Mesh problem/ coarse OK  fine not OK
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Hello everyone,
I am trying to simulate maximum flow inside a tiny pipe using totalPressure = 106325 Pa boundary and fixedPressure=101325 Pa. Dimensions of pipe is (0.004 m length and 0.003 mm diameter) Using a very coarse netgen mesh and about 15000 iterations, a fully converged solution is obtained. However, when refine the mesh, a solution cannot be obtained due to failure in the thermophyical or the pressure model. Anyone having ideas why the refined mesh cannot converge. Pictures are attached, 'fine2' is the fine mesh and 'coarse' is the coarse mesh. Coarse picture is posted separatley. Thanks 
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Coarse mesh attached

hi
did you use both totalPressure and fixedValue? which is converged?both act same? 
Thanks for a quick answer.
I used inlet { type totalPressure; p0 uniform 106325; value uniform 106325; gamma 1.4; } outlet { type outletInlet; value uniform 101325; outletValue 101325; } How do I know from the output if inlet or outlet has converged? Furthermore, it appears that the underlying problem might be k or epsilon. If I change the relaxation factors for the coarse model to a slightly higher value than 0.4, OpenFOAM returns the same problem. 
In your problem you have pressure in both the inlet and the outlet?
I think pressure on both inlet and outlet is a classical CFD headache. Maybe try to follow how they do it in the Tjunction tutorial (link to p setup): https://github.com/OpenFOAM/OpenFOAM.../TJunction/0/p I believe you have to reduce the pressure as the velocity increases using the relation ptot=p0U^2/2 at the inlet. They put it in the form of a table in the p file. It is however a transient problem that uses pimpleFoam. Ignore this, your mesh is very simple, it is unlikely that it is leaky: Quote:

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@JR22
Interesting idea but I am not sure I follow you. Please explain further. I have uploaded the system as well the bc files in case someone has time to look through it (valid for both meshes with the result that the coarse mesh is working and the fine not working). 
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I have attached the second last iteration before the solver crash on the fine mesh. The last iteration looks rouhgly the same but in the lower left corner (inlet, left side) the maximum magnitude of U, epsilon, p locally spikes to values of ~1e18, 2e25, 1e22, respectivley.
The flow direction follows Z axis While writing this message further investigated the pictures and added a glyph filter which brings a lot of more information and maybe an explanation as well. It seems like I have vortices close to the wall/inlet. My guess is that this comes from no slip BC. Maybe a coarse mesh is very forgiving and does not allow the flow to turn backwards as there is no small cells to represent the turbulence flow. A glyph picutre is also attached for the fine mesh. In case this is a BC problem, can someone give further guidance of how to properly set up the BC:s for this kind of problem? Thanks! 
Problem solved
Solutions: Using a structured mesh Choosing second order upwind Fine tuning k e initial values Fine tuning relaxation parameters during running solver. I found an old post yesterday pointing out that ke is very hard to get working. A more stable way is to use RNG /realizable or omegaSST. 
Can you post what your fvSchemes looks like when you start your run? Thanks

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snGradSchemes default corrected interpolationSchemes default linear laplacianSchemes Gauss linear corrected divSchemes div(phi,U) bounded Gauss upwind > switch to Gauss linearUpwind phi after some it div((muEff*dev2(T(grad(U)))) Gauss linear others div(phi, XXX) bounded Gauss cubic gradSchemes default linear ddtSchemes default steadyState 
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I have an issue on this problem.the pressure goes very low and velocity goes very high. whats the reason? when i limit U on the ptch to 350m/s the neighbour cells act as i told above again. why table is inverse from low value to high value for p? 
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