  Switched reluctance machines (SRMs) have recently become popular in the
automotive market as they are a good alternative to the permanent magnet
machines commonly employed for an electric powertrain. Lumped parameter thermal
networks are usually used for thermal analysis of motors due to their low
computational cost and relatively accurate results. A critical aspect to be
modelled is the rotor-stator air-gap heat transfer, and this is particularly
challenging in an SRM due to the salient pole geometry. This work presents
firstly a review of the literature including the most relevant correlations for
this geometry, and secondly, numerical CFD simulations of air-gap heat transfer
for a typical configuration. A new correlation has been derived:
$\mathbf{Nu=0.181\ Ta_m^{0.207}}$
