Slow run with rhoCentralFoam
 

helo ,
As a beginner in OF , i want to simulate the flow through my geometry after conversion . I have fuel and air inlet with different velocity . I am trying to use the rhoCentralFoam solver . but after giving a run my simulation is goin on from last 24 hours and i had given a end time of 10 and delta t as 0.0025 .
any anybody please guide me why this is happening ?

Greetings Sonu,

Since your a beginner with OpenFOAM, I have to ask: have you studied the first tutorial in the OpenFOAM User Guide? Namely this one: http://www.openfoam.org/docs/user/cavity.php#x5-40002.1

In addition, if you run checkMesh, you'll see some important information about your mesh, such as:

• The total number of cells.
• The minimum cell volume.

Best regards,
Bruno

I didn't understand your problem,you mean it has taken a long time?

helo Bruno ,
i had read the tutorials and the problem is that its taking long time to finish simulation . and the mesh info is as follows :

P { margin-bottom: 0.08in; }

Mesh stats
points: 298650
internal points: 0
faces: 594092
internal faces: 295444
cells: 148256
faces per cell: 6
boundary patches: 6
point zones: 0
face zones: 0
cell zones: 0
Min volume = 0.030014. Max volume = 26.4353. Total volume = 329080. Cell volumes ok

whats your case,maybe its the nature of your problem,my run takes 6 hours for .000933 s !
its hard to answer without further information,if its not the case,maybe your settings are not correct.what you have set maxCo if use?

Well, reading doesn't mean that you studied it ;)

OK then, a few questions:

1. In the output of the rhoCentralFoam solver, what Courant number values is it giving you for each time iteration?
2. Are you running the case in serial or in parallel?
3. How long does it take to run each time iteration?
4. How exactly did you run the case? More specifically, what steps did you take to run it?
5. What settings do you have inside the files "system/fvSchemes" and "system/fvSolution"?
   • (Attach the files or follow the instructions from the second link on my signature for pasting code with "[CODE]".)
6. On which tutorial case did you base your case on?

helo Ehsan ,
actually my problenm is just simple i am just trying to simulate flow through my geometry which has 2 inlets one for fuel and other is for air . I had given end time as 10 s and its around 20 hrs and only 4 s simulation is over till now ....i had given only p,u and t variables in the 0 file .

so can you please guide me is there anything wrong ?? thanks alot

helo bruno ,

I am running it in series . and for running it i used following commands :
fluentMeshToFoam //for mesh conversion)
P { margin-bottom: 0.08in; } transformPoints -scale '(0.01 0.01 0.01)' ///scaling of geometry
rhoCentralFoam //solver


it is based on the tutorial of the oblique shock under the compressible flow in rhocentralfoam solver .



this is what its showing in the output :


Mean and max Courant Numbers = 0.0229302 0.200008
deltaT = 4.3472e-14
Time = 4.45301e-09

diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
diagonal: Solving for rhoUx, Initial residual = 0, Final residual = 0, No Iterations 0
diagonal: Solving for rhoUy, Initial residual = 0, Final residual = 0, No Iterations 0
diagonal: Solving for rhoE, Initial residual = 0, Final residual = 0, No Iterations 0
ExecutionTime = 70775.2 s ClockTime = 70801 s

and i am using the files of system of oblique shock tutorials only .



thanks for helping ....

deltaT = 4.3472e-14 ???????
your BC's has some trouble,how much is the maximum velocity?when velocity be too high deltaT becomes too low so that courant number stay constant.

helo Ehsan ,

The maximum velocity is 30 m/s i.e for fuel inlet and the maximum CO no in control dict file is .0.2 .

then the problem may be with the mesh,maybe it has some too small cells.do a checkMesh as Bruno said and submit it here in the forum.

Sonu already posted that info in post #4.

@Sonu: My guess is that you have a cell somewhere that does not have a good-enough shape for the massive speed you have.
I suggest that you stop the run and do some post-processing with ParaView, namely use the "Slice" filter and check where the speeds are the highest (by representing the "U" field).

In addition, you can calculate the Courant number onto a field by running the following command, after the case has stopped:
It should give you a new field named "Co" that you can see in ParaView. Use that field and the Slice to search for where you have the highest Courant number values.


Beyond this, I suggest that you also read this post: http://www.cfd-online.com/Forums/ope...tml#post446350 post #17 - it should give you some ideas on how to diagnose cases.

Best regards,
Bruno

ok i will do the above said and check my mesh again .
thanks alot Bruno and Ehsan for helping ...:)

helo ,

sori but i tried to see what happen when i wl give the run time as 1 s in control dict . but i think now also its gonna take long time for it as its showing in o/p :

Mean and max Courant Numbers = 0.0212188 0.20001
deltaT = 4.3461e-16
Time = 1.16148e-12

diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
diagonal: Solving for rhoUx, Initial residual = 0, Final residual = 0, No Iterations 0
diagonal: Solving for rhoUy, Initial residual = 0, Final residual = 0, No Iterations 0
diagonal: Solving for rhoE, Initial residual = 0, Final residual = 0, No Iterations 0
ExecutionTime = 1882.22 s ClockTime = 1882 s
i.e

large delta T so what it mean? please tell me :)

Hi Sonu,

The post on the other is just an example. On that other case, setting the total time to 1s was enough.
But for you, given that it quickly reduces to such a small delta T, I advise you to change the keywords to the following ones in your "system/controlDict" file:
Best regards,
Bruno

helo Bruno ,
yes it worked and it stops at very next time :) . but i am wondering whats wrong with my mesh if everything else is rite , i had done simulation with this mesh only in fluent and there its working fine ....

Hi Suno
I can have a look into the case if you want and send it to me to see if I can do something for the case.

Hi Sonu
1)mesh seems not be correct,it has lower resolution near walls,is it what you want?
2)p in outlet should not be zeroGradient,you have to set a back pressure in outlet.
check these and let me know.

greetings Ehsan ,

sori for late reply . mesh resolution is kept low near wall purposely and when i am giving the back pressure at outlet it is not accepting it , suggesting to choose other options . but same case when i tried in rhoPimpleFoam its working fine .

Maximum velocity in rhoCentralFoam
 

Please tell me what is the maximum velocity for operation in rhoCentralFoam, Since I can't exceed above 50 m/s.