Novel In-slot Direct Cooling Structure of Concentrated Winding Permanent Magnet Electrical Machine for Aerospace Propulsion

With the development of high-power density electrical machines, in-slot direct cooling has become a key method to overcome power density limitations. To further enhance the thermal performance of stator oil direct cooling, three novel cooling structures are proposed and systematically compared, with the optimal structure being identified. The structure introduces tooth-side and wedge-side oil paths to increase the contact area between the winding and coolant, and further incorporates oil-blocking teeth at the slot bottom to adjust the flow rate and velocity distribution of different paths. First, three novel direct cooling structures and a conventional structure are introduced, and their coolant flow paths are analyzed. To simplify modeling, a thermal conductivity equivalent model for formed Litz wires is developed and validated. In addition, electromagnetic and mechanical performance are evaluated. Finite element results show stable torque across all designs, while harmonic response analysis indicates that the added features enhance stiffness and reduce vibration near excitation frequencies. Computational fluid dynamics simulations are then conducted to assess flow distribution, coolant velocity, and temperature under various conditions. Results show the proposed structures effectively reduce winding temperature rise. A stator tooth-slot module is also tested, and the experimental results align well with simulations, validating the analysis and thermal model.