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

Passive scalar

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

Like Tree1Likes
  • 1 Post By LuckyTran

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 6, 2018, 15:13
Default Passive scalar
  #1
New Member
 
Join Date: Jul 2017
Posts: 12
Rep Power: 8
alialemana is on a distinguished road
Hello everyone,

I can't find anything about my problem in the internet so I guess it is quite obvious but I can't find the solution:

I want to simulate the transportation of a passive scalar. I have two inlets and in both flows water --> water-water-simulation.
The problem is by defining the mixture with just one fluid (water) the species mass fractions option in the inlet boundary condition is disabled. So how should I define the concentration (one inlet 1, other 0)?

I would really appreciate your help!
Thanks a lot
alialemana is offline   Reply With Quote

Old   March 6, 2018, 15:55
Default
  #2
Senior Member
 
Cees Haringa
Join Date: May 2013
Location: Delft
Posts: 607
Rep Power: 0
CeesH is on a distinguished road
I am not sure if I get what you mean - how do you define a mixture with just one species..? that's not a mixture, it's a pure liquid.

If you want to make a mixture with 2 species that both have the properties of water, just make 2 fluids with any name, say water_1 and water_2, that have the same physical properties, and combine them into one mixture. That will allow you to set the mass fraction of water_1 at the boundary as desired.
CeesH is offline   Reply With Quote

Old   March 6, 2018, 16:10
Default
  #3
New Member
 
Join Date: Jul 2017
Posts: 12
Rep Power: 8
alialemana is on a distinguished road
Dear CeesH,

thanks a lot for your fast reply. I does not have to be a mixture but as soon as I switch the species transport on I have to define a mixture or do you have a different idea how to simulate a passive scalar transport in a water-water simulation?

Greetings
alialemana is offline   Reply With Quote

Old   March 6, 2018, 16:13
Default
  #4
Senior Member
 
Cees Haringa
Join Date: May 2013
Location: Delft
Posts: 607
Rep Power: 0
CeesH is on a distinguished road
yes, you will have to define a mixture in species transport. Just give the mixture and all components the properties of water (don't forget to switch density from ideal gas to volume weighted mixing!) and you should be good to go.
CeesH is offline   Reply With Quote

Old   March 6, 2018, 16:15
Default
  #5
New Member
 
Join Date: Jul 2017
Posts: 12
Rep Power: 8
alialemana is on a distinguished road
Ok perfect this is the way I already tried it but I thought there might be a easier or a more "official" way.
Thanks anyway!!
alialemana is offline   Reply With Quote

Old   March 6, 2018, 23:57
Default
  #6
Senior Member
 
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,664
Rep Power: 65
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Passive scalar might be the right approach...

Having one passive scalar or only one mass fraction doesn't mean you only have one substance, it obviously implies there is at least another.

When you do species transport it is solved the same way. The difference is whether you have an active scalar, which needs a species transport or a passive scalar. If you only need to tag the origin of the fluid, then the passive scalar might be the way to go. In Fluent, passive scalar is performed via the "user-defined scalar"
granzer likes this.
LuckyTran is offline   Reply With Quote

Old   March 17, 2018, 11:24
Default
  #7
New Member
 
Join Date: Jul 2017
Posts: 12
Rep Power: 8
alialemana is on a distinguished road
Quote:
Originally Posted by LuckyTran View Post
Passive scalar might be the right approach...

Having one passive scalar or only one mass fraction doesn't mean you only have one substance, it obviously implies there is at least another.

When you do species transport it is solved the same way. The difference is whether you have an active scalar, which needs a species transport or a passive scalar. If you only need to tag the origin of the fluid, then the passive scalar might be the way to go. In Fluent, passive scalar is performed via the "user-defined scalar"
Dear LuckyTran,

so you are saying species Transport is not the right approach for my passive scalar, it would be better using UDF? I tried it and the results were horrible.
alialemana is offline   Reply With Quote

Reply

Tags
passive scalar, species mass fraction, species transport

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
problem during mpi in server: expected Scalar, found on line 0 the word 'nan' muth OpenFOAM Running, Solving & CFD 3 August 27, 2018 04:18
Division by zero exception - loop over scalarField Pat84 OpenFOAM Programming & Development 6 February 18, 2017 05:57
Issue symmetryPlane 2.5d extruded airfoil simulation 281419 OpenFOAM Running, Solving & CFD 5 November 28, 2015 13:09
Diverging solution in transonicMRFDyMFoam tsalter OpenFOAM Running, Solving & CFD 30 July 7, 2014 06:20
compressible flow in turbocharger riesotto OpenFOAM 50 May 26, 2014 01:47


All times are GMT -4. The time now is 20:52.