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Trushar August 25, 2002 23:56

convergence problem
hi to all At present i m working on boiler second pass analysis using PHOENICS 3.4. My domain soze is x=19M y=18M z=30M. I am using K-epsiolon model for that. but when grid is coarse then no problem but when apply fine grid around 4,00,000 grid point then there is a converge problen

This is my fundamental run till i can't apply any detail obstacal like eco. tube bundle, reheater tube bundle, etc. If i apply all this detail then i think this software is not capable to hendle this type of problem. it just for simple problem.

In past year any people can handle this type of problem whit this software or not.

So plzz gide me that this type of problem can be handle by this software or it is not possiable

If i take all detail of different tube bundle then my grid point will be above 60,00,000 or more then what is happend.

Trushar Gohil Mech-Well Industries PVT. LTD. Mumbai India

leon mills August 26, 2002 18:43

Re: convergence problem

When refining your mesh you may need to revisit your relaxation parameters and or your global convergance criteria.

Look at the tutorials on fine grid meshing, where by the user places a fine mesh over areas of importance. This allows a coarser mesh to be used elsewhere and save on the number of grid points.

If you have a re-compliable version of P3.4 you can change the maximum number of cells the P3.4 can handle - I don't have this capacity but I know that it can be done.

Hope this helps.


Trushar August 26, 2002 23:52

Re: convergence problem
Thanks leon mills

can u sujest me normal range of convergence for this type of problem where grid point increase above 10,00,000.

second things is that when i apply porocity to some blockage then there is a convergence problem with K-E model so what to do.

thanks for ur valuable time. trushar

Vikas Kumar August 27, 2002 01:16

Re: convergence problem

Leon has pointed rightly that you have to refine grid in the area of importance and coarse grid should be used in other region. If you refine grid you have to reduce relaxation factor based on the residence time. It is suggested that you always start with coarse grid and keep on refining based on the accuracy required and computing time.

Vikas Kumar

leon mills August 27, 2002 20:13

Re: convergence problem

The relaxation parameters are more closely related to cell size, and the expected values (eg vel), in the cell being monitored.

Porosity & blockages - not sometime I know alot about as I dont really uses themthat much, but I have found that these areas need to have 1) a finer mesh 2) to be set up correctly - read the manuals and POLIS to get the exact details.

Also, check the point where you a inspecting convergence. Is it an accurate place, or a usefull place for convergence. Also look at the units - visually it may not have converged but if you are talk about 0.1 deg C in 1000 deg C it may have converged enough.

hope this helps.


Trushar August 27, 2002 23:40

Re: convergence problem
Thanks leon

i will trai for that. hope that will help me


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