Abstract: A bulb tubular turbine generator, due to its compact internal structure and the significant heat generated by its electromagnetic losses, urgently needs improvement in its ventilation and heat dissipation capability. Aimed at this goal, this paper optimizes its internal airflow path structure based on multi-physical field coupling. First, for a 24 MW bulb tubular turbine generator, we construct a numerical model of its 2D electromagnetic fields based on the finite element method, and develop a 3D fluid-thermal model using the finite volume method. Both are validated against experimental data of electromagnetic and temperature measurements. Then, for its original design, we make a qualitative analysis of the flow field and temperature field characteristics of its airflow path structure, and a quantitative analysis of its ventilation duct's flow distribution and the variation trends of temperature inside it. And, the impact of rear cover plate length on the airflow and heat exchange is examined. Finally, we discuss the mechanism of how the blade installation angle of the rotor ribs affects airflow based on the velocity triangle theory, and evaluate the effects of different blade installation angles on rotor ribs through coupled numerical analysis. The results show that a short rear cover plate can prevent air from spilling over its sides while ensuring air re-enters the cooling cycle; rotor rib blades installed at an angle of 66° significantly improve the flow and thermal fields and lower the temperature at all monitoring points; under two different ventilation conditions, the stator winding temperatures are lowered by 9% and 20.4% respectively.

Key words: bulb tubular turbine generator, ventilation and heat dissipation capability, electromagnetic-fluid-thermal coupling, rear cover plate, rotor ribs