Investigation of dominant frequencies in transition Reynolds number range of flow around a circular cylinder Part I: Experimental study of the relation between vortex shedding and transition frequencies

A comprehensive hot wire investigation of the flow around a circular cylinder is carried out in an 18″ × 18″ wind tunnel to look into the dominant frequencies at the stagnation, separation and separated shear layers in the transition Reynolds number range. The majority of the experiments are carried out at Reynolds number of 4.5 ×10⁴, with additional transition frequency tests at Reynolds numbers of 2.9 × 10⁴, 3.3 × 10⁴ and 9.7 × 10⁴ respectively. The results are analyzed in terms of power spectral density. While the frequency associated with stagnation is found to be essentially due to vortex shedding, frequency doubling of vortex shedding is also evident in the separated shear layers. Two peaks associated with transition frequencies are detected and their possible implications are presented.