Improving the off-design performance and turndown capability of power cycles for concentrated solar power (CSP) applications is critical considering possible heat source and cooling fluctuations. In this paper, the effect of different flow path geometrical parameters on the aerodynamic performance of large-scale axial turbines operating with supercritical carbon dioxide (sCO2) mixtures is evaluated at both design and off-design conditions. 3D steady-state multi-stage Reynolds-Averaged Navier Stokes equations Computational Fluid Dynamics (CFD) simulations are performed where the k-ω SST turbulence model is used. The number of stages, stator/rotor axial gap, leading-edge thickness, inlet wedge angle, and stagger angle are varied to evaluate their impact on the turbine operational flexibility, defined by the minimum acceptable ratio of mass flow rate to the design value. The ranges of variation are defined based on practical considerations and careful consideration of various design criteria such as the slenderness ratio and bending stresses. The results revealed that the stagger angle has the largest influence on the operational flexibility with a change of 17.1% in the minimum allowable part-load mass flow ratio corresponding to a change in the stagger angle between -5° and +5° from the reference design angle. This increase in the stagger angle resulted in an increase in the design point total-to-total efficiency of 2.3 percentage points. The leading-edge thickness has the least influence with a maximum change in the minimum part load mass flow ratio of 0.63% as obtained for the investigated range and a negligible change in the design point efficiency. The flow field investigations revealed that increasing the stagger angle leads to smaller separation regions caused by high incidence angles, despite the resulting increase in bending stresses.

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Compressors used in aircraft gas turbines must require fewer stages than those used in industrial gas turbines while maintaining high efficiency and a wide operating range. In such a case, the compressor's diffused cascades are subject to three-dimensional separation, or corner separation, which occurs fatally at the corner between the suction surface and the endwall, resulting in compressor efficiency drop. Furthermore, when the compressor is operated at slottled condition, the incidence angle of the blade near the endwall increases, causing corner stall where flow separates from the leading edge of the blade, resulting in unstable compressor operation. In this study, a means was devised to further suppress the corner stall by utilizing an ejector effect of the slot jet flow. A detailed three-dimensional flow analysis was conducted using the Detached-eddy simulation (DES). As a result, the effectiveness of this means to suppress the corner stall was confirmed.

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With the continuous improvement of centrifugal compressor pressure ratio, vaned diffuser gradually becomes one of the key factors restricting the stability of centrifugal compressor. A novel vaned diffuser casing treatment has been created to increase the stable operating range at low mass flow rates. This paper employs a parameterization approach to investigate the impact of varying recirculating mass flow rates on stability enhancement via examination of tube diameter in the context of recirculation technology. The results demonstrate that a higher recirculating flow rate allows for operation under lower mass flow rate conditions. Nevertheless, this leads to an increase in flow loss within the diffuser. The increase in stall margin signifies a comprehensive alteration in mass flow rate and total pressure ratio, and serves as a benchmark for assessing the enhancement of the operating range. For a recirculating tube diameter of 1.5mm, the maximum increase in stall margin is 3.21%.

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This study aims at analysing hybrid-electric operation of a twospool high-bypass turbofan for a narrow-body aircraft during the climb trajectory. Boundaries of safe hybrid-electric operation are investigated and methods for controlling the electric power along the trajectory are demonstrated. This is crucial, as hybrid-electric operation induces throttling of the low-pressure compressor and the effect intensifies with increasing altitude during climb. Furthermore, operational loads are extracted and applied to lifetime prognostics for the turbofan engine, electric machine and power electronic system. The results show an influence of the hybridisation on the gas turbine by nearly −20% in SVR and +7% in TOW. Higher electric assistance unloads the gas turbine and increases operational time, but requires higher bleed air extraction for compressor stability. The electric drive train shows variations in lifetime consumption up to 150% for the electric machine and 135% for the power electronics capacitors. The semiconductors show strong interdependence with small scale temperature cycling of the operating profile, which shows the need for more sophisticated thermal mission modelling.

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A variety of aircraft propulsion architectures are available for a sustainable transformation, ranging from all electric to hybrid-electric, based on batteries, fuel cells and electric motors. These hybrid-electric architectures are an extension of the electric architecture with a gas turbine burning sustainable fuels. Most of these architectures require a compressor, either as part of the gas turbine or to supply gas to the fuel cell. The different system integration depending on the architecture specify new demands on the compressor compared to the compressor in a conventional turbofan engine. When fuel cell systems are used, further requirements for the compressor arise due to the necessary matching between the fuel cell stack and the air supply system. These new requirements must be developed during the system design. The compressor design is based on the requirements from the modeling of the propulsion architecture. Subsequently, the main dimensions can be determined followed by the meridional shape and the blade modeling before the design is simulated by computational fluid dynamics. Finally, the design is adjusted until the required boundary conditions are achieved. In this study the requirements for compressors in the cathode gas supply of a fuel cell are summarized. Afterwards a compressor for the cathode gas supply system is designed for a regional reference aircraft that uses fuel cells as part of the propulsion system. First, the boundary conditions for the design are determined, then the compressor performance map is calculated and the general challenges for the compressor design as part of the air supply system are discussed. Due to the different compressor operating points required for efficient fuel cell operation, detailed component matching between the fuel cell and the air management system as well as careful selection of an operating strategy is required prior to design.

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In recent years, research and development on sustainable aviation fuel (SAF) has been conducted by many researchers and aviation industries. In this study, we focused on coconut SAF produced by the co-solvent method, which achieves a minimum emission of waste and a low consumption of energy. The aim of this paper is to clarify the combustion performance of blends of coconut SAF and jet fuel. The combustion experiment was performed using a J-850 jet engine. The applied fuel composition rates were between 10 and 50% coconut SAF in the jet fuel blends. Fuel blends of coconut SAF show higher combustion efficiency than only jet fuel. However, engine performance becomes less effective in the case of increasing the coconut SAF. The reason was that the capric acid methyl and caproic acid methyl, which include the coconut SAF, carbon chain generally improves the ignition quality of the fuel because of the presence of oxygen elements; thus, the turbine inlet temperature increases. Furthermore, we investigate NOx emissions in the case of a blend of coconut SAFs using the NOx emission index (EINOx) prediction method.

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A study to modify and develop a turbofan engine using a micro turboprop engine has been conducted. The turbofan engine has been designed by adding a fan blade module as well as other required accessories to the existing turboprop engine. CFD and FEM methods were used for numerical analyses of the additional fan module to assess its aerodynamic performance and structural stability. Components of the fan module were fabricated with consideration for manufacture and assembly, and a test rig was also designed and built to measure the turbofan engine performance. The performances of turbofan engine were measured and compared to an existing micro-turbojet engine. The performance tests were conducted in two phases. In the first phase, the robustness of the designed turbofan and test rig were investigated and in the second phase, the maximum power test has been conducted to measure performance variables such as engine thrust, engine exhaust temperature (EGT) and fuel flow rate according to the engine RPM. The test results indicated that the turbofan engine SFC was reduced by 40~50% of the existing turbojet engine, demonstrating the successful implementation of turbofan characteristics.

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