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Aerospace, Volume 8, Issue 7 (July 2021) – 27 articles

Cover Story (view full-size image): The low-pressure turbine drives the fan, which produces most of the thrust in modern high-bypass ratio turbojet engines. Modern front-loaded high-lift airfoils promise overall weight savings but suffer from increased endwall losses. Large-eddy simulations of a 50% reaction stage and a linear cascade with two different bar wake generators were carried out to obtain insight into the mean flow topology and unsteady flow physics. By comparing the results from the simulations, the effect of the three-dimensional wake components on the downstream flow field is ascertained. For the chosen chord Reynolds number of 50,000, the stator laminar separation is substantial. Nevertheless, the passing wakes almost entirely suppress the laminar separation from the rotor blades. View this paper
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Article
A Simplified Finite Element Model of Riveted Joints for Structural Analyses with Consideration of Nonlinear Load-Transfer Characteristics
Aerospace 2021, 8(7), 196; https://doi.org/10.3390/aerospace8070196 - 19 Jul 2021
Viewed by 772
Abstract
A simplified finite element model of riveted joints for structural analyses which effectively incorporates nonlinear response of riveted joints is proposed. Load-transfer characteristics of riveted joints were experimentally and numerically studied. First, a detailed finite element analysis for the process of a tensile [...] Read more.
A simplified finite element model of riveted joints for structural analyses which effectively incorporates nonlinear response of riveted joints is proposed. Load-transfer characteristics of riveted joints were experimentally and numerically studied. First, a detailed finite element analysis for the process of a tensile test of a single-row joint which consists of squeezing of the rivet and tensile loading to the joint was conducted to confirm the validity of a conventional method of analysis. The load–relative displacement behaviors of single-row joints observed in the detailed finite element analysis and previously conducted experiments agreed well. Then, a simplified method of the analysis was developed based on the detailed analysis and the experiments and was applied to analyses of multiple-row joints. A nonlinear relationship between load and relative displacement in the simplified analyses had good agreement with the detailed one. Distributed loads to the multiple rivets in the simplified analysis coincided with those of the detailed analysis under the maximum load. Memory and CPU time required to run the simplified analyses were reduced to about 1/4 and 1/6 compared to those of the detailed analysis, respectively. Full article
(This article belongs to the Section Aeronautics)
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Article
PSO-Based Soft Lunar Landing with Hazard Avoidance: Analysis and Experimentation
Aerospace 2021, 8(7), 195; https://doi.org/10.3390/aerospace8070195 - 19 Jul 2021
Cited by 1 | Viewed by 827
Abstract
The problem of real-time optimal guidance is extremely important for successful autonomous missions. In this paper, the last phases of autonomous lunar landing trajectories are addressed. The proposed guidance is based on the Particle Swarm Optimization, and the differential flatness approach, which is [...] Read more.
The problem of real-time optimal guidance is extremely important for successful autonomous missions. In this paper, the last phases of autonomous lunar landing trajectories are addressed. The proposed guidance is based on the Particle Swarm Optimization, and the differential flatness approach, which is a subclass of the inverse dynamics technique. The trajectory is approximated by polynomials and the control policy is obtained in an analytical closed form solution, where boundary and dynamical constraints are a priori satisfied. Although this procedure leads to sub-optimal solutions, it results in beng fast and thus potentially suitable to be used for real-time purposes. Moreover, the presence of craters on the lunar terrain is considered; therefore, hazard detection and avoidance are also carried out. The proposed guidance is tested by Monte Carlo simulations to evaluate its performances and a robust procedure, made up of safe additional maneuvers, is introduced to counteract optimization failures and achieve soft landing. Finally, the whole procedure is tested through an experimental facility, consisting of a robotic manipulator, equipped with a camera, and a simulated lunar terrain. The results show the efficiency and reliability of the proposed guidance and its possible use for real-time sub-optimal trajectory generation within laboratory applications. Full article
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Article
Sensitivity Analysis of Maximum Circulation of Wake Vortex Encountered by En-Route Aircraft
Aerospace 2021, 8(7), 194; https://doi.org/10.3390/aerospace8070194 - 16 Jul 2021
Viewed by 986
Abstract
Wake vortex encounters (WVE) can pose significant hazard for en-route aircraft. We studied the sensitivity of wake vortex (WV) circulation and decay to aircraft mass, altitude, velocity, density, time of catastrophic wake demise event, eddy dissipation rate, wing span, span-wise load factor, and [...] Read more.
Wake vortex encounters (WVE) can pose significant hazard for en-route aircraft. We studied the sensitivity of wake vortex (WV) circulation and decay to aircraft mass, altitude, velocity, density, time of catastrophic wake demise event, eddy dissipation rate, wing span, span-wise load factor, and WV core radius. Then, a tool was developed to compute circulations of WV generated/encountered by aircraft en-route, while disregarding unrealistic operational conditions. A comprehensive study is presented for most aircraft in the Base of Aircraft Data version 4.1 for different masses, altitudes, speeds, and separation values between generator and follower aircraft. The maximum WV circulation corresponds to A380-861 as generator: 864 and 840 m2/s at horizontal separation of 3 and 5 NM, respectively. In cruise environment, these WV may descend 1000 ft in 2.6 min and 2000 ft in 6.2 min, while retaining 74% and 49% of their initial strength, respectively. The maximum circulation of WV encountered by aircraft at horizontal separation of 3 NM from an A380-861 is 593, 726, and 745 m2/s, at FL200, FL300, and FL395, respectively. At 5 NM, the circulations decrease down to 578, 708, and 726 m2/s. Our results allow reducing WVE simulations only to critical scenarios, and thus perform more efficient test programs for computing aircraft upsets en-route. Full article
(This article belongs to the Special Issue Aircraft Operations and CNS/ATM)
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Article
SU2-NEMO: An Open-Source Framework for High-Mach Nonequilibrium Multi-Species Flows
Aerospace 2021, 8(7), 193; https://doi.org/10.3390/aerospace8070193 - 16 Jul 2021
Cited by 5 | Viewed by 1843
Abstract
SU2-NEMO, a recent extension of the open-source SU2 multiphysics suite’s set of physical models and code architecture, is presented with the aim of introducing its enhanced capabilities in addressing high-enthalpy and high-Mach number flows. This paper discusses the thermal nonequilibrium and finite-rate chemistry [...] Read more.
SU2-NEMO, a recent extension of the open-source SU2 multiphysics suite’s set of physical models and code architecture, is presented with the aim of introducing its enhanced capabilities in addressing high-enthalpy and high-Mach number flows. This paper discusses the thermal nonequilibrium and finite-rate chemistry models adopted, including a link to the Mutation++ physio-chemical library. Further, the paper discusses how the software architecture has been designed to ensure modularity, incorporating the ability to introduce additional models in an efficient manner. A review of the numerical formulation and the discretization schemes utilized for the convective fluxes is also presented. Several test cases in two- and three-dimensions are examined for validation purposes and to illustrate the performance of the solver in addressing complex nonequilibrium flows. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics on High-Speed and Non-Equilibrium Flows)
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Article
Experimental CanSat Platform for Functional Verification of Burn Wire Triggering-Based Holding and Release Mechanisms
Aerospace 2021, 8(7), 192; https://doi.org/10.3390/aerospace8070192 - 16 Jul 2021
Cited by 2 | Viewed by 1326
Abstract
In this study, we present the Diverse Holding and Release Mechanism Can Satellite (DHRM CanSat) platform developed by the Space Technology Synthesis Laboratory (STSL) at Chosun University, South Korea. This platform focuses on several types of holding and release mechanisms (HRMs) for application [...] Read more.
In this study, we present the Diverse Holding and Release Mechanism Can Satellite (DHRM CanSat) platform developed by the Space Technology Synthesis Laboratory (STSL) at Chosun University, South Korea. This platform focuses on several types of holding and release mechanisms (HRMs) for application in deployable appendages of nanosatellites. The objectives of the DHRM CanSat mission are to demonstrate the design effectiveness and functionality of the three newly proposed HRMs based on the burn wire triggering method, i.e., the pogo pin-type HRM, separation nut-type HRM, and Velcro tape-type HRM, which were implemented on deployable dummy solar panels of the CanSat. The proposed mechanisms have many advantages, including a high holding capability, simultaneous constraints in multi-plane directions, and simplicity of handling. Additionally, each mechanism has distinctive features, such as spring-loaded pins to initiate deployment, a plate with a thread as a nut for a high holding capability, and a hook and loop fastener for easy access to subsystems of the satellite without releasing the holding constraint. The design effectiveness and functional performance of the proposed mechanisms were demonstrated through an actual flight test of the DHRM CanSat launched by a model rocket. Full article
(This article belongs to the Special Issue Vibration Control for Space Application)
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Article
A Comparative Analysis of Multi-Epoch Double-Differenced Pseudorange Observation and Other Dual-Satellite Lunar Global Navigation Systems
Aerospace 2021, 8(7), 191; https://doi.org/10.3390/aerospace8070191 - 15 Jul 2021
Cited by 2 | Viewed by 818
Abstract
In this study, dual-satellite lunar global navigation systems that consist of a constellation of two navigation satellites providing geo-spatial positioning on the lunar surface were compared. In our previous work, we proposed a new dual-satellite relative-positioning navigation method called multi-epoch double-differenced pseudorange observation [...] Read more.
In this study, dual-satellite lunar global navigation systems that consist of a constellation of two navigation satellites providing geo-spatial positioning on the lunar surface were compared. In our previous work, we proposed a new dual-satellite relative-positioning navigation method called multi-epoch double-differenced pseudorange observation (MDPO). While the mathematical model of the MDPO and its behavior under specific conditions were studied, we did not compare its performance with other dual-satellite relative-positioning navigation systems. In this paper, we performed a comparative analysis between the MDPO and other two dual-satellite navigation methods. Based on the difference in their mathematical models, as well as numerical simulation results, we developed useful insights on the system design of dual-satellite lunar global navigation systems. Full article
(This article belongs to the Special Issue New Space: Advances in Space Science and Engineering)
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Review
Challenges of Ablatively Cooled Hybrid Rockets for Satellites or Upper Stages
Aerospace 2021, 8(7), 190; https://doi.org/10.3390/aerospace8070190 - 14 Jul 2021
Cited by 2 | Viewed by 893
Abstract
Ablative-cooled hybrid rockets could potentially combine a similar versatility of a liquid propulsion system with a much simplified architecture. These characteristics make this kind of propulsion attractive, among others, for applications such as satellites and upper stages. In this paper, the use of [...] Read more.
Ablative-cooled hybrid rockets could potentially combine a similar versatility of a liquid propulsion system with a much simplified architecture. These characteristics make this kind of propulsion attractive, among others, for applications such as satellites and upper stages. In this paper, the use of hybrid rockets for those situations is reviewed. It is shown that, for a competitive implementation, several challenges need to be addressed, which are not the general ones often discussed in the hybrid literature. In particular, the optimal thrust to burning time ratio, which is often relatively low in liquid engines, has a deep impact on the grain geometry, that, in turn, must comply some constrains. The regression rate sometime needs to be tailored in order to avoid unreasonable grain shapes, with the consequence that the dimensional trends start to follow some sort of counter-intuitive behavior. The length to diameter ratio of the hybrid combustion chamber imposes some packaging issues in order to compact the whole propulsion system. Finally, the heat soak-back during long off phases between multiple burns could compromise the integrity of the case and of the solid fuel. Therefore, if the advantages of hybrid propulsion are to be exploited, the aspects mentioned in this paper shall be carefully considered and properly faced. Full article
(This article belongs to the Special Issue Hybrid Rocket(Volume II))
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Article
Ion Source—Thermal and Thermomechanical Simulation
Aerospace 2021, 8(7), 189; https://doi.org/10.3390/aerospace8070189 - 14 Jul 2021
Cited by 1 | Viewed by 677
Abstract
The main purpose of this work is to conduct ground development testing of the ion source intended for use the space debris contactless transportation system. In order to substantiate the operating capability of the developed ion source, its thermal and thermomechanical simulation was [...] Read more.
The main purpose of this work is to conduct ground development testing of the ion source intended for use the space debris contactless transportation system. In order to substantiate the operating capability of the developed ion source, its thermal and thermomechanical simulation was carried out. The ion source thermal model should verify the ion source operating capability under thermal loading conditions, and demonstrate the conditions for ion source interfacing with the systems of the service spacecraft with the ion source installed as a payload. The mechanical and mathematical simulation for deformation of the ion source ion-extraction system profiled electrodes under thermal loading in conjunction with the prediction of the strained state based on the numerical simulation of the ion source ion-extraction system units, making it possible to ensure the stability of the ion source performance. Good agreement between the thermal and thermo-mechanical ion source simulation results and experimental data has been demonstrated. It is shown that the developed ion source will be functional in outer space and can be used as an element of the space debris contactless transportation system into graveyard orbits. Full article
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Review
A Review on the Current Status of Icing Physics and Mitigation in Aviation
Aerospace 2021, 8(7), 188; https://doi.org/10.3390/aerospace8070188 - 14 Jul 2021
Cited by 6 | Viewed by 1355
Abstract
Icing on an aircraft is the cause of numerous adverse effects on aerodynamic performance. Although the issue was recognized in the 1920s, the icing problem is still an area of ongoing research due to the complexity of the icing phenomena. This review article [...] Read more.
Icing on an aircraft is the cause of numerous adverse effects on aerodynamic performance. Although the issue was recognized in the 1920s, the icing problem is still an area of ongoing research due to the complexity of the icing phenomena. This review article aims to summarize current research on aircraft icing in two fundamental topics: icing physics and icing mitigation techniques. The icing physics focuses on fixed wings, rotors, and engines severely impacted by icing. The study of engine icing has recently become focused on ice-crystal icing. Icing mitigation techniques reviewed are based on active, passive, and hybrid methods. The active mitigation techniques include those based on thermal and mechanical methods, which are currently in use on aircraft. The passive mitigation techniques discussed are based on current ongoing studies in chemical coatings. The hybrid mitigation technique is reviewed as a combination of the thermal method (active) and chemical coating (passive) to lower energy consumption. Full article
(This article belongs to the Special Issue Deicing and Anti-Icing of Aircraft (Volume II))
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Article
A Modular Framework for the Life Cycle Based Evaluation of Aircraft Technologies, Maintenance Strategies, and Operational Decision Making Using Discrete Event Simulation
Aerospace 2021, 8(7), 187; https://doi.org/10.3390/aerospace8070187 - 14 Jul 2021
Cited by 2 | Viewed by 1074
Abstract
Current practices for investment and technology decision making in aeronautics largely rely on regression-based cost estimation methods. Although quick to implement and easy to use, they suffer from a variety of limitations, both in temporal space and scope of applicability. While recent research [...] Read more.
Current practices for investment and technology decision making in aeronautics largely rely on regression-based cost estimation methods. Although quick to implement and easy to use, they suffer from a variety of limitations, both in temporal space and scope of applicability. While recent research and development in this area addresses these to a certain extent, aerospace engineering still lacks a flexible and customizable valuation framework. To this end, a generic environment for economic and operational assessment of aircraft and related products named LYFE is presented. This tool employs a discrete event simulation which models the product life cycle from its order through decades of operation and maintenance until disposal. This paper introduces its key characteristics and default methods alongside its modular program architecture. The capabilities are demonstrated with a case study of on-wing engine cleaning procedures which are triggered by a customized decision making module. Thereby, the impact on engine health, fuel efficiency and overall economic viability is quantified. On the whole, the framework introduced in this paper can be used to analyze not only physical products but also operational procedures and maintenance strategies as well as specified decision making algorithms in terms of their impact on an aircraft’s or system’s life cycle. Full article
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Systematic Review
Water Recognition on the Moon by Using THz Heterodyne-Spectrometer for Identifying the Appropriate Locations to Extract Water for Providing Oxygen for Breathing and Fuel for Spaceships’ Propulsion on the Moon with CubeSat
Aerospace 2021, 8(7), 186; https://doi.org/10.3390/aerospace8070186 - 12 Jul 2021
Viewed by 973
Abstract
Asteroid mining offers vital sources for improving human lives and provides opportunities for interplanetary missions and space travel. There are many professional commercial space companies that are only investing billions of dollars on asteroids mining, but prior to that, one condition for asteroid [...] Read more.
Asteroid mining offers vital sources for improving human lives and provides opportunities for interplanetary missions and space travel. There are many professional commercial space companies that are only investing billions of dollars on asteroids mining, but prior to that, one condition for asteroid mining could be planetary stations to refuel the pioneers’ spacecraft or human colonies on alien planets; hence, one of the vital sources for these purposes is water. Water can be harvested to split oxygen for breathing and hydrogen for refueling spaceships’ propulsions, and Earth-to-space water payload transporting is extremely expensive; therefore, discovering extraterrestrial water in outer space is economically beneficial. This paper presents a Lunar CubeSat Injector to deliver four 3U CubeSats into Low Lunar Orbit to make a constellation to identify locations of water sources on the Moon by using a THz heterodyne-spectrometer. In sum, this project can help scientists to recognize more water resources for those who will colonize the Moon and for those planning to go beyond it. Full article
(This article belongs to the Special Issue Small Satellite Technologies and Mission Concepts)
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Article
Tuning of NASA Standard Breakup Model for Fragmentation Events Modelling
Aerospace 2021, 8(7), 185; https://doi.org/10.3390/aerospace8070185 - 12 Jul 2021
Cited by 3 | Viewed by 940
Abstract
The continuous growth of space debris motivates the development and the improvement of tools that support the monitoring of a more and more congested space environment. Satellite breakup models play a key role to predict and analyze orbital debris evolution, and the NASA [...] Read more.
The continuous growth of space debris motivates the development and the improvement of tools that support the monitoring of a more and more congested space environment. Satellite breakup models play a key role to predict and analyze orbital debris evolution, and the NASA Standard Breakup Model represents a widely used reference, with current activities relevant to its evolution and improvements especially towards fragmentation of small mass spacecraft. From an operational perspective, an important point for fragmentation modelling concerns the tuning of the breakup model to achieve consistency with orbital data of observed fragments. In this framework, this paper proposes an iterative approach to estimate the model inputs, and in particular, the parents’ masses involved in a collision event. The iterative logic exploits the knowledge of Two Line Elements (TLE) of the fragments at some time after the event to adjust the input parameters of the breakup model with the objective of obtaining the same number of real fragments within a certain tolerance. Atmospheric re-entry is accounted for. As a result, the breakup model outputs a set of fragments whose statistical distribution, in terms of number and size, is consistent with the catalogued ones. The iterative approach is demonstrated for two different scenarios (i.e., catastrophic collision and non-catastrophic collision) using numerical simulations. Then, it is also applied to a real collision event. Full article
(This article belongs to the Special Issue New Space: Advances in Space Science and Engineering)
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Article
Large-Eddy Simulation of Low-Pressure Turbine Cascade with Unsteady Wakes
Aerospace 2021, 8(7), 184; https://doi.org/10.3390/aerospace8070184 - 08 Jul 2021
Cited by 1 | Viewed by 909
Abstract
To better understand the wake effects at low Reynolds numbers, large-eddy simulations of a 50% reaction low-pressure turbine stage and a linear cascade with two different bar wake generators were carried out for a chord Reynolds number of 50,000. For the chosen front-loaded [...] Read more.
To better understand the wake effects at low Reynolds numbers, large-eddy simulations of a 50% reaction low-pressure turbine stage and a linear cascade with two different bar wake generators were carried out for a chord Reynolds number of 50,000. For the chosen front-loaded high-lift airfoil, the endwall structures are stronger than for more traditional mid-loaded moderate-lift airfoils. By comparing the 50% reaction stage results with the bar wake generator results, insight is gained into the effect of the three-dimensional wake components on the downstream flow field.For the cases with bar wake generator, the endwall boundary layer is growing faster because of the relative motion of the endwall with respect to the freestream. The half-width of the wake is approximately matched for the larger one of the two considered bar wake generators. To improve the quality of the phase-averaged flow fields, the proper orthogonal decomposition was employed as a filter to remove the low-energy unsteady flow field content. Both the mean flow and filtered phase-averaged flow fields were analyzed in detail. Visualizations of the phase-averaged flow field reveal a periodic suppression of the laminar suction side separation from the downstream airfoil even for the smaller bar wake generator. The passage vortex is entirely suppressed for the 50% reaction stage and for the larger bar wake generator. Furthermore, the phase-averaged data for the 50% reaction stage reveal a new longitudinal flow structure that is traced back to near-wall wake vorticity. This flow structure is missing for the bar wake generator cases. Full article
(This article belongs to the Special Issue Large Eddy Simulation in Aerospace Engineering)
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Article
Some Special Types of Orbits around Jupiter
Aerospace 2021, 8(7), 183; https://doi.org/10.3390/aerospace8070183 - 08 Jul 2021
Cited by 2 | Viewed by 795
Abstract
This paper intends to show some special types of orbits around Jupiter based on the mean element theory, including stationary orbits, sun-synchronous orbits, orbits at the critical inclination, and repeating ground track orbits. A gravity model concerning only the perturbations of J2 [...] Read more.
This paper intends to show some special types of orbits around Jupiter based on the mean element theory, including stationary orbits, sun-synchronous orbits, orbits at the critical inclination, and repeating ground track orbits. A gravity model concerning only the perturbations of J2 and J4 terms is used here. Compared with special orbits around the Earth, the orbit dynamics differ greatly: (1) There do not exist longitude drifts on stationary orbits due to non-spherical gravity since only J2 and J4 terms are taken into account in the gravity model. All points on stationary orbits are degenerate equilibrium points. Moreover, the satellite will oscillate in the radial and North-South directions after a sufficiently small perturbation of stationary orbits. (2) The inclinations of sun-synchronous orbits are always bigger than 90 degrees, but smaller than those for satellites around the Earth. (3) The critical inclinations are no-longer independent of the semi-major axis and eccentricity of the orbits. The results show that if the eccentricity is small, the critical inclinations will decrease as the altitudes of orbits increase; if the eccentricity is larger, the critical inclinations will increase as the altitudes of orbits increase. (4) The inclinations of repeating ground track orbits are monotonically increasing rapidly with respect to the altitudes of orbits. Full article
(This article belongs to the Special Issue Spacecraft Dynamics and Control)
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Article
The Lunar Radiation Environment: Comparisons between PHITS, HETC-HEDS, and the CRaTER Instrument
Aerospace 2021, 8(7), 182; https://doi.org/10.3390/aerospace8070182 - 08 Jul 2021
Viewed by 854
Abstract
Understanding the radiation environment near the lunar surface is a key step towards planning for future missions to the Moon. However, the complex variety of energies and particle types constituting the space radiation environment makes the process of replicating such environment very difficult [...] Read more.
Understanding the radiation environment near the lunar surface is a key step towards planning for future missions to the Moon. However, the complex variety of energies and particle types constituting the space radiation environment makes the process of replicating such environment very difficult in Earth-based laboratories. Radiation transport codes provide a practical alternative covering a wider range of particle energy, angle, and type than can be experimentally attainable. Comparing actual measurements with simulation results help in validating particle flux input models, and input collision models and databases involving nuclear and electromagnetic interactions. Thus, in this work, we compare the LET spectra simulated using the Monte Carlo transport code PHITS with measurements made by the CRaTER instrument that is currently orbiting the Moon studying its radiation environment. In addition, we utilize a feature in PHITS that allows the user to run the simulations without Vavilov energy straggling to test whether it is the root cause of erroneous phenomena exhibited in similar studies in literature. The results herein show good agreement between the LET spectra of PHITS and the CRaTER instrument. They also confirm that using a Vavilov distribution correction would ultimately provide a better agreement between CRaTER measurements and the previous LET spectra from the transport codes HETC-HEDS and HZETRN. Full article
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Article
Optimal Design of Electrically Fed Hybrid Mars Ascent Vehicle
Aerospace 2021, 8(7), 181; https://doi.org/10.3390/aerospace8070181 - 06 Jul 2021
Cited by 2 | Viewed by 938
Abstract
The optimal design of the propulsion system for a potential Mars Ascent Vehicle is analyzed, in the context of the Mars Sample Return Mission. The Mars Ascent Vehicle has to perform an initial ascent phase from the surface and then circularize into a [...] Read more.
The optimal design of the propulsion system for a potential Mars Ascent Vehicle is analyzed, in the context of the Mars Sample Return Mission. The Mars Ascent Vehicle has to perform an initial ascent phase from the surface and then circularize into a 170 km orbit. A two-stage launcher is taken into account: the same hybrid rocket engine is considered for both stages in order to limit the development costs. A cluster of two, three or four engines is employed in the first stage, whereas a single engine is always used in the second stage. Concerning the feeding system, three alternatives are taken into consideration, namely a blow down, a regulated and an electric turbo-pump feed system. The latter employs an electric motor to drive the oxidizer turbopump, whereas the power is supplied to the motor by lithium batteries. All the design options resulted in viable Mars Ascent Vehicle configurations (payloads are in the range of 70–100 kg), making the hybrid alternative worth considering for the sample return mission. The use of an electric turbo-pump feed system determines the highest vehicle performance with an estimated 10–25% payload gain with respect to gas-pressure feed systems. Full article
(This article belongs to the Special Issue Hybrid Rocket(Volume II))
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Article
FMI-Based Multi-Domain Simulation for an Aero-Engine Control System
Aerospace 2021, 8(7), 180; https://doi.org/10.3390/aerospace8070180 - 02 Jul 2021
Cited by 1 | Viewed by 1007
Abstract
The simulation of an aero-engine control system involves numerous disciplines due to its complex functions and architecture, which generally consist of mechanical, hydraulic and electrical, and electronic systems. For each discipline, the modeling and simulation are usually dependent on different commercial software and [...] Read more.
The simulation of an aero-engine control system involves numerous disciplines due to its complex functions and architecture, which generally consist of mechanical, hydraulic and electrical, and electronic systems. For each discipline, the modeling and simulation are usually dependent on different commercial software and tools, which makes the simulation, integration, and verification of system-level models very difficult. To meet this challenge, a multi-domain co-simulation method based on the Functional Mock-up Interface (FMI) standard is proposed to integrate models developed by different software or tools. The simulation and testing results demonstrate that multi-disciplinary model integration and cross-platform simulation based on the FMI standard can be realized for an aero-engine control system, which lays a foundation for high-fidelity control system design, simulation, integration, and testing. Full article
(This article belongs to the Special Issue Progress in Jet Engine Technology II)
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Article
The Effect of Real-World Interference on CNN Feature Extraction and Machine Learning Classification of Unmanned Aerial Systems
Aerospace 2021, 8(7), 179; https://doi.org/10.3390/aerospace8070179 - 01 Jul 2021
Cited by 2 | Viewed by 1089
Abstract
Small unmanned aerial systems (UASs) present many potential solutions and enhancements to industry today but equally pose a significant security challenge. We only need to look at the levels of disruption caused by UASs at airports in recent years. The accuracy of UAS [...] Read more.
Small unmanned aerial systems (UASs) present many potential solutions and enhancements to industry today but equally pose a significant security challenge. We only need to look at the levels of disruption caused by UASs at airports in recent years. The accuracy of UAS detection and classification systems based on radio frequency (RF) signals can be hindered by other interfering signals present in the same frequency band, such as Bluetooth and Wi-Fi devices. In this paper, we evaluate the effect of real-world interference from Bluetooth and Wi-Fi signals concurrently on convolutional neural network (CNN) feature extraction and machine learning classification of UASs. We assess multiple UASs that operate using different transmission systems: Wi-Fi, Lightbridge 2.0, OcuSync 1.0, OcuSync 2.0 and the recently released OcuSync 3.0. We consider 7 popular UASs, evaluating 2 class UAS detection, 8 class UAS type classification and 21 class UAS flight mode classification. Our results show that the process of CNN feature extraction using transfer learning and machine learning classification is fairly robust in the presence of real-world interference. We also show that UASs that are operating using the same transmission system can be distinguished. In the presence of interference from both Bluetooth and Wi-Fi signals, our results show 100% accuracy for UAV detection (2 classes), 98.1% (+/−0.4%) for UAV type classification (8 classes) and 95.4% (+/−0.3%) for UAV flight mode classification (21 classes). Full article
(This article belongs to the Special Issue AI/Machine Learning in Aerospace Autonomy)
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Article
Development of Detailed FE Numerical Models for Assessing the Replacement of Metal with Composite Materials Applied to an Executive Aircraft Wing
Aerospace 2021, 8(7), 178; https://doi.org/10.3390/aerospace8070178 - 01 Jul 2021
Cited by 2 | Viewed by 1175
Abstract
This work provides a feasibility and effectiveness analysis, through numerical investigation, of metal replacement of primary components with composite material for an executive aircraft wing. In particular, benefits and disadvantages of replacing metal, usually adopted to manufacture this structural component, with composite material [...] Read more.
This work provides a feasibility and effectiveness analysis, through numerical investigation, of metal replacement of primary components with composite material for an executive aircraft wing. In particular, benefits and disadvantages of replacing metal, usually adopted to manufacture this structural component, with composite material are explored. To accomplish this task, a detailed FEM numerical model of the composite aircraft wing was deployed by taking into account process constraints related to Liquid Resin Infusion, which was selected as the preferred manufacturing technique to fabricate the wing. We obtained a geometric and material layup definition for the CFRP components of the wing, which demonstrated that the replacement of the metal elements with composite materials did not affect the structural performance and can guarantee a substantial advantage for the structure in terms of weight reduction when compared to the equivalent metallic configuration, even for existing executive wing configurations. Full article
(This article belongs to the Special Issue Aircraft Modelling for Design, Simulation and Control)
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Article
Investigation of Reynolds Number Effects on Aerodynamic Characteristics of a Transport Aircraft
Aerospace 2021, 8(7), 177; https://doi.org/10.3390/aerospace8070177 - 01 Jul 2021
Cited by 1 | Viewed by 1075
Abstract
The scale difference between the real flight vehicle and the experimental model results in the Reynolds number effect, which makes it unreliable to predict the aerodynamic characteristics of flight vehicles by wind tunnel testing. To understand the mechanism of Reynolds number effects on [...] Read more.
The scale difference between the real flight vehicle and the experimental model results in the Reynolds number effect, which makes it unreliable to predict the aerodynamic characteristics of flight vehicles by wind tunnel testing. To understand the mechanism of Reynolds number effects on the aerodynamic characteristics of the supercritical wing that is commonly used in transport aircraft in more detail, surface pressure wind tunnel tests of a transport aircraft reference model with a wing-body configuration were conducted in the European Transonic Windtunnel (ETW) at different Reynolds numbers. There are 495 pressure taps in total equipped on the surface of the test model with the Mach numbers ranging from 0.6 to 0.86 and Reynolds number varying from 3.3 × 106 to 35 × 106. In addition, an in-house developed CFD tool that has been validated by extensive experimental data was used to correct the wing deformation effect of the test model and achieve detailed flow structures. The results show that the Reynolds number has a significant impact on the boundary layer displacement thickness, surface pressure distribution, shock wave position, and overall aerodynamic force coefficients of the transport aircraft in the presence of shock wave and the induced boundary layer separation. The wind tunnel data combined with flow fields achieved from CFD show that the essence of the Reynolds number effect on the aerodynamic characteristics of transport aircraft is the difference of boundary layer development, shock wave/boundary layer interaction, and induced flow separation at different Reynolds numbers. Full article
(This article belongs to the Special Issue Advances in Aerospace Sciences and Technology II)
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Article
\({\mathcal{L}_1}\) Adaptive Loss Fault Tolerance Control of Unmanned Hypersonic Aircraft with Elasticity
Aerospace 2021, 8(7), 176; https://doi.org/10.3390/aerospace8070176 - 29 Jun 2021
Cited by 1 | Viewed by 815
Abstract
This paper investigates the fault tolerance control of hypersonic aircrafts with L1 adaptive control method in the presence of loss of actuator effectiveness fault. The hypersonic model considers the uncertainties caused by the features of nonlinearities and couplings. Elasticity is taken into [...] Read more.
This paper investigates the fault tolerance control of hypersonic aircrafts with L1 adaptive control method in the presence of loss of actuator effectiveness fault. The hypersonic model considers the uncertainties caused by the features of nonlinearities and couplings. Elasticity is taken into account in hypersonic vehicle modeling which makes the model more accurate. A velocity L1 adaptive controller and an altitude L1 adaptive controller are designed to control flexible hypersonic vehicle model with actuator loss fault. A PID controller is designed as well for comparison. Finally, the simulation results are used to analyze the effectiveness of the controller. Compared to the results of PID controller, L1 controllers have better performance. Full article
(This article belongs to the Special Issue Spacecraft Dynamics and Control)
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Article
Design Process and Environmental Impact of Unconventional Tail Airliners
Aerospace 2021, 8(7), 175; https://doi.org/10.3390/aerospace8070175 - 28 Jun 2021
Cited by 1 | Viewed by 1070
Abstract
The future of aviation depends on reducing the environmental impact of the aircraft. Unconventional configurations can be the change the industry needs to achieve that goal. Therefore, the development of a tool that allows analyzing these configurations will contribute to their being considered [...] Read more.
The future of aviation depends on reducing the environmental impact of the aircraft. Unconventional configurations can be the change the industry needs to achieve that goal. Therefore, the development of a tool that allows analyzing these configurations will contribute to their being considered more easily in future designs. This design procedure is based on an aerodynamic model and a weight methodology validated for unconventional tail designs. The load cases selected to size the structure were extracted from the certification regulations in force. In order to validate the methodology, the V-tail configuration was selected as a case study. The fuel savings reached with this tail configurations are around 0.7%, and the reduction in NOx emissions are even greater. Thus, the methodology has been validated and it can be easily adapted to other unconventional tail configurations. Full article
(This article belongs to the Special Issue Smart Wing Aircraft)
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Article
Vibro-Acoustical Sensitivities of Stiffened Aircraft Structures Due to Attached Mass-Spring-Dampers with Uncertain Parameters
Aerospace 2021, 8(7), 174; https://doi.org/10.3390/aerospace8070174 - 28 Jun 2021
Viewed by 618
Abstract
The slightest manufacturing tolerances and variances of material properties can indeed have a significant impact on structural modes. An unintentional shift of eigenfrequencies towards dominant excitation frequencies may lead to increased vibration amplitudes of the structure resulting in radiated noise, e.g., reducing passenger [...] Read more.
The slightest manufacturing tolerances and variances of material properties can indeed have a significant impact on structural modes. An unintentional shift of eigenfrequencies towards dominant excitation frequencies may lead to increased vibration amplitudes of the structure resulting in radiated noise, e.g., reducing passenger comfort inside an aircraft’s cabin. This paper focuses on so-called non-structural masses of an aircraft, also known as the secondary structure that are attached to the primary structure via clips, brackets, and shock mounts and constitute a significant part of the overall mass of an aircraft’s structure. Using the example of a simplified fuselage panel, the vibro-acoustical consequences of parameter uncertainties in linking elements are studied. Here, the fuzzy arithmetic provides a suitable framework to describe uncertainties, create combination matrices, and evaluate the simulation results regarding target quantities and the impact of each parameter on the overall system response. To assess the vibrations of the fuzzy structure and by taking into account the excitation spectra of engine noise, modal and frequency response analyses are conducted. Full article
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Article
Exploring the Habitability of Venus: Conceptual Design of a Small Atmospheric Probe
Aerospace 2021, 8(7), 173; https://doi.org/10.3390/aerospace8070173 - 25 Jun 2021
Viewed by 982
Abstract
The possible presence of life in the atmosphere of Venus has been debated frequently over the last 60 years. The discussion was recently reignited by the possible detection of phosphine (PH3), but several other chemicals potentially relevant for life processes are [...] Read more.
The possible presence of life in the atmosphere of Venus has been debated frequently over the last 60 years. The discussion was recently reignited by the possible detection of phosphine (PH3), but several other chemicals potentially relevant for life processes are also found in the middle atmosphere. Moreover, the reasons for the heterogeneous ultraviolet (UV) absorption between 320 and 400 nm in the altitude range ∼40–70 km are still not well understood. These aspects could be further studied in-situ by UV Raman and fluorescence instruments. Here, the conceptual design of a small balloon probe (<20 kg) is presented, including a science payload comprising a UV laser, spectrometer, and a telescope. The goal of the proposed mission is to analyse the absorption of UV light in Venus’ atmosphere, to study the atmospheric composition, and to verify the possible presence of biomarkers. Current state-of-the-art technologies would allow a more cost-efficient and easy to develop mission, as compared to previous Venus probes. This article is focused on the scientific instrumentation, as well as on the mass and power budgets required to realise the proposed mission. Full article
(This article belongs to the Special Issue Small Satellite Technologies and Mission Concepts)
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Article
Effect of the Reynolds Number and Clearance Flow on the Aerodynamic Characteristics of a New Variable Inlet Guide Vane
Aerospace 2021, 8(7), 172; https://doi.org/10.3390/aerospace8070172 - 25 Jun 2021
Viewed by 727
Abstract
Recently, a new type of low-loss variable inlet guide vane (VIGV) was proposed for improving a compressor’s performance under off-design conditions. To provide more information for applications, this work investigated the effect of the Reynolds number and clearance flow on the aerodynamic characteristics [...] Read more.
Recently, a new type of low-loss variable inlet guide vane (VIGV) was proposed for improving a compressor’s performance under off-design conditions. To provide more information for applications, this work investigated the effect of the Reynolds number and clearance flow on the aerodynamic characteristics of this new type of VIGV. The performance and flow field of two representative airfoils with different chord Reynolds numbers were studied with the widely used commercial software ANSYS CFX after validation was completed. Calculations indicate that, with the decrease in the Reynolds number Rec, the airfoil loss coefficient ω and deviation δ first increase slightly and then entered a high growth rate in a low range of Rec. Afterwards, a detailed boundary-layer analysis was conducted to reveal the flow mechanism for the airfoil performance degradation with a low Reynolds number. For the design point, it is the appearance and extension of the separation region on the rear portion; for the maximum incidence point, it is the increase in the length and height of the separation region on the former portion. The three-dimensional VIGV research confirms the Reynolds number effect on airfoils. Furthermore, the clearance leakage flow forms a strong stream-wise vortex by injection into the mainflow, resulting in a high total-pressure loss and under-turning in the endwall region, which shows the potential benefits of seal treatment. Full article
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Article
Propulsion Sizing Correlations for Electrical and Fuel Powered Unmanned Aerial Vehicles
Aerospace 2021, 8(7), 171; https://doi.org/10.3390/aerospace8070171 - 24 Jun 2021
Cited by 5 | Viewed by 1081
Abstract
Despite the increasing demand of Unmanned Aerial Vehicles (UAVs) for a wide range of civil applications, there are few methodologies for their initial sizing. Nowadays, classical methods, mainly developed for transport aircraft, have been adapted to UAVs. However, these tools are not always [...] Read more.
Despite the increasing demand of Unmanned Aerial Vehicles (UAVs) for a wide range of civil applications, there are few methodologies for their initial sizing. Nowadays, classical methods, mainly developed for transport aircraft, have been adapted to UAVs. However, these tools are not always suitable because they do not fully adapt to the plethora of geometrical and propulsive configurations that the UAV sector represents. Therefore, this work provides series of correlations based on off-the-shelf components for the preliminary sizing of propulsion systems for UAVs. This study encompassed electric and fuel-powered propulsion systems, considering that they are the most used in the UAV industry and are the basis of novel architectures such as hybrid propulsion. For these systems, weight correlations were derived, and, depending on data availability, correlations regarding their geometry and energy consumption are also provided. Furthermore, a flowchart for the implementation of the correlations in the UAV design procedure and two practical examples are provided to highlight their usability. To summarize, the main contribution of this work is to provide parametric tools to size rapidly the propulsion system components, which can be embedded in a UAV design and optimization framework. This research complements other correlation studies for UAVs, where the initial sizing of the vehicle is discussed. The present correlations suit multiple UAV categories ranging from micro to Medium-Altitude-Long-Endurance (MALE) UAVs. Full article
(This article belongs to the Collection Unmanned Aerial Systems)
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Article
Visual Search and Conflict Mitigation Strategies Used by Expert en Route Air Traffic Controllers
Aerospace 2021, 8(7), 170; https://doi.org/10.3390/aerospace8070170 - 23 Jun 2021
Cited by 4 | Viewed by 931
Abstract
The role of the en route air traffic control specialist (ATCS) is vital to maintaining safety and efficiency within the National Airspace System (NAS). ATCSs must vigilantly scan the airspace under their control and adjacent airspaces using an En Route Automation Modernization (ERAM) [...] Read more.
The role of the en route air traffic control specialist (ATCS) is vital to maintaining safety and efficiency within the National Airspace System (NAS). ATCSs must vigilantly scan the airspace under their control and adjacent airspaces using an En Route Automation Modernization (ERAM) radar display. The intent of this research is to provide an understanding of the expert controller visual search and aircraft conflict mitigation strategies that could be used as scaffolding methods during ATCS training. Interviews and experiments were conducted to elicit visual scanning and conflict mitigation strategies from the retired controllers who were employed as air traffic control instructors. The interview results were characterized and classified using various heuristics. In particular, representative visual scanpaths were identified, which accord with the interview results of the visual search strategies. The highlights of our findings include: (1) participants used systematic search patterns, such as circular, spiral, linear or quadrant-based, to extract operation-relevant information; (2) participants applied an information hierarchy when aircraft information was cognitively processed (altitude -> direction -> speed); (3) altitude or direction changes were generally preferred over speed changes when imminent potential conflicts were mitigated. Potential applications exist in the implementation of the findings into the training curriculum of candidates. Full article
(This article belongs to the Special Issue Aircraft Operations and CNS/ATM)
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