Aircraft Propulsion Research Articles

Preface

The purpose of the three-day 2022 International Conference on Aerospace and Control Engineering (ICoACE 2022), held via virtual form on December 23rd-25th, 2022 in Guangzhou, China, was to create a timely forum for multi-disciplinary discussions related to the recent developments on control engineering triggered by aerospace.As usual, the program of the meeting consisted of keynote speeches, oral presentations, the former including speeches delivered by six sophisticated professors from different areas. The speakers covered three main topics: i) Several Key Issues for High-Fidelity Simulation Requirement of Modern Aeroengine; ii) Aircraft Power Supply System Development: From Multi-Electric Aircraft to Electric Propulsion Aircraft; iii) Based on IoTs Parking Navigation With Continuous Information Potential Field Research. Among them, the first report mainly introduced the current situation of high fidelity simulation technology of aeroengine, the application of high fidelity simulation technology in Aeroengine development process, and the future demand of the digital twin applied in the aeroengine high fidelity simulation technology.In the framework of experimental and theoretical approaches, the conference gathered together 100 delegates from all over the world and addressed a number of highly relevant aspects of aerospace and control engineering. Covering Materials Surface Physics, Electric Automation, Distributed Control System, Physics of Gases, Plasma Physics, the selected contributions of this Special Issue provide guidance for future interdisciplinary developments. In this way, the multi-scale aspects of material-based aerospace, mechanics and control engineering should be considered.We received various manuscripts of invited papers and contributions presented at the Seminar. All of these have been peer reviewed and are collected in this volume. We would like to thank all the anonymous colleagues who have acted as referees to assess the suitability of the various articles for publication in the Journal of Physics: Conference Series. We are confident that the high quality of both invited and contributed papers contained in these Proceedings will be appreciated by the aerospace community.We would like to express our thanks to all the authors for their time and genuine efforts, and to the reviewers for their fruitful comments during the preparation of this volume. We also acknowledge the support provided in various ways by Nanchang Institute of Technology who acted as host to the Conference.The Committee of ICoACE 2022List of Committee member is available in this Pdf.

Reliability analysis of multilevel and matrix converters used in more electric aircraft

AbstractThis paper presents the current scenario related to the application of power electronics converters in aviation industries, major challenges and their reliability aspects. Recent developments in power electronics have given a major breakthrough in the aviation industry. These developments are not only limited to the more electric aircraft (MEA) but also in the field of electric propulsion, popularised as electric propulsion aircraft (EPA). The aircraft requires a well‐established protection scheme of these converter topologies. The overall reliability of aircraft solely depends on its protection and fast mitigation of any fault if occurs in the cruise time. This paper aims to provide a comprehensive analysis of power converters applications in MEA and EPA. Further, a review of various topologies of Power Converters and their reliability assessment is also described in detail. The physics of Failure of switches, their lifetime estimation and thermal cycling have also been discussed. Finally, the reliability assessment of different topologies and their comparison has been discussed for overall performance enhancement of the MEA and EPA.

Comparative study of fuel types on solid oxide fuel cell – gas turbine hybrid system for electric propulsion aircraft

As a novel aviation power generation system, the solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system has high electrical efficiency. Because aviation applications are sensitive to weight, the research of this system should not only consider thermodynamic performance but also focus on mass. Fuel is the energy source of the aircraft powered by SOFC-GT hybrid system, and the types not only affect the power generation performance and mass of the system but also determine the storage capacity. Therefore, the impact of fuel types on the SOFC-GT aircraft can be fully evaluated through the comprehensive analysis of the performance and mass. In this paper, the aircraft powered by SOFC-GT hybrid system fueled by hydrogen, ethanol and alkanes (n-decane, n-octane and liquid methane) are investigated. By establishing the thermodynamic model and mass model, the influence of fuel types on the performance of autothermal reforming, SOFC-GT hybrid system, and aircraft cruise is studied in sequence. The results show that in the reforming process, methane has the best hydrogen production performance and makes SOFC efficiency the highest. However, the performance of the SOFC-GT system is influenced by many factors. For non-hydrogen fuels, n-decane can achieve higher electrical efficiency, while methane has lower fuel consumption. The thermodynamic performance of the hydrogen-fueled system has absolute advantages, but it depends on the larger heat exchanger. Furthermore, for the electric regional aircraft powered by the SOFC-GT hybrid system, the range of aircraft fueled by hydrogen and ethanol is poor, and liquid hydrogen can only take advantage of its high energy density at lower payload due to the mass penalty of the cryogenic tanks, while n-decane and n-octane are superior. Meanwhile, CO2 emissions can still be significantly reduced by matching n-decane with the efficient SOFC-GT hybrid system.

Certification-Constrained Vertical Tail Sizing and Power Split Optimization for Distributed Electric Propulsion Aircraft

Distributed electric propulsion (DEP) concepts leverage the synergistic benefits of aeropropulsive coupling and improve the overall flight efficiency by placing propulsors at optimal locations, such as the wingtip. However, placing propulsors far away from the aircraft centerline may bring aircraft difficulties in complying with critical-engine-inoperative flight certification rules. To investigate the impact of certification requirements on the DEP aircraft design, this paper takes NASA’s PEGASUS concept as a use case and presents a study of certification-constrained vertical tail sizing and propulsive power split optimization. For comparison, a vertical tail retrofit study is also conducted on the ATR 42-500 aircraft using the same design space, to gain insights into the different impacts of certification constraints on the design process between conventional and unconventional aircraft. In each study, a design space exploration is performed, including a feasibility test and a multi-objective optimization. The feasibility test shows that the certification constraints yield a much smaller feasible design space for the DEP concept when compared to the conventional aircraft. Despite a much smaller feasible design space, the constrained Pareto optima of the PEGASUS still exhibit lower cruise drag coefficient, fuel burn, and operational energy cost when compared to those of the ATR 42.

Numerical Study on Fluid Dynamic Characteristics of a Cross-Flow Fan

This paper focuses on the application of a cross-flow fan (CFF) to generate propulsion for a submersible aircraft with a flying wing configuration. A numerical method is established to simulate the CFF operating both in the air and underwater. This paper then investigates the fluid dynamic characteristics of the CFF, including the velocity field, the pressure field, the cavitation distribution, the lift, and the thrust. It is concluded that proper lifts and thrusts can be obtained when the rotating speed and the angle of attack are reasonably designed. This work provides a valuable numerical methodology for studying the fluid dynamic characteristics of the CFF operating in different media and offers a technical basis for the selection of a motor system for submersible aircraft.

Preliminary design optimization of a fully superconducting motor based on disk-up-down-assembly magnets

The transition to electric propulsion for aircraft provides an effective way to reduce fuel consumption and achieves low-carbon aviation. Due to the advantages of high magnetic field and ultra-compactness of superconducting disk-up-down-assembly (‘DUDA’) magnets, they have a promising use in superconducting motors. Therefore, this paper presents a design of a fully superconducting motor using superconducting DUDA magnets with Halbach arrays. In order to study the feasibility of the superconducting DUDA magnets in electric motors, preliminary studies of two sets of 4-layer superconducting DUDA magnets were carried out. The manufacturing method with lap joints of the DUDA magnets was proposed and then the manufactured magnets were tested in liquid nitrogen. The contact resistance and critical current at each lap joint have been calculated and the magnetic field distribution of the magnets has been measured. The magnetic fields of the magnets were also verified by simulation and then the magnets were scaled up in size to meet the magnetic field magnitude for the motor. It has been proved that the DUDA magnets can generate a constant magnetic field above 1.11 T along the x-axis without iron materials, which meets the requirements of motors. Based on the analysis of electromagnetic performance, the structural parameters of the superconducting DUDA magnets were optimized with different pole-slot number combination in order to obtain higher efficiency and specific power density. To calculate the efficiency, finite element models in Comsol evaluated the AC losses of the superconducting DUDA magnets. By changing the slot type and winding configuration, the optimized motor is able to achieve a specific power density of 11.55 kW kg−1 with an efficiency of 98% at 30 K.

Study on the Engagement Characteristics and Control Strategy of High Speed Difference Dry Friction Clutch

In the short/vertical take-off and landing aircraft propulsion system, the vertical take-off/landing and rapid flight are switched through the engagement and disconnection of the dry friction clutch. The smooth and rapid connection of the friction clutch is crucial for the mobility and reliability of this type of aircraft. However, the friction clutch vibrates and generates a large amount of heat at high speed, which affects the engagement performance of the clutch. In practice, when the engagement pressure rises quickly, the clutch engagement time is short, and the temperature rise is small, but the impact torque is large, and vice versa. In view of this problem, with a short/vertical take-off aircraft dry friction clutch as the research object, considering the nonlinear variation of friction coefficient and lift fan load torque, the dynamics model and temperature field model of the high speed difference dry friction clutch are established to analyze the clutch engagement time, impact torque, and temperature change. The engagement test at the high speed of the clutch shows that the simulation results of the kinetic model and temperature field model are consistent with the test results. To realize low temperature rise, low impact torque, and short engagement time, the variable slope engagement pressure control method is proposed. Compared with the traditional fixed slope engagement pressure, the proposed variable slope engagement pressure can reduce the engagement time, impact torque and temperature rise simultaneously. The research results can provide a reference for the friction clutch engagement control of short-range take-off and landing aircraft, reduce the development cost of such aircraft, and improve the reliability of the design.

Improvement of Take-Off Performance for an Electric Commuter Aircraft Due to Distributed Electric Propulsion

The need for environmentally responsible solutions in aircraft technology is now considered the priority for global challenges related to the limited supply of traditional fuel sources and the potential global hazards associated with emissions produced by traditional aircraft propulsion systems. Several projects, including research into highly advanced subsonic aircraft concepts to drastically reduce energy or fuel usage, community noise, and emissions associated with aviation, are currently ongoing. One of the proposed propulsion concepts that address European environmental goals is distributed electric propulsion. This paper deals with the detailed aerodynamic analyses of a full-electric commuter aircraft with fuel cells, which expects two primary electric motors at the wing tip and eight other electric motors distributed along the wingspan as secondary power sources. The main objective was the numerical estimation of propulsive effects in terms of lift capabilities at take-off conditions to quantify the possible reduction of take-off field length. However, the aircraft was designed from scratch, and therefore a great effort was spent to design both propellers (for the tip and distributed electric motors) and the wing flap. In this respect, several numerical tests were performed to obtain one of the best possible flap positions. This research work estimated a reduction of about 14% of the take-off field length due to only the propulsive effects. A greater reduction of up to 27%, if compared to a reference conventional commuter aircraft, could be achieved thanks to a combined effect of distributed propulsion and a refined design of the Fowler flap. On the contrary, a significant increment of pitching moment was found due to distributed propulsion that may have a non-negligible impact on the aircraft stability, control, and trim drag.

Detailed Design and Prototyping of a High Power Density Slotless PMSM

This article describes the detailed design and development of a 300 kW permanent magnet (PM) synchronous motor for electric aircraft propulsion, taking into consideration manufacturability, balancing ease, and cost of high-volume production with motor performance. The motor consists of a slotless stator structure with custom litz wire and an outer rotor with a Halbach PM array. The design of the proposed motor is based on multi-physics performance including electromagnetic field, thermal and mechanical analysis. For ease of manufacturing and economies of scale, the detailed design is refined by altering the PM segment number, PM shape and litz wire construction. The impacts of changing these parameters are evaluated in detail using analytical and finite element methods. The simulation results are compared with experimental results in terms of torque production, back electromotive force, and current level.

Influence of Single External Store on Geometrical Nonlinear Flutter of High-aspect-ratio Wings

High-altitude and long-endurance UAVs, distributed electric propulsion aircraft and large passenger aircraft often use high-aspect-ratio wings, which have obvious geometric nonlinear large deformation effect, and are usually arranged with a certain number of external stores, which have an impact on their geometric nonlinear aeroelastic characteristics. Based on the “quasi-linear” hypothesis, the updated Lagrange incremental finite element method and doublet-lattice method are used to perform the geometrically nonlinear static aeroelastic analysis, and the mass, stiffness and aerodynamic matrices of large deformation are updated, and the geometrically nonlinear flutter characteristics of high-aspect-ratio wings are calculated. The influence of the position and mass of the external store on geometrical nonlinear flutter characteristics of high-aspect-ratio wing structure is investigated. Results show that the change of the position and mass of the external store causes the relative position between the elastic axis and the center of gravity of the wing, and the wing’s large deformation equilibrium state to change, resulting in differences in the stiffness characteristics of the wing and the natural vibration frequency of the equilibrium state, thus affecting the wing flutter characteristics. When a single external store is installed near the wing root, changing the mass and direction of the store has no significant effect on the geometric nonlinear flutter characteristics of the wing. The improvement of wing flutter speed is most obvious when the hanging point is moved to the leading edge of the wing near 0.65 times the wingspan.

Parameterization investigation on distributed electric propulsion aircraft aerodynamic characteristics

Revealing the principle of distributed electric propulsion (DEP) plane aerodynamic design under the effect of strong aerodynamic coupling of distributed power-wing and the change law of total gain is the key to carrying out the design of distributed electric propulsion plane. For the distributed electric propulsion plane aerodynamic layout, the aerodynamic performance of the DEP configuration is studied based on the VLM-ADT aerodynamic characteristics fast solver method. This paper gives a set of fast parametric methods to research the aerodynamic performance of DEP layout, which mainly includes three comprehensive indexes such as lift-to-drag ratio L/D, power loading T/P, and lift loading L/P—focused on; the factor of propeller number, which affects the aerodynamic performance of DEP aerodynamic layout. As the propeller number increases, the lift-to-drag ratio decreases, but the wing’s lift efficiency increases.

Special issue on all‐electric and hybrid‐electric flight

Special issue on all‐electric and hybrid‐electric flight

Aerodynamic Performance Benefits of Over-the-Wing Distributed Propulsion for Hybrid-Electric Transport Aircraft

The goal of this study is to analyze how the aeropropulsive benefits of an over-the-wing distributed-propulsion (OTWDP) system at the component level translate into an aeropropulsive benefit at the aircraft level, as well as to determine whether this enhancement is sufficient to lead to a reduction in overall energy consumption. For this, the preliminary sizing of a partial-turboelectric regional passenger aircraft is performed, and its performance metrics are compared to a conventional twin-turboprop reference for the 2035 timeframe. The changes in lift, drag, and propulsive efficiency due to the OTWDP system are estimated for a simplified unducted geometry using a lower-order numerical method, which is validated with experimental data. For a typical cruise condition and the baseline geometry evaluated in the experiment, the numerical method estimates a 45% increase in the local sectional lift-to-drag ratio of the wing, at the expense of a 12% reduction in propeller efficiency. For an aircraft with 53% of the wingspan covered by the OTWDP system, this aerodynamic coupling is found to increase the average aeropropulsive efficiency of the aircraft by 9% for a 1500 n mile mission. Approximately 4% of this benefit is required to offset the losses in the electrical drivetrain. The reduction in fuel weight compensates for the increase in powertrain weight, leading to a takeoff mass comparable to the reference aircraft. Overall, a 5% reduction in energy consumption is found, albeit with a uncertainty due to uncertainty in the aerodynamic modeling alone.

The effects of spacing to diameter ratio on mixing characteristics of circular and elliptical twin jets

Twin jets are encountered in many engineering and industrial applications, such as aircraft propulsion systems and combustors. Twin jets create a flow field that is more complex than a single jet due to its interaction with the individual jets. This paper investigates the effects of spacing to diameter ( S/ D e) ratio and orientation on the mixing properties of circular and elliptical twin jets at four different S/ D e ratios of 1.25, 1.50, 1.75, and 2.0, respectively. The numerical simulations of twin jets are carried out with a jet Mach number of 0.8 using the Shear Stress Transport ( SST) K- ω turbulence model. The results show that near the orifice exit, the twin jets are issuing into ambient conditions separately and resemble a free jet, leading to a potential core length independent of S/ D e. The merging and combined point locations change linearly from the exit with an increasing S/ D e ratio. The decay rate is higher for Twin Ellipse Minor than those in Twin Circle and Twin Ellipse Major, verified by a shorter converging region. In addition, near the jet exit, the spread rate is higher for Twin Ellipse Minor, which is consistent with the closer merging point location. The jet mixing is superior for twin minor elliptical configuration compared to twin circle and twin major elliptical jets at all S/ D e ratios.

Thermodynamic Performance Comparisons of Ideal Brayton Cycles Integrated with High Temperature Fuel Cells as Power Sources on Aircraft

Developing hybrid electric aircraft is propitious to reducing carbon dioxide emissions and fuel consumption. Combustion engines coupled with solid oxide fuel cells are proposed for aircraft propulsion systems, where the compressor is powered by fuel cells instead of turbines. The thermal cycle of the new engine is obviously different from that of conventional combustion engines and can be characterized in the temperature entropy diagram under some reasonable assumptions, which were analyzed and investigated. Performance parameters, such as the specific thrust, are derived and can be expressed by several fundamental thermal parameters. Three different cycles integrating Brayton cycles and SOFC are shown. The main conclusions are as follows: (1) The maximum operating pressure ratio of the Brayton cycles integrated with fuel cells is 32. The maximum thermal efficiency of the cycle at the lowest combustion temperature is 82.2%, while that of the BC is 65.1% at the high combustion temperature. (2) The new cycles can not work if the combustion temperature is lower than 1350 K. Otherwise, the fuel utilization will be too huge.

System Identification Approach for eVTOL Aircraft Demonstrated Using Simulated Flight Data

This paper describes a system identification method for electric vertical takeoff and landing (eVTOL) aircraft. The approach merges fixed-wing and rotary-wing modeling techniques with new strategies to develop a modeling method for eVTOL vehicles using flight-test data. The eVTOL aircraft system identification approach is demonstrated through application to the NASA Langley Aerodrome No. 8 tandem tilt-wing, distributed electric propulsion aircraft using a high-fidelity flight dynamics simulation. Orthogonal phase-optimized multisine inputs are applied to each control surface and propulsor at numerous flight conditions throughout the flight envelope to collect informative flight data. An aero-propulsive model is identified at each flight condition using the equation-error method in the frequency domain. The local model parameters are then blended to create a global model across the nominal flight envelope. The identified models are shown to provide a good fit to modeling data with good prediction capability. The methodology is developed with a discussion of unique eVTOL vehicle aerodynamic characteristics and practical strategies intended to inform future flight-based system identification efforts for eVTOL aircraft.

A smooth control allocation method for a distributed electric propulsion VTOL aircraft test platform

AbstractDistributed electronic propulsion (DEP) aircraft with vertical take‐off and landing (VTOL) ability mostly equipped with multiple redundant tiltable propulsors, which are used to provide not only thrusts, but also control torque in all flight mode. The features make the control allocation problem of these aircraft both complex and important. Therefore, this paper proposes: (і) a prototype platform for DEP VTOL aircraft that allows researchers to design and analyse control allocation strategies, and (іі) a uniform hierarchical control allocation method that can be adapted to both MC and FW modes. The platform contains ten fully actuated thrusters, which are distributed in the scaled geometry of a typical DEP‐VTOL aircraft. The proposed control allocation strategy uses hierarchical structure to avoid high‐dimensional matrix operations for the redundant actuators. The additional constraints on the thrust and tilt angles of the actuators are addressed by adopting cascade generalized inversion (CGI) to force decompensation (FD)‐based methods by a coordinate transformation. A novel smooth strategy through Schur Complement is also presented to achieve steady and smooth transition from MC to FW mode. Finally, the proposed method is implemented in the authors’ novel platform in both simulations and flight experiments to demonstrate its effectiveness and smoothness.

Techno-economic-environmental evaluation of aircraft propulsion electrification: Surrogate-based multi-mission optimal design approach

Driven by the sustainability initiatives in the aviation sector, the emerging technologies of aircraft propulsion electrification have been identified as the promising approach to realize sustainable and decarbonized aviation. This study proposes a surrogate-based multi-mission optimal design approach for aircraft propulsion electrification, which innovatively incorporates realistic aviation operations into the electric aircraft design, with the aim of improving the overall aircraft fuel economy over multiple flight missions and conditions in practical scenarios. The proposed optimal design approach starts with the flight route data analysis to cluster the flight operational data using gaussian mixture model, so that a concise representation of flight mission profiles can be achieved. Then, an optimal orthogonal array-based Latin hypercubes are employed to generate sampling points of design variables for electrified aircraft propulsion. The mission analysis is performed with coupled propulsion-airframe integration in order to propose energy management strategy for mission-dependent aircraft performance. Consequently, fuel economy surrogate model is established via support vector machines to obtain the optimal design points of electrified aircraft propulsion. For assessing the viability of novel propulsion technologies, techno-economic evaluation is conducted using sensitivity analysis and breakeven electricity prices under a series of environmental regulatory policy scenarios.

Novel processing, testing and characterization of copper/carbon nanotube (Cu/CNT) yarn composite conductor

AbstractSustainable electrified aircraft propulsion (EAP) is likely to lead to an increase in the electrical wiring contained within a single aircraft. Since the electrical resistance and mass of copper (Cu) conductors are associated with power losses, it is desirable to design high‐conductivity lightweight conductor materials, thus reducing the mass of components like motor windings, low‐voltage signal cables, and transmission cables for data and power to improve the overall energy efficiency. This paper describes a unique framework for manufacturing metalized carbon nanotube (CNT) composite conductors, measuring their electrical conductivity and strength, and modeling the overall conductivity and current sharing within such composites. Tensile testing was conducted on the processed composite conductor cables with the use of acoustic emission and electrical resistivity to determine stress‐dependent‐failure mechanisms while monitoring the electrical conductivity. The average of measured electrical conductivities of annealed Cu/CNT samples from batch 5 was greater than theoretical predictions by 9.8 percent and was also greater than the conductivity of pure annealed Cu by 4.8 percent and had comparable ultimate tensile strengths. Additionally, those Cu/CNT samples provide a 13.5% weight saving over current state of the art copper wires. Theories explaining improved intrinsic conductivity are discussed.

A H‐type architecture for electric/hybrid‐electric aircraft propulsion systems

AbstractIn this paper, an H‐type electric/hybrid electric aircraft propulsion architecture is proposed to address the issues associated with the radial electric propulsion architecture. In a radial architecture, a fault on the main bus or failure of the generator leads to shut down of all the propulsion motors in that channel, thus increasing the burden on the remaining motors to maintain the power required by the aeroplane. As a result, it is necessary to oversize the motors for the purpose of compensating for the loss of other motors. To mitigate these issues, a new H‐type architecture is introduced to isolate the particular faulty section while still maintaining power flow to the remaining healthy motors. The proposed architecture minimises the oversizing of various components in the system as compared to radial propulsion architecture. The sizing of components and the amount of overall mass reduction is discussed by using the proposed architecture. Typhoon Hardware in the Loop platform is used to validate the performance of both the architectures for faults at different locations, and the results are presented.