Search Results (299)

Integrating a heat exchanger (HEX) into the cooling duct of a high-power fuel-cell-based aircraft presents a critical trade-off between thermal performance and aerodynamic penalties. The present study addresses this challenge through the design and system-level analysis of a HEX integrated into the cooling duct. Developed as part of the Clean Aviation project FAME, the design features a rectangular inlet, a circular outlet, and a tilted HEX. The evaluation is performed using high-fidelity Large Eddy Simulations (LESs). The HEX is modeled with a porous media approach based on the Darcy–Forchheimer equation, while the simulations are carried out using a self-adapted version of the pisoFoam solver, termed pisoTempFoam, to account for heat transfer. The study reveals that while component-level design choices, such as a straight inlet and tilted HEX configuration, successfully mitigate local flow separation and duct-induced losses, a critical system-level performance issue emerges. The analysis demonstrates that the cooling duct design, when subjected to realistic operational conditions, generates the high pressure head to overcome the resistance of the HEX. The external aerodynamic analysis also indicates that the HEX resistance is a critical factor, and without overcoming it the system fails to capture the required air mass flow rate, compromising thermal management. The findings highlight the necessity to optimize the design, by an adapted duct shape or an auxiliary fan, to overcome the HEX-induced pressure drop. The porous media approach is thereby validated as an effective tool for rapid system-level design analysis, despite its inherent limitation in capturing detailed downstream turbulence. Full article

The development of future electrical aircraft, such as the Hybrid-Electric Regional Aircraft (HERA) platform, presents challenging cooling demands due to the heat generated by electric powerplants, fuel cells and power electronics. Traditional heat exchangers in ram air channels may not be sufficient, necessitating alternative solutions like Skin Heat Exchangers (SHXs) to enhance heat transfer and reduce parasitic drag. Aircraft drag reduction and efficiency increase are expected with the integration of SHXs in two-phase cooling systems. This study employs Computational Fluid Dynamics (CFD) models, specifically the Volume of Fluid (VOF) multiphase model together with the Lee model, to simulate the condensation process of two Hydrofluoroolefin (HFO) refrigerants in SHX channels (R1233zd(E) and R1234yf). An analytical model based on empirical equations is used to preliminarily correlate and validate the CFD results, showing deviations below 15%. The simulations reveal distinct flow behaviours for each refrigerant, influenced by the differences in liquid and gas densities. The study also establishes a basis for understanding and selecting the inverse of the relaxation time coefficient, which is crucial for multiphase CFD modelling. The CFD models used in this article could be of great importance for future SHX design optimization. Full article

The aviation sector is under increasing pressure to cut emissions, prompting strong interest in alternative propulsion systems. This study examines the potential of hybrid-electric aircraft relying on electrochemical energy storage and conversion units (EC-ESC), consisting of proton exchange membrane fuel cell systems coupled with batteries. A design space exploration framework is proposed to size and control these systems for regional aircraft, treating fuel cell system nominal power and battery C-rate as key design variables, while also accounting for in-flight degradation. A flexible degradation-aware control strategy manages power sharing within the co-design strategy, which seeks a configuration minimizing the total EC-ESC equivalent mass. The entire procedure is designed versatilely enough to be applicable for the model-based design and energy management of EC-ESC units destined for several end uses, e.g., short/medium-haul, and long-haul aircraft or automotive. Full article

Effective thermal management is crucial for the development of future electrified aircraft propulsion systems. One of the most challenging phases is the take-off phase, which imposes particularly high demands on cooling systems. In addition, the aerodynamic drag during cruise flight has to be kept to a minimum. This study introduces a novel experimental thermal management system using a test stand with a modular air duct (TMTmad), which is designed specifically to investigate different configurations of air supply and heat exchanger in fuel cell-based electrified propulsion systems. Given the versatility of nacelle-integrated electrified propulsion architectures, this approach offers high flexibility in the design and integration of thermal management systems. This includes aspects such as the location, orientation and geometry of an air-cooled heat exchanger (HEX), as well as the inlet and outlet configurations. Moreover, the optimization of the uniform flow guidance of the duct flow within the nacelle and the integration of additional fans to ensure airflow under critical conditions can be studied. The main heat source delivers up to 6 $\mathrm{k}\mathrm{W}$ of heating power with a temperature range from −20 °C to 200 °C. The study measures the heat flux and pressure losses within these systems and includes a thorough fluid flow analysis. Furthermore, the experimental data serves as a valuable resource for validating numerical models of cooling ducts, enhancing the accuracy and reliability of future design iterations. Full article

Future aircraft propulsion concepts (e.g., water-enhanced engines and fuel cells) will depend on efficient water recovery to enhance cycle efficiency and environmental performance. Operating conditions commonly involve droplet (mist) transport in turbulent air and wall-bounded films formed by droplet–wall interactions. This work develops an Eulerian–Lagrangian model within the RANS/URANS framework that accounts for air–droplet–wall phenomena—interfacial shear, impingement, and film advection. A dynamic contact-angle model, implemented and calibrated from static contact angle measurements performed in this study, represents wall wetting at the liquid–solid interface. The model is validated against experiments using two design metrics: pressure loss across the unit and recovered water mass fraction. At a low Mach number ($Ma=0.1$), saturated and dry air produce nearly identical pressure losses in the circular test section, whereas the separation lip geometry exerts a strong influence via local acceleration and separation. The simulations reproduce measured pressure drops and water mass recovery with close agreement. Full article

The development of aircraft with high-aspect-ratio (HAR) wings and flexible lightweight structures is at the forefront of efforts for a more sustainable aviation. Nevertheless, this change in aircraft configuration is accompanied by significant complexity. Specifically, it calls for the modelling of strong aero-structural couplings and the concurrent synthesis of active control laws to mitigate the higher structural loads generated by HAR wings. Managing these challenges from the very onset of the preliminary design phase demands a unified approach. Consequently, this paper leverages a Flexible Wing Co-design framework that integrates aeroelastic wing design and robust $H_{\infty }$ controller synthesis for gust load alleviation (GLA). This co-design capability is deployed to conduct a sensitivity analysis of wing aspect ratio effects, as well as a multidisciplinary design optimisation (MDO) approach focused on minimising mission block fuel. The results confirm that the proposed approach delivers substantial mass savings and superior aircraft performance, establishing it as an indispensable tool for the early stage development of next generation configurations. Full article

Modern aircraft fuel tank explosion protection relies critically on inerting efficiency. This study presents and investigates a novel scrubbing deoxygenation strategy utilizing mixed inert gas (MIG) generated by oxygen-consuming inerting systems for high-vapor-pressure RP5 aviation fuel. A high-fidelity computational fluid dynamics (CFD) numerical framework was established using the Eulerian–Eulerian two-fluid model coupled with Higbie’s penetration theory, with experimental validation ensuring computational accuracy (maximum errors for ullage oxygen concentration and dissolved oxygen in fuel controlled within 4.11% and 5.23%, respectively). The research systematically elucidates the influence mechanisms of bubble diameter, MIG temperature, and superficial gas velocity on mass transfer characteristics (oxygen mass transfer coefficient and volumetric mass transfer coefficient). Key findings reveal that reducing bubble diameter achieves localized polarization of mass transfer intensity in the central plume region through an “area-velocity” synergistic effect, with the oxygen volumetric mass transfer coefficient at 1.0 mm diameter increasing by 51.3% compared to 2.5 mm. The performance enhancement from superficial gas velocity primarily stems from the “area multiplication effect” triggered by surging gas holdup. Notably, MIG temperature exhibits a unique three-stage reversal characteristic of “kinetically dominated early stage, thermodynamically controlled late stage” on deoxygenation performance. These results provide critical physical foundations for the forward design of next-generation multifunctional onboard inerting systems. Full article

The aircraft landing problem (ALP) poses significant challenges for traditional Monte Carlo Tree Search (MCTS) due to its vast search space and reliance on inefficient random simulations. To overcome these limitations, this paper proposes a novel Transformer-Augmented Monte Carlo Tree Search (TMCTS) algorithm. Our approach integrates a reinforcement learning framework that incorporates key operational constraints, including wake turbulence separation and time windows, and employs a cost function aimed at minimizing both delay time and fuel consumption. A core innovation is the replacement of the conventional random simulation phase in MCTS with a Transformer-based value predictor. This leverages the Transformer’s superior ability to model sequences and capture global dependencies among flights, thereby dramatically accelerating search convergence. Specifically, we designed a two-head Transformer network (comprising policy and value heads) to provide informed prior knowledge, which effectively guides the selection and expansion steps of the MCTS tree. The model is trained within an Actor–Critic framework, utilizing behavior cloning for pre-training followed by reinforcement learning for fine-tuning. Experimental evaluations on the standard OR-Library benchmark demonstrate that our TMCTS method significantly reduces scheduling deviation compared to state-of-the-art baselines (including FCFS, DPALO+GA, DPALO+PSO, and CPLEX). Moreover, it achieves a 93.7% reduction in computation time relative to the CPLEX method, highlighting its superior efficiency and practical applicability for real-time scheduling. Full article

Liquid Hydrogen (LH2) as an energy carrier for passenger aircraft has the potential to combine low climate impact and high lifecycle energy efficiency. Due to its significantly different physical properties compared to kerosene, the integration of LH2 fuel storage and distribution systems interacts with the general configuration of the aircraft. In order to assess promising configuration combinations quantitatively, an aircraft design and assessment framework is further developed. These additions are aimed at capturing the interdependencies originating from the fuel system integration choices at the aircraft level and quantifying the effect of trim drag. The framework is applied to a selection of LH2 mid-to-long-range aircraft designs. A comparison of the mass breakdown, aerodynamics breakdown and performance indicators such as specific energy consumption is carried out for the framework-generated aircraft models. A trim drag induced block fuel penalty is quantified for the aircraft selection as well as a mitigation strategy based on operational constraints. Full article

In this work, a dynamic polymer electrolyte membrane (PEM) fuel cell system is modelled in Modelica using the in-house developed, open-source library ThermoFluidStream. The focus lies on the fuel cell stack, the hydrogen fuel supply and the air supply. Additionally, the thermal management and the power electronics are considered in a simplified manner. Dynamic simulations are carried out for this system over an exemplary aircraft gate-to-gate mission. Simultaneously, a baseline control scheme is developed to provide the fuel cell with sufficient product gases in a suitable state regarding the temperature, pressure and relative humidity. The results indicate that the fuel cell system performs well with standard PI controllers. Only when strong dynamics occur, such as when going from taxi to take-off, does the control scheme show some weaknesses, as expected. This fuel cell system together with its control is a powerful baseline for future investigations. Full article

The aviation industry is transitioning toward hydrogen propulsion to meet sustainability goals, introducing novel fire safety risks that require updated regulatory frameworks. This study addresses the certification challenges for liquid hydrogen fuel systems by advancing the Certification Readiness Level through a model-driven approach. Using a Model-Based Safety Assessment, this research applies Bow-Tie Diagrams within the NASA AdvoCATE software to analyze in-flight fire risks for a tube-and-wing aircraft architecture. The study models critical threats, including cryogenic embrittlement and leakage, mapping them to specific prevention and protection barriers derived from a regulatory gap analysis. The assessment identifies leakage as the primary failure condition and proposes a safety architecture that emphasizes prevention barriers. Quantitative safety case modeling demonstrates, with proposed means of mitigation and barrier integrity, the feasibility to compute the residual probability of a catastrophic in-flight fire according to EASA CS 25.1309 requirements. These findings validate the use of safety architectures to bridge the gap between design and rulemaking, offering a scalable framework to support early-stage certification and the safe integration of hydrogen technologies into commercial aviation. Full article

The design of low-emission alternative-propulsion aircraft requires multidisciplinary collaboration across distributed academic and industrial environments, challenging the applicability of conventional Multidisciplinary Design Analysis and Optimization (MDAO) frameworks. This paper presents the Holistic Collaborative MDAO Selection (HCMS) methodology, which provides a structured approach for selecting MDAO architectures based on socio-technical feasibility (intellectual property protection, disciplinary autonomy, and IT governance) and computational feasibility (coupling strength and model fidelity). The methodology supports a transition from centralized to distributed workflows while ensuring secure and efficient cross-organizational integration. The approach is demonstrated through a multi-institutional case study of a dual-fuel (hydrogen and kerosene) business jet using Remote Component Environment (RCE) and Common Parametric Aircraft Configuration Schema (CPACS). Results demonstrate that the proposed methodology enables stable and scalable distributed MDAO execution while explicitly accounting for socio-technical constraints, with consistent convergence behavior and communication overhead (approximately 25 s per iteration) remaining small relative to disciplinary computation time. The case study further illustrates the impact of hydrogen integration, showing an increase in operating empty weight of approximately 14.06% for a 600 NM mission and a reduction in kerosene capacity of approximately 12.9%, while enabling hydrogen-powered operation for the primary mission segment. These findings confirm that the proposed framework effectively supports secure, collaborative MDAO under realistic socio-technical constraints while providing meaningful system-level design insights. Full article

Decarbonizing air travel poses a major technological challenge, driven by the substantial power requirements of the drivetrain and the demanding weight and volume constraints of airborne systems. One promising avenue involves leveraging the high specific energy of hydrogen by designing compact, high-power fuel cell stacks to supply power for electric drivetrains. However, a key drawback of such propulsion architectures is the substantial heat generated within the fuel cells, which necessitates bulky and heavy thermal management systems to ensure safe and continuous operation. This study investigates a proposed air-based thermal management system, which operates by introducing pulsating heat pipes into the bipolar plates of a High-Temperature Polymer Electrolyte Membrane Fuel Cell (HT-PEM FC) stack. If proven to be feasible, heat pipe assisted air cooling may provide the benefit of reducing overall system complexity by decreasing the number of components in the thermal management system. To evaluate the thermal performance of the proposed system, a one-dimensional thermal model was initially developed in a previous study to describe the temperature distribution along the length of a heat pipe. Building upon this foundation, the present work extends the model by incorporating a two-dimensional Computational Fluid Dynamic (CFD) analysis to account for geometry-specific effects within the hexagonal design. Results indicate that the heat transfer from the hexagonal heat pipe geometry to the coolant air flow was marginally overestimated in previous analytical calculations. Revised heat transfer rates led to a shift in the predicted temperature distributions, resulting in the need for either increased external airflow, extended condenser sections, or reduced inlet temperatures to maintain target operating conditions. Although these adjustments may result in a slight increase in system mass and parasitic power consumption, the overall impact is limited, and the heat pipe-assisted air cooling approach remains theoretically feasible. Based on the results, design modifications are proposed and their impact on thermal performance is evaluated to address the challenges of heat rejection and temperature uniformity. A modification based on variation and optimization of PHP meander lengths was evaluated using the updated model and it significantly improved temperature homogeneity across the evaporator. Full article

The development of supersonic aircraft presents significant challenges in ensuring safety during early design stages, particularly for fuel tank systems exposed to extreme thermal and structural loads. Conventional document-based zonal safety analysis methods are limited in their ability to capture dynamic interactions between spatial subsystem configurations and functional system behavior during early conceptual design, leading to delayed hazard identification. This study proposes an integrated framework combining computer-aided design (CAD) and model-based systems engineering (MBSE) to support early-stage zonal hazard analysis. The framework links spatial subsystem modelling with functional system architecture to enable iterative hazard identification and mitigation. Applied to the SA-24 Phoenix conceptual supersonic aircraft, the approach identifies critical risks, including fuel vaporization, over-pressurization, and structural fatigue, and evaluates mitigation strategies such as thermal insulation and redundant venting. Functional hazard analysis and fault tree analysis are used to assess failure scenarios and ensure compliance with EASA CS-25 requirements. Results indicate an estimated reduction of up to 40% in risk priority number (RPN) values for key thermal hazard pathways and a 25% reduction in conceptual design iteration time compared with conventional approaches. The findings demonstrate that CAD–MBSE integration offers a scalable and efficient methodology for early hazard identification, contributing to safer and more reliable supersonic aircraft design. Full article

Fuel vapor can be ignited by lightning through various means, particularly through hot spot formation on fuel tank skins. The wing fuel tank cover and its surrounding outer plates together form part of the aerodynamic shape of an aircraft. The lightning protection design of the fuel system, including wing fuel tank, is of great significance for ensuring the aircraft safety. Based on the Joule heating and implosion effect, the damage response of a composite fuel tank cover subjected to lightning strikes is analyzed in this paper. The adopted method combines electrical–thermal coupling with explicit dynamics analysis. Firstly, a finite element model of the fuel tank cover is established using electrical–thermal coupling elements, and the lightning current impact simulation is carried out under given electrical boundary conditions and thermal boundary conditions. On one hand, the ablation criterion is determined by the Joule heating effect and the sublimation temperature of materials. The thermal damage of composite materials subjected to transient high currents is obtained through transient thermal analysis. On the other hand, special implosion elements are selected according to the temperature distribution obtained from the electrical–thermal coupling analysis. The original composite material model in the implosion region needs to be replaced with a new material model described by the high-explosive material model and the JWL equation of state. The von Mises stress distribution and pressure distribution on the structure after implosion are discussed in detail. The results show that concave pits are formed near the implosion zone. Unlike the thermal damage morphology defined by the ablation criterion, the implosion effect makes the damage distribution deviate from the initial fiber direction of each layer. The implosion dynamic method reveals the internal damage and pit and bulge phenomenon around the lightning attachment area to a certain extent. Full article