| Based on summaries of predecessor's research findings, the hydraulic characteristics of three types of plug which are linear plug, stepped plug and gradually contracted plug were studied by means of experiment, numerical simulation and theoretical analysis. Research contents included energy dissipation rate, the mechanism of energy dissipation, incipient cavitation number of the three types of plug. The design procedure of multi-stage plug spill tunnel was put forward and model test of plug spill tunnel of a hydro-power project was done in this dissertation. Main research findings are as follows:1,Lengths of pressure recovering in plug and after plug were experimentally and numerically gained. The relationship between the length and area contraction ratio of plug was given.2,The head loss coefficients of three types of plug were formulated. The Renolds number has few affection on the head loss coefficients.3,As far as stepped plug was concerned, the best ratio of diameter of auxiliary plug to that of main plug should be 1.1. The best length of auxiliary plug should be 0.4 times of tunnel diameter.4,An ideal ratio of inlet diameter to outlet diameter of the gradually contracted plug exists and the author formulated the ratio.
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