Preliminary Design Considerations for Integrating a Composite Impeller in a Brushless Permanent Magnet Motor

Traditional turbomachine design is generally characterized by a shaft driven impeller that was created using common manufacturing processes. However, a cutting edge and innovative impeller design involves the manufacturing of the impeller on a winding machine. Through the use of such a machine, a lightweight and high-strength impeller with carbon fibers or other fibers can be prototyped quickly and easily while also produced in large quantities. The impeller will not only be a composite of multiple parts, but a single solid piece. One of the most interesting attributes of this impeller however, is the ability to integrate it as the rotor for a permanent magnet electric motor. Using the concepts of permanent magnet motor design, current can be applied to the housing of the impeller, which would generate forces that would serve the purpose of both rotating the impeller, and securing it into place. This has the advantage of eliminating most of the moving parts in a turbomachine design, but also creating a durable, lightweight and cheap design to prototype and reproduce. Another key advantage to this design is where the torque on the impeller is applied. Traditional turbomachines generally have the torque generated from forces applied from the shaft, which requires higher tangential forces and hence shear stresses due to a much smaller moment arm. But the integration of magnetics into the outer shroud of the impeller allows for the forces to be applied to the outer edge, which requires less force due to a much greater moment arm. Furthermore, this type of motor inherently allows for all of the electrical components to be outside of the fluid flow, which reduces the need for extensive sealing and insulation. In this paper, basic concepts behind the design of electric motors are outlined, as well as how they can be integrated with a rotor impeller, such that together they could act as a turbomachine.