Study On Water Hammer Model Test Of Hydropower Pressure Piping System With Time Scale Distortion

Pressure diversion system is an important part of the hydropower station, as the grid’s load changes, the unit’s load changes as well, the opening of the wicket needs to be adjusted to fit the changes of the unit’s load. It appears the phenomenon that one constant flow state converts to unsteady flow state, then changes to another constant flow state in the diversion system, we call it the hydraulic transient process of hydropower station. In the transition process, the reference of the unit changes quickly, it makes the pressure of the diversion system rise and fall alternately, we call it water hammer. The phenomenon of water hammer is inevitable, if the water hammer pressure is too large, it may make the pressure pipe a strong vibration, deformation and even burst, to reduce the influence that water hammer takes to the diversion system of the hydropower station, we usually arrange a surge tank in the diversion system, because it can damage the closure of the diversion system. The problem of water hammer and surge tank relates to the safe operation of the hydropower station directly, it has been become the most concerned problem in the research of the hydropower station.In this thesis, the extension project of Liujiaxia hydropower station has been studied with the following methods: theoretical analysis, model test and numerical simulation.Firstly, reviewed the historical background of water hammer briefly, then introduced the research status and development trend of the basic theory, the calculation method and model test of the hydropower station’s transition process.Secondly, discussed the problem that the water hammer wave velocity was not similar with the prototype in the traditional water hammer model test, to solve this problem, this thesis used the new design method of model test with time scale distortion, and then proved that the new method is feasible in theory. Next, deduced the similarity rules of the physical model based on the basic equations of water hammer and surge tank, the physical model of pipeline system with geometric scale normal and time scale distortion had been manufactured. In the model test, the control condition of generation with losing and increasing the unit’s load suddenly has been studied. The outcome of the model test got the distribution of head water in the pipeline system, the maximum and minimum elevation of the surge tank, the entrance of the pipeline system also had been knew.Finally, established the mathematical model of water hammer and surge tank in combined operation, because of the advantage that its physical concept was clear and it was easy to use, so the characteristic line method was used widely. In the thesis, based on the characteristic line method, simulated the transition process of the pressure pipeline system with the help of matlab. The calculation result was consistent with the result of the model test, it showed that the new method was feasible and it could provide a convenient for the design and manufacture of water hammer physical model, recommended to use this method to design water hammer physical model with larger scale. In addition, in view of the water hammer pressure was too large in the condition of losing load, a preliminary optimization of the closing rule of the wicket was adopted, so the water hammer pressure fell to a reasonable range.