https://scholars.lib.ntu.edu.tw/handle/123456789/80405
Title: | 突張流場之流場結構及不穩定現象實驗研究 An experimental study on the flow structure and the instabilities of a flow over a sudden-expansion |
Authors: | 沈弘俊 | Keywords: | 二維突張階梯流場;流場型態;流場結構;不穩定現象;Two-dimensional sudden expansion;flow pattern;flow structure;instabilities | Issue Date: | 31-Jul-2001 | Publisher: | 臺北市:國立臺灣大學應用力學研究所 | Abstract: | 本計劃乃以實驗方法探討含中心擋體 之二維突張階梯流場和不含中心擋體之二 維突張階梯流場,在不同突張階梯高下, 隨雷諾數變化所展現出的流場結構特性。 在實驗方法上,採用熱線測速儀來量取流 場的速度、和紊流強度,並利用小型煙霧 產生器及煙霧注入法產生煙霧,配合雷射 切頁,觀察迴流區再接觸長度的變化,歸 納出不同突張階梯下,再接觸長度隨雷諾 數的變化趨勢。同時,藉由數位CCD 攝 影機及影像擷取卡之助,擷取在不同情形 下的流場顯影照片,以利觀測流場結構。 從實驗結果得知不含中心擋體和含中心擋 體的再接觸長度變化趨勢,發現到再接觸 長度隨雷諾數的變化皆具有類似的趨勢; 對含中心擋體和不含中心擋體的迴流區做 比較,歸納出含中心擋體與不含中心擋體 的異同,其中並對長邊、短邊迴流區的交 換現象有較清楚的分析;另外在固定的雷 諾數下,改變背向階梯的高度,發現長邊 及短邊迴流區的生成位置有其固定性,並 不會隨階梯的改變而造成變換,而是由主 流的偏向來決定。 This project is a continuous work to our previous research which was a study on an axisymmetric sudden-expansion flow. This study further investigates a two-dimensional flow over a sudden-expansion, with and without a center-body plate. The flow structures behind the expansion step, under various expansion ratios and Reynolds numbers, and flow instability phenomena are investigated by experiments. The experimental techniques used include flow visualization, thermal anemometry, laser-Doppler velocimetry (LDV) and particle image velocimetry (PIV). The major parameters are the Reynolds number and the height of the sudden expansion. The first part of this study is to investigate the flow characteristics for a two-dimensional flow over a sudden expansion. These properties include the reattachment length, the flow symmetry, and the interchanges of the long and the short recirculation zones. Further, a flow with a center plate is studied. Comparisons for these two different flows are made. The detailed mechanism on the effects of the center plate on the two recirculation zones, the variations of the recirculation length with the Reynolds number, and the effects of the step heights on the recirculation zones are investigated experimentally. Moreover, the effects of the transient large-scale vortex shedding on the flow structure and the shedding phenomena at further downstream are studied. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/21603 | Other Identifiers: | 892212E002150 | Rights: | 國立臺灣大學應用力學研究所 |
Appears in Collections: | 應用力學研究所 |
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892212E002150.pdf | 276.22 kB | Adobe PDF | View/Open |
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