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I additionally tried using segregated solvers (2 segregated solvers 1 for pressure and velocity and 1 for temperature). I have read this should help solve highly nonlinear problems. But again after about 30 seconds into the transient solutions, the solution fails.

Edited: I added some of the solutions so readers do not have to open and run the model. Solutions are plotted for times 20, 30 and 40 seconds into the simulation.

Can anyone offer any tips or solution. I am still struggling with this problem. Thanks

Hi

for me your model is missing a few things:

1) you have some nodes not defined on any BC
2) you have no inlets (not strictly required)
3) outlets as inlets might act in both directions, but you must define the boundary temperature somewhere
5) if you do not force an inlet your outlet might become an inlet but T is not defined there
6) check carefully the equations for "open Boundary" and see if you cannot use that instead of outlet & outflow
7) if you use 6, note that you then do not have any gauge pressure defined, you need to add a fixed point or BC with a p=0 somewhere, note that p changes with elevation by about 12 Pa/m at sea level

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Good luck
Ivar

I will try your tips and post the results.
Thanks,
Lucas

Here are the results as promised in case there are others with this problem.
I tried to refine the mesh and the problem seemed to have trouble converging. Has anyone experienced this behavior before?

Hi,

I am also facing the same problem in getting the stationary solution converged for my conj.ht. model (attached). I had been advised to study it in two steps:
1- transient (say 0-1 sec) in order to set reasonable initial values for the stationary solution.
2- stationary with dependent variables on the previous time dependent solution.

But it also did not help. I tried also to set different mesh sizes/strategies, again it did not help. I tried to change solver options, it did not help.

@ Ivar, if you looked to my model you will find it includes all basic BCs/suggestions you advised to Lucas. But it is still not converging.

The model is really not that complicated. If we can not just get the steady state solution, It would be nice if we can get some physical explanation why?

Thanks a lot,
Tamer

I forgot to clarify that, that my model works fine in transient but the problem is in the stationary solution.

Thanks,
tamer

Hi

first of all I'll advise you to check if you cannot upload the latest patch to v4.3a, you do not have the latest version I see

then I would propose that you fillet off all your corners with small radii, your sharp edges makes singularities

Further I'm not sure why you solve first for time and then a stationary, as for t=0 you do already solve the equivalent of a stationary case

T follow what is going on, I recommend to turn ON the plot while solving FORA all solver steps, you will then notice that your fluid is rapidly getting turbulent and that your solver has issues to find steady solutions

Finally I would also recommend that you rebuild your model from scratch, you have disabled a few nodfes, bu I notice that I cannot even delete these, so it's as if your internal pointers in the file have become corrupted. This happens sometimes, when you modify heavily a model, adding and removing nodes and solvers over longer periodes


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Good luck
Ivar