
[Sponsors] 
May 27, 2008, 15:05 
Why should it be better with 1

#21 
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,894
Rep Power: 26 
Why should it be better with 1e15 instead than 1e4 from a numerical point of view? This limitation is useful when alpha goes to zero, because you divide by it, so 1e4 should have a better "stabilizing effect".
Moreover, you can set the inferior limit of alpha, in the case of a particle flow to something under 1e4 (1e6 is what is used in the kinetic theory framework, and it's conservative) without problems from a physical point of view, because the flow is so dilute that you can't consider the twofluid equations valid in those conditions, and, as a consequence, you should not use them anyway. Regards, Alberto 

May 28, 2008, 01:15 
What I meant is that max(alpha

#22 
Member
Juho Peltola
Join Date: Mar 2009
Location: Finland
Posts: 80
Rep Power: 8 
What I meant is that max(alpha,anumber) only affects alpha values smaller than anumber (clips the scale at the bottom) while (alpha+anumber) affects all the alpha values. (moves the whole scale upwards)
To me, the clipping seems like a more elegant solution. Assuming the max() function doesn't introduce new problems  like the dimension mentioned by Rasmus. Thank you all very much for your responses on the whole issue! 

May 28, 2008, 09:23 
Hello,
yes, sorry. I was no

#23 
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,894
Rep Power: 26 
Hello,
yes, sorry. I was not discussing about clipping. I agree with you on that. I was just pointing out that you can happily clip alpha at a numerically safe value around (like 10^6) instead than to a very small value, that in a division would return a huge coefficient. Regards, Alberto 

May 28, 2008, 17:42 
Hi Rasmus,
I have implement

#24 
Senior Member
Join Date: Mar 2009
Posts: 854
Rep Power: 13 
Hi Rasmus,
I have implemented your changes in our 1.5 release candidate and all seems well. Thanks Henry 

May 29, 2008, 07:45 
Thanks Henry!

#25 
Senior Member
Rasmus Hemph
Join Date: Mar 2009
Location: Sweden
Posts: 108
Rep Power: 8 
Thanks Henry!


August 29, 2008, 19:05 
I think that in "liftDragCoeff

#26 
Member
Danielle PRL
Join Date: Mar 2009
Posts: 42
Rep Power: 8 
I think that in "liftDragCoeffs.H" file for blended case
K should be calculated as: K = (alpha*Ka + beta*Kb); not: K = (beta*Ka + alpha*Kb); 

September 9, 2008, 08:34 
are you agree with me !!!

#27 
Member
Danielle PRL
Join Date: Mar 2009
Posts: 42
Rep Power: 8 
are you agree with me !!!


September 9, 2008, 09:12 
assume phase a to be the discr

#28 
Super Moderator
Niklas Nordin
Join Date: Mar 2009
Location: Stockholm, Sweden
Posts: 693
Rep Power: 19 
assume phase a to be the discrete one and b to be the continous.
standard approach would be to calculate the drag as K = Ka, right? alpha = 0 > pure gas. so... as alpha > 0 we should have K > Ka but with your approach K > Kb so no, i dont agree. 

May 28, 2011, 19:53 

#29 
New Member
Prashant Gupta
Join Date: Mar 2011
Location: Edinburgh
Posts: 29
Rep Power: 6 
Hey Guys,
I think I am on the right thread. But I am trying to write a new drag law for my calculations. I found this : http://openfoamwiki.net/index.php/Ad...lerFoam_solver I really cannot understand why  The Syamlal and O'Brien drag model can be implemented in OpenFOAM by dividing the β' < math > bytheproductofthetwovolumefractions < math > αβ to obtain K. N.B. Every drag formulation has to be divided by the product αβ before beeing implemented in twoPhaseEulerFoam because this product has been extracted for numerical reasons. Why do we devide by the product of voulme fractions and where in the source code do we multiply them back ??? Please help me with this. Best Wishes Prashant 

May 29, 2011, 03:54 

#30 
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,894
Rep Power: 26 
Hi Prashant,
you divide by the product of the phase fractions because of how the momentum equation is treated (phaseintensive form). You might want to check Henrik Rusche's Ph.D. thesis for some more detail on the implementation. P.S. Notice that all the models listed there are already part of OpenFOAM now. Best,
__________________
Alberto Passalacqua GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image. OpenQBMM  An opensource implementation of quadraturebased moment methods Last edited by alberto; May 29, 2011 at 03:56. Reason: Added P.S. 

June 6, 2011, 05:25 

#31 
New Member
Prashant Gupta
Join Date: Mar 2011
Location: Edinburgh
Posts: 29
Rep Power: 6 
Hey,
Thank you very much for useful info, I had another question on calculations and use of solid volume fractions for different species. I am trying to do a segregation study on fluidized bed , hence I require total volume fraction(alpha) and volume fraction of each of two species of particles ( different sizes). I am not sure where to look for them. I am trying to access the species volume fraction in order to calculate drag on individual species. Waiting eagerly for a reply Best Wishes Prashant 

June 11, 2011, 15:55 

#32 
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,894
Rep Power: 26 
The code deals with monodisperse flows. If you need more than one dispersed phase, you'll have to extend it.
Best, 

November 5, 2011, 15:03 
more than one discrete phase simulation

#33 
New Member
pramod kumar
Join Date: Sep 2011
Posts: 3
Rep Power: 5 
hi,
I want to simulate binary fluidized bed problem with OpenFoam, In my case more than one discrete phase are present. My question is can I use twoPhaseEulerFoam for more than one discrete phase.???? If yes than please give me some hint. thank you Pramod Kumar 

November 5, 2011, 15:08 

#34 
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,894
Rep Power: 26 
Hi Pramod,
twoPhaseEulerFoam can deal with one particle phase. Best, 

November 6, 2011, 01:54 

#35 
New Member
pramod kumar
Join Date: Sep 2011
Posts: 3
Rep Power: 5 
hi Alberto,
can you please tell me how to set a case for more than one disperse phase in openFoam. I'm very new with this software. thank you Pramod 

November 6, 2011, 02:06 

#36 
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,894
Rep Power: 26 
There is no EulerEuler multifluid solver in OF at the moment.


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
TwoPhaseEulerFoam  sara  OpenFOAM Running, Solving & CFD  2  November 6, 2008 20:26 
Bug in twoPhaseEulerFoam  alberto  OpenFOAM Bugs  2  May 20, 2008 21:25 
TwoPhaseEulerFoam Bug  alondono  OpenFOAM Bugs  1  February 19, 2008 21:01 
TwoPhaseEulerFOAM application  hemph  OpenFOAM Bugs  0  November 16, 2006 08:27 
TwoPhaseEulerFoam  newbee  OpenFOAM  0  March 27, 2006 08:41 