In this paper, the unsteady performance of a turbofan engine is illustrated and modelled using the Pseudo Bond Graph approach. The Pseudo Bond Graph method allows multiphysical and interdisciplinary systems to be described analytically and comprehensibly across disciplines. In this study, a high bypass ratio turbofan engine is modelled using a Pseudo Bond Graph model that can be adapted for hybrid electric propulsion systems. The development of the model is followed by a full-scale test run of the in-house V2500-A1 turbofan engine. The highly instrumented turbofan engine enables the time-resolved recording of performance-specific variables, thus facilitating the validation of the numerical model. Slam acceleration and deceleration are performed to analyse the unsteady performance. It is shown that the Pseudo Bond Graph model is able to predict the dynamics of the turbofan engine. High deviations are explained by the incomplete modelling of the control system.

Power electronics design offers many options to achieve the high required power density to replace conventional aircraft components. Two promising approaches are to increase the power supply voltage and use wide-bandgap semiconductors. However, there are many concerns about the high-voltage approach, particularly regarding reliability and fault tolerance. Improving the power density with high voltages requires wide-bandgap semiconductors, which further stresses the insulation. Furthermore, the environmental stressors are partly unknown because of the need for a design basis. Existing industrial standards and other investigations address this issue only partly. This publication uses a mission profile and a design of experiment-based reliability assessment approach for creepage distances on printed circuit boards to overcome the concerns against the promising high voltage approach in aviation applications from the perspective of power electronics. The investigation delivers experimentally and mathematically described wet and dry surface flashover results. Furthermore, the influence of degradation of creepage distances caused by wide-bandgap semiconductors is experimentally investigated. The publication also gives design recommendations for gaining reliability and fault tolerance of creepage distances on printed circuit boards for operating power-dense power electronics in integrated electrified propulsion systems.

AbstractWithin the Collaborative Research Centre 871, geometrical variances caused by repair procedures and deterioration are evaluated for the turbomachinery of a high-bypass aircraft engine. Part of this evaluation is the investigation of the influence of isolated and combined geometric variances on the overall aircraft engine performance. For this purpose, a virtual twin of a research aircraft engine is developed in sub-project D6. This virtual aircraft engine is based on the Pseudo Bond Graph approach, which allows for transient manoeuvres and the effects of interactions to be simulated with a higher degree of accuracy compared to conventional methods. After validation of the model, a design of experiments is performed to analyse the sensitivities between the variances of modules and engine performance. Within the sensitivity analysis, it is shown that the evaluated steady-state and transient performances are mainly influenced by the high-pressure modules, especially by the mass flow and efficiency variances. Furthermore, it is shown that the sensitivities strongly depend on the operating points. However, significant interactions are found which can be attributed to both the high-pressure and low-pressure modules.

A novel design for the cathode air supply system of a fuel cell-based aircraft propulsion system is presented in this study. Herein, the state-of-the-art Electrically driven Cathode air Supply system (ECS) is replaced by a H2-fuelled micro gas turbine (GTCS) with the main goals of 1) decreased total fuel cell power demand and, therefore, 2) reduced low temperature waste heat. Therefore, no parasitic power is required to drive the cathode air supply. The proposed system design is simulated for a regional, distributed propulsion aircraft. Adaptation to other aircraft layouts is easily possible. The operating characteristics of both systems are compared and advantages of the novel architecture are quantified. The advantages are, among others, a substantial reduction of the fuel cell waste heat as well as the reduction of the overall component size within the air supply system. For the most demanding operating point take-off, fuel cell waste heat can be reduced by 25% at maximum operating pressure while heat exchanger size is decreased by up to 16% and humidifier size by up to 20%. Further synergies from the novel architecture are the possibility to use up to 45% of hydrogen from the anode exhaust in the combustor instead of recirculating or venting it. This may lead to a substantial size reduction in the anode side recirculation cycle. Considering the overall system weight, the novel system can achieve a 26% lower weight than the state-of-the-art ECS system. The fuel consumption however is up 9.6% above the ECS system due to poor thermal efficiency of the core. However, it remains to be evaluated in the context of overall aircraft design whether the advantages in component size and weight due to reduced waste heat rejection requirements can outweigh the drawbacks in fuel consumption.

The development of commercial aircraft with hybrid-electric propulsion systems is currently a subject of extensive research in order to improve local air quality and reduce combustion emissions. Among the various types of engines being studied, the two-spool parallel hybrid-electric turbofan engine is particularly challenging due to the low-pressure compressor (LPC). The hybridisation process tends to throttle the LPC, accentuating its significance in the propulsion system. For reliable operation of such systems, accurate predictions of the LPC performance during time-sensitive manoeuvres such as a go-around are important. These manoeuvres are heavily influenced by time-dependent effects that govern the propulsion system’s performance. Often, the aerothermodynamic interplay between these effects is overlooked in propulsion models. In this study, the influence of these aerothermodynamic interdependencies on the modelling results is investigated. To investigate these aerothermodynamic interactions, a dynamic model is developed to simulate the performance of the hybrid-electric turbofan engine. In comparison, a constant mass flow model is used, which is not able to simulate these interdependencies. The results show that the aerothermodynamic interdependencies significantly affect the modelled time-resolved performance, especially for surge margin of the LPC, with this effect becoming more pronounced at higher levels of hybridisation. Therefore, the study recommends the adoption of dynamic simulation methodologies for hybrid-electric engines to guarantee high simulation precision, enhance reliability, and satisfy safety standards.

Aero engine performance and condition deterioration are a function of operational severity. Operational severity is determined by various aspects such as airborne contaminants, derates, ambient temperature, humidity, and precipitation. More severe operating environments induce cost, which should be managed by using earth observation (EO) data in engine health monitoring. This paper presents an analytical approach that incorporates a broad set of EO data into engine health management and subsequent maintenance planning. Current approaches to gas path analysis are extended by incorporating EO data. The analytical approach is presented in combination with a literature review. The literature review covers the following topics: flight trajectory modeling, EO/environmental condition data, as well as engine performance, condition, and deterioration modeling. Methods and data sources in these different areas are reviewed while simultaneously presenting the currently researched analytical approach. The researched analytical approach creates high-resolution contamination profiles for a flight trajectory on a global scale. Weather conditions and the ingestion of aerosols and sand are monitored and correlated with aero engine condition and performance. A wide range of data sources are presented, which however only partly cater to the needs of the Maintenance, Repair and Overhaul community.

The German chemical industry is one of the most energy-intensive sectors, which accounts for approximately 8% of Germany’s total energy consumption. One energy-intensive process is distillation, which can be operated as an open heat pump process. This involves compressing steam to a higher pressure level so that the waste heat can be reused to heat the process. The greatest opportunity for this mechanical vapour compression is in the electrification of chemical processes using green energy sources. A preliminary compressor design process for mechanical vapour compression must consider the wide range of possible applications. The preliminary compressor design must take into account other aspects such as different compressor architectures, fluid properties and process boundary conditions. Since the priority is on evaluating the potential of the overall process, generic compressors are used for compressor design. The generic compressor maps can be adjusted by correlation to account for the fluid properties. The influence of the fluid properties on the performance of a centrifugal compressor is investigated using numerical simulation to verify the plausibility that simple correlations can be used to adjust the compressor maps within the preliminary compressor design. With CFD it is shown that the gas properties have a significant influence on the efficiency, the chocking mass flow and the pressure ratio. In addition, various correlations are applied and compared to predict these changes. It is shown that this correlation enables an approximation, but depending on the fluid there are considerable deviations from the CFD calculation.

This paper investigates the cathode air supply system of a medium-range fuel cell-powered aircraft. The main focus is on determining a suitable system architecture. Based on the literature, promising humidification and cooling strategies for cathode gas preconditioning are identified and evaluated. System configurations with membrane and spray humidification as well as intercooling between compressor stages and wet compression are calculated using a thermodynamic cycle calculation model. By analysing the design parameter spaces of the cathode air supply systems, the different configurations are compared in terms of their influence on key system parameters such as specific fuel and parasitic power consumption or heat exchanger size to find the most promising architecture. Further, the operating limits of the systems at different operating pressures and temperatures are determined. The second area of focus is the identification of a suitable system design point. It is discussed that the most critical operating points of the individual components are located at different flight conditions. Therefore, off-design performance is taken into account in order to design the entire system. A model based on the constant mass flow method is introduced to calculate steady state operating points for the system using membrane humidification. It can be seen that the turbo components have their design point at top of climb operating point, while the heat exchanger has to be designed for the maximum waste heat at take-off and the humidifier for the most critical operating point in terms of membrane water content at cruise.

In the wake of the push towards knowledge-based maintenance of jet engines, a process for analysing and evaluating the performance of deteriorated aero engine components was developed. This process automatically generates CFD-simulations from 3D-scans of compressor blades and inputs the calculated performance maps into a gath-path analysis of the jet engine. The uncertainties of such a process are important for the interpretation of its results. Therefore, the uncertainties of a specific part of the process, the geometric analysis, are investigated. Special focus is put on the impact the input data quality has on the uncertainties and how the specific process implementation responds to variations in quality. Test procedures are developed to calculate the uncertainties of individual process steps for specific input data qualities. It is shown, that the noise level of the 3D-scans has a significant impact on the uncertainties. The point-cloud density also has an influence on the uncertainties, which however is small as long as a certain minimum threshold of 189 per profile section is reached. It is also shown that the uncertainties are sufficiently small to capture real geometric variances of deteriorated compressor blades when input data with noise levels of 15 mu m and 316 profile points or better is used.

The primary focus of modern civil jet engine intake design is to enhance propulsive efficiency through an increase in the bypass ratio of the turbofan engine, which requires an enlargement in fan diameter. However, this enlargement results in increased weight and drag due to the need for a larger nacelle to surround the fan. To mitigate these issues, efforts are being made to shorten the axial length of the aircraft engine intakes. Nonetheless, this reduction leads to more vulnerable fan aerodynamics since the diffusion within the intake must occur over a shorter distance, causing a higher possibility of flow separation. Common intake design methods employ throughflow nacelle models that do not consider the aerodynamic effects of the fan, including blockage, mass flow redistribution, and suction. The utilization of a full annulus domain numerical setup, which is necessary to capture inlet distortions, demands excessive computational resources particularly during the design phase. As a result, reduced order models, such as the body force model, can be utilized to simulate fan intake aerodynamics. This paper will assess the body force model and its abilities by comparing conventional bladed single passage simulations with the body force approach.

Within the Cluster of Excellence for Sustainable and Energy-Efficient Aviation (SE²A), technological advances to reduce carbon emissions of current propulsion architectures are investigated. In order to enhance the efficiency of the fan and compressor components of a turbofan engine during off-design operation, shape-adaptive fan and compressor blading is considered. This investigation introduces shape-adaptive blading for the fan stage of a V2500-A1 high-bypass turbofan engine, operated on Airbus A320 single-isle civil transport aircraft. Integrating piezoelectric actuators into the fan rotor blading allows varying the rotor twist and camber upon actuation. Special emphasis lies on an improvement of part-load operation, where lower efficiencies are expected and the surge-margin becomes more critical. During flight phases where the fan operates well outside its aerodynamic design point, a variable fan rotor shape allows reducing flow incidence and deviation. Especially during climb, where atmospheric conditions and engine thrust change with altitude, an improvement is shown. To assess the shape-morphing effects on the chosen aircraft configuration, previous morphing results are generalised and applied to the performance maps of the fan of the V2500-A1 turbofan engine. Within this investigation, two morphing configurations are considered and analysed on a whole mission-basis for three different flight scenarios. The morphing effect on the turbofan engine performance is quantified by combining structural morphing simulations with CFD simulations and a thermodynamic turbofan engine performance calculation tool. Special emphasis thereby lies on the mission specific fuel consumption (SFC) and the feasible fuel saving through introducing shape-adaptive fan blading. Results indicate, that small variations in blade angle already show an effect in SFC and motivate for future investigation of flight-phase optimised morphing strategies and application of the method to modern turbofan engines.

In the following, an approach currently being researched, is presented. The objective of this approachis to more precisely model engine performance and condition deterioration with the help of Mode S andEarth observation data. The fusion of Mode S with Earth observation data is described with a focus onthe contributions of Mode S data. Also, the Earth observation data contained in Mode S data is pointedto. Research in progress is presented and user needs are highlighted.From the preliminary findings, one can conclude that the usage of Mode S data is essential to engineperformance and condition deterioration modeling in situations in which no aircraft position data can beobtained. ADS-B data provides the means to achieve a mapping of the aircraft location to outputs fromaerosol models, such as the Copernicus Atmospheric Modelling Service’s global reanalysis, and otherambient condition data from in-situ sources or satellites.Aero engine condition and hence, engine performance deterioration is a function of the severity of theoperational environment. Exposure of aero engines to contaminants leads to fouling, erosion, and corrosion.Additional maintenance, repair, and overhaul costs, and excess emissions result from exposingaircraft engines to harsh operating environments. ADS-B and Enhanced Surveillance (EHS) data bear theopportunity to better determine the exposure to and the impact of contamination on aero engine conditionand performance. Subsequent data analysis and generation of decision-critical information willideally decrease operational costs and the environmental footprint.

Hybrid-electric propulsion for commercial aircraft is currently a key industry interest. Consequently, publications on its design and performance estimation are manifold. However, models addressing characteristics of maintenance, repair, and overhaul (MRO) are virtually unavailable — even though direct maintenance costs (DMC) represent a significant part of direct operating costs in commercial aviation. Detailed analysis of hybrid-electric aircraft propulsion degradation and maintenance scenarios must integrate both methods of sizing and design as well as operational factors for conventional and electric subsystems, as operator-specific utilisation strongly influences MRO. Accordingly, a holistic engine analysis model is currently being developed using the example of an Airbus A320 aircraft, taking into account flight mission, engine performance, degradation, and MRO. This paper presents an implementation of hybridisation into the gas turbine thermodynamic cycle calculation for parallel hybrid-electric engine architectures with 2 and 5 MW electric motors, and the approach necessary for re-sizing hybridised gas turbine components. Turbomachinery loading throughout representative short-haul missions is analysed for conventional and hybrid-electric configurations based on the V2500 high-bypass turbofan engine, whereby unknown or uncertain boundary conditions are considered in a probabilistic sensitivity study. As a result, MRO-driving quantities such as engine performance parameters, atmospheric conditions, and ingested aerosols can be compared. The findings suggest that DMC related to the gas turbine may be considerably lowered through hybridisation, as it allows for reduced peak temperatures and more uniform gas turbine operation. However, these gains are at least partially offset by additional components’ DMC. For electric machines, bearings and the stator winding insulation are life-limiting; where the latter becomes increasingly dominant for higher power densities associated with high current densities and copper losses. Thermo-mechanical stresses are considered as driving mechanisms in power electronic systems degradation. Consequently, powerful lightweight machines must be balanced against tolerable thermal and electrical loads to achieve suitable service life.

The effects of real combined variances in components and modules of aero engines, due to production tolerances or deterioration, on the performance of an aircraft engine are analysed in a knowledge-based process. For this purpose, an aerothermodynamic virtual evaluation process that combines physical and probabilistic models to determine the sensitivities in the local module aerodynamics and the global overall performance is developed. Therefore, an automatic process that digitises, parameterises, reconstructs and analyses the geometry automatically using the example of a real turbofan highpressure turbine blade is developed. The influence on the local aerodynamics of the reconstructed blade is investigated via a computational fluid dynamics (CFD) simulations. The results of the high-pressure turbine (HPT) CFD as well as of a Gas- Path-Analysis for further modules, such as the compressors and the low-pressure turbine, are transferred into a simulation of the performance of the whole aircraft engine to evaluate the overall performance. All results are used to train, validate and test several deep learning architectures. These metamodels are utilised for a global sensitivity analysis that is able to evaluate the sensitivities and interactions. On the one hand, the results show that the aerodynamics (especially the efficiency hHPT and capacity m˙ HPT ) are particularly driven by the variation of the stagger angle. On the other hand, hHPT is significantly related to exhaust gas temperature (Tt5), while specific fuel consumption (SFC) and mass flow m˙ HPT are related to HPC exit temperature (Tt3). However, it can be seen that the high-pressure compressor has the most significant impact on the overall performance. This novel knowledge-based approach can accurately determine the impact of component variances on overall performance and complement experience-based approaches.

Malfunctions in the combustion chamber of aircraft engines influence downstream turbines. If individual burners vary in their performance, cold or hot streaks can enter and propagate through the turbine section and alter the temperature distribution in the exhaust of the engine. Analysing the variances in the temperature distribution of the exhaust jet provides information on the failure modes of the combustor. This can be used to identify damage to the aircraft engine, accelerate the inspection process and reduce maintenance cost. To investigate the influence of combustor failure on the temperature distribution, CFD simulations of a defined defect are carried out in this paper for a real size gasturbine engine. For this purpose, the total failure of one fuel nozzle in the combustion chamber, which results in a cold gas streak entering the turbine, is simulated. The cold streak is analysed by performing a turbine simulation for which the combustor exit profile is used on as an inlet condition. The simulations were performed using two different techniques. A frozen-rotor approach was used for the steady-state method to estimate the geometric influence on the mixing. The influence of the blade rotation is considered via unsteady simulation. The disturbance width and propagation were determined for both methods. The mixing and dispersion processes are found to be strong in the high pressure part of the turbine and are strongly influenced by the engine rotational speed.

A mobile fuel cell systems power output can be increased by pressure amplification using an electric turbocharger. These devices are subject to frequent transient manoeuvres due to a multitude of load changes during the mission in automotive applications. In this paper, the authors describe a simulation approach for an electric turbocharger, considering the impact of moist air and condensation within the cathode gas supply system. Therefore, two simulation approaches are used: an iterative simulation method and one based on a set of ordinary differential equations. Additional information is included from turbine performance maps taking into account condensation using Euler–Lagrange CFD simulations, which are presented. The iterative calculation approach is well suited to show the impact of condensation and moist air on the steady state thermodynamic cycle and yields a significant shift of the steady state operating line towards the surge line. It is shown that a substantial risk of surge occurs during transient deceleration manoeuvres triggered by a load step.

View Video Presentation: https://doi.org/10.2514/6.2022-3741.vid In aircraft conceptual design, propulsion models are often highly simplified. For hybrid-electric aircraft, these simplifications can have a significant effect on the feasible design space. A credible hybrid-electric aircraft conceptual design thus should include a higher-fidelity design of their energy network, that is able to give a more detailed insight into the effects of energy network components. A new energy network model is presented that does not rely on statistical values for the performance and mass values of its components, but that is able to model the main components of hybrid-electrical networks individually, leading to a higher resolution in electric network sizing. Four main network architectures are implemented: Full-electric, parallel-electric, serial-electric and conventional ultra-high bypass turbofan. These architectures are designed to cover the full range of modern and future aircraft with varying degree of electrification. The network allows a variety of design options for all individual parts, allowing a designer to assess a wide range of potential network assemblies. All parts of the network are verified and validated against reference values from currently existing components or scientific literature or validated software when necessary. To showcase the functionality of the model and the effect different design choices can have on an aircraft-level energy network, a baseline parallel-electric aircraft design is created. The effects of a variety of different design parameters on the mass and power losses of the network is evaluated. The system voltage, electric machine type and the conductor material prove to have significant influence on the total system. A comparison with a current battery system against the assumed futuristic system highlights the necessity of large advances in battery technology before such a system becomes a realistic option for sustainable aviation.