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

Compressible flow

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 6, 2009, 16:58
Default Compressible flow
  #1
New Member
 
hassan
Join Date: Oct 2009
Posts: 6
Rep Power: 7
hassan.rouhani is on a distinguished road
Hi guys,

I am modeling a converging diverging geometry, like all oyu know the nozzle-diffuser.

it is a compressible flow of air. my BC is :

pressure inlet: 3.18 atm (gauge total pressure), 1 atm (supersonic/gauge) and total temprature 417. (actually i set inlet mach number1.4 and i computed these condition by putting the ration of outlet to throat equal 2).

pressure outlet : 1 atm and total temrature 300.

my solver is pressure based, energy eq., vis : spalart. material air, density ideal gas. operating pre. eq. zero.

under relaxation deafault, adapt gradient/ pressure with coarsen threshold 0 and refine 0.3.

why it is diverging?

thanks a lot.
hassan.rouhani is offline   Reply With Quote

Old   November 7, 2009, 05:05
Default
  #2
jsm
Senior Member
 
JSM
Join Date: Mar 2009
Location: India
Posts: 155
Rep Power: 11
jsm is on a distinguished road
Hi,

Converging the solution with pressure inlet and pressure outlet is difficult especially for compressible flow simulations. I don't know your geometry size and solver set up. Just try these suggestion.
If possible try with mass flow inlet boundary condition or gradually increase the inlet pressure to your desired value.
__________________
With regards,
JSM
jsm is offline   Reply With Quote

Old   November 8, 2009, 10:44
Default
  #3
New Member
 
hassan
Join Date: Oct 2009
Posts: 6
Rep Power: 7
hassan.rouhani is on a distinguished road
Quote:
Originally Posted by jsm View Post
Hi,

Converging the solution with pressure inlet and pressure outlet is difficult especially for compressible flow simulations. I don't know your geometry size and solver set up. Just try these suggestion.
If possible try with mass flow inlet boundary condition or gradually increase the inlet pressure to your desired value.
--------

Hi,

Thanks for your reply.
Goemetry: 6 cm length and 8 mm height. I am trying these methods, it is better now, but not perfect.
hassan.rouhani is offline   Reply With Quote

Old   November 10, 2009, 20:34
Default
  #4
Senior Member
 
Chris
Join Date: Jul 2009
Location: Ohio, USA
Posts: 169
Rep Power: 8
Chris D is on a distinguished road
Try extending your outlet boundary past the end of the diffuser. When you do this, stretch the grid. Also, is your y+ in the correct range for the S-A model?
Chris D 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
Compressible Fluid Flow in COMSOL Multiphysics BBG Main CFD Forum 1 November 19, 2008 15:05
Mass flow inlet compressible flow richard FLUENT 2 June 1, 2008 11:44
compressible flow algorithm ztdep Main CFD Forum 4 April 27, 2008 20:41
free on line compressible flow book genick bar-meir Main CFD Forum 4 December 5, 2005 01:25
Solving unsteady compressible low speed flow atit Main CFD Forum 8 July 31, 2000 13:19


All times are GMT -4. The time now is 00:04.