Air-Gap Convection in a Switched Reluctance Machine

TL;DR

This paper investigates the heat transfer in the air-gap of switched reluctance machines, reviewing existing models and introducing a new correlation based on CFD simulations to improve thermal analysis accuracy.

Contribution

It provides a comprehensive review of existing correlations and introduces a novel heat transfer correlation specific to SRM air-gaps based on CFD results.

Findings

New correlation for air-gap heat transfer in SRMs: Nu=0.181 Ta_m^{0.207}

CFD simulations validated against literature data

Enhanced understanding of rotor-stator heat transfer in SRMs

Abstract

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: $\mathbf{Nu=0.181\ Ta_m^{0.207}}$