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

Passive Scalar Dispersion

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

Like Tree3Likes
  • 3 Post By A CFD free user

Reply
 
LinkBack Thread Tools Display Modes
Old   April 20, 2013, 16:58
Default PLZ HELP!!! (Urgent) Passive Scalar Dispersion
  #1
New Member
 
Join Date: Apr 2013
Posts: 1
Rep Power: 0
manast is on a distinguished road
Hi,

I am new to FLUENT, and am trying to simulate an unsteady passive scalar dispersion on FLUENT 14.0. It is for a 2D axisymmetric sudden expansion geometry. I am using K-epsilon for turbulence modelling, with a 15m/s velocity inlet and 0.4% turbulence intensity. I am unsure how to simulate a passive scalar, and I would really appreciate any help in this, thank you!

manast

Last edited by manast; April 20, 2013 at 18:16.
manast is offline   Reply With Quote

Old   April 22, 2013, 10:56
Default Dispersion
  #2
New Member
 
Francois
Join Date: Apr 2013
Posts: 2
Rep Power: 0
amakson is on a distinguished road
Hello,
I'm new user of Ansys Fluent. I want simulate a passive scalar but i dont know which boundaries conditions, i can take. I study substances dispersion in the lentic water (pond, tank,...).
Please, some persons can help me?
Thanks
amakson is offline   Reply With Quote

Old   April 23, 2013, 07:31
Default
  #3
Senior Member
 
A CFD free user's Avatar
 
A-A Azarafza
Join Date: Jan 2013
Posts: 187
Rep Power: 4
A CFD free user is on a distinguished road

__________________
Regard yours
A CFD free user is offline   Reply With Quote

Old   April 23, 2013, 07:41
Default
  #4
Senior Member
 
A CFD free user's Avatar
 
A-A Azarafza
Join Date: Jan 2013
Posts: 187
Rep Power: 4
A CFD free user is on a distinguished road
User Defined Scalars (UDS) are used to solve any arbitrary generic transport equations, something like species transport equations. You can use species transport equations to solve only mass fractions of species, but you can use UDS to solve any transport equations you want, for instance, you can use them to solve electric potential or magnetic field or injecting a tracer into media to obtain RTD. Fluent allows you to define up to 50 UDS. An arbitrary generic Scalar( UDS) has a form like this:



As you see the left hand side of the generic equation has three terms. The first one is used in a transient (if you need to consider time), the second term is convective flux and the third one is diffusive flux. The right hand term is source which can be defined depending on your problem, for instance, if your scalars are consumed or produced.

is diffusivity which should be defined by user. it can be considered as isotropic or anisotropic. An anisotropic diffusivity is defined as a tensor. There are several methods for diffusivity in Fluent, you can access them via Fluent material panel.
F, is flux function which in case of mass flow, it is defined as multiplication of density by velocity. For other cases should be defined separately.
How to run a UDS in Fluent:
To run UDS in Fluent, first define the numbers of UDS in Define/ User defined/ Scalars. UDS index is used to recognize the UDSs and it starts from zero. It means that for instance, the second UDS has index 1, the fourth UDS has index 3 and so on. You need to select the solution zones for your scalars as well. If you interested in considering flux function, then define it too, otherwise leave it as none (In this case you only solve the diffusion term).
By doing this, you'll be directed to material panel where you need to define the diffusivity for your scalars as I mentioned above. One more thing, you have to adjust the scalars on wall boundaries of your solution zones too either as a specified value or flux.
That's a brief procedure of defining a UDS.
Hope it helps
Attached Images
File Type: jpg 1.JPG (14.0 KB, 51 views)
Mazze[ITA], crevoise and Tarantino like this.
__________________
Regard yours

Last edited by A CFD free user; May 13, 2013 at 13:01.
A CFD free user is offline   Reply With Quote

Old   April 24, 2013, 11:59
Default Thank you
  #5
New Member
 
Francois
Join Date: Apr 2013
Posts: 2
Rep Power: 0
amakson is on a distinguished road
Hello Azarafza,
Thank you for your answers (helps).

Best regards
amakson is offline   Reply With Quote

Reply

Tags
axisymmetric 2d fluent, fluent, passive scalar, sudden expansion, unsteady

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 flow in turbocharger riesotto OpenFOAM 50 May 26, 2014 01:47
whats the cause of error? immortality OpenFOAM Running, Solving & CFD 11 April 22, 2014 12:32
is internalField(U) equivalent to zeroGradient? immortality OpenFOAM Running, Solving & CFD 7 March 29, 2013 02:27
passive scalar for carbon monoxide kraizy STAR-CCM+ 0 October 12, 2009 20:13
solving passive scalar by user function in AVLFIRE huyp Main CFD Forum 0 September 4, 2008 10:21


All times are GMT -4. The time now is 12:13.