Strouhal number data for two staggered circular cylinders

Vortex shedding from two staggered circular cylinders of equal diameters was studied experimentally at Re=3.2×104–7.4×104. The centre-to-centre pitch ratio ranged from P/D=1.125 to 4.0 and the incidence angle was varied in small increments from α=0° to 90°. The behaviour of the Strouhal number data depended on whether the cylinders were closely, moderately, or widely spaced. For closely spaced staggered cylinders, P/D<1.5, the flow pattern is similar to a single bluff body, and only a single Strouhal number is measured. For moderately spaced cylinders, 1.5⩽P/D⩽2.5, two distinct Strouhal numbers are measured when α>30°, but there is some scatter in the Strouhal data when α<30°. For widely spaced cylinders, P/D>2.5, the Strouhal numbers are close to the single-cylinder value.