Study on Air-entrainment and Its Decay Downstream Aerator in Spillway

• Main Authors: Chen, Ming Ren, 陳明仁
• Other Authors: Yan, Qing Lian
• Format: Others
• Language: zh-TW
• Published: 1995
• Online Access: http://ndltd.ncl.edu.tw/handle/58438827163457181322

博士 === 國立臺灣大學 === 土木工程學研究所 === 83 === The purpose of this study is to investigate the variation of air concentration, downstream from aerator, as the reference for aerator spacing design. The non-dimensional parameters, which affect the variation of air-concentration downstream aerator, was investigated by dimensional analysis, and the major non-dimensional paramenters: alpha, Ｆ are planned to design sets of experiments. According to the situation of prototype, three slope angle conditions,15, 30 and 55 degrees, with 4 different Froude number conditions, are given for expreiment. The results, combined dimensional analysis, model test and numerical simulation, of this study are as follows: 1. The primary affected non-dimensional parameters are Froude number and slope angle of spillway. Let 7 % concentration, within 1 cm near bed, as the minimum critiria for prevent cavitation, the non-dimensional protection length Lp/H v.s. different alpha and Ｆare :if alpha is not exactly be 15, 30 or 55 degree, the protection length can be calculated by interpolated as equations above. 2. The experiment results show that the larger the alpha and Froude number, the more slower decay the longitudinal air concentration variation. 3. A ''Separate and Statistic'' method is developed for measure air concentration and air bubble gradation, and the results of calibrated tank are used for calibrate the parameter. It is more precise than conductivity probe,and the measured technique can avoid the shortcoming of selecting threshold method which can''t measure the gradation of air bubbles.