CFD validation of pressure fluctuations in a pump turbine

With growing environmental awareness, power producers turn their attention to renewable energy sources. Favorable government support has in many countries lead to a dramatic increase of wind power development. This has in turn raised demand for hydro pumped storage plants to guarantee the stability of the power grids. To allow for increased reliability and operating range, manufacturers focus on learning more about the dynamic behavior of pump turbines. The Hydrodyna research project is a collaboration project between turbine manufacturers and Ecole Polytechnique Federale de Lausanne, Switzerland, which aims to improve the understanding of high head pump turbine dynamics. It is not unusual that modern pump turbines operate at heads around 500 - 700 m. For such high heads, rotor stator interaction is known to be of greater significance due to higher water velocities and thicker geometries in stay and guide vanes. The Hydrodyna research project aims to break through a technology gap in the understanding of pressure fluctuations due to rotor stator interaction. This work describes the results from simulations of the turbine operating at full load and its comparison to laboratory measurements. The commercial software Ansys CFX 5 has been used to perform transient simulations with second order backward Euler transient scheme and the k-epsilon turbulence model on structured, high density meshes. The simulations have been run on a twelve CPU cluster with 0.2 degree runner rotation in each time step. The dynamic behavior of rotor stator interaction is visualized and examined at key frequencies on the pressure and suction side of a runner blade. In order to find the best setup, different simulations have been run on guide vanes and runner with combinations including the stay vanes and draft tube. The results are validated against laboratory pressure measurements on a runner blade. The transient pressure readings, from transducers with measurement error below 0.001 bar, make it possible to determine the accuracy of the CFD code. A comparison is also made with Laser Doppler Velocimetry (LDV) measurements of flow velocities in a guide vane channel.Validerat; 20101217 (root