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題 名 | 低雷諾數環形噴流經突張管之實驗研究=An Experimental Study of Low-Reynolds-Number Annular Flow Over Axisymmetric Sudden-Expansion |
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作 者 | 沈弘俊; 陳維鈞; 吳敬熙; | 書刊名 | 力學 |
卷 期 | 12:4 1996.12[民85.12] |
頁 次 | 頁457-464 |
分類號 | 440.137 |
關鍵詞 | 環形流; 突張管; 中心柱體; 流場視察法; 雷射測速儀; Annular flow; Sudden-expansion; Center-body; Flow visualization; LDA; |
語 文 | 中文(Chinese) |
中文摘要 | 本論文以實驗方法探討低雷諾數範圍中,具有中心柱體(center body)的環型噴 流流經軸對稱突張管的流場結構與其不穩定性。本研究用流場視察的技術做再接觸長度的定 量量測,並利用照相機拍攝由煙霧顯現出的流場型態。以雷射都卜勒測速儀,量測整個流場 結構。而由頻譜分析結果可以驗證相片上所看到的流場結構。由實驗結果,我們發現四種不 同的流場型態,以及其相關再接觸長度的變化。在雷諾數上升以及下降的路徑之間存在的分 歧現象,此分歧範圍可由增加及減少雷諾數路徑中再接觸長度的變化得到,約在 230 < Re < 440。由雷射測速儀之速度量測配合頻譜分析,發現雷諾數小於 440,流場型態是穩定的 ,雷諾收大於 440 以上時變得比較不穩定而且週期性愈來愈明顯。 依附在中心柱體後中心 迴流區內的渦漩流逸( vortex-shedding )則扮演了影響再接觸長度的角色, 並藉由頻譜 分析,本論文將說明渦漩流逸在不同雷諾數狀況下,沿下游距離發展的過程。 |
英文摘要 | In this paper an experimental investigation is described for an annular flow over an axisymmetric sudden-expansion of diameter expansion ratio 1:2 by using the methods of flow visualization and laser-Doppler anemometry. Depending upon the Reynolds number and thr routes of the increasing and decreasing Reynolds number, four typical flow patterns were classified by the characteristics of the central and the corner recirculation zones. Birfurcation for this flow occurred when 230 < Re < 440 and was sufficiently verified by observing the variation of the reattachment length. Measurements of time-averaged velocities and velocity fluctuations, in conjunction with spectral analyses, demonstrated that the flow was stable when Re < 440 except in the vortexshedding regime. At higher Reynolds number, Re > 440, the flow became less stable and periodicity became increasingly important. The central recirculation region behind the center-body was found to exhibit both shear-layer and expelling vortex-shedding, which played a dominant role in affecting the corner recirculation region. The vortex-shedding process and its evolution with the Reynolds number were also explained by spectral analyses. |
本系統中英文摘要資訊取自各篇刊載內容。