chtMultiRegionSimpleFoam Boundary Conditions
 

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

For my pressure boundary conditions I have tried several other ones such as :

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

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

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.

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

jI actually used the following boundary conditions for pressure:

and it is giving me better results (meaning outlet velocities higher than the ones at inlet)

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

pressure outlet bc on chtMultiRegionSimpleFoam OF 1.6-x
 

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:
and in the end the solution diverges. I guess the problem is on pressure BC. Any suggestions on the subject?

mad

Pressure Outlet bc on OF 1.7-x
 

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