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

Particle Tracking and Erosion modeling in CFX

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 17, 2016, 01:14
Default Particle Tracking and Erosion modeling in CFX
  #1
New Member
 
Srinidhi
Join Date: Sep 2009
Posts: 10
Rep Power: 16
srinidhi4u is on a distinguished road
Hi all,

I am working on a problem with annular cylinder with cone shaped structure at the bottom. I inject 3 different diameter solid particles from the bottom of the annular space which hits the cones and leads to erosion of it.

This is a steady state compressible air flow problem. I inject the particles from bottom and there is a fluid jet around the cone which hits this bottom annular space, carry the particles and bombard it against the cones and erode it before exiting on the top of annular surface. I am using Tabakoff and Grant erosion model which should help me to find the erosion rate on the cones.

I am facing problem of non-uniform erosion results after each particle iteration. I am using 20 as particle iteration frequency. When I try to check for erosion rate density at one time step and the next one there is a change(even though it is not very major). It is kind of fluctuating and coming back to almost same values if I check values of say 10 particle iterations like a cycle. Is this common to happen in Lagrangian particle tracking? Does turbulent particle dispersion has any role to play here?

I am monitoring air pressure and mass flow and it has normalised. I am using 2 way particle and air coupling to address the issues of particles affecting the air flow. My particle loading is less than 12% which tells me that I should be using Lagrangian approach for modelling particles. Can someone guide me why there should be non-uniform values between particle to particle iterations even though it has converged? Or should I take average of say 10 time steps approximately to say that this is my erosion density rate?

Thanks in advance

Best regards,

Shri
srinidhi4u is offline   Reply With Quote

Old   June 17, 2016, 02:23
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,746
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Have you read the documentation? A quick search found:

Note: If you encounter convergence difficulties when using a turbulence dispersion model in conjunction with Segregated volume fraction coupling, then you should consider reducing the physical time scale, or switching to Coupled volume fraction coupling.

There is plenty of other information on this in the documentation as well.
ghorrocks is offline   Reply With Quote

Old   June 17, 2016, 02:43
Default
  #3
New Member
 
Srinidhi
Join Date: Sep 2009
Posts: 10
Rep Power: 16
srinidhi4u is on a distinguished road
Thanks Glenn. I have not seen this. I will check for that.

What are your thoughts? is it because of the convergence problem from turbulent dispersion we see the difference between the particle iterations?

Is my approach to the problem appropriate?
srinidhi4u is offline   Reply With Quote

Old   June 17, 2016, 02:50
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,746
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
I would try what the documentation suggests first (reduce time scale, coupled VF solver). If that does not work I recall that convergence can be difficult in turbulent dispersion force simulations as the turbulent dispersion force is recalculated periodically and is applied as a random force on the particles. That means whenever it recalculates the residuals will go up, then it converges on that for a while then recalculates again and the residuals go up again. This means it is difficult to get convergence in the normal sense. So best to use a parameter of importance to you (such as flow rate, pressure drop or whatever) and monitor that parameter for convergence.
ghorrocks is offline   Reply With Quote

Old   June 17, 2016, 04:32
Default
  #5
New Member
 
Srinidhi
Join Date: Sep 2009
Posts: 10
Rep Power: 16
srinidhi4u is on a distinguished road
Thanks a lot Glenn. I will try with the suggested approach.
srinidhi4u is offline   Reply With Quote

Old   June 17, 2016, 06:01
Default
  #6
New Member
 
Srinidhi
Join Date: Sep 2009
Posts: 10
Rep Power: 16
srinidhi4u is on a distinguished road
Glenn, I am confused how important is it to consider Turbulent dispersion in my problem. If I skip dispersion will I be missing to capture the actual physics?
srinidhi4u is offline   Reply With Quote

Old   June 17, 2016, 06:15
Default
  #7
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,746
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
That is up to you to decide. Turbulence dispersion force is a difficult and expensive model to include so only include it if you have to. So you have to work out if it is significant in your case or not.

The easiest way is to do a benchmark run with it on and off and see if it makes any difference. A better approach is to estimate dispersion due to the various forces and see if turbulence is significant or not.
ghorrocks is offline   Reply With Quote

Old   June 17, 2016, 06:24
Default
  #8
New Member
 
Srinidhi
Join Date: Sep 2009
Posts: 10
Rep Power: 16
srinidhi4u is on a distinguished road
That makes perfect sense to me. I have started the simulation without dispersion and I am already seeing all the particle integration error disappear, which I had seen earlier. I will compare the two cases and see if I see a big difference.

Thanks a ton again.
srinidhi4u is offline   Reply With Quote

Reply

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
particles leave domain Steffen595 CFX 9 March 7, 2016 16:19
Discrete Phase Modeling (Pipe erosion) in OF 2.1.0 mecbe2002 OpenFOAM 3 February 2, 2012 01:17
Check particle impaction with User Fortran Julian K. CFX 3 January 12, 2012 09:46
Particle tracking in DPM Harpreet FLUENT 0 August 27, 2011 04:12
Questions regarding Particle Tracking and Rotating Frame of reference Maxime Gauthier CFX 1 May 9, 2011 15:07


All times are GMT -4. The time now is 07:45.