CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CFX

error in vacuum

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   October 7, 2016, 10:26
Default error in vacuum
  #1
New Member
 
julie
Join Date: Oct 2016
Posts: 16
Rep Power: 3
kykylalac is on a distinguished road
Hello, please, I'm trying to count not difficult task: at the inlet to a vessel supplied with gas at a pressure 40torr, in the vessel a vacuum, but as I understand it, in ANSYS CFX can not set the vacuum cleaner and you have at least some small pressure set , right?

I wanted to ask 40torr for entry and for example, 1 torr in the vessel, but errors all the time. I increase a little pressure in the vessel - still error at the same place, but when put in the vessel 20 Torr, all consider, but it is not a vacuum.

just tell me what is the difference between the reference pressure in the basic setting and relative pressure in the initialization?

ask reference pressure, relative pressure when tried everything took off, regardless of the pressure enter values
kykylalac is offline   Reply With Quote

Old   October 9, 2016, 07:11
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 14,098
Rep Power: 109
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
Before you do anything you need to make sure you are in a regime suitable for continuum models (such as CFX with the Navier Stokes equations). You need to work out if your Knudsen number (https://en.wikipedia.org/wiki/Knudsen_number) is OK for a continuum model.

If your Knudsen number is OK then we will discuss how to implement your model.
ghorrocks is offline   Reply With Quote

Old   October 14, 2016, 08:43
Default
  #3
New Member
 
julie
Join Date: Oct 2016
Posts: 16
Rep Power: 3
kykylalac is on a distinguished road
thanks for answer, my Knudsen number is normal for continuum model.
may be, does the error associated with time step?
kykylalac is offline   Reply With Quote

Old   October 15, 2016, 18:49
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 14,098
Rep Power: 109
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
OK, good.

Then to answer your original question:
Reference pressure is used to normalise all other pressures to values near zero. This reduces numerical round off errors and makes the solver more accurate and more numerically stable.

All pressures are relative to the reference pressure.
ghorrocks is offline   Reply With Quote

Old   October 16, 2016, 15:44
Default
  #5
New Member
 
julie
Join Date: Oct 2016
Posts: 16
Rep Power: 3
kykylalac is on a distinguished road
okay, if i use reference pressure with value 2torr and other pressures is 0,it's mistake?
kykylalac is offline   Reply With Quote

Old   October 16, 2016, 18:48
Default
  #6
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 14,098
Rep Power: 109
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
No, that approach would be good if the system you are modelling had the system running at about 2 torr.
ghorrocks is offline   Reply With Quote

Old   October 17, 2016, 02:58
Default
  #7
New Member
 
julie
Join Date: Oct 2016
Posts: 16
Rep Power: 3
kykylalac is on a distinguished road
may be error is in something else . could you tell me about vacuum in ansys cfx? What are settings for it?
kykylalac is offline   Reply With Quote

Old   October 17, 2016, 05:36
Default
  #8
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 14,098
Rep Power: 109
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
As I said previously, as long as the Knudsen number is in the regime indicating the continuum assumption is appropriate then CFX is OK to model it.

What error are you getting?
ghorrocks is offline   Reply With Quote

Old   October 17, 2016, 12:04
Default
  #9
New Member
 
julie
Join Date: Oct 2016
Posts: 16
Rep Power: 3
kykylalac is on a distinguished road
ERROR #004100018 has occurred in subroutine FINMES. | | Message: | | Fatal overflow in linear solver.
very popular error
kykylalac is offline   Reply With Quote

Old   October 17, 2016, 17:38
Default
  #10
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 14,098
Rep Power: 109
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
Yes, very popular error. Popular enough to get its own FAQ: http://www.cfd-online.com/Wiki/Ansys...do_about_it.3F

Have you tried the suggestions in the FAQ?
ghorrocks is offline   Reply With Quote

Old   October 21, 2016, 08:17
Default
  #11
New Member
 
julie
Join Date: Oct 2016
Posts: 16
Rep Power: 3
kykylalac is on a distinguished road
thanks for link. very useful.
could you explain me what does this notice mean?
****** Notice ****** |
| A wall has been placed at portion(s) of an OUTLET |
| boundary condition (at 44.2% of the faces, 44.3% of the area) |
| to prevent fluid from flowing into the domain. |
| The boundary condition name is: free. |
| The fluid name is: Fluid 1. |
| If this situation persists, consider switching |
| to an Opening type boundary condition instead.
kykylalac is offline   Reply With Quote

Old   October 22, 2016, 04:50
Default
  #12
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 14,098
Rep Power: 109
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
That one is the very next FAQ on the list: http://www.cfd-online.com/Wiki/Ansys...f_an_OUTLET.22
ghorrocks is offline   Reply With Quote

Old   November 30, 2016, 05:21
Default
  #13
New Member
 
julie
Join Date: Oct 2016
Posts: 16
Rep Power: 3
kykylalac is on a distinguished road
what minimum pressure can i use? how can i count the min pressure?
i must have vacuum
kykylalac is offline   Reply With Quote

Old   November 30, 2016, 05:25
Default
  #14
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 14,098
Rep Power: 109
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
CFX is a fluid dynamics solver. A total vacuum means there is no fluid so you can't use a fluid dynamics solver (if that is what you mean).

The minimum pressure CFX can use depends on the application. You simply have to try some values until you find what fails to converge in your case.

And what are you trying to model a vacuum for? What pressure are you intending to use?

Last edited by ghorrocks; November 30, 2016 at 06:38.
ghorrocks is offline   Reply With Quote

Old   November 30, 2016, 14:40
Default
  #15
New Member
 
julie
Join Date: Oct 2016
Posts: 16
Rep Power: 3
kykylalac is on a distinguished road
I'm trying to count not difficult task: at the inlet to a container supplied with gas at a pressure 40torr, in the container a vacuum.
i tried 1 torr in the container.
and i must to use heat transfer on wall. i want to set wall tempreture condotion, but i have error that solver is overflow. i know about link for solve this problem. i don't know where is my mistake.
whene i use heat transfer coef my task solved, but i don't have heat transfer
kykylalac is offline   Reply With Quote

Old   November 30, 2016, 18:05
Default
  #16
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 14,098
Rep Power: 109
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
If there is a flow from a pressure source at 40 torr into a chamber at a vacuum - well the vacuum chamber has to be at some finite pressure. It cannot be absolute zero pressure. So you should look at whether CFX can model the vacuum chamber at its pressure, and check that the knudsen number is OK for it to be assumed as a continuum.
ghorrocks is offline   Reply With Quote

Old   December 1, 2016, 00:35
Default
  #17
New Member
 
julie
Join Date: Oct 2016
Posts: 16
Rep Power: 3
kykylalac is on a distinguished road
Okay, I understand it, thank you. Could you help me with wall heat transfer and more specifically with wall temperature. When the wall has adiabetic and heat transfer coef. (random number) conclusion the task solves, when I set wall temperature the task has error.
kykylalac is offline   Reply With Quote

Old   December 1, 2016, 00:51
Default
  #18
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 14,098
Rep Power: 109
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
Please attach an image of what you are modelling, an image of your mesh and you output file (including both the CCL at the start and the error which finished it)
ghorrocks is offline   Reply With Quote

Old   December 1, 2016, 07:58
Default
  #19
New Member
 
julie
Join Date: Oct 2016
Posts: 16
Rep Power: 3
kykylalac is on a distinguished road
my task: you know the wording

outputSTART (1).txt

??????????1.jpg

??????????12.jpg

??????????3.jpg
kykylalac is offline   Reply With Quote

Old   December 1, 2016, 08:14
Default
  #20
Senior Member
 
Join Date: Feb 2011
Posts: 461
Rep Power: 11
Antanas is on a distinguished road
Have you specified proper initial conditions? May you share your project?
Antanas is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Strange non vacuum behavior in DSMC DS3V julien91 Main CFD Forum 4 December 31, 2016 10:03
Modeling a vacuum region in solar collector with fluent amirokhovat FLUENT 2 November 4, 2016 07:36
radiation modeling in vacuum mirko OpenFOAM Programming & Development 7 May 20, 2016 08:31
Assistance in Vacuum pump simulation enr_venkat CFX 5 November 20, 2012 12:50
Radiation in vacuum nitin CFX 0 July 6, 2009 01:49


All times are GMT -4. The time now is 20:24.