# Problem going to second order

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 February 7, 2008, 19:36 I have a fully converged solut #1 Member   Andrew Burns Join Date: Mar 2009 Posts: 36 Rep Power: 8 I have a fully converged solution (residuals between 1e-6 and 1e-8) using first order upwind discretisation. I want to switch to second order to get more accurate drag results however every time I try switching to a second order scheme my k and epsilon values go unbounded (negative) within a few iterations, stay that way and my forces go dodgy. My discretization schemes are currently: gradSchemes { default Gauss linear; grad(p) Gauss midPoint; grad(U) Gauss linear; } divSchemes { default none; div(phi,U) Gauss limitedLinearV 1; div(phi,k) Gauss limitedLinear 1; div(phi,epsilon) Gauss limitedLinear 1; div(phi,R) Gauss linear; div(R) Gauss linear; div(phi,nuTilda) Gauss linear; div((nuEff*dev(grad(U).T()))) Gauss linear; } laplacianSchemes { default none; laplacian (nuEff,U) Gauss linear corrected; laplacian ((1|A(U)),p) Gauss linear limited 1; laplacian (DkEff,k) Gauss linear limited 1; laplacian (DepsilonEff,epsilon) Gauss linear limited 1; laplacian (DREff,R) Gauss linear corrected; laplacian (DnuTildaEff,nuTilda) Gauss linear corrected; } Running a simple steady-state solution in simpleFoam. My current relaxation factors are p 0.3 U 0.5 k 0.3 epsilon 0.2 R 0.7 nuTilda 0.7 I've also tried: QUICK linearUpwind (which threw me an error for some reason) limitedVanLeer (strictly bound to be positive for k and epsilon, which it appeared to ignore) SFCD Of all of those the most stable one appeared to be SFCD but even so k and epsilon unbounded fairly rapidly. Can someone help me out? I know other people must be able to perform successful second order solutions in openfoam but I just can't make it work.

 February 11, 2008, 18:28 Can anyone help me here? It se #2 Member   Andrew Burns Join Date: Mar 2009 Posts: 36 Rep Power: 8 Can anyone help me here? It seems that if I take any fully converged first order solution and then switch to second order my k and epsilon (and omega when using komegaSST) go unbounded and stay there.

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