Appraisal of Strouhal number in wind turbine engineering

Flows around blunt bodies at high Reynolds numbers generate a periodic release of staggered vortices. The dimensionless frequency of vortex shedding, the Strouhal number St, was found successful in describing periodic fluid flows. In fact, several literature datasets proved that the number St~0.16 describes with reasonable (at times, excellent) approximation a large variety of periodic fluid phenomena, many of them having no clear affinity. The first motivation of the present study is to collect under one cover the results disseminated in various sources; the second purpose is to double-check the constancy of Strouhal number in wind turbines as well. The St number is here elaborated in a more informative way for horizontal-axis wind turbines, showing that it includes the tip speed ratio and the number of blades; the law St~0.16 is here corroborated by further findings which includes wake meandering and the flow fields produced by three wind turbines (a two-bladed HAWT; a three-bladed lift-driven Darrieus VAWT; and a two-bladed drag-driven Savonius VAWT). The present findings suggest a design criterion for wind turbines.