Advancing Transport Decarbonisation: Aerodynamic Optimisation of Flywheel Energy Storage for Low-Carbon Powertrains

Given the pressing need to reduce carbon emissions and the significant role of the transportation sector in global carbon dioxide output, Flywheel Energy Storage Systems (FESS) offer excellent energy recovery potential to significantly improve energy efficiency and reduce emissions in low-carbon powertrains. However, a gap exists between theoretical potential and practical application, as current FESS technologies have not been fully optimised for aerodynamic efficiency, limiting their adoption in real-world applications. Enhancing FESS to operate at optimal aerodynamic efficiency promises greater energy storage and retrieval efficiencies for vehicles and enables a broader range of applications in the search for transport decarbonisation. This thesis introduces a new concept for the aerodynamic optimisation of FESS, utilising an integrated approach of Computational Fluid Dynamics (CFD) and Design of Experiments (DoE) analysis. This concept is explored through analytical models and CFD simulations tailored to the unique characteristics of FESS. The implementation of this optimised FESS demonstrates, through various design modifications and operational conditions, an ability to significantly reduce standby losses and enhance overall energy efficiency, with potential applications extending to medium-duration storage solutions. A comprehensive evaluation of current FESS technologies highlighted barriers to achieving optimal aerodynamic efficiency. To overcome these challenges, the thesis proposes a refined FESS design that incorporates adjustments to airgap size, radial and axial radius ratios, and enhanced surface roughness. Notably, the integration of reversed trapezoidal slit shapes, operating at reduced pressure levels of 200 mbar and using helium as the gas medium, led to significant enhancements, reducing windage losses by 88% and increasing the Nusselt number by up to 18%, indicative of improved heat transfer efficiency. These aerodynamic enhancements were validated by a substantial 580% increase in standby time in the optimised model, demonstrating the effectiveness of the design modifications. Vehicle simulations using MATLAB/Simulink, specifically for the Vauxhall Corsa model, revealed that the initial integration of the baseline FESS model into a Hybrid Electric Vehicle (HEV) resulted in a 13% reduction in fuel consumption and a 10% decrease in carbon dioxide emissions, demonstrating FESS's benefits for vehicle efficiency. Further refinements in the FESS integration, particularly in the most optimised Model, resulted in an 18% reduction in fuel consumption and a 15% decrease in carbon dioxide emissions across various Worldwide Harmonised Light Vehicle Test Procedure (WLTP) classes. The FESS transformation from a short-duration to a medium-to-short-duration storage solution broadens its application spectrum, accommodating both short and extended vehicular journeys. These findings signify a considerable advancement towards closing the gap between the current capabilities and the theoretical potential of FESS in contributing to the decarbonisation of the transportation sector, paving the way for future developments in low-carbon vehicle technologies.