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Aerospace, Volume 6, Issue 5 (May 2019)

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Cover Story (view full-size image) Modern aircraft engines must operate at ever-higher temperatures, pressures, and rotational speeds, [...] Read more.
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Open AccessArticle
Solar Module Integrated Converters as Power Generator in Small Spacecrafts: Design and Verification Approach
Received: 18 April 2019 / Revised: 17 May 2019 / Accepted: 17 May 2019 / Published: 27 May 2019
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Abstract
As small satellites are becoming more widespread for new businesses and applications, the development time, failure rate and cost of the spacecraft must be reduced. One of the systems with the highest cost and the most frequent failure in the satellite is the [...] Read more.
As small satellites are becoming more widespread for new businesses and applications, the development time, failure rate and cost of the spacecraft must be reduced. One of the systems with the highest cost and the most frequent failure in the satellite is the Electrical Power System (EPS). One approach to achieve rapid development times while reducing the cost and failure rate is using scalable modules. We propose a solar module integrated converter (SMIC) and its verification process as a key component for power generation in EPS. SMIC integrates the solar array, its regulators and the telemetry acquisition unit. This paper details the design and verification process of the SMIC and presents the in-orbit results of 12 SMICs used in Ten-Koh satellite, which was developed in less than 1.5 years. The in-orbit data received since the launch reveal that solar module withstands not only the launching environment of H-IIA rocket but also more than 1500 orbits in LEO. The modular approach allowed the design, implementation and qualification of only one module, followed by manufacturing and integration of 12 subsequent flight units. The approach with the solar module can be followed in other components of the EPS such as battery and power regulators. Full article
(This article belongs to the Special Issue Verification Approaches for Nano- and Micro-Satellites)
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Open AccessArticle
Unsteady Flow Structures within a Turbine Rim Seal Cavity in the Presence of Purge Flow—An Experimental and Computational Unsteady Aerodynamics Investigation
Received: 18 March 2019 / Revised: 14 May 2019 / Accepted: 14 May 2019 / Published: 25 May 2019
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Abstract
Flow within the space between the rotor and stator of a turbine disk, and an area referred to as the rim seal cavity, develops azimuthal velocity component from the rotor disk. The fluid within develops unsteady structures that move at a fraction of [...] Read more.
Flow within the space between the rotor and stator of a turbine disk, and an area referred to as the rim seal cavity, develops azimuthal velocity component from the rotor disk. The fluid within develops unsteady structures that move at a fraction of the rotor speed. A test is designed to measure the number of unsteady structures and the rotational speed at which they are moving in the rim seal cavity of an experimental research rig. Data manipulation was developed to extract the speed, and the numbers of structures present using two fast-response aerodynamic probes measuring static pressure on the surface of the nozzle guide vane (NGV)-side rim seal cavity. A computational study is done to compare measured results to a transient unsteady Reynolds-averaged Navier–Stokes (URANS). The computational simulation consists of eight vanes and ten blades, carefully picked to reduce the error caused by blade vane pitch mismatch and to allow for the structures to develop correctly, and the rim seal cavity to measure the speed and number of the structures. The experimental results found 15 structures moving at 77.5% of the rotor speed, and the computational study suggested 14.5 structures are moving at 81.7% rotor speed. The agreement represents the first known test of its kind in a large-scale turbine test rig and the first known “good” agreement between computational and experimental work. Full article
(This article belongs to the Special Issue Secondary Air Systems in Gas Turbine Engines)
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Open AccessArticle
Optimization of the Energy Storage of Series-Hybrid Propelled Aircraft by Means of Integer Differential Evolution
Received: 4 February 2019 / Revised: 8 March 2019 / Accepted: 22 March 2019 / Published: 23 May 2019
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Abstract
The possibility of realizing full electric or hybrid electric propulsion for aircraft has been considered due to the constant growth in the use of electric technologies in aircraft and the availability of high-power-density electrical machines and converters. In this paper, an optimized design [...] Read more.
The possibility of realizing full electric or hybrid electric propulsion for aircraft has been considered due to the constant growth in the use of electric technologies in aircraft and the availability of high-power-density electrical machines and converters. In this paper, an optimized design approach is proposed with reference to the optimal trade-off between energy storage system sizing and the fuel mass of a series of hybrid aircraft. The problem is approached using an integer optimization algorithm based on differential evolution and by mixing both the flight mechanics and the electrical issues inherent to hybrid flights. This method has been validated by means of implementing numerical simulations and the results are reported and discussed in the paper. Full article
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Open AccessArticle
Taxonomy of Gas Turbine Blade Defects
Received: 4 April 2019 / Revised: 27 April 2019 / Accepted: 17 May 2019 / Published: 21 May 2019
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Abstract
Context—The maintenance of aero engines is intricate, time-consuming, costly and has significant functional and safety implications. Engine blades and vanes are the most rejected parts during engine maintenance. Consequently, there is an ongoing need for more effective and efficient inspection processes. Purpose—This paper [...] Read more.
Context—The maintenance of aero engines is intricate, time-consuming, costly and has significant functional and safety implications. Engine blades and vanes are the most rejected parts during engine maintenance. Consequently, there is an ongoing need for more effective and efficient inspection processes. Purpose—This paper defines engine blade defects, assigns root-causes, shows causal links and cascade effects and provides a taxonomy system. Approach—Defect types were identified from the literature and maintenance manuals, categorisations were devised and an ontology was created. Results—Defect was categorised into Surface Damage, Wear, Material Separation and Material Deformation. A second categorisation identified potential causes of Impact, Environmental causes, Operational causes, Poor maintenance, Poor manufacturing and Fatigue. These two categorisations were integrated with an ontology. Originality—The work provides a single comprehensive illustrated list of engine blade defects, and a standardised defect terminology, which currently does not exist in the aviation industry. It proposes a taxonomy for both engine blade defects and root-causes, and shows that these may be related using an ontology. Full article
(This article belongs to the Special Issue Managing Data and Information of Aerospace Product Lifecycle)
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Open AccessArticle
Accurate 2-D Modelling of Transonic Compressor Cascade Aerodynamics
Received: 15 April 2019 / Revised: 9 May 2019 / Accepted: 15 May 2019 / Published: 19 May 2019
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Abstract
Modern aeronautic fans are characterised by a transonic flow regime near the blade tip. Transonic cascades enable higher pressure ratios by a complex system of shockwaves arising across the blade passage, which has to be correctly reproduced in order to predict the performance [...] Read more.
Modern aeronautic fans are characterised by a transonic flow regime near the blade tip. Transonic cascades enable higher pressure ratios by a complex system of shockwaves arising across the blade passage, which has to be correctly reproduced in order to predict the performance and the operative range. In this paper, we present an accurate two-dimensional numerical modelling of the ARL-SL19 transonic compressor cascade. A large series of data from experimental tests in supersonic wind tunnel facilities has been used to validate a computational fluid dynamic model, in which the choice of turbulence closure resulted critical for an accurate reproduction of shockwave-boundary layer interaction. The model has been subsequently employed to carry out a parametric study in order to assess the influence of main flow variables (inlet Mach number, static pressure ratio) and geometric parameters (solidity) on the shockwave pattern and exit status. The main objectives of the present work are to perform a parametric study for investigating the effects of the abovementioned variables on the cascade performance, in terms of total-pressure loss coefficient, and on the shockwave pattern and to provide a quite large series of data useful for a preliminary design of a transonic compressor rotor section. After deriving the relation between inlet and exit quantities, peculiar to transonic compressors, exit Mach number, mean exit flow angle and total-pressure loss coefficient have been examined for a variety of boundary conditions and parametrically linked to inlet variables. Flow visualisation has been used to describe the shock-wave pattern as a function of the static pressure ratio. Finally, the influence of cascade solidity has been examined, showing a potential reduction of total-pressure loss coefficient by employing a higher solidity, due to a significant modification of shockwave system across the cascade. Full article
(This article belongs to the Special Issue Progress in Jet Engine Technology)
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Open AccessFeature PaperReview
The Application of Computational Thermo-Fluid-Dynamics to the Simulation of Hybrid Rocket Internal Ballistics with Classical or Liquefying Fuels: A Review
Received: 20 February 2019 / Revised: 7 May 2019 / Accepted: 11 May 2019 / Published: 16 May 2019
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Abstract
The computational fluid dynamics of hybrid rocket internal ballistics is becoming a key tool for reducing the engine operation uncertainties and development cost as well as for improving experimental data analysis. Nevertheless, its application still presents numerous challenges for the complexity of modeling [...] Read more.
The computational fluid dynamics of hybrid rocket internal ballistics is becoming a key tool for reducing the engine operation uncertainties and development cost as well as for improving experimental data analysis. Nevertheless, its application still presents numerous challenges for the complexity of modeling the phenomena involved in the fuel consumption mechanism and its coupling with the chemically reacting flowfield. This paper presents a review of the computational thermo-fluid-dynamic models developed for the internal ballistics of hybrid rockets burning gaseous oxygen with classical polymeric or paraffin-based fuels, with a special focus on the interaction between the fluid and the solid fuel surface. With the purpose of predicting the local fuel regression rate, which is the main parameter needed for the hybrid rocket design, the model is coupled with an improved gas/surface interface treatment based on local mass, energy and mean mixture-fraction balances, combined to either a pyrolysis-rate equation in the case of classical polymers, or to an additional equation for the liquid paraffin entrainment fraction of the total fuel consumption rate. A number of experimental test cases obtained from the static firing of two different laboratory-scale rockets are simulated to determine the models’ capabilities, showing very good agreement between the calculated and measured fuel regression rates with both standard pyrolyzing and liquefying fuels. The prediction of the chamber pressure measured with paraffin fuel resulted in it being more cumbersome for the single-phase flow assumption. The advantages and limitations of the models are discussed. Full article
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Open AccessArticle
Investigation of Micro Gas Turbine Systems for High Speed Long Loiter Tactical Unmanned Air Systems
Received: 6 March 2019 / Revised: 24 April 2019 / Accepted: 7 May 2019 / Published: 14 May 2019
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Abstract
In this study, the on-going research into the improvement of micro-gas turbine propulsion system performance and the suitability for its application as propulsion systems for small tactical UAVs (<600 kg) is investigated. The study is focused around the concept of converting existing micro [...] Read more.
In this study, the on-going research into the improvement of micro-gas turbine propulsion system performance and the suitability for its application as propulsion systems for small tactical UAVs (<600 kg) is investigated. The study is focused around the concept of converting existing micro turbojet engines into turbofans with the use of a continuously variable gearbox, thus maintaining a single spool configuration and relative design simplicity. This is an effort to reduce the initial engine development cost, whilst improving the propulsive performance. The BMT 120 KS micro turbojet engine is selected for the performance evaluation of the conversion process using the gas turbine performance software GasTurb13. The preliminary design of a matched low-pressure compressor (LPC) for the proposed engine is then performed using meanline calculation methods. According to the analysis that is carried out, an improvement in the converted micro gas turbine engine performance, in terms of thrust and specific fuel consumption is achieved. Furthermore, with the introduction of a CVT gearbox, the fan speed operation may be adjusted independently of the core, allowing an increased thrust generation or better fuel consumption. This therefore enables a wider gamut of operating conditions and enhances the performance and scope of the tactical UAV. Full article
(This article belongs to the collection Unmanned Aerial Systems)
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Open AccessArticle
Engineering Methodology for Student-Driven CubeSats
Received: 31 December 2018 / Revised: 25 March 2019 / Accepted: 25 March 2019 / Published: 13 May 2019
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Abstract
CubeSats are widely used by universities and research institutions all over the world. Their popularity is generally attributed to the use of low-cost components, free student labor and simple design. They have been shown to encourage Science, Technology, Engineering and Math (STEM) students [...] Read more.
CubeSats are widely used by universities and research institutions all over the world. Their popularity is generally attributed to the use of low-cost components, free student labor and simple design. They have been shown to encourage Science, Technology, Engineering and Math (STEM) students to become involved in designing, implementing and testing a real functioning spacecraft system. Projects like this encourage students from different disciplines to team up to design and build CubeSats, providing interdisciplinary work experience. Participating students vary in their expertise in developing such systems. Some will work on the project for years while others are not willing to spend two or three consecutive semesters developing a CubeSat project. Despite their simplicity in design and low cost, CubeSats are considered great engineering systems for exploring space. Nevertheless, a large number of CubeSat projects fail due to having an unclear mission, ambiguous system requirements and a lack of documentation. Students need to have a clear vision of how to build a real CubeSat system that can be launched and that can function in space. Thus, this paper proposes engineering methodologies and tools to help students develop CubeSat systems. These tools can help students with planning, collecting, eliciting and documenting the requirements in a well-defined manner. This paper focuses on student-driven CubeSat projects designed by students and faculty members. Additionally, data is presented in this paper to identify the challenges and needs of CubeSat developers. Plans for future work are also discussed. Full article
(This article belongs to the Special Issue Verification Approaches for Nano- and Micro-Satellites)
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Open AccessArticle
Innovating the Maintenance Repair and Overhaul Phase through Digitalization
Received: 28 March 2019 / Revised: 6 May 2019 / Accepted: 7 May 2019 / Published: 9 May 2019
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Abstract
Improving processes in a company starts from a deep knowledge of the current context, of the needs for improvement and of the objectives to be satisfied. Sometimes, traditional processes can benefit from a techno-organizational innovation that changes the way of work by introducing [...] Read more.
Improving processes in a company starts from a deep knowledge of the current context, of the needs for improvement and of the objectives to be satisfied. Sometimes, traditional processes can benefit from a techno-organizational innovation that changes the way of work by introducing new routines and solutions. The service industry related to maintenance, repair and overhaul (MRO) is characterized by performance linked with the knowledge about the components involved. The emerging technologies and the need for enhanced competitiveness has led to transform and innovate this kind of industry, introducing changes in organizational and technological aspects. MRO processes are characterized by high variability, caused by the uncertainty about the arrival status of a part to be maintained and the intervention needed. The management of MRO processes is, thus, one of the most important challenges for the research community. This paper aims to describe the result of a study carried out by university researchers and industrial engineers of an aerospace company. The proposed solution, the applied approach and expected impacts and benefits are described in the paper in order to lead future activities in the managerial and academic fields. Full article
(This article belongs to the Special Issue Managing Data and Information of Aerospace Product Lifecycle)
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Open AccessArticle
A Numerical–Analytical Approach for the Preliminary Design of Thin-Walled Cylindrical Shell Structures with Elliptical Cut-Outs
Received: 5 March 2019 / Revised: 26 April 2019 / Accepted: 29 April 2019 / Published: 6 May 2019
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Abstract
The presence of cut-outs within thin-walled shell structures is unavoidable, holes being needed for the passage of electrical cables, fuel, or just to reduce the weight of the components. Nevertheless, the high stress concentration can lead to a premature collapse of the structure. [...] Read more.
The presence of cut-outs within thin-walled shell structures is unavoidable, holes being needed for the passage of electrical cables, fuel, or just to reduce the weight of the components. Nevertheless, the high stress concentration can lead to a premature collapse of the structure. For this reason, the preliminary design of cylindrical shell structures with holes needs a profound knowledge of the stress distribution for different loading conditions and constraints. In this paper, a parametric study of a fiber-reinforced composite shell cylinder with an elliptical cut-out has been performed. Three different loading conditions were analyzed: Tension, bending, and torsion. Ansys® script, capable of easily generating and analyzing different geometrical configurations, was used to study the dependence of the geometry on the stress distribution near the cut-out. Finally, graphical and analytical relationships were tentatively extrapolated from numerical results, aimed at linking the geometrical parameters of the cut-out to the maximum stress near the cut-out. Full article
(This article belongs to the Special Issue Structural Stability of Aerospace Structures)
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Open AccessArticle
Environment for Planning Unmanned Aerial Vehicles Operations
Received: 28 February 2019 / Revised: 29 April 2019 / Accepted: 30 April 2019 / Published: 4 May 2019
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Abstract
Planning and executing missions in terms of trajectory generation are challenging problems in the operational phase of unmanned aerial vehicles (UAVs) lifecycle. The growing adoption of UAVs in several civil applications requires the definition of precise procedures and tools to safely manage UAV [...] Read more.
Planning and executing missions in terms of trajectory generation are challenging problems in the operational phase of unmanned aerial vehicles (UAVs) lifecycle. The growing adoption of UAVs in several civil applications requires the definition of precise procedures and tools to safely manage UAV missions that may involve flight over populated areas. The paper aims at providing a contribution toward the definition of a reliable environment, called FLIP (flight planner) for route planning and risk evaluation in the framework of mini- and micro-UAV missions over populated areas. The environment represents a decision support system (DSS) for UAV operators and other decision makers, like airports authorities and aviation agencies. A new ICT tool integrating an innovative procedure for evaluating the risk related to the use of UAV over populated areas is proposed. Full article
(This article belongs to the Special Issue Managing Data and Information of Aerospace Product Lifecycle)
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Open AccessArticle
Comparison of Solar Radiation Torque and Power Generation of Deployable Solar Panel Configurations on Nanosatellites
Received: 26 February 2019 / Revised: 25 April 2019 / Accepted: 29 April 2019 / Published: 2 May 2019
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Abstract
Nanosatellites, like CubeSat, have begun completing advanced missions that require high power that can be obtained using deployable solar panels. However, a larger solar array area facing the Sun increases the solar radiation torque on the satellite. In this study, we investigated solar [...] Read more.
Nanosatellites, like CubeSat, have begun completing advanced missions that require high power that can be obtained using deployable solar panels. However, a larger solar array area facing the Sun increases the solar radiation torque on the satellite. In this study, we investigated solar radiation torque characteristics resulting from the increased area of solar panels on board the CubeSats. Three common deployable solar panel configurations that are commercially available were introduced and their reference missions were established for the purpose of comparison. The software algorithms used to simulate a variety of orbit scenarios are described in detail and some concerns are highlighted based on the results obtained. The solar power generation of the respective configurations is provided. The findings are useful for nanosatellite developers in predicting the characteristics of solar radiation torques and solar power generation that will be encountered when using various deployable solar panels, thus helping with the selection of a suitable configuration for their design. Full article
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Open AccessArticle
Effect of Ingress on Flow and Heat Transfer Upstream and Downstream of a Rotating Turbine Disc
Received: 31 January 2019 / Revised: 16 April 2019 / Accepted: 18 April 2019 / Published: 26 April 2019
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Abstract
Ingress is the penetration of a hot mainstream gas in a turbine annulus through the rim seal into the wheel-space between the rotating turbine disc (the rotor) and the adjacent stationary casing (the stator). Purge flow is used to prevent or reduce ingress, [...] Read more.
Ingress is the penetration of a hot mainstream gas in a turbine annulus through the rim seal into the wheel-space between the rotating turbine disc (the rotor) and the adjacent stationary casing (the stator). Purge flow is used to prevent or reduce ingress, and the sealing effectiveness relates the flow rates of the purge and ingress. In this paper, an adiabatic effectiveness is used to relate the temperatures of a thermally-insulated rotor, the purge flow and the ingress. A non-dimensional buffer parameter, Ψ, is used to relate the sealing effectiveness on the stator and the adiabatic effectiveness on the rotor, respectively. This paper reports the first experimental study of the effect of ingress and purge flow on the adiabatic temperatures of both upstream and downstream surfaces of the rotor. Measurements of concentration and swirl over a range of purge have been obtained in wheel-spaces upstream and downstream of the rotor in a turbine rig. In transient heating tests, fast-response thermocouples were used to measure the temperature of the air in the wheel-space core; simultaneously, the temperatures of the upstream and downstream rotor surfaces were determined from infra-red sensors. The extrapolated steady-state temperatures (obtained using a maximum-likelihood estimation analysis) were used to determine the adiabatic effectiveness as a function of purge flow rate. The buffer effect of the purge flow for both wheel-spaces was quantified via comparisons between the variation of Ψ with purge flow rate. It was shown that the sealing effectiveness for the downstream wheel-space was larger than for the upstream. Consequently, and consistent with the theoretical model, the buffering effect of the purge flow was shown to be smaller downstream. Full article
(This article belongs to the Special Issue Secondary Air Systems in Gas Turbine Engines)
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Aerospace EISSN 2226-4310 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
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