Electric Ducted Fan Aerodynamics and Optimisation

This research investigates fully integrated electric ducted fan propulsion system characteristics for future novel air-vehicle configuration designs. The eventual aim of the research is to develop a performance metric and design guidelines considering the interdependent aerodynamic effects between body and propulsion system.

The full integration of the propulsion system into an airframe can offer overall system benefits as propulsion mounting components can be omitted, reducing both wetted area (friction drag) and system weight while allowing for a more compact airframe design as well as compact storage and transportation possibilities. The interactions between airframe and propulsion system though result in an increased aerodynamic complexity. Unlike conventional configurations where the resulting drag of an airframe is overcome by a propulsion system producing thrust from ingesting free stream air, the investigated configuration will ingest the fluid responsible for part of the vehicle's drag. Despite the increased aerodynamic complexity, the so-called boundary layer ingestion (BLI) can potentially benefit the overall performance of the air-vehicle. For axisymmetric bodies, theoretical studies suggest efficiency improvements in the order of 20%. The concept investigated in this study has an axisymmetric body together with a fully integrated tail mounted in-line boundary layer ingesting Electric Ducted Fan (EDF).

Many theoretical approaches though neglect or insufficiently integrate the interdependence between the air-vehicle and propulsion system. As the boundary layer of the vehicle's airframe is being ingested, the fan will impose a pressure gradient onto the flow upstream, essentially affecting the boundary layer around the body. Thus, the drag will be altered through BLI by the acceleration of its surrounding flow. The interdependence of thrust and drag when employing the ingestion of the body's boundary layer void the division of thrust and drag as two independent parameters as traditionally done in performance quantification of air-vehicles.

Detailed investigation of the aerodynamic characterises of the boundary layer are therefore an essential part of this research. Computational Fluid Dynamics (CFD) can simulate aerodynamic behaviour, whereas the accuracy is greatly dependant on flow complexity as well as computational resources. The added variables of aerodynamic interdependence of the airframe and propulsion system are insufficiently validated by present computational methods.

This research therefore aims to combine experimental with computational techniques. By developing a bespoke low-cost modular experimental wind tunnel model, high quality experimental data can be generated and used for validation of CFD. Experimentally validated CFD tools will increase confidence in their use, enabling further insight into the flow-physics beyond the scope of experimental measurement techniques. The combined use of experimental and computational approaches will underpin development of suitable performance metrics which can then be used for subsequent integration and optimisation. The aim is then to quantify the interdependence of the body and propulsion system, in order to define design guidelines for future applications having closely integrated propulsion systems with boundary layer ingestion.

This research will incorporate:
- Low-cost modular experimental wind tunnel model for experimentally investigating a variety of different shapes/configurations
- Powered Wind Tunnel testing
- Electric propulsion and investigation of associated aerothermal effects
- Efficient and effective coupling of experimental and computational methods
- Derivation of suitable performance metrics and subsequent performance optimization
- Development of future design methodology for in-line EDF air-vehicle integration

The research benefits through close collaboration with QinetiQ.