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

Residence Time Distribution

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

Reply
 
LinkBack Thread Tools Display Modes
Old   July 18, 2001, 07:48
Default Residence Time Distribution
  #1
rajeev
Guest
 
Posts: n/a
Can I calculate RTD when I am using a turbulence model or I have to use a different model. If different model has to be used to find the RTD then which one is most appropriate.

Has anyone tried the above problem. Please let me know the steps.

Thanks in advance Rajeev
  Reply With Quote

Old   July 18, 2001, 12:10
Default Re: Residence Time Distribution
  #2
Alain
Guest
 
Posts: n/a
I can't see the relationship between residence time and turbulence models ?

In my point of view, residence time deals with mean velocities. So, you can calculate a residence time for your flow with any turbulence model.

Can you give more precision on your problem.

Best regards
  Reply With Quote

Old   July 19, 2001, 16:18
Default Re: Residence Time Distribution
  #3
Lanre
Guest
 
Posts: n/a
Are you referring to http://www.fluent.com/solutions/examples/x93.htm

then track the transient dispersion of a tracer species.
  Reply With Quote

Old   July 20, 2001, 05:38
Default Re: Residence Time Distribution
  #4
Jin-Wook LEE
Guest
 
Posts: n/a
You can do it by particle tracking for the partilce of very small particle. Then slip velocity can be negligible, so that particle residence time is nearly same as gas residence time. Then you can obtain RTD.

For reference, my approach is as follow.

1) set the particle size very small(e.g., 1.e-09) 2) set the density of particle as mean of gas phase.

Sincerely, Jinwook

  Reply With Quote

Old   July 25, 2001, 09:35
Default Re: Residence Time Distribution
  #5
Peter Kolb
Guest
 
Posts: n/a
How can I achieve a dirac (delta) signal in the simulation?? Can I also realise that when I am using translational periodic BC ?
  Reply With Quote

Old   July 25, 2001, 11:02
Default Re: Residence Time Distribution
  #6
Kuochen
Guest
 
Posts: n/a
The best way to do it is to use the DPM model with very small particles. Also turn on the stochastic model so you can get a smooth RTD. With more than 500 particles you can get a pretty decent RTD, but be sure to turn off the length scale option and use the tracking steps (>20) so particles spend enough time in each cell. The average RTD should be close, but not exactly, to the mean residence time. If the display option takes a long time, then try the DPM sampling and histogram option. It is lot faster.
  Reply With Quote

Old   July 25, 2001, 13:51
Default Re: Residence Time Distribution
  #7
Alain
Guest
 
Posts: n/a
You can also use a fluid as a tracer. It's quite faster than particle tracking.

This is my method :

1. calculate your solution,

2. Enable multispecies model

3. Create a species "tracer" as a copy of your fluid.

4. "Inject" your tracer in the domain at a boundary or by using the patch command.

5. freeze your solution except for species (disble equation in flow solver) and then run in transient mode.

6. You can obtain a RDT by local value (probe) or mean value at bourdary (surface averaging).

Best regards
  Reply With Quote

Old   July 25, 2001, 14:25
Default Re: Residence Time Distribution
  #8
Kuochen
Guest
 
Posts: n/a
Two problem with this method: 1. Transient simulation is needed to compute RTD at the outlet, which could be quite time-consuming. 2. More cells are needed for accuracy due to numerical diffusion.
  Reply With Quote

Old   July 26, 2001, 04:42
Default Re: Residence Time Distribution
  #9
rajeev
Guest
 
Posts: n/a
Thanks a lot guys.

One more question. What should be the correct steps.

1. Calculate the steady state flow field based on turbulent model. Once it converges. then

2. Switch on the DPM. Use the calculated flow field in step 1 and solve for unsteady state the particle concentretation at outlet to get the RTD.

Correct me if my steps are wrong.

Thanks again Rajeev
  Reply With Quote

Old   July 26, 2001, 09:11
Default Re: Residence Time Distribution
  #10
Kuochen
Guest
 
Posts: n/a
Not the particle concentration, but the time variable at each particle.
  Reply With Quote

Old   July 26, 2001, 12:45
Default Re: Residence Time Distribution
  #11
Peter Kolb
Guest
 
Posts: n/a
...and it does not have to be unsteady! or I am wrong?
  Reply With Quote

Old   July 26, 2001, 13:49
Default Re: Residence Time Distribution
  #12
Kuochen
Guest
 
Posts: n/a
Correct.
  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
TimeVaryingMappedFixedValue irishdave OpenFOAM Running, Solving & CFD 28 May 28, 2015 13:37
Superlinear speedup in OpenFOAM 13 msrinath80 OpenFOAM Running, Solving & CFD 18 March 3, 2015 06:36
How to write k and epsilon before the abnormal end xiuying OpenFOAM Running, Solving & CFD 8 August 27, 2013 15:33
Pathline colored by time = residence time pkleb FLUENT 0 June 20, 2010 17:52
How to get residence time distribution? bigfans FLUENT 0 April 27, 2009 09:39


All times are GMT -4. The time now is 03:07.