CFD of Air Flow in Hydro Power Generators

Licentiate thesis, 2010

The air flow through a generator has been numerically investigated with different rotor and stator designs to give a better understanding of the flow for cooling purposes. A simple rotor design has been chosen to start with, and modified through a set of changes, where stepwise modifications have been imposed to the design of the rotor and the stator. The flow properties for all cases have been compared to each other to see the effect of each parameter change on the flow inside the machine. The flow is predicted with the OpenFOAM solver MRFSimpleFOAM, which uses the Frozen Rotor concept. This means that there is no actual mesh movement in this study, but instead, the rotating regions in the domain are provided with source terms that account for rotation. The choice of the turbulence model for solving the air flow in the generator was based on a study of the turbulence models and validation test cases. All incompressible RAS turbulence models in OpenFOAM-1.5.x were studied and the implementations were compared to the original models. Many of the mentioned turbulence models were tested on a backward-facing step test case. The numerical results were compared to the experimental data and the most appropriate turbulence model was chosen. Details on turbulence model studies are discussed in Appendix A. A laminar Couette flow between two concentric cylinders was run and the numerical velocity and pressure distributions between the cylinders were compared to the analytical resutls. More details on the validation test cases are found in Appendix B.