Experimental Study on the Characteristics of Conical Vortices over a Flat Roof

• Main Authors: Michael Lai, 賴葦帆
• Other Authors: Cheng Lin
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/53121985948351503035

碩士 === 國立中興大學 === 土木工程學系 === 93 === When an uniform flow encounters an oblique building with square cross-section, a three-dimensional flow field, so called conical vortex, is formed above the roof of the building. The flow structure and characteristics of the conical vortex were studied experimentally by using two flow visualization techniques and particle image velocimetry (PIV). The Reynolds numbers (Re), based on the free stream velocity (U0) and the edge length of the roof (D), range from 6000 to 30000. The purpose of the present study is to provide the qualitative and quantitative properties of the conical vortex. By lowering the Reynolds number from 30000 to 6000, the flow field structure of the conical vortex was observed by flow visualization methods and found to appear a distinct change. The conical vortex appeared in a pair when Re=18000、24000、 30000 and only on one side when Re=6000、12000. With regard the conditions for the Reynolds numbers are 6000 and 30000, detail characteristics of the conical vortex behavior, including the position of vortex core line and the vortex strength varies with different transverse cross-section, are quantified and discussed in the present study.