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

Backward Facing Step

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 28, 2000, 08:08
Default Backward Facing Step
  #1
Pete
Guest
 
Posts: n/a
I have a question about the backward facing step problem. At low Reynolds numbers (based on velocity upstream of step and step height), the reattachment length increases linearly with the Reynolds number. As the Re number gets larger, does the reattachment length stop increasing with further increases in Re? Does it approach a constant value for that particular geometry?
  Reply With Quote

Old   June 28, 2000, 14:22
Default Re: Backward Facing Step
  #2
John C. Chien
Guest
 
Posts: n/a
(1). A good question, but I am not sure. (2). Within laminar assumption, I guess, this self similar behavior will continue. (3). For turbulent flow , it is around six step height.
  Reply With Quote

Old   June 28, 2000, 17:45
Default Re: Backward Facing Step
  #3
Kalyan
Guest
 
Posts: n/a
With laminar assumption, I guess the length would increase with Re in a typical case.

However, I am not too sure if the Re (as defined based on velocity and step height) is a relevant quantity at very high Re. The vortex shedding at the bend may be depend a lot on the step height. I do not think any self-similar behavior exists in this problems due to the singular behavior at the bend and the reattatchment point.
  Reply With Quote

Old   June 28, 2000, 19:03
Default Re: Backward Facing Step
  #4
Jitendra
Guest
 
Posts: n/a
pete,

It is true that at low reynolds no. if you increase Re reattachment length increases.At higher Re this reattachment length decreases ... interseting fact indeed.

Have a look at landmark paper in Journal of Fluid mechanics. Vol 117. n1. Page 17-23.

I forgot the author.

good luck

jitendra
  Reply With Quote

Old   June 28, 2000, 19:12
Default Re: Backward Facing Step
  #5
Guus Jacobs
Guest
 
Posts: n/a
The following paper will probably answer most of your questions:

B.F. Armaly, F. Durst, J.C.F. Pereira: "Experimental and theoretical investigation of backward-facing step flow", J.Fluid.Mech Vol.127,pp.473-496,1983

As you said for low Reynolds number the reattachement length will increase approximately linearly. For a Re number based on the maximum inlet velocity and the hydraulic diameter of the inlet section (in case the inlet section has a channel like configuration) that is between 1200 and 6600 the flow is in a transition region and the average reattachement length will decrease gradually to a constant average reattachement length of about 6 for turbulent flows. For other inlet sections (say a boundary layer) these numbers will probably differ a bit.
  Reply With Quote

Old   June 28, 2000, 21:40
Default Re: Backward Facing Step
  #6
John C. Chien
Guest
 
Posts: n/a
(1). Yes, I was thinking about the steady state solution of the shear layer. (2). The structure of the recirculation region will be somewhat different. (3). For the transient flow solution, it is a completely different issue.
  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
How to write k and epsilon before the abnormal end xiuying OpenFOAM Running, Solving & CFD 8 August 27, 2013 15:33
Backward facing step. Fluids Main CFD Forum 7 December 4, 2012 12:28
Upgraded from Karmic Koala 9.10 to Lucid Lynx10.04.3 bookie56 OpenFOAM Installation 8 August 13, 2011 04:03
IcoFoam parallel woes msrinath80 OpenFOAM Running, Solving & CFD 9 July 22, 2007 02:58
Could anybody help me see this error and give help liugx212 OpenFOAM Running, Solving & CFD 3 January 4, 2006 19:07


All times are GMT -4. The time now is 09:50.