DOI: 10.1615/TSFP6
EXPERIMENTAL INVESTIGATION OF THE WAKE BEHIND A DISCONTINUOUS CYLINDER
摘要
The effect of a discontinuous cylinder geometry on the near wake structures was investigated experimentally. This 'discontinuous' circular cylinder has gaps so that solid segments 5D long are followed by gaps 2.5D long, in a repeating pattern, where D is the diameter of the cylinder. A thin steel plate was used to hold all of the cylinder pieces together. Thus, a three-dimensional (3D) wake was created at the origin with the intent to force the near wake flow to have similar structural characteristics to the far wake behind an 'infinite' cylinder, i.e., a near wake flow with horseshoes or double rollers formed by rapid kinking of Karman-like vortices. Since the kinetic energy associated with the fluctuations of these near-wake 3D vortical structures was high, the flow system was considered suitable to clarify the role of these velocity patterns in the entrainment process of wake flows, which is still the subject of controversy. Particle image velocimetry (PIV) measurements were made in the wake behind the discontinuous cylinder up to x/D=56, at a Reynolds number Re=10,000. The development of double rollers resulting from the interaction between the high momentum flow through the gaps and the Karman-like vortices formed behind the solid cylindrical segments was confirmed. They have a dominant role in the initial wake growth which occurs under significant momentum transfer in the spanwise direction. This overall flow dynamics is similar to the momentum transfer that takes place at the scale of the intermittent turbulent bulges that protrude from the wake in the far region and that were reported to be associated with double rollers.