Strouhal number for 3D bluff body

esha · February 9, 2020, 10:01

Hi, It is very simple question but I have a problem. I am trying to find Strouhal number(St= fD/u) for 3D cylinder. I used Ansys Fluent for simulation. until it was a periodic wake, I calculated Strouhal number by two ways (i) read data for cylinder and and check its period time manually.
(ii) Strouhal number by using Fluent built in function.
Values I found by these techniques have much difference.
Why is there difference in these values? How could I solve this problem. Is there any other way I could find accurate Strouhal number.
I need to solve it for my project. Please let me know!

flotus1 · February 9, 2020, 12:58

I have no idea what happens behind the curtain when you let Fluent determine a Strouhal number. But I guess that it uses reference length and velocity from the reference values tab. So make sure to enter values that match your simulation settings. And you probably need to ensure that only results after the initial transient are used.
A third method could be to monitor lift forces for the cylinder, and apply FFT to the signal.

February 9, 2020, 10:01	Strouhal number for 3D bluff body	#1
esha Member Join Date: Aug 2018 Posts: 85 Rep Power: 7	Hi, It is very simple question but I have a problem. I am trying to find Strouhal number(St= fD/u) for 3D cylinder. I used Ansys Fluent for simulation. until it was a periodic wake, I calculated Strouhal number by two ways (i) read data for cylinder and and check its period time manually. (ii) Strouhal number by using Fluent built in function. Values I found by these techniques have much difference. Why is there difference in these values? How could I solve this problem. Is there any other way I could find accurate Strouhal number. I need to solve it for my project. Please let me know! Last edited by esha; February 10, 2020 at 08:33.

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February 9, 2020, 12:58		#2
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	I have no idea what happens behind the curtain when you let Fluent determine a Strouhal number. But I guess that it uses reference length and velocity from the reference values tab. So make sure to enter values that match your simulation settings. And you probably need to ensure that only results after the initial transient are used. A third method could be to monitor lift forces for the cylinder, and apply FFT to the signal.