Prediction Of On-cam Performance Of Large Discharge Low Head Bulb Turbine

As the guide vane and runner vane constitute the dual regulating agency, the bulb turbine under the large discharge runs on a flat efficiency curve. The guide vane openingγG and the runner vane angleφR maintain the optimum (On-Cam) relation under the control of the governor, so the flow is always in a preferable working condition. However, since the bulb turbine has a small number of blades and a large discharge, it owns a poor coefficient of cavitation. Research on turbine optimal conditions can effectively prevent the hydraulic loss and cavitaion.Generally, the optimum (On-Cam) relation between the guide vane openingγG and the runner vane angleφR can only be obtained through the model test under the given operating condition of a bulb turbine. This dissertation presents how to predict the on-cam relation at the design stage through the geometrical analysis of the guide vane and runner vane channels. The results of the geometrical analysis can be used as the initial conditions of the three-dimensional numerical flow analysis, which will improve the capability and accuracy. The experience show that this method is simple and feasible.In order to verify the accuracy and reliability of geometrical analysis, it is important to do the steady flow analysis for the model and discuss the energy budget as well as the flow visualization, including the velocity distribution, euler energy distribution, total energy distribution, kinetic energy distribution and pressure energy distribution. The flow between guide vane and runner vane is acceptable and less circulation remain at the outlet of the runner vane. This implies that the geometrical analysis is successful. On the hub profile and tip profile of the blade, there is the pressure decrease, which is due to the fast flow and most likely lead to cavitation. Then, we should improve the flow by the new design of the blade.According to the issue of the flow analysis, profiles of the runner vane blade have been improved. The blade thickness distribution is reasonable and the camber angle distribution is logical after the calculation of the velocity triangle. The contour of the blade is smooth enough, which can effectively avoid hydraulic loss and cavitaion. At the same time, pressure fluctuation and mechanical vibration will be well prevented. Production safety will be protected.Physical tests are an important part of the research. At the end of the dissertation, the author describes the major technical problems about the building of model experiment, and introduces the conditions for testing equipment. And then compare the model tests performance to the result of flow analysis. The research will be more objective.