Aerospace

20 pages, 5345 KiB

Open AccessArticle

The Accuracy and Computational Efficiency of the Loewner Framework for the System Identification of Mechanical Systems

by Gabriele Dessena, Marco Civera, Dmitry I. Ignatyev, James F. Whidborne, Luca Zanotti Fragonara and Bernardino Chiaia

Aerospace 2023, 10(6), 571; https://doi.org/10.3390/aerospace10060571 - 20 Jun 2023

Cited by 2 | Viewed by 1246

Abstract

The Loewner framework has recently been proposed for the system identification of mechanical systems, mitigating the limitations of current frequency domain fitting processes for the extraction of modal parameters. In this work, the Loewner framework computational performance, in terms of the elapsed time [...] Read more.

The Loewner framework has recently been proposed for the system identification of mechanical systems, mitigating the limitations of current frequency domain fitting processes for the extraction of modal parameters. In this work, the Loewner framework computational performance, in terms of the elapsed time till identification, is assessed. This is investigated on a hybrid, numerical and experimental dataset against two well-established system identification methods (least-squares complex exponential, LSCE, and subspace state space system identification, N4SID). Good results are achieved, in terms of better accuracy than LSCE and better computational performance than N4SID. Full article

(This article belongs to the Special Issue Structural Dynamics and Control (2nd Edition))

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31 pages, 8327 KiB

Open AccessArticle

Combined Experimental and Numerical Investigation of a Hypersonic Turbulent Boundary Layer by Means of FLDI and Large-Eddy Simulations

by Giannino Ponchio Camillo, Alexander Wagner, Takahiko Toki and Carlo Scalo

Aerospace 2023, 10(6), 570; https://doi.org/10.3390/aerospace10060570 - 20 Jun 2023

Cited by 3 | Viewed by 1519

Abstract

This work investigates a hypersonic turbulent boundary layer over a

7^{°}

half angle cone at a wall-to-total temperature ratio of 0.1,

M_{\infty} = 7.4

and

R e_{\infty m} = 4.2 \times 10^{6}

m

^{- 1}

, in terms of [...] Read more.

This work investigates a hypersonic turbulent boundary layer over a

7^{°}

half angle cone at a wall-to-total temperature ratio of 0.1,

M_{\infty} = 7.4

and

R e_{\infty m} = 4.2 \times 10^{6}

m

^{- 1}

, in terms of density fluctuations and the convection velocity of density disturbances. Experimental shock tunnel data are collected using a multi-foci Focused Laser Differential Interferometer (FLDI) to probe the boundary layer at several heights. In addition, a high-fidelity, time-resolved Large-Eddy Simulation (LES) of the conical flowfield under the experimentally observed free stream conditions is conducted. The experimentally measured convection velocity of density disturbances is found to follow literature data of pressure disturbances. The spectral distributions evidence the presence of regions with well-defined power laws that are present in pressure spectra. A framework to combine numerical and experimental observations without requiring complex FLDI post-processing strategies is explored using a computational FLDI (cFLDI) on the numerical solution for direct comparisons. Frequency bounds of 160 kHz

< f < 1

MHz are evaluated in consideration of the constraining conditions of both experimental and numerical data. Within these limits, the direct comparisons yield good agreement. Furthermore, it is verified that in the present case, the cFLDI algorithm may be replaced with a simple line integral on the numerical solution. Full article

(This article belongs to the Section Aeronautics)

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15 pages, 9708 KiB

Open AccessArticle

Passive Transonic Shock Control on Bump Flow for Wing Buffet Suppression

by Davide Di Pasquale and Simon Prince

Aerospace 2023, 10(6), 569; https://doi.org/10.3390/aerospace10060569 - 20 Jun 2023

Cited by 1 | Viewed by 1660

Abstract

Since modern transport aircraft cruise at transonic speeds, shock buffet alleviation is one indispensable challenge that civil transport research needs to be addressed. Indeed, in the transonic flow regime shock-induced separation and transonic buffet compromise the flight envelope of an aircraft, and therefore [...] Read more.

Since modern transport aircraft cruise at transonic speeds, shock buffet alleviation is one indispensable challenge that civil transport research needs to be addressed. Indeed, in the transonic flow regime shock-induced separation and transonic buffet compromise the flight envelope of an aircraft, and therefore its operational safety and structural integrity. One possible solution is to control and delay the boundary layer separation. The aim of this work was to study whether sub-boundary layer scale period roughness, which locally increases the boundary layer displacement thickness, can act as a virtual shock bump, with aim of bifurcating the foot of the shock wave to reduce the shock’s adverse effect on the boundary layer in the same way as solid shock bumps are known to act. This passive approach can then enhance the buffet margin, consequently extending the safe flight envelope. An experimental investigation was performed, applying this passive technique on a wind tunnel wall bump model which simulated the flow over the upper surface of an aerofoil. The results, in terms of surface pressure distribution and corresponding shadowgraph flow visualisation, showed that such periodic roughness can, indeed, bifurcate the shock wave and delay shock-induced separations, depending on the orientation of the roughness and its periodicity. A virtual shock bump effect can be produced using the displacement effect of periodic sub-boundary layer scale roughness. Full article

(This article belongs to the Special Issue Transonic Flow)

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19 pages, 20050 KiB

Open AccessArticle

Pressure Characteristics and Vortex Observation in Chiral-Symmetric Space Orthogonal Bifurcation

by Zixuan Fang, Dingwei Zhang, Xiaokang Liu, Jingxuan Li, Lijun Yang and Qingfei Fu

Aerospace 2023, 10(6), 568; https://doi.org/10.3390/aerospace10060568 - 19 Jun 2023

Viewed by 1106

Abstract

In aerospace engine delivery systems, “one-in-two-out” bifurcation structures are commonly used for flow distribution to downstream pipelines. There are two common “one-in-two-out” bifurcation structures in aircraft engines: the planar orthogonal bifurcation and the spatial orthogonal bifurcation. By adjusting the flow supply upstream and [...] Read more.

In aerospace engine delivery systems, “one-in-two-out” bifurcation structures are commonly used for flow distribution to downstream pipelines. There are two common “one-in-two-out” bifurcation structures in aircraft engines: the planar orthogonal bifurcation and the spatial orthogonal bifurcation. By adjusting the flow supply upstream and the cross-sectional diameter downstream, the flow distribution in the two branches can be adjusted, i.e., the “splitting ratio” changes. In this paper, a dismantling and flexible experimental system is constructed to measure the pressure signals in each channel and use non-linear dynamic analysis methods to extract pressure characteristics. The particle image velocimetry (PIV) technique combined with the fine rope tracing technique is creatively used to observe the vortex structure in the cross section of the downstream branch. The study found that for spatial orthogonal bifurcation, the pressure signal characteristics in each channel are basically the same at larger splitting ratios, regardless of the chirality. As the splitting ratio decreases, the difference in pressure signal characteristics between the two branches gradually becomes evident and becomes related to the chirality. Moreover, unlike the planar orthogonal bifurcation structure, a complete large vortex structure has not been found in the downstream branch of the spatial orthogonal bifurcation structure, regardless of changes in the splitting ratio, and it is unrelated to the chirality. Full article

(This article belongs to the Special Issue Heat Transfer, Combustion and Flow Dynamics in Propulsion Systems)

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21 pages, 3931 KiB

Open AccessArticle

Mathematical Modelling of a Propellent Gauging System: A Case Study on PRISMA

by Riyaaz Uddien Shaik, Naresh Relangi and Kathiravan Thangavel

Aerospace 2023, 10(6), 567; https://doi.org/10.3390/aerospace10060567 - 18 Jun 2023

Cited by 1 | Viewed by 976

Abstract

Propellant gauging is crucial for a spacecraft approaching the end of its lifespan. Current gauging systems for satellites typically have an accuracy rate of a few months to a year at the end of their operational life. Therefore, it is essential to determine [...] Read more.

Propellant gauging is crucial for a spacecraft approaching the end of its lifespan. Current gauging systems for satellites typically have an accuracy rate of a few months to a year at the end of their operational life. Therefore, it is essential to determine the appropriate gauging system for mission operations. This research focuses on modeling the propellant gauging system for PRISMA, an Earth Observation (EO) satellite of the Italian Space Agency. The analysis centers on implementing algorithms that calibrate the remaining propellant mass in the satellite tank using traditional methods such as bookkeeping (BKP) and pressure-volume-temperature (PVT). To enhance accuracy in quantification, an unconventional approach called thermal propellant gauging (TPG) has been considered. Preliminary computations were conducted using data obtained from the PRISMA thermal model to understand the calibration accuracy of the three methods. At the end of its operational life, the BKP and PVT methods exhibited error rates of 4.6% and 4.8%, respectively, in calculating the mass. In contrast, the TPG method demonstrated a significantly higher precision with an error rate of 1.86%. However, at the beginning of the satellite’s operational life, the PVT and TPG methods showed error rates of 1.0% and 1.3%, respectively, while the BKP technique reported an error rate of 0.1%. Based on these findings, it has been concluded that combining the BKP and TPG approaches yields superior results throughout the satellite’s lifespan. Furthermore, the researchers have determined the specific time duration for which each of these distinct approaches can be effectively utilized. Full article

(This article belongs to the Section Astronautics & Space Science)

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42 pages, 4627 KiB

Open AccessArticle

Design Investigation of Potential Long-Range Hydrogen Combustion Blended Wing Body Aircraft with Future Technologies

by Stanislav Karpuk, Yiyuan Ma and Ali Elham

Aerospace 2023, 10(6), 566; https://doi.org/10.3390/aerospace10060566 - 17 Jun 2023

Cited by 6 | Viewed by 2589

Abstract

Present work investigates the potential of a long-range commercial blended wing body configuration powered by hydrogen combustion engines with future airframe and propulsion technologies. Future technologies include advanced materials, load alleviation techniques, boundary layer ingestion, and ultra-high bypass ratio engines. The hydrogen combustion [...] Read more.

Present work investigates the potential of a long-range commercial blended wing body configuration powered by hydrogen combustion engines with future airframe and propulsion technologies. Future technologies include advanced materials, load alleviation techniques, boundary layer ingestion, and ultra-high bypass ratio engines. The hydrogen combustion configuration was compared to the configuration powered by kerosene with respect to geometric properties, performance characteristics, energy demand, equivalent CO₂ emissions, and Direct Operating Costs. In addition, technology sensitivity studies were performed to assess the potential influence of each technology on the configuration. A multi-fidelity sizing methodology using low- and mid-fidelity methods for rapid configuration sizing was created to assess the configuration and perform robust analyses and multi-disciplinary optimizations. To assess potential uncertainties of the fidelity of aerodynamic analysis tools, high-fidelity aerodynamic analysis and optimization framework MACH-Aero was used for additional verification. Comparison of hydrogen and kerosene blended wing body aircraft showed a potential reduction of equivalent CO₂ emission by 15% and 81% for blue and green hydrogen compared to the kerosene blended wing body and by 44% and 88% with respect to a conventional B777-300ER aircraft. Advancements in future technologies also significantly affect the geometric layout of aircraft. Boundary layer ingestion and ultra-high bypass ratio engines demonstrated the highest potential for fuel reduction, although both technologies conflict with each other. However, operating costs of hydrogen aircraft could establish a significant problem if pessimistic and base hydrogen price scenarios are achieved for blue and green hydrogen respectively. Finally, configurational problems featured by classical blended wing body aircraft are magnified for the hydrogen case due to the significant volume requirements to store hydrogen fuel. Full article

(This article belongs to the Special Issue Aircraft Design (SI-5/2023))

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25 pages, 7955 KiB

Open AccessArticle

Unstable Approach Detection and Analysis Based on Energy Management and a Deep Neural Network

by Tzu-Ying Chiu and Ying-Chih Lai

Aerospace 2023, 10(6), 565; https://doi.org/10.3390/aerospace10060565 - 16 Jun 2023

Cited by 1 | Viewed by 1128

Abstract

The study of managing risk in aviation is the key to improving flight safety. Compared to the other flight operation phases, the approach and landing phases are more critical and dangerous. This study aims to detect and analyze unstable approaches in Taiwan through [...] Read more.

The study of managing risk in aviation is the key to improving flight safety. Compared to the other flight operation phases, the approach and landing phases are more critical and dangerous. This study aims to detect and analyze unstable approaches in Taiwan through historical flight data. In addition to weather factors such as low visibility and crosswinds, human factors also account for a large part of the risk. From the accidents studied in the stochastic report of the Flight Safety Foundation, nearly 70% of the accidents occurred during the approach and landing phases, which were caused by improper control of aircraft energy. Since the information of the flight data recorder (FDR) is regarded as the airline’s confidential information, this study calculates the aircraft’s energy-related metrics and investigates the influence of non-weather-related factors on unstable approaches through a publicly available source, automatic dependent surveillance-broadcast (ADS-B) flight data. To evaluate the influence of weather- and non-weather-related factors, the outliers of each group classified by weather labels are detected and eliminated from the analysis by applying hierarchical density-based spatial clustering of applications with noise (HDBSCAN), which is utilized for detecting abnormal flights that are spatial anomalies. The deep learning method was adopted to detect and predict unstable arrival flights landing at Taipei Songshan Airport. The accuracy of the prediction for the normalized total energy and trajectory deviation of all flights is 85.15% and 82.11%, respectively. The results show that in different kinds of weather conditions, or not considering the weather, the models have similar good performance. The input features were analyzed after the model was obtained, and the flights detected as abnormal are discussed. Full article

(This article belongs to the Special Issue Machine Learning for Aeronautics)

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18 pages, 8835 KiB

Open AccessArticle

Heat Transfer and Flow Structure Characteristics of Regenerative Cooling in a Rectangular Channel Using Supercritical CO₂

by Jian Liu, Mengyao Xu, Pengchao Liu and Wenxiong Xi

Aerospace 2023, 10(6), 564; https://doi.org/10.3390/aerospace10060564 - 16 Jun 2023

Viewed by 1126

Abstract

At an extremely high Mach number, the regenerative cooling of traditional kerosene cannot meet the requirement of the heat sink caused by aerodynamic heating and internal combustion in a scramjet propulsion system. As a supplement of traditional regenerative cooling, supercritical CO₂ is [...] Read more.

At an extremely high Mach number, the regenerative cooling of traditional kerosene cannot meet the requirement of the heat sink caused by aerodynamic heating and internal combustion in a scramjet propulsion system. As a supplement of traditional regenerative cooling, supercritical CO₂ is regarded as an effective coolant in severe heating environments due to its excellent properties of heat and mass transportation. In this paper, the heat transfer and flow structure characteristics of regenerative cooling in a rectangular channel using supercritical CO₂ are analyzed numerically using a validated model. The effect of heat flux magnitude, nonuniform heat flux, acceleration and buoyancy and flow pattern are considered to reveal the regenerative cooling mechanism of supercritical CO₂ in the engine condition of a scramjet. The results indicate that the heat transfer deterioration phenomenon becomes obvious in the cooling channel loaded with relatively high heat flux. Compared with the cooling channels loaded with increased heat flux distribution, the maximum temperature increased for the channel loaded with decreased heat flux distributions. When larger acceleration is applied, a relatively lower wall temperature distribution and higher heat transfer coefficients are obtained. The wall temperature distribution becomes more uniform and the high-temperature region is weakened when the coolants in adjacent channels are arranged as a reversed flow pattern. Overall, the paper provides some references for the utilization of supercritical CO₂ in regenerative cooling at an extremely high Mach number in a scramjet. Full article

(This article belongs to the Special Issue Heat Transfer, Combustion and Flow Dynamics in Propulsion Systems)

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18 pages, 6805 KiB

Open AccessArticle

Mathematical Modelling and Fluidic Thrust Vectoring Control of a Delta Wing UAV

by Ahsan Tanveer and Sarvat Mushtaq Ahmad

Aerospace 2023, 10(6), 563; https://doi.org/10.3390/aerospace10060563 - 16 Jun 2023

Cited by 2 | Viewed by 1961

Abstract

Pitch control of an unmanned aerial vehicle (UAV) using fluidic thrust vectoring (FTV) is a relatively novel technique requiring no moving control surfaces, such as elevators. In this paper, the authors’ previous work on the characterization of a static co-flow FTV rig is [...] Read more.

Pitch control of an unmanned aerial vehicle (UAV) using fluidic thrust vectoring (FTV) is a relatively novel technique requiring no moving control surfaces, such as elevators. In this paper, the authors’ previous work on the characterization of a static co-flow FTV rig is further validated using the free to pitch dynamic test bench. The deflection of a primary jet after injection of a high-velocity secondary jet was captured using the tuft flow visualization technique, along with the experimental recording of subsequent normal force impinged on the Coanda surface resulting in the pitching moment. The effect of primary and secondary flow velocities on exhaust jet deflection, as well as on the pitch angle of the aircraft, is examined. Aerodynamic gain as well as the inertia of a delta wing UAV test bench are computed through experiments and fed into the equation of motion (e.o.m). The e.o.m developed aided in the design of a model-based PID controller for pitch motion control using the multi-parameter root locus technique. The root locus tuned controller serves as a benchmark controller for performance evaluation of the genetic algorithm (GA) and particle swarm optimization (PSO) tuned controllers. Furthermore, the frequency domain metric of gain and phase margins were also employed to reach a robust control design. Experiments conducted in a simulation environment reveal that PSO-PID results in a better response of the UAV in comparison to the baseline pitch controller. Full article

(This article belongs to the Section Aeronautics)

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20 pages, 8487 KiB

Open AccessArticle

UAV Path Planning Based on Improved Artificial Potential Field Method

by Guoqiang Hao, Qiang Lv, Zhen Huang, Huanlong Zhao and Wei Chen

Aerospace 2023, 10(6), 562; https://doi.org/10.3390/aerospace10060562 - 15 Jun 2023

Cited by 9 | Viewed by 2041

Abstract

The obstacle avoidance system of a drone affects the quality of its flight path. The artificial potential field method can react quickly when facing obstacles; however, the traditional artificial potential field method lacks consideration of the position information between drones and obstacles during [...] Read more.

The obstacle avoidance system of a drone affects the quality of its flight path. The artificial potential field method can react quickly when facing obstacles; however, the traditional artificial potential field method lacks consideration of the position information between drones and obstacles during flight, issues including local minima, unreachable targets, and unreasonable obstacle avoidance techniques that lengthen flight times and consume more energy get encountered. Therefore, an improved artificial potential field method is proposed. First, a collision risk assessment mechanism was introduced to avoid unreasonable obstacle avoidance actions and reduce the length of unmanned aerial vehicle flight paths. Then, to solve the problem of local minimum values and unreachable targets, a virtual sub-target was set up and the traditional artificial potential field model was modified to enable the drone to avoid obstacles and reach the target point. At the same time, a virtual sub-target evaluation factor was set up to determine the reasonable virtual sub-target, to achieve a reasonable obstacle avoidance path compared to the traditional artificial potential field method. The proposed algorithm can plan a reasonable path, reduce energy consumption during flight, reduce drone turning angle changes in the path, make the path smoother, and can also be applied in complex environments. Full article

(This article belongs to the Section Aeronautics)

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13 pages, 13305 KiB

Open AccessArticle

Cross-Scale Light Absorption Properties of Surface Bionic Microstructures for Spacecraft Stealth

by Yuhuan Qiu, Guohua Kang, Xunlong Cheng and Jiaqi Wu

Aerospace 2023, 10(6), 561; https://doi.org/10.3390/aerospace10060561 - 15 Jun 2023

Cited by 1 | Viewed by 1199

Abstract

To address the problem that the black coating for spacecraft optical stealth easily falls off, this study constructs a light-absorbing spacecraft surface based on a micro/nanostructure through imitating a natural light-trapping structure. In this paper, we first analyze the optical properties of a [...] Read more.

To address the problem that the black coating for spacecraft optical stealth easily falls off, this study constructs a light-absorbing spacecraft surface based on a micro/nanostructure through imitating a natural light-trapping structure. In this paper, we first analyze the optical properties of a basic stealth structure with the finite difference time domain (FDTD) method and establish a mapping relationship between the light absorption rate of the basic stealth structure and its multiscale factors. Then, imitating the microstructural characteristics of the blackened parts of butterfly wings, we design a multilayered and multiscale complex stealth structure to achieve the optical stealth characteristics of low reflection and high absorption of sunlight on the surface of the spacecraft. Simulation analysis shows that the bionic microstructure can be used to change the optical properties of the metal surface to a certain wavelength band; the complex stealth structure designed based on the butterfly wing can absorb 80.18% of visible light and reduce the overall brightness of the high-orbiting spacecraft by four orders of magnitude. Full article

(This article belongs to the Section Aeronautics)

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42 pages, 9066 KiB

Open AccessArticle

Assistant Based Speech Recognition Support for Air Traffic Controllers in a Multiple Remote Tower Environment

by Oliver Ohneiser, Hartmut Helmke, Shruthi Shetty, Matthias Kleinert, Heiko Ehr, Sebastian Schier-Morgenthal, Saeed Sarfjoo, Petr Motlicek, Šarūnas Murauskas, Tomas Pagirys, Haris Usanovic, Mirta Meštrović and Aneta Černá

Aerospace 2023, 10(6), 560; https://doi.org/10.3390/aerospace10060560 - 14 Jun 2023

Viewed by 1377

Abstract

Assistant Based Speech Recognition (ABSR) systems for air traffic control radiotelephony communication have shown their potential to reduce air traffic controllers’ (ATCos) workload. Related research activities mainly focused on utterances for approach and en-route traffic. This is one of the first investigations of [...] Read more.

Assistant Based Speech Recognition (ABSR) systems for air traffic control radiotelephony communication have shown their potential to reduce air traffic controllers’ (ATCos) workload. Related research activities mainly focused on utterances for approach and en-route traffic. This is one of the first investigations of how ABSR could support ATCos in a tower environment. Ten ATCos from Lithuania and Austria participated in a human-in-the-loop simulation to validate ABSR support within a prototypic multiple remote tower controller working position. The ABSR supports ATCos by (1) highlighting recognized callsigns, (2) inputting recognized commands from ATCo utterances in electronic flight strips, (3) offering correction of ABSR output, (4) automatically accepting ABSR output, and (5) feeding the digital air traffic control system. This paper assesses human factors such as workload, situation awareness, and usability when ATCos are supported by ABSR. Those assessments result from a system with a relevant command recognition rate of 82.9% and a callsign recognition rate of 94.2%. Workload reductions and usability improvement with p-values below 0.25 are obtained for the case when the ABSR system is compared to the baseline situation without ABSR support. This motivates the technology to be brought to a higher technology readiness level, which is also confirmed by subjective feedback from questionnaires and objective measurement of workload reduction based on a performed secondary task. Full article

(This article belongs to the Special Issue Automatic Speech Recognition and Understanding in Air Traffic Management)

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13 pages, 4805 KiB

Open AccessArticle

Analysis of the Sound Field Structure in the Cabin of the RRJ-95NEW-100 Prototype Aircraft

by Vladimir Lavrov, Petr Moshkov and Dmitry Strelets

Aerospace 2023, 10(6), 559; https://doi.org/10.3390/aerospace10060559 - 14 Jun 2023

Viewed by 1011

Abstract

The results of in-flight experiments to determine the structure of the sound field in the cabin and pressure fluctuation fields on the surface of the fuselage of the RRJ-95NEW-100 prototype aircraft are presented here. Wall pressure fluctuation spectrums are obtained for three zones [...] Read more.

The results of in-flight experiments to determine the structure of the sound field in the cabin and pressure fluctuation fields on the surface of the fuselage of the RRJ-95NEW-100 prototype aircraft are presented here. Wall pressure fluctuation spectrums are obtained for three zones of measuring windows (forward, center, and rear fuselage) in cruising flight mode. The effect of the jet on the pressure fluctuation levels in the tail fuselage is considered. For an aircraft without an interior, the contribution of the main sources to the total intensity calculated through A-weighted overall sound pressure levels is determined. It has been determined that the main noise sources in the cabin of the RRJ-95NEW-100 prototype aircraft in cruising flight mode are pressure fluctuation fields on the fuselage surface (turbulent boundary layer noise) and the air conditioning system. The ratio between the sources varies along the length of the cabin. Full article

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20 pages, 18259 KiB

Open AccessArticle

Compressor Performance Prediction Based on the Interpolation Method and Support Vector Machine

by Lingfeng Zhong, Rui Liu, Xiaodong Miao, Yufeng Chen, Songhong Li and Haocheng Ji

Aerospace 2023, 10(6), 558; https://doi.org/10.3390/aerospace10060558 - 13 Jun 2023

Cited by 5 | Viewed by 1835

Abstract

Compressors are important components in various power systems in the field of energy and power. In practical applications, compressors often operate under non-design conditions. Therefore, accurate calculation on performance under various operating conditions is of great significance for the development and application of [...] Read more.

Compressors are important components in various power systems in the field of energy and power. In practical applications, compressors often operate under non-design conditions. Therefore, accurate calculation on performance under various operating conditions is of great significance for the development and application of certain power systems equipped with compressors. To calculate and predict the performance of a compressor under all operating conditions through limited data, the interpolation method was combined with a support vector machine (SVM). Based on the known data points of compressor design conditions, the interpolation method was adopted to obtain training samples of the SVM. In the calculation process, preliminary screening was conducted on the kernel functions of the SVM. Two interpolation methods, including linear interpolation and cubic spline interpolation, were used to obtain sample data. In the subsequent training process of the SVM, the genetic algorithm (GA) was used to optimize its parameters. After training, the available data were compared with the predicted data of the SVM. The results show that the SVM uses the Gaussian kernel function to achieve the highest prediction accuracy. The prediction accuracy of the SVM trained with the data obtained from linear interpolation was higher than that of cubic spline interpolation. Compared with the back propagation neural network optimized by the genetic algorithm (GA-BPNN), the genetic algorithm optimization of extreme learning machine neural network (GA-ELMNN), and the genetic algorithm optimization of generalized regression neural network (GA-GRNN), the support vector machine optimized by the genetic algorithm (GA-SVM) has a better generalization, and GA-SVM is more accurate in predicting boundary data than the GA-BPNN. In addition, reducing the number of original data points still enables the GA-SVM to maintain a high level of predictive accuracy. Full article

(This article belongs to the Special Issue Machine Learning for Aeronautics)

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24 pages, 3332 KiB

Open AccessArticle

Data-Driven Modeling of Air Traffic Controllers’ Policy to Resolve Conflicts

by Alevizos Bastas and George A. Vouros

Aerospace 2023, 10(6), 557; https://doi.org/10.3390/aerospace10060557 - 13 Jun 2023

Viewed by 1212

Abstract

With the aim to enhance automation in conflict detection and resolution (CD&R) tasks in the air traffic management (ATM) domain, this article studies the use of artificial intelligence and machine learning (AI/ML) methods to learn air traffic controllers’ (ATCOs) policy in resolving conflicts [...] Read more.

With the aim to enhance automation in conflict detection and resolution (CD&R) tasks in the air traffic management (ATM) domain, this article studies the use of artificial intelligence and machine learning (AI/ML) methods to learn air traffic controllers’ (ATCOs) policy in resolving conflicts among aircraft assessed to violate separation minimum constraints during the en route phase of flights, in the tactical phase of operations. The objective is to model

h o w

conflicts are being resolved by ATCOs. Towards this goal, the article formulates the ATCO policy learning problem for conflict resolution, addresses the challenging issue of an inherent lack of information in real-world data, and presents AI/ML methods that learn models of ATCOs’ behavior. The methods are evaluated using real-world datasets. The results show that AI/ML methods can achieve good accuracy on predicting ATCOs’ actions given specific conflicts, revealing the preferences of ATCOs for resolution actions in specific circumstances. However, the high accuracy of predictions is hindered by real-world data-inherent limitations. Full article

(This article belongs to the Collection Air Transportation—Operations and Management)

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13 pages, 5463 KiB

Open AccessArticle

Impact of Hydrogen Peroxide Concentration on Manganese Oxide and Platinum Catalyst Bed Performance

by Adrian Parzybut, Pawel Surmacz and Zbigniew Gut

Aerospace 2023, 10(6), 556; https://doi.org/10.3390/aerospace10060556 - 12 Jun 2023

Cited by 1 | Viewed by 1552

Abstract

This study investigates the use of Mn_xO_y/Al₂O₃ and Pt/Al₂O₃ catalysts for the decomposition of hydrogen peroxide in thrusters. It describes the purpose, procedures, performance, and conclusions coming from the test campaign of the [...] Read more.

This study investigates the use of Mn_xO_y/Al₂O₃ and Pt/Al₂O₃ catalysts for the decomposition of hydrogen peroxide in thrusters. It describes the purpose, procedures, performance, and conclusions coming from the test campaign of the catalyst lifetimes. In particular, eight different propellant samples with two different catalysts were tested twice (in order to exclude uncertainty). Similar operating and starting conditions were applied. All hot tests were performed in a thruster-like catalyst bed configuration with a propellant injector and outlet nozzle. Each bed was filled with the same mass of catalyst (for the same type of catalyst). The results show that platinum is a more effective catalyst than manganese oxides for the decomposition of hydrogen peroxide. The findings have important implications for the development of catalysts for “green” propellants. Full article

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20 pages, 2898 KiB

Open AccessArticle

Future Trends in UAV Applications in the Australian Market

by Iryna Heiets, Yi-Wei Kuo, Jiezhuoma La, Richard C.K. Yeun and Wim Verhagen

Aerospace 2023, 10(6), 555; https://doi.org/10.3390/aerospace10060555 - 12 Jun 2023

Cited by 2 | Viewed by 2310

Abstract

The world has been proactively seeking solutions to control the spread of the COVID-19 virus since 2020. A major defensive action is implementing contactless services into everyday activities to reduce viral spread. Drones can provide contactless services in transporting goods and medical supplies, [...] Read more.

The world has been proactively seeking solutions to control the spread of the COVID-19 virus since 2020. A major defensive action is implementing contactless services into everyday activities to reduce viral spread. Drones can provide contactless services in transporting goods and medical supplies, thus reducing the risk of spreading the virus. This paper aims to investigate the future trends of commercial uses for drones in Australia in the next five years. It will explore the impact of the COVID-19 pandemic on the unmanned aerial vehicles (UAVs) industry and its different applications in Australia over the same timeframe; it also considers whether the use of drones in medical services will increase due to the epidemic. Primary data are gathered and evaluated to consider these issues, supported by a set of secondary data. The research aims to provide a holistic direction for the UAV industry, and in particular, for the Australian drone service providers and regulator to modify their operation strategies. Full article

(This article belongs to the Special Issue Advanced Air Mobility)

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18 pages, 3266 KiB

Open AccessArticle

A Review of Flapping Mechanisms for Avian-Inspired Flapping-Wing Air Vehicles

by Jae-Hung Han, Yu-Jeong Han, Hyeon-Ho Yang, Sang-Gil Lee and Eun-Hyuck Lee

Aerospace 2023, 10(6), 554; https://doi.org/10.3390/aerospace10060554 - 12 Jun 2023

Cited by 3 | Viewed by 3945

Abstract

This study focuses on the flapping mechanisms found in recently developed biometric flapping-wing air vehicles (FWAVs). FWAVs mimic the flight characteristics of flying animals, providing advantages such as maneuverability, inconspicuousness, and excellent flight efficiency in the low Reynolds number region. The flapping mechanism [...] Read more.

This study focuses on the flapping mechanisms found in recently developed biometric flapping-wing air vehicles (FWAVs). FWAVs mimic the flight characteristics of flying animals, providing advantages such as maneuverability, inconspicuousness, and excellent flight efficiency in the low Reynolds number region. The flapping mechanism is a critical part of determining the aerodynamic performance of an FWAV since it is directly related to the wing motion. In this study, the flight characteristics of birds and bats are introduced, the incorporation of these flight characteristics into the development of FWAVs is elucidated, and the utilization of these flight characteristics in the development of FWAVs is explained. Next, the classification and analysis of flapping mechanisms are conducted based on wing motion and the strategy for improving aerodynamic performance. Lastly, the current research gap is elucidated, and potential future directions for further research are proposed. This review can serve as a guide during the early development stage of FWAVs. Full article

(This article belongs to the Section Aeronautics)

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9 pages, 4160 KiB

Open AccessCommunication

Effect of Air Jet Vortex Generators on the Shock Wave Boundary Layer Interaction of Transonic Wing

by Tingkai Dai and Bo Zhang

Aerospace 2023, 10(6), 553; https://doi.org/10.3390/aerospace10060553 - 11 Jun 2023

Viewed by 1130

Abstract

The interaction between shock waves and turbulent boundary layers (SBLI) is a common phenomenon in transonic and supersonic aircraft wings. In this study, we simulated the SBLI of a classical NACA0012 wing at an angle of attack (AOA) of 1.4° and Mach number [...] Read more.

The interaction between shock waves and turbulent boundary layers (SBLI) is a common phenomenon in transonic and supersonic aircraft wings. In this study, we simulated the SBLI of a classical NACA0012 wing at an angle of attack (AOA) of 1.4° and Mach number (Ma) of 0.78 using the open-source software OpenFOAM. Our results show that an air-jet vortex generator can effectively reduce the length of the separation zone and improve the lift coefficient of the airfoil. The vortex structure generated by the jet vortex generator significantly reduces the separation caused by SBLI. We conducted simulations with jet angles of 30°, 45°, and 60° and found that the larger the jet angle, the stronger the vortex and the greater the improvement in the lift coefficient. When the jet angle was 60°, the vortex structure generated by the jet vortex generator transformed the normal shock wave into a λ shock wave, resulting in a maximum increase in the lift coefficient of 2.35%. The simulations focused on exploring the effect of the jet angle and determined that that optimal jet parameters that effectively reduce SBLI damage and improve the lift coefficient of the airfoil. Full article

(This article belongs to the Special Issue Flow Control and Drag Reduction)

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23 pages, 12772 KiB

Open AccessArticle

Numerical and Experimental Investigation on Nosebleed Air Jet Control for Hypersonic Vehicle

by Lin Zhang, Junli Yang, Tiecheng Duan, Jie Wang, Xiuyi Li and Kunyuan Zhang

Aerospace 2023, 10(6), 552; https://doi.org/10.3390/aerospace10060552 - 09 Jun 2023

Cited by 1 | Viewed by 1099

Abstract

A new idea of nosebleed air jets with strong coupled internal and external flow is put forward using the lateral jet control principle to improve the maneuverability and fast reaction capabilities of hypersonic vehicles. The hypersonic vehicle’s nose stagnant high-pressure and high-temperature gas [...] Read more.

A new idea of nosebleed air jets with strong coupled internal and external flow is put forward using the lateral jet control principle to improve the maneuverability and fast reaction capabilities of hypersonic vehicles. The hypersonic vehicle’s nose stagnant high-pressure and high-temperature gas is utilized as the drive source for long-term jet control. The significant coupled jet interaction of the internal and external flow changes the aerodynamic characteristics. As a result, the structure is basic and does not rely on any external source to achieve flight attitude control. The complicated flow characteristics of the nosebleed jet in supersonic crossflow surrounding the vehicle were numerically and experimentally investigated. The jet interaction characteristics and the aerodynamic characteristic changes generated by the nosebleed air jet are verified by comparing the flow field with and without the jet. Results indicate that the nosebleed air jet alters the center-of-pressure coefficient, which is subsequently coupled with the interference aerodynamic force. This results in a variation in pitch moment. The jet decreases the pitching moment coefficient when compared with the case without a jet. It is probable that combining nosebleed air jets with model centroid adjustment yields an optimal trim angle of attack. Full article

(This article belongs to the Special Issue Jet Flows)

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22 pages, 17402 KiB

Open AccessArticle

Numerical Investigation on the Effect of Height-to-Radius Ratio on Flow Separation Features in S-Shaped Diffuser with Boundary Layer Ingestion

by Zhiping Li, Yujiang Lu, Tianyu Pan and Yafei Zhang

Aerospace 2023, 10(6), 551; https://doi.org/10.3390/aerospace10060551 - 09 Jun 2023

Cited by 1 | Viewed by 1105

Abstract

The flow separation occurring in the S-shaped diffuser with boundary layer ingestion (BLI) has a significant effect on the performance of the embedded engine. Previous studies have found that the area ratio (AR) as well as the length-to-offset ratio (LOR) of the S-shaped [...] Read more.

The flow separation occurring in the S-shaped diffuser with boundary layer ingestion (BLI) has a significant effect on the performance of the embedded engine. Previous studies have found that the area ratio (AR) as well as the length-to-offset ratio (LOR) of the S-shaped diffuser are the key contributing factors that affect the flow separation features. Based on the flow phenomena observed in previous studies of an S-shaped diffuser with 100% BLI, a hypothesis that the parameter height-to-radius ratio (HRR) may also have significant effect on the flow separation features in the S-shaped diffuser is proposed. The purpose of this paper is to verify this hypothesis and to further investigate the effect of HRR on the flow separation features in the S-shaped diffuser with BLI using numerical methods. First, the hypothesis that HRR has an effect on the flow separation features in the S-shaped diffuser is verified under uniform inlet condition. Second, the effect of HRR on the flow separation features is investigated under different relative heights of inlet BLI. It is found that the flow separation features in the S-shaped diffuser are very sensitive to the change in HRR but not to the change in relative height of inlet BLI. Finally, for the fixed boundary layer height generated from the airframe, the S-shaped diffuser with a smaller design HRR can significantly suppress the flow separation and thus achieve a higher total pressure recovery and a lower distortion coefficient. The results provide improved understandings of the factor affecting the flow separation features in the S-shaped diffuser, and are useful for improving the aerodynamic performance of the embedded engine with BLI. Full article

(This article belongs to the Section Aeronautics)

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17 pages, 3744 KiB

Open AccessArticle

State-of-Charge Estimation of Batteries for Hybrid Urban Air Mobility

by Min Young Yoo, Jung Heon Lee, Joo-Ho Choi, Jae Sung Huh and Woosuk Sung

Aerospace 2023, 10(6), 550; https://doi.org/10.3390/aerospace10060550 - 08 Jun 2023

Viewed by 1138

Abstract

This paper proposes a framework for accurately estimating the state-of-charge (SOC) and current sensor bias, with the aim of integrating it into urban air mobility (UAM) with hybrid propulsion. Considering the heightened safety concerns in an airborne environment, more reliable state estimation is [...] Read more.

This paper proposes a framework for accurately estimating the state-of-charge (SOC) and current sensor bias, with the aim of integrating it into urban air mobility (UAM) with hybrid propulsion. Considering the heightened safety concerns in an airborne environment, more reliable state estimation is required, particularly for the UAM that uses a battery as its primary power source. To ensure the suitability of the framework for the UAM, a two-pronged approach is taken. First, realistic test profiles, reflecting actual operational scenarios for the UAM, are used to model the battery and validate its state estimator. These profiles incorporate variations in battery power flow, namely, charge-depleting and charge-sustaining modes, during the different phases of the UAM’s flight, including take-off, cruise, and landing. Moreover, the current sensor bias is estimated and corrected concurrently with the SOC. An extended Kalman filter-based bias estimator is developed and experimentally validated using actual current measurements from a Hall sensor, which is prone to noise. With this correction, a SOC estimation error is consistently maintained at 2% or lower, even during transitions between operational modes. Full article

(This article belongs to the Special Issue Predictive Maintenance for Complex Systems—from Sensor Measurements to Prognostics to Maintenance Planning)

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16 pages, 13927 KiB

Open AccessArticle

Numerical Investigation of the Oblique Detonation Waves and Stability in a Super-Detonative Ram Accelerator

by Zhanlin Feng, Kuanliang Wang and Honghui Teng

Aerospace 2023, 10(6), 549; https://doi.org/10.3390/aerospace10060549 - 08 Jun 2023

Viewed by 1033

Abstract

This study numerically investigates the effects of diluent gas proportion, the overdrive factor, and throat width on the wave structure and thrust performance of a ram accelerator operating in super-detonative mode. For premixed gas of a high energy density, a typical unstart oblique [...] Read more.

This study numerically investigates the effects of diluent gas proportion, the overdrive factor, and throat width on the wave structure and thrust performance of a ram accelerator operating in super-detonative mode. For premixed gas of a high energy density, a typical unstart oblique detonation wave system is observed due to the ignition on the front wedge of the projectile, and the detonation waves move downstream to the shoulder as the energy density decreases. In the start range of the overdrive factor, the wave position also shows a tendency to move downstream as the projectile velocity increases, accompanied by oscillations of the wave surface and thrust. As the throat width increases, the wave standing position changes non-monotonously, with an interval of upstream movement and Mach reflection. The typical wave structure of a ram accelerator in super-detonative mode is identified, as well as the unstart stable wave features and the unstable process for choking, which can provide theoretical guidance for avoiding unstart issues in ram accelerators and optimizing their performance. Full article

(This article belongs to the Special Issue Fundamental Detonation Mechanism and Advanced Detonation Propulsion Technology)

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20 pages, 5475 KiB

Open AccessArticle

Numerical Study on Convective Heat Transfer of Liquid Metal Gallium in Turbine Guide Vane

by Zhe Zhang, Zeyu Wu, Xiang Luo and Weitong Liu

Aerospace 2023, 10(6), 548; https://doi.org/10.3390/aerospace10060548 - 08 Jun 2023

Cited by 1 | Viewed by 1179

Abstract

The traditional blade cooling method can no longer meet the requirements of high cooling efficiency in modern engines. In order to solve this cooling problem, this paper proposes cooling turbine guide blades based on liquid metal. The feasibility was preliminarily verified using a [...] Read more.

The traditional blade cooling method can no longer meet the requirements of high cooling efficiency in modern engines. In order to solve this cooling problem, this paper proposes cooling turbine guide blades based on liquid metal. The feasibility was preliminarily verified using a one-dimensional heat conduction model. Then, using a numerical method, we found that the cooling effect of liquid metal is much better than that of air cooling. The main reason for its good cooling effect is that the heat transfer coefficient of liquid metal reaches a magnitude of tens of thousands. Moreover, as the inlet temperature of the liquid metal decreases and the inlet Reynolds number increases, the liquid cooling effect becomes better. The definition of the heat transfer quality factor can reflect the reasons for the influence of the inlet temperature of the liquid metal. Full article

(This article belongs to the Section Aeronautics)

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23 pages, 7874 KiB

Open AccessArticle

Micro- and Nanosatellite Sensorless Electromagnetic Docking Control Based on the High-Frequency Injection Method

by Guangzheng Ruan, Lijian Wu, Yaobing Wang, Bo Wang and Runqi Han

Aerospace 2023, 10(6), 547; https://doi.org/10.3390/aerospace10060547 - 07 Jun 2023

Viewed by 1189

Abstract

This paper proposes a sensorless electromagnetic docking method suitable for micro- and nanosatellites. Based on the circuit model of the electromagnetic docking device, an algorithm for calculating the distance between two satellites on the basis of the high-frequency injection (HFI) method has been [...] Read more.

This paper proposes a sensorless electromagnetic docking method suitable for micro- and nanosatellites. Based on the circuit model of the electromagnetic docking device, an algorithm for calculating the distance between two satellites on the basis of the high-frequency injection (HFI) method has been developed. In the specific implementation, first, a high-frequency (HF) voltage is injected into one of the two electromagnets; second, the HF currents induced by both electromagnets are measured and their respective root-mean-squares (RMSs) are calculated; third, two RMSs are substituted into a specific formula to obtain a variable carrying distance information; finally, the variable is utilized to calculate the distance estimation using the look-up table interpolation method. This paper presents a closed-loop electromagnetic docking controller which includes an outer distance loop and an inner speed loop and adopts the distance estimation as the feedback. The proposed sensorless electromagnetic docking method is verified by the distance estimation tracking response test and the ground-based docking test. The results indicate that low-impact docking can be achieved under the initial condition that the two satellites have a certain degree of misalignment. The proposed method can be adopted as a primary or as a redundant electromagnetic docking solution for resource-critical micro- and nanosatellites. Full article

(This article belongs to the Section Aeronautics)

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20 pages, 7904 KiB

Open AccessArticle

Experimental Firing Test Campaign and Nozzle Heat Transfer Reconstruction in a 200 N Hybrid Rocket Engine with Different Paraffin-Based Fuel Grain Lengths

by Daniele Cardillo, Francesco Battista, Giuseppe Gallo, Stefano Mungiguerra and Raffaele Savino

Aerospace 2023, 10(6), 546; https://doi.org/10.3390/aerospace10060546 - 07 Jun 2023

Cited by 4 | Viewed by 1378

Abstract

Firing test campaigns were carried out on a 200 N thrust-class hybrid rocket engine, using gaseous oxygen as an oxidizer and a paraffin-wax-based fuel. Different fuel grain lengths were adopted to extend the fuel characterization under different operating conditions, and to evaluate rocket [...] Read more.

Firing test campaigns were carried out on a 200 N thrust-class hybrid rocket engine, using gaseous oxygen as an oxidizer and a paraffin-wax-based fuel. Different fuel grain lengths were adopted to extend the fuel characterization under different operating conditions, and to evaluate rocket performances and internal ballistics in the different configurations. In addition to data collected under a 220 mm propellant grain length, two further test campaigns were carried out considering 130 mm and 70 mm grain lengths. Two different injector types were adopted in the 130 mm configuration; in particular, a showerhead injection system was used with the aim to contain high-amplitude pressure oscillations observed during some firing tests in this engine configuration. Parameters such as the chamber pressure and temperature inside the graphite nozzle, space-averaged fuel regression rate and nozzle throat diameter were measured. The results allowed for the investigation of different issues related to hybrid rockets (e.g., fuel regression rate, engine performance, nozzle ablation under different conditions). The focus was mainly directed to the nozzle heat transfer, through the reconstruction of the convective heat transfer coefficient for different tests in the 70 mm grain length engine configuration. The reconstruction took advantage of the experimental data provided by the nozzle embedded thermocouple. Then, the experimental convective heat transfer coefficient was used to validate the results from some empirical correlations. The results showed significant differences between the experimental convective heat transfer coefficients when considering tests with different oxidizer mass flow rates. Furthermore, the predictions from the empirical correlations proved to be more reliable only in cases characterized by oxidizer-rich conditions. Full article

(This article belongs to the Special Issue Fluid-Dynamics and Heat Transfer in Aerospace Propulsion Systems)

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25 pages, 7141 KiB

Open AccessArticle

Effects of Local Mixing Ratios and Mass Flow Rates on Combustion Performance of the Fuel-Rich LOX (Liquid Oxygen)/kerosene Gas Generator in the ATR (Air Turbo Rocket) Engine

by Yuankun Zhang, Qingjun Zhao, Bin Hu, Qiang Shi, Wei Zhao and Xiaorong Xiang

Aerospace 2023, 10(6), 545; https://doi.org/10.3390/aerospace10060545 - 07 Jun 2023

Cited by 2 | Viewed by 1360

Abstract

This paper presents a numerical simulation analysis of the flow and combustion characteristics of a fuel-rich LOX (liquid oxygen)/kerosene gas generator in an ATR (air turbo rocket) engine, examining the effects of local parameters on the combustion flow field and performance. The analysis [...] Read more.

This paper presents a numerical simulation analysis of the flow and combustion characteristics of a fuel-rich LOX (liquid oxygen)/kerosene gas generator in an ATR (air turbo rocket) engine, examining the effects of local parameters on the combustion flow field and performance. The analysis considers variations in unit injector mixing ratios and unit mass flow rates. The results indicate that as the mixing ratio in the inner-ring injectors increases (while the mixing ratio in the middle-ring injectors decreases), the oxygen concentration area near the axis zone and the 50% radius zone of the gas generator expands. Conversely, the kerosene concentration area near the axis zone decreases while gradually increasing near the 50% radius zone. In the flow direction section, there is an inverse relationship between the variation trend of local temperature and the oxygen concentration in the local area. As the oxygen concentration increases, the temperature decreases. The temperature distribution across the cross-section of the gas generator exhibits a circular pattern. When the mixing ratio (or mass flow rates) of the unit injector are perfectly balanced, the temperature distribution becomes highly uniform. A larger disparity in flow rate between the inner ring injector and the middle ring injector leads to a lower combustion efficiency. This effect differs from the effect of the mixing ratio difference between the two injector rings. Increasing the mixing ratio in the inner-ring injectors (or decreasing the mixing ratio in the middle-ring injectors) initially leads to a rise in combustion efficiency, followed by a subsequent decline. The maximum combustion efficiency of 89.10% is achieved when the mixing ratio is set to Km_-1 = 0.7 and Km_-2 = 2.79, respectively. Increasing the flow rate in the inner-ring injectors (or decreasing the flow rate in the middle-ring injectors) initially leads to an improvement in combustion efficiency, followed by a subsequent reduction. The maximum combustion efficiency of 86.13% is achieved when the mass flow rate is set to m_-1 = m_-2 = 0.1 kg/s. Full article

(This article belongs to the Special Issue Aerospace Combustion Engineering)

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10 pages, 3047 KiB

Open AccessArticle

Experimental Research on Characteristics of Impulse Coupling and Plasma Plume Generated by Laser Irradiating Copper Target with Nanosecond Pulsed Laser Propulsion

by Chenghao Yu, Jifei Ye, Hao Chang, Weijing Zhou, Xiao Han, Mingyu Li and Heyan Gao

Aerospace 2023, 10(6), 544; https://doi.org/10.3390/aerospace10060544 - 07 Jun 2023

Cited by 1 | Viewed by 1100

Abstract

The ejection of the plasma plume produced by laser ablation is an important process for inducing mechanical effects. Therefore, in this paper, the characteristics of the plasma plume are investigated in order to analyze the impulse coupling mechanism with two laser spot diameters, [...] Read more.

The ejection of the plasma plume produced by laser ablation is an important process for inducing mechanical effects. Therefore, in this paper, the characteristics of the plasma plume are investigated in order to analyze the impulse coupling mechanism with two laser spot diameters, 300 μm and 1100 μm, respectively. The impulse generated by laser irradiating the copper target was measured by the torsion pendulum, and the plasma plume was investigated using fast photography and optical emission spectroscopy. The experimental results show that the optimal laser intensity is independent of the beam spot size. However, when the laser intensity is greater than 2.8 × 10⁹ W/cm², the impulse coupling coefficient with the small beam spot starts to gradually decrease, while that with the large beam spot tends to saturate. Additionally, the stream-like structure and the semi-ellipsoid structure of the plasma plume were observed, respectively. Furthermore, the electron number density was estimated using the Stark broadening method, and the effect of the plasma plume on the impulse coupling coefficient was discussed. The results provide a technical reference for several applications including orbital debris removal with lasers, laser thrusters, and laser despinning. Full article

(This article belongs to the Special Issue Laser Propulsion Science and Technology)

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14 pages, 2988 KiB

Open AccessArticle

Performance Investigation of the Conjunction Filter Methods and Enhancement of Computation Speed on Conjunction Assessment Analysis with CUDA Techniques

by Phasawee Saingyen, Sittiporn Channumsin, Suwat Sreesawet, Keerati Puttasuwan and Thanathip Limna

Aerospace 2023, 10(6), 543; https://doi.org/10.3390/aerospace10060543 - 07 Jun 2023

Cited by 1 | Viewed by 1158

Abstract

The growing number of space objects leads to increases in the potential risks of damage to satellites and generates space debris after colliding. Conjunction assessment analysis is the one of keys to evaluating the collision risk of satellites and satellite operators require the [...] Read more.

The growing number of space objects leads to increases in the potential risks of damage to satellites and generates space debris after colliding. Conjunction assessment analysis is the one of keys to evaluating the collision risk of satellites and satellite operators require the analyzed results as fast as possible to decide and execute collision maneuver planning. However, the computation time to analyze the potential risk of all satellites is proportional to the number of space objects. The conjunction filters and parallel computing techniques can shorten the computation cost of conjunction analysis to provide the analyzed results. Therefore, this paper shows the investigation of the conjunction filter performances (accuracy and computation speed): Smart Sieve, CSieve and CAOS-D (combination of both Smart Sieve and CSieve) in both a single satellite (one vs. all) and all space objects (all vs. all) cases. Then, all the screening filters are developed to implement an algorithm that executes General-purpose computing on graphics processing units (GPGPU) by using NVIDIAs Compute Unified Device Architecture (CUDA). The analyzed results show the comparison results of the accuracy of conjunction screening analysis and computation times of each filter when implemented with the parallel computation techniques. Full article

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14 pages, 1883 KiB

Open AccessArticle

Experimental Investigation of Flame Anchoring Behavior in a LOX/LNG Rocket Combustor

by Jan Martin, Michael Börner, Justin Hardi, Dmitry Suslov and Michael Oschwald

Aerospace 2023, 10(6), 542; https://doi.org/10.3390/aerospace10060542 - 06 Jun 2023

Viewed by 1166

Abstract

Hot fire tests of a multi-injector research combustor were performed with liquid-oxygen and liquefied-natural-gas (LOX/LNG) propellants at chamber pressures from 30 up to 67 bar, hence at conditions similar to an upper stage rocket engine. Within these tests shear coaxial injectors were tested [...] Read more.

Hot fire tests of a multi-injector research combustor were performed with liquid-oxygen and liquefied-natural-gas (LOX/LNG) propellants at chamber pressures from 30 up to 67 bar, hence at conditions similar to an upper stage rocket engine. Within these tests shear coaxial injectors were tested with and without a recessed LOX post. In both configurations, operating conditions with flames anchored at the LOX post tip and thus, if available, pre-combustion in the recess volume as well as lifted flames were observed. Flame anchoring was indirectly detected via acoustic measurements, using mean speed of sound to indicate the presence of flame in the head end of the combustion chamber. While the injector without recess showed only stable combustion irrespective of the flame anchoring behavior, the recessed injector featured short-lived bursts of oscillatory combustion and sustained combustion instabilities. Analysis of the test data showed that stable flame anchoring could not be ensured at momentum flux ratios below 20 for a non-recessed and below 45 for a recessed injector. Full article

(This article belongs to the Special Issue Liquid Rocket Engines)

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