彩色質點影像測速法於瞬間潰壩流場之試驗研究

Abstract

本文旨在利用CPIV法進行流場可視化之研究，係利用雷射光及多彩聲光調變器（PCAOM）將雷色光束區分為藍綠兩光束形成二維雷射光頁，再利用彩色數位相機（Color CCD）之技術所組合成。在流體中加入與水相近密度之顯影塑膠顆粒（1.1 g/cm3），在藍綠相間隔之雷射光頁下顯影其流場變化，並擷取流場變化之數位影像。再將所擷取之數位影像訊號，進行數位相關法分析求得位移量，再除以曝光時間間距而得知速度值。 其CPIV方法之準確性分析係利用定速轉盤驗證之，於已知轉盤速度下進行影像擷取、影像分析與數為相關計算，求得之速度值再進行比對，作為試驗計算之驗證對照組。隨後進行光滑及糙度底床試驗之瞬間流場之研究，因床質材料糙度增加，造成流場於近底床附近有明顯地變化，形成渦流現象。最後應用於瞬間潰壩後流場流況作分析，將瞬間潰霸所形成之變量流利用攝影機拍攝，並分析其水位隨時間之變化情形、及動床底床因瞬間潰決後下游底床利用描繪方式記錄床形變化，及利用CPIV法將所設定之不同渠段之流場，透過數位影像及運算程式進行可視化分析研究 。

The purpose of this study is to investigate flow field visualization by using the color particle image velocimetry (CPIV) method. This method uses the laser light, polychromatic acousto-optic modulator (PCAOM) which separates the laser beam into blue and green color light sheets, and digital color charge coupled device (CCD). Polystyrene of diameter 75μm and density 1.1 g/cm3 is used as the seeding material. The obtained digital image is first transferred into digital signal data, and then the displacement of the seeding particles is estimated by the cross correlation analysis. The corresponding velocity of the particle is equal to the displacement divided by the exposure time interval. To velocity the accuracy of the CPIV method, the experiment on the stability rotating disc is executed. The computed rotating velocity is compared with the known rotating velocity and the relative error is acceptable. Then, the CPIV method is applied to study the flow fields for smooth and rough channel beds. Irregular eddy zones occur due to the existence of the rough bed. Finally, the CPIV method associated with the video camera is applied to study the flow field of instantaneous dam-break case. The variations of water surface and bed surface are recorded by the video camera. In the same time, flow field visualization of propagation of the model dam-break wave is by the CPIV method.