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Abstract

The oscillating flow modes, frequency selection, and response of periodic frequency to change of characteristic flow modes behind a NACA 0012 wing model are studied experimentally. The functional relationships of the dominant mechanisms in limiting ranges of Reynolds number are justified analytically. The oscillating instabilities in wake region possess four characteristic modes: laminar, subcritical, transitional, and supercritical. In viscous effect dominated regime of laminar mode, Strouhal number is inversely proportional to Reynolds number. In inertial effect or pressure gradient dominated regime of supercritical mode, Strouhal remains constant. In regime between limiting cases, Strouhal number increases nonlinearly with Reynolds number and drops to a low value as shed vortices change from laminar to subcritical mode. The increase of free-stream turbulent fluctuations causes the decrease of Strouhal number only at low Reynolds numbers. In high Reynolds number regime, the effect is not apparent.

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