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We can see a clear sinusoidal pattern, a sign of sustained vortex shedding process after 40s.This plot can be used to compute the correct value of Strouhal number. The problem is non-dimensionalized (D = 2, U = 1) and Sr = f*D/U = 0.0846 * 2 = 0.169. The results matches fairly well with the value ( 0.183 ) as reported by Williamson (link)
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