Abstract
In order to elucidate the effects of positive pressure gradient on flame structure and stabilization mechanism, it is first necessary to clarify those on turbulence characteristics and eddy structure not only in a cold shear layer, but also in a cold wake flow behind a bluff body. In this study, the influences of pressure gradient in the flow direction on the surface pressure around a circular cylinder and the eddy-shedding process are investigated in a two-dimensional cold air flow without combustion. Flow visualization and an FFT analysis of the oscillating surface pressure are made to examine time-averaged and fluctuating properties concerning the eddy-shedding process. It is found that increasing the free stream pressure gradient causes a transition of the wake flow pattern from an alternative eddy-shedding type to a symmetric one without Karman vortex. An increase in the pressure gradient extends the wake region, and simultaneously lowers the pressure drag force, which may be regarded as one of the most important characteristics of the divergent flow.
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