Solving navier stokes equation gives no convergence

[ggg]

I already solved the stokes equation and was trying to generalize it to solve the steady NS equation.

I saw the step-57 tutorial but I have a mesh from file (while the tutorial create in dealii and refine, things that I'm not allowed to do) and also uses line search algorithm, which also can't perform.

The general structure of the program is: setup vectors, sparsity and matrices (pressure and  velocity), newton iteration where first solve the stokes problem to get the initial guess for newton (Re will always be < 200 in my test case, for now), and the start to iterate, at each iteration:

- assemble the system

- solve the linearized system

I know the stokes solution is correct. But for the NS solution I have the residual decreasing at first 2 steps and then increasing, leading to divergence (around step 16 dealii fires the no convergence). The assembly is the same as the tutorial at step-57.

It's becoming really frustrating, so if anyone can help I really appreciate. I give you the code in case my explanation wasn't clear.

https://drive.google.com/drive/folders/1igXMgWq2g6UPRxaRE9Ot1jU5L_eUW9Wk?usp=sharing

PS: the mesh is fine since already used for previous problems.

[blais...@gmail.com]

Can you tell us a bit more about what you have tried? For example, in the limit of low Re (say Re=0.1 or Re=1) does your non-linear solver converge? 

Have you tried making a manufactured solution to get your convergence order to see if everything is all fine?

RE=200 can be quite heavy for straight-up Newton solver. The linear-search generally really helps for cases when you are trying to get a steady-state solution.

[ggg]

I've tried with really smalls re (also 0.1) and no, it doesn't converge. I'll try the manufactured solution