High-tech machinery increasing demands results in more and more heat output by it’s components. To lower the temperature of these components cooling channels are used. The performance of these cooling channels can be increased by adding flow disrupting structures inside the channel. This study explores the use of density-based topology optimization to optimize the geometry of these structures. A Darcy-Forchheimer penalization method is used combined with a vorticity-based objective to avoid the use of the heat transfer model during optimization. The resulting designs show increased heat transfer as the amount of vorticity increases. However, post-processing results show that overall thermal performance largely related to the pressure drop in the channel rather than detailed geometry. Under these very specific conditions increased flow velocity by narrowing the channel has more effect on thermal performance than disrupting the flow. However, more research is needed making use of a turbulence flow model or different restrictions to the design. ... Read more

The Elysian E9X, a 90-seat battery-electric aircraft with an 800 km range, offers potential to reduce aviation-sector CO₂ emissions by up to 14%, with future range extensions targeting a segment responsible for 43% of emissions. Achieving this requires an efficient thermal management system (TMS), as battery-electric aircraft rely on active cooling that may introduce significant weight and drag penalties. This thesis presents a systematic methodology to optimize condenser and radiator heat exchangers arranged in series within the E9X ram air ducts. The work comprises three components: development of a multi-point optimization framework using reduced-order models (ROM), implementation of a computational fluid dynamics (CFD) methodology using porous media modeling (PMM), and application of these models to assess the impact of heat exchanger design parameters on overall TMS performance.

A multi-objective optimization framework is developed using the in-house finite-volume heat exchanger code HeXacode coupled with the NSGA-II genetic algorithm. The optimization minimizes both heat exchanger mass and weighted air-side pressure drop across eight operating points spanning the E9X mission profile. Air-side pressure drop is converted to equivalent battery mass through its impact on ram air duct drag, enabling system-level optimization that balances structural mass with aerodynamic penalties.

A 2D RANS CFD approach is implemented in Ansys Fluent using PMM with calibrated momentum and energy source terms. Key methodological contributions include wall temperature correlations enabling off-design heat transfer prediction and improved momentum source term calibration that addresses consistent pressure drop deviations observed in earlier studies. ROM and CFD predictions agree within 1–5% for system-level metrics.

The methodology is applied in three studies. First, offset strip fins (OSF) consistently outperform louvered fins (LF), reducing total equivalent system mass by approximately 100 kg. Second, heat exchanger inclination from 0° to 60° is systematically evaluated. Inclination increases effective frontal area, reducing inlet velocity and enabling denser fin configurations. CFD simulations reveal inclination introduces additional pressure losses due to flow turning (15% increase at 60°). A correction factor correlation is developed and incorporated into the ROM. Despite this penalty, 60° inclination reduces total equivalent system mass by 60 kg. Third, two TMS architectures are compared: a series configuration with eight ram air ducts each containing both condenser and radiator, and a separate-duct configuration with 16 total ducts (eight for condensers, eight for radiators). Despite suboptimal radiator performance due to preheated air, the series configuration reduces total equivalent system mass by 213 kg by having only half the number of ram air ducts and thereby reducing frontal area and external drag.

Combined effects yield cumulative savings of approximately 326 kg, corresponding to a 10 km (+1%) range increase, demonstrating the significant influence of TMS design on battery-electric aircraft performance. The methodology can be extended to alternative architectures, operating conditions, and 3D CFD analysis.
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This thesis explores the magnetic stabilisation of strained hydrogen flames, focusing on mitigating thermodiffusive instabilities in lean premixed laminar hydrogen flames while preserving their inherent NOx reduction benefits. Utilising comprehensive numerical simulations of counterflow flame configurations, the study reveals that radially decreasing magnetic field gradients modify flame structure, predominantly through indirect mech-
anisms. These mechanisms involve magnetically induced alterations to the bulk flow field, which subsequently couple with differential diffusion effects to influence the distribution of reactants, affecting mixture fraction and the temperature field. Key findings demonstrate that the representative thermal thickness of the flame remains effectively unchanged, with a kernel-density (KDE) mode shift of 0.16 %. Crucially, total kinematic stretch is reduced by approximately 5-13 % near the axis, driven primarily by the curvature-induced contribution. Tangential strain exhibits a distinct two-regime response, decreasing by about 5-8 % in the preheat zone but increasing by 6-8 % in the reaction zone. Furthermore, a two-regime velocity-field redistribution is observed, where the axial component broadly weakens, while the radial velocity decreases for low progress variable (C) near the axis and strengthens for C ≳ 0.5. This research clarifies that direct magnetic effects are intrinsically weak and negligible
for practical control, with effective manipulation relying on these indirect pathways. The study also highlights that the efficacy of magnetic control diminishes with increasing strain rates and richer equivalence ratios. This work provides novel insights into the fundamental mechanisms governing magnetic control in premixed hydrogen flames, offering a framework for advancing sustainable combustion technologies. ... Read more

The Air Generation department at Airbus Operations GmbH has the aim to create optimization tools for the performance and sizing of air generation systems, such as the environmental control system. These type of tools will support the development of novel systems for next-generation aircraft, whose designs are driven by environmental and energy efficiency requirements. In support of this goal, this thesis focuses on the centrifugal compressor, one of the key components in aircraft air systems. The work concentrates on the development of a preliminary design and performance prediction tool that is well suited to the broad design space and future integration into a system analysis. The objective is to enable fast and robust design and performance analysis, with support for vaneless, vaned and variable vaned diffuser configurations. The method is designed to be broadly applicable, minimizing the reliance on empirical correlations commonly found in existing models, and accessible to users without extensive experience with turbomachinery design.

The methodology is based on mean-line analysis, with component models implemented in Python to ensure computational efficiency and user accessibility. While the impeller and volute are modeled using established formulations, the diffuser model is developed with a novel structure for the vaned configuration that solves the flow conditions in the channel passage using a strong interaction model for the viscid and inviscid zones. The geometric design of the vaned diffuser uses a throat area matching approach relative to the impeller in order to maximize performance without sacrificing operating range. To ensure the accuracy of the predicted impeller exit conditions, the mixing losses are computed using a two-zone model to estimate the wake area fraction.

The model is validated against six different compressor designs from open literature, four of which include both vaneless and vaned diffuser configurations, resulting in a total of ten validation cases. The validation is based on comparison of the experimental data from open literature and the model’s prediction of the performance maps for total to total pressure ratio and total to total efficiency. The model shows overall good agreement with the experimental data, with a consistent marginal underprediction of the total to total efficiency of about 1-3%.

The design and analysis tool (DACT-A) is sufficiently accurate for its purpose and has a broad applicability. However, the model is expected to have a margin of error and higher fidelity flow simulations are necessary if a higher degree of accuracy is required for the flow analysis. The validation shows good agreement for the computed losses and operating range of the vaned diffuser, but the question remains whether the flow characteristics accurately represent reality and further research and validation in this area is recommended. Furthermore, it was found that adequate flow analysis in the diffuser requires highly accurate prediction of impeller exit conditions, leading to the conclusion that, for vaned diffuser configurations, the impeller model must also possess sufficient fidelity to ensure good results. ... Read more

With climate change posing increasing risks, the Advisory Council for Aviation Research and Innovation in Europe (ACARE) aims to reduce CO2 emissions by 75% and NOx emissions by 90% per passenger kilometer by 2050, compared to a baseline aircraft from 2000. The ARENA project addresses this by developing a waste heat recovery system using aircraft engine exhaust gases, improving fuel efficiency. This thesis focuses on integrating the condenser of such a system into the propulsion unit, aiming to minimize drag from the ram air cooling duct by evaluating different heat exchanger topologies and duct designs.

The study uses the IMOTHEP Distributed fans Research Aircraft with electric Generators by ONERA (DRAGON) concept, a hybrid electric aircraft with two tail-mounted turbogenerators. The research proceeds in several stages. Initially, a multipass-condenser's potential to reduce pressure drop was examined by adjusting the heat exchanger blockage factor per pass, but results showed no reduction in pressure drop.

Next, a lumped parameter model was developed to analyze drag, pressure drop, temperature increase, and ram air duct length. This model evaluated the sensitivity of duct geometrical parameters on the drag recovery factor—a dimensionless number indicating net thrust. Findings revealed that inclining the heat exchanger efficiently increases the drag recovery factor, while the diffuser area ratio has a similar effect but is less space-efficient. The mass flow rate ratio showed less sensitivity, and fin height or pitch had the smallest effect on drag recovery.

Using the lumped parameter model, an optimal preliminary ram air duct design was identified for different spatial constraints. The study found that inline plain tube bundle and flat tube offset strip fin heat exchangers provided more compact solutions with higher drag recovery factors. For large diffuser-blocked area fractions, optimal duct geometry remained independent of heat exchanger type, characterized by a 70-degree maximum inclination angle, a 0.7 mass flow rate ratio, and maximized diffuser area ratio within spatial constraints.

A verification study of the lumped parameter model was conducted using a two-dimensional Reynolds Averaging Navier Stokes (RANS) computational fluid dynamics (CFD) analysis with k-ω SST turbulence and a porous zone to mimic the heat exchanger. The CFD analysis confirmed the lumped parameter model's predictions, with a 0.8% difference in drag recovery factor for optimal duct geometry. Across various geometries, the mean absolute difference in drag recovery factor between models was 1.082%, with a standard deviation of 0.584%.

In conclusion, integrating the condenser in the propulsion unit within spatial constraints results in positive thrust, thus supporting Meredith's 1935[2] claim. This integration reduces net drag and improves overall efficiency, contributing to significant emission reductions in line with ACARE's targets. ... Read more

Climate change is a pressing issue. Hydrogen aircraft are an excellent alternative to current kerosene aircraft, and appear to be the most viable long-term solution for net-zero flight. One of the main challenges for hydrogen aircraft is to sustain a low boil-off rate. This research explores the solution of active cooling of the LH2 mixture in the fuel tank. It focusses on the construction of a thermodynamic model for cryogenic liquid hydrogen fuel storage in aircraft, a system model for single-stage Reverse Turbo-Brayton Cryocoolers (RTBC), and the conceptual design of the RTBC’s miniature high-speed compressor. This is used for the integrated modelling of the RTBC, compressor and LH2 fuel tank for an exploration study of the carbon neutral hydrogen concept of the long-range Flying-V aircraft. Results show that the RTBC might offer a valuable addition to the Flying-V design space for boil-off control in addition to careful design of the insulation and tank shape. ... Read more

The rise in temperature attributed to human CO2 emissions and the escalating energy needs of society necessitates the development of clean energy production. Solar and wind energy, both renewable sources, have emerged as cost-effective alternatives to conventional fossil fuel systems. They now account for a substantial portion of the world's electricity generation (IEA, 2022). However, their intermittent nature poses a challenge to their reliability. To overcome this, the implementation of grid-scale energy storage systems is crucial. Such systems can store excess energy produced during peak periods and release it during low-generation or high-demand periods, ensuring a stable and dependable power supply to the grid.

Pumped Thermal Energy Storage (PTES) is one such type of promising grid-scale storage solution based on the concept of storing electricity in the form of heat. These systems are not reliant on rare earth metals, are not restricted by geographical location, and are relatively economical over their lifetime. They employ a heat pump cycle for charging and a heat engine cycle during times of discharge. Often, in the thermodynamic modelling of PTES systems, a fixed value of turbomachinery efficiency is assumed. This approach holds well for the first estimate of performance, but for better accuracy and further analysis, meanline models could be used to arrive at the efficiency value and preliminary geometric design. Hence, this work presents a method for developing meanline models for centrifugal compressors and radial inflow turbines. Modelling techniques and guidelines from the literature are noted and presented here. The accuracy of these models is dependent mainly on the loss models used. Using suitable models selected from the literature, a fair agreement was found between the meanline model's prediction and experimental data from open literature, validating the methodology.

An essential function of energy storage is to provide load flexibility, meaning its charging and discharging cycles must adjust to match the net load curve. As a result, the turbomachinery would need to operate under off-design conditions to meet these demands. Therefore, this report introduces an approach to extend the PTES model by Radi (2023) for off-design operation based on turbomachine performance.
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This study analyses the feasibility of an engine architecture using bypass cooled cooling air as a method for reducing specific fuel consumption of current and future high bypass turbofan engines. As cooled cooling air reduces required turbine cooling massflow, a major source of loss in modern aeroengines, it is believed that the concept can improve engine efficiency. No extensive or explicit study on the merits of this concept has been performed, however.
Using the 0-D engine analysis software GSP, engine performance parameters at Take-Off and Cruise, such as, specific fuel consumption and (specific) thrust were evaluated against altering feed cooling air temperature by 0 to -300K and heat exchanger induced pressure losses of 0 to 8% in the bypass. This was done for two test cases; the Leap-1A engine (TOC OPR 50, CRZ BPR 11.1, TO FN 121kN) representing current conventional technology and GTF2050, a geared turbofan engine (TOC OPR 75, CRZ BPR 17.1, TO FN 174kN) with entry into service of 2050. For the Leap-1A engine the specific fuel consumption increased up to 1.9% at cruise and for GTF2050, the increase was up to 4.1%. It is shown that the change in fuel consumption is linear with the decrease in cooling fraction, as for both engines the specific fuel consumption increases by +0.34% per percent cooling air reduction.
With a reduction in cooling fraction, the exhaust pressure of the core increases, resulting in a higher thrust (up to 2.3%). It is shown that the optimal take-off bypass ratio for minimum fuel consumption shifts up, for the GTF2050 engine from 16.4 to 17.5.
Furthermore, scenario tests and an exergy analysis were performed to find that the impact of different mechanisms; the pressure loss in heat exchanger has minor impact on performance; change in turbine efficiency has small impact; the effect of changed turbine massflow and heat rejection into the bypass are the dominant phenomena.
It is concluded that as a method for reducing fuel consumption, cooled cooling air with the bypass as a heat sink is not feasible for conventional architectures even with extreme design parameters such as high OPR and BPR. Heat rejection to the bypass cannot be effectively utilised and no improvement in core efficiency from reduced cooling air can compensate. In the edge case where there is no heat transfer in cruise, there is an observed specific fuel consumption benefit of up to 4%. The achievable benefit will be lower, however, when accounting for installation penalties.
It is recommended to focus turbine cooling studies on the impact and feasibility of active cooling massflow control without heat rejection, investigate alternative heat sinks for cooled cooling air (e.g. cryogenic fuel), and only consider bypass cooled cooling air as last resort when up-flowing cooling
schemes is not permissible or ineffective. ... Read more

The world is moving towards sustainability and there is immense pressure on Aerospace Industry to reduce its emissions to contribute to a carbon-neutral world. However, maturing gas turbine technology is a big bottleneck towards this goal and hence, this project focuses on the technical and economic feasibility of a new type of propulsion system, called Solid-Oxide Fuel Cell- Gas Turbine or SOFC-GT hybrid propulsion system. SOFC- GT, even though being a low TRL technology, has the potential to reduce fuel consumption, emissions, and operation costs, making it a suitable candidate for a future propulsion system.

This research concludes that in order to achieve the full potential of the SOFC-GT hybrid, engine parameters like BPR, FPR and cooling air requirements need to be changed. The Thrust-Specific Fuel Consumption (TSFC) for the propulsion system has decreased by 6.03% and 19.89% for 1 MW and 4 MW fuel cell power output in Off-Design (Cruise) condition. Along with this, core mass flow rate or size, cooling air requirement and Turbine Inlet Temperature for Cruise condition has decreased. The emission results show that the NOx emissions have been reduced by 29.11% and 78.05% respectively. Sensitivity analysis shows that the thermodynamic efficiency is most sensitive to engine parameters but the impact of fuel cell parameters is increasing as the fuel cell power output is increased.

The economic analysis done in this study shows that the SOFC-GT hybrid is not feasible for the commercially available fuel cell because of the substantial increase in weight of the propulsion system. However, the propulsion system will become feasible at the fuel cell system specific power of 2.30 kW/kg and 2.10 kW/kg for no emission tax and highest emission tax scenario respectively at a fuel price of $ 6/kg. Along with this, increasing the fuel cell power output leads to the increase in required specific power for fuel cell or has a negative impact on the overall economics. The overall economics of the aircraft is most sensitive to aircraft parameters but increasing the fuel cell power output decreases sensitivity substantially. In the end, the emission has a low impact on the overall economics of the aircraft.

This research shows that it is possible to integrate a SOFC with the turbofan if the fuel cell technology improves in the future. Along with this, the research provides multiple novel methodologies for technical and economic analysis of the SOFC-GT hybrid. ... Read more

The constant pressure on the maritime sector to reduce Greenhouse Gas (GHG) emissions has led the shipping industry to search for alternatives, such as zero-emissions propulsion systems, which would allow meeting the 2050 target imposed by International Maritime Organization (IMO) regulation. Fuel cells have demonstrated to substantially contribute to the greening of energy conversion technologies. Specifically, Solid Oxide Fuel Cells have proven to be a reliable technology to produce energy from Liquid Natural Gas (LNG). However, the limited understanding of the effect of the components around the stack (also known as Balance of Plant, BoP) in SOFC power generation system represents one of the reasons of the slow development of this technology. The main objective of this research is to gain insight in the performance of the BoP components and their influence on the SOFC power generation system for maritime applications. A dynamic model describing a complete SOFC power generation system is developed in this work. The chosen system configuration consists of three blowers, two heat exchangers, a mixer, an external pre-reformer, an SOFC stack and an afterburner. Specifically, each BoP component is modelled dynamically using a 0-D approach and verified individually by using the software Cycle-Tempo. Then, the BoP models are integrated with an existing 1-D SOFC stack model. A dedicated control system is implemented and the load following capabilities of the complete system are studied. The model developed is able to simulate the time variation of all the BoP component characteristics and provides insights in the system efficiency when varying operating parameters such as stack current, anode recirculating ratio and fuel utilization. In particular, it is proven that working at low current enables higher cell voltage and, thus, higher system and stack efficiency. System fuel utilization significantly contributes to the system efficiency, which reaches the highest value for the highest fuel utilization. Additionally, the effect of the fuel utilization rate on the stack and system is the highest at lower currents. System and stack efficiency of respectively 58 % and 66 % are possible with the chosen system configuration. Anode recirculating contributes more to the system efficiency than the stack efficiency. The highest system efficiency is obtained for low current values and high recirculating ratio. Moreover, significant CO2 emission reduction is obtained for high recirculating ratio. The chosen control strategy succeeds on ensuring thermal safe operation, but does not guarantee fast response to load changes. In particular, a system response within 2 hours is achieved with the controller developed when the stack current is changed from 27 A to 23 A . Moreover, a load ramp of the stack current is a better choice in terms of thermal safe operation than a stepped change. The developed model represents a solid base for future development and research in the modelling of SOFC power generation systems for maritime applications. Nevertheless, future investigations on model validation, control system, start-up operations and system optimization are recommended. ... Read more

Organic Rankine Cycle (ORC) Power Plants can be of greatimportance in the energy transition as they are suitable for converting wasteheat to power and can utilize renewable energy for their operation. To improvethe efficiency of ORC Power Plants, the physical phenomena inside thesemachines must be understood. Understanding the boundary layer of complexorganic fluid flows in these systems is crucial, as it is estimated to beresponsible for one-third of the losses in turbomachinery. n this thesis, two-dimensional steady state boundarylayer flows of nonideal gas have been investigated numerically. The objectivewas to find the influence of complex fluid nonideality, characterized by idealgas departure, on boundary layer flows. In particular, a high-speed densevapour expansion of organic fluid Hexamethyldisiloxane (MM) inside a de Lavalnozzle test section has been studied. The nozzle is part of a measurementcampaign to collect experimental data with the purpose of validation andcalibration of Non-Ideal Compressible Fluid Dynamics (NICFD) software.  MATLAB program was developed for solving thetwo-dimensional steady state boundary layer equations including generalthermophysical properties. Transition prediction methods, the algebraicCebeci-Smith turbulence model (CS-model), and state-of-the-art thermophysicalmodels were implemented. The program was verified and validated for air withliterature. The turbulence model was validated with experimental data oflarge-scale zero pressure gradient adiabatic flows. The results match for theentire Mach-number range from 0.2 up to 2.8. The program also proved to becapable of predicting the turbulent boundary layer along a flat wall inside ade Laval nozzle expanding air. Deterministic simulations of the boundary layer along thecurved wall surface of the aforementioned nozzle expanding MM were performed.The results showed a larger decrease in the newly defined property C_e inthe core flow along expansion compared to air. In contrast, the propertygradients; namely density ratio c and Chapman-Rubesin parameter C,inside the boundary layer were found to be negligible. Furthermore, the resultsshow that the influence of the pressure history upstream of the nozzle throatis relatively small or even negligible in the diverging nozzle section. Theboundary layer displacement thickness for both laminar and turbulent flow wasfound to be negligible compared to the nozzle cross section, which results in anegligible effect on the nozzle core flow. The program needs further validation for flows departingfrom ideal gas. First, the flow condition in de Laval nozzles, laminar orturbulent, needs to be obtained by conducting experiments. Then, sensitivitystudies need to prove if the inviscid nozzle design is a robust design forviscous flows too; namely, being insensitive to changes in total inputconditions, uncertainties in closure coefficients, and variations in upstreampressure history. ... Read more