CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

use of cavitation model

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 30, 2002, 10:52
Default use of cavitation model
  #1
gdv
Guest
 
Posts: n/a
hi everyone,

I used cavitation model in my case but pressure values in some zones remain absurdly under the vaporization pressure value (negative values too). I tried to use different n values and different time steps but nothing seems to change. How can I avoid this?

Thank you
  Reply With Quote

Old   July 31, 2002, 02:58
Default Re: use of cavitation model
  #2
Lanre
Guest
 
Posts: n/a
Check the Courant number for your problem. You may require an absurdely low time step, e.g., ~1e-6s or less. Try bracketing your pressure by setting max and min pressure limits for your simulation. Use low underrelaxation for pressure, e.g., 1e-3. The bubble density should affect your results so specify a realistic value.
  Reply With Quote

Old   July 31, 2002, 04:53
Default Re: use of cavitation model
  #3
hvn
Guest
 
Posts: n/a
Hi,

By negative values of pressure, do you speak about absolute or relative pressure?

Regards,

HV
  Reply With Quote

Old   July 31, 2002, 05:10
Default Re: use of cavitation model
  #4
gdv
Guest
 
Posts: n/a
Thank you for your responce,

I mean, unfortunately, negative absolute pressure.

Regards,

gdv
  Reply With Quote

Old   July 31, 2002, 05:18
Default Re: use of cavitation model
  #5
gdv
Guest
 
Posts: n/a
Thanks for your responce, I can try to reduce time steps during the unsteady solution but i can't reduce CFL number because i'm using segregated solver and, ,moreover, unfortunately, i can't limit pressure values because my flow in incompressible. I will tell you the new results.

Regards

gdv

  Reply With Quote

Old   August 1, 2002, 02:55
Default Re: use of cavitation model
  #6
Lanre
Guest
 
Posts: n/a
I meant for you to use the Solve->Controls->Limits... to set min and max absolute pressures to control your solution. Once you have the solution progressing you can relax the min and max limits to be more realistic.
  Reply With Quote

Old   August 6, 2002, 04:57
Default Re: use of cavitation model
  #7
Mark Render
Guest
 
Posts: n/a
Hi,

reading your discussion the question came to my mind:

Is it really so strange or even impossible that the absolute pressure becomes negative ?

If there is a small nuclei content in the water perhaps the water won't vaporize at the saturation pressure but only at lower pressures.

Any opinions on that ?

Regards,

Mark

  Reply With Quote

Old   August 7, 2002, 12:48
Default Re: use of cavitation model
  #8
gdv
Guest
 
Posts: n/a
Thank you Mark,

I think that your observation is correct if we want to see qualitatively where cavitation occurs but absolute negative pressures affect the velocity field overestimating local velocity values (in the case one imposes a pressure drop on an incompressible flow) and so possible choking effects on flow rate through an orifice cannot be observed.

Regards
  Reply With Quote

Reply


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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
cavitation model pressure distribution Rahmat Arazgaldy FLUENT 1 May 16, 2012 16:48
Cavitation model with non-isothermal flow pitisrisuk CFX 0 July 14, 2009 15:30
Cavitation Model Umesh Shah FLUENT 0 June 26, 2006 18:09
About Cavitation Model and General setting wayland Siemens 0 January 15, 2006 22:30
Mixture Model (cavitation) Victor FLUENT 3 April 5, 2005 05:38


All times are GMT -4. The time now is 07:56.