| 1. |
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| 2. |
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| 3. |
- Okda, Sherif, et al.
(author)
-
Testing of the Aerodynamic Characteristics of an Inflatable Airfoil Section
- 2020
-
In: Journal of Aerospace Engineering. - 1943-5525 .- 0893-1321. ; 33:5
-
Journal article (peer-reviewed)abstract
- Inflatable structures are characterized by being light and easy to manufacture and deploy. Hence, they find many applications in aerospace and aeronautical engineering. In this paper, an inflatable segment with a The National Advisory Committee for Aeronautics (NACA) 0021 airfoil cross-section is designed, fabricated, and tested. The geometrical accuracy of the manufactured inflatable segment is measured using laser scanning. Measurements show that the average normalized error of the chord length and thickness are 2.97% and 0.554%, respectively. The aerodynamic behavior of the inflatable segment is then tested in a wind tunnel at different wind speeds and angles of attack. Lift forces are measured using a six-component balance, while the drag forces are calculated from the wake measurements. The lift and drag coefficients of the inflatable section are compared to those of a standard NACA 0021 airfoil. Finally, flow visualization is examined at different angles of attack using two methods: smoke and tufts. Both methods show that flow separation starts at 15° and full stall occurs at 25°. Results indicate that inflatables can find more applications in the design and construction of aerodynamic structures, such as wings.
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| 4. |
- Wadekar, Sandip, 1989
(author)
-
Large-Eddy Simulation of Gasoline Fuel Spray Injection at Ultra-High Injection Pressures
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- Gasoline direct injection is a state-of-the-art technique that reduces hydrocarbon and particulate emissions. However, further improvement is needed to meet current as well as future emission regulations. A prominent solution is to increase the fuel injection pressure which allows faster fuel droplet atomization, quick evaporation and improves fuel-air mixture formation under realistic engine conditions. In this work, the gasoline fuel injection process at ultra-high injection pressures ranging from 200 to 1500 bar was analyzed using numerical models. In particular, the Large-Eddy Simulation (LES) method, with the standard Smagorinsky turbulence model, was utilized using the Eulerian formulation for the continuous phase. The discrete droplet phase was treated using a Lagrangian formulation together with spray sub-models. In the first part of study, spray was injected into an initially quiescent constant volume chamber using two different nozzle hole shape geometries: divergent and convergent. The numerical results were calibrated by reproducing experimentally observed liquid penetration length and efforts were made to understand the influence of ultra-high injection pressures on spray development. The calibrated models were then used to investigate the impact of ultra-high injection pressures on mean droplet sizes, droplet size distribution, spray-induced large-scale eddies and entrainment rate. The results showed that, at ultra-high injection pressures, the mean droplet sizes were significantly reduced and the droplets achieving very high velocities. Integral length scales of spray-induced turbulence and air entrainment rate were better for the divergent-shaped injector, and considerably larger at higher injection pressures compared to lower ones. In the second part of the study, four consecutive full-cycle cold flow LES simulations were carried out to generate realistic turbulence inside the engine cylinder. The first three cycles were ignored, with the fourth cycle being used to model the injection of the fuel using the divergent-shaped injector only (which was found to be better in the previous part of this study) at different injection pressures. In addition to the continuous gas phase (Eulerian) and the dispersed liquid (Lagrangian), the liquid film feature (Finite-Area) was used to model the impingement of fuel spray on the engine walls and subsequent liquid film formation. The simulation results were used to evaluate spray-induced turbulence, fuel-air mixing efficiency and the amount of liquid mass deposited on the walls. The limitation of the high-pressure injection technique with respect to liquid film formation was optimized using a start of injection (SOI) sweep. Overall results showed that the mixing efficiency increased at high injection pressure and that SOI should occur between early injection and late injection to optimize the amount of mass being deposited on the engine walls.
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| 5. |
- Mihaescu, Mihai
(author)
-
Computational Aeroacoustics Based on Large Eddy Simulation and Acoustic Analogies
- 2005
-
Doctoral thesis (other academic/artistic)abstract
- The thesis presents a numerical method developed by the author and its applications for computing the generated sound by an unsteady flow field and its propagation. The full equations of motion for compressible and unsteady flows describe both flow field and sound generation and propagation. It is assumed that the flow variables can be decomposed into semi-compressible / incompressible components and inviscid, irrotational acoustic components. The present method is based on Large Eddy Simulation (LES) to compute the turbulent flow and an approach based on an inhomogeneous wave equation to compute the radiated acoustic field. In this way one can avoid the necessity for a very large computational effort associated with direct simulation of the near- and specially far- field sound generated by a turbulent flow. The governing equations are written in the form of a non-homogeneous wave equation for the acoustic fluctuation with acoustic sources on the right-hand side. The thesis includes the details of the coupling between the flow solver and the acoustic one, as well as the results for test cases employed to validate the numerical algorithm and the implemented boundary conditions. The method has been successfully applied to compute the near- and far- acoustic fields generated by various unsteady flows such as a round hot turbulent jet ejected from a pipe close to a solid boundary, coaxial turbulent non-isothermal jets (separate exhaust system), or the flow around a wind-turbine.
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| 6. |
- Lejon, Marcus, 1986, et al.
(author)
-
Multidisciplinary Design of a Three Stage High Speed Booster
- 2017
-
In: ASME Turbo Expo 2017: Turbine Technical Conference and Exposition. - : ASME Press. ; 2B-2017
-
Conference paper (peer-reviewed)abstract
- The paper describes a multidisciplinary conceptual design of an axial compressor, targeting a three stage, high speed, high efficiency booster with a design pressure ratio of 2.8. The paper is outlined in a step wise manner starting from basic aircraft and engine thrust requirements, establishing the definition of the high speed booster interface points and its location in the engine. Thereafter, the aerodynamic 1D/2D design is carried out using the commercial throughflow tool SC90C. A number of design aspects are described, and the steps necessary to arrive at the final design are outlined. The SC90C based design is then carried over to a CFD based conceptual design tool AxCent, in which a first profiling is carried out based on a multiple circular arc blade definition. The design obtained at this point is referred to as the VINK compressor. The first stage of the compressor is then optimized using an in-house optimization tool, where the objective functions are evaluated from detailed CFD calculations. The design is improved in terms of efficiency and in terms of meeting the design criteria put on the stage in the earlier design phases. Finally, some aeromechanical design aspects of the first stage are considered. The geometry and inlet boundary conditions of the compressor are shared with the turbomachinery community on a public server. This is intended to be used as a test case for further optimization and analysis.
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| 7. |
- Li, Xiaojian, 1991, et al.
(author)
-
Installation effects on engine design
- 2020
-
Conference paper (other academic/artistic)abstract
- Increasing the engine bypass ratio is one way to improve propulsive efficiency. However, an increase in the bypass ratio (BPR) has usually been associated with an increase in the fan diameter. Consequently, there can be a notable increase in the impact of the engine installation on the overall aircraft performance. In order to achieve a better balance between those factors, it requires novel nacelle and engine design concepts. This report mainly reviews installation effects on engine design. Firstly, the installation effects assessment methods are introduced. Then, the installation effects on engine cycle design, intake design and exhaust design are sequentially reviewed.
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| 8. |
- Kyprianidis, Konstantinos, 1984, et al.
(author)
-
Multidisciplinary Analysis of a Geared Fan Intercooled Core Aero-Engine
- 2014
-
In: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 136:1
-
Journal article (peer-reviewed)abstract
- The reduction of CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, along with the reduction of engine nacelle drag and weight. One alternative design approach to improving specific fuel consumption is to consider a geared fan combined with an increased overall pressure ratio intercooled core performance cycle. The thermal benefits from intercooling have been well documented in the literature. Nevertheless, there is very little information available in the public domain with respect to design space exploration of such an engine concept when combined with a geared fan. The present work uses a multidisciplinary conceptual design tool to analyze the option of an intercooled core geared fan aero engine for long haul applications with a 2020 entry into service technology level assumption. With minimum mission fuel in mind, the results indicate as optimal values a pressure ratio split exponent of 0.38 and an intercooler mass flow ratio of 1.18 at hot-day top of climb conditions. At ISA midcruise conditions a specific thrust of 86 m/s, a jet velocity ratio of 0.83, an intercooler effectiveness of 56%, and an overall pressure ratio value of 76 are likely to be a good choice. A 70,000 lbf intercooled turbofan engine is large enough to make efficient use of an all-axial compression system, particularly within a geared fan configuration, but intercooling is perhaps more likely to be applied to even larger engines. The proposed optimal jet velocity ratio is actually higher than the value one would expect by using standard analytical expressions, primarily because this design variable affects core efficiency at midcruise due to a combination of several different subtle changes to the core cycle and core component efficiencies at this condition. The analytical expressions do not consider changes in core efficiency and the beneficial effect of intercooling on transfer efficiency, nor do they account for losses in the bypass duct and jet pipe, while a relatively detailed engine performance model, such as the one utilized in this study, does. Mission fuel results from a surrogate model are in good agreement with the results obtained from a rubberized-wing aircraft model for some of the design parameters. This indicates that it is possible to replace an aircraft model with specific fuel consumption and weight penalty exchange rates. Nevertheless, drag count exchange rates have to be utilized to properly assess changes in mission fuel for those design parameters that affect nacelle diameter.
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| 9. |
- Thulin, Oskar, 1987, et al.
(author)
-
First and Second Law Analysis of Radical Intercooling Concepts
- 2018
-
In: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 140:8, s. 081201-081201-10
-
Journal article (peer-reviewed)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.
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| 10. |
- Thulin, Oskar, 1987
(author)
-
On the Analysis of Energy Efficient Aircraft Engines
- 2017
-
Doctoral thesis (other academic/artistic)abstract
- Aero engine performance analysis is highly multidimensional using various measures of component performance such as turbomachinery and mechanical efficiencies, and pressure loss coefficients. Using conventional performance analysis, relying on only the laws of thermodynamics, it is possible to understand how the performance parameters affect the component performance, but it is difficult to directly compare the magnitude of various loss sources. A comprehensive framework has been detailed to analyze aero engine loss sources in one common currency. As the common currency yields a measure of the lost work potential in every component, it is used to relate the component performance to the system performance. The theory includes a more detailed layout of all the terms that apply to a propulsion unit than presented before. The framework is here adopted to real gases to be used in state of the art performance codes. Additionally, the framework is further developed to enable detailed studies of two radical intercooling concepts that either rejects the core heat in the outer nacelle surfaces or uses the core heat for powering of a secondary cycle. The theory is also extended upon by presenting the installed rational efficiency, a true measure of the propulsion subsystem performance, including the installation effects of the propulsion subsystem as it adds weight and drag that needs to be compensated for in the performance assessment.
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| 11. |
- Heshmati, Mohsen, 1987, et al.
(author)
-
Dependency of cohesive laws of a structural adhesive in Mode-I and Mode-II loading on moisture, freeze-thaw cycling, and their synergy
- 2017
-
In: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 122, s. 433-447
-
Journal article (peer-reviewed)abstract
- In recent years, adhesive bonding has found its way to construction applications such as bridges. Given the harsh conditions that such structures are usually exposed to, it is necessary to account for environmental factors, particularly moisture and temperature, in the design phase. Cohesive zone modelling has attracted much attention in the last decade as a promising method to design adhesive joints. Despite this interest, the effects of moisture and thermal cycles on cohesive laws have not been investigated to the knowledge of the authors. In this paper, we present a method to directly measure the environmental-dependent cohesive laws of a structural adhesive loaded in pure Mode-I and Mode-II. Special consideration is given to overcome issues such as the time-consuming nature of moisture ingression and specimen dimensions, which could be problematic due to the size-limitations of conditioning equipment. The accuracy of this method was verified through simulation of the experiments using the finite element analysis. The effects of exposure to 95% relative humidity, immersion in saltwater and distilled water, and freeze-thaw cycles in the presence or absence of moisture were investigated. The results indicate the damaging effects of combined saltwater and freeze-thaw cycles which were clearly reflected on the shape of the cohesive laws.
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| 12. |
- Ottersten, Martin, 1981, et al.
(author)
-
Inlet Gap Influence on Low-Frequency Flow Unsteadiness in a Centrifugal Fan
- 2022
-
In: Aerospace. - : MDPI AG. - 2226-4310. ; 9:12
-
Journal article (peer-reviewed)abstract
- In this study, unsteady low-frequency characteristics in a voluteless low-speed centrifugal fan operating at a high mass flow rate are studied with improved delayed detached eddy simulation (IDDES). This study is motivated by a recent finding that the non-uniformly distributed pressure inside this type of fan could be alleviated by improving the gap geometry. The present simulation results show that the velocity magnitudes of the gap have distinct low and high regions. Intensive turbulent structures are developed in the low-velocity regions and are swept downstream along the intersection between the blade and shroud, on the pressure side of the blade. Eventually, the turbulence gives rise to a high-pressure region near the blade’s trailing edge. This unsteady flow behavior revolves around the fan rotation axis. Additionally, its period is 5% of the fan rotation speed, based on the analysis of the time history of the gap velocity magnitudes and the evolution of the high-pressure region. The same frequency of high pressure was also found in previous experimental measurements. To the authors’ knowledge, this is the first time that the trigger of the gap turbulence, i.e., the unsteady local low velocity, has been determined.
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| 13. |
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| 14. |
- Klomp, Rolf, et al.
(author)
-
Experimental Evaluation of a Joint Cognitive System for 4D Trajectory Management
- 2013
-
In: Proceedings of the SESAR Innovation Days (2013). - Brussels : Eurocontrol. - 9782874970740 ; , s. 1-7
-
Conference paper (peer-reviewed)abstract
- Effective joint human-automation coordination is essential in order to support the central role of the human operator in foreseen future trajectory-based air traffic operations. The SESAR WP-E project C-SHARE aims to achieve this by taking a Cognitive Systems Engineering approach, based upon accomplishing joint human and automation cognition through a shared representation of 4D-trajectory management. In foregoing research, a work domain model and a joint humanmachine interface has been developed to support the human operator in the task of en-route 4D trajectory re-planning. This paper presents the findings of two experiments that aimed to determine the effect of both the initial level of traffic orderliness (i.e., structured versus unstructured traffic) and the scale of perturbations acting upon the airspace (e.g., number of conflicts and restricted areas) on the overall effectiveness of such a system. The findings of the experimental evaluation show that the CSHARE approach to joint human-automation coordination in perturbation management is promising. Further, the experiment subjects accepted the tool and found it supportive for the task at hand, resulting in a manageable degree of workload during all experiment scenarios.
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| 15. |
- Li, Xiaojian, 1991, et al.
(author)
-
A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles
- 2020
-
In: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:19
-
Journal article (peer-reviewed)abstract
- Supercritical Carbon Dioxide (SCO2) is considered as a potential working fluid in next generation power and energy systems. The SCO2 Brayton cycle is advantaged with higher cycle efficiency, smaller compression work, and more compact layout, as compared with traditional cycles. When the inlet total condition of the compressor approaches the critical point of the working fluid, the cycle efficiency is further enhanced. However, the flow acceleration near the impeller inducer causes the fluid to enter two-phase region, which may lead to additional aerodynamic losses and flow instability. In this study, a new impeller inlet design method is proposed to achieve a better balance among the cycle efficiency, compressor compactness, and inducer condensation. This approach couples a concept of the maximum swallowing capacity of real gas and a new principle for condensation design. Firstly, the mass flow function of real gas centrifugal compressors is analytically expressed by non-dimensional parameters. An optimal inlet flow angle is derived to achieve the maximum swallowing capacity under a certain inlet relative Mach number, which leads to the minimum energy loss and a more compact geometry for the compressor. Secondly, a new condensation design principle is developed by proposing a novel concept of the two-zone inlet total condition for SCO2 compressors. In this new principle, the acceptable acceleration margin (AAM) is derived as a criterion to limit the impeller inlet condensation. The present inlet design method is validated in the design and simulation of a low-flow-coefficient compressor stage based on the real gas model. The mechanisms of flow accelerations in the impeller inducer, which form low-pressure regions and further produce condensation, are analyzed and clarified under different operating conditions. It is found that the proposed method is efficient to limit the condensation in the impeller inducer, keep the compactness of the compressor, and maintain a high cycle efficiency.
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| 16. |
- Tofique, Muhammad Waqas, 1986-, et al.
(author)
-
Development of the distributed dislocation dipole technique for the analysis of closure of complex fractures involving kinks and branches
-
Other publication (other academic/artistic)abstract
- This paper presents the development of the distributed dislocation dipole technique (DDDT) for the analysis of crack surface closure of crack cases involving kinks and branches. Crack cases in which closure occurs are analyzed by reformulating the Bueckner's principle taking the contact stresses at the contacting portions of the crack surfaces into account. Stress intensity factors corresponding to opening and sliding mode of deformation at the crack tips are computed. Three test cases involving kinked and/or branched cracks with at least one of the crack segments undergoing crack surface closure when subjected to remote tensile loading are analyzed. The results obtained from the DDDT are compared to those obtained from the Finite Element Method (FEM) analysis of the same crack cases. This comparison shows that the computation of stress intensity factors for the crack cases involving crack surface closure are less acurate compared to fully open crack cases. However, the stress intensity factors are still computed to an accuracy of within 2 percent if the Jacobi polynomial expansions of at least the sixth order are used to represent the crack surface opening and sliding displacements. Higher order Jacobi polynomials lead to increased accuracy.
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| 17. |
- Shetty, Sandeep
(author)
-
Optimization of Vehicle Structures under Uncertainties
- 2017
-
Doctoral thesis (other academic/artistic)abstract
- Advancements in simulation tools and computer power have made it possible to incorporate simulation-based structural optimization in the automotive product development process. However, deterministic optimization without considering uncertainties such as variations in material properties, geometry or loading conditions might result in unreliable optimum designs. In this thesis, the capability of some established approaches to perform design optimization under uncertainties is assessed, and new improved methods are developed. In particular, vehicle structural problems which involve computationally expensive Finite Element (FE) simulations, are addressed.The first paper focuses on the evaluation of robustness, given some variation in input parameters, the capabilities of three well-known metamodels are evaluated. In the second paper, a comparative study of deterministic, reliability-based and robust design optimization approaches is performed. It is found that the overall accuracy of the single-stage (global) metamodels, which are used in the above study, is acceptable for deterministic optimization. However, the accuracy of performance variation prediction (local sensitivity) must be improved. In the third paper, a decoupled reliability-based design optimization (RBDO) approach is presented. In this approach, metamodels are employed for the deterministic optimization only while the uncertainty analysis is performed using FE simulations in order to ensure its accuracy.In the fifth paper, two new sequential sampling strategies are introduced that aim to improve the accuracy of the metamodels efficiently in critical regions. The capabilities of the methods presented are illustrated using analytical examples and a vehicle structural application.It is important to accurately represent physical variations in material properties since these might exert a major influence on the results. In previous work these variations have been treated in a simplified manner and the consequences of these simplifications have been poorly understood. In the fourth paper, the accuracy of several simple methods in representing the real material variation has been studied. It is shown that a scaling of the nominal stress-strain curve based on the Rm scatter is the best choice of the evaluated choices, when limited material data is available.In this thesis work, new pragmatic methods for non-deterministic optimization of large scale vehicle structural problems have been developed. The RBDO methods developed are shown to be flexible, more efficient and reasonably accurate, which enables their implementation in the current automotive product development process.
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| 18. |
- Sarkar, Saptarshi, 1992, et al.
(author)
-
Transient torque reversals in indirect drive wind turblnes
- 2023
-
In: Wind Energy. - 1099-1824 .- 1095-4244. ; 26, s. 691-716
-
Journal article (peer-reviewed)abstract
- The adverse effect of transient torque reversals (TTRs) оп wind turЬine gearboxes сап Ье severe due to their magnitude and rapid occurrence compared with other equipment. The primary damage is caused to the bearings as the bearing loaded zone rapidly changes its direction. Other components are also affected Ьу TTRs (such as gear tooth); however, its impact оп bearings is the largest. While the occurrence and severity of TTRs are acknowledged in the industry, there is а lack of academic literature оп their initiation, propagation and the associated risk of damage. Furthermore, in the wide range of operation modes of а wind turЬine, it is not known which modes сап lead to TTRs. Further, the interdependence of TTRs оп environmental loading like the wind is also not reported. This paper aims to address these unknowns Ьу expanding оп the understanding of TTRs using а high-fidelity numerical model of an indirect drive wind turЬine with а douЬly fed induction generator (DFIG). То this end, а multibody model of the drivetrain is developed in SIMPACK. The model of the drivetrain is explicitly coupled to state-of-the-art wind turЬine simulator OpenFAST and а grid-connected DFIG developed in MATLAB®'s Simulink® allowing а coupled analysis of the electromechanical system. А metric termed slip risk duration is proposed in this paper to quantify the risk associated with the TTRs. The paper first investigates а wide range of IEC design load cases to uncover which load cases сап lead to TTRs. lt was found that emergency stops and symmetric grid voltage drops сап lead to TTRs. Next, the dependence of the TTRs оп inflow wind parameters is investigated using а sensitivity analysis. lt was found that the instantaneous wind speed at the onset of the grid fault or emergency shutdown was the most influential factor in the slip risk duration. The investigation enaЫes the designer to predict the occurrence of TTRs and quantify the associated risk of damage. The paper concludes with recommendations for utility-scale wind turЬines and directions for future research.
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| 19. |
- Kyprianidis, Konstantinos, et al.
(author)
-
Dynamic performance investigations of a turbojet engine using a cross-application visual oriented platform
- 2008
-
In: Aeronautical Journal. - 0001-9240. ; 112:1129, s. 161-169
-
Journal article (peer-reviewed)abstract
- This paper presents the development of visual oriented tools for the dynamic performance simulation of a turbojet engine using a cross-application approach. In particular, the study focuses on the feasibility of developing simulation models using different programming environments and linking them together using a popular spreadsheet program. As a result of this effort, a low fidelity cycle program has been created, capable of being integrated with other performance models. The amount of laboratory sessions required for student training during an educational procedure, for example for a course in gas turbine performance simulation, is greatly reduced due to the familiarity of most students with the spreadsheet software. The model results have been validated using commercially available gas turbine simulation software and experimental data from open literature. The most important finding of this study is the capability of the program to link to aircraft performance models and predict the transient working line of the engine for various initial conditions in order to dynamically simulate flight phases including take-off and landing.
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| 20. |
- Kyprianidis, Konstantinos, et al.
(author)
-
Multi-disciplinary Analysis of a Geared Fan Intercooled Core Aero-Engine
- 2013
-
In: <em><em>Proc. ASME</em>.</em> 55133; Volume 2: Aircraft Engine; Coal, Biomass and Alternative Fuels; Cycle Innovations, V002T07A027. GT2013-95474. - 9780791855133
-
Conference paper (peer-reviewed)abstract
- Reduction of CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, as well as the reduction of engine nacelle drag and weight. One alternative design approach to improving specific fuel consumption is to consider a geared fan combined with an increased overall pressure ratio intercooled core performance cycle. Thermal benefits from intercooling have been well documented in the literature. Nevertheless, there is very little information available in the public domain with respect to design space exploration of such an engine concept when combined with a geared fan. The present work uses a multidisciplinary conceptual design tool to analyse the option of an intercooled core geared fan aero engine for long haul applications with a 2020 entry into service technology level assumption.With minimum mission fuel in mind, the results indicate as optimal values a pressure ratio split exponent of 0.38 and an intercooler mass flow ratio just below 1.2 at hot-day top of climb conditions. At ISA mid-cruise conditions a specific thrust of 86m/s, a jet velocity ratio of 0.83, an intercooler effectiveness of 55% and an overall pressure ratio value of 76 are likely to be a good choice. A 70,000lbf intercooled turbofan engine is large enough to make efficient use of an all-axial compression system, particularly within a geared fan configuration, but intercooling is perhaps more likely to be applied to even larger engines.The proposed optimal jet velocity ratio is actually higher than the value one would expect by using standard analytical expressions primarily because this design variable affects core efficiency at mid-cruise due to a combination of several different subtle changes to the core cycle and core component efficiencies at this condition. Analytical expressions do not consider changes in core efficiency and the beneficial effect of intercooling on transfer efficiency, nor account for losses in the bypass duct and jet pipe, whilst a relatively detailed engine performance model such as the one utilised in this study does.Mission fuel results from a surrogate model are in good agreement with the results obtained from a rubberised-wing aircraft model for some of the design parameters. This indicates that it is possible to replace an aircraft model with specific fuel consumption and weight penalty exchange rates. Nevertheless, drag count exchange rates have to be utilised to properly assess changes in mission fuel for those design parameters that affect nacelle diameter.
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| 21. |
- Edman, Jonas, 1973
(author)
-
Modeling Diesel spray combustion using a Detailed Chemistry Approach
- 2005
-
Doctoral thesis (other academic/artistic)abstract
- The rapid development of computer hardware during the past decade has contributed substantially to advances in almost all branches of science. Computer modeling is being applied to increasingly small physical scales and increasingly large domains, facilitating the generation of advanced phenomenological models and models based on first principles. These developments have been especially valuable in fields where highly complex micro-scale events are observed or modeled, such as combustion studies, allowing (for instance) the incorporation of complex chemical combustion kinetics into engine spray combustion models. The crude models and global curve fits that were previously used to represent combustion phenomena have now been largely replaced by models based on "first principles". These modeling developments have coincided fortuitously with a shift in the focus of combustion concepts, from mixing-oriented combustion modes like Diesel and stratified charge Otto combustion to the kinetically controlled combustion modes usually referred to as Homogeneous Charge Compression Ignition (HCCI). The driving forces behind the development of the HCCI concept are environmental considerations, manifested in the form of emission legislation. Theoretically, HCCI combustion (characterized by fuel lean mixtures and low peak temperatures) has the potential to reduce soot and NOx emissions to current emission legislation levels even without after-treatment systems. In practical production engine applications, due to current drawbacks such as poor high load capability, the capacity to switch to conventional mode at high load operation is required. For the above reasons, computer modeling that is capable of describing both old and new combustion modes is required. In the work underlying this thesis, CFD modeling was applied to the passenger car Dl Diesel engine operated in both HCCI and conventional Diesel combustion modes. The aim was to couple chemical combustion kinetics and turbulent mixing in order to capture relevant phenomena related to ignition and emission formation for both modes. The resulting, coupled model is referred to as the Partially Stirred Reactor model (PaSR), and is the main component in the Detailed Chemistry Approach currently utilized in combustion modeling at Chalmers University of Technology (CTH). Other essential components of the Detailed Chemistry Approach are the Reference Species Technique (used to determine the relevant chemical timescales) and the Diesel fuel surrogate model (constructed to facilitate realistic treatment of the fuel in both liquid and gaseous states). The gaseous kinetic treatment of the Diesel fuel surrogate model, represented by a blend of aliphatic and aromatic components, consists of a chemical kinetic mechanism considering -75 chemical species participating in -330 elementary or global reactions describing n-heptane and toluene oxidation. Although most of the modeling was done in the CFD code KIVA-3V rel2, the development and validation of the chemical kinetic combustion mechanism was done using the SENKIN code and the CHEMKIN package. The chemical kinetic modeling has provided a kinetic mechanism for Diesel combustion that is capable of reproducing experimental ignition delay characteristics of both n-heptane and toluene oxidation in both low and high pressure regimes. In addition, it reproduces the negative temperature coefficient behavior that is an important feature of commercial Diesel fuels. It has also been able to reproduce cool flame phenomena, which play important roles in HCCI combustion. Results from the constant volume spray modeling have shown that the spray development, liquid and gas penetration and ignition characteristics observed in high pressure Diesel spray experiments are properly reproduced. Furthermore, major combustion variables such as ignition timing, heat release and pressure traces generated in engine simulations have satisfactorily reproduced experimental data acquired in tests using a single cylinder engine at Chalmers University of Technology.
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| 22. |
- Sundin, Maria, 1965, et al.
(author)
-
Space Sports - Sailing in Space
- 2016
-
In: Proceedings from icSports 2016, 4th International Conference on Sport Sciences Research and Technology Support, Porto, Portugal, 7-9 november 2016. - : SCITEPRESS - Science and Technology Publications. - 9789897582059 ; , s. 141-146
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Conference paper (peer-reviewed)abstract
- Titan is the largest moon of Saturn, and apart from the Earth it is the only body in our solar system where a liquid exists on the surface. Within the last ten years a system of lakes and rivers have been discovered. The climate and seasonal cycles of Titan are still not very well known, but the composition and pressure are fairly well established. Perhaps in the future boats will sail the lakes of Titan for research purposes or even sport. The purpose of this paper is to give an overview of the concept of space sports, the conditions of Titan and to calculate important parameters of sailing such as floatability, stability, hull resistance and sail forces. This paper shows that if a sailing yacht on Titan will have twice as large displacement as on Earth, it will be 2.6 times less stable for the same beam. Since friction will be smaller, it will be faster than on Earth at low speed, but significantly slower at high speeds due to the wave generation. The same sail area is required to get the same sail forces if the average wind is 3 m/s, while a 9 times larger sail area is required for if the wind speed is only 1 m/s.
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| 23. |
- Safavi, Edris, et al.
(author)
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Implementation of collaborative multidisciplinary design optimization for conceptual design of a complex engineering product
- 2016
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In: Concurrent Engineering - Research and Applications. - : Sage Publications. - 1063-293X .- 1531-2003. ; 24:3, s. 251-265
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Journal article (peer-reviewed)abstract
- This study investigates the performance of the collaborative multidisciplinary design optimization framework and how it facilitates the knowledge integration process. The framework is used to design and optimize an innovative concept of a tidal water power plant. The case study helps to highlight the challenges that may occur during implementation. The result is presented as a modified framework with less implementation difficulties. The improved framework shows significant reduction in design time and improvement in collaborative design optimization for a design team. The geometry of the product is optimized to minimize weight and maximize the power generated by the turbine with respect to some mechanical constraints.
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| 24. |
- Forslund, Anders, 1982
(author)
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Uncertainty and Robustness in Aerospace Structures
- 2016
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Doctoral thesis (other academic/artistic)abstract
- Engineering is not an exact science. In fact, all engineering activity contain some degree of assumption, simplification, idealization, and abstraction. When engineered creations meet reality, every manufactured product behaves differently. This variation can be detrimental to product quality and functionality. In an aerospace context, this variation may even result in serious threats to the safety and reliability of aircraft. However, it is not the variation in and of itself that is harmful, but the effects it imposes on functionality—an important distinction to make. Reducing sources of variation is often associated with tightening tolerances and increasing cost. Instead, it is preferable to eliminate the effects of this variation by making designs more robust. This idea is at the core of robust design methodology. Aerospace is an industry characterized by the complexity of its products and the multidisciplinary nature of its product development. In such contexts, there are significant barriers against implementing uncertainty-based design practices. The research presented in this thesis aims at identifying the role of robust design in general, and geometry assurance in particular, in the early phases of aerospace component design. Further, this thesis proposes a methodology by which geometry assurance practices may be implemented in this setting. The methodology consists of a modelling approach linked to a multidisciplinary simulation environment. In a series of case studies, the methodology is tested in an industrial setting. The capability of the methodology is demonstrated through several applications, in which the effects of geometric variation on the aerodynamic, thermal, and structural performance of a load-bearing turbofan component are analysed. Investigated effects include part variation, fixture variation, part configuration and welding. The proposed methodology overcomes many of the current barriers, making it more feasible to assess geometric variation in the early design phases. Despite some limitations, the methodology contributes to an academic understanding of how to evaluate geometric variation in multidisciplinary simulations and provides a tool for industry. Geometric variation is only one source of uncertainty amongst many others. By evaluating geometric variation against the framework of uncertainty quantification, this thesis addresses the relative importance of geometry assurance against other product development activities.
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| 25. |
- Klomp, Rolf, et al.
(author)
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Ecological interface design : Control space robustness in future trajectory-based Air Traffic control decision support
- 2014
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In: 2014 IEEE International Conference on Systems, Man, and Cybernetics (SMC). - : IEEE conference proceedings. - 9781479938407 - 9781479938414 - 9781479938391 ; 2014:January, s. 329-334
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Conference paper (peer-reviewed)abstract
- Abstract:The current evolution of the Air Traffic Management system towards trajectory-based operations is foreseen to bring large changes to the work domain of the Air Traffic Controller. Although this new form of Air Traffic Control leans heavily on the introduction of advanced automation, the general consensus is that the human must remain actively involved in the decision-making loop, and retain the ultimate responsibility for the safety of operations. These responsibilities, together with the complexities of the new task, require the development of innovative decision support tools. In previous research, and following the principles of Ecological Interface Design, a constraint-based decision support tool has been developed for the task of strategic trajectory manipulation. Rather than presenting discrete optimized solutions to the controller, this Travel Space Representation visualizes the constraints for safe control in the form of a set of `go' and `no go' areas. A validation experiment demonstrated that when using this tool, controllers sometimes opted for controlling close to the boundaries of safe control, or for resolutions in narrow control spaces. These results gave rise to concern that such a representation could actually work against the flexibility of the system to cope with inherent system variability. In this study, a metric and two measures have been developed in order to quantify and compare trajectory-based robustness to probabilistic disturbances. A batch-analysis has been performed to investigate how these measures vary for a crossing pair of aircraft under various geometry. Results show that the metric captures additional information which is currently not represented in the tool. When visualized to the controller, this could support them to choose more robust control strategies.
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