Air-gap convection in a switched reluctance machine

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: Nu = 0.181 Ta 0.207 m . This paper is part of the ADvanced Electric Powertrain Technology (ADEPT) project which is an EU funded Marie Curie ITN project, grant number 607361. Within ADEPT a virtual and hardware tool are created to assist the design and analysis of future electric propulsion, especially within the context of the paradigm shift from fuel powered combustion engines to alternative energy sources (e.g. fuel cells, solar cells, and batteries) in vehicles like motorbikes, cars, trucks, boats, planes. The design of these high performance, low cost and clean propulsion systems has stipulated an international cooperation of multiple disciplines such as physics, mathematics, electrical engineering, mechanical engineering and specialisms like control engineering and safety. By cooperation of these disciplines in a structured way, the ADEPT program provides a virtual research lab community from labs of European universities and industries [1].

Advanced Lumped Parameter Model for Switched Reluctance Motors With High Performance Cooling

“…The different thermal interface resistances used in the model are based on findings and correlations from literature. For the heat transfer in the air gap the correlation of Romanazzi et al is used [19] specifically obtained for a SRM. The correlation is based on the so-called modified Taylor number calculated by = , where is the rotation speed, the gap width, the kinematic viscosity of the air, is the mean radius and is a geometrical factor, see [19] for more details.…”

“…For the heat transfer in the air gap the correlation of Romanazzi et al is used [19] specifically obtained for a SRM. The correlation is based on the so-called modified Taylor number calculated by = , where is the rotation speed, the gap width, the kinematic viscosity of the air, is the mean radius and is a geometrical factor, see [19] for more details. The Nusselt number of the heat transfer between the rotor and stator can be calculated by = 0.181 0.207 , which is valid for 10 2 < < 3 * 10 4 .…”

Thermal model of electric machines with correction of critical parameters

“…To achieve a small error valid Nusselt-correlations are needed for every heat film coefficient α for the different The references for the Nusselt-correlations used to calculate the heat film coefficients are given in table III.1. The Nusseltcorrelation for the airgap is given in [7] and [8] and its known as the correlation by Becker and Kaye [9]. Compared to [9], [10] gives the Nusselt-correlation in the airgap for a rotational movement and a flow in axial direction.…”

“…Compared to [9], [10] gives the Nusselt-correlation in the airgap for a rotational movement and a flow in axial direction. The influence of slots in the rotor like in switched reluctance machines is analysed numerically by [8]. In this paper we use the correlation from [9] and [10] with the correlation for the turbulent case given by equation (27) in [11].…”

Temperature Field Accurate Modeling and Cooling Performance Evaluation of Direct-Drive Outer-Rotor Air-Cooling In-Wheel Motor

“…The air-gap domain is not built, and HTCs of the rotor-side and stator-side cylinders are determined using an empirical formula for the Nusselt number. The two concentric cylinders of the air-gap contribute a convection connection [6][7][8]. The second is the coupled field method (CFM).…”