Experimental Research On Energy Dissipation Of Stepped Spillways

Stepped spillways is a type of new spillway structure. The centralized energy dissipation form of traditional spillway depended on outlet is changed by it, then the energy of flow is dissipated gradually during discharging. So cavitation damage of structure is avoided effectively, energy dissipation establishment of downriver is predigested and project cost is saved. Therefore, ,since 1970's the study on it is not interrupted. In this paper, Stepped spillway is investigated primarily by model test.According to the difference between the ratio y_c/s of critical depth y_c and step height s and the angle ? of spillway slope and the horizontal, the flow regime of stepped spillway can be distinguished, that is nappe flow, transition flow and skimming flow. In practice a new method distinguishing the regime is watching developing extent of burble on steps.If there is not burble on steps the flow regime is nappe flow;if there are burbles but the burbles don't touch the erect borders of stepts and their free shape can be kept the flow regime is transition flow; if the burbles touch the erect border and their shape is unique right angle, the flow regime is skimming flow.Water is a kind of flow phenomenon during less runoff on steep stepped spillway. The study on it has practical significance. The conclusions as follows can be found by investigation: water wing is given birth to on the first step of spillway upriversometimes, it exist in the whole runoff range of nappe flow and goes on to the transition flow; when the dam height and the bottom slope are fixed minishing the step size on which water wing is come into being firstly can reduce the height of it and the runoff range in which water wing exist; along with the augment of the bottom slope of spillway the height of water wing increases correspondingly and the pressure of level surface of step present the max..The study on energy dissipation rate is the key to investigate the stepped spillway. The study on friction energy dissipation rate and total energy dissipation rate of steps by indirect method and the conclusions as follows can be found: along with the augment of relative dam height H_das/y_c energy dissipation rate increases and relative dam height is the main factor working on energy dissipation rate; when the dam height and the bottom slope are fixed the effect of step size on energy dissipation rate is less; when other conditions are fixed the effect of the bottom slope of spillway on energy dissipation rate is less; if relative dam height is independent variable and energy dissipation rate is dependent variable the relation of them answer for the double curve function; the energy dissipation rate of steps account for more than 60% of the whole energy dissipation rate.