臺灣博碩士論文加值系統

　　本研究以實驗方式探討圓柱表面流場在雷諾數為1.73×10^5~5.86×10^5間的空氣動力特性。實驗首先量測臨界區中，基部壓力隨雷諾數之變化情形，再利用圓柱左右兩側±900位置的擾動壓力係數來判斷圓柱流場進入單分離泡區的最低雷諾數，如此一來，即定義出圓柱流場在預臨界區、單分離泡區及雙分離泡區中，雷諾數分布的範圍。
　　在瞭解各子區域的雷諾數範圍後，選定四組雷諾數以量測各個子區域內圓柱表面的壓力分布情形，再藉由油流實驗進行視流觀察，並與實驗量測之結果相互比對，成功地找出流動分離及再回覆現象發生的位置，並利用量測所得的壓力分布，以積分方法計算出圓柱在臨界區中的升、阻力係數。
　　至於瞬時頻率的分析，藉由小波轉換進行數據處理，吾人得以在預臨界區中層流分離發生的位置，解析出壓力訊號中夾帶的瞬時溢放頻率，此分析方法貢獻了快速富立葉轉換無法提供的瞬時資訊；而在單分離泡形成之初，圓柱表面的溢放訊號呈不連續分布且劇烈振盪，此乃溢放行為與分離泡之形成產生交互作用所致，分離泡發生前後，流場中會出現兩溢放主頻。
　　最後，亦可藉此實驗研究之結果對風洞進行性能驗證，以進一步證實風洞的流場品質符合原先設計之要求。

　In this study, we investigated the aerodynamic characteristics of the flows around circular cylinders at Reynolds numbers 1.73×10^5~5.86×10^5. First of all, the base pressures across the critical regime were measured, therefore the relation between base-pressure coefficient and Reynolds number was reduced. Then, we determined the lowest Reynolds number at which the flow field entered the one-bubble regime by comparing the root-mean-square values of the pressure coefficients on two sides of a cylinder. In this way, all the sub-regimes in the critical regime were classified.
　After the ranges of Reynolds number in each of the sub-regimes had been confirmed, the pressure distributions around circular cylinders at four specific Reynolds numbers were measured. By comparing the results of oil-flow visualization with the pressure measurements, the positions where laminar/turbulent separation and reattachment took place were successfully identified. Subsequently, the lift and drag coefficients by integrating the pressure distributions on the surface of circular cylinders were made.
　We analyzed the instantaneous behavior of vortex shedding by processing the measured data with wavelet transformation. This method offers instantaneous information that fast Fourier transformation can not provide. At the Reynolds number near lower end of one bubble regime, the unsteadiness of a bubble causes the instantaneous frequency of vortex shedding to vary discontinuously and fluctuate violently.
　At last, by comparing the above results with references, the flow quality of the ABRI wind tunnel was verified.

目 錄
頁次
中文摘要………………………………………………I
英文摘要………………………………………………II
誌謝……………………………………………………IV
目錄……………………………………………………V
表目錄…………………………………………………IX
圖目錄…………………………………………………X
符號說明………………………………………………XV

第一章 序論……………………………………………1
1.1 研究動機與目的………………………………1
1.2 文獻回顧………………………………………2
1.2.1 二維圓柱流場…………………………………2
1.2.2 紊流強度及表面粗糙度之影響………………6

第二章 實驗設備與模型………………………………8
2.1 風洞設備………………………………………8
2.2 壓力轉換器……………………………………8
2.3 熱線測速儀量測系統…………………………9
2.4 資料擷取系統…………………………………9
2.4.1 IOTech ADC488/8SA資料擷取系統……………9
2.4.2 NI PCI-6143資料擷取卡……………………10
2.5 圓柱模型………………………………………10
2.5.1 座標定義………………………………………10
2.5.2 壓克力圓柱……………………………………11
2.5.3 不銹鋼圓柱……………………………………11
2.6 其他設備及材料………………………………12
2.6.1 攜帶式壓力校正器……………………………12
2.6.2 雷射墨線儀……………………………………12
2.6.3 小型移動機構…………………………………12
2.6.4 油流配方………………………………………12

第三章 實驗步驟與方法……………………………14
3.1 參數分析………………………………………14
3.1.1 雷諾數…………………………………………14
3.1.2 無因次頻率……………………………………14
3.1.3 相對粗糙度……………………………………15
3.1.4 壓力係數………………………………………15
3.1.5 阻力係數與升力係數…………………………16
3.2 二維圓柱表面壓力量測………………………17
3.2.1 基部壓力之量測………………………………18
3.2.2 圓柱表面壓力分布之量測……………………18
3.3 渦流溢放頻率之量測…………………………18
3.3.1 小波轉換………………………………………19
3.4 油流觀察………………………………………20

第四章 實驗結果與討論……………………………21
4.1 臨界區的劃分…………………………………21
4.2 圓柱表面之壓力分布…………………………22
4.2.1 預臨界區………………………………………22
4.2.1.1 不銹鋼圓柱……………………………………22
4.2.1.2 壓克力圓柱……………………………………23
4.2.2 單分離泡區……………………………………23
4.2.2.1 不銹鋼圓柱……………………………………23
4.2.2.2 壓克力圓柱……………………………………24
4.2.3 雙分離泡區……………………………………24
4.2.3.1 不銹鋼圓柱……………………………………24
4.2.3.2 壓克力圓柱……………………………………25
4.2.4 紊流再回覆現象………………………………25
4.2.5 本實驗與前研究之比較………………………26
4.3 升力係數及阻力係數…………………………27
4.4 油流實驗………………………………………29
4.4.1 預臨界區………………………………………29
4.4.2 單分離泡區……………………………………29
4.4.3 雙分離泡區……………………………………30
4.5 表面壓力分布與油流結果之比較……………31
4.6 不銹鋼圓柱與壓克力圓柱之比較……………31
4.7 溢放頻率………………………………………32
4.7.1 臨界區中St的分布……………………………33
4.7.2 單分離泡的形成………………………………33
4.7.2.1 快速富立葉轉換………………………………33
4.7.2.2 小波轉換………………………………………34
4.7.3 預臨界區中的非定常分離現象………………35

第五章 結論與建議…………………………………37
5.1 結論……………………………………………37
5.2 未來建議………………………………………38
參考文獻…………………………………………………40

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