A study on flow around two circular cylinders in staggered arrangements (2nd report, estimation of strouhal number using in combination with wavelet analysis)

Characteristics of vortex shedding of two identical circular cylinders in staggered configurations were investigated experimentally at a Reynolds number of 5.5 × 10⁴. Measurements were performed for stagger angles α=10°, 25°, 45°, 60° and 75°, and gap spacing T/D = 0.1-5.0, where α is the angle between the free-stream flow and the line connecting the centers of the cylinders, T is the gap width between the cylinders, and D is the diameter of the cylinders. The estimation of vortex shedding frequencies was done by using in combination with wavelet analysis results of fluctuating pressures on surface of two cylinders. The new findings for vortex shedding frequencies of two cylinders as follows. (i) For a = 10°, two Strouhal numbers appears for the range of T/D=0.1-2.1, in which two flow patterns switch from one to the other. (ii) For α=25°, in the range of T/D<1.1, the two cylinders behave like a single bluff body at least with regard to vortex shedding frequency. Also, for the range of T/D = 1.1-1.8, two stable flow patterns with regard to vortex shedding frequency persist, (iii) For α=45°, two stable flow patterns with regard to Strouhal numbers persist for T/D, =0.8-2.1. (iv) Strouhal number distibutions for a = 60° and 75° are almost the same in nature as those for α=45°.