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1.	Grönstedt, Tomas, 1970, et al. (författare) Multidisciplinary assessment of a year 2035 turbofan propulsion system 2022 Ingår i: 33rd Congress of the International Council of the Aeronautical Sciences, ICAS 2022. - : International Council of the Aeronautical Sciences. - 9781713871163 ; 7, s. 4981-4990 Konferensbidrag (refereegranskat)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.
2.	Zhao, Xin, 1986, et al. (författare) Experimental Validation of the Aerodynamic Characteristics of an Aero-engine Intercooler 2017 Ingår i: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 139:5 Tidskriftsartikel (refereegranskat)abstract Porous media model computational fluid dynamics (CFD) is a valuable approach allowing an entire heat exchanger system, including the interactions with its associated installation ducts, to be studied at an affordable computational effort. Previous work of this kind has concentrated on developing the heat transfer and pressure loss characteristics of the porous medium model. Experimental validation has mainly been based on the measurements at the far field from the porous media exit. Detailed near field data are rare. In this paper, the fluid dynamics characteristics of a tubular heat exchanger concept developed for aero-engine intercooling by the authors are presented. Based on a rapid prototype manufactured design, the detailed flow field in the intercooler system is recorded by particle image velocimetry (PIV) and pressure measurements. First, the computational capability of the porous media to predict the flow distribution within the tubular heat transfer units was confirmed. Second, the measurements confirm that the flow topology within the associated ducts can be described well by porous media CFD modeling. More importantly, the aerodynamic characteristics of a number of critical intercooler design choices have been confirmed, namely, an attached flow in the high velocity regions of the in-flow, particularly in the critical region close to the intersection and the in-flow guide vane, a well-distributed flow in the two tube stacks, and an attached flow in the cross-over duct.
3.	Camilleri, William, et al. (författare) Concept description and assessment of the main features of a geared intercooled reversed flow core engine 2015 Ingår i: Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering. - : SAGE Publications. - 0954-4100 .- 2041-3025. ; 229:9, s. 1631-1639 Tidskriftsartikel (refereegranskat)abstract Intercooled turbofan cycles allow higher overall pressure ratios to be reached which gives rise to improved thermal efficiency. Intercooling also allows core mass flow rate to be reduced which facilitates higher bypass ratios. A new intercooled core concept is proposed in this paper which promises to alleviate limitations identified with previous intercooled turbofan designs. Specifically, these limitations are related to core losses at high overall pressure ratios as well as difficulties with the installation of the intercooler. The main features of the geared intercooled reversed flow core engine are described. These include an intercooled core, a rear-mounted high-pressure spool fitted rearwards of the low-pressure spool as opposed to concentrically as well as a mixed exhaust. In these studies, the geared intercooled reversed flow core engine has been compared with a geared intercooled straight flow core engine with a more conventional core layout. This paper compares the mechanical design of the high-pressure spools and shows how different high-pressure compressor and high-pressure turbine blade heights can affect over-tip leakage losses. In the reversed configuration, the reduction in high-pressure spool mean diameter allows for taller high-pressure compressor and turbine blades to be adopted which reduces over-tip leakage losses. The implication of intercooler sizing and configuration, including the impact of different matrix dimensions, is assessed for the reversed configuration. It was found that a 1-pass intercooler would be more compact although a 2-pass would be less challenging to manufacture. The mixer performance of the reversed configuration was evaluated at different levels of mixing effectiveness. This paper shows that the optimum ratio of total pressure in the mixing plane for the reversed flow core configuration is about 1.02 for a mixing effectiveness of 80%. Lower mixing effectiveness would result in a higher optimum ratio of total pressure in the mixing plane and fan pressure ratio.
4.	Hecken, Tobias, et al. (författare) Conceptual Design Studies of “Boosted Turbofan” Configuration for short range 2020 Ingår i: AIAA 2020-0506 Session: Hybrid Electric Aircraft Design Under Clean Sky 2 (LPA WP1.6.1.4). - Reston, Virginia : American Institute of Aeronautics and Astronautics. Konferensbidrag (refereegranskat)abstract This paper describes the current activities at the German Aerospace Center (DLR) and an associated consortium related to conceptual design studies of an aircraft configuration with hybrid electric propulsion for a typical short range commercial transport mission. The work is implemented in the scope of the European Clean Sky 2 program in the project “Advanced Engine and Aircraft Configurations” (ADEC) and “Turbo electric Aircraft Design Environment” (TRADE). The configuration analyzed incorporates parallel hybrid architecture consisting of gas turbines, electric machines, and batteries that adds electric power to the fans of the engines. A conceptual aircraft sizing workflow built in the DLR’s “Remote Component Environment” (RCE) incorporating tools of DLR that are based on semi-empirical and low level physics based methods. The TRADE consortium developed a simulation and optimization design platform with analysis models of higher fidelity for an aircraft with hybrid electric propulsion architecture. An implementation of the TRADE simulation and optimization design platform into the DLR’s RCE workflow by replacing the DLR models was carried out. The focus of this paper is on the quantitative evaluation of the “Boosted Turbofan” configuration utilizing the resulting workflow. In order to understand the cooperation between the DLR and TRADE consortium, a brief overview of the activities is given. Then the multi-disciplinary overall aircraft sizing workflow for hybrid electric aircraft built in RCE is shown. Hereafter, the simulation and optimization models of the TRADE design platform are described. Subsequently, an overview of the aircraft configuration considered in the scope of this work is given. The design space studies of the “Boosted Turbofan” configuration are presented. Finally, the deviations of the results between the workflows with and without the TRADE modules are discussed.
5.	Jouannet, Christopher, et al. (författare) SUSTAINABLE AVIATION FOR SWEDEN - TECHNOLOGY & CAPABILITY ASSESSMENT TARGETING 2045 2022 Ingår i: 33rd CONGRESS OF THE INTERNATIONAL COUNCIL OF THE AERONAUTICAL SCIENCES. - 2958-4647. Konferensbidrag (refereegranskat)abstract The goal of this project is to analyse the possibilities offered by different technological solutions to achieve zero emission aviation, firstly in the Swedish/Nordic network context and secondly extend this to the European context. This project will investigate the potential and feasibility of new or upgraded aircraft types based on the different technologies mapped from both, various published roadmaps and national expertise from Swedish aerospace universities and companies. This involves developing aircraft conceptual designs studies and trade analysis with regards to different fuel types, propulsion technologies, structure, operations, network and fleet management, and all relevant technologies. The project will, on a common technology basis, analyse a range of zero carbon fuels and associated technologies through operational studies and optimization to accelerate the introduction of fossil free aircraft technology and choosing optimal paths for making aviation sustainable.
6.	Ma, Jinchen, et al. (författare) Sulfur fate during in-situ gasification chemical looping combustion (iG-CLC) of coal 2021 Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 406 Tidskriftsartikel (refereegranskat)abstract Sulfur conversion during in-situ gasification chemical looping combustion (iG-CLC) of coal is consisted by pyrolysis and char gasification. Insight into the fate of sulfur in these two processes is essential for exploring appropriate strategies for sulfur emission control, whereas in most of works the pyrolysis and gasification could not be fully identified. In this case, a two-stage fluidized bed reactor system comprising a lower and a higher reactor was used to generate in-situ and separate gases from pyrolysis and gasification in this work. Sulfurous gases including H2S, COS, CS2 and SO2 were experimentally studied under various conditions by changing operation temperature (T), O/fuel ratio (Φ) and OC reduction degree (XOC), while the solid samples were regularly collected for the characterization using different techniques. It was found that the sol-gel Fe2O3/Al2O3 was a sulfur resistant OC during the iG-CLC process, thus no formation of sulfur components in the material. The values of T and Φ have positive effect on the conversion of sulfurous gases to SO2, whereas a lower XOC value can improve the conversion of H2S. The main components from volatiles (mainly H2S and CS2) and from char (mainly COS) can be effectively converted to SO2 by the OC material. The coal ash exhibited a desulfurization function, as some sulfur contents were retained as CaSO4 during the iG-CLC tests. Finally, the fate of sulfur in coal during iG-CLC was comprehensively mapped, which would be significant for developing strategies for sulfur emission control.
7.	Petit, Olivier, 1980, et al. (författare) An outlook for radical aero engine intercooler concepts 2016 Ingår i: Proceedings of ASME Turbo Expo 2016: Turbine Technical Conference and Exposition, Seoul, South Korea, Jun 13-17, 2016. - 9780791849743 ; 3 Konferensbidrag (refereegranskat)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%.
8.	Sahoo, Smruti, et al. (författare) A Review of Concepts, Benefits, and Challenges for Future Electrical Propulsion-Based Aircraft 2020 Ingår i: Aerospace. - : MDPI AG. - 2226-4310. ; 7:4 Forskningsöversikt (refereegranskat)abstract Electrification of the propulsion system has opened the door to a new paradigm of propulsion system configurations and novel aircraft designs, which was never envisioned before. Despite lofty promises, the concept must overcome the design and sizing challenges to make it realizable. A suitable modeling framework is desired in order to explore the design space at the conceptual level. A greater investment in enabling technologies, and infrastructural developments, is expected to facilitate its successful application in the market. In this review paper, several scholarly articles were surveyed to get an insight into the current landscape of research endeavors and the formulated derivations related to electric aircraft developments. The barriers and the needed future technological development paths are discussed. The paper also includes detailed assessments of the implications and other needs pertaining to future technology, regulation, certification, and infrastructure developments, in order to make the next generation electric aircraft operation commercially worthy.
9.	Seitz, Arne, et al. (författare) Proof of concept study for fuselage boundary layer ingesting propulsion 2021 Ingår i: Aerospace. - : MDPI AG. - 2226-4310. ; 8:1, s. 1-65 Tidskriftsartikel (refereegranskat)abstract Key results from the EU H2020 project CENTRELINE are presented. The research activities undertaken to demonstrate the proof of concept (technology readiness level-TRL 3) for the so-called propulsive fuselage concept (PFC) for fuselage wake-filling propulsion integration are discussed. The technology application case in the wide-body market segment is motivated. The developed performance bookkeeping scheme for fuselage boundary layer ingestion (BLI) propulsion integration is reviewed. The results of the 2D aerodynamic shape optimization for the bare PFC configuration are presented. Key findings from the high-fidelity aero-numerical simulation and aerodynamic validation testing, i.e., the overall aircraft wind tunnel and the BLI fan rig test campaigns, are discussed. The design results for the architectural concept, systems integration and electric machinery pre-design for the fuselage fan turbo-electric power train are summarized. The design and performance implications on the main power plants are analyzed. Conceptual design solutions for the mechanical and aerostructural integration of the BLI propulsive device are introduced. Key heuristics deduced for PFC conceptual aircraft design are presented. Assessments of fuel burn, NOx emissions, and noise are presented for the PFC aircraft and benchmarked against advanced conventional technology for an entry-into-service in 2035. The PFC design mission fuel benefit based on 2D optimized PFC aero-shaping is 4.7%.
10.	Sielemann, M., et al. (författare) Introduction to multi-point design strategies for aero engines 2020 Ingår i: Proceedings of the ASME Turbo Expo. - : American Society of Mechanical Engineers (ASME). - 9780791884157 ; 6 Konferensbidrag (refereegranskat)abstract Classic gas turbine design relies on the definition of a design point, and the subsequent assessment of the design on a range of off-design conditions. On the design point, both component sizing (e.g., in terms of physical dimensions or in terms of map scaling parameters) and a solution to the off-design governing equations are established. With this approach, it is however difficult to capture the contradicting requirements on the full operating envelope. Thus, practical design efforts rely on various multi-point design approaches. This paper introduces a simplified notation of such multi-point approaches via synthesis matching tables. It then summarizes two academic state-of-the-art multi-point design schemes using such tables in a comprehensible fashion. The target audience are students and engineers familiar with the basics of classic cycle design and analysis looking for a practical introduction to such multi-point design approaches. Application examples are given in terms of a simple turbojet and a typical geared turbofan as modeled in state-of-the-art academic cycle design and analysis efforts. The results of the classic design point approach are compared to those of multi-point approaches. Copyright © 2020 ASME
11.	Sielemann, M., et al. (författare) Multi-point design of parallel hybrid aero engines 2020 Ingår i: AIAA Propulsion and Energy 2020 Forum. - Västerås : Institute of Electrical and Electronics Engineers Inc.. - 9781624106026 ; , s. 1-18 Konferensbidrag (refereegranskat)abstract A parallel hybrid configuration is a feasible means to reduce fuel consumption of gas turbines propelling aircraft. It introduces an electric drive on one of the spools of the gas turbine, typically the low pressure spool. The electric drive is supplied by a battery, which can also be charged when excess power is available (for instance during conditions requiring handling bleed in conventional designs). It also requires a thermal management system to dissipate heat away from electric components. While the scientific literature describes parallel hybrid studies and anticipated benefits assuming various future entry into service dates, there is limited information on the design of the gas turbine component of such a system. For conventional gas turbines, multi-point design schemes are used. This paper describes, in a consistent fashion and based on a formalized notation, how such multi-point design schemes are applied to parallel hybrid aero engines. It interprets published approaches, fills gaps in methodology descriptions with meaningful assumptions and summarizes design intent. It also discusses cycle designs generated by different methodologies based on the same cycle model. Results show that closure equations prescribing boost power can be preferable over closure equations prescribing temperature ratios for uniqueness and engineering intuitiveness while the latter can be beneficial in a second step for design space exploration.
12.	Sielemann, M., et al. (författare) ON the SHAFT SPEED SELECTION of PARALLEL HYBRID AERO ENGINES 2021 Ingår i: Proceedings of the ASME Turbo Expo. - : American Society of Mechanical Engineers (ASME). - 9780791884898 ; 1 Konferensbidrag (refereegranskat)abstract The boosted turbo fan or parallel hybrid is a promising means to reduce fuel consumption of gas turbines on aircraft. With an electric drive on the low-pressure spool of the gas turbine, it requires a trade-off between the characteristics of the gas turbine and the electric power sub-systems. Reducing specific thrust at a given thrust requirement results in a larger fan with a lower pressure ratio. This leads to improved propulsive efficiency but at the expense of increased weight and nacelle drag. At a given design relative tip Mach number, increasing fan size and hence tip diameter means the fan shaft speed will need to be reduced. This will, according to occasionally quoted rules of thumb', make the directly coupled electrical drive more efficient but heavier. The objective of this paper is to expose some key aspects of this trade-off in terms of efficiency and weight, and relate them to these guidelines. The paper applies sophisticated methodology in both addressed domains. For the gas turbine, multi-point design is used. Here, established synthesis matching schemes focusing on gas turbine performance parameters are extended with parameters from the sizing and weight estimation such as diameters and tip speeds. For the electrical machine, fully analytical sizing capturing the impact of cooling supply is used. The paper reports estimated gas path and machine geometries. It gives an understanding of the interactions between both sub-systems and allows concluding which low pressure spool speed gives the best instantaneous performance. It largely confirms the quoted rules of thumb but exposes that the factors affecting machine efficiency are more involved than implied for an integrated design.
13.	Thoma, Evangelia Maria, 1996, et al. (författare) Assessment of an Open-Source Aircraft Noise Prediction Model Using Approach Phase Measurements 2024 Ingår i: Journal of Aircraft. - 0021-8669 .- 1533-3868. ; 61:3, s. 745-760 Tidskriftsartikel (refereegranskat)abstract An open-source simulation model for aircraft noise prediction is presented and validated using backpropagated noise measurements for a state-of-the-art engine and aircraft. The validation is focused on approach procedures and was performed using ground-based noise measurements that were taken at 17 recording stations for a total of 18 consecutive flights carried out during the morning of 8 April 2021. The flights were performed using two A321neo aircraft with LEAP-1A engines. It is demonstrated that the presented noise model provides a satisfactory estimation of the source noise for varying approach configurations and flight conditions. Configurations using a greater number of high-lift devices are particularly well predicted in the mid- and high-frequency regions, whereas the lower configuration settings show greater spectral deviations, which are partly attributed to measurement uncertainties caused by the increased aircraft–microphone distance. The model can predict the overall mean total sound intensity level within a 2 dB accuracy for all configurations, while the average predicted level at each microphone differs by less than 3 dB from the measurement average, for all cases except one. Variation in aircraft speed showed to have a strong impact on the predicted total noise, which matches the well-recognized sixth-power Mach number far-field sound intensity scaling law for airframe noise models, while the measurements indicated a less significant dependency. This is mainly due to installation effects and noise reduction measures that are not included in the models. Nevertheless, the variations in the spectra of the predicted and measured noise showed similar patterns.
14.	Thoma, Evangelia Maria, 1996, et al. (författare) Environmental Assessment of Noise Abatement Approach Trajectories 2022 Ingår i: 33rd Congress of the International Council of the Aeronautical Sciences, ICAS 2022, International Council of the Aeronautical Sciences. - : International Council of the Aeronautical Sciences. ; 7, s. 5308-5320 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Noise abatement procedures are one of the main actions implemented to reduce noise pollution around airports. In this study, the focus is turned on approach operations and their environmental impact. The assessment starts from standard optimized procedures, namely the Continuous Descent Approach (CDA) and the Low Drag Low Power (LDLP) and the aim is to look into more advanced procedures, such as a Steep and a Segmented CDA, an Advanced LDLP and an optimized trajectory for the specific flight conditions. The procedures are designed for an A321neo and compared and evaluated for noise and emissions. It is demonstrated that multidisciplinary design and adaptation to specific conditions are required for the assessment of these interdependencies for flight procedures.
15.	Thoma, Evangelia Maria, 1996, et al. (författare) Noise from Flight Procedure Designed with Statistical Wind: Auralization and Psychoacoustic Evaluation 2024 Ingår i: 30th AIAA/CEAS Aeroacoustics Conference. Konferensbidrag (refereegranskat)
16.	Thoma, Evangelia Maria, 1996, et al. (författare) Quantifying the Environmental Design Trades for a State-of-the-Art Turbofan Engine 2020 Ingår i: Aerospace. - : MDPI AG. - 2226-4310. ; 7:10, s. 1-16 Tidskriftsartikel (refereegranskat)abstract Aircraft and engine technology have continuously evolved since their introduction and significant improvement has been made in fuel efficiency, emissions, and noise reduction. One of the major issues that the aviation industry is facing today is pollution around the airports, which has an effect both on human health and on the climate. Although noise emissions do not have a direct impact on climate, variations in departure and arrival procedures influence both CO2 and non-CO2 emissions. In addition, design choices made to curb noise might increase CO2 and vice versa. Thus, multidisciplinary modeling is required for the assessment of these interdependencies for new aircraft and flight procedures. A particular aspect that has received little attention is the quantification of the extent to which early design choices influence the trades of CO2, NOx, and noise. In this study, a single aisle thrust class turbofan engine is optimized for minimum installed SFC (Specific Fuel Consumption). The installed SFC metric includes the effect of engine nacelle drag and engine weight. Close to optimal cycles are then studied to establish how variation in engine cycle parameters trade with noise certification and LTO (Landing and Take-Off) emissions. It is demonstrated that around the optimum a relatively large variation in cycle parameters is allowed with only a modest effect on the installed SFC metric. This freedom in choosing cycle parameters allows the designer to trade noise and emissions. Around the optimal point of a state-of-the-art single aisle thrust class propulsion system, a 1.7 dB reduction in cumulative noise and a 12% reduction in EINOx could be accomplished with a 0.5% penalty in installed SFC.
17.	Thulin, Oskar, 1987, et al. (författare) First and second law analysis of radical intercooling concepts 2017 Ingår i: Proceedings of the ASME Turbo Expo. - 9780791850770 ; 1 Konferensbidrag (refereegranskat)abstract An exergy framework was developed taking into consideration a detailed analysis of the heat exchanger (intercooler) component irreversibilities. Moreover, it was further extended to include an adequate formulation for closed systems, e.g. a secondary cycle, moving with the aircraft. Afterwards the proposed framework was employed to study two radical intercooling concepts. The first proposed concept uses already available wetted surfaces, i.e. nacelle surfaces, to reject the core heat and contribute to an overall drag reduction. The second concept uses the rejected core heat to power a secondary organic Rankine cycle and produces useful power to the aircraft-engine system. Both radical concepts are integrated into a high bypass ratio turbofan engine, with technology levels assumed to be available by year 2025. A reference intercooled cycle incorporating a heat exchanger in the bypass duct is established for comparison. Results indicate that the radical intercooling concepts studied in this paper show similar performance levels to the reference cycle. This is mainly due to higher irreversibility rates created during the heat exchange process. A detailed assessment of the irreversibility contributors, including the considered heat exchangers and the secondary cycle major components is made. A striking strength of the present analysis is the assessment of the component irreversibility rate and its contribution to the overall aero-engine losses.
18.	Thulin, Oskar, 1987, et al. (författare) First and Second Law Analysis of Radical Intercooling Concepts 2018 Ingår i: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 140:8, s. 081201-081201-10 Tidskriftsartikel (refereegranskat)abstract An exergy framework was developed taking into consideration a detailed analysis of the heat exchanger (HEX) (intercooler (IC)) component irreversibilities. Moreover, it was further extended to include an adequate formulation for closed systems, e.g., a secondary cycle (SC), moving with the aircraft. Afterward, the proposed framework was employed to study two radical intercooling concepts. The first proposed concept uses already available wetted surfaces, i.e., nacelle surfaces, to reject the core heat and contributes to an overall drag reduction. The second concept uses the rejected core heat to power a secondary organic Rankine cycle and produces useful power to the aircraft-engine system. Both radical concepts are integrated into a high bypass ratio (BPR) turbofan engine, with technology levels assumed to be available by year 2025. A reference intercooled cycle incorporating a HEX in the bypass (BP) duct is established for comparison. Results indicate that the radical intercooling concepts studied in this paper show similar performance levels to the reference cycle. This is mainly due to higher irreversibility rates created during the heat exchange process. A detailed assessment of the irreversibility contributors, including the considered HEXs and SC, is made. A striking strength of the present analysis is the assessment of the component-level irreversibility rate and its contribution to the overall aero-engine losses.
19.	Zhao, Xin, 1986 (författare) Aero Engine Intercooling 2016 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Intercooling has the potential to provide a shortcut to the next generation aero engines with higher bypass ratio (BPR), higher overall pressure ratio (OPR) and higher turbine inlet temperature (TIT) by lowering the high pressure compressor (HPC) delivery temperature. To be able to establish a systematic understanding of aero engine intercooling, the heat transfer and pressure loss characteristics of a given intercooler architecture need to be known in the parameter range anticipated for the engine optimization. A two-pass cross flow tubular heat exchanger for aero engine intercooling applications was hence developed by the means of computational fluid dynamics (CFD). Optimizations with this intercooler installed were performed by considering the intercooler design parameters and the engine design simutaneously. A geared variant was adopted to complement the use of intercooling as it could support high OPR engines better by allowing a lower position installtion of the HPC. For a flight mission, further optimization of the intercooled engines was acheived by controlling the amount of intercooling for different engine operating points in two ways. One is intercooler external flow control by a separate variable nozzle and another one is intercooler internal flow variable flow path. As the flight altitude strongly influences the working condition for an aero engine, considerable SFC benefit can be obtained by limiting intercooling at high altitude operation. Nevertheless, the precondition is to enable a higher OPR at the take-off operation by intercooling. Compared to a reference non-intercooled geared engine, an optimal intercooled geared engine with intercooling control shows a 4.9\% better mission fuel burn under the same engine technology level assumptions. However, the optimum is still constrained by the last stage compressor blade height. To further explore the potentialof intercooling the constraint limiting the axial compressor last stage blade height isrelaxed by introducing an axial-radial combined HPC. The axial–radialhigh pressure ratio configuration allows for an ultrahigh OPR. With anoptimal top-of-climb (TOC) OPR of 140, the configuration provides a 5.3\% fuel burn benefitover the geared reference engine.Experimental validation of the intercooler design and the CFD design tool is also presented in this thesis. With the help of particle image velocimetry (PIV) and pressure measurements, flow topology inside the intercooler was visualized. Generally, by comparing the CFD results and the experimental data, the computational capability of porous media modeling predicting the flow distribution within the tubular heat transfer units was confirmed. The flow topology within the associated ducts was considered well-described by CFD.
20.	Zhao, Xin, 1986, et al. (författare) Aero Engine Intercooling Optimization Using a Variable Flow Path 2015 Ingår i: The 22nd international symposium of air breathing engines, Phoenix, U.S. 2015. Konferensbidrag (refereegranskat)abstract Intercooling, as a way to higher overall pressure ratio (OPR) and more efficient gas turbines, has recently drawn a substantial attention to aero engine applications. In contrast to the stationary gas turbines, aero engine intercooler system installation is very challenging. The focus of current intercooling research is mostly on developing the intercooler and associated ducting system in a highly compact, low weight and low loss way. For aero engine applications, operating points such as take-off, top-of-climb and cruise result in different working conditions, and hence also in a varying intercooling demand. In a previous study carried out at Chalmers University, a two-pass cross flow intercooler concept with an auxiliary nozzle showed considerable improvement in cruise SFC [ISABE2013 1215]. To further optimize the intercooler for the cooling demand in different operating conditions, a variable flow path concept controlling the core flow at different flight phases, see Figure 1, is studied. The concept is designed for an intercooled geared large turbofan engine. Results indicate that, with half of the core flow passing through the variable flow path at cruise, a further reduction of 0.5% cruise SFC can be achieved for the intercooled geared engine, resulting in a total of 4.9% fuel burn reduction compared with an optimized advanced geared engine.
21.	Zhao, Xin, 1986, et al. (författare) Assessment of the performance potential for a two-pass cross flow intercooler for aero engine applications 2013 Ingår i: International Society for Airbreathing Engines, ISABE, Busan, South Korea, 2013, ( ISABE-2013-1215 ). Konferensbidrag (refereegranskat)abstract Intercoolers have recently received a considerable attention as a means to improve aero engine efficiency. Intercoolers have the potential to improve engine SFC, ease the design of an efficient turbine cooling system by reducing compressor exit temperatures and hence cooling air temperatures, as well as reducing NOx emissions. Intercooling may also provide benefits by increasing the specific output of the engine core and therefore reduce total engine weight. The performance potential for a two-pass cross flow intercooler has been estimated through an analysis of a long range mission for a geared turbofan engine. The application of a set of CFD based correlations allows the simultaneous coupled optimization of the intercooler conceptual design parameters and the engine design. The coolant air for the intercooler is ejected through a separate variable exhaust nozzle which is used to optimize the engine performance in cruise. By comparing the optimized intercooled geared engine with an optimized advanced non-intercooled geared engine, a reduction of 4.8% fuel burn is observed.
22.	Zhao, Xin, 1986, et al. (författare) Conceptual design of a two-pass cross-flow aeroengine intercooler 2015 Ingår i: Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering. - : SAGE Publications. - 0954-4100 .- 2041-3025. ; 229:11, s. 2006-2023 Tidskriftsartikel (refereegranskat)abstract Establishing an optimal intercooled aeroengine constitutes a coupled problem where the conceptual design of the intercooler and the engine has to be considered simultaneously. The heat transfer and pressure loss characteristics will depend on the choice of the intercooler architecture. Hence, to be able to optimize the performance of an intercooled aeroengine, the performance characteristics of a given intercooler architecture has to be known in the parameter range anticipated for the aeroengine optimization. Here, the conceptual design of a tubular two-pass cross-flow intercooler architecture intended for a turbofan aeroengine application is presented. The internal flow is simulated applying a porous media model for the intercooler tubes, whereas the connecting ducts are analyzed with three-dimensional simulations allowing the assessment of a number of design solutions. The external flow is treated with two-dimensional simulations investigating the external pressure loss and heat transfer characteristics of the two elliptical tube stacks. The intercooler performance is then generalized by developing a reduced order correlation covering a parameter range anticipated for a turbofan conceptual design optimization. The paper constitutes a first effort to establish an open literature complete set of correlations for the prediction of aeroengine intercooler performance.
23.	Zhao, Xin, 1986, et al. (författare) Conceptual Mean-line Design of a Low Pressure Turbine for a Geared Turbofan with Rear Structure Interaction 2019 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract One of the most important features of a geared turbofan (GTF) is a reduced number of low pressure turbine (LPT) stages resulting from a faster spinning spool. Compared to a direct drive turbofan (DDTF), in which the LPT normally constitutes a considerable part of the engine total weight, from 10% to more than 25%, dependent on the engine bypass ratio (BPR), fewer stages can cut the weight into half or even less for the LPT. With this benefit, the weight of the LPT alone is no longer a dominating factor for the selection of its configuration. To obtain an optimal LPT configuration for a GTF requires a new balance between weight and performance involving both the LPT and the downstream component, the turbine rear structure (TRS). A conceptual design of the LPT for a mid- to long-range GTF is presented here to clarify this new balance. By comparing a range of designs based on different number of stages and turbine hade angles, the selection of the LPT design for the GTF is described. More importantly, interactions between the LPT design and the TRS design are considered. Results indicate that a joint design is necessary as the TRS plays an important role in designing the LPT of a GTF. It is shown that if the LPT design is done in isolation from the TRS design, a 3-stage LPT performs better than a 4-stage design from a fuel burn perspective. However, when the TRS design is considered, the advantage of the 3-stage LPT design is offset by the associated TRS weight and loss increase, compared to the 4-stage LPT design.
24.	Zhao, Xin, 1986, et al. (författare) Development of an aerodynamic analysis tool for boundary layer ingestion concept design 2022 Ingår i: 33rd Congress of the International Council of the Aeronautical Sciences, ICAS 2022. ; 2, s. 974-985 Konferensbidrag (refereegranskat)abstract The methods incorporated in an aerodynamic analysis tool are introduced to support aircraft conceptual designs, where a boundary layer ingestion (BLI) propulsion system is deployed. In order to integrate the BLI model to a generic tool for aircraft designs, two methods of approximating boundary layer profiles along the airframe/fuselage have been examined. For an airfoil-shaped wing/body configuration, the airfoil analysis program XFOIL is used and, alternatively, the flat plate boundary layer theory may be adopted. With the boundary layer characteristics approximated from these methods, the fan performance in terms of pressure ratio and efficiency is corrected considering the inflow distortion incurred by the boundary layer ingested, based on a simplified parallel compressor method. Given the corrected fan pressure ratio and efficiency, an equivalent velocity bookkeeping method is used for predicting the BLI fan performance in terms of power requirement and thrust generation. A validation against the boundary layer approximation is also presented in comparison with the RANS-based CFD simulations for a blended wing body (BWB) aircraft.
25.	Zhao, Xin, 1986, et al. (författare) First and second law analysis of intercooled turbofan engine 2015 Ingår i: ASME Turbo Expo 2015, Montreal Canada, GT2015-43187. ; 1 Konferensbidrag (refereegranskat)abstract Although the benefits of intercooling for aero engine applications have been realized and discussed in many publications, quantitative details are still relatively limited. In order to strengthen the understanding of aero engine intercooling, detailed performance data on optimized intercooled turbofan engines are provided. Analysis is conducted using an exergy breakdown, i.e. quantifying the losses into a common currency by applying a combined use of the first and second law of thermodynamics.Optimal intercooled geared turbofan engines for a long range mission are established with CFD based two-pass cross flow tubular intercooler correlations. By means of a separate variable nozzle, the amount of intercooler coolant air can be optimized to different flight conditions. Exergy analysis is used to assess how irreversibility is varying over the flight mission, allowing for a more clear explanation and interpretation of the benefits.The optimal intercooled geared turbofan engine provides a 4.5% fuel burn benefit over a non-intercooled geared reference engine. The optimum is constrained by the last stage compressor blade height. To further explore the potential of intercooling the constraint limiting the axial compressor last stage blade height is relaxed by introducing an axial radial high pressure compressor. The axial-radial high pressure ratio configuration allows for an ultra-high overall pressure ratio. With an optimal top-of-climb overall pressure ratio of 140, the configuration provides a 5.3% fuel burn benefit over the geared reference engine.The irreversibilities of the intercooler are broken down into its components to analyze the difference between the ultra-high overall pressure ratio axial-radial configuration and the purely axial configuration. An intercooler conceptual design method is used to predict pressure loss heat transfer and weight for the different overall pressure ratios. Exergy analysis combined with results from the intercooler and engine conceptual design are used to support the conclusion that the optimal pressure ratio split exponent stays relatively independent of the overall engine pressure ratio.

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