# Spinning Cylinder

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

 June 7, 2001, 17:36 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

 June 7, 2001, 21:10 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.

 June 8, 2001, 00:39 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

 June 8, 2001, 00:48 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.

 June 8, 2001, 09:53 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.

 June 8, 2001, 10:25 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

 June 9, 2001, 01:21 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.

 June 9, 2001, 10:22 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

 June 10, 2001, 00:45 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.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post ozzythewise Main CFD Forum 8 June 13, 2012 06:24 blaise OpenFOAM Meshing & Mesh Conversion 0 May 10, 2010 03:56 doctsh FLOW-3D 18 February 19, 2010 09:41 Tim Daly FLUENT 1 November 10, 2008 00:02 Mirek Kabacinski FLUENT 0 July 23, 2003 18:40

All times are GMT -4. The time now is 14:31.