Use of HMB3 for the simulation of compound rotorcraft

Compound rotorcraft is a generalisation of the term compound helicopters proposed by Graham[1]:"a rotorcraft which, in flight, and at slow speed derives the substantial proportion of its lift from a rotary wing system but at speed can generate lifting and longitudinal thrust from a suitable combination of rotary wing system, fixed lifting surface(s) and auxiliary propulsor(s)". For conventional helicopters, through compounding, the inherent speed limitations can be effectively overcome. The result is superior performance e.g. high payload/lift capacity, lower fuel burn, and increased range and speed. Their increased capabilities allow compound rotorcraft to bridge the gap between traditional helicopters and fixed-wing aircraft, and fill the mission gap between airplanes and conventional low-speed helicopters.
 

The very need for high performance motivated the development of dozens of experimental compound configurations over the past 7 decades, yet only the V-22 tilt-rotor can be found in service. This is because the combination of multiple sources of lift and thrust brings significant challenges in terms of aerodynamic interactions, vibration and instability, control and trim difficulties, power allocation and etc. Nevertheless, compound rotorcraft research is now emerging mainly in Europe and the USA, as the appeal for better civil rotorcraft is growing. Several demonstrators e.g. the Eurocopter X3 and the Sikorsky X2 have been delivered illustrating the superior performance of compound rotorcraft.  Ahead of routine deployment of compound rotorcraft, there is still significant research and development to be carried out.

Rotor/Rotor Interaction

Rotor/wing interactions

Rotor/Wing Interaction

 

The purpose of this project is to conduct simulation work in the general area of compound rotorcraft. Configurations and performance, aeromechanical interactions, and trim methods of compound rotorcraft, throughout their flight envelope, are investigated and analysed using modern CFD methods. Gradient-based aerodynamic design and configuration optimisation is also attempted. In the present study, numerical methods for aerodynamic simulations and optimization are proposed and evaluated through analyses of the ducted propeller, a promising choice of propulsion for future compound rotorcraft. In addition, acoustics is accounted for as a key topic, since many novel rotorcraft are designed for operations close to urban areas where rapid ingress/outgress is required with minimal impact on communities. Also, compound rotorcraft must comply with strict emissions and noise guidelines set by the EU and the US regardless of their superior performance. Simulation methods of several fidelity levels using steady/unsteady actuator disks and resolved blades are evaluated for rotor/rotor and rotor/wing interactions. Further work will focus on the adjoint-based optimisation of the compound shape and configuration for improved aerodynamic performance.

 

Resolved Blades

Actuator Line Model

 

 

Contacts

 G. Barakos (Professor), George.Barakos@glasgow.ac.uk

 T.Zhang(PhD student), t.zhang.4@research.gla.ac.uk

Publication

Zhang, T., Barakos, G. N., "Towards Optimisation of Compound Rotorcraft," 45th European Rotorcraft Forum, Warsaw, Poland, 2019.

Zhang, T., Barakos, G. N., "Development of Simulation Tools for High Fidelity Analysis of Compound Rotorcraft." In AIAA Scitech 2020 Forum, p. 1258. 2020.

References

[1] Graham, J., “Definition of a Rotorcraft,” https://www.aerosociety.com/Assets/Docs/Publications/SpecialistPapers/Definition_of_a_Rotorcraft.pdf, February 2013, Special paper of the Royal Aeronautical Society, available on-line.

Aerodynamic/Aeroacoustic Analysis and Optimisation of Ducted Propeller

Open Propeller

Ducted Propeller

Open Propeller Wake

Ducted Propeller Wake

The ducted propeller is a propeller enclosed by an annular duct with aerofoil-like sections. The ducted propeller can be an ideal choice of propulsion for future novel rotorcraft configurations operating in urban environments. The duct alters the inflow condition for the propeller inside and offers extra thrust at no torque cost. The ducted propeller is often more efficient at low speeds, especially in hover, over the un-ducted counter-part. Also, due to the expansion at the duct diffuser, the propulsor wake is less intrusive. Moreover, by shielding the propeller, the duct provides protection to ground personnel and equipment. In emergencies, the duct can be used as containment, preventing further damage to the airframe. Tests also showed acoustic reductions due to the duct shielding, while maintaining high efficiency.

Open Propeller Near-field Acoustics

Ducted Propeller Near-field Acoustic

Far-field Fly-by Acoustics

The current work aims to quantitatively study the near-/far-field acoustic performance of the ducted
propeller comparing to the open propeller counterpart, and to investigate the aerodynamic performance optimisation by altering the duct and blade shapes upon adjoint methods. High-fidelity CFD methods are adopted for accurate predictions of aerodynamic performance and for high resolution of the near-field acoustics. The near-field acoustics of the ducted/un-ducted propeller is directly extracted from the CFD solution. The far-field acoustics is calculated using the Ffowcs Williams-Hawkings (FW-H) equation taking the CFD solution as input.

The sensitivity-based aerodynamic optimisation study is driven by the adjoint method, for its fine compatibility with CFD methods and its efficient handling of many design variables. The optimisation of the blade and duct shapes improves the performance at higher advance ratios by altering the thrust distribution between the rotor and the duct.

Adjoint-based Optimisation of Duct and Blade Shapes

Performance Changes through Optimisation

 

 Check our ECCOMAS2020 presentation here!

Publications:

Zhang, Tao, and George N. Barakos. "Review on ducted fans for compound rotorcraft." Aeronautical Journal 124, no. 1277 (2020): 941-974.

Zhang, Tao, and George N. Barakos. "High-Fidelity CFD Validation and Assessment of Ducted Propellers for Aircraft Propulsion." Journal of the American Helicopter Society (2020).

Zhang, Tao, and George N. Barakos. "Numerical Simulation of Ducted Fan Aerodynamics and Aeroacoustics."8th European Congress on Computational Methods in Applied Science and Engineering (ECCOMAS 2020) & 14th World Congress on Computational Mechanics (WCCM XIV) (2021).