Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/1753
標題: 空穴中振盪流場之實驗分析與控制
Experimental Analysis and Control on Oscillatory Characteristics of Cavity Shear Layer
作者: 黃士豪
Huang, Shr-Hau
關鍵字: cavity flow;空穴剪力流;feedback interruption;self-sustaining oscillation;回授阻斷;自激式振盪
出版社: 機械工程學系
摘要: 
本研究是以實驗方法探討空穴結構中分離剪力層之不穩定特性,期能了解
並抑制空穴中因流場不穩定所造成的強烈震盪特性。本研究之實驗在低速
循環迴路式水槽中進行,流場可視化是以螢光染液釋放法進行,以了解空
穴結構的定性演化情形,並輔以雷射測速儀系統進行定量速度場的量測。
本研究主要內容分為三方面進行:(1)探討外加上蓋平板之前緣形狀對於
空穴上方剪力層不穩定特性之影響,(2)探討不同空穴之底部形狀,對於
空穴中分離剪力層不穩定特性之影響,(3)探討不同的回授阻斷條件對空
穴中分離剪力層不穩定特性之影響。針對第一部分的實驗結果顯示:具有
不同前緣形狀的上蓋平板將產生不同的近板面流場結構,提供強度不等之
加速作用及擾動量,此二項原因是引發空穴內部強烈自激式振盪流場之主
要原因,當加速程度超越某一臨界值時,自激式振盪之頻率亦將突然躍升
至另一振盪模式。第二部分的實驗結果顯示:空穴中的底部幾何結構不同
時,其剪力層沿下游發展所產生的不穩定波動特性將有明顯的不同。值得
注意的是,在三角形的空穴幾何結構中,其剪力層不穩定波動頻率不再出
現,且沒有明顯的波動振幅產生。由此可知,空穴內具有不同斜率的底部
將會對剪力層初始形成的敏感區、空穴內部迴流渦漩與剪力層撞擊下游角
落...具有明顯的影響,使剪力層往下游發展及產生不穩性波動結構有明顯
的改變。第三部分的實驗結果顯示:在穩態阻斷條件下,改變不同的阻斷
位置,確能有效阻斷迴流結構往上游角落回饋激擾的位置與強度。再者,
在固定的阻斷位置下,不同的阻斷角度也將對迴流結構往上游角落回饋激
擾產生不同影響,進而影響剪力層的不穩定振盪強度。另外,在非穩態阻
斷條件下,對空穴內部大尺度迴流結構施加不同擾動頻率的激擾與阻斷,
僅可以改變剪力層波動的低頻調幅特性並無法有效使空穴自激式振盪躍升
至另一振盪模式中。關鍵詞:空穴剪力流,回授阻斷,自激式振盪

The mechanism leading to suppression and control on the self-
sustaining oscillation over the cavity are investigated
experimentally in this study. Quantitative velocity measurement
and qualitative flow visualization were performed by ways of LDA
system and the laser sheet technique. The main objects in this
study are : (1)Influence of the leading-edge profile of the
horizontal top plate on self-sustaining oscillation over a
rectangular cavity (2)Influence of the bottom slope on self-
sustaining oscillation (3)Influence of feedback interruption on
self-sustaining oscillation. Some important results are found
and concluded as follows:(1) Different leading-edge profiles of
the cover plate will produce different near-surface flow
structures leading to different extent of mean flow acceleration
and different level of velocity fluctuation that are the key
mechanism to promote the oscillatory characteristics of the
cavity shear-layer. In case of remarkable flow acceleration, the
mode of self-sustaining oscillation will jump to the mode of
higher frequency.(2) Cavity with positive bottom slope will
limit the feedback location within the downstream corner of the
cavity. However, negative bottom slope will provide adverse
effect for the feedback to move further upstream. Both will
diminish the self-sustaining oscillation within the cavity.(3)
For steady state condition, feedback interruption at different
positions and angles can modify the strength and the upstream
extent location for the feedbck to reach,thus,the self-
sustaining oscillation ca n be either suppressed or enhence. On
the other hand, applying different frequency perturbation to the
large recirculaton in the cavity only can enhence the low
frequency modullation, but can''t promote the self-sustaning
oscillation to jump to another mode.Keyword: cavity flow,
feedback interruption, self-sustaining oscillation
URI: http://hdl.handle.net/11455/1753
Appears in Collections:機械工程學系所

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