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

Bounded scheme gives unbounded solution

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

Reply
 
LinkBack Thread Tools Display Modes
Old   February 20, 2009, 14:49
Default Hi everyone With almost
  #1
Senior Member
 
su_junwei's Avatar
 
su junwei
Join Date: Mar 2009
Location: Xi'an China
Posts: 151
Rep Power: 10
su_junwei is on a distinguished road
Send a message via MSN to su_junwei
Hi everyone

With almost all the bounded scheme for alpha, twoPhaseEulerFoam always gives the negative values for alpha in my test cases.

The numerical schemes I used are listed below

FoamFile
{
version 2.0;
format ascii;
class dictionary;
object fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
default CrankNicholson 1;
//ddt(alpha) boundedBackward 0.5;
}

gradSchemes
{
default Gauss linear;
}

divSchemes
{
default none;
div(phia,Ua) Gauss MUSCL ;
div(phib,Ub) Gauss MUSCL ;
div(phib,k) Gauss Gamma 1;
div(phib,epsilon) Gauss Gamma 1;
div(phi,alpha) Gauss Gamma01 1;
div(phir,alpha) Gauss Gamma01 1;
div(phi,Theta) Gauss Gamma 1;
div(Rca) Gauss linear;
div(Rcb) Gauss linear;
}

laplacianSchemes
{
default none;
laplacian(nuEffa,Ua) Gauss linear limited 1.0;
laplacian(nuEffb,Ub) Gauss linear limited 1.0;
laplacian((rho*(1|A(U))),p) Gauss linear limited 1.0;
laplacian(alphaPpMag,alpha) Gauss linear limited 1.0;
laplacian((alphak*nuEffb),k) Gauss linear limited 1.0;
laplacian((alphaEps*nuEffb),epsilon) Gauss linear limited 1.0;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
p;
}

A segment for residual is

DILUPBiCG: Solving for alpha, Initial residual = 0.000124877, Final residual = 3.70067e-14, No Iterations 5
Dispersed phase volume fraction = 0.22513 Min(alpha) = -5.31042e-05 Max(alpha) = 1
DILUPBiCG: Solving for alpha, Initial residual = 0.000124877, Final residual = 3.70067e-14, No Iterations 5
Dispersed phase volume fraction = 0.22513 Min(alpha) = -5.31042e-05 Max(alpha) = 1
DILUPBiCG: Solving for alpha, Initial residual = 1.3635e-05, Final residual = 1.13321e-15, No Iterations 4
Dispersed phase volume fraction = 0.22513 Min(alpha) = -5.58751e-11 Max(alpha) = 1.00002
DILUPBiCG: Solving for alpha, Initial residual = 1.3635e-05, Final residual = 1.13321e-15, No Iterations 4

Sometimes the Max(alpha) > 1

I have used the low diffusion bounded scheme for both unsteady term and convection term. Why the negative alpha always appears.

Any suggestion is appreciated.

Regards, Junwei
su_junwei is offline   Reply With Quote

Old   October 10, 2011, 04:34
Default
  #2
New Member
 
ehsan yasari
Join Date: Mar 2009
Location: Gothenburg, Sweden
Posts: 14
Rep Power: 8
ehsanyasari is on a distinguished road
Hi Junwei

I have the similar problem with my simulation. Did you figure it out how to fix this problem? I was wondering if you could help me.

Thanks,
Ehsan
ehsanyasari is offline   Reply With Quote

Old   October 11, 2011, 06:34
Default
  #3
ata
Senior Member
 
ata's Avatar
 
ata kamyabi
Join Date: Aug 2009
Location: Kerman
Posts: 322
Rep Power: 8
ata is on a distinguished road
Hi
This is not an unusual situation. I think these schemes are bounded on a quadrangular and orthogonal mesh. But I think if you use a good mesh with good boundary conditions alpha remains almost bounded.
As your results show upper bound of alpha (Max(alpha) = 1.00002 ) has problem not the min of it (Min(alpha) = -5.58751e-11). May be you can get better results with changing BC.s our may be using better initial conditions.
Good luck
Bets regards

Ata
ata is offline   Reply With Quote

Old   November 18, 2011, 03:35
Default
  #4
New Member
 
H Kh
Join Date: Dec 2010
Location: Tehran , Iran
Posts: 15
Rep Power: 6
hkhosravi is on a distinguished road
Hi su junwei

did u try with smaller deltaT? it has a very important role.
hkhosravi 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
Bounded slice in Tecplot possible? Sam Tecplot 1 August 20, 2008 12:18
Calculation of bounded scalars ankgupta8um OpenFOAM Running, Solving & CFD 1 June 19, 2006 05:03
Question about meshing / solution scheme of CFX Coriolius CFX 8 August 1, 2004 18:39
single liquid fuel droplet combustion(unbounded) Dipankar Chatterjee FLUENT 0 March 18, 2002 07:35
Spectral methods, unbounded region Igor Antropov Main CFD Forum 0 June 29, 1998 15:45


All times are GMT -4. The time now is 05:50.