An experimental study on the vertical incompressible flow past a finite-length horizontal cylinder

• Main Authors: Willy Stevanus, 張威力
• Other Authors: Yi-Jiun Peter Lin
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/19765343296241150752

碩士 === 國立臺灣科技大學 === 機械工程系 === 101 === The research studies the characteristics of the vertical incompressible flow past a finite-length horizontal cylinder in the near wake region with subcritical range of ReD from 250 to 1080. The experiments are performed in a vertical closed-loop water tunnel. Flow fields are observed by the particle tracer approach for flow visualization and measured by the Particle Image Velocimetry (P.I.V.) approach for velocity fields. The characteristics of vortex formation in the wake of the finite-length cylinder change at different regions from the tip to the base of it. Near the tip, a pair of vortices in the wake is observed and the size of the vortex increases as the observed section is away from the tip. Around a distance of 3 diameters of the cylinder from its tip, the vortex street in the wake is observed for some Reynolds numbers. The characteristics of vortex formation also change with Reynolds numbers. At X/D = -3, a pair of voctices is observed in the wake for ReD = 250, but as ReD increases to 560 the vortex street is observed at the same section. The vortex shedding frequency is analyzed by Fast Fourier Transform (FFT). Experimental results show that the downwash flow changes the vortex shedding frequency even to 5 diameters of the cylinder from its tip and vanishes about 10 diameters of the cylinder from its tip. For the capped finite-length cylinder, flow visualization results show that the cap reduces the downwash effect. At X/D = -1, the vortex street is observed already at the lowest Reynolds number, ReD = 250. The vortex street is more obvious as the observed section is away from the tip.