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1.	Dahal, Karna, 1984, et al. (author) Techno-economic review of alternative fuels and propulsion systems for the aviation sector 2021 In: Renewable and Sustainable Energy Reviews. - : Elsevier BV. - 1879-0690 .- 1364-0321. ; 151 Research review (peer-reviewed)abstract Substitution of conventional jet fuel with low-to zero-carbon-emitting alternative aviation fuels is vital for meeting the climate targets for aviation. It is important to understand the technical, environmental, and economic performance of alternative aviation fuels and prospective engine and propulsion technologies for future aircraft. This study reviews alternative fuels and propulsion systems, focusing on costs and technical maturity, and presents conceptual aircraft designs for different aviation fuels. The cost review includes minimum jet fuel selling price (MJFSP) for alternative aviation fuels. Direct operating cost (DOC) is estimated based on the conceptual aircraft designs and the reviewed MJFSP. The DOCs for bio-jet fuel (5.0–9.2 US cent per passenger-kilometer (¢/PAX/km)), fossil and renewable liquefied hydrogen (5.9–10.1 and 8.1–23.9 ¢/PAX/km, respectively), and electro-methane and electro-jet fuel (5.6–16.7 and 9.2–23.7 ¢/PAX/km, respectively) are higher than for conventional jet fuel (3.9–4.8 ¢/PAX/km) and liquefied natural gas (4.2–5.2 ¢/PAX/km). Overall, DOC of renewable aviation fuels is 15–500 % higher than conventional jet fuels. Among the bio-jet fuels, hydroprocessed esters and fatty acids (23–310 $/GJ) and alcohol-to-jet (4–215 $/GJ) pathways offer the lowest MJFSPs. The implementation of alternative fuels in existing aircraft engines and the design and development of appropriate propulsion systems and aircraft are challenging. The overall cost is a key factor for future implementation. Bio-jet fuel is most promising in the near term while hydrogen and electrofuels in the long term. The level of carbon tax on fossil jet fuels needed for the latter options to be competitive depend on the hydrogen production cost.
2.	Abedi, Hamidreza, 1979, et al. (author) Preliminary Analysis of Compression System Integrated Heat Management Concepts Using LH 2 -Based Parametric Gas Turbine Model 2022 In: Aerospace. - : MDPI AG. - 2226-4310. ; 9:4 Journal article (peer-reviewed)abstract The investigation of the various heat management concepts using LH2 requires the development of a modeling environment coupling the cryogenic hydrogen fuel system with turbofan performance. This paper presents a numerical framework to model hydrogen-fueled gas turbine engines with a dedicated heat-management system, complemented by an introductory analysis of the impact of using LH2 to precool and intercool in the compression system. The propulsion installations comprise Brayton cycle-based turbofans and first assessments are made on how to use the hydrogen as a heat sink integrated into the compression system. Conceptual tubular compact heat exchanger designs are explored to either precool or intercool the compression system and preheat the fuel to improve the installed performance of the propulsion cycles. The precooler and the intercooler show up to 0.3% improved specific fuel consumption for heat exchanger effectiveness in the range 0.5–0.6, but higher effectiveness designs incur disproportionately higher pressure losses that cancel-out the benefits.
3.	Capitao Patrao, Alexandre, 1988, et al. (author) Compact heat exchangers for hydrogen-fueled aero engine intercooling and recuperation 2024 In: Applied Thermal Engineering. - 1359-4311. ; 243 Journal article (peer-reviewed)abstract This study investigates the application of compact heat exchangers for the purpose of intercooling and recuperation systems for short-to-medium range aircraft equipped with hydrogen-fueled turbofan engines. The primary objective is to assess the potential effects of engine-integrated compact heat exchangers on fuel consumption and emissions. The paper encompasses the conceptual design of integrated heat exchangers and associated ducts, followed by aerodynamic optimization studies to identify suitable designs that minimize air-side pressure losses and ensure flow uniformity at the inlet of the high-pressure compressor. Pressure drop correlations are then established for selected duct designs and incorporated into a system-level performance model, allowing for a comparison of their impact on specific fuel consumption, NOx emissions, and fuel burn against an uncooled baseline engine. The intercooled-recuperated engine resulted in the most significant improvement in take-off specific fuel consumption, with a reduction of up to 7.7% compared to the baseline uncooled engine, whereas the best intercooled engine resulted in an improvement of about 4%. Furthermore, the best configuration demonstrated a decrease in NOx emissions by up to 37% at take-off and a reduction in mission fuel burn by 5.5%. These enhancements were attributed to reduced compression work, pre-heating of the hydrogen fuel, and lower high-pressure compressor outlet temperatures.
4.	Capitao Patrao, Alexandre, 1988, et al. (author) Compact Heat Exchangers With Curved Fins for Hydrogen Turbofan Intercooling 2024 In: Journal of Engineering for Gas Turbines and Power. - 1528-8919 .- 0742-4795. ; 146:11 Journal article (peer-reviewed)abstract Hydrogen is being considered as a possible path toward carbon-neutral aviation. There are additional advantages besides its main benefit ofCO2-free combustion. One application is to use it for aero engine heat management due to its cryogenic temperature and high heat capacity, including intercooling and exhaust heat recuperation. The focus of this paper is on the design of a compact heat exchanger (HEX) integrated into an intermediate compressor duct (ICD), which could decrease compression work and specific fuel consumption (SFC). This compact heat exchanger features curved fins to promote flow turning and decrease pressure losses compared to more conventional straight fin heat exchangers. Conceptual design and duct shape optimization has been carried out which produced integrated ICD heat exchanger designs with significantly lower air-side total pressure losses compared to their conventional straight fin counterparts, which could improve system level integration and engine performance. A direct outcome of this study is a pressure loss correlation, which can be used in future engine system-level trade studies.
5.	Capitao Patrao, Alexandre, 1988, et al. (author) Numerical modeling of laminar-turbulent transition in an interconnecting compressor duct 2022 In: 33rd Congress of the International Council of the Aeronautical Sciences, ICAS 2022. ; 2022:3, s. 2033-2044 Conference paper (peer-reviewed)abstract Cryogenic hydrogen is being considered as a future aviation fuel since it eliminates CO2, CO, soot, sulphur, and unburnt hydrocarbons emissions. The storage temperature and high cooling capacity of cryogenic hydrogen also makes it a suitable coolant. In this paper a integrated heat exchanger in an interconnecting compressor duct (ICD) is analyzed with respect to heat transfer and transition.
6.	Capitao Patrao, Alexandre, 1988, et al. (author) The heat transfer potential of compressor vanes on a hydrogen fueled turbofan engine 2024 In: Applied Thermal Engineering. - 1359-4311. ; 236 Journal article (peer-reviewed)abstract Hydrogen is a promising fuel for future aviation due to its CO2-free combustion. In addition, its excellent cooling properties as it is heated from cryogenic conditions to the appropriate combustion temperatures provides a multitude of opportunities. This paper investigates the heat transfer potential of stator surfaces in a modern high-speed low-pressure compressor by incorporating cooling channels within the stator vane surfaces, where hydrogen is allowed to flow and cool the engine core air. Computational Fluid Dynamics simulations were carried out to assess the aerothermal performance of this cooled compressor and were compared to heat transfer correlations. A core air temperature drop of 9.5 K was observed for this cooling channel design while being relatively insensitive to the thermal conductivity of the vane and cooling channel wall thickness. The thermal resistance was dominated by the air-side convective heat transfer, and more surface area on the air-side would therefore be required in order to increase overall heat flow. While good agreement with established heat transfer correlations was found for both turbulent and transitional flow, the correlation for the transitional case yielded decent accuracy only as long as the flow remains attached, and while transition was dominated by the bypass mode. A system level analysis, indicated a limited but favorable impact at engine performance level, amounting to a specific fuel consumption improvement of up to 0.8 % in cruise and an estimated reduction of 3.6 % in cruise NOx. The results clearly show that, although it is possible to achieve high heat transfer rate per unit area in compressor vanes, the impact on cycle performance is constrained by the limited available wetted area in the low-pressure compressor.
7.	Dias, Filipe, et al. (author) Analysis and Comparison of Different Chemistry Models for the Computation of Reacting Flows on Re-entry and Hypersonic Vehicles 2019 In: AIAA Propulsion and Energy Forum and Exposition, 2019. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624105906 ; 2019 Conference paper (peer-reviewed)abstract An aircraft in hypersonic flight regime is enveloped in a plasma layer due to the high temperatures involved. This electronic plasma layer will be responsible for cutting-off communications to and from the aircraft, in a phenomenon known as radio blackout. Several methods have been proposed to mitigate radio blackout, amongst which is the "magnetic window". In the magnetic window method a magnetic field is imposed near the antenna, opening a spectral window, allowing the passage of electromagnetic waves without distortion. Experimental replication of hypersonic flight is extremely costly, generating a keen interest in the development of numerical codes capable of simulating weakly ionized flow around a hypersonic vehicle. This is specially relevant for investigating blackout mitigation methods, since a validated numerical code will allow the preliminary design and optimization of new concepts, in a much faster and cheaper way. A numerical code that is used to simulate a plasma layer around an aircraft needs to accurately predict the electron density and associated plasma properties. Several distinct chemistry models have been proposed. In this paper, four chemistry models will be studied, each accounting for 11 species commonly found in an atmospheric plasma layer: N2; O2; NO; N; O; N2+ ; O2+ ; NO+; N+; O+ and e−. The electron number density calculated with each model is compared with the electron number density calculated in the RAM-C II experimental flight. The models will be compared in terms of simulation runtime as well, in an attempt to assess which requires less processing power.
8.	Dias, F., et al. (author) Numerical analysis of a multi-species MHD model for plasma layer control of re-entry vehicles 2018 In: ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE). - 9780791852002 ; 1 Conference paper (peer-reviewed)abstract Several critical aspects control the successful reentry of vehicles on the earth’s atmosphere: continuous communication, GPS signal reception and real-time telemetry. However, there are some common issues that can interfere with the instruments operation, the most typical being the radio blackout, in which the plasma layer frequency modifies the electromagnetic waves in a way that makes communications to and from the spacecraft impossible. So far, there have been several proposed techniques to mitigate radio blackout, one of which is the usage of electromagnetic fields. Previous studies have proven the effectiveness of the usage of an electric and/or magnetic fields to manipulate plasma layers. Experiments on plasma layer manipulation during hypersonic flight regime are extremely costly. Therefore, there has been a continuous interest in the development of cheaper solutions, that can guarantee a reliable degree of accuracy, such as the development of complex multiphysics computational models. These models are becoming increasingly realistic and accurate, as more and more physical aspects can be considered, greatly increasing the accuracy and range of models. However, those models need to be validated with recourse to experimental data. In this paper we propose a model that uses a Low Magnetic Reynolds number, and accounts for five common neutral species: N2, O2, NO, N and O, along with several of their respective reactions: dissociation of molecular nitrogen and oxygen, and exchange. The model chemistry is then validated based on experimental data gathered by several authors.
9.	Dias, F., et al. (author) Numerical Computations of MHD Flow on Hypersonic and Re-Entry Vehicles 2016 In: Proceedings of the ASME International Mechanical Engineering Congress and Exposition (IMECE2016). ; 1, s. Paper No. IMECE2016-65676 Conference paper (peer-reviewed)abstract In hypersonic flight of reentry vehicles the radio blackout is a typical problem, in particular because it arises during a critical mission operation point. To mitigate this radio blackout the magnetic window concept is proposed. In this work a numerical model is presented to accurately simulate the effect of a magnetic field interacting with ionized plasma surrounding the vehicle. The numerical model is based on the MHD flow equations. Initially, the code is validated for pure hypersonic gas dynamics. Diverse high resolution spatial discretisation schemes, within a Finite Volume framework, are analyzed for robustness. Afterwards, the numerical code is further validated for MHD flows using the well-known Hartmann case. A very good comparison between numerical and analytical results is verified. This allows a proper validation of the method in terms of Lorentz force, in particular under low-magnetic Reynolds number conditions. A very tough test-case is finally computed, being typical of a reentry capsule geometry. The accuracy of the model is then verified for different applied magnetic fields.
10.	Grewe, V., et al. (author) Evaluating the climate impact of aviation emission scenarios towards the Paris agreement including COVID-19 effects 2021 In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 12:1 Journal article (peer-reviewed)abstract Aviation is an important contributor to the global economy, satisfying society’s mobility needs. It contributes to climate change through CO2 and non-CO2 effects, including contrail-cirrus and ozone formation. There is currently significant interest in policies, regulations and research aiming to reduce aviation’s climate impact. Here we model the effect of these measures on global warming and perform a bottom-up analysis of potential technical improvements, challenging the assumptions of the targets for the sector with a number of scenarios up to 2100. We show that although the emissions targets for aviation are in line with the overall goals of the Paris Agreement, there is a high likelihood that the climate impact of aviation will not meet these goals. Our assessment includes feasible technological advancements and the availability of sustainable aviation fuels. This conclusion is robust for several COVID-19 recovery scenarios, including changes in travel behaviour.
11.	Grönstedt, Tomas, 1970, et al. (author) Multidisciplinary assessment of a year 2035 turbofan propulsion system 2022 In: 33rd Congress of the International Council of the Aeronautical Sciences, ICAS 2022. - : International Council of the Aeronautical Sciences. - 9781713871163 ; 7, s. 4981-4990 Conference paper (peer-reviewed)abstract A conceptual design of a year 2035 turbofan is developed and integrated onto a year 2035 aircraft model. The mission performance is evaluated for CO2, noise and NOx and is compared with a notional XWB/A350-model. An OGV heat exchanger is then studied rejecting heat from an electric generator, and its top-level performance is evaluated. The fan, the booster and the low-pressure turbine of the propulsion system are subject to more detailed aero design based on using commercial design tools and CFD-optimization. Booster aerodynamic modelling output is introduced back into the performance model to study the integrated performance of the component. The top-level performance aircraft improvements are compared to top-level-trends and ICAO estimates of technology progress potential, attempting to evaluate whether there is some additional margin for efficiency improvement beyond the ICAO technology predictions for the same time frame.
12.	Grönstedt, Tomas, 1970, et al. (author) Ultra low emission technology innovations for mid-century aircraft turbine engines 2016 In: ASME Turbo EXPO 2016, Seoul, June 13-17, South Korea. - 9780791849743 ; 3:GT2016-56123 Conference paper (peer-reviewed)abstract Commercial transport fuel efficiency has improved dramatically since the early 1950s. In the coming decades the ubiquitous turbofan powered tube and wing aircraft configuration will be challenged by diminishing returns on investment with regards to fuel efficiency. From the engine perspective two routes to radically improved fuel efficiency are being explored; ultra-efficient low pressure systems and ultra-efficient core concepts. The first route is characterized by the development of geared and open rotor engine architectures but also configurations where potential synergies between engine and aircraft installations are exploited. For the second route, disruptive technologies such as intercooling, intercooling and recuperation, constant volume combustion as well as novel high temperature materials for ultra-high pressure ratio engines are being considered. This paper describes a recently launched European research effort to explore and develop synergistic combinations of radical technologies to TRL 2. The combinations are integrated into optimized engine concepts promising to deliver ultra-low emission engines. The paper discusses a structured technique to combine disruptive technologies and proposes a simple means to quantitatively screen engine concepts at an early stage of analysis. An evaluation platform for multidisciplinary optimization and scenario evaluation of radical engine concepts is outlined.
13.	Jonsson, Isak, 1990, et al. (author) Design and pre-test evaluation of a low-pressure compressor test facility for cryogenic hydrogen fuel integration 2021 In: Proceedings of the ASME Turbo Expo. ; 2A-2021 Conference paper (peer-reviewed)abstract The use of hydrogen as aviation fuel is again resurfacing with unprecedented vigor. It is well known that hydrogen is a formidable heat sink and the use of heat sinks in the compression system of an aero engine may enable not only preheating of the fuel but also improve the gas turbine cycle itself. One such opportunity arises from extracting heat to the fuel as part of the compression process. This work presents the design process and pre-test evaluation of a low-speed compressor test facility dedicated to aerothermal measurements. The design has been derived from a high-speed transonic compressor developed for a large sized geared turbofan engine. The proposed pre-test evaluation methodology provides a comprehensive and affordable way to estimate facility accuracy by virtually addressing all the experimental procedures, from data acquisition to a final performance map. The evaluation of gathering compressor performance parameters via a gas-path investigation process was achieved while relying on results from numerical simulations. The pre-test evaluation details uncertainties introduced throughout this process with transducers, flow and probe specific errors, traverse discretization, and data normalization. A suitable instrumentation configuration is presented which shows that the performance parameters pressure ratio (P) and isentropic efficiency (hc) can be determined with uncertainties below 1% for most operating conditions and below 0.5% at design conditions.
14.	Jonsson, Isak, 1990, et al. (author) Design of Chalmers new low-pressure compressor test facility for low-speed testing of cryo-engine applications 2021 In: 14th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2021. ; 14 Conference paper (peer-reviewed)abstract As a part of the ongoing Horizon 2020 ENABLEH2 project, a new low-speed compressor test facility is being constructed at the Chalmers University Laboratory of Fluids and Thermal Sciences. The ENABLEH2 project investigates critical technologies for cryogenic H2 applications in commercial aviation, including new combustion and heat management systems. This paper revolves around the design and construction of a core cooling flow facility which was commissioned to study and verify the potential benefits of incorporating a heat management system into the intermediate compressor duct (ICD). The test facility is designed to operate continuously at rotor midspan chord Reynolds number up to 600,000 to allow for detailed aerothermal studies at a technical readiness level four. The two-stage axial compressor is representative of the low-pressure compressor and ICD of a mid-size commercial jet engine. The compressor is powered by a 147kW electric motor at 1920 RPM. The mass-flow and pressure ratio are controlled by restricting valves located at the inlet of the facility. A compact volute settling chamber, with an integrated thermal control system is used to control the inlet temperature and remove flow non-uniformities downstream the restrictor valves before entering the compressor. At the compressor inlet, a turbulence mesh is mounted to increase the turbulence intensity levels to 3-4% at the leading edge of the variable inlet guide vanes. The compressor is mounted vertically to allow for easy access to the downstream ICD and mitigate non-axisymmetric mechanical loads. The compressor unit allows for optical and traverse access at two +- 9-degree sectors for all the rotor-stator interfaces. Upstream the OGV, there are four independent $\pm$ 180-degree access traverse systems. In the ICD, measurements are carried out by a single ABB robot with a U-shaped probe mount, providing full volume probing access of the ICD. At the first design iteration the ICD is designed to be instrumented with multi-hole probes, hot-wire anemometry and heat transfer measurement using IR-thermography. The paper describes the facility and the process of achieving a high case similarity (engine representative) while maximising the quality of the experimental data over a large test domain, targets that often produce conflicting design demands.
15.	Jonsson, Isak, 1990, et al. (author) Effect of heat exchanger integration in aerodynamic optimization of an aggressive S-duct 2022 In: ICAS PROCEEDINGS. - 2958-4647. ; 7, s. 4920-4928 Conference paper (peer-reviewed)abstract Intercooling the core flow in the compression process using bypass air can potentially reduce fuel consumption in commercial aviation. However, one of the critical challenges with intercooling is the installation and weight penalty due to complex ducting and large surface area for air-to-air heat exchangers (HEX). The recent interest in cryogenic hydrogen (LH2) as a potentially carbon-neutral fuel for commercial aviation expands the propulsive system’s design space due to the vastly different fuel properties between classical Jet-A and LH2. Regarding intercooling, LH2 adds a formidable heat sink with a high specific heat capacity and low storage temperature at 20K and, if utilised in the intercooling process, should allow for increased cooling power density with less installation penalties than an air-to-air HEX. Furthermore, the heat is transferred to the fuel instead of ejected into the bypass air which has potential thermodynamical benefits. The HEX can further be synergistically used to radial turn the core flow in the ICD. This paper presents the integration of a compact air-to-LH2 heat exchanger inside the gas path of the intermediate compressor duct (ICD) as the shape of a truncated cone. Axisymmetric numerical simulations areutilised to evaluate the duct performance and optimise hub and shroud lines for minimal pressure drop andoutlet uniformity. The HEX sizing was based on a preliminary system model of an LH2 commercial aviation engine with 70,000 lbs of thrust.
16.	Jonsson, Isak, 1990, et al. (author) Feasibility Study of a Radical Vane-Integrated Heat Exchanger for Turbofan Engine Applications 2020 In: Proceedings of the ASME Turbo Expo. ; 7C Conference paper (peer-reviewed)abstract The density of liquid hydrogen (LH2), at the normal boiling point, is two times higher than that of highly compressed hydrogen. This makes LH2 the prime candidate for hydrogen storage in aviation. However, LH2 is stored at cryogenic temperatures that require adequate insulation, as well as the integration of heat exchangers to warm up the hydrogen on its way to the combustion chamber. Ideally, the required heat exchangers are strategically placed in the engine core to produce optimum heat management, thus improving the engine efficiency, increase its durability as well as to reduce emissions. Moreover, the combination of hydrogen high specific heat with cryogenic temperatures results in formidable cooling capacity, that can be explored by more compact HEX solutions. The present work numerically investigates a novel concept of a compact compressor vane-integrated heat exchanger, for application in cryogenically fuelled gas turbine engines. The baseline engine used for establishing the HEX requirements is a large geared turbofan, operating on liquid hydrogen. The HEX aero-thermal performance is first estimated using zero-dimensional models and Chalmers in-house gas turbine performance tool GESTPAN. After, the conceptual design of an outlet guide vane-HEX is developed and integrated into a three-stage low-pressure compressor. The baseline compressor geometry is a lightly loaded high-speed booster with a design pressure ratio of 2.8. The multi-stage compressor with the integrated HEX is evaluated using steady-state computational fluid dynamics. Results allow to estimate the heat exchanger performance in terms of total pressure loss, heat transfer effectiveness, and the potential enhanced radial flow turning capability. Further, the impact of the new developed OGV-HEX on the compressor characteristics is also reported and discussed.
17.	Moraes Da Silva, Lucilene, 1987, et al. (author) Analysis of Blade Aspect Ratio’s Influence on High-Speed Axial Compressor Performance 2024 In: Aerospace. - 2226-4310. ; 11:4 Journal article (peer-reviewed)abstract The ratio between blade height and chord, named the aspect ratio (AR), plays an important role in compressor aerodynamic design. Once selected, it influences stage performance, blade losses and the stage stability margin. The choice of the design AR involves both aerodynamic and mechanical considerations, and an aim is frequently to achieve the desired operating range while maximizing efficiency. For a fixed set of aerodynamic and geometric parameters, there will be an optimal choice of AR that achieves a maximum efficiency. However, for a state-of-the-art aero-engine design, optimality means multi-objective optimality, that is, reaching the highest possible efficiency for a number of operating points while achieving a sufficient stability margin. To this end, the influence of the AR on the performance of the first rotor row of a multistage, multi-objective, high-speed compressor design is analyzed. A careful setup of the high-speed aerodynamic design problem allows the effect of the AR to be isolated. Close to the optimal AR, only a modest efficiency variation is observed, but a considerable change in compressor stability margin (SM) is noted. Decreasing the AR allows for increasing efficiency, but at the expense of a reduced surge margin. This allows the designer to trade efficiency for stability. Increasing the AR, however, is shown to reduce both the surge margin and efficiency; hence, a distinct optimality in stability is observed for the analyzed rotor blade row. In this work, optimality in the surge margin with respect to the AR is observed, whereas there is a close to optimal efficiency. The predicted range from AR = 1.10 to AR = 1.64 is only indicative, considering that the definition of multi-objective optimality requires balancing efficiency and the surge margin and that the choice of balancing these two criteria requires making a design choice along a pareto optimal front.
18.	Petit, Olivier, 1980, et al. (author) An outlook for radical aero engine intercooler concepts 2016 In: Proceedings of ASME Turbo Expo 2016: Turbine Technical Conference and Exposition, Seoul, South Korea, Jun 13-17, 2016. - 9780791849743 ; 3 Conference paper (peer-reviewed)abstract A state of the art turbofan engine has an overall efficiency of about 40%, typically composed of a 50% thermal and an 80% propulsive efficiency. Previous studies have estimated that intercooling may improve fuel burn on such an engine with a 3-5% reduction depending on mission length. The intercooled engine benefits stem firstly from a higher Overall Pressure Ratio (OPR) and secondly from a reduced cooling flow need. Both aspects relate to the reduced compressor exit temperature achieved by the intercooler action. A critical aspect of making the intercooler work efficiently is the use of a variable intercooler exhaust nozzle. This allows reducing the heat extracted from the core in cruise operation as well as reducing the irreversibility generated on the intercooler external surface which arises from bypass flow pressure losses. In this respect the improvements, higher OPR and lower cooling flow need, are achieved indirectly and not by directly improving the underlying thermal efficiency. This paper discusses direct methods to further improve the efficiency of intercooled turbofan engines, either by reducing irreversibility generated in the heat exchanger or by using the rejected heat from the intercooler to generate useful power to the aircraft. The performance improvements by using the nacelle wetted surface to replace the conventional intercooler surface is first estimated. The net fuel burn benefit is estimated at 1.6%. As a second option a fuel cooled intercooler configuration, operated during the climb phase, is evaluated providing a net fuel burn reduction of 1.3%. A novel concept that uses the rejected heat to generate additional useful power is then proposed. A secondary cycle able to convert rejected intercooler heat to useful thrust is used to evaluate three possible scenarios. The two first cases investigate the impact of the heat transfer rate on the SFC reduction. As a final consideration the geared intercooled engine cycle is re-optimized to maximize the benefits of the proposed heat recovery system. The maximum SFC improvement for the three cycles is established to 2%, 3.7% and 3%.
19.	Quaranta, Giuseppe, et al. (author) Aeroelastic Analysis of a Cycloidal Rotor Under Various Operating Conditions 2018 In: Journal of Aircraft. - 0021-8669 .- 1533-3868. ; 55:4, s. 1675-1688 Journal article (peer-reviewed)abstract The aeroelasticity of a cycloidal rotor in forward flight is investigated using an analytical and a numerical model; the latter is based on a multibody dynamics approach. Three experimental sources are used to validate the multibody model. The influence of the number of blades, their stiffnesses, and their skin thicknesses are investigated. At high pitch angles, before stall and flexibility effects occur, increasing the number of blades produces more thrust for the same power. Flexibility and skin thickness considerably affect the required pivot rod strength and blade deformation. Simply supported blades exhibit severe deformations when compared to clamped blades. Thrust and power are both influenced in a similar and moderate way by flexibility. The rotor response to wind gusts is also analyzed. The angular velocity of the rotor significantly affects the response of the rotor to wind gusts. The direction of the gusting wind has an important influence on power, whereas thrust increases regardless of wind direction. Finally, the rotor response lags minimally behind the arrival of the gust.
20.	Rodriguez Acero, Patxi Daniel, 1983, et al. (author) Experimental investigation of waste heat recovery concept in turbine rear structure for a Liquid Hydrogen Gas-Turbine 2023 In: Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer. - 2377-2816 .- 2642-5629. ; 1:10, s. 725-728 Conference paper (peer-reviewed)abstract The increasing governmental restrictions over CO2 emissions have made aviation companies search for another source of fuel to help in this reduction challenge. Liquid Hydrogen is emerging again as a possible clean substitute for conventional aircraft fuel. One of the main challenges is the increase of inlet fuel temperature from cryogenic to a more typical condition, such operation could be done by utilizing the otherwise wasted exhaust heat. This work presents an aerothermal experimental investigation of the outlet guide vanes in the Turbine Rear Structure, for its use as heat exchangers. The experimentation was carried out in the LPT-OGV test facility at Chalmers Laboratory of Thermal Sciences where the convective heat transfer coefficient was evaluated on the surfaces of a new OGV concept with two split-angled coupled vanes using an infrared thermography technique. The results of this study provide valuable insights for further development of heat-management systems in aviation, contributing towards sustainable and efficient aircraft propulsion.
21.	Rolt, Andrew, et al. (author) Scale effects on conventional and intercooled turbofan engine performance 2017 In: Aeronautical Journal. - : Cambridge University Press (CUP). - 0001-9240 .- 2059-6464. ; 121:1242, s. 1162-1185 Journal article (peer-reviewed)abstract New commercial aero engines for 2050 are expected to have lower specific thrusts for reduced noise and improved propulsive efficiency, but meeting the ACARE Flightpath 2050 fuel-burn and emissions targets will also need radical design changes to improve core thermal efficiency. Intercooling, recuperation, inter-turbine combustion and added topping and bottoming cycles all have the potential to improve thermal efficiency. However, these new technologies tend to increase core specific power and reduce core mass flow, giving smaller and less efficient core components. Turbine cooling also gets more difficult as engine cores get smaller. The core-size-dependent performance penalties will become increasingly significant with the development of more aerodynamically efficient and lighter-weight aircraft having lower thrust requirements. In this study the effects of engine thrust and core size on performance are investigated for conventional and intercooled aeroengine cycles. Large intercooled engines could have 3%-4% SFC improvement relative to conventional cycle engines, while smaller engines may only realize half of this benefit. The study provides a foundation for investigations of more complex cycles in the EU Horizon 2020 ULTIMATE programme.
22.	Sethi, V., et al. (author) Enabling Cryogenic Hydrogen-Based CO 2 -Free Air Transport: Meeting the demands of zero carbon aviation 2022 In: IEEE Electrification Magazine. - 2325-5889 .- 2325-5897. ; 10:2, s. 69-81 Journal article (other academic/artistic)abstract Flightpath 2050 from the European Union (EU) sets ambitious targets for reducing the emissions from civil aviation that contribute to climate change. Relative to aircraft in service in year 2000, new aircraft in 2050 are to reduce CO2 emissions by 75% and nitrogen oxide (NOx) emissions by 90% per passenger kilometer flown. While significant improvements in asset management and aircraft and propulsion-system efficiency and are foreseen, it is recognized that the Flightpath 2050 targets will not be met with conventional jet fuel. Furthermore, demands are growing for civil aviation to target zero carbon emissions in line with other transportation sectors rather than relying on offsetting to achieve 'net zero.' A more thorough and rapid greening of the industry is seen to be needed to avoid the potential economic and social damage that would follow from constraining air travel. This requires a paradigm shift in propulsion technologies. Two technologies with potential for radical decarbonization are hydrogen and electrification. Hydrogen in some form seems an inevitable solution for a fully sustainable aviation future. It may be used directly as a fuel or combined with carbon from direct air capture of CO2 or other renewable carbon sources, to synthesize drop-in replacement jet fuels for existing aircraft and engines. As a fuel, pure hydrogen can be provided as a compressed gas, but the weight of the storage bottles limits the practical aircraft ranges to just a few times that is achievable with battery power. For longer ranges, the fuel needs to be stored at lower pressures in much lighter tanks in the form of cryogenic liquid hydrogen (LH2).
23.	Silva, Vinicius T., et al. (author) Powered Low-Speed Experimental Aerodynamic Investigation of an Over-Wing-Mounted Nacelle Configuration 2024 In: Journal of Aircraft. - 0021-8669 .- 1533-3868. ; 61:2, s. 415-424 Journal article (peer-reviewed)abstract Over-wing integration of ultrahigh bypass turbofan engines can be a solution for next-generation commercial transport aircraft since it eliminates the ground clearance issue and it has the potential to reduce ground noise due to acoustic shielding. Moreover, a unique characteristic of this installation type is the powered lift benefit at low-speed flight conditions. This paper aims to experimentally investigate the effect of the engine power setting on the low-speed aerodynamic performance of an over-wing-mounted nacelle configuration comprising a conventional tube-and-wing layout. Thus, low-speed wind tunnel tests were performed for a half-span powered scale model of the aforementioned configuration. The effect of the engine power setting on the wing lift and spanwise pressure distributions was investigated. The experiments were carried out for angles of attack varying from 0 to 6 degrees and inlet mass flow ratios up to 2.4. The results were used to validate computational fluid dynamics simulations conducted for the same wind tunnel conditions. It has been shown that a significant powered lift benefit can be achieved for the studied configuration, without a penalty in the net propulsive force and that the lift increases linearly with the inlet mass flow ratio. Furthermore, it was observed that the engine power setting largely influences the pressure distributions along the wing, especially at the spanwise sections closer to the nacelle. The low-momentum zone created upstream of the engine at high power settings reduces the pressure at the wing's upper surface, which is the main factor responsible for the increased lift. By taking advantage of such behavior, drag can potentially be reduced at takeoff and climb due to a lower flap setting required for the same lift.
24.	Sjögren, Oliver, 1993, et al. (author) Estimation of Design Parameters and Performance for a State-of-the-Art Turbofan 2021 In: Proceedings of the ASME Turbo Expo. ; 1 Conference paper (peer-reviewed)abstract The aim of this study is to explore the possibility of matching a cycle performance model to public data on a state-of-the-art commercial aircraft engine (GEnx-1B). The study is focused on obtaining valuable information on figure of merits for the technology level of the low-pressure system and associated uncertainties. It is therefore directed more specifically towards the fan and low-pressure turbine efficiencies, the Mach number at the fan-face, the distribution of power between the core and the bypass stream as well as the fan pressure ratio. Available cycle performance data have been extracted from the engine emission databank provided by the International Civil Aviation Organization (ICAO), type certificate datasheets from the European Union Aviation Safety Agency (EASA) and the Federal Aviation Administration (FAA), as well as publicly available data from engine manufacturer. Uncertainties in the available source data are estimated and randomly sampled to generate inputs for a model matching procedure. The results show that fuel performance can be estimated with some degree of confidence. However, the study also indicates that a high degree of uncertainty is expected in the prediction of key low-pressure system performance metrics, when relying solely on publicly available data. This outcome highlights the importance of statistic-based methods as a support tool for the inverse design procedures. It also provides a better understanding on the limitations of conventional thermodynamic matching procedures, and the need to complement with methods that take into account conceptual design, cost and fuel burn.
25.	Sjögren, Oliver, 1993, et al. (author) FAN STAGE DESIGN AND PERFORMANCE OPTIMIZATION FOR LOW SPECIFIC THRUST TURBOFANS 2023 In: International Journal of Turbomachinery, Propulsion and Power. - 2504-186X. ; 8:4 Journal article (peer-reviewed)abstract In modern turbofan engines the bypass section of the fan stage alone provides the majority of the total thrust in cruise and the size of the fan has a considerable effect on overall engine weight and nacelle drag. Thrust requirements in different parts of the flight envelope must also be satisfied together with sufficient margins towards stall. An accurate description of the interdependencies of relevant performance and design attributes of the fan stage alone - such as efficiency, surge margin, fan-face Mach number, stage loading, flow coefficient and aspect ratio - are therefore necessary to estimate system level objectives such as mission fuel burn and direct operating cost with enough confidence during the conceptual design phase. The contribution of this study is to apply a parametric optimization approach to conceptual design of fan stages for low specific thrust turbofans based on the streamline curvature method. Trade-offs between fan stage attributes for Pareto-optimal solutions are modelled by training a Kriging surrogate model on the results from the parametric optimization. The trends predicted by the resulting surrogate model are analyzed both quantitatively and qualitatively. Most of the trends could be justified with some degree of physical reasoning or comparison with common guidelines from the literature. Trends of stage efficiency with Mach number and stage loading may indicate that shock losses have a larger impact on stage efficiency for designs with low stage loading compared to designs with high stage loading. Means to reduce the strength of the passage shock wave, such as blade sweep, may therefore be of more importance as stage loading is reduced.

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