Strouhal number and multiple freq
 

I have a question,

As I calculating the flow around a square cylinder, there are inevitably multi-frequencies.

So how did you guys calculate the Strouhal number then?

I saw the definition of St as against vortex shedding frequency, but in a relatively high Re, there will be more than one vortex shedding frequency, how to judge which is the biggest, if there are two biggest...

Will you do the average?