CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM

alpha1 grows unbounded in interDyMFoam

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree5Likes
  • 3 Post By tayo
  • 2 Post By Hale

Reply
 
LinkBack Thread Tools Display Modes
Old   March 24, 2013, 23:08
Default alpha1 grows unbounded in interDyMFoam
  #1
Member
 
Tayo
Join Date: Aug 2012
Location: FL
Posts: 93
Rep Power: 3
tayo is on a distinguished road
Hello all,

I'm running rising bubble case using interDyMFoam. The issue is that alpha1 blows up whenever I run with flow velocity i.e. maximum alpha1 grows unbounded beyond 1 and minimum alpha1 also grows beyond zero even after the first time step. However, it behaves fine when I run without flow velocity.

I've tried running implicitly and then played around with the div(phi,alpha) & div(phirb,alpha) in fvSchemes, and then with calpha and nAlphaSubCycles in fvSolution. I've even set maxCo & maxAlphaCo to 0.01 yet it still grows. Please I need ideas on how to make alpha1 stay bounded between 0 and 1 irrespective of flow velocity. I would really appreciate any help. Thank you.
tayo is offline   Reply With Quote

Old   March 27, 2013, 17:10
Default
  #2
Member
 
Tayo
Join Date: Aug 2012
Location: FL
Posts: 93
Rep Power: 3
tayo is on a distinguished road
Please I'm still waiting for response/ideas on how to keep alpha1 bounded using interDyMFoam. Thank you.
tayo is offline   Reply With Quote

Old   March 27, 2013, 17:47
Default
  #3
Senior Member
 
Lieven
Join Date: Dec 2011
Location: Mol, Belgium
Posts: 292
Rep Power: 11
Lieven will become famous soon enough
Hi Tayo,

A thing you can try (at least this is what I would do) is to select the 'upwind' interpolation for all operators in the fvSchemes. It is first order, so you don't want to keep it, but it is bounded. So you should not get the under/overshoots. Next, replace each upwind by a second order scheme until you see the problem arising. For that operation you need to pick a more advanced scheme (TVD, explicitly bounded scheme, filtered, ...).

Cheers,

Lieven
Lieven is offline   Reply With Quote

Old   March 27, 2013, 18:44
Question
  #4
Member
 
Tayo
Join Date: Aug 2012
Location: FL
Posts: 93
Rep Power: 3
tayo is on a distinguished road
Thanks Lieven,

I've just tried upward scheme on div(phi,alpha) but it still grows unbounded, then, I tried vanLeer01 but same result. I'm currently using limitedVanLeer 0 1 but it's not looking any different. I'm currently running at time step of 1e-6sec. The wield thing is that when I ran the case without adaptive meshing (interFoam), alpha1 didn't blow up although I had to use maxCo and maxAlphaCo of 0.1. So I strongly think it has to do with interDyMFoam but I don't know how to correct the solver. I really need adaptive meshing for my case.
tayo is offline   Reply With Quote

Old   March 28, 2013, 09:16
Default
  #5
Senior Member
 
Lieven
Join Date: Dec 2011
Location: Mol, Belgium
Posts: 292
Rep Power: 11
Lieven will become famous soon enough
hi Tayo,

I really meant to use the upward scheme for all operators as starting point. At this point, there is really no reason yet to think it is a problem of the solver. Low mesh quality or poor initial conditions e.g. are more likely.

Cheers,

L
Lieven is offline   Reply With Quote

Old   April 1, 2013, 15:18
Default
  #6
Member
 
Tayo
Join Date: Aug 2012
Location: FL
Posts: 93
Rep Power: 3
tayo is on a distinguished road
Update!
I noticed that I got worst void fraction results as I increased calpha and calpha = 0 had "best result" (instead of the reverse occuring). Upward schemes also made it worst as expected too. Could this "unboundedness" be as a result of the interfaceCompression scheme? Any other recommendable schemes for the div(phi, alpha) and div(phirb, alpha)?

Last edited by tayo; April 1, 2013 at 16:28.
tayo is offline   Reply With Quote

Old   April 4, 2013, 03:42
Default
  #7
Member
 
Tayo
Join Date: Aug 2012
Location: FL
Posts: 93
Rep Power: 3
tayo is on a distinguished road
Hello all,

I've been able to fix the issue. First of all, I discovered that the problem of unbounded alpha1 was not unique to interDyMFoam alone, it also blew up in interFoam. By the way, my flow velocity was quite high (~1m/s) but alpha1 still blew up even with low vel (~0.01m/s). The div schemes did not help much, neither did a very very low maxAlphaCo (0.01).

To solve it, I solved the solution implicitly setting Sp as zero. But for Su term, I defined as divU*alpha1. This extra divergence term helped keep the alpha1 equation stable along with the right combination of maxAlphaCo. This has kept my max alpha1 bounded to 1 while you won't lose computation time since maxAlphaCo of 0.4 has worked fine. Hope this helps anyone else with unbounded alpha1 issue. Thanks
nimasam, vbnhfylbh and mecman like this.
tayo is offline   Reply With Quote

Old   July 14, 2013, 10:36
Default
  #8
New Member
 
Kshitij kunte
Join Date: Jun 2011
Posts: 16
Rep Power: 5
k.kshitij is on a distinguished road
Hi,

I simulating a nozzle flow using k-e turbulence model in interFoam, and getting a negative phase fraction. I'm a newbie to C programming, can you tell where to add the corrections you have given. I ran a grep command to find out where the SpType is used and found
these locations
applications/solvers/multiphase/interFoam/LTSInterFoam/MULESTemplates.C
src/finiteVolume/fvMatrices/solvers/MULES/MULESTemplates.C

But didnt find where Sp is defined in them, can you please guide me through this.
k.kshitij is offline   Reply With Quote

Old   July 17, 2013, 17:38
Default
  #9
Member
 
Tayo
Join Date: Aug 2012
Location: FL
Posts: 93
Rep Power: 3
tayo is on a distinguished road
Quote:
Originally Posted by k.kshitij View Post
Hi,

I simulating a nozzle flow using k-e turbulence model in interFoam, and getting a negative phase fraction. I'm a newbie to C programming, can you tell where to add the corrections you have given. I ran a grep command to find out where the SpType is used and found
these locations
applications/solvers/multiphase/interFoam/LTSInterFoam/MULESTemplates.C
src/finiteVolume/fvMatrices/solvers/MULES/MULESTemplates.C

But didnt find where Sp is defined in them, can you please guide me through this.
Hi Kshitij, you're probably solving interFoam explicitly. See interPhaseChangeFoam for example on how to add Sp & Su terms and then solve implicitly. You're probably not doing any phase change for now so set Sp to zero. However, to ensure that alpha1 stays bounded, include "divU*alpha1" in the Su term. Hope this helps.
tayo is offline   Reply With Quote

Old   September 5, 2013, 03:09
Default
  #10
Member
 
Hale
Join Date: May 2013
Posts: 53
Rep Power: 3
Hale is on a distinguished road
Quote:
Originally Posted by tayo View Post
Hi Kshitij, you're probably solving interFoam explicitly. See interPhaseChangeFoam for example on how to add Sp & Su terms and then solve implicitly. You're probably not doing any phase change for now so set Sp to zero. However, to ensure that alpha1 stays bounded, include "divU*alpha1" in the Su term. Hope this helps.
Hi Tayo,

I am very new to OpenFoam and C++ coding and I'm facing the same problem as yours where alpha1 becomes negative. Would you please post the files with required changes in order to avoid this problem?

I really appreciate your help.
Hale
Hale is offline   Reply With Quote

Old   September 10, 2013, 03:13
Default
  #11
Member
 
Jens Höpken
Join Date: Apr 2009
Location: Duisburg, Germany
Posts: 78
Rep Power: 7
jhoepken is on a distinguished road
Send a message via Skype™ to jhoepken
Quote:
Originally Posted by Hale View Post
Hi Tayo,

I am very new to OpenFoam and C++ coding and I'm facing the same problem as yours where alpha1 becomes negative. Would you please post the files with required changes in order to avoid this problem?

I really appreciate your help.
Hale
Have you double checked your boundary conditions?
jhoepken is offline   Reply With Quote

Old   September 13, 2013, 08:14
Default
  #12
Member
 
Hale
Join Date: May 2013
Posts: 53
Rep Power: 3
Hale is on a distinguished road
Quote:
Originally Posted by jhoepken View Post
Have you double checked your boundary conditions?
I solved the problem. There was problems with the boundary conditions :-)
Hale is offline   Reply With Quote

Old   September 17, 2013, 04:42
Default
  #13
New Member
 
Galchenko Olga
Join Date: Nov 2012
Posts: 14
Rep Power: 3
Galchenko is on a distinguished road
Hi Hale!

I'm having the same problem as discussed before, though adding Su term as tayo adviced didn't help. What boundary conditions caused you problem? May be I have some similliar mistake..

Regards,
Olga
Galchenko is offline   Reply With Quote

Old   September 17, 2013, 05:00
Default
  #14
Member
 
Hale
Join Date: May 2013
Posts: 53
Rep Power: 3
Hale is on a distinguished road
Hi Galchenko,

I had zeroGradient on the both pressure and velocity for the inlet and zeroGradient for the velocity and a negative pressure for the outlet, which was equal to the pressure difference between inlet and outlet. This was apparently a very poorly defined boundary condition for my system which made it very unstable and therefore alpha1 became negative.

My intention by setting those boundary conditions was to let the model determine the velocity at the inlet but the system was apparently an overdetermined system which could not be solved in OF.

I changed the BC to the following and it worked fine:

Inlet:
U: fixedValue uniform (x 0 0);
p_rgh: buoyantPressure;

Outlet
U: zeroGradient
p_rgh: fixedValue uniform 0;
tikulju and vbnhfylbh like this.
Hale is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Negative alpha1 using interDyMFoam jrrygg OpenFOAM Running, Solving & CFD 14 March 2, 2013 10:26
same geometry,structured and unstructured mesh,different behaviour. sharonyue OpenFOAM Running, Solving & CFD 13 January 2, 2013 22:40
alpha1 is unbounded GerhardHolzinger OpenFOAM Running, Solving & CFD 1 October 17, 2012 05:25
What is alpha1 in interDyMFoam physics1 OpenFOAM Running, Solving & CFD 2 July 4, 2012 07:20
alpha or alpha1 in interFoam & interDyMFoam wavytracy OpenFOAM Bugs 3 September 10, 2009 02:51


All times are GMT -4. The time now is 05:48.