CFD Online Logo CFD Online URL
Home > Forums > Main CFD Forum

Non-Reflecting BC

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

LinkBack Thread Tools Display Modes
Old   December 26, 2006, 06:54
Default Non-Reflecting BC
Posts: n/a
I've written my own code program simulating 2D, incompressible and viscous flow about an airfoil. I'm using for that structured C-grid generation (far-field boundary is 15xcord). The problem is that my code program diverges after about 5000 itterations. Mister Ganesh who is an active and helpfull on this Site suggested to use non-reflecting BC at far-field instead of free stream BC. My question is: Are that type of BC can be applied to incompressible flow, and how can i implement non reflecting BC.
  Reply With Quote

Old   December 26, 2006, 17:52
Default Re: Non-Reflecting BC
Posts: n/a
Most of the non reflecting BC are derived from the characteristics of the Euler equation and they usually try to absorb correctly the outgoing acoustic,vorticity and entropy wave and are derived for systems where the speed of sound is finite.

You can try implementing an absorbing buffer zone.A simple way of implementing it is as follows:

The equation would be

df/dt=RHS+sigma* f

where the factor sigma=sigma0*((x-xb)/D)^beta.sigma0 is a constant based on the grid ( I use sigma0=2/dx for most cases, beta=3 ).D is the thickness of the sponge layer.xb is the location where the sponge layer begins.A sponge layer of 10-20 points works for me.



I have not tested the buffer zone for incompressible systems and am not sure if they might help. =)

  Reply With Quote


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
udf for reflecting bondary condition for particle at outflow.. bhanwar Fluent UDF and Scheme Programming 5 September 13, 2012 02:05
Partially reflecting boundary condition Rachel FLUENT 1 July 1, 2008 18:20
Reflecting bc kupiainen OpenFOAM Running, Solving & CFD 15 July 13, 2005 08:00
User Defined Non Reflecting Boundary Condition Tengc FLUENT 1 November 17, 2004 14:58
NRBC's (Non Reflecting Boundary Conditions) Vinayak Barve FLUENT 0 March 3, 2004 18:41

All times are GMT -4. The time now is 06:22.