed case involving buoyantPressure boundary conditions. Good luck and hopefully this helps. Miguel |
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