# Air flow over a cylinder - what regime?

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 November 17, 2008, 20:33 Air flow over a cylinder - what regime? #1 momentum_waves Guest   Posts: n/a Air flows over a cylinder in a 2D domain. What flow regime can we consider the fluid to be in, with a Reynold's number of 1100 relative to cylinder diameter, domain entry velocity & air kinematic viscosity? Would a clear fluid structure flow pattern be expected, behind the cylinder? Would this flow pattern be distance-dependent relative to the cylinder? mw...

 November 17, 2008, 22:04 Re: Air flow over a cylinder - what regime? #2 Ahmed Guest   Posts: n/a Please Check this study http://www.grc.nasa.gov/WWW/wind/val...l/lam_cyl.html in this paper results for Re=100-2000 are given http://www.mate.tue.nl/mate/pdfs/889.pdf some nice pictures http://www.eng.fsu.edu/~shih/succeed...m#Introduction http://amath.colorado.edu/faculty/fo...0_Fl_p_cyl.pdf

 November 17, 2008, 23:01 Re: Air flow over a cylinder - what regime? #3 momentum_waves Guest   Posts: n/a Hi Ahmed, Thanks for those very interesting links - you are a true goldmine of useful information. Now, to re-visit the original question (slightly extended): With 'do-nothing' boundaries on top, bottom & exit (flow in a freestream), with a Re~1100, what regime would we characterise the flow to exist in - laminar, transition, turbulent, fully-turbulent? What would the flow field look like in the L/D range of 20-40? mw...

 November 17, 2008, 23:04 Addition: Air flow over a cylinder - what regime? #4 momentum_waves Guest   Posts: n/a mw wrote: What would the flow field look like in the L/D range of 20-40? where: L = distance behind cylinder D = cylinder diameter mw...

 November 17, 2008, 23:42 Re: Addition: Air flow over a cylinder - what regi #5 Ahmed Guest   Posts: n/a Right now, what I can say is that it is unsteady flow (vortex shedding on the down stream side). There is a nice FLUENT tutorial, I have it in paper form, but if you google you might be lucky, you can find the whole documentation on some University sites, I am inclined to say at this Re the flow is turbulent, but I have to check some old notes before. There is a reference to an article mentioned by Jed few days ago http://www.cfd-online.com/Forum/main.cgi?read=62578 referring to the No Boundary condition instead of the classical outflow BC so please check it, and good luck

 November 18, 2008, 01:07 Re: Addition: Air flow over a cylinder - what regi #6 momentum_waves Guest   Posts: n/a Thanks Ahmed. Could I respectfully ask you to forward a copy of the paper to my e-mail address? Many thanks. I've been using the 'do nothing' or 'no boundary' condition for years. In most flow problems it makes sense to not impose constraints (boundaries) where none exist in nature - especially if we wish to observe a natural flow event. mw...

 November 19, 2008, 12:08 Re: Addition: Air flow over a cylinder - what regi #7 momentum_waves Guest   Posts: n/a Any further ideas on what flow regime we are working with? mw... www.adthermtech.com/wordpress3