Study On Air Entrainment To Alleviate Cavitations And Energy Dissipation & Scour Protection Of The High Head Spillway

With the development of the enterprise of hydropower, a lot of newly-built large outlet structures have the characteristic of high head, heavy discharge and narrow river valley. The problems of high-velocity hydromechanics became outstanding, velocity of flow is about 40m/s and even higher. And this high velocity of flow will lead some special water phenomena, such as aerification, fluctuation, cavitation and atomization, etc, which will bring great danger to the structure.The condition when the cavitation took place was analyzed theoretically, which show that the damage of cavitation was caused by the crumble of vacuole which took place close to the side wall. Base on this, and with the example of aerification mitigation cavitation in the built projects, the theory of aerification mitigation cavitation was analyzed carefully. And it show that it was not strict that using that density of aerification as the standard of aerification mitigation cavitation. With analizing the data of the model test, the aerification mitigation cavitation plan for the overfall spill engineering of Bashan water power station was put forward in this thesis.Analyzing the disequiligrium force condition of a typical rock in the scour foss, the formula of couch nonscouring velocity was obtained. Meanwhile, some empirical equations which used in evaluating the scour depth was analyzed, and the affecting factor of the scour depth was generalized. Compared with the scour depth in the downstream of spillway of Bashan water power station, the energy method which was proposed by a Canadian scholar K.J.W.Spurr was used to evaluate the scour depth, the calculation result was in accordance with the model test data, and the origin of error was analyzed in the thesis.Finally, the body type of flip bucket of spillway of Bashan water power station was optimized through the model test., With compare of several plans, multiply twist bucket was proposed, which dissolve the problems that caused by wide width, high head and the bad condition in the downstream for energy dissipation of spillway of Bashan water power station. The test result show that this plan is the optimum.