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

Use periodic boundary conditions with DES - Urgent!

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 22, 2012, 05:40
Default Use periodic boundary conditions with DES - Urgent!
  #1
New Member
 
Hesham Khalil
Join Date: Nov 2012
Posts: 9
Rep Power: 4
HeKhalil is on a distinguished road
Hye guys,

This might be an elementary question but i still not sure about its answer.

I am simulating a flame-vortex interaction in a premixed swirl stabilized combustor. Basically, i try to evaluate the effect of vortex shedding on the flame using fluent.
I would like to use DES in my simulation.
Due to the enormous computational cost i only considered quarter section of the combustor while applying rotational periodic boundary conditions in the span-wise direction.
My question is, am i ok with applying the periodic boundary conditions while using DES or i shall consider the complete combustor knowing that the geometry is symmetrical and the flow enters the domain perfectly premixed.

your help is highly appreciated!
HeKhalil is offline   Reply With Quote

Old   November 22, 2012, 19:05
Default
  #2
Senior Member
 
Julien de Charentenay
Join Date: Jun 2009
Location: Australia
Posts: 229
Rep Power: 9
julien.decharentenay is on a distinguished road
Send a message via Skype™ to julien.decharentenay
Hi Hesham,

The use of periodicity will limit/constraint the spanwise vortices frequency that can be captured by the simulation. Although it might be acceptable in some cases, I would not recommend it.

From a practical perspective, my suggestion would be to compare a simulation with a complete combustor and a simulation with rotational periodic boundary conditions (it could be half, quarter, or third) and assess the impact of the periodicity assumptions.

Good luck. Julien
__________________
---
Julien de Charentenay
julien.decharentenay is offline   Reply With Quote

Old   November 22, 2012, 19:10
Default
  #3
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 1,568
Rep Power: 20
FMDenaro will become famous soon enough
Simulation of turbulence in portion of a domain with cyclic conditions must be limited to RANS formulation
FMDenaro is offline   Reply With Quote

Old   November 22, 2012, 20:46
Default
  #4
Far
Super Moderator
 
Far's Avatar
 
Sijal Ahmed Memon (turboenginner@gmail.com)
Join Date: Mar 2009
Location: Islamabad Pakistan
Posts: 3,905
Blog Entries: 6
Rep Power: 38
Far will become famous soon enoughFar will become famous soon enough
Send a message via Skype™ to Far
see this http://cfd.mace.manchester.ac.uk/des..._MStrelets.pdf
Far is offline   Reply With Quote

Old   November 23, 2012, 12:31
Default
  #5
New Member
 
Hesham Khalil
Join Date: Nov 2012
Posts: 9
Rep Power: 4
HeKhalil is on a distinguished road
Thanks guys, but i have a question for you julien, the problem of mine is to capture the longitudinal instability frequency due to flame vortex interaction as a result of vortex shedding to the flame. this frequency is equal to the acoustic quarter wave mode of the combustor. so i am interested only in the longitudinal frequency of vortex shedding (stream wise direction), can't this allow me to use periodicity? or the span wise frequency might affect that?

Also, i cannot do the simulation twice! one for the complete one and one for the quarter section and compare because of the enormous time consumed in each. i use 3 million cell resolution in only quarter section which takes along 5 days to complete one integral time (time of flow to enter and exit the domain once).

By the way, the combustor diameter is 110 mm. i use 220 cell in the cross-stream direction and 60 cells in span wise direction. this grid is totally uniform and structural grid with spatial step of 0.5 mm in both stream wise and cross stream directions. the grid as i said is more coarse in span wise direction to reduce computational cost. this gives me y+ of 50 near the wall and the effective DES length scale (by fluent) is positive every where except near the wall. am i ok with this grid? i know that the grid shall be refined near the shear layer down stream the dump plane of the combustor but i couldn't do this due to meshing difficulties so is this grid is ok?
HeKhalil 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
periodic boundary conditions fro pressure Salem Main CFD Forum 21 April 10, 2013 00:44
Periodic boundary conditions in 3D Eulerian granular flow simulations dsm FLUENT 4 March 2, 2012 20:04
Domain Imbalance HMR CFX 3 March 6, 2011 21:10
Problem with using periodic boundary conditions Sun FLUENT 0 January 14, 2011 10:47
mesh file for flow over a circular cylinder Ardalan Main CFD Forum 6 April 17, 2010 23:40


All times are GMT -4. The time now is 01:44.