Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/47870
標題: 具有不等直徑之錯列圓柱間流場結構與鎖定現象的實驗分析
Experimental Study on Flow Structures and Lock-On Characteristics of Two Staggered Cylinders of Unequal Diameters
作者: 郭正雄
關鍵字: 太空科技
應用研究
摘要: 中文計畫名稱:具不等直徑之錯列圓柱間流場結構與鎖定現象的實驗分析本計劃擬分三年的時程,以「具不等直徑之錯列圓柱間流場結構與鎖定現象的實驗分析」為主題,雷諾數約為10005000,直徑比為D/d=24。利用高速PIV,以及LDV等量測系統進行量化。針對具不等直徑、不同中心間距之錯列圓柱的間隙流渦漩(gap vortices)結構之形成、交互作用進行了解,並加以分類。另外,當圓柱間流場受到不同頻率之擾動時,圓柱的間隙流渦漩(gap vortices)結構之頻譜隨著下游之演化,以及下游寬、窄域尾流結構特徵頻率之改變、被鎖定之頻段分佈與周圍流場特性之關連性等均是本研究之重點。各年度之工作重點如下:第一年:具不等直徑之錯列圓柱間流場結構與鎖定現象的實驗分析 (一)以D/d=24 (不等直徑)為目標,藉由流場可視化,針對具不同中心間距之錯列圓柱的間隙流渦漩(gap vortices)結構之形成、交互作用進行了解,並加以分類。以LDA測速儀量測圓柱的間隙流渦漩(gap vortices)結構之特徵頻率,以及其頻譜隨著下游之演化,期望深入了解交互作用之機制與寬、窄域尾流特徵頻率之關係。另外,再以高速PIV系統量測下游寬、窄域尾流結構之瞬間速度場、渦度、環流量隨時間之變化等、長時間平均之擾動能量,以及雷諾剪應力等之分布,期望了解寬、窄域尾流特性之差異,以及可擾動性或可控制性,以作為第二年研究受到不同頻率之擾動時,探討具不同中心間距之錯列圓柱間流場被鎖定特性之基礎。第二年:具不等直徑之錯列圓柱間流場結構與鎖定現象的實驗分析 (二)以D/d=2為目標,探討受到不同頻率之擾動時,具不同中心間距之錯列圓柱的間隙流渦漩(gap vortices)結構特性、交互作用等,量化其被鎖定頻段之分佈與周圍流場結構之關連性。擾動方式係分別以大或小圓柱中心為軸,適當之擾動振幅對圓柱間流場作週期性之旋轉擾動。經擾動後,先以LDA系統量測下游寬、窄域尾流結構特徵頻率之形成原因;圓柱的間隙流渦漩(gap vortices)兩側的不穩定剪力層被鎖定時的形成相位之變化、交互作用機制等。再以高速PIV系統量測下游寬、窄域尾流結構之渦度、環流量隨時間之變化、長時間平均之擾動能量,以及雷諾剪應力等分布之影響,釐清寬、窄域尾流特性之差異與被控制性難易的原因。第三年:具不等直徑之錯列圓柱間流場結構與鎖定現象的實驗分析 (三)變化直徑比為D/d=3及4,藉由流場可視化了解錯列圓柱的間隙流渦漩(gap vortices)結構之形成、交互作用。以LDA測速儀以及高速PIV等系統量測間隙流渦漩(gap vortices)結構之特徵頻率,以及其頻譜隨著下游之演化,以及下游寬、窄域尾流結構之瞬間速度場、渦度、環流量隨時間之變化等、長時間平均之擾動能量,以及雷諾剪應力等分布之影響。當具有外加擾動時,量化其被鎖定頻段之分佈與周圍流場結構之關連性。釐清在不同的直徑比時,Mode 1及Mode 2等寬、窄域尾流特性之差異與被控制性難易的原因,以作為流場控制之基礎。
Experimental Study on Flow Structures and Lock-on Characteristics of Two Staggered Cylinders of Unequal DiametersThis project is proposed to investigate experimentally the flow structures and the lock-on characteristics of two staggered cylinders of unequal diameters via the flow visualization, LDA and PIV techniques. The Reynolds number ranges from 1000 to 5000, and the diameter ratio varies between 2 and 4. It is to understand the characteristics of the gap vortices, mutual interaction, and its relation to the formation of the wide and narrow wakes. Further, the lock-on frequency band and the mechanism leading to lock-on will be revealed. This project will proceed within three years. The contents of each year are listed as follows.In the first year: For D/d=24, dye flow visualization is employed to categorize the interactions and evolutions of the gap vortices and the eventual formation of the wide and narrow wakes downstream. The LDA and PIV system are employed to investigate quantitatively the characteristic frequencies of the gap vortices, the streamwise evolution of their velocity spectra, the time-dependent flow structures, the corresponding vorticity distributions, and the circulation evolution, the distributions and evolution of the fluctuating energy as well as the Reynolds stresses within the wide and the narrow wakes. It is expected to understand how the interactions of the gap vortices affect the formation of the wide and the narrow wakes behind the staggered cylinders of unequal diameters. The unperturbed results will be served as a reference for the second-year project to understand how the perturbations affect the structures of the narrow and the wide wakes.In the second year: Based on the results of D/d=2, the evolutions of the gap vortices and the eventual formation of the wakes behind the staggered cylinders will be categorized while the perturbations in form of rotary oscillation about the cylinder center are applied at various excitation frequencies. As the lock-on occurs, the flow structures, the downstream evolution of the gap vortices and the corresponding velocity spectra will be quantified via the LDA system. Further, the evolutions of vorticity distributions, the circulation, the distributions of the Reynolds stresses within the narrow and wide wakes will be investigated by the PIV system. The lock-on frequency band and its link to the surrounding flow structures around the staggered cylinders will be revealed for D/d=2.In the third year: The investigation will be extended to D/d=3 and 4 to study the evolution of the gap vortices, the vorticity distributions, the circulation and the distributions of the Reynolds stresses within the narrow and wide wakes with and without the external perturbations. Through the measured physical quantities mentioned above, it is expected to reveal the formation mechanism, the controllability of the wide and narrow wakes for Modes 1 and 2, as well as the link between the lock-on frequency bands and the flow structures of staggered cylinders of different diameter and gap ratios.
URI: http://hdl.handle.net/11455/47870
其他識別: NSC99-2221-E005-029-MY3
文章連結: http://grbsearch.stpi.narl.org.tw/GRB/result.jsp?id=2399223&plan_no=NSC99-2221-E005-029-MY3&plan_year=101&projkey=PB10101-2989&target=plan&highStr=*&check=0&pnchDesc=%E5%85%B7%E6%9C%89%E4%B8%8D%E7%AD%89%E7%9B%B4%E5%BE%91%E4%B9%8B%E9%8C%AF%E5%88%97%E5%9C%93%E6%9F%B1%E9%96%93%E6%B5%81%E5%A0%B4%E7%B5%90%E6%A7%8B%E8%88%87%E9%8E%96%E5%AE%9A%E7%8F%BE%E8%B1%A1%E7%9A%84%E5%AF%A6%E9%A9%97%E5%88%86%E6%9E%90
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