Articles techniques et présentations

Modern micro-jet engines remain limited by anisotropic temperature distributions and over-reliance on legacy analytical design methods, which fail to capture relevant viscous effects and impose bold geometry approximations, restricting efficiency, durability, and integration with UAV propulsion systems. Despite the potential of Computational Fluid Dynamics, with the capability to resolve these phenomena with far greater resolution, it is underutilised in current design practice, rarely coupled with optimisation algorithms. To address these shortcomings, we must focus on the annular combustor and its effectiveness upon mixing coolant and reacted fluids. With a goal to i) implement a tangential annulus flow pattern design ruling and ii) optimise fluid interaction, resulting in improved combustor performance and durability. Combustor geometry was generated from a combination of Lefebvre-based preliminary analysis and atomiser design principles, using outlet conditions of diffuser design studies as boundary conditions. A three-dimensional COMSOL Multiphysics Cold run Computational Fluid Dynamics model was validated against analytical problems and previous academic work [1], complemented by a mesh convergence study (1.4 million cells) concerning the convergence of energy weighted average vorticity in the primary zone – a variable encapsulating density, the local velocity field and vorticity field, Figure 1. The simulations revealed limitations in traditional analytical predictions, as well as quantifying improvements from implementing the T.A.P principle. Concerning hot run CFD, heat transfer was added to the simulation with a source in the primary zone, with a heat flux synonymous with the power released from the fuel. Further simulation of the atomiser validated the analytical approach due to similarities with experimental correlation. However, considering cost and machinability, it is concluded that commercially available technology can achieve the same performance. Multi-fidelity mesh optimisation of airflow characteristics resulted in corrected oxygen supply in the primary zone, Figure 2; hence, reasonable grounds to assume the equivalence ratio shall be actuated upon running the combustor. Furthermore, improvements in Pattern Factor via Nelder Mead optimisation, altering dilution zone and secondary zone positions, reached 72% with negligible pressure and efficiency losses and an optimised value of 0.136. This improvement is shown in Figure 3, with the heatmap of Pattern Factor for varying designs shown, as well as the physical temperature distribution in the turbine inlet plane. Beyond the specific findings, this report suggests an elegant design principle (Tangential Annulus Flow, illustrated by a tenth slice of the combustor simulation shown in Figure 4) and provides a practical pathway to further research by using a multi-dimensional optimisation algorithm, for more efficient and maintainable micro-jet engine combustors.