Transition to turbulence on a cylinder in axial oscillatory flow
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The transition to turbulence in oscillatory flow along a smooth cylinder, aligned axially with the ambient flow, was investigated through direct measurement of the wall shear stress, the phase lead of the maximum wall shear stress over the maximum free stream velocity, and the use of flow visualization with a laser light sheet. The results have shown that the Reynolds number clearly delineates the boundaries of the laminar stable flow (less than 420), transitional flow (between 420 and 780), and turbulent flow (greater than 780) at the start of which the phase angle decreases rapidly from about 34 degrees to 13 degrees, the friction coefficient increases rapidly, and the turbulent motion prevails over larger fractions of the flow cycle. The transitional and turbulent states are rich with nonaxisymmetric radial and vortical motions which burst themselves into existence most intensely during the later stages of the deceleration phase. 28 refs.
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