Experimental validation of CFD modelling for heat transfer coefficient predictions in axial flux permanent magnet generators

This paper describes the experimental validation of CFD modelling for heat transfer coefficients in an axial flux permanent magnet (AFPM) generator. A large scale low speed test rig was designed and constructed. The geometric parameters and the rotational speed of the test rig were determined by dimensional analysis, to ensure the flow characteristic remains unchanged as compared with commercial AFPM generators. The heat transfer coefficients in the test rig were measured at rotational Reynolds number, Re_ω from 0 to 2 × 10⁶, non-dimensional flow rate, C_w up to 11,000 and gap ratio, G = 0.016, by using the combination of heat flux sensors and thermocouples. Due to the large size of the scaled-up rig, natural convection played a significant part in the heat transfer and this had to be compensated for in the forced convection heat transfer coefficient calculations. Extra experiments were designed and conducted to identify the effect of natural convection on the machine’s cooling. The experimentally determined results were compared to heat transfer coefficients predicted by CFD models and good agreement was obtained.