# Bounded scheme gives unbounded solution

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

 February 20, 2009, 14:49 Hi everyone With almost #1 Senior Member     su junwei Join Date: Mar 2009 Location: Xi'an China Posts: 151 Rep Power: 12 Sponsored Links 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

 October 10, 2011, 04:34 #2 New Member   ehsan yasari Join Date: Mar 2009 Location: Gothenburg, Sweden Posts: 14 Rep Power: 10 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

 October 11, 2011, 06:34 #3 Senior Member     ata kamyabi Join Date: Aug 2009 Location: Kerman Posts: 323 Rep Power: 11 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

 November 18, 2011, 03:35 #4 New Member   Hamed Kh. Join Date: Dec 2010 Location: Tehran , Iran Posts: 18 Rep Power: 8 Hi su junwei did u try with smaller deltaT? it has a very important role.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Sam Tecplot 1 August 20, 2008 12:18 ankgupta8um OpenFOAM Running, Solving & CFD 1 June 19, 2006 05:03 Coriolius CFX 8 August 1, 2004 18:39 Dipankar Chatterjee FLUENT 0 March 18, 2002 07:35 Igor Antropov Main CFD Forum 0 June 29, 1998 15:45