Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/2744
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dc.contributor.advisor陳志敏zh_TW
dc.contributor.advisorChen, J. M.en_US
dc.contributor.author陳洪正zh_TW
dc.contributor.authorChen, H.C.en_US
dc.date1999zh_TW
dc.date.accessioned2014-06-05T11:43:52Z-
dc.date.available2014-06-05T11:43:52Z-
dc.identifier.urihttp://hdl.handle.net/11455/2744-
dc.description.abstract本文以實驗方法探討圓柱以來回旋轉方式振盪的渦漩鎖定特性。實驗在開放式低速風洞中進行,基於圓柱直徑的雷諾數為4500。首先擷取尾流速度的擾動訊號做頻譜分析,觀察鎖定過程及鎖定邊界。由於鎖定會改變渦漩形成結構,所以本實驗利用熱線探針擷取不同水平站位的速度擾動訊號找出渦漩形成長度,並藉由平均及擾動表面壓力分佈觀察圓柱附近流場的特性。另外,本實驗利用動量缺陷法估算尾流的平均阻力係數,以討論阻力的變化,同時配合煙線觀察相互比較近尾流場結構變化。 本實驗主要的參數為振盪頻率及振幅。實驗結果發現圓柱發生鎖定時背壓值會下降,渦漩形成長度縮短及阻力值的上升。在變化不同振盪頻率方面,結果顯示以鎖定邊界內的中間頻率(fe/fn = 0.992)振盪時阻力最高,並且在低頻(fe/fn = 0.906)逼近時,渦漩的剝離方向會與原來的運動方向相反,造成表面擾動壓力劇升及背壓些微不穩定的現象。zh_TW
dc.description.abstractThe study reports the results of the experiments on the lock-on of vortex shedding from a circular cylinder that is forced to oscillate rotationally in a uniform stream. The experiments were performed in an open-type wind tunnel. The Reynolds number is 4500 based on the diameter of the cylinder. The on-set of lock-on, which depends on the combination of the frequency and amplitude of the forcing, is determined by employing spectral analysis of the wake velocity. The details of the route leading to lock-on and the lock-on regime are presented. In the lock-on regime, it is found that the phase of the shed vortex with respect to the cylinder motion switches by approximately π as the forcing frequency (fe) changes from a value above the natural shedding frequency (fn) to a lower one (fe/fn=0.906). The flow visualization confirms the phase switch due to the change of the forcing frequency. The fluctuating surface pressure measured within 90 deg of the stagnation point of the cylinder exhibit to be relatively large for the lower lock-on frequency as compared with those for the higher lock-on frequencies. The drag coefficients of the cylinder for different forcing frequencies and amplitudes are calculated from the surface pressure and the momentum defect measurements. These calculations are correlated with the results of flow visualization and the vortex formation length determined from the wake velocity fluctuations measured at different downstream stations.en_US
dc.description.tableofcontents目 錄 摘要…………………………………………………………………Ⅰ 英文摘要……………………………………………………………Ⅱ 誌謝…………………………………………………………………Ⅲ 目錄…………………………………………………………………Ⅳ 圖目錄………………………………………………………………Ⅶ 符號說明……………………………………………………………Ⅸ 第一章 前言……………………………………………………....1 1.1 研究動機………………………………………………..1 1.2 文獻回顧………………………………………………..2 1.3 實驗目的………………………………………………..7 第二章 實驗設備與模型………………………………………...9 2.1 風洞設備………………………………………………..9 2.2 模型……………………………………………………..9 2.3 振盪機構………………………………………………10 2.4 頻率量測系統…………………………………………10 2.5 壓力量測系統…………………………………………11 2.6 速度量測系統…………………………………………11 2.7 數據擷取系統…………………………………………12 2.8 流場可視化設備………………………………………12 第三章 實驗方法及程序……………………………………….14 3.1 實驗參數………………………………………………14 3.2 儀器校驗………………………………………………15 3.2.1 風速校驗……………………………………...15 3.2.2 壓力轉換器校驗……………………………..16 3.2.3 熱線測速儀校驗……………………………..16 3.3 阻力估算方法…………………………………………17 3.3.1 動量缺陷法……………………………………17 3.4 實驗步驟………………………………………………19 3.4.1 尾流頻率量測………………………………..19 3.4.2 表面壓力量測………………………………...20 3.4.3 渦漩形成長度量測…………………………..20 3.4.4 流場速度及靜壓量測………………………..20 3.4.5 相位差量測……………………………………21 3.4.6 流場可視化觀察……………………………..21 3.5 不準確度分析…………………………………………22 3.5.1 表面壓力量測………………………………..22 3.5.2 尾流速度及靜壓量測………………………..23 第四章 量測結果與討論……………………………………….24 4.1 鎖定行徑及鎖定邊界………………………………...24 4.1.1 鎖定行徑………………………………………24 4.1.2 鎖定邊界………………………………………26 4.2 表面平均壓力…………………………………………27 4.2.1 靜態圓柱………………………………………27 4.2.2 鎖定後變化振幅……………………………..29 4.2.3 鎖定後變化頻率……………………………..30 4.3 渦漩形成長度及流場可視化………………………..31 4.3.1 靜態與鎖定時………………………………..31 4.3.2 鎖定後變化振幅……………………………..32 4.3.3 鎖定後變化頻率……………………………..33 4.4 平均阻力及尾流平均速度…………………………..33 4.4.1 動量缺陷法…………………………………..34 4.4.2 表面壓力積分法……………………………..37 4.4.3 綜合討論………………………………………38 4.5 表面擾動壓力及相位變動………………….……….38 4.5.1 表面擾動壓力………………………..……….39 4.5.2 相位變動………………………………..…….41 第五章 結論與建議…………………………………………….44 5.1 結論……………………………………………………44 5.2 檢討與建議……………………………………………46 5.3 未來研究方向…………………………………………46 參考文獻……………………………………………………………48 附圖…………………………………………………………………52zh_TW
dc.language.isoen_USzh_TW
dc.publisher機械工程學系zh_TW
dc.subjectCircular Cylinderen_US
dc.subject圓柱zh_TW
dc.subjectRotationally Oscillatingen_US
dc.subjectLock-onen_US
dc.subject旋轉振盪zh_TW
dc.subject鎖定zh_TW
dc.title圓柱旋轉振盪之渦漩鎖定現象zh_TW
dc.titleThe Vortex Lock-on Phenomenon of a Rotationally Oscillating Circular Cylinderen_US
dc.typeThesis and Dissertationzh_TW
item.openairecristypehttp://purl.org/coar/resource_type/c_18cf-
item.openairetypeThesis and Dissertation-
item.cerifentitytypePublications-
item.fulltextno fulltext-
item.languageiso639-1en_US-
item.grantfulltextnone-
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