| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 99 === The evolution processes of the surface flow and wake behind an impulsively started square cylinder at different incidence angles have been studied experimentally in a water towing tank. Particle tracking flow visualization method (PTFV) and particle image velocimetry (PIV) were used to obtain clear flow images for Reynolds numbers between 103 and 104. The incidence angles were also varied from 0 to 45 degrees. Vortex shedding characteristics were measured by a single-component hot-film anemometer for Reynolds numbers. Flows around the square cylinder were identified in five categories. The incidence angles between 13 to 15 degrees exhibited as a dividing line, between which low-incidence angle region and high incidence-angle region. The low incidence-angle region was divided into three modes. The region for which incidence angle below 5 degree and Reynolds number lower than 2259±30 were identified as region I. Reynolds numbers above 2289 were identified as region II. The region where incidence angle was between 5 and 13 degrees are identified as region III. Flow characteristics in three categories prominently different. The high-incidence angle region were divided into two modes. Reynolds number below 3300 were identified as region IV and Reynolds number above 3360 were categorized as region V. Region IV and V have two modes based on incidence angle α. These angles were identified as 15 < α < 38 and 38 < α < 45. At incidence angle 45 degree, a symmetric wedge flow is observed on the two surfaces facing windward. Flow modes of dual bubble, single bubble, attached flow and recirculation bubble were identified from PIV study. From hot-film anemometer study vortex shedding frequency was highest for square column at incidence angle about 14 degree.
|
|---|
