Numerical investigation of novel rotorcraft propulsion systems

Qiao, Geng (2025) Numerical investigation of novel rotorcraft propulsion systems. PhD thesis, University of Glasgow.

Abstract

In recent years, an upsurge in advanced air mobility (AAM) aircraft can be noticed worldwide, e.g. , Rolls Royce, Airbus, NASA, DARPA, Advanced Aircraft Company, Bell Helicopter, Aurora, Honeywell, and others. Future AAM will operate near the ground in the urban area, and thus it should be environmentally and community-friendly while maintaining excellent aerodynamic performance. As is known, a high-intensity of sound is emitted by the VTOL aircraft, but noise emission is crucial in the VTOL aircraft certification process and urban operation. It is clear that the propulsors are generating most of the noise from the whole aircraft. Therefore, there is a growing demand for low-noise emission propulsors, reduced wake interference, and improved aerodynamic performance. Previous works show that distributed and wingtip mounted propulsion systems are promising candidates as a novel compact propulsor with excellent performance. However, the combination of multiple sources of lift and thrust brings significant challenges in terms of aerodynamic interactions, noise emissions, vibration, instability, control, trim difficulties, power allocation, and others. Nevertheless, AAM research is emerging mainly in Europe, the USA, and Asia, as the appeal for better civil rotorcraft is growing. Several demonstrators, e.g. the US DARPA XV-24A, Joby S4, and the VX4 from Vertical Aerospace, have been delivered, illustrating the superior performance of AAM aircraft. Ahead of routine deployment of AAM aircraft, there is still significant aerodynamic/aeroacoustic research and development to be carried out.

This thesis aims to investigate novel propulsion concepts, including tip mounted propellers and distributed propulsion systems, through CFD verification, optimisation, and aerodynamic performance evaluation. The first part of the study validates the employed multi-fidelity simulation methods using experimental data from the NASA Workshop for Integrated Propeller Prediction (WIPP) and the Folding Conformal High Lift Propeller (HLP) project for isolated and installed cases under various conditions. Additionally, aerodynamic and aeroacoustic validation via the hybrid methods for rotor-rotor interactions was also conducted using the GARTEUR Action Group 26 measurements.

Applying the same methods and simulation strategies used in the validation, the thesis further examines a series of installed propeller configurations with actuator disks to identify performance differences based on their position relative to a lifting wing. The reduced-order method was cost-effective and suggested the approximate optimal position of the distributed propellers. The actuator disk method has successfully captured the leading-edge suction induced by inflow. In addition, the performance of the propulsion system changes due to different installation effects. Furthermore, additional surfaces from nacelle and pylon structures will also have an impact on the propulsion system. Therefore, additional verification cases utilising high-fidelity methods were carried out, and the investigation of the conventional tractor and the optimal over-the-wing (OTW) configurations was conducted for different numbers of propellers and conditions.

Wingtip-mounted propellers are known to be a promising configuration for reducing induced drag through favourable wake interactions. This thesis presents, for the first time, the integration of wingtip-mounted propellers with an OTW distributed propulsion (DP) system, investigated using high-fidelity, fully resolved simulations. To investigate this novel tip-mounted propeller–distributed propulsion (TMP-DP) configuration, equivalent-performance propulsion systems were proposed based on realistic aircraft operational conditions. The study examines complex interactional flow phenomena inherent to such systems, including propeller–wing, propeller–propeller, propeller–slipstream, and propeller–wake interactions. Given the intricacy of the distributed propulsion setup, key aerodynamic and propulsive parameters, such as thrust and power distribution, wing lift, drag, lift-to-drag ratio (L/D), and pitching moments, are thoroughly analysed and reported.

To harness the benefits of multirotors in a distributed propulsion system, synchrophasing has been implemented as a means of reducing noise. Tandem rotors, with and without vertical offset, are investigated using fully resolved simulations under both hover and edgewise flight conditions. A comprehensive synchrophasing study reveals varying levels of cumulative rarefaction and compression effects in the resulting acoustic waves. To better account for the relative loudness as perceived by the human ear, A-weighting and one-third octave band analysis have been employed. These approaches help to identify how different frequency components contribute to the overall acoustic signature and can inform targeted noise control and mitigation strategies. Finally, this study quantifies noise reductions across the frequency spectrum for each synchrophasing case and identifies the most effective phase angles. These optimal phase configurations can be tuned to achieve maximum noise reduction at specific observer locations.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: T Technology > TL Motor vehicles. Aeronautics. Astronautics
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Barakos, Professor George
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85211
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 18 Jun 2025 13:54
• Last Modified: 18 Jun 2025 13:56
• Thesis DOI: 10.5525/gla.thesis.85211
• URI: https://theses.gla.ac.uk/id/eprint/85211

Related URLs

• Article DOI
• Article DOI
• Article DOI
• Article DOI
• Conference proceeding