delta T decreases suddenly in pimplefoam
hi
I have simulated tiny pipe with newtoniam incompressible flow which is laminar by pimplefoam but the time steps are getting smaller and smaller during the solution process(it start from 0.003 and after 10 time steps gets to 10e-23 and more)and finally it is divrged .courant was set as 1 and nothing has changed by increasing the amounts of nOuterCorrectors ,nCorrectors and nNonOrthogonalCorrector.what should I do ?any suggestion? Code:
Create time |
there is no idea?
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- Best Regards! |
thanks for your answer
these are fv solution and scheme Code:
solvers Code:
ddtSchemes |
You're welcome!
In fvscheme file try these instead of mentioned ones. Best is to try with 1st order and check your results. divSchemes { default none; div(phi,U) Gauss upwind; div(phi,k) Gauss upwind; div(phi,epsilon) Gauss upwind; div(phi,R) Gauss upwind; div(R) Gauss linear; div(phi,nuTilda) Gauss upwind; div((nuEff*dev(T(grad(U))))) Gauss linear; } Let us know about your results. post your reply here - Best Regards! |
that works and everyting is ok
thank you but may I ask you to explain how did you find that I mean what the big differnces are there between these two div schemes? thanks |
Good!
Actually, there are various ways to avoid such situations. One such problem could be due to the above situation. You can find the reference for these in any of the CFD books. These "div schemes" differ in order of accuracy and many other facts. Quick Hint: Upwind scheme is unconditionally stable of all. |
thanks
As you know yhis is a first order scheme, thus too diffusive and I will not get a good solution,am I right?and what is the solution |
Please, excuse for late reply. I was away from the desk.
Yes you're correct. With increased mesh resolution you can obtain very close solutions. I don't know the details of your problem case. It's always wise to compare the CFD results with the available resources (experimental or analytical). Anyways, with experience and literature survey you can gain grip over many of these CFD techniques. Best of Luck for your future endeavour. - Best Regards! |
thanks for protect and excuse me for lots of question (I am so curious ) but I promise that this is the last one :o
I think one way to decrease inaccuracy in using upwind linear in starting the algorithm with upwind and then changing it to more accurate schemes but I dont know when is the right time to do that,I mean is there any clue in the terminal that can aware us? thanks alot |
Actually, you can get comparable solution with upwind scheme too depending upon your problem case. Sometime, results obtained are comparable with the available resources. You can find many literature in which 1st order scheme give very near comparable solutions.
This is because CFD solution doesn't depend on these factors only. There are many other factors which are equally important for CFD solutions. It's always best to monitor residuals. Generally, convergence check tell us when to stop our iterations. I hope I tried to answer your queries. :) - Best Regards! |
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