[YinJian]

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.

[hjasak]

Try using upwind on convection and limited laplacian on diffusion. If this does not help, Your outlet boundary conditions are wrong.