[MisterTummy]

Hi there,

I have two simulations of a pipe with a junction at an angle. Both the simulations have exactly the same parameters, the only thing that varies is the geometry (one of them has both pipes straight, the other has a pipe with a helical shape). I have solved a steady solution and both converged to a reasonable amount. However, once I run an implicit unsteady solver, only the straight pipe sim converges, the other diverges.

I have no idea why they won't both converge.

Parameters are:

- base size 0.02m
- implicit unsteady timestep: 0.01s
- Re = 800

- Laminar solver
- Segregated flow solver
- Constant density

Inlet is a velocity profile at the left and a negative velocity profile on the right, and a pressure outlet on the top.





Thanks for your help

[fluid23]

Show a plot of your residuals for your diverging transient case.

[MisterTummy]

Thanks for offering help though