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

Cyclone Simulation Convergence Problem

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

Reply
 
LinkBack Thread Tools Display Modes
Old   July 26, 2007, 07:31
Default Cyclone Simulation Convergence Problem
  #1
Sal
Guest
 
Posts: n/a
Hello every one.

I am simulating a cyclone seperator and I have easily got convergence using K-E, K-E RNG both first and second order discritization. Using the RSM model i can only get convergence for first order but cant seem to get convergence for second order. I am using 517000 tetrahedral cells in the mesh. Can some one help me on this please Thank you in Advance.

Sal
  Reply With Quote

Old   July 26, 2007, 08:07
Default Re: Cyclone Simulation Convergence Problem
  #2
Joe
Guest
 
Posts: n/a
Restart the RSM solution from a converged two equation solution. Adjust your under relaxation factors.
  Reply With Quote

Old   July 26, 2007, 08:15
Default Re: Cyclone Simulation Convergence Problem
  #3
Sal
Guest
 
Posts: n/a
Should i start it from the first order discretization. Steady, unsteady, boundary conditions bottom outlet as wall or pressure outlet and if unsteady what would u recomend the time step to be and should I use transient controls and which one? I appreciate this.

Sal
  Reply With Quote

Old   July 26, 2007, 12:00
Default Re: Cyclone Simulation Convergence Problem
  #4
Bubble
Guest
 
Posts: n/a
I would recommend that u start using steady state first to build up pressure to create a swirling flow. Once the residual gets stable change to unsteady state because the vortex will move in quasi periodic movement. You can adjust the time step to get better convergence or u can adjust your relaxation factor.

  Reply With Quote

Old   July 26, 2007, 18:18
Default Re: Cyclone Simulation Convergence Problem
  #5
Sal
Guest
 
Posts: n/a
For the bottom wall what do you recomend me to use as a boundary condition. At the moment it is defined as a wall. Do i need to change? if yes what to and would I have to enter any other parameters. Thank you for the help in advance.

Sal
  Reply With Quote

Old   July 27, 2007, 08:16
Default Re: Cyclone Simulation Convergence Problem
  #6
Sal
Guest
 
Posts: n/a
While running the boundary conditions i get no reverse flow. Does any one know how to correct this. Thank You. Sal
  Reply With Quote

Old   July 28, 2007, 01:53
Default Re: Cyclone Simulation Convergence Problem
  #7
JSM
Guest
 
Posts: n/a
Hi,

For cyclone, there are some basic steps in CFD.

1. For meshing - Always use structured mesh (hexahedral elements) with aspect ratio within the range 5 to 10. 2. solver setup - RSM turbulence model is recommended. First solve with default setup with RSM. Once converged, then go to higer order discretization with increased converge monitor 1e-6. 3. Choose time setup size as analysis should converge in every time step.

Note: first order converged solution always gives some appropriate values. dont worry about. Cyclone phenomena is purely unsteady. So unsteady with higher order discretization, you can more accurate solution.
  Reply With Quote

Old   December 17, 2014, 04:32
Default Another viscous model besides rsm
  #8
New Member
 
fatih syakban
Join Date: Dec 2014
Posts: 1
Rep Power: 0
fatih-ITS is on a distinguished road
Iam still running Cyclone with double inlet with section angle 30 degree, 2 phase coal and air
Iam going to asking too, can I use another viscous model like k-epsilon realizable to get correct separation efficiency and pressure drop ??
Can you give me advice setting for double inlet cyclone to me ?
because Iam very depressed with my final assignment,
Thank you for your attention




Quote:
Originally Posted by JSM
;143944
Hi,

For cyclone, there are some basic steps in CFD.

1. For meshing - Always use structured mesh (hexahedral elements) with aspect ratio within the range 5 to 10. 2. solver setup - RSM turbulence model is recommended. First solve with default setup with RSM. Once converged, then go to higer order discretization with increased converge monitor 1e-6. 3. Choose time setup size as analysis should converge in every time step.

Note: first order converged solution always gives some appropriate values. dont worry about. Cyclone phenomena is purely unsteady. So unsteady with higher order discretization, you can more accurate solution.
fatih-ITS is offline   Reply With Quote

Old   December 17, 2014, 08:46
Default
  #9
Senior Member
 
ghost82's Avatar
 
Daniele
Join Date: Oct 2010
Location: Italy
Posts: 899
Rep Power: 15
ghost82 will become famous soon enough
As suggested above rsm turbulence model is the most appropriate.
If you want to switch to k-epsilon I suggest the rng model with the swirl option switched on.

PS: don't be depressed
__________________
Google is your friend and the same for the search button!
ghost82 is offline   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
Heat Transfer simulation: No convergence problem fiqs CFX 2 April 21, 2010 15:47
History Convergence: Graphical problem Bedotto NUMECA 1 March 18, 2010 00:40
Convergence problem suthichock Main CFD Forum 27 May 11, 2009 07:05
3D Fluid Flow Convergence problem Emily FLUENT 2 March 21, 2007 23:18
CONVERGENCE PROBLEM - oil boiler MM FLUENT 1 February 15, 2007 06:24


All times are GMT -4. The time now is 18:49.