An efficient cooling design strategy for the embedded driving motor under the hub by using the high-pressure airflow after the rotor in an electrical ducted fan system

The ducted fan, with its advantages of high efficiency and low pollution, is being considered as the power unit for the next generation of electrical aircraft. As a key component, its driving motor is typically installed within the limited internal space of the blade hub wall so as to reduce the axial length of the electrical fan system. However, continuous high-power output can lead to rapid temperature rise in the motor's permanent magnets and external control components, resulting in a failure operation and decreased lifespan of the driving motor. Therefore, an efficient integrated cooling design is crucial for ensuring the lightweight and durability of the electrical ducted fan system. This paper develops a cooling method for the ducted fan and motor system based on the swirling airflow generated by the fan to assist the heat dissipation of the driving motor. In specific, by constructing an annular cooling channel between the motor and the hub, the airflow generated by the thrust fan itself can be utilized to inject into the cooling channel through the bleed slot to participate in the heat dissipation of the motor. It is found that the geometric design of the bleed slot at the inlet of the cooling channel can greatly ensure the mass flow and swirl characteristics of the gas entering the cooling channel, so as to improve the convective heat transfer coefficient of the motor surface and effectively control the motor surface temperature. Numerical simulation results indicate that, with a constant inlet area for the cooling channel, there exists an optimal bleed angle. Compared with the original rectangular bleed slot, the optimal inclined bleed slot thermal design scheme could achieve a reduction of the averaged motor surface temperature by 84 K when the aircraft is in the cruise condition. In the meanwhile, the thrust loss of the fan can be kept within 5 % and the adiabatic efficiency degradation is kept under 1 %.