CFD investigation of thermal management and flow behavior in an optimized air-cooled tail rotor propulsion system

• CFD-based optimization applied to air-cooled electric tail rotor system. • Demonstrates passive design strategies for enhanced thermal management. • Highlights the role of duct geometry and shaft blades in airflow control. • Establishes a balance between aerodynamic performance and heat dissipation. • Provides scalable insights for next-generation electric rotorcraft propulsion. As aerospace propulsion steadily transitions toward electrification, effectively dissipating heat in compact electric tail rotor motors has become a pressing design challenge. In this study, a high-fidelity computational fluid dynamics (CFD) framework is employed to investigate an air-cooled propulsion system specifically configured for helicopter tail rotor applications. Three passive geometric modifications are examined in detail: widening of lateral duct openings, introducing a 15° inclination to the duct sidewalls, and incorporating rotating blades along the central shaft. The optimized configuration demonstrated substantial thermal gains, reducing peak temperatures by 10.38% in the winding, 8.23% in the magnet, and 19.0% in the shaft. This enhancement was primarily attributed to enhanced airflow penetration, boundary-layer thinning, and the development of favorable secondary recirculation zones. Convective heat transfer performance was also elevated, with Nusselt numbers increasing by up to 11.6% across key components. Importantly, these thermal benefits were achieved while maintaining aerodynamic integrity, as the simulated thrust deviated by only 1.34% from experimental rig measurements. The results highlight how targeted, flow-physics-based passive design strategies can simultaneously improve cooling performance and preserve propulsion efficiency. This approach offers a scalable and integration-friendly pathway for next-generation electric rotorcraft requiring lightweight, thermally resilient tail rotor systems.