# bounding k and bounding epsilon over the limit

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October 7, 2023, 12:37
bounding k and bounding epsilon over the limit
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Hello,

I am using multiphaseInterFoam to simulate one case.The model consists of a horizontally positioned cylindrical pipe with a diameter of 115mm and a length of 5m. On the left side of the pipe is a velocity inlet with a velocity of 12 m/s, and on the right side is a wall boundary. Along the side of the pipe, there are multiple vertically oriented cylindrical small pipes with a diameter of 12mm and a length of 500mm each. The pressure outlet is located at the end of these small pipes, with a pressure of 0. For this case i am using k-epsilon turbulence model.

I have created unstructured mesh and quality of mesh seems to be right. CheckMesh report is as given below:
Checking geometry...
Overall domain bounding box (0 -0.556 -0.48451) (5 0.556 0.48451)
Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
Mesh has 3 solution (non-empty) directions (1 1 1)
Boundary openness (2.06719e-17 4.86465e-18 1.85385e-17) OK.
Max cell openness = 4.18769e-16 OK.
Max aspect ratio = 18.761 OK.
Minimum face area = 1.70871e-12. Maximum face area = 5.02513e-05. Face area magnitudes OK.
Min volume = 7.33752e-10. Max volume = 2.49585e-07. Total volume = 0.0532077. Cell volumes OK.
Mesh non-orthogonality Max: 65.9097 average: 8.02965
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 2.57036 OK.
Coupled point location match (average 0) OK.
Mesh OK.

When I run the simulation, the values of k and epsilon suddenly become negative, and the positive values become extremely large, eventually leading to divergence.

What should I do to ensure that the simulation runs smoothly? Thanks for the help in advance.
Attached Images
 model1.png (48.0 KB, 11 views) mesh.png (109.2 KB, 13 views) meshcheck.jpg (69.4 KB, 10 views)
Attached Files
 case.zip (9.8 KB, 1 views)

 October 8, 2023, 09:34 #2 Senior Member   Hrvoje Jasak Join Date: Mar 2009 Location: London, England Posts: 1,902 Rep Power: 32 Try using upwind on convection and limited laplacian on diffusion. If this does not help, Your outlet boundary conditions are wrong. __________________ Hrvoje Jasak Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk

 Tags bounding epsilon, bounding k