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

Axis Boundary Condition..what is it?

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

Reply
 
LinkBack Thread Tools Display Modes
Old   February 1, 2007, 16:14
Default Axis Boundary Condition..what is it?
  #1
CFDtoy
Guest
 
Posts: n/a
I am modeling a gas-in-gas process, gas exiting from a cirular tube into still air.

I am using a 3D slice with periodic boundary condition and an axis boundary condition.

Could someone tell me what does an axis boundary condition do? Is it symmetry or some kind of reflecting boundary condition?

how are the flow variables computed near the axis type?

Thanks for the clarification

CFDtoy

  Reply With Quote

Old   February 2, 2007, 01:50
Default Re: Axis Boundary Condition..what is it?
  #2
ravindra
Guest
 
Posts: n/a
HI cfd toy i think you are modeling 3-d, generally axis boundary condition is applicable for 2-d geomtry. for 3-d symetry is applicable, since we have planes so it will consider as symetry plane which ever you define. and also if u are modelling flow in which hot fluid flows to comparatively ambient it is not advisible to use symmetry condition ok, this is according to my knowledge bye
  Reply With Quote

Old   February 2, 2007, 09:48
Default Re: Axis Boundary Condition..what is it?
  #3
CFDtoy
Guest
 
Posts: n/a
Hello Ravindra: Thanks for your reply. I am modeling 3D flow with more than 5 cells in circumferential direction. Now, at the axis, which is actually an edge, I was wondering how the flow variables are calculated.

I know axis is not a boundary condition. But I am not sure about the implementation. Could you detail me on some numerics into axis type boundary implementation?

Thanks

CFDtoy
  Reply With Quote

Old   February 5, 2007, 01:44
Default Re: Axis Boundary Condition..what is it?
  #4
ravindra
Guest
 
Posts: n/a
hi if you are doing 2-d axi-symmetric problem then only you can calculate the flow variables at that axis,if you give axis as one of the boundary condition. but if you are doing computations in 3-dimension then i think you should select that plane of symmetry by using symmetry boundary condition and try to calculate the flow variables at that plane. this is ny opinion. bye
  Reply With Quote

Old   February 8, 2007, 06:52
Default abt: residuals
  #5
ravindra
Guest
 
Posts: n/a
hi cfdtoy i am finding temperature and velocity distribution of engine plume.i have used k-e method for solving it. the k and e residuals are oscillating around 1e-2 and continuity is oscillating around 1e-3 for some eighty thousand iterations. can u give me any idea how to bring the residuals down. whether it means that the solution may not converge at all? waiting for your reply ravindra

  Reply With Quote

Old   February 12, 2007, 21:22
Default Re: abt: residuals
  #6
CFDtoy
Guest
 
Posts: n/a
Reduce ur under relaxation. Typically, k,e use 0.4 or less. Not higher. What kind of convective schemes are you using? Use Upwind to see if the diffusion effects lead to convergence. If you get convergence with upwind then we can start playing with other things. If in effect you are unable to obtain convergence with upwinding process, it would then imply that even with sufficient numerical diffusion your solution diverges.

Please let me know once you are through these steps. Normally, k and eps models are strongly dependent on the boundary and intiial conditions as well.

Btw, Are you running transient or steady state?

CFDtoy!

  Reply With Quote

Old   February 13, 2007, 06:51
Default Re: abt: residuals
  #7
ravindra
Guest
 
Posts: n/a
hi im using first order upwinding scheme for density,momentum, energy... etc. pressure and velocity coupling i have used the simple algorithm, since im simulating only steady state flow. i will apply and see , what wll happen and come back to u. thanks for reply ravindra

  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
Boundary Conditions Thomas P. Abraham Main CFD Forum 20 July 7, 2013 05:05
Setting outlet Pressure boundary condition using CAFFA code Mukund Pondkule Main CFD Forum 0 March 16, 2011 04:23
Domain Imbalance HMR CFX 3 March 6, 2011 21:10
asking for Boundary condition in FLUENT Destry FLUENT 0 July 27, 2010 00:55
How to set boundary condition in Fluent for the fo Peiyong FLUENT 1 November 10, 2006 12:44


All times are GMT -4. The time now is 19:02.