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-   -   Karman Vortex street (http://www.cfd-online.com/Forums/star-ccm/95184-karman-vortex-street.html)

Apocolapse December 8, 2011 10:18

Karman Vortex street
 
Hi all,

I am having difficulty producing a karman vortex in Star CCM. I am a new user to the program, so the problem could be any number of things!

I am using a cylinder with a diameter of 0.016m and velocity of 0.0075m/s with water as my fluid.
So, according to the formula here (http://en.wikipedia.org/wiki/K%C3%A1..._vortex_street) I have a reynolds number of ~135. This should be enough to create the karman vortex effect, but my result vortex is different.

Attatched is a screenshot http://i.imgur.com/f8KF8.jpg

The physics conditions are:
  • laminar
  • implicit unsteady
  • liquid
  • constant density
  • segregated flow
  • three dimensional

And my mesh uses:
Prism Layer mesher
Trimmer
Surface Remesher

base size = 0.016m
minimum = 25%
Then I created a box in which to make the mesh finer, which can be seen in the image, here the mimimum size is 10%.

I cannot recall my simulation step time, but the image above was obtained after a VERY lengthy run, so there was not going to be much more change.

Could someone please point out where I have gone wrong?

Or, even better, could someone send me a .sim file with the vortex running correctly so I can reverse engineer the problem?

Big thanks to you all

lava12005 December 8, 2011 20:00

As far as I know, for low reynolds number it takes quite sometime.
But the wake behind the cylinder has started to oscillate, so what do you mean by the vortex result being different?
Try to calculate the Strouhal number, and compare with the existing data..

anunu December 12, 2011 10:53

Hi,

Regarding of flow pass through cylinder, you can look for two examples in the user guide. One is in the validation samples, and another is in the aeroacoustic tutorial.


Best Regards,


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