I have a very long elbow tube. Convergence is too slow(by mass eq). How could I accelerate the convergence.

StarCD 3.26

Regards!

Maybe use the traditional approach: Starting of with a 1'st order solver scheme, then switch to 2'nd order later. Try to adjust the under relaxation factors to a lower level. It might help.

Convergence on mass is generally slow.

You might have to create a more suitable mesh.

try amg solver

If you are using second order differencing schemes, convergence will be slower in the beginning. But after reaching a stable stage, low relaxation factor doesn't help much and can be increased upto some level. But upto what level it is safe, i can't say as it depends very much on mesh, geometry and differencing scheme.

you can dynamically change the relaxation factor after a stable residual is reached.