Experimental Investigation of Spanwise Effects for Flow Around Two Circular Cylinders in a Tandem Arrangement

• Main Author: 李思賢
• Other Authors: Jerry M. Chen
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/27389635642468744516

碩士 === 國立中興大學 === 機械工程學系 === 90 === The spanwise effects for flow around two identical circular cylinders in a tandem arrangement have been studied experimentally. The experiments were performed in an open-type wind tunnel for Reynolds number of 4500. In addition to the case of two stationary cylinders, the oscillating case involves a rotationally oscillating upstream cylinder. The spanwise vortex shedding frequency, and spanwise surface pressures are described. This study employs the cross-correlation as well as Hilbert transformation to examine the spanwise effects caused by the oscillation of upstream cylinder. At the critical spacing (L/D = 3.88 - 4.22) dual vortex shedding frequencies have been observed for the stationary case well as for the oscillating case. The occurrence of dual shedding frequencies indicates switching of the flow patterns between two stable modes and is referred to as the bistable flow. In the stationary case, as the spanwise cross-correlation coefficient decreases it is also found that difference measured using Hilbert transformation increases. In the oscillating case, research is emphasized on the phase difference when bistable flow occurs. This is attained by rotationally oscillating the upstream cylinder while holding the downstream cylinder stationary. The bistable flow can also occur when the vortex shedding is locked-on to the oscillating upstream cylinder. The lock-on of vortex shedding to the oscillating upstream cylinder leads an increase in the spanwise cross-correlation and a decrease in the phase difference.