# Natural Convection with icoFoam

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 July 23, 2012, 17:03 Natural Convection with icoFoam #1 Member   ,... Join Date: Apr 2011 Posts: 92 Rep Power: 7 Sponsored Links Hey Foamers I have added energy equation to icoFoam, and I am solving natural convection in cavity. The problem is that as I am using smaller and smaller time steps, the velocities become smaller and smaller, and I can not get a results which is independent of time step. So do you have any ideas to help me getting time step independent results?

 July 24, 2012, 04:23 #2 Senior Member     A_R Join Date: Jun 2009 Posts: 120 Rep Power: 10 dear mahdi do you add temperature truly? it seams that your solver has a problem. you should attach your solver. it is hard to make decision without looking to your solver

 July 24, 2012, 11:26 #4 Senior Member     A_R Join Date: Jun 2009 Posts: 120 Rep Power: 10 your changes are strange. for U: fvVectorMatrix UEqn ( fvm::ddt(U) + fvm::div(phi, U) - fvm::laplacian(nu, U) == -beta*(T - T0)*g ); for T: solve ( fvm::ddt(T) + fvm::div(phi, T) - fvm::laplacian(DT, T) ); where nu is viscosity and DT is conductivity your equation seems have a problem.

 July 24, 2012, 13:01 #5 Member   ,... Join Date: Apr 2011 Posts: 92 Rep Power: 7 Hi niaz Thanks for your comments. I tried with the new equations, but still have problem with dt. any more comments?

 July 24, 2012, 15:41 #6 Senior Member     A_R Join Date: Jun 2009 Posts: 120 Rep Power: 10 solve(UEqn == GravityVector*g*Density*(BetaT*(T-TNot)) - (fvc::grad(p))); I think that before the GravityVector, you should have (-)

 July 24, 2012, 15:45 #7 Member   ,... Join Date: Apr 2011 Posts: 92 Rep Power: 7 Thank you. But it will not fix the problem. It will only change the direction of U and V.

 July 24, 2012, 16:09 #8 Senior Member     A_R Join Date: Jun 2009 Posts: 120 Rep Power: 10 Can you show a contour of two results? your case is a bit strange.

 July 24, 2012, 16:10 #9 Senior Member     A_R Join Date: Jun 2009 Posts: 120 Rep Power: 10 at first, I suggest you to solve a forced convection to prove the exactness of the solver then add boussinesqe term to equation.

 July 26, 2012, 14:07 #10 Member   ,... Join Date: Apr 2011 Posts: 92 Rep Power: 7 I fixed the problem. The key is in order to get a proper behavior of velocity-pressure coupling in PISO algorithm, I should include the source term inside the velocity equation such that fvVectorMatrix UEqn ( fvm::ddt(U) +fvm::div(phi,U) -fvm::laplacian(ModifVisc,U) == GravityVector*betaT*(T-Tnot) ); solve(UEqn == -fvc::grad(p) );

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