LES simulation parameters
 

Hi Foamers,

I'm currently working on fireFoam. I'm trying to compare the results of fireFoam with the Fire Dynamic Simulator (FDS) which is well known tool for fire modelling. fireFoam and FDS both uses the Large Eddy Simulations for turbulence modelling. Coming to the case part I considered a small room of 0.4 mx0.4 mx0.4 m with the burner of size 0.08x0.08 m2. Four sides of room are open and top of the room is closed. I defined same fire source in fireFoam and FDS. If I see the results of temperature contour(Attached fireFoam_T_75s.png) from both the solvers in fireFoam the temperature is uniform along the Z no fluctuation yet all. If I see the temperature plot in FDS(Attached PoolFire_FDS_T75s.png) it is fluctuating in X and Y along the Z direction and breaking into eddies.

What might be causing the temperature(Velocity is also uniform) to be uniform in fireFoam where as nonuniform in FDS? Is it because of LES turbulence parameters?


If I want to make the flow to break into eddies in fireFoam what parameters are to be changed in the LES model?


Please help me.

Thanks
Manjunath Reddy N

I know that FDS introduces a fluctuation as a random background noise but probably also introduces a random fluctuation at the burner vent. You should probably do something similar for the inlet patch for the fireFoam calculation. This may work with a turbulentInlet

see:
$FOAM_SRC/finiteVolume/fields/fvPatchFields/derived/turbulentInlet/turbulentInletFvPatchField.H

Hi Tom Fahner,

Thank you very much for your valuable reply. Yes Tom, FDS introduces Noise which breaks the symmetry. It might also introducing some random fluctuations.

Actually I defined flowRateInletVelocity boundary condition at the burner now if want to add the turbulentInlet boundary condition along with the flowRateInletVelocity is it possible?


Thanks
Manjunath Reddy N

Hi Manjunath Reddy N,

Unfortunately that is not possible. The flowRateInletVelocity boundary condition does allow a time varying (spatially uniform) flowrate to be used, so you might be able to make it fluctuate in time. Another option would be to use groovyBC (look around on the forum) or calculate the average velocity upfront and use the turbulentInlet with that. Or you would need to generate a new boundary condition that combines the functionality of the flowRateInletVelocity with the turbulentInlet.

Regards,
Tom

Hi Tom,

Thank you for your reply, I will work out on implementing boundary condition using swak4Foam.


Thank you
Manjunath

fire simulation
 

Hi friends
I just start to use OpenFOAM and want to simulate a pool fire in a compartment. But I do not know how can I start and which tutorial can help me?
Please help me.
In do not want use fireFoam.
thank you.