Convergence problem

kulkarni_arjun · October 12, 2010, 03:10

Dear All,
Q1) While doing the simulation in cfx it gives me error as "floating point exception". I am working on turbomachinery . I have profiled pressure inlet and Zero static pressure outlet.
Q2) I have experimental results of turbine cascade, so is it ok to select component as rotor and give speed as Zero RPM.
Please reply..
Arjun

vidhya · April 5, 2011, 08:58

this is the error i got for multiphase simulation.. i have gone through enough threads regarding this.. still its not solved.. someone please help out with this....
-------------------------------------------------------------------+
| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| Floating point exception: Overflow |
| |
| |
| |
| |
| |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| Writing crash recovery file |
+--------------------------------------------------------------------+

Details of error:-
----------------
Error detected by routine POPDIR
CRESLT = ILEG

Current Directory : /FLOW/NAMEMAP

+--------------------------------------------------------------------+
| An error has occurred in cfx5solve: |
| |
| The ANSYS CFX solver exited with return code 1. No results file |
| has been created.

kulkarni_arjun · April 5, 2011, 10:38

Vidhya,
I had also faced same problem.
1) First you check your boundary conditions, if they are correct then
2) Refine your meshing.if still not solved
3) Extend your outlet i.e increase fluid domain for you search in CFD help you will find in what ration you have to extend outlet.

Arjun

vidhya · April 6, 2011, 01:17

hi arjun,
thanks for the tips..
but i am facing a different problem now..
i am simulating multiphase gas-liquid flow using 2 rushton and 1 pitch blade.. when i use this combination i dont get any errors.. even if i get i can easily set it right by changing timestep value or initial conditions.
but when i ran the same using 3 rushton i am having problem.. what will be the reason for it..!!
i am using multiple reference frame approach and mesh quality is fine.
even single phase simulation is not possible with 3rushton combinations.

kulkarni_arjun · April 6, 2011, 05:28

Vidhya,
return flow error occurs when flow take place towards inlet i.e in opposite direction, so it creates wall to avoid it and when it creates wall at 100% of area it shows this error. for this flow has to simulate slowly.
I don't know what is rushton means.
which cfx version you are using?

refine your mesh further it may help you.

vidhya · April 6, 2011, 07:48

i am using cfx 11.. and impellers here are nothing but turbine blades. rushton mainly for radial flow.. i am new to cfd. jus started learning it.. so may be i wil decrease the timescale factor and see for results and let u kno.. thanks

delaneyluke · April 7, 2011, 02:41

POPDIR refers to a memory management subroutine. So it could imply that the memory is not sufficient or not being distributed.
Floating point overflow refers to a variable divided by zero which is generally evidence of divergence, so a larger timestep might help.

October 12, 2010, 03:10	Convergence problem	#1
kulkarni_arjun New Member Arjun Join Date: Oct 2010 Location: India, IIT Madras Posts: 6 Rep Power: 16	Dear All, Q1) While doing the simulation in cfx it gives me error as "floating point exception". I am working on turbomachinery . I have profiled pressure inlet and Zero static pressure outlet. Q2) I have experimental results of turbine cascade, so is it ok to select component as rotor and give speed as Zero RPM. Please reply.. Arjun

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April 5, 2011, 08:58		#2
vidhya New Member Join Date: Jan 2011 Posts: 24 Rep Power: 16	this is the error i got for multiphase simulation.. i have gone through enough threads regarding this.. still its not solved.. someone please help out with this.... -------------------------------------------------------------------+ \| ERROR #001100279 has occurred in subroutine ErrAction. \| \| Message: \| \| Floating point exception: Overflow \| \| \| \| \| \| \| \| \| \| \| +--------------------------------------------------------------------+ +--------------------------------------------------------------------+ \| Writing crash recovery file \| +--------------------------------------------------------------------+ Details of error:- ---------------- Error detected by routine POPDIR CRESLT = ILEG Current Directory : /FLOW/NAMEMAP +--------------------------------------------------------------------+ \| An error has occurred in cfx5solve: \| \| \| \| The ANSYS CFX solver exited with return code 1. No results file \| \| has been created.

April 5, 2011, 10:38		#3
kulkarni_arjun New Member Arjun Join Date: Oct 2010 Location: India, IIT Madras Posts: 6 Rep Power: 16	Vidhya, I had also faced same problem. 1) First you check your boundary conditions, if they are correct then 2) Refine your meshing.if still not solved 3) Extend your outlet i.e increase fluid domain for you search in CFD help you will find in what ration you have to extend outlet. Arjun

April 6, 2011, 01:17		#4
vidhya New Member Join Date: Jan 2011 Posts: 24 Rep Power: 16	hi arjun, thanks for the tips.. but i am facing a different problem now.. i am simulating multiphase gas-liquid flow using 2 rushton and 1 pitch blade.. when i use this combination i dont get any errors.. even if i get i can easily set it right by changing timestep value or initial conditions. but when i ran the same using 3 rushton i am having problem.. what will be the reason for it..!! i am using multiple reference frame approach and mesh quality is fine. even single phase simulation is not possible with 3rushton combinations.

April 6, 2011, 05:28		#5
kulkarni_arjun New Member Arjun Join Date: Oct 2010 Location: India, IIT Madras Posts: 6 Rep Power: 16	Vidhya, return flow error occurs when flow take place towards inlet i.e in opposite direction, so it creates wall to avoid it and when it creates wall at 100% of area it shows this error. for this flow has to simulate slowly. I don't know what is rushton means. which cfx version you are using? refine your mesh further it may help you.

April 6, 2011, 07:48		#6
vidhya New Member Join Date: Jan 2011 Posts: 24 Rep Power: 16	i am using cfx 11.. and impellers here are nothing but turbine blades. rushton mainly for radial flow.. i am new to cfd. jus started learning it.. so may be i wil decrease the timescale factor and see for results and let u kno.. thanks

April 7, 2011, 02:41		#7
delaneyluke Senior Member Join Date: Mar 2009 Location: Indiana, US Posts: 186 Rep Power: 18	POPDIR refers to a memory management subroutine. So it could imply that the memory is not sufficient or not being distributed. Floating point overflow refers to a variable divided by zero which is generally evidence of divergence, so a larger timestep might help.