Free end effects on the near wake flow structure behind a finite circular cylinder. J Wind Eng Ind Aerodyn

Journal of Wind Engineering and Industrial Aerodynamics (Impact Factor: 1.41). 12/2000; 88(2-3):231-246. DOI: 10.1016/S0167-6105(00)00051-9


The free end effect on the near wake of a finite circular cylinder in a cross flow has been investigated experimentally. Three finite cylinders with aspect ratios (L=D) of 6, 10 and 13 were tested in a subsonic wind tunnel at a Reynolds number of 20 000. A hot-wire anemometer was employed to measure the wake velocity. Mean pressure distributions on the cylinder surface were also measured. The flow near the free end was visualized to observe the flow structure qualitatively in a circulating water channel. The experimental results from these finite cylinder (FC) models were compared with those of a two-dimensional circular cylinder. The flow past the FC free end shows a complicated three-dimensional wake structure. As the FC aspect ratio decreases, the vortex shedding frequency is decreased and the vortex formation region is elongated. The free end effect becomes dominant close to the FC free end. The three-dimensionality of the FC wake may be attributed mainly to the strong entrainment of irrotational fluids, caused by the downwash of counter-rotating vortices separated from the FC free end. The downwash flow is concentrated in the central region of the wake. A peculiar flow structure having a 24 Hz frequency component was observed near the free end using spectral analysis and cross-correlation of the velocity signals. This 24 Hz frequency component is closely related to the counter-rotating twin vortices formed near the FC free end.

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    • "Figure 12 shows the computed streamwise velocity profile behind the human body in X direction at Z = 1.15 m. The distance between this location and the head vertex of the human body in Y direction is 1.45 m, 5 times of the back width of the human (5D), which is far enough to ensure the wake and turbulence is sufficiently developed in three-dimension (Park and Lee 2000, 2002; Krajnovic 2011). Figure 12a indicates that the streamwise velocity is significantly large in the wake behind the human body (X ranges from 0.8 to 1.2 m). "
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    • "However, a significant amount of fluctuating energy is observed for St % 0:0720:08, but it is hard to characterize it because of its high irregularity. This feature is in good agreement with what was found in Park and Lee (2000) where a dominant spectral component at St % 0:07 was found with a fluctuating energy that decreases with reducing h/d, even if it was not clearly detectable anymore already for a model with h/d ¼6. "
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