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肥皂膜中之斜震波實驗研究
Experimental Studies of Oblique Shock Waves in Soap Films
摘要
由過去幾年的研究中發現，肥皂膜流中有類似水躍(Hydraulic Jump)的現象，且在理論推導研究上已找出此現象和氣體動力學之間的類比關係，即肥皂膜流中的馬崙葛尼彈性(Marangoni Elasticity)過程可視爲比熱比γ=1的二維氣體。本文將進行肥皂膜流中斜震波實驗的流場可視化及定量分析，將實驗結果與理論研究中所推導的馬崙葛尼彈性過程θ-β-M作圖（流場偏向角－震波偏向角－自由流馬赫數）比較，企圖進一步證明肥皂膜可類比於γ=1的二維氣體。從拍攝的流場照片可看到肥皂膜震波經過模型時所產生的斜震波與擴張波，此現象在定性上與氣體動力學中所攝得之震波現象極爲類似。然而在定量上，實驗結果發現所量測得的震波偏向角(β)比理論值小，推測應爲肥皂膜與三角形模型邊界之間的表面張力所造成。
並列摘要
In the earlier theoretical and experimental investigations of the analogical hydraulic jump phenomenon in soap films (Wen and Lai, 2002; Wen, Chang-Jian and Chuang, 2002), low-concentration soap films with Marangoni elasticity processes are found to be analogous to compressible gases of specific heat ratio γ=1. In this paper, the analogous θ-β-M curve in soap films is presented with the help of high-speed flash photography and line scan CCD camera. The oblique shocks attached to the vertex and expansion waves from the base of the wedge are clearly seen. These flow features are qualitatively similar to their counterparts in gases. Quantitatively, the experimental data do not agree with the theoretical θ-β-M curve. The discrepancy is suspected caused by the surface tension between the test model and the soap film.