Numerical approach for thermal analysis of heat transfer into a very narrow air gap of a totally enclosed permanent magnet integrated starter generator

Abstract

This paper proposes a detailed numerical model of a very narrow air gap of a permanent magnet synchronous machine without an imposed axial flow. The flow structure analysis and the convective heat transfer are carefully investigated using an axisymmetric model of two concentric cylinders where the inner cylinder is rotating and the outer cylinder is stationary. For the different cases, only isothermal boundary conditions have been considered. The impact of the air gap mean temperature and of the rotation speed are thoroughly studied and all numerical findings are compared with analytical dimensionless correlations. CFD simulations show the existence of two critical Taylor numbers corresponding to the onset of further instabilities into the air gap which matches with theoretical and experimental previous results found in the literature. The Nusselt number distribution given by CFD shows a disparity with the dimensionless correlations which underestimate the effective convective heat transfer in very narrow air gaps. The numerical simulations allow the definition of a piecewise expression able to fit well the overall Nusselt number distribution over a relatively large range of Taylor numbers up to 3×10 4 . The present work shows the contribution of CFD numerical methods on the estimation of convection thermal resistances in very narrow air gaps.

Investigation into Taylor-Couette-Poiseuille flow heat transfer for supercritical carbon dioxide turbomachinery

“…Figure 2.21: Global Nusselt number against Taylor number identifying the effect of various turbulence models on the resulting Nusselt correlation for T-C flow. Reproduced from [12] Simulations performed by Nachouane et al [12] for a low Taylor number range (< 10 4 ) are displayed in Figure 2.22 and are displayed together with existing literature correlations, in particular the correlations of Becker and Kaye [51] and that of Aoki et al [66]. The results of the axis-symmetric CFD model shows good agreement with the two experimental correlations and clearly displays the three areas of differing heat transfer.…”

“…Nachouane et al in 2015 [12] performed CFD simulations on a permanent magnet synchronous machine without an imposed axial flow (T-C flow). The study was carried out with an axis-symmetric model using a Pressure-Based solver in a steady state configuration.…”

“…Nachouane et al [12] produced results of global Nusselt numbers for a range Taylor numbers (up to 10 7 ) using three different turbulence models. The results of which are shown in Figure 2.21 alongside experimental data produced by Bouafia et al [69].…”

“…Existing heat transfer correlations within literature cover operating conditions, up to an axial Reynolds number of 10 5 and up to a Taylor number of 10 11 . However, the operating Taylor number for typical sCO 2 cooling systems is likely to be of the order of 10 12 . This thesis presents the development of a validated methodology and experimental test facility for collecting heat transfer correlations at these high Taylor number Taylor-Couette-Poiseuille flow regimes and experimental data that is relevant to future sCO 2 applications.…”

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

“…The third is the equivalent thermal conductivity (ETC) method. The air-gap is seen as solid, and the ETC of the air-gap is obtained using empirical formulas [10,11]. In terms of high to low accuracies, the arrangement of the methods starts from CFM, HTC, to ETC.…”