Optimum Performance Determination of Single-Stage and Dual-Stage (Contra-Rotating) Rim Driven Fans for Electric Aircraft

Abstract

Electrical Rim Driven Fan (RDF) technology is a novel application to aircraft propulsion, and there are many factors that play a part in determining its optimal achievable performance, for example, the electrical, magnetic and thermal properties of the rim driven motor architectures; the mechanical strength, mass and friction properties of the materials used; the aerodynamics of the fans and the efficiency of the motor drive and control circuitries. Each of these factors could easily warrant their own lengthy and indepth analyses. The aims of this paper are to provide a starting point from which to get a feel for the rough-ordermagnitude of an RDFs performance and to elucidate a conventional calculative methodology suitable for a quick and easy reality-check before undertaking more accurate numerical analysis techniques. Initially, the properties of an existing aerospace fan design, namely that of the IAE V2500-A5 turbo-fan engine, is used to validate this approach and then the same methodology is used to estimate a first-guess performance prediction for a range of single-stage RDFs of varying sizes from 100mm to 500mm diameter, operating over a range of speeds from zero to 25 kRPM. Finally, a comparison between a single-stage and a dual-stage (contrarotating) 200mm diameter RDF for a UAV application is conducted. The performance limits of the RDFs considered in this analysis have been established to ensure that the fan blades are always operating within the subsonic flow regime.

The Application of Slotless Skewed Windings to a Rim Driven Fan for Aircraft Electrical Propulsion (AEP)

“…The windings aim is to be incorporated into a motor powering a rim driven fan, therefore the winding sizing is very different from the research done in this field. The sizing requirement is driven by the need for multiple-stage contrarotating fans to maximise the thrust produced [1], [10]. The axial length of the winding should be short and the diameter should be large to accommodate the fan.…”

“…Several studies [2], [6], [19]- [21] determined the suitability of this configuration for AEP due to its highpower density and efficiency. In this study, a three-phase I and is based on data from [10] for a dual-stage rim driven fan for AEP.…”

“…However, aerospace propulsion applications require large motors with high power density and efficiency. As a promising solution, thin and large motors for new multistage contra-rotating rim driven fan (RDF) configurations are considered in [4], [10].…”

Review of Low Aspect Ratio Blade Dynamics for Electrical Axial Fans and Compressors

“…Then, in a much later paper, reasoned that a rim-driven fan or compressor stages could operate independently, allowing the designers to implement counter-rotating stages; Fig. 2 is their demonstration of a static thrust comparison for small (200 mm diameter) single-stage and contra-rotating dualstage rim driven fan (RDF) [5].…”

Torque-Speed Characteristics for Electrically Powered Rim Driven Fans and Thrust Comparison with a Small Conventional Fan Jet Engine

“…Such as an increase in thrust per frontal area owing to the removal of the flow restriction caused by the hubmounted motor; shorter overall length of the fan assembly; a reduction in the motor tangential forces required to generate torque owing to an increase in the radial moment arm; improved fan aerodynamics; provision of cooling for the motor windings and the ability to easily install two contra-rotating RDFs in tandem. This latter advantage also enables increased Fan Pressure Ratios (FPRs) to be generated [6] thus allowing faster efflux velocities and flying speeds. A drawback to an RDF configuration can be its weight if the electromagnetic circuit is not sized or constructed efficiently.…”