Simulation framework development for multidisciplinary design of novel propulsion systems for rotorcraft

Abstract

Rotorcraft constitute highly flexible and versatile vehicles with a unique Vertical Take-off and Landing (VTOL) capability that have been predominantly used for medical, fire suppression, and police services. Increasing demands for fast, reliable, and sustainable transportation gave rise to Urban Air Mobility (UAM), which is a new emerging market within the aviation industry. In acknowledgment of its forecasted growth, industry and academia are exploring novel UAM rotorcraft and propulsion systems targeting sustainable solutions. In this context, electrification, advanced cycles, hydrogen fuel and fuel cells are some of the main propulsion technologies considered for UAM. These configurations introduce new degrees of freedom and hence, the relevance of adopting new design and control strategies becomes evident. Effective evaluation of these technologies integrated within rotorcraft is of vital importance in preliminary design phases. Consequently, the adoption of multidisciplinary approaches to quantify their impact and utility is deemed a prerequisite. This work elaborates on the development and application of a multidisciplinary methodology for the design, optimization and assessment of integrated novel rotorcraft-powerplant architectures. The approach comprises a series of modelling methods including rotor aerodynamics, flight dynamics, engine performance, gaseous emissions prediction, electric powertrain performance, weight estimation, and mission analysis, which are validated individually and integrated into a framework. Through the utilization of the developed framework, the aspect of optimal design and assessment of each of those technologies for a generic tilt-rotor is tackled in this work. A holistic method for designing parallel hybrid-electric systems for rotorcraft with implicit consideration of power management optimization is developed providing new guidelines for the design and operation of such systems. A comprehensive investigation of the potential use of electrification as an enabler for recuperated cycles is deployed and the associated trade-offs between performance and gaseous emissions are quantified. The potential use of hydrogen fuel in a gas turbine or a fuel cell for rotorcraft is investigated and its effects on overall performance, mission economy and thermal management system weight are evaluated. An integrated approach is deployed for the derivation of optimized schedules for variable rotor speed and power management strategy offering new insight into optimal rotor and engine control allocation for rotorcraft. The contribution to knowledge arising from the successful completion of this work comprises both the development of methodologies for rotorcraft-powerplant design and assessment, as well as the synthesis and classification of the investigated technologies in terms of their potential to reduce fuel, energy, CO₂, and NOX as well as to sustain payload-range capacity. It is demonstrated that parallel hybridelectric architectures are more favourable for Air Taxi operations (short ranges) with the recuperated hybrid resulting to the highest potential benefit relative to the conventional tilt-rotor. The hydrogen-based solutions on the other hand are proven to be more relevant for Air Metro operations (long ranges). Finally, the use of variable rotor speed offers significant benefits and can be combined with all the above architectures making this concept an attractive solution for both Air Metro and Air Taxi operations.