摘要
本文是以實驗的方法來探討細小圓柱線在二維噴射流內剪切層中的流體誘發振動現象，由於剪切層內的流場型態是一種十分複雜且充滿渦流的流場，所以流體引致振動的現象勢必有別於在一般均勻流場中的現象。本實驗的目的既是分別探討細小圓柱線振動的現象，以及細小圓柱線對流場的影響。
在流場的量測方面，本實驗是以熱線測速儀做量測，而在振動量測方面，利用電磁學的原理，自行研發出一套新的量測技術，此種量測技術可成功的量測到細小圓柱線兩方向的振動，因此可以描繪出振動的軌跡，在量測時流場的量測和振動的量測是同時進行的，如此便可以探討流場及細小圓柱線之間的相互關係。
由實驗得知當流場的出口速度不斷的增加直到某一特定速度時時，圓柱線會發生劇烈的振動，此時稱為振動的臨界速度，而若加以一瞬間激擾時，圓柱線會提前發生劇烈的振動。在臨界條件時，細小圓柱線振動的頻率會恰等於自然振動頻率，但是隨著速度的增加，其振動頻率會有逐漸升高的趨勢，而在施加一瞬間激擾時亦會發生此一情形。另外亦發現reduced velocity(Ucri/fnD)和mass damping(m(2px)/rD2)之間有一特定的關係，在軌跡圖方面皆可得到一近似橢圓形的軌跡，而且在不同reduced velocity時會有不同的振動軌跡，由reduced velocity對應振動振幅及特徵頻率的關係圖中，可以由不同的reduced velocity劃分成三個區域，在其三個區域分別有不同的振動軌跡，且有不同的振動模式。在流場方面，不同的Y軸位置時細小圓柱線的振動對於整個流場的平均速度及剪切層的速度梯度並無太大影響，但是對於剪切層內流場擾動值的確有明顯變小，而在剪切層內細小圓柱線下游不同X位置的流場皆被振動明顯的影響，流場的頻率與振動的特徵頻率一致，且流場的型態隨著振動速度的不同會有不同的變化，由研究得知，細小圓柱線的振動並不是會一直影響流場的，必須在一定的振動範圍內，流場才會被振動強烈的影響。

Vibrations of small cylinder in a jet flow are investigated experimentally. Because of the flow field in shear layers of jet flow is very complex and filled with vortex structures, so the flow induced vibration phenomena in jet flow is different from the flow induced vibration in uniform flow. The major subject in this experiment is to discuss the major cause of small cylinder vibrations, and the flow field influenced by the cylinder vibration.
About flow measurement, velocity measurement by hot-wire is applied. As for the vibration measurement, by using the principle of electromagnetic, a new measurement technology was successfully developed. This new vibration measurement can measure the vibrations in two axial, so as to describe the orbit of vibrations. To find the interrelation of flow field and cylinder vibrations, flow measurement and vibration measurement was carry on at the same time.
It is shown that when the jet velocity is increased constantly, small cylinder will vibration intensely. The fixed velocity is called critical velocity. If add a perturb, the vibration will occur in advance. The dominant frequency of cylinder vibration, fr, will be the same with it's nature frequency, fn, in the critical velocity, but when the flow velocity keep on increasing, the dominant frequency, fr, will also increase. Besides, the relation of reduced velocity and mass damping was found in this case. The orbits of vibrations are all like ellipse, and the orbit is different with different reduced velocity. The vibration amplitude be changed into three sections that have different reduced velocity, and different orbit.
About the flow field, the velocity profile in potential core is not influenced by vibrations of small cylinder, but the velocity fluctuations in shear layer indeed be inflected. At the fixed velocity region, the dominant frequency of flow is the same with dominant frequency of vibrations when the flow at downstream of small cylinder in shear layer. This phenomena only exist when the vibration amplitude under the fixed range.

目 錄
摘要……………………………………………………………i
目錄……………………………………………………………ii
圖目錄…………………………………………………………v
符號說明………………………………………………………viii
一、前言………………………………………………………1
1-1文獻回顧………………………………………………1
1-1.1渦流結構之形成……………………………………1
1-1.2流體引致振動的產生………………………………3
1-2研究範圍與目的………………………………………4
二、實驗設備、儀器與方法…………………………………5
2-1實驗設備………………………………………………5
2-2實驗儀器………………………………………………6
2-2.1振動量測…………………………………………….6
2-2.3 流場訊號擷取部分…………………………………8
2-3實驗方法………………………………………………10
三、結果與討論……………………………………………….12
3-1 流體引致振動的主因…………………………………13
3-2 臨界速度與振動的的關係…………………………… 16
3-3 細小圓柱線頻譜的分析……………………………….19
3-4 振動軌跡分析………………………………………….21
3-4.1 振動軌跡與reduced velocity的關係………………..22
3-5 振動對流場的影響………………………… ………….23
四、結論與建議………………………………………………...27
4-1 結論……………………………………………………..27
4-2 建議……………………………………………………...29
參考文獻………………………………………………………….30
附錄……………………………………………………………….92

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