Numerical experiments on helium flow in superconducting generators

Numerical experiments on helium flow patterns in a superconducting generator are reported. The simulations were conducted with a thermohydraulic analysis program which integrates the equations of motion for one dimensional coolant mass flow rates in a rotating channel network. The method includes frictional, buoyant, and inertial forces. Heat generation and transfer as well as thermophysical material properties are modeled realistically. As a result, a complete picture of the hydraulic and thermodynamic state in the cooling system during transients is obtained. A simplified five-channel model was investigated for the KWU/Siemens Test Rotor. The model includes a rotating supply bath and self-pumping exhaust system. A number of unexpected flow patterns detected are explained. It is concluded that in normal operation, refilling from the supply bath may occur discontinuously combined with flow oscillations in the supply channels. Also, in parallel heated channels, parallel inward flow, antiparallel flow, and flow oscillations may occur.