T Junction Stability
I am running a T-Junction case (both water and pipes), using the chtMultiRegionFoam solver.
First I run a steady state and now I am doing a URANS with the steady state output as initial value.
I use k-OmegaSST Low Reynolds model.
I don't know why but the simulation always crashes after 3 iterations... I changed parameters in fvSolution and fvSchemes, but still, it's always after 3 iterations.
My time step is so low that the initial Courant is only 0.1
The problem is at the outflow pipe. Inflow is in another place with much higher velocity but it's working fine. I attach some pictures
No problems at all in checkMesh.
Any idea of how to solve this?
I would really appreciate any kind of comments.
A few things you can easily try:
1. Set the time step 10x smaller such that courant number < 1.0
2. Take upwind-schemes to increase stability. It might not be interestiging from numerical point of view, but at this moment the priority is not obtaining 'a' result and not the 'best' result. Later-on you can switch to 2nd order schemes with the upwind-solution as initial condition.
3. First run a few timesteps with potentialFoam to improve the initial conditions
Thanks for the response Lieven!
1 and 2 I have already tried them. But I don't see any improvement in the simulation.
I will see what happens with the potentialFoam
I found out a strange thing playing around with the case.
If I change the density at thermphysicalProperties file it's stable! (the commented part is what I changed) Although the min/max temperature start decreasing/increasing with the iteration
Thanks a lot
Ok, best thing to do then is first let the simulation run with
(863.76 0 0 0 0 0 0 0)
(863.76 1.2436 0 0 0 0 0 0)
and finally with
(863.76 1.2436 -0.0026 0 0 0 0 0)
So always start from the previous simulation as initial condition. If the simulation gets unstable, try to figure out why.
By the way, you write 1.2436 but according to your correlation it should be -1.2436
Oh, mistake. The code is correct, the commented equation isn't.
We are now doing the process that you said. I will tell you how it goes.
Thanks again Lieven!
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