本研究利用熱線測速儀與實驗室自製之MEMS熱膜感測器，量測脈動式非定常管流流場之層紊流轉換現象。控制此脈動式非定常管流場之平均雷諾數、雷諾數振幅於Womersley Number，並利用希爾伯特黃轉換可以拆解複合訊號與將訊號-時間轉換為頻率-時間-強度知三維特性之優點，並利用ensamble average的方式，將長時間所量得的大量數據平均，以得到一個流場速度變化循環內，流場平均現象，研究此流場發生初始不穩定擾動時，此不穩定擾動現象之頻率特性。
於本研究之實驗結果中發現，當womerslry介於28.6至40.4之間、平均雷諾數介於10000至18000、雷諾數振幅介於2600至5100時，此脈動式管流場之層紊流轉換皆會在流場速度最低處產生一回流現象，然後產生一誘發的二次渦流，出現在流場加速區段，並隨著流場加速向下游傳遞，此渦流產生之不穩定擾動多在30-50Hz之間，以之與穩態流場邊界層之不穩定擾動頻率做比較，其擾動對應之無因次參數約在damping與amplified 範圍之間，且隨著流場向下游傳遞，此不穩定擾動也隨之放大。

This study employed the hotwire anometer and self-made MEMS hot-film sensors to measure the laminar-turbulent transition in a pulsating pipe flow. In this study, the parameters are the mean Reynolds Numbers, amplitude of Reynolds Numbers and Womersley Numbers. In order to decompose the raw data, Hilbert-Huang Transition analysis method were used to get the frequency-amplitude-time characteristic. Also apply the ensamble average method to obtain the mean frequency characteristic of the laminar-turbulent transition in a pulsating pipe flow.

As the mean Reynolds Numbers from 10000 to 180000, amplitude of Reynolds Numbers from 2600 to 5100 and Womersley Numbers from 28.6 to 40.4, the results of this study show that the back-flow appeared at lowest velocity phase. Then the secondary vortices will be induced by the back-flow. Secondary vortices will convect downstream and grow in size. The frequency characteristic is between 30 to 50 Hz. Compared with steady boundary layer laminar-turbulent transition instability diagram, the disturbances frequency is close to the neutral stability curve.

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