Detailing the Giants: CFD in Service of Optimization of the Air Flow through Hydro Generators

In the process of the design of hydro generators, analytical tools based on lumped parameter models are traditionally used. The accuracy of these models is significantly determined by embedded mathematical models, as well as by empirical data obtained on built objects. Parallel with the growth of computer power, numerical tools based on the different numerical methods became more and more important. This paper demonstrates the usage of computational fluid dynamics (CFD) analysis of the air flow and heat transfer of the entrance zone of the stator radial ducts to embed a more accurate correlations for calculation of heat transfer coefficient (HTC) within existing lumped parameter models. A parametric study of the dependence of HTC on both the windward and leeward faces of the stator winding on the airflow conditions in the air gap was performed. To achieve mesh independent solution, mesh dependency test was carried out. A series of conjugate heat transfer (CHT) simulations have shown that the mean HTC at the windward and leeward side of the stator winding in the slot depends significantly not just on radial velocity component, but also a peripheral velocity. While this dependency shows clear correlation for windward side, situation for leeward side is much more complex.