An Experimental Investigation of the Evolution of a Horseshoe Vortex

• Main Authors: Shou-Yen, Chao, 趙守嚴
• Other Authors: 周榮華
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/14170289208502361106

博士 === 國立成功大學 === 工程科學系 === 87 === Flow visualization and surface pressure measurements are preformed to study the evolution of a horseshoe vortex upstream of a surface mounted cylinder with aspect ratios ranging from 0.67 to 17. The Reynolds numbers are 500 for visualization experiments and 1900 to 3800 for wind tunnel tests. The cross sectional shape of the cylinder is rectangular, semi-circle, quarter-circle or triangular. The height ratio(normalized by the largest height) of the cylinder varies from 0.1 to 1. The experimental results indicate that a horseshoe vortex will branch itself into smaller regular vortices of U shape for aspect ratios greater than 10. The end planes cause the U vortices to occur at a smaller aspect ratio and also make their sizes become more uniform. The U vortices will be suppressed by changing the cross sectional shape or the height ratio. For rectangular cylinders, when the height ratio is near or greater then 0.2, a horseshoe vortex will be developed and branched subsequently. The number of branched smaller vortices increases as the aspect ratio increases, but decreases as height ratio increases further. The branching of a horseshoe vortex is caused by decreases in both the streamwise adverse pressure gradient and spanwise favorable pressure gradient upstream of the cylinder.