Ventilation of a Model Hydro-Generator, An Experimental and Numerical Study

Licentiate thesis, 2015

Generators are sophisticated machines used to convert the mechanical energy of a prime mover into electrical energy. Electromagnetic and mechanical losses accompany this energy conversion process. Cooling systems remove the heat, generated by losses, from these machines. An efficient cooling and ventilation must be considered during the electro-mechanical design of a generator. Having a complete picture of the losses, the ventilation flow and the temperatures inside the machine is a key prerequisite for an optimal design of cooling system. The present work aims at providing experimental and numerical tools essential for a better understanding of ventilation flow attributes inside hydro-generators and coming up with comprehensive study of flow based on these tools. In particular, flow inside the stator ventilation channels is addressed. The obtained knowledge can be used for improvement in design of generator cooling system. A generator model was manufactured taking into consideration the needs of both the experimental and numerical methodologies. A new intake section and fan is designed for the existing generator model to increase the volume flow rate and make it possible to measure it accurately. A CFD-based procedure is utilized for their design. The experimental results point out the effectiveness of the new parts. A new stator with modified ventilation channel configuration is also designed with better optical experimental access. Total pressure rake, 5-hole probe and hot-wire anemometer are used for taking measurements. Particle image velocimetry (PIV) is carried out inside the ventilation channels. The computational fluid dynamics simulations are performed using the FOAM-extend CFD toolbox. The steady-state multiple frames of reference method is used for the numerical simulations. The frozen rotor and mixing plane approaches are used to handle the rotor-stator interaction. The effect of three different stator channel configurations on the ventilation flow properties is studied. The flow and pressure field in the model generator are analyzed. The numerical and experimental results show a good agreement, which indicates the applicability of both methods.