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Aerospace, Volume 5, Issue 1 (March 2018)

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Cover Story (view full-size image) This turbofan engine is a cooperation between MTU Aero Engines located in Munich and Pratt & [...] Read more.
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Editorial

Jump to: Research, Review

Open AccessEditorial Acknowledgement to Reviewers of Aerospace in 2017
Aerospace 2018, 5(1), 7; doi:10.3390/aerospace5010007
Received: 10 January 2018 / Revised: 10 January 2018 / Accepted: 10 January 2018 / Published: 10 January 2018
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Abstract
Peer review is an essential part in the publication process, ensuring that Aerospace maintains high quality standards for its published papers [...] Full article

Research

Jump to: Editorial, Review

Open AccessArticle Molecular Dynamics Electrospray Simulations of Coarse-Grained Ethylammonium Nitrate (EAN) and 1-Ethyl-3-Methylimidazolium Tetrafluoroborate (EMIM-BF4)
Aerospace 2018, 5(1), 1; doi:10.3390/aerospace5010001
Received: 30 September 2017 / Revised: 20 December 2017 / Accepted: 25 December 2017 / Published: 28 December 2017
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Abstract
In this work, the use of molecular dynamics as a predictive tool for modeling the atomistic behavior of electrospray propulsion is discussed. 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) and ethylammonium nitrate (EAN) were considered as two limits of ionic liquid (IL) propellants that tend
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In this work, the use of molecular dynamics as a predictive tool for modeling the atomistic behavior of electrospray propulsion is discussed. 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF 4 ) and ethylammonium nitrate (EAN) were considered as two limits of ionic liquid (IL) propellants that tend to operate in an ion versus a droplet mode. The emission modes were found to depend on the electro-chemical properties of the IL propellant. The aprotic EMIM-BF 4 -based electrospray emitted primarily monomers and trimers as the dominant species and only small quantities of droplets. In contrast, trimers were the dominant emitted species in the protic EAN emissions with a significantly large contribution from droplets towards the total emission current, suggesting that EMIM-BF 4 -based colloid thrusters operate in ion mode and EAN-based devices operate in the droplet mode. Furthermore, the formation of the Taylor cone was found to depend on the mass flow rate and the external electric field strength. This paper provides a framework that can be extended for use to simulate any other ILs or their combinations. Full article
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Open AccessArticle Application of an Efficient Gradient-Based Optimization Strategy for Aircraft Wing Structures
Aerospace 2018, 5(1), 3; doi:10.3390/aerospace5010003
Received: 8 December 2017 / Revised: 26 December 2017 / Accepted: 2 January 2018 / Published: 4 January 2018
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Abstract
In this paper, a practical optimization framework and enhanced strategy within an industrial setting are proposed for solving large-scale structural optimization problems in aerospace. The goal is to eliminate the difficulties associated with optimization problems, which are mostly nonlinear with numerous mixed continuous-discrete
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In this paper, a practical optimization framework and enhanced strategy within an industrial setting are proposed for solving large-scale structural optimization problems in aerospace. The goal is to eliminate the difficulties associated with optimization problems, which are mostly nonlinear with numerous mixed continuous-discrete design variables. Particular emphasis is placed on generating good initial starting points for the search process and in finding a feasible optimum solution or improving the chances of finding a better optimum solution when traditional techniques and methods have failed. The efficiency and reliability of the proposed strategy were demonstrated through the weight optimization of different metallic and composite laminated wingbox structures. The results show the effectiveness of the proposed procedures in finding an optimized solution for high-dimensional search space cases with a given level of accuracy and reasonable computational resources and user efforts. Conclusions are also inferred with regards to the sensitivity of the optimization results obtained with respect to the choice of different starting values for the design variables, as well as different optimization algorithms in the optimization process. Full article
(This article belongs to the collection Feature Papers in Aerospace)
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Open AccessArticle An Efficient Processing Architecture for Range Profiling Using Noise Radar Technology
Aerospace 2018, 5(1), 4; doi:10.3390/aerospace5010004
Received: 4 November 2017 / Revised: 24 December 2017 / Accepted: 3 January 2018 / Published: 6 January 2018
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Abstract
The importance of high resolution range profiles (HRRPs) for radar applications like tracking or classification is well known. In the scientific literature several approaches have been investigated to obtain HRRPs from wideband radar signals. Recent works show that noise radar waveforms can be
[...] Read more.
The importance of high resolution range profiles (HRRPs) for radar applications like tracking or classification is well known. In the scientific literature several approaches have been investigated to obtain HRRPs from wideband radar signals. Recent works show that noise radar waveforms can be exploited in this sense due to their high resolution and low peak to sidelobe ratio (PSLR) properties. However their use can cause some issues in applications where long time integrations are required, e.g., in the presence of a low effective radiated power (ERP) transmitter: recording the reference signal in this case would be difficult due to the big quantity of data. This work proposes a real time digital processing schematic based on linear feedback shift registers (LFSRs) which is very flexible and has a low computational burden: its internal state can be easily controlled and reproduced in reception, where a multichannel correlator is exploited as matched filter. The resulting signal, compared to typical “pulse compression” and noise radar waveforms, shows similar performances but a lower order of complexity in terms of real time generation and reception. Full article
(This article belongs to the Special Issue Radar and Aerospace)
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Open AccessArticle Preliminary Correlations for Remotely Piloted Aircraft Systems Sizing
Aerospace 2018, 5(1), 5; doi:10.3390/aerospace5010005
Received: 28 October 2017 / Revised: 20 December 2017 / Accepted: 5 January 2018 / Published: 8 January 2018
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Abstract
The field of Remotely Piloted Aircraft Systems (RPAS) is currently undergoing a noteworthy expansion. The diverse types of missions that these aircraft can accomplish, both in military and civil environments, have motivated an increase of interest in their study and applications. The methods
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The field of Remotely Piloted Aircraft Systems (RPAS) is currently undergoing a noteworthy expansion. The diverse types of missions that these aircraft can accomplish, both in military and civil environments, have motivated an increase of interest in their study and applications. The methods chosen to develop this study are based on the statistical analysis of a database including numerous models of RPAS and the estimation of different correlations in order to develop a design method for rapid sizing of H-tail RPAS. Organizing the information of the database according to relevant characteristics, information relative to the state-of-the-art design tendencies can be extracted, which can serve to take decisions relative to the aerodynamic configuration or the power plant in the first phases of the design project. Furthermore, employing statistical correlations estimated from the database, a design method for rapid-sizing of H-tail RPAS has been conducted, which will be focused on the sizing of the wing and tail surfaces. The resulting method has been tested by applying it to an example case so as to validate the proposed procedure. Full article
(This article belongs to the collection Feature Papers in Aerospace)
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Open AccessArticle A Macroscopic Performance Analysis of NASA’s Northrop Grumman RQ-4A
Aerospace 2018, 5(1), 6; doi:10.3390/aerospace5010006
Received: 1 December 2017 / Revised: 2 January 2018 / Accepted: 4 January 2018 / Published: 10 January 2018
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Abstract
This paper presents the process of identification, from a macroscopic point of view, of the Northrop Grumman RQ-4A Global Hawk Remote-Piloted Aircraft System from real, but limited flight information. Performance parameters and operational schemes will be extracted by analyzing available data from two
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This paper presents the process of identification, from a macroscopic point of view, of the Northrop Grumman RQ-4A Global Hawk Remote-Piloted Aircraft System from real, but limited flight information. Performance parameters and operational schemes will be extracted by analyzing available data from two specific science flights flown by the Global Hawk back in 2010. Each phase of the flight, take-off, climb, cruise climb, descent and landing, is analyzed from various points of view: speed profile, altitude, climb/descent ratios and rate of turn. The key performance parameters derived from individual flights will be confirmed by performing a wider statistical validation with additional flight trajectories. Derived data are exploited to validate a simulated RQ-4A vehicle employed in extensive real-time air traffic management simulated integration exercises and to complement the development of a future RQ-4A trajectory predictor. Full article
(This article belongs to the Special Issue Aircraft Dynamics & Control)
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Open AccessArticle Fast Aircraft Turnaround Enabled by Reliable Passenger Boarding
Aerospace 2018, 5(1), 8; doi:10.3390/aerospace5010008
Received: 24 November 2017 / Revised: 31 December 2017 / Accepted: 9 January 2018 / Published: 15 January 2018
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Abstract
Future 4D aircraft trajectories demand comprehensive consideration of environmental, economic, and operational constraints, as well as reliable prediction of all aircraft-related processes. Mutual interdependencies between airports result in system-wide, far-reaching effects in the air traffic network (reactionary delays). To comply with airline/airport challenges
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Future 4D aircraft trajectories demand comprehensive consideration of environmental, economic, and operational constraints, as well as reliable prediction of all aircraft-related processes. Mutual interdependencies between airports result in system-wide, far-reaching effects in the air traffic network (reactionary delays). To comply with airline/airport challenges over the day of operations, a change to an air-to-air perspective is necessary, with a specific focus on the aircraft ground operations as major driver for airline punctuality. Aircraft ground trajectories primarily consists of handling processes at the stand (deboarding, catering, fueling, cleaning, boarding, unloading, loading), which are defined as the aircraft turnaround. Turnaround processes are mainly controlled by ground handling, airport, or airline staff, except the aircraft boarding, which is driven by passengers’ experience and willingness/ability to follow the proposed boarding procedures. This paper provides an overview of the research done in the field of aircraft boarding and introduces a reliable, calibrated, and stochastic aircraft boarding model. The stochastic boarding model is implemented in a simulation environment to evaluate specific boarding scenarios using different boarding strategies and innovative technologies. Furthermore, the potential of a connected aircraft cabin as sensor network is emphasized, which could provide information on the current and future status of the boarding process. Full article
(This article belongs to the collection Air Transportation—Operations and Management)
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Open AccessArticle Pneumatically Powered Drilling of Carbon Fibre Composites Using Synthetic Biodegradable Lubricating Oil: An Experimental Study
Aerospace 2018, 5(1), 9; doi:10.3390/aerospace5010009
Received: 27 November 2017 / Revised: 7 January 2018 / Accepted: 11 January 2018 / Published: 16 January 2018
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Abstract
Carbon fibre composites are a key component of aircraft structures because of their enhanced material properties such as favourable strength to weight ratios when compared to metal alloys. During the assembly process of an aircraft, carbon fibre components are joined to other structures
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Carbon fibre composites are a key component of aircraft structures because of their enhanced material properties such as favourable strength to weight ratios when compared to metal alloys. During the assembly process of an aircraft, carbon fibre components are joined to other structures using rivets, bolts, and fasteners, and as part of the joining process, the components will need to be machined or drilled. Unlike metal alloys, composites are sensitive to heat and are vulnerable to internal structural damage from machining tools. They are also susceptible to a reduction in strength when fibres are exposed to moisture. In the machining process, carbon fibre composites may be drilled using oils to lubricate carbide machining tools. In this study, a description of the experimental apparatus is provided along with an investigation to determine the influence synthetic biodegradable lubricating oil has on drill rotational speed, drilling load, and drilling temperature when using a pneumatic drill to machine carbon fibre composite material. Full article
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Open AccessArticle Formal Verification of Simulation Scenarios in Aviation Scenario Definition Language (ASDL)
Aerospace 2018, 5(1), 10; doi:10.3390/aerospace5010010
Received: 28 November 2017 / Revised: 1 January 2018 / Accepted: 15 January 2018 / Published: 17 January 2018
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Abstract
Formal methods offer well-defined means for mathematical verification of the functional specifications of software systems. For model-based engineering, model checking is a verification technique that explores all possible system states. The Aviation Scenario Definition Language is a domain-specific language designed based on a
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Formal methods offer well-defined means for mathematical verification of the functional specifications of software systems. For model-based engineering, model checking is a verification technique that explores all possible system states. The Aviation Scenario Definition Language is a domain-specific language designed based on a scenario development process from a model-driven engineering perspective. It aims at providing a well-structured definition language to specify departure, en route, re-route, and landing scenarios. This paper uses statecharts and a model checker for the verification of each scenario generated and uses examples to demonstrate conformance to the rules established in the statecharts to verify the logic of all future scenarios. Full article
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Open AccessArticle Experimental Implementation of a Passive Millimeter-Wave Fast Sequential Lobing Radiometric Seeker Sensor
Aerospace 2018, 5(1), 11; doi:10.3390/aerospace5010011
Received: 22 November 2017 / Revised: 11 January 2018 / Accepted: 16 January 2018 / Published: 18 January 2018
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Abstract
The paper investigates the theory of operation of a passive millimeter-wave seeker sensor using a fast electronic sequential-lobing technique and the experimental validation obtained through laboratory trials. The paper analyzes in detail the theoretical performance of a difference channel sensor and a pseudo-monopulse
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The paper investigates the theory of operation of a passive millimeter-wave seeker sensor using a fast electronic sequential-lobing technique and the experimental validation obtained through laboratory trials. The paper analyzes in detail the theoretical performance of a difference channel sensor and a pseudo-monopulse sensor deriving agile formulas for the estimation of target angular tracking accuracy and the subsequent experimental validation. Full article
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Open AccessArticle Numerical Investigation on Windback Seals Used in Aero Engines
Aerospace 2018, 5(1), 12; doi:10.3390/aerospace5010012
Received: 16 November 2017 / Revised: 4 January 2018 / Accepted: 12 January 2018 / Published: 20 January 2018
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Abstract
Seals are considered one of the most important flow elements in turbomachinery applications. The most traditional and widely known seal is the labyrinth seal but in recent years other types like the brush or carbon seals were introduced since they considerably reduce the
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Seals are considered one of the most important flow elements in turbomachinery applications. The most traditional and widely known seal is the labyrinth seal but in recent years other types like the brush or carbon seals were introduced since they considerably reduce the sealing air consumption. When seals are used for sealing of aero engine bearing chambers they are subjected to high “bombardment” through oil particles which are present in the bearing chamber. These particles mainly result from the bearings as a consequence of the high rotational speeds. Particularly when carbon or brush seals are used, problems with carbon formation (coking) may arise when oil gets trapped in the very tight gap of these seals. In order to prevent oil migration into the turbomachinery, particularly when the pressure difference over a seal is small or even negligible, significant improvement can be achieved through the introduction of so called windback seals. This seal has a row of static helical teeth (thread) and below this thread a scalloped or smooth shaft section is rotating. Depending on the application, a windback seal can be used alone or as a combination with another seal (carbon, brush or labyrinth seal). A CFD analysis carried out with ANSYS CFX version 11 is presented in this paper with the aim to investigate this seal type. The simulations were performed by assuming a two-phase flow of air and oil in the bearing compartment. Design parameters like seal clearance, thread size, scallop width, were investigated at different operating conditions. Full article
(This article belongs to the Special Issue Secondary Air Systems in Gas Turbine Engines)
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Open AccessArticle Mathematical Modeling of Liquid-fed Pulsed Plasma Thruster
Aerospace 2018, 5(1), 13; doi:10.3390/aerospace5010013
Received: 19 December 2017 / Revised: 16 January 2018 / Accepted: 18 January 2018 / Published: 22 January 2018
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Abstract
Liquid propellants are fast becoming attractive for pulsed plasma thrusters due to their high efficiency and low contamination issues. However, the complete plasma interaction and acceleration processes are still not very clear. Present paper develops a multi-layer numerical model for liquid propellant PPTs
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Liquid propellants are fast becoming attractive for pulsed plasma thrusters due to their high efficiency and low contamination issues. However, the complete plasma interaction and acceleration processes are still not very clear. Present paper develops a multi-layer numerical model for liquid propellant PPTs (pulsed plasma thrusters). The model is based on a quasi-steady flow assumption. The model proposes a possible acceleration mechanism for liquid-fed pulsed plasma thrusters and accurately predicts the propellant utilization capabilities and estimations for the fraction of propellant gas that is completely ionized and accelerated to high exit velocities. Validation of the numerical model and the assumptions on which the model is based on is achieved by comparing the experimental results and the simulation results for two different liquid-fed thrusters developed at the University of Tokyo. Simulation results shows that up-to 50 % of liquid propellant injected is completely ionized and accelerated to high exit velocities (>50 Km/s), whereas, neutral gas contribute to only 7 % of the total specific impulse and accelerated to low exit velocity (<4 Km/s). The model shows an accuracy up-to 92 % . Optimization methods are briefly discussed to ensure efficient propellant utilization and performance. The model acts as a tool to understand the background physics and to optimize the performance for liquid-fed PPTs. Full article
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Open AccessArticle Wake-Model Effects on Induced Drag Prediction of Staggered Boxwings
Aerospace 2018, 5(1), 14; doi:10.3390/aerospace5010014
Received: 30 November 2017 / Revised: 23 December 2017 / Accepted: 12 January 2018 / Published: 24 January 2018
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Abstract
For staggered boxwings the predictions of induced drag that rely on common potential-flow methods can be of limited accuracy. For example, linear, freestream-fixed wake models cannot resolve effects related to wake deflection and roll-up, which can have significant affects on the induced drag
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For staggered boxwings the predictions of induced drag that rely on common potential-flow methods can be of limited accuracy. For example, linear, freestream-fixed wake models cannot resolve effects related to wake deflection and roll-up, which can have significant affects on the induced drag projection of these systems. The present work investigates the principle impact of wake modelling on the accuracy of induced drag prediction of boxwings with stagger. The study compares induced drag predictions of a higher-order potential-flow method that uses fixed and relaxed-wake models, and of an Euler-flow method. Positive-staggered systems at positive angles of attack are found to be particularly prone to higher-order wake effects due to vertical contraction of wakes trajectories, which results in smaller effective height-to-span ratios than compared with negative stagger and thus closer interactions between trailing wakes and lifting surfaces. Therefore, when trying to predict induced drag of positive staggered boxwings, only a potential-flow method with a fully relaxed-wake model will provide the high-degree of accuracy that rivals that of an Euler method while being computationally significantly more efficient. Full article
(This article belongs to the collection Feature Papers in Aerospace)
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Open AccessArticle Fully-Deterministic Execution of IEC-61499 Models for Distributed Avionics Applications
Aerospace 2018, 5(1), 15; doi:10.3390/aerospace5010015
Received: 31 October 2017 / Revised: 28 December 2017 / Accepted: 22 January 2018 / Published: 3 February 2018
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Abstract
The development of time-critical Distributed Avionics Applications (DAAs) pushes beyond the limit of existing modeling methodologies to design dependable systems. Aerospace and industrial automation entail high-integrity applications where execution time is essential for dependability. This tempts us to use modeling technologies from one
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The development of time-critical Distributed Avionics Applications (DAAs) pushes beyond the limit of existing modeling methodologies to design dependable systems. Aerospace and industrial automation entail high-integrity applications where execution time is essential for dependability. This tempts us to use modeling technologies from one domain in another. The challenge is to demonstrate that they can be effectively used across domains whilst assuring temporally dependable applications. This paper shows that an IEC61499-modeled DAA can satisfy temporal dependability requirements as to end-to-end flow latency when it is properly scheduled and realized in a fully deterministic avionics platform that entails Integrated Modular Avionics (IMA) computation along with Time-Triggered Protocol (TTP) communication. Outcomes from the execution design of an IEC61499-based DAA model for an IMA-TTP platform are used to check runtime correctness through DAA control stability. IEC 61499 is a modeling standard for industrial automation, and it is meant to facilitate distribution and reconfiguration of applications. The DAA case study is a Distributed Fluid Control System (DFCS) for the Airbus-A380 fuel system. Latency analysis results from timing metrics as well as closed-loop control simulation results are presented. Experimental outcomes suggest that an IEC61499-based DFCS model can achieve desired runtime latency for temporal dependability when executed in an IMA-TTP platform. Concluding remarks and future research direction are also discussed. Full article
(This article belongs to the Special Issue Challenges in Reliability Analysis of Aerospace Electronics)
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Open AccessArticle Discontinuous Galerkin Finite Element Investigation on the Fully-Compressible Navier–Stokes Equations for Microscale Shock-Channels
Aerospace 2018, 5(1), 16; doi:10.3390/aerospace5010016
Received: 24 November 2017 / Revised: 10 January 2018 / Accepted: 30 January 2018 / Published: 3 February 2018
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Abstract
Microfluidics is a multidisciplinary area founding applications in several fields such as the aerospace industry. Microelectromechanical systems (MEMS) are mainly adopted for flow control, micropower generation and for life support and environmental control for space applications. Microflows are modeled relying on both a
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Microfluidics is a multidisciplinary area founding applications in several fields such as the aerospace industry. Microelectromechanical systems (MEMS) are mainly adopted for flow control, micropower generation and for life support and environmental control for space applications. Microflows are modeled relying on both a continuum and molecular approach. In this paper, the compressible Navier–Stokes (CNS) equations have been adopted to solve a two-dimensional unsteady flow for a viscous micro shock-channel problem. In microflows context, as for the most gas dynamics applications, the CNS equations are usually discretized in space using finite volume method (FVM). In the present paper, the PDEs are discretized with the nodal discontinuous Galerkin finite element method (DG–FEM) in order to understand how the method performs at microscale level for compressible flows. Validation is performed through a benchmark test problem for microscale applications. The error norms, order of accuracy and computational cost are investigated in a grid refinement study, showing a good agreement and increasing accuracy with reference data as the mesh is refined. The effects of different explicit Runge–Kutta schemes and of different time step sizes have also been studied. We found that the choice of the temporal scheme does not really affect the accuracy of the numerical results. Full article
(This article belongs to the Special Issue Computational Aerodynamic Modeling of Aerospace Vehicles)
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Open AccessArticle Robust Control Design for Quad Tilt-Wing UAV
Aerospace 2018, 5(1), 17; doi:10.3390/aerospace5010017
Received: 8 December 2017 / Revised: 30 January 2018 / Accepted: 2 February 2018 / Published: 7 February 2018
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Abstract
This paper describes the design method of a flight control system of a Quad Tilt-Wing (QTW) Unmanned Aerial Vehicle (UAV). A QTW-UAV is necessary to design a controller considering its nonlinear dynamics because of the appearance of the nonlinearity during transition flight between
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This paper describes the design method of a flight control system of a Quad Tilt-Wing (QTW) Unmanned Aerial Vehicle (UAV). A QTW-UAV is necessary to design a controller considering its nonlinear dynamics because of the appearance of the nonlinearity during transition flight between hovering and level flight. A design method of a flight control system using Dynamic Inversion (DI) that is one of linearization method has been proposed for the UAV. However, the design method based on an accurate model has a possibility of deterioration of control performance and system stability. Therefore, we propose a flight control system that considers uncertainties such as modeling error and disturbances by applying an H-infinity controller to the linearized system. The validity of the proposed control system is verified through numerical simulation and experiment. Full article
(This article belongs to the Special Issue Aircraft Dynamics & Control)
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Open AccessArticle Robust Autoland Design by Multi-Model ℋ Synthesis with a Focus on the Flare Phase
Aerospace 2018, 5(1), 18; doi:10.3390/aerospace5010018
Received: 29 November 2017 / Revised: 26 January 2018 / Accepted: 7 February 2018 / Published: 9 February 2018
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Abstract
Recent advances in the resolution of multi-model and multi-objective control problems via non-smooth optimization are exploited to provide a novel methodology in the challenging context of autoland design. Based on the structured H control framework, this paper focuses on the demanding flare
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Recent advances in the resolution of multi-model and multi-objective control problems via non-smooth optimization are exploited to provide a novel methodology in the challenging context of autoland design. Based on the structured H control framework, this paper focuses on the demanding flare phase under strong wind conditions and parametric uncertainties. More precisely, the objective is to control the vertical speed of the aircraft before touchdown while minimizing the impact of windshear, ground effects, and airspeed variations. The latter is indeed no longer controlled accurately during flare and strongly affected by wind. In addition, parametric uncertainties are to be considered when designing the control laws. To this purpose, extending previous results published by the authors in a conference paper, a specific multi-model strategy taking into account variations of mass and center-of-gravity location is considered. The methodology is illustrated on a realistic aircraft benchmark proposed by the authors, which is fully described in this paper and freely available from the SMAC (Systems Modeling Analysis & Control) toolbox website (http://w3.onera.fr/smac). Full article
(This article belongs to the Special Issue Aircraft Dynamics & Control)
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Open AccessArticle Thrust Augmentation by Airframe-Integrated Linear-Spike Nozzle Concept for High-Speed Aircraft
Aerospace 2018, 5(1), 19; doi:10.3390/aerospace5010019
Received: 8 December 2017 / Revised: 2 February 2018 / Accepted: 6 February 2018 / Published: 9 February 2018
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Abstract
The airframe-integrated linear-spike nozzle concept applied to an external nozzle for high-speed aircraft was evaluated with regard to the thrust augmentation capability and the trim balance. The main focus was on the vehicle aftbody. The baseline airframe geometry was first premised to be
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The airframe-integrated linear-spike nozzle concept applied to an external nozzle for high-speed aircraft was evaluated with regard to the thrust augmentation capability and the trim balance. The main focus was on the vehicle aftbody. The baseline airframe geometry was first premised to be a hypersonic waverider design. The baseline aftbody case had an external nozzle comprised of a simple divergent nozzle and was hypothetically replaced with linear-spike external nozzle configurations. Performance evaluation was mainly conducted by considering the nozzle thrust generated by the pressure distribution on the external nozzle surface at the aftbody portion calculated by computer simulation at a given cruise condition with zero angle of attack. The thrust performance showed that the proposed linear-spike external nozzle concept was beneficial in thrust enhancement compared to the baseline geometry because the design of the proposed concept had a compression wall for the exhaust flow, which resulted in increasing the wall pressure. The configuration with the boattail and the angled inner nozzle exhibited further improvement in thrust performance. The trim balance evaluation showed that the aerodynamic center location appeared as acceptable. Thus, benefits were obtained by employing the airframe-integrated linear-spike external nozzle concept. Full article
(This article belongs to the Special Issue Propulsion/Airframe Integration)
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Open AccessArticle Rupture of a Cryogenic Composite Overwrapped Pressure Vessel Following a High-Speed Particle Impact
Aerospace 2018, 5(1), 20; doi:10.3390/aerospace5010020
Received: 2 January 2018 / Revised: 8 February 2018 / Accepted: 14 February 2018 / Published: 18 February 2018
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Abstract
A primary spacecraft design consideration is the anticipation and mitigation of the possible damage that might occur in the event of an on-orbit micro-meteoroid or orbital debris (MMOD) particle impact. While considerable effort has been expended in the study of non-pressurized spacecraft components
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A primary spacecraft design consideration is the anticipation and mitigation of the possible damage that might occur in the event of an on-orbit micro-meteoroid or orbital debris (MMOD) particle impact. While considerable effort has been expended in the study of non-pressurized spacecraft components under room temperature conditions to MMOD impacts, technical and safety challenges have limited the number of tests that have been conducted on pressurized elements of such spacecraft, especially under cryogenic conditions. This paper presents the development of a data-driven equation for composite material pressure vessels under cryogenic operating conditions that differentiate between impact conditions that, given a tank wall perforation, would result in only a small hole or crack from those that would cause catastrophic tank failure. This equation would be useful to a spacecraft designer who might be able to tailor the design parameters and operating conditions of, for example, a fuel tank so that if such a tank were to be struck and perforated by the impact of an MMOD particle, then only a hole would occur and neither catastrophic spacecraft failure nor additional sizable debris would be created as a result of that impact. Full article
(This article belongs to the Special Issue Space Debris: Impact and Remediation)
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Open AccessArticle Modeling and Dynamics of HTS Motors for Aircraft Electric Propulsion
Aerospace 2018, 5(1), 21; doi:10.3390/aerospace5010021
Received: 15 December 2017 / Revised: 6 February 2018 / Accepted: 12 February 2018 / Published: 22 February 2018
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Abstract
In this paper, the methodology of how a dynamic model of a conventional permanent magnet synchronous motor (PMSM) may be modified to model the dynamics of a high-temperature superconductor (HTS) machine is illustrated. Simulations of a typical PMSM operating under room temperature conditions
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In this paper, the methodology of how a dynamic model of a conventional permanent magnet synchronous motor (PMSM) may be modified to model the dynamics of a high-temperature superconductor (HTS) machine is illustrated. Simulations of a typical PMSM operating under room temperature conditions and also at temperatures when the stator windings are superconducting are compared. Given a matching set of values for the stator resistance at superconducting temperature and flux-trapped rotor field, it is shown that the performance of the HTS PMSM is quite comparable to a PMSM under normal room temperature operating conditions, provided the parameters of the motor are appropriately related to each other. From these simulations, a number of strategies for operating the motor so as to get the propeller to deliver thrust with maximum propulsive efficiency are discussed. It is concluded that the motor–propeller system must be operated so as to deliver thrust at the maximum propulsive efficiency point. This, in turn, necessitates continuous tracking of the maximum propulsive efficiency point and consequently it is essential that the controller requires a maximum propulsive efficiency point tracking (MPEPT) outer loop. Full article
(This article belongs to the Special Issue Electric Aircraft)
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Open AccessArticle Predicting Non-Linear Flow Phenomena through Different Characteristics-Based Schemes
Aerospace 2018, 5(1), 22; doi:10.3390/aerospace5010022
Received: 18 November 2017 / Revised: 7 January 2018 / Accepted: 18 February 2018 / Published: 24 February 2018
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Abstract
The present work investigates the bifurcation properties of the Navier–Stokes equations using characteristics-based schemes and Riemann solvers to test their suitability to predict non-linear flow phenomena encountered in aerospace applications. We make use of a single- and multi-directional characteristics-based scheme and Rusanov’s Riemann
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The present work investigates the bifurcation properties of the Navier–Stokes equations using characteristics-based schemes and Riemann solvers to test their suitability to predict non-linear flow phenomena encountered in aerospace applications. We make use of a single- and multi-directional characteristics-based scheme and Rusanov’s Riemann solver to treat the convective term through a Godunov-type method. We use the Artificial Compressibility (AC) method and a unified Fractional-Step, Artificial Compressibility with Pressure-Projection (FSAC-PP) method for all considered schemes in a channel with a sudden expansion which provides highly non-linear flow features at low Reynolds numbers that produces a non-symmetrical flow field. Using the AC method, our results show that the multi-directional characteristics-based scheme is capable of predicting these phenomena while the single-directional counterpart does not predict the correct flow field. Both schemes and also Riemann solver approaches produce accurate results when the FSAC-PP method is used, showing that the incompressible method plays a dominant role in determining the behaviour of the flow. This also means that it is not just the numerical interpolation scheme which is responsible for the overall accuracy. Furthermore, we show that the FSAC-PP method provides faster convergence and higher level of accuracy, making it a prime candidate for aerospace applications. Full article
(This article belongs to the Special Issue Computational Aerodynamic Modeling of Aerospace Vehicles)
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Open AccessArticle Experimental and Numerical Investigation of the Outer Ring Cooling Concept in a Hybrid and in an All-Steel Ball Bearing Used in Aero-Engines by the Introduction of a Helical Duct
Aerospace 2018, 5(1), 23; doi:10.3390/aerospace5010023
Received: 27 November 2017 / Revised: 14 February 2018 / Accepted: 18 February 2018 / Published: 28 February 2018
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Abstract
Rolling element bearings for aero engine applications have to withstand very challenging operating conditions because of the high thermal impact due to elevated rotational speeds and loads. The high rate of heat generation in the bearing has to be sustained by the materials,
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Rolling element bearings for aero engine applications have to withstand very challenging operating conditions because of the high thermal impact due to elevated rotational speeds and loads. The high rate of heat generation in the bearing has to be sustained by the materials, and in the absence of lubrication these will fail within seconds. For this reason, aero engine bearings have to be lubricated and cooled by a continuous oil stream. When the oil has reached the outer ring it has already been heated up, thus its capability to remove extra heat from the outer ring is considerably reduced. Increasing the mass flow of oil to the bearing is not a solution since excess oil quantity would cause high parasitic losses (churning) in the bearing chamber and also increase the demands in the oil system for oil storage, scavenging, cooling, hardware weight, etc. A method has been developed for actively cooling the outer ring of the bearing. The idea behind the outer ring cooling concept was adopted from fins that are used for cooling electronic devices. A spiral groove engraved in the outer ring material of the bearing would function as a fin body with oil instead of air as the cooling medium. The method was first evaluated in an all steel ball bearing and the results were a 50% reduction in the lubricating oil flow with an additional reduction in heat generation by more than 25%. It was then applied on a Hybrid ball bearing of the same size and the former results were reconfirmed. Hybrid bearings are a combination of steel made parts, like the outer ring, the inner ring, and the cage and of ceramic rolling elements. This paper describes the work done to-date as a follow up of the work described in, and demonstrates the potential of the outer ring cooling for a bearing. Friction loss coefficient, Nusselt number, and efficiency correlations have been developed on the basis of the test results and have been compared to correlations from other authors. Computational Fluid Dynamics (CFD) analysis with ANSYS CFX has been used to verify test results and also for parametric studies. Full article
(This article belongs to the Special Issue Aeroengine)
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Open AccessArticle Design of a Facility for Studying Shock-Cell Noise on Single and Coaxial Jets
Aerospace 2018, 5(1), 25; doi:10.3390/aerospace5010025
Received: 12 January 2018 / Revised: 24 February 2018 / Accepted: 25 February 2018 / Published: 1 March 2018
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Abstract
Shock-cell noise occurs in aero-engines when the nozzle exhaust is supersonic and shock-cells are present in the jet. In commercial turbofan engines, at cruise, the secondary flow is often supersonic underexpanded, with the formation of annular shock-cells in the jet and consequent onset
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Shock-cell noise occurs in aero-engines when the nozzle exhaust is supersonic and shock-cells are present in the jet. In commercial turbofan engines, at cruise, the secondary flow is often supersonic underexpanded, with the formation of annular shock-cells in the jet and consequent onset of shock-cell noise. This paper aims at describing the design process of the new facility FAST (Free jet AeroacouSTic laboratory) at the von Karman Institute, aimed at the investigation of the shock-cell noise phenomenon on a dual stream jet. The rig consists of a coaxial open jet, with supersonic capability for both the primary and secondary flow. A coaxial silencer was designed to suppress the spurious noise coming from the feeding lines. Computational fluid dynamics (CFD) simulations of the coaxial jet and acoustic simulations of the silencer have been carried out to support the design choices. Finally, the rig has been validated by performing experimental measurements on a supersonic single stream jet and comparing the results with the literature. Fine-scale PIV (Particle Image Velocimetry) coupled with a microphone array in the far field have been used in this scope. Preliminary results of the dual stream jet are also shown. Full article
(This article belongs to the Special Issue Under-Expanded Jets)
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Open AccessArticle Experimental Study and Neural Network Modeling of Aerodynamic Characteristics of Canard Aircraft at High Angles of Attack
Aerospace 2018, 5(1), 26; doi:10.3390/aerospace5010026
Received: 29 December 2017 / Revised: 18 February 2018 / Accepted: 28 February 2018 / Published: 2 March 2018
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Abstract
Flow over an aircraft at high angles of attack is characterized by a combination of separated and vortical flows that interact with each other and with the airframe. As a result, there is a set of phenomena negatively affecting the aircraft’s performance, stability
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Flow over an aircraft at high angles of attack is characterized by a combination of separated and vortical flows that interact with each other and with the airframe. As a result, there is a set of phenomena negatively affecting the aircraft’s performance, stability and control, namely, degradation of lifting force, nonlinear variation of pitching moment, positive damping, etc. Wind tunnel study of aerodynamic characteristics of a prospective transonic aircraft, which is in a canard configuration, is discussed in the paper. A three-stage experimental campaign was undertaken. In the first stage, a steady aerodynamic experiment was conducted. The influence of a reduced oscillation frequency and angle of attack on unsteady aerodynamic characteristics was studied in the second stage. In the third stage, forced large-amplitude oscillation tests were carried out for the detailed investigation of the unsteady aerodynamics in the extended flight envelope. The experimental results demonstrate the strongly nonlinear behavior of the aerodynamic characteristics because of canard vortex effects on the wing. The obtained data are used to design and test mathematical models of unsteady aerodynamics via different popular approaches, namely the Neural Network (NN) technique and the phenomenological state space modeling technique. Different NN architectures, namely feed-forward and recurrent, are considered and compared. Thorough analysis of the performance of the models revealed that the Recurrent Neural Network (RNN) is a universal approximation tool for modeling of dynamic processes with high generalization abilities. Full article
(This article belongs to the Special Issue Computational Aerodynamic Modeling of Aerospace Vehicles)
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Open AccessArticle Field Trial Measurements to Validate a Stochastic Aircraft Boarding Model
Aerospace 2018, 5(1), 27; doi:10.3390/aerospace5010027
Received: 2 February 2018 / Revised: 1 March 2018 / Accepted: 5 March 2018 / Published: 7 March 2018
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Abstract
Efficient boarding procedures have to consider both operational constraints and the individual passenger behavior. In contrast to the aircraft handling processes of fueling, catering and cleaning, the boarding process is more driven by passengers than by airport or airline operators. This paper delivers
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Efficient boarding procedures have to consider both operational constraints and the individual passenger behavior. In contrast to the aircraft handling processes of fueling, catering and cleaning, the boarding process is more driven by passengers than by airport or airline operators. This paper delivers a comprehensive set of operational data including classification of boarding times, passenger arrival times, times to store hand luggage, and passenger interactions in the aircraft cabin as a reliable basis for calibrating models for aircraft boarding. In this paper, a microscopic approach is used to model the passenger behavior, where the passenger movement is defined as a one-dimensional, stochastic, and time/space discrete transition process. This model is used to compare measurements from field trials of boarding procedures with simulation results and demonstrates a deviation smaller than 5%. Full article
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Open AccessArticle Multi-UAV Doppler Information Fusion for Target Tracking Based on Distributed High Degrees Information Filters
Aerospace 2018, 5(1), 28; doi:10.3390/aerospace5010028
Received: 1 January 2018 / Revised: 14 February 2018 / Accepted: 22 February 2018 / Published: 8 March 2018
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Abstract
Multi-Unmanned Aerial Vehicle (UAV) Doppler-based target tracking has not been widely investigated, specifically when using modern nonlinear information filters. A high-degree Gauss–Hermite information filter, as well as a seventh-degree cubature information filter (CIF), is developed to improve the fifth-degree and third-degree CIFs proposed
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Multi-Unmanned Aerial Vehicle (UAV) Doppler-based target tracking has not been widely investigated, specifically when using modern nonlinear information filters. A high-degree Gauss–Hermite information filter, as well as a seventh-degree cubature information filter (CIF), is developed to improve the fifth-degree and third-degree CIFs proposed in the most recent related literature. These algorithms are applied to maneuvering target tracking based on Radar Doppler range/range rate signals. To achieve this purpose, different measurement models such as range-only, range rate, and bearing-only tracking are used in the simulations. In this paper, the mobile sensor target tracking problem is addressed and solved by a higher-degree class of quadrature information filters (HQIFs). A centralized fusion architecture based on distributed information filtering is proposed, and yielded excellent results. Three high dynamic UAVs are simulated with synchronized Doppler measurement broadcasted in parallel channels to the control center for global information fusion. Interesting results are obtained, with the superiority of certain classes of higher-degree quadrature information filters. Full article
(This article belongs to the collection Unmanned Aerial Systems)
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Open AccessArticle Prilling and Coating of Ammonium Dinitramide (ADN) Solid Green Propellant in Toluene Mixture Using Ultrasound Sonication
Aerospace 2018, 5(1), 29; doi:10.3390/aerospace5010029
Received: 18 December 2017 / Revised: 6 March 2018 / Accepted: 7 March 2018 / Published: 9 March 2018
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Abstract
Ammonium Dinitramide (ADN) in its generic form has a long needle shaped structure, which hinders higher solid loading. Therefore, it is of utmost importance to optimize its crystal morphology into octagonal shapes. Moreover, the low critical humidity level of ADN renders it unusable
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Ammonium Dinitramide (ADN) in its generic form has a long needle shaped structure, which hinders higher solid loading. Therefore, it is of utmost importance to optimize its crystal morphology into octagonal shapes. Moreover, the low critical humidity level of ADN renders it unusable in a humid climate. Hence, encapsulation with a hydrophobic polymer is necessary. In the present work, ADN was synthesized by nitration of potassium sulfamate with mixed acid nitration. The product was then mixed with toluene, graphene, citryl ammonium butyl, Cab-o-sil, and coating polymer (Polystyrene or HTPB) and treated with ultrasound to obtain semi-spherical ADN-coated particles. The method offers a reduction in operating temperature and elimination of ADN melting in the shape-altering process. In addition, the ADN product has a similar particle size and thermal stability compared to those in a conventional ADN melt-prilling method. The ADN product investigated under SEM confirms the particle morphological change from long needles into semi-spherical shapes. The particle size obtained, in the micrometer range, is ideal for higher theoretical maximum density. Furthermore, the ultrasound-treated ADN particles show significant reduction in moisture absorption, from 68% to 16% at 65% relative humidity. The DSC result shows no degradation of thermal stability of the coated particles. Full article
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Open AccessArticle Numerical Simulation of Heat Transfer and Chemistry in the Wake behind a Hypersonic Slender Body at Angle of Attack
Aerospace 2018, 5(1), 30; doi:10.3390/aerospace5010030
Received: 13 December 2017 / Revised: 22 February 2018 / Accepted: 24 February 2018 / Published: 11 March 2018
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Abstract
The effect of thermal and chemical boundary conditions on the structure and chemical composition of the wake behind a 3D Mach 7 sphere-cone at an angle of attack of 5 degrees and an altitude of roughly 30,000 m is explored. A special emphasis
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The effect of thermal and chemical boundary conditions on the structure and chemical composition of the wake behind a 3D Mach 7 sphere-cone at an angle of attack of 5 degrees and an altitude of roughly 30,000 m is explored. A special emphasis is placed on determining the number density of chemical species which might lead to detection via the electromagnetic spectrum. The use of non-ablating cold-wall, adiabatic, and radiative equilibrium wall boundary conditions are used to simulate extremes in potential thermal protection system designs. Non-ablating, as well as an ablating boundary condition using the “steady-state ablation” assumption to compute a surface energy balance on the wall are used in order to determine the impacts of ablation on wake composition. On-body thermal boundary conditions downstream of an ablating nose are found to significantly affect wake temperature and composition, while the role of catalysis is found to change the composition only marginally except at very high temperatures on the cone’s surface for the flow regime considered. Ablation is found to drive the extensive production of detectable species otherwise unrelated to ablation, whereas if ablation is not present at all, air-species which would otherwise produce detectable spectra are minimal. Studies of afterbody cooling techniques, as well as shape, are recommended for further analysis. Full article
(This article belongs to the Special Issue Computational Aerodynamic Modeling of Aerospace Vehicles)
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Open AccessArticle CFD Validation and Flow Control of RAE-M2129 S-Duct Diffuser Using CREATETM-AV Kestrel Simulation Tools
Aerospace 2018, 5(1), 31; doi:10.3390/aerospace5010031
Received: 17 January 2018 / Revised: 9 March 2018 / Accepted: 14 March 2018 / Published: 16 March 2018
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Abstract
The flow physics modeling and validation of the Royal Aircraft Establishment (RAE) subsonic intake Model 2129 (M2129) are presented. This intake has an 18 inches long S duct with a 5.4 inches offset, an external and an internal lip, forward and rear extended
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The flow physics modeling and validation of the Royal Aircraft Establishment (RAE) subsonic intake Model 2129 (M2129) are presented. This intake has an 18 inches long S duct with a 5.4 inches offset, an external and an internal lip, forward and rear extended ducts, and a center-positioned bullet before the outlet. Steady-state and unsteady experimental data are available for this duct. The measurements include engine face conditions (pressure recovery, static pressure to free-stream total pressure ratio, and distortion coefficient at the worst 60 sector or DC60), as well as wall static pressure data along the duct. The intake has been modeled with HPCMP CREATE TM -AV Kestrel simulation tools. The validation results are presented including the effects of turbulence models on predictions. In general, very good agreement (difference errors are less than 6%) was found between predictions and measurements. Secondary flow at the first bend and a region of flow separation are predicted at the starboard wall with an averaged DC60 coefficient of 0.2945 at the engine face. Next, a passive and an active flow control method are computationally investigated. The passive one uses vane-type vortex generators and the active one has synthetic jet actuators. The results show that considered passive and active flow control methods reduce the distortion coefficient at the engine face and the worst 60 sector to 0.1361 and 0.0881, respectively. The flow control performance trends agree with those obtained in experiments as well. These results give confidence to apply the Kestrel simulation tools for the intake design studies of new and unconventional vehicles and hence to reduce the uncertainties during their flight testing. Full article
(This article belongs to the Special Issue Computational Aerodynamic Modeling of Aerospace Vehicles)
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Review

Jump to: Editorial, Research

Open AccessReview Modeling Plasma via Electron Impact Ionization
Aerospace 2018, 5(1), 2; doi:10.3390/aerospace5010002
Received: 17 November 2017 / Revised: 26 December 2017 / Accepted: 28 December 2017 / Published: 2 January 2018
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Abstract
Variable and potential plasma applications in aerospace engineering are exemplified by ion thrusters, flow control by plasma actuator, enhanced ignition and combustion stability. The operational environments span a range from the rarefied to continuum gasdynamic regimes; however, the ionization process in practical applications
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Variable and potential plasma applications in aerospace engineering are exemplified by ion thrusters, flow control by plasma actuator, enhanced ignition and combustion stability. The operational environments span a range from the rarefied to continuum gasdynamic regimes; however, the ionization process in practical applications is mostly by electron impact. The fundamental ionization mechanisms by electron impact consist of electron secondary mission and the cascading process. In an alternating electric field, unsteady and random micro discharges or streamers are always presented; therefore the discharge physics imposes a formidable challenge for incisive understanding. Meanwhile, the ionized species constitute hundreds of metastable chemical species; under this circumstance the physics-based modeling for analyzing the inhomogeneous medium becomes necessary. A summary of the physics-based modeling for electron impact ionization from the Boltzmann distribution equation to the inelastic particle kinetics formulation is delineated. Full article
(This article belongs to the collection Feature Papers in Aerospace)
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Open AccessReview Testing-Based Approach to Determining the Divergence Speed of Slung Loads
Aerospace 2018, 5(1), 24; doi:10.3390/aerospace5010024
Received: 15 December 2017 / Revised: 19 February 2018 / Accepted: 25 February 2018 / Published: 28 February 2018
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Abstract
When a rotorcraft carries an external slung load, flight speed is often limited by the fear of divergent oscillations, rather than vehicle performance. Since slung objects can be of any shape, incorporating the aerodynamics with sufficient accuracy to predict safe speed has been
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When a rotorcraft carries an external slung load, flight speed is often limited by the fear of divergent oscillations, rather than vehicle performance. Since slung objects can be of any shape, incorporating the aerodynamics with sufficient accuracy to predict safe speed has been a problem. The uncertainty forces certifying authorities to set conservative limits on speed to avoid divergence. Obtaining the aerodynamic coefficients of bluff bodies was excessively time-consuming in experiments, and impractical in computations. This review traces the evolution of progress in the area. Prior thinking was to use computations for prediction, with the computational codes validated using a few samples of experiments. This approach has not led to valid general predictions. Data were sparse and a-priori predictions were rarer. A continuous rotation approach has enabled swift measurements of 6-degrees-of-freedom aerodynamic load maps with high resolution about several axes of rotation. The resulting knowledge base in turn permits a swift determination of dynamics up to divergence, with wind tunnel tests where necessary to fill interpolation gaps in the knowledge base. The essence of efficient and swift dynamics simulation with a few well-tested assumptions is described. Under many relevant conditions, the vehicle flight dynamics can be safely decoupled from those of the slung load. While rotor wake swirl causes the payload to rotate at liftoff and landing, this effect can be incorporated into the simulation. Recent success in explaining two well-documented flight test cases provides strong evidence that predictions can be made for most missions swiftly. Full article
(This article belongs to the Special Issue Aircraft Dynamics & Control)
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Open AccessReview Buoyancy-Induced Heat Transfer inside Compressor Rotors: Overview of Theoretical Models
Aerospace 2018, 5(1), 32; doi:10.3390/aerospace5010032
Received: 16 February 2018 / Revised: 12 March 2018 / Accepted: 13 March 2018 / Published: 17 March 2018
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Abstract
Increasing pressures in gas-turbine compressors, particularly in aeroengines where the pressure ratios can be above 50:1, require smaller compressor blades and an increasing focus on blade-clearance control. The blade clearance depends on the radial growth of the compressor discs, which in turn depends
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Increasing pressures in gas-turbine compressors, particularly in aeroengines where the pressure ratios can be above 50:1, require smaller compressor blades and an increasing focus on blade-clearance control. The blade clearance depends on the radial growth of the compressor discs, which in turn depends on the temperature and stress in the discs. As the flow inside the disc cavities is buoyancy-driven, calculation of the disc temperature is a conjugate problem: the heat transfer from the disc is coupled with the air temperature inside the cavity. The flow inside the cavity is three-dimensional, unsteady and unstable, so computational fluid dynamics is not only expensive and time-consuming, it is also unable to achieve accurate solutions at the high Grashof numbers found in modern compressors. Many designers rely on empirical equations based on inappropriate physical models, and recently the authors have produced a series of papers on physically-based theoretical modelling of buoyancy-induced heat transfer in the rotating cavities found inside compressor rotors. Predictions from these models, all of which are for laminar flow, have been validated using measurements made in open and closed compressor rigs for a range of flow parameters representative of those found inside compressor rotors. (The fact that laminar buoyancy models can be used for large Grashof numbers (up to 10 12 ), where most engineers expect the flow to be turbulent, is attributed to the large Coriolis accelerations in the fluid core and to the fact that there is only a small difference between the rotational speed of the core and that of the discs.) As many as 223 separate tests were analysed in the validation of the models, and good agreement between the predictions and measurements was achieved for most of these cases. This overview paper has collected together the equations from these papers, which should be helpful to designers and research workers. The paper also points out the limitations of the models, all of which are for steady flow, and shows where further experimental evidence is needed. Full article
(This article belongs to the Special Issue Secondary Air Systems in Gas Turbine Engines)
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