Ventilation and heat transfer in a symmetrically ventilated salient pole synchronous machine

The results of a continuing effort to broaden understanding of heat transfer and ventilation in large synchronous salient pole electrical machines are presented. Heat transfer coefficients measured on an experimental four pole rotor for selected operational parameters are given and compared to computational fluid dynamics (CFD) predictions. The experimental programme was carried out on an hydraulically smooth rotor and corresponding heat transfer coefficients measured for the purpose of CFD validation are presented. The effects of surface roughness on the predicted values of heat transfer coefficients are then considered. Particular attention is given to the field coil faces where "strip-on-edge" windings are extended to give a ribbed surface. A method using an equivalent roughness, to account for the enhanced heat transfer, without increasing demands for mesh density is explained. The data presented demonstrate clearly the link between the flow field and the heat transfer coefficient. The potential use of CFD as a design tool to examine the effects of operating parameters and geometric modifications on heat transfer is illustrated.