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

Spinning Cylinder

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 7, 2001, 17:36
Default Spinning Cylinder
  #1
Luiz Eduardo Bittencourt Sampaio
Guest
 
Posts: n/a
Hi everyone, I need to know if a cylinder (2 meters diameter) spinning at 1000 rpm would be able to induce its wall speed to the adjacent layers of the fluid or if the turbulence effect will not allow this. I mean, analitically (and assuming laminar flow), this cylinder (assume first an infinit heigth) would create a field velocity such as v/r where v is the wall speed. But I dont know how those magic turbulence phenomenon would modify this formula. I tried to run some CFD codes, but I can never trust my results.

Does any one have an empirical or CFD data on this subject? Is there an analitic turbulent solution?

Best Regards, Luiz
  Reply With Quote

Old   June 7, 2001, 21:10
Default Re: Spinning Cylinder
  #2
John C. Chien
Guest
 
Posts: n/a
(1). Because of the viscous effect, the surrounding flow will eventually become a solid body rotation.(assuming that the air around it is free to rotate.
  Reply With Quote

Old   June 8, 2001, 00:39
Default Re: Spinning Cylinder
  #3
Luiz Eduardo Bittencourt Sampaio
Guest
 
Posts: n/a
Thank you Mr. Chien. You mean, the velocity will be something like v=wr (w being the angular speed of the cylinder) instead of v=wR^2/r (where R is the cylinder radi and r is the distance to the cylinder axis)? All beacause of turbulence??? (In laminar flow we would expect v=wR^2/r, rigth?) What is the domain validation for this behaviour since it cannot extend to infinity (otherwise, we would have a big - infinit - velocity far away from the cylinder, which is not phisically possible)?

Best regards and thank you again, Luiz
  Reply With Quote

Old   June 8, 2001, 00:48
Default Re: Spinning Cylinder
  #4
John C. Chien
Guest
 
Posts: n/a
(1). I think it is like a plate moving at a constant speed. If the far field is not constraint, then eventually you will have constant velocity moving at the plate velocity. (2). If the far field is constraint, or fixed, then you will have the 2-D Couette flow. (linear velocity between the wall and the fixed outer boundary, for laminar flow. For turbulent flow, the velocity profile will be different.) (3). You can extend the 2-D case to the cylindrical case. (4). for finite length, you will have 3-D flows. I think, it has been discussed here, long time ago. There are many websites on this problem. You can do some Internet searches first.
  Reply With Quote

Old   June 8, 2001, 09:53
Default Re: Spinning Cylinder
  #5
Dr Strangelove
Guest
 
Posts: n/a

If your cylinder is spinning in quiescent air, it sounds like the Reynolds number will be about 7e6, which is getting high enough that a transition to turbulence cannot be ruled out.

Critical Reynolds numbers, (Re_x), for flow past flat plates, have been measured between 3.5e5 and 1e6, for example.

Every geometry is different, so, as John Chien has suggested, you should research the literature for more information.
  Reply With Quote

Old   June 8, 2001, 10:25
Default Re: Spinning Cylinder
  #6
Luiz Eduardo Bittencourt Sampaio
Guest
 
Posts: n/a
Thank you again, Mr.Chien, I ve been looking in the web for this. I looked in cfd-online, in CFD companies (sometimes they provide examples and movies), but I couldn'tfind any. Could you provide any pointers to this?

Best Regards, luiz
  Reply With Quote

Old   June 9, 2001, 01:21
Default Re: Spinning Cylinder
  #7
John C. Chien
Guest
 
Posts: n/a
(1). Try to use the key words "rotating couette flow" or "Taylor couette flow" in the serach engine.
  Reply With Quote

Old   June 9, 2001, 10:22
Default Re: Spinning Cylinder
  #8
Luiz Eduardo Bittencourt Sampaio
Guest
 
Posts: n/a
Thank you Mr. Chien, I was able to find very good web sites, with a lot of experimental data. All of them talk about Taylor vortices and velocities of the fluid, but no one mentioned about the pressures. Do you know what happens to the pressure behaviour when this kind of vortex appears? I mean, is the pressure gradient lower than when in laminar flows? Best Regards, Luiz
  Reply With Quote

Old   June 10, 2001, 00:45
Default Re: Spinning Cylinder
  #9
John C. Chien
Guest
 
Posts: n/a
(1). If the dominating factor is the tangential velocity, then I think, the radial pressure distribution will have to be balanced by the centrifugal force.
  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
Incorrect Drag and Drag Coefficient for flow over a cylinder ozzythewise Main CFD Forum 8 June 13, 2012 06:24
Specifying boundary faces failes in blockMesh blaise OpenFOAM Meshing & Mesh Conversion 0 May 10, 2010 03:56
Spinning cylinder in viscous liquid - a serious doubt doctsh FLOW-3D 18 February 19, 2010 08:41
rotating cylinder using sliding mesh Tim Daly FLUENT 1 November 9, 2008 23:02
Turbulent steady flow around a circular cylinder Mirek Kabacinski FLUENT 0 July 23, 2003 18:40


All times are GMT -4. The time now is 22:26.