Endwall Flow Mechanisms in Electric Propulsors

Over the last decades, the dramatic growth of the aviation industry and its emissions has caused an increased interest in the electrification of aviation. The battery and motor technology limit the possible range of electric aircraft, making them suitable only for short missions in urban environments. Due to the infrastructure limitations in these environments, most of these aircraft are designed for vertical take-off and landing (e-VTOLs).

Shaft-driven ducted fans are commonly used for the propulsion of e-VTOLs leading to safe and quiet missions. However, recent research projects suggest that placing the electric motor at the rotor's shroud (Rim-Driven Fan, RDF) could enhance the propulsor's performance. The rim provides support against mechanical stresses, and the motor cooling and wiring become less complex as cables do not cross the gas path. Nonetheless, the rotating shroud would modify the flow field and affect the system's efficiency.

From the existing literature, it is clear that the flow patterns developed at the tip region of the rotor, referred to as endwall flows, affect the aerodynamic loss and stability of ducted fans. Most of the work already done is focused on conventional, cantilevered rotor blades and does not apply to RDFs. Hence, this PhD project aims to analyse the effect of shroud on the aerodynamic performance, in terms of both efficiency and stall margin, and assess the trade-offs between the different designs of fans for e-VTOLs.

Steady and unsteady CFD simulations will be carried out to investigate the flow field developed within the engine throughout the e-VTOL flight mission. Unsteady simulations for such designs have not been conducted in previous studies and are necessary to understand the causes and consequences of flow instabilities appearing under certain operating conditions of the engine.

The designs examined will be rapidly manufactured and tested in an e-VTOL dedicated rig in the Whittle laboratory. To assess the feasibility of RDFs an integrated-system approach will be adopted, accounting for the impact of the new design on all the engine components.