脈動式管流初始不穩定現象之流場控制

徐晏婷

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脈動式管流初始不穩定現象之流場控制

Flow control on the initial instabilities in pulsating pipe flow

徐晏婷 , Masters　　Advisor：苗君易　　

繁體中文

脈動式管流；反曲點；流動不穩定性；混合層流模型；邊界層； Rayleigh instability criterion ； Trip wire ； Pulsating pipe flow ； Inflection point ； Flow instability ； Mixing layer model ； Boundary layer ； Rayleigh instability criterion ； Trip wire

Abstract │ Reference (53) │ Altmetrics

Abstract 〈TOP〉

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This study is aimed at investigating the initial instability in pulsating pipe flow with installing a trip wire at the inlet to manipulate the control of flow instability. The pulsation of pipe flow was produced by a flow regulator situated downstream of the pipe flow, which was driven by a servo motor and monitored by an optical sensor. The instantaneous velocity information at a point in the flow field was obtained by a boundary-layer type hot-wire probe, then phase-averaged according to the output signals of the optical sensor mentioned. For data analysis, the method of Ensemble Empirical Mode Decomposition (EEMD) was employed to extract the disturbance component due to flow instability from the phase-averaged signal trace studied. Then, we employed either Hilbert-Huang Transformation or Wavelet Transformation to obtain the characteristic frequency of the initial unstable disturbance. Moreover, a phase-averaged velocity profile was smoothened by a six-order regression curve, subsequently the inflection points were identified. Then, the flow instability observed was examined with the Rayleigh instability criterion based on a mixing-layer model. By this procedure, one was able to identify the cases of which the flow instability characteristics are complied with the mixing-layer model, which is referred to the inviscid mechanism. Otherwise, the cases not agreed with the inviscid model would be considered due to the viscous effect.
    In this study, experimental results obtained with different trip wires under a number of pulsating flow conditions confirm that the flow instability phenomenon observed in the developing region could be due to the inviscid or viscous mechanism. Moreover, the installation of a trip wire could effectively alter the development of boundary layer, therefore affected the locations of the inflection points in the unsteady velocity profile.
As a consequence, the development of flow instability was affected pronouncedly, that the flow instability could be initiated at further upstream location due to either of inviscid or viscous mechanism. The present results illustrate the effectiveness of installing a trip wire to control of flow instability, based on which detailed discussion was carried out concerning the situations associated with the inviscid mechanism and those with the viscous mechanism.

Reference ( 53 ) 〈TOP〉

[1] O. Reynolds,“An experimental investigation of the circumstances which determine whether the motion of water shall be direct or sinuous and of the law of resistance in parallel channels,”Philosophical Transactions of the Royal Society of London, vol. 174, pp. 935–982, 1883.
連結：
[2] 黃日暉, 應用MEMS熱模感測器於非定常管流層紊流轉換之初始
連結：
[3] 羅洪森, 應用MEMS熱模感測器與希爾伯特黃轉換分析脈動式管
連結：
[4] 劉昊, 脈動式管流之初始不穩定現象探討. 碩士論文, 國立成功大學, 2011.
連結：
[5] 戴君毅, 脈動式管流初始不穩定之現象探討. 碩士論文, 國立成功大學, 2013.
連結：

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