2011

Levitated Duct Fan (LDF) Aircraft Auxiliary Generator

This all-electric design eliminates mechanical bearings and enables more efficient aircraft electrical systems.

This generator concept includes a novel stator and rotor architecture made from composite material with blades attached to the outer rotating shell of a ducted fan drum rotor, a non-contact support system between the stator and rotor using magnetic fields to provide levitation, and an integrated electromagnetic generation system. The magnetic suspension between the rotor and the stator suspends and supports the rotor within the stator housing using permanent magnets attached to the outer circumference of the drum rotor and passive levitation coils in the stator shell. The magnets are arranged in a Halbach array configuration.

The electromagnetic generation system also uses permanent magnets attached to the outer circumference of the drum rotor with coils placed in the stator shell. The generation system uses the same magnets as the levitation system, but incorporates generator coils in the stator that are interwoven with passive levitation coils. The levitation system is inherently stable, is fail-safe, and does not require active control as required by traditional magnetic bearings. Also, the overall efficiency of the suspension system improves with speed, whereas the performance of conventional bearings degrades as speed increases.

This innovation will greatly advance aircraft electrical power systems with the development of an efficient, reliable, maintenance-free, and safe electrical generation system. The use of magnetic suspension minimizes concerns associated with traditional bearings, such as active lubrication, contact wear, and limited rotational speed. The ducted hardware can translate into improved efficiency and reliability. The concept lends itself to a configuration in which the units can be used individually or clustered for distributed power applications. In addition, the concept can be readily scaled into a variety of sizes for specified power delivery with similar geometric configuration. The rotor operates in compression, which results in a 2× improvement in fatigue life, and the extensive use of composites minimizes weight and reduces noise due to the higher dampening properties of composites.

A prototype stator and assembly and rotor have been designed and developed to study and evaluate subsystem level characteristics of the generation and levitation systems in a laboratory environment, and to verify theoretical predictions. The test setup has been used to measure successfully the flux density emanating from the rotor, the induced current in the stator winding as the rotor is driven at various speeds, the associated induced current, and the generated repulsive force. Experi - mental results correlate well with performance characteristics predicted using the derived theoretical equations. The goal of the final design is a selfcontained suspension and electrical generation system free from mechanical couplings. The use of magnetic suspension minimizes concerns associated with traditional bearings, such as active lubrication and limited rotational speeds.

This work was done by Dennis J. Eichenberg, Dawn C. Emerson, Christopher A. Gallo, and William K. Thompson of Glenn Research Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steven Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. LEW-18658-1

This Brief includes a Technical Support Package (TSP).

Levitated Duct Fan (LDF) Aircraft Auxiliary Generator (reference LEW-18658-1) is currently available for download from the TSP library.

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