Session: 13-04 - Transients, Unsteadiness and Swirl

Paper Number: 120895

120895 - Transient Simulation and Characterization of Conjugate Heat Transfer at Hydro Generator Polewindings 

Effective cooling schemes are essential for the integrity of turbomachinery components. An accurate prediction of the heat and fluid flow is necessary for the identification of potential design improvements. This applies to thermal but also electrical turbomachinery such as hydropower generators. Due to Ohmic losses occurring for example in the copper windings inside the rotor, heat must be removed from the system effectively to avoid exceeding critical temperature limits.

Hence, a thermodynamic cycle is realized to transport cooling air through the generator. The rotor supplies shaft work to the fluid providing the energy for the coolant to overcome the total pressure losses in the system. From an aerothermal perspective the rotor can be considered as a radial compressor impeller surging cooling air at its axial ends and convecting it radially outwards passing by the windings. As the direction of the bulk flow is radially outwards, the flow is influenced by Coriolis force effects. Furthermore, the wavy geometry of the windings and a positive pressure gradient in the bulk flow shape challenging conditions for the boundary layers.

In the present paper the relevant transport processes of the problem such as the convection of fluid, the convection of heat and the diffusion of heat in the solid are illustrated. The corresponding characteristic time scales are introduced. The time scale disparity between thermal transport processes in the fluid and the solid is pointed out. As local solid temperatures must be predicted, conjugate heat transfer simulations are required avoiding or bridging the time scale disparity. For this purpose, three potential numerical setups are presented and benchmarked to each other. The Bi-Fo time scaling approach demonstrates to deliver the best match between prediction and measurements, while requiring the lowest numerical effort.

The impact of unsteadiness and turbulence modeling on the prediction of the polewinding temperatures is analyzed and demonstrated to have a significant impact on the winding temperatures. Local temporal fluctuations in the velocity field are identified and visualized. While steady state RANS simulations perform best in terms of numerical effort, DES simulations deliver the best match between numerical data and measurements.

Summing up, the paper offers new fundamental insights into the numerical prediction of heat and fluid flow in the challenging environment in between the poles of a hydro generator. Bi-Fo scaling is applied and demonstrates to deliver the best results compared to measurements in terms of quality and efficiency. According to previous studies published in literature, the resolution of temporal fluctuations by scale resolving approaches yields best congruency between predictions and measurements.

Presenting Author: Thilo Dauch Voith Hydro Holding GmbH & Co. KG

Presenting Author Biography: 2008-2014: Bachelor and Master studies in Energy Engineering - Turbomachinery and Jet Propulsion at RWTH Aachen University, Aachen, Germany
2014-2020: Research assistant and PhD candidate at the Institute of Thermal Turbomachinery at Karlsruhe Institute of Technology (KIT), Karlsruhe Germany
Since 2020: Development Engineer at Voith Hydro Holding GmbH & Co. KG in Heidenheim, Germany - Scope of work: Thermal management of hydro power generators - CFD - High Performance Computing

Authors:

Thilo Dauch Voith Hydro Holding GmbH & Co. KG
Bastian Diebel Voith Hydro Holding GmbH & Co. KG
Roland Jester-Zuerker Voith Hydro Holding GmbH & Co. KG