2 Replies Latest reply on Mar 7, 2018 12:02 PM by Luis Costa

# Strouhal Number

Hi,

This has been asked before. But the last answer was from 2009...and inconclusive...

Anyway, I'm doing a very simple simulation, where my goal is to find the frequency of the vortex created by the wind blowing to a cylindrical tube with 200mm diameter 5mm thick, and 1m lenght. The tube/pole is fixed at one of the flat faces, and the wind is blowing (red arrow) perpendicular to the tube.

Wind velocity 55.6m/s

I've already run various simulations, using flowsimulation, but I wanted to understand how I can extract the strouhal number, or the lenght of the vortex, or the vortex frequency....

the strouhal number shows up on the help menu, in the topics...but you can't find it anywhere else...I've searched through the parameters lists ( when you create a plot, and click on more parameters) and nothing... you have turbulence lenght, turbulence intensity...but nothing referring to vortex shedding frequency...

Does anyone knows, how to get around this problem...??

• ###### Re: Strouhal Number

for VIV (Vortex Induced Vibrations) you can assume a Strohal number of 0.2 and calculate the frequency. Run a transient simulation and count the number of vortices that shed. You can split the structure into two halfs (maybe quarters is better) and put goals for side load and downwind load and you can get a plot of the frequency vs. time as well. The program won't just spit out a frequency, well at least I haven't bothered to figure it out as it would likely require an FFT of the goal plot.

• ###### Re: Strouhal Number

Hi Bill,

(was already running a transient simulation)

I just counted the vortex frame by frame in a 1 sec interval.

Thanks