strouhal

mina.p · July 14, 2014, 11:35

Hi
would anybody please explain an accurate method to find strouhal number or natural frequeny of vortex shedding form a cylinder in cfx?
Thanks

ghorrocks · July 14, 2014, 18:14

Put a monitor point watching pressure or velocity in the wake region and run the simulation. Then extract the frequency from the monitor point data, either by simple estimation or FFT or other more advanced techniques.

singer1812 · July 16, 2014, 16:53

If I had to guess, I think he means setting up the turbulence, not pulling out the data

mina.p · July 18, 2014, 02:17

http://www.scribd.com/doc/140205598/...ortex-Shedding
I found this workshop about vortex shedding but my monitor points in solver are a straight line and don't fluctuate like this workshop.
can anybody tell me the dimensions in this example?
thanks

mvoss · July 18, 2014, 05:26

page 6 ...
also check the scaling in the monitors since often the very first peak pushes the scales up high.

ghorrocks · July 18, 2014, 06:06

If you are asking why don't I get shedding rather than how I extract the data....

This is an FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

In particular vortex shedding requires accurate time and space discretisation, so use second order for both. You also need a mesh size and time step sized correctly by a sensitivity study.

saeed bahrami · July 18, 2014, 11:08

you're persian ?

saeed.bahrami92@yahoo.com

July 14, 2014, 11:35	strouhal	#1
mina.p New Member mina Join Date: Nov 2013 Posts: 20 Rep Power: 13	Hi would anybody please explain an accurate method to find strouhal number or natural frequeny of vortex shedding form a cylinder in cfx? Thanks saeed bahrami likes this.

July 18, 2014, 11:08	hi mina.p	#7
saeed bahrami New Member saeed Join Date: Jul 2014 Posts: 7 Rep Power: 12	you're persian ? saeed.bahrami92@yahoo.com

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July 14, 2014, 18:14		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,970 Rep Power: 145	Put a monitor point watching pressure or velocity in the wake region and run the simulation. Then extract the frequency from the monitor point data, either by simple estimation or FFT or other more advanced techniques.

July 16, 2014, 16:53		#3
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 21	If I had to guess, I think he means setting up the turbulence, not pulling out the data

July 18, 2014, 02:17		#4
mina.p New Member mina Join Date: Nov 2013 Posts: 20 Rep Power: 13	http://www.scribd.com/doc/140205598/...ortex-Shedding I found this workshop about vortex shedding but my monitor points in solver are a straight line and don't fluctuate like this workshop. can anybody tell me the dimensions in this example? thanks

July 18, 2014, 05:26		#5
mvoss Senior Member Matthias Voß Join Date: Mar 2009 Location: Berlin, Germany Posts: 449 Rep Power: 21	page 6 ... also check the scaling in the monitors since often the very first peak pushes the scales up high.

July 18, 2014, 06:06		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,970 Rep Power: 145	If you are asking why don't I get shedding rather than how I extract the data.... This is an FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F In particular vortex shedding requires accurate time and space discretisation, so use second order for both. You also need a mesh size and time step sized correctly by a sensitivity study.