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

CFX 12.1 Notice

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 10, 2011, 12:25
Default CFX 12.1 Notice
  #1
Senior Member
 
Roland Rakos
Join Date: Mar 2009
Posts: 122
Rep Power: 8
Roland R is on a distinguished road
Dear CFX Users,

As far as I know, you have already run into the next problem:

****** Notice ****** |
| The non-dimensional near wall temperature (T+) has been clipped |
| for calculation of Wall Heat Transfer Coefficient. |
| |
| Boundary Condition : WALL_MINI_B |
| T+ clip value = 1.0000E-10 |
| |
| If this situation persists and you are using the High Speed Model, |
| consider enabling Mach number based blending between low speed and |
| high speed wall functions. You can do so by specifying a Mach |
| number threshold as follows: |
| |
| EXPERT PARAMETERS: |
| highspeed wf mach threshold = 0.1 # default=0.0 (off) |
| END


- What does it mean?
- How large numerical error can it cause in the results?
- And where can be found "highspeed wf mach threshold" ? (I haven't found it in the expert parameters.)

Thanks in advance;
Roland
Roland R is offline   Reply With Quote

Old   March 10, 2011, 14:17
Default
  #2
Senior Member
 
Edmund Singer P.E.
Join Date: Aug 2010
Location: Minneapolis, MN
Posts: 495
Rep Power: 11
singer1812 is on a distinguished road
I usually get this when I try to hammer start a model with high speed compressible flow, by being hasty or lazy.

For example, steady state high speed external aerodynamics, M>1, starting from a clean def file, usually IC's set to inlet speed, and temps etc. Timescale factor set at 1.0.

Alot of times, CFX will work through the nasty startup, but more often than not, it fails, with above warnings, and those are usaully accompanied by very high, unrealistic mach numbers.

When that happens, I back up, put a little more effort in, either interpolate a lower mach, or similar run results onto new analysis, or reduce the timescale way down, or do both or those, and slowly ramp the timescale back up to 1.

Not knowing what your model is or looks like, I would put forward the uninformed decision that it is a bad thing, you should get rid of it, and it will cause large numerical errors.

If you wish to follow the expert parameters advice (which I would think is not your problem), just add that one in via command (it might not be seen in gui).
singer1812 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
CFX 12.1: y+ value for SST Aragorn25 CFX 16 January 23, 2015 06:40
Tutorial to help tank sloshing modelling (CFX 12.1) enghamed CFX 13 August 21, 2011 20:43
[ICEM] icem mesh to CFX 12.1 atturh ANSYS Meshing & Geometry 6 February 24, 2011 15:33
Notice of wall condition in cfx td2e09 CFX 0 August 5, 2010 10:17
Notice in CFX Marek CFX 1 November 18, 2008 08:56


All times are GMT -4. The time now is 11:37.