Validation of a numerical model for hot-spot detection on the surface of a rotor pole using a scale model of a hydroelectric generator

Abstract

To meet the ever-increasing demand for electricity, Hydro-Québec is investigating the viability of running its existing hydroelectric generators at higher power levels than their current operating limits. To assist in this investigation, numerical models capable of simulating the conjugate turbulent air flow and heat transfer phenomena in these generators were formulated and then validated, by using them to predict these phenomena within a scale model of a hydroelectric generator available at Hydro-Québec’s Research Institute and comparing the results to complementary experimental data. Reynolds-averaged governing equations were used, with turbulent stresses and heat fluxes approximated using eddy-viscosity and eddy-diffusivity approaches, in conjunction with the standard k − ɛ and a k − ω shear-stress-transport models, constant turbulent Prandtl number, and specialized treatments of the near-wall regions. Variable- and constant-fluid-property formulations (with coupled and decoupled solutions of the fluid flow and heat transfer) were assessed. The discretization of the complex geometry and the governing equations, and solutions of the discretized equations, were done using commercial codes. These numerical models gave favorable and comparable results, with predictions of global flow quantities (such as windage losses and overall mass flow rates) lying within 4%, and average and maximum temperatures of the pole surface within 5 °C and 3 °C, respectively, of the corresponding experimental data when using the constant-property, coupled, standard k − ɛ model with specialized wall functions. However, the equivalent decoupled model, which was the least computationally intensive, was also adequate for the task at hand. Numerical assessments of two alternate ventilation configurations in the scale model were also undertaken. They showed that increasing the surface area of the spider arms reduced the maximum temperature of the pole by 2.6 °C; and restricting the rotor inlet area reduced the windage losses and the maximum temperature of the pole by 4.7% and 1.5 °C, respectively. • 3D Conjugate heat transfer simulations of a hydroelectric generator scale model. • Validation of flow and temperature distributions by way of experimental measurements. • In contrast with design assumptions, flow across the rotor rim ducts is non-uniform. • Numerical predictions of hot-spots on the scale model’s rotor to within 2.7 °C. • Proposed modifications to the rotor design to reduce rotor pole hot-spot temperatures.