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

How to enable incompressible/compressible flow in Fluent?

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

Like Tree2Likes
  • 2 Post By sbaffini

Reply
 
LinkBack Thread Tools Display Modes
Old   June 20, 2013, 13:33
Default How to enable incompressible/compressible flow in Fluent?
  #1
New Member
 
Join Date: Jun 2013
Posts: 7
Rep Power: 6
A.L.Verminburger is on a distinguished road
I have encountered a distinction being made between compressible and incompressible flows quite often. I don't really understand why it is so important?

I do understand that the problem I am working on has an incompressible flow, i.e. 0.3 > M.

But where do I enable the incompressible setting in Fluent? I do not seem to find the answer neither in the user guide nor the tutorials?
A.L.Verminburger is offline   Reply With Quote

Old   June 20, 2013, 16:51
Thumbs up
  #2
Member
 
farzadpourfattah
Join Date: Mar 2013
Posts: 41
Rep Power: 6
farzadpourfattah is on a distinguished road
if you select in material type "ideal gas" your gas will consider compressible gas.
farzadpourfattah is offline   Reply With Quote

Old   June 21, 2013, 06:00
Default
  #3
Senior Member
 
sbaffini's Avatar
 
Paolo Lampitella
Join Date: Mar 2009
Location: Italy
Posts: 742
Blog Entries: 17
Rep Power: 21
sbaffini will become famous soon enough
What is hidden from the user, in Fluent, is that selecting different density specifications will activate different solvers, ss said by farzadpourfattah. However, the distinction between compressible or incompressible flows is quite imortant, physically as well as numerically and you should investigate it more deeply.
sbaffini is offline   Reply With Quote

Old   June 21, 2013, 06:52
Default
  #4
New Member
 
Join Date: Jun 2013
Posts: 7
Rep Power: 6
A.L.Verminburger is on a distinguished road
OK, so Fluent does this automatically, depending on the material specification - got it. It seems that the most significant difference between incompressible and compressible flows is the presence of shock waves and chocked flow in the latter (I would be inclined to associate these phenomena with Aerospace applications).
A.L.Verminburger is offline   Reply With Quote

Old   June 21, 2013, 07:23
Default
  #5
Senior Member
 
sbaffini's Avatar
 
Paolo Lampitella
Join Date: Mar 2009
Location: Italy
Posts: 742
Blog Entries: 17
Rep Power: 21
sbaffini will become famous soon enough
You don't actually need to reach M=1 to see differences. Also, from the numerical point of view, the algorithms are completely different due to the nature of the flow itself. It is more a matter of "will pressure changes cause density changes?" You can't do (direct) aeroacoustics with an incompressible solver, as the pressure is just treated as a lagrange multiplier and not like a thermodynamic variable (elliptic versus hyperbolic nature).

Check this discussion:

http://www.cfd-online.com/Forums/mai...-enigma-2.html
sbaffini is offline   Reply With Quote

Old   November 29, 2013, 18:08
Default
  #6
Senior Member
 
Tanjina Afrin
Join Date: May 2013
Location: South Carolina
Posts: 168
Rep Power: 6
Tanjina is on a distinguished road
Hello,

I have similar problem with defining the compressible/ incompressible fluid. I chose "constant" when I selected the material. But after completing the calculation, from fluent I found two different value for area weighted average velocity and mass weighted average velocity. But it should be the same. Is there any way so that I can assign "incompressible" fluid?

Any suggestion will be highly appreciated.

Regards,
Tanjina.
Tanjina is offline   Reply With Quote

Old   February 7, 2017, 13:13
Default
  #7
New Member
 
Vinny Fry
Join Date: Oct 2016
Posts: 5
Rep Power: 2
vindiggity is on a distinguished road
Tanjina were you able to solve this? I'm running into the same problem - I have one velocity inlet and one outlflow and the mass weighted average velocity at the outflow fluctuates wildly and is at some points 100's of times larger than at the inlet. I'm simply using air as defined by fluent and really have no idea why this is happening
vindiggity is offline   Reply With Quote

Old   March 2, 2017, 20:03
Default
  #8
New Member
 
Mahdi
Join Date: May 2014
Posts: 8
Rep Power: 5
mahbood is on a distinguished road
what the activation of "compressibility effect" does (under KW- SST option) ? while we set to the ideal gas model and activate the energy equation?
Also if I activate it in the middle of my calculation, does it have some effects on my results? I mean should I run enough to pass the errors?
mahbood is offline   Reply With Quote

Old   March 2, 2017, 22:47
Default
  #9
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 1,880
Rep Power: 26
LuckyTran will become famous soon enoughLuckyTran will become famous soon enough
Quote:
Originally Posted by mahbood View Post
what the activation of "compressibility effect" does (under KW- SST option) ? while we set to the ideal gas model and activate the energy equation?
Also if I activate it in the middle of my calculation, does it have some effects on my results? I mean should I run enough to pass the errors?
This isn't a full answer, but that's an additional correction for the turbulence model to include extra compressibility effects. It's not related to compressible effects of the mean flow (the laminar flow for example).
LuckyTran is offline   Reply With Quote

Reply

Tags
compressible, fluent, incompressible

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
fully developed flow simualtion with fluent bryant_k FLUENT 2 January 1, 2013 12:19
Review: Reversed flow CRT FLUENT 0 July 20, 2012 13:03
help for ANSYS Fluent - cylindrical flow slimmsk ANSYS 0 April 17, 2012 17:00
reversed flow in unsteady simulation with dynamic mesh (fluent 12.1) zhaoyu_001 FLUENT 0 April 7, 2010 00:24
Inviscid Drag at subsonic, subcritical Mach # Axel Rohde Main CFD Forum 1 November 19, 2001 13:19


All times are GMT -4. The time now is 15:53.