This paper investigates components of mechanical loss together with heat transfer effects in an axial-flux PM motor. The mechanical loss components generated within electrical machines are well known, however, their prediction or derivation has not been widely reported in the literature. These, together with the electromagnetic loss sources and heat transfer effects are crucial and must be accounted for when considering high-power-density, high-speed and/or compact machine designs. This research is focused on separating the mechanical loss components to gain a more in depth understanding of the effects and their importance. Both experimental and theoretical techniques have been employed in the analysis of a machine demonstrator. In particular, hardware tests with dummy rotors have been performed to measure the bearing and windage/drag loss components. These have been supplemented with CFD analysis to theoretically evaluate the aerodynamic effects occurring within the mechanical air-gap accounting for loss and heat transfer. It has been identified that the analysed hardware demonstrator suffered from bearing loss significantly higher than that suggested by the bearing manufacturer. This has been attributed to design of the mechanical assembly accommodating bearings, which resulted in inappropriate bearing preload. The excessive bearing loss had a significant detrimental effect on the machine thermal behaviour. In contrast, the aerodynamic effects have been found to have less pronounced effects here, due to fully enclosed and naturally cooled machine construction.Index Terms-Axial-flux PM machine, mechanical loss, heat transfer, computational fluid dynamics, thermal equivalent circuit, bearing loss, windage loss.
One-dimensional wave-action engine models have become an essential tool within engine development including stages of component selection, understanding system interactions, and control strategy development. Simple turbocharger models are seen as a weak link in the accuracy of these simulation tools, and advanced models have been proposed to account for phenomena including heat transfer. In order to run within a full engine code, these models are necessarily simple in structure yet are required to describe a highly complex 3D problem. This paper aims to assess the validity of one of the key assumptions in simple heat transfer models, namely, that the heat transfer between the compressor casing and intake air occurs only after the compression process. Initially, a sensitivity study was conducted on a simple lumped capacity thermal model of a turbocharger. A new partition parameter was introduced αA, which divides the internal wetted area of the compressor housing into pre- and postcompression. The sensitivity of heat fluxes to αA was quantified with respect to the sensitivity to turbine inlet temperature (TIT). At low speeds, the TIT was the dominant effect on compressor efficiency, whereas at high speed αA had a similar influence to TIT. However, modeling of the conduction within the compressor housing using an additional thermal resistance caused changes in heat flows of less than 10%. Three-dimensional computational fluid dynamics (CFD) analysis was undertaken using a number of cases approximating different values of αA. It was seen that when considering a case similar to αA = 0, meaning that heat transfer on the compressor side is considered to occur only after the compression process, significant temperature could build up in the impeller area of the compressor housing, indicating the importance of the precompression heat path. The 3D simulation was used to estimate a realistic value for αA which was suggested to be between 0.15 and 0.3. Using a value of this magnitude in the lumped capacitance model showed that at low speed there would be less than 1% point effect on apparent efficiency which would be negligible compared to the 8% point seen as a result of TIT. In contrast, at high speeds, the impact of αA was similar to that of TIT, both leading to approximately 1% point apparent efficiency error.
This paper investigates components of the mechanical loss together with heat transfer effects in an axialflux PM motor. The mechanical loss components generated within electrical machines are well known, however, their prediction or derivation has not been widely reported in the literature. These, together with the electromagnetic loss sources and heat transfer effects are crucial and must be accounted for when considering high-power density, high-speed and/or compact machine design. This research is focused on separating the mechanical loss components to gain a more in depth understanding of the effects and their importance. Both experimental and theoretical techniques have been employed in the analysis. In particular, hardware tests with dummy rotors have been performed to measure the bearing and windage/drag loss components. These have been supplemented with CFD analysis to theoretically evaluate the aerodynamic effects occurring within the mechanical air-gap accounting for loss and heat transfer. Further to these, a 3D lumped parameter thermal model of the axial-flux PM demonstrator has been developed to validate predictions of the mechanical loss components and heat transfer mechanisms. The theoretical findings show good agreement with experimental data. Moreover, the research outcomes suggest that the mechanical and aerodynamic effects require careful consideration when a less conventional machine design is considered. I.
This paper is part of a two-part publication that aims to design, simulate and test an internally air cooled radial turbine. To achieve this, the additive manufacturing process, Selective Laser Melting (SLM), was utilized to allow internal cooling passages within the blades and hub. This is, to the authors’ knowledge, the first publication in the open literature to demonstrate an SLM manufactured, cooled concept applied to a small radial turbine. In this paper, the internally cooled radial turbine was investigated using a Conjugate Heat Transfer (CHT) numerical simulation. Topology Optimisation was also implemented to understand the areas of the wheel that could be used safely for cooling. In addition, the aerodynamic loss and efficiency of the design was compared to a baseline non-cooled wheel. The experimental work is detailed in Part 2 of this two-part publication. Given that the aim was to test the rotor under representative operating conditions, the material properties were provided by the SLM technology collaborator. The boundary conditions for the numerical simulation were derived from the experimental testing where the inlet temperature was set to 1023 K. A polyhedral unstructured mesh made the meshing of internal coolant plenums including the detailed supporting structures possible. The simulation demonstrated that the highest temperature at the blade leading edge was 117 K lower than the uncooled turbine. The coolant mass flow required by turbine was 2.5% of the mainstream flow to achieve this temperature drop. The inertia of the turbine was also reduced by 20% due to the removal of mass required for the internal coolant plenums. The fluid fields in both the coolant channels and downstream of the cooled rotor were analyzed to determine the aerodynamic influence on the temperature distribution. Furthermore, the solid stress distribution inside the rotor was analyzed using Finite Element Analysis (FEA) coupled with the CFD results.
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