Numerical Simulation For Cavitations Flow Inside Fluid Machinery

This thesis is supported by the National Natural Science Foundation of China (NO: 90410013). In the operating process of fluid machinery (Pumps, hydraulic turbine, etc.), cavitation may cause corrosion to its flow parts, produce noise and vibration. If the cavitation is serious, the mechanical efficiency will drop remarkably, even cannot function normally. Therefore, cavitation of fluid machinery is the primarily concerned problem for fluid machinery designing, manufacturing and scientific researching, also is the important subject for the improving of its performance and quality.With the development of computational fluid dynamics and rapid improvement of computer capacity, it has been possible to research the inner flow inside fluid machinery by numerical simulation. Numerical simulation can estimate the parameters that are difficult to measure in experiment. In the analysis and engineering design process of fluid machinery, numerical simulation improves reliability and reduces the cost significantly. Numerical method has become an important tool to design fluid machinery.Based on hydromechanics computation knowledge, taking commercial CFD software Fluent as tool, using Realizable κ-ε two equations model of Reynolds averaged method and mixed multiphase flow model, cavitations in an impeller of a low specific speed centrifugal pump and an runner of a francis turbine are simulated. Through simulation, cavitation flow situations of thepump's impeller under varies flows are obtained which have vital significance to the impeller optimized design. Meanwhile through result analysis, the axial symmetry flow hypothesis in some computations and design is denied, the design method of enlarging flow from another angle is also verified. The hydraulic turbine's cavitation coefficient calculated from the simulation results agrees well with the cavitation coefficient obtained through model test for HL240 hydraulic turbine under the design condition. The dynamic determination method for the hydraulic turbine cavitation coefficient is also proposed. Total cavitation region on blade by using this method can be accurately obtained, and cavitation degree on each region of blade can be estimated. Thus numerical results provide theory instruction on when to carry on examining and repairing to the hydraulic turbine, and enables the hydroelectric power station to achieve the maximum economic efficiency.