| A pump turbine is designed mainly for its pump mode. A “hump region” existing in the external characteristic curve has a negative influence on the stable operation of the device when the pump turbine works in p ump mode. The pressure fluctuation is the main reason among many of the factors that lead to the unstable operation of a pump turbine. It is necessary to conduct a deep res earch on the internal flow of a pump turbine and then provide reference to the design and stable operation of a pump turbine.In order to achieve the goals above, this research has conducted steady and unsteady simulation for a reduced scale model pump turbine. The RANS method and the LES method and the compressibility of the working fluid are considered in the pump mode of a pump turbine to investigate the unsteady characteristic and the pressure pulsation regularity. The fluid structure interaction is also considered to compare the pressure oscillation in this research. The detailed contents of this research are as follows:Firstly, the SST k-? turbulence model provided by the commercial code ANSYS FLUENT is chosen to conduct the simulation, while the fluid compressibility is included and not included. Then the result of the compressible simulation and incompressible simulation is compared to analyze the influence of the fluid compressibility on the pressure oscillation of a pump turbine.Secondly, the RANS method and the LES method is introduced in this research to conduct simulation for the whole passage of a model pump turbine. The external characteristic curve at pump mode of a model pump turbine is obtained with the simulation result. The pressure field, velocity vector field as well as the vorticity field inner the flow passage of a model pump turbine is also analyzed. And then the pressure oscillation of the flow field simulated by RANS method and LES method is compared.Finally, the commercial code Mp CCI is used as the connector of the coupling code with ANSYS FLUENT simulating the flow field of a prototype pump turbine and ANSYS APDL simulating the structure field of the guide vane. Meanwhile, the asynchronous time step is first achieved to conduct bi-direction fluid structure coupling. The pressure oscillation result obtained from the bi-direction fluid structure coupling is compared with the non-coupling fluid field simulation, and the influence of the fluid structure interaction on the pressure oscillation of a pump turbine at pump mode is investigated.According to the simulation that the fluid compressibility is not considered, it appears that, the 9 times, 18 times and 27 times runner frequencies in the flow field from the draft tube to the stay vanes are mainly caused by the runner stator interaction. The pressure oscillation of the flow field of a model pump turbine obtained from the LES method and the RANS method with the fluid compressibility considered shows that the magnitude of the pressure oscillation amplitude is higher than the result from the RANS method that the fluid compressibility is not considered. Dynamic stall exists in the runner passages of a model pump turbine according to the LES result. According to the bi-direction coupling result, the coupling vane displaces about 0.5 millimeter at middle height of the leading edge at pump mode. The magnitude of the pressure oscillation amplitude of the bi-direction coupling is higher than the non-coupling result. However, the amplitudes of the 9 times and 18 times runner frequency component are mainly lower than the non-coupling result. |
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