Latest Advancements in Aeronautics and Astronautics: Celebrating the 70th Anniversary of Nanjing University of Aeronautics and Astronautics

A special issue of Aerospace (ISSN 2226-4310).

Deadline for manuscript submissions: closed (30 November 2022) | Viewed by 44816

Special Issue Editors


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Guest Editor
College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Interests: hypersonic aerodynamics; experimental fluid mechanics; flow stability and transition

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Guest Editor
College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Interests: dynamic load identification; vibration test and data processing; active and passive vibration control; virtual instrument design and implementation

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Guest Editor
College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Interests: aircraft design; helicopter design; helicopter aerodynamics; aerodynamic noise and control; virtual flight test technology; applied computational fluid dynamics

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Guest Editor
College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Interests: computational fluid mechanics; wind energy
College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Interests: computational fluid dynamics; optimization design; flow control; aircraft aerodynamic design; artificial intelligence algorithms and uncertainty quantification; on-board air flow field and landing simulation

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Guest Editor
College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Interests: aircraft landing gear design; UAV launch and recovery technology; aircraft structural dynamics
Special Issues, Collections and Topics in MDPI journals

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Guest Editor
College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Interests: numerical simulation method of aircraft icing; aircraft anti-icing technology; ice wind tunnel test technology; ice detection technique

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Guest Editor
College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Interests: aircraft environment control; study on theory and test method of anti-icing system of aircraft; refrigeration and air conditioning engineering

Special Issue Information

Dear Colleagues,

This Special Issue celebrates the 70th anniversary of Nanjing University of Aeronautics and Astronautics. Nanjing University of Aeronautics and Astronautics, commonly referred to as NUAA, is a leading research-oriented comprehensive university which focuses on multiple disciplines in engineering technology, natural sciences, business and management, and social sciences. Established in 1952, NUAA strives to conduct world-level research and teaching with an emphasis on aerospace technology, astronautics, and civil aviation.

We seek research papers focusing on the latest progress in the aeronautics and astronautics fields, including valuable principal research and experimental studies. Review papers that provide a comprehensive view of a particular subject are welcome as well.

Prof. Dr. Hao Dong
Prof. Dr. Jinhui Jiang
Prof. Dr. Yongjie Shi
Dr. Linlin Tian
Dr. Yibin Wang
Prof. Dr. Xiaohui Wei
Dr. Chengxiang Zhu
Prof. Dr. Chunling Zhu
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (25 papers)

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Research

21 pages, 7640 KiB  
Article
Flush Airdata System on a Flying Wing Based on Machine Learning Algorithms
by Yibin Wang, Yijia Xiao, Lili Zhang, Ning Zhao and Chunling Zhu
Aerospace 2023, 10(2), 132; https://doi.org/10.3390/aerospace10020132 - 31 Jan 2023
Cited by 1 | Viewed by 1336
Abstract
By using an array of pressure sensors distributed on the surface of an aircraft to measure the pressure of each port, the flush airdata sensing (FADS) system is widely applied in many modern aircraft and unmanned aerial vehicles (UAVs). Normally, the pressure transducers [...] Read more.
By using an array of pressure sensors distributed on the surface of an aircraft to measure the pressure of each port, the flush airdata sensing (FADS) system is widely applied in many modern aircraft and unmanned aerial vehicles (UAVs). Normally, the pressure transducers of the FADS system should be mounted on the leading edge of the aircraft, where they are sensitive to changes in pressure. For UAVs, however, the leading edge of the nose and wing may not be available for pressure transducers. In addition, the number of transducers is limited to 8–10, making it difficult to maintain accuracy in the normal method for FADS systems. An FADS system model for an unmanned flying wing was developed, and the pressure transducers were all located outside the regions of the leading edge areas. The locations of the transducers were selected by using the mean impact value (MIV), and ensemble neural networks were developed to predict the airdata with a very limited number of transducers. Furthermore, an error detection method was also developed based on artificial neural networks and random forests. The FADS system model can accurately detect the malfunctioning port and use the correct pressure combination to predict the Mach number, angle of attack, and angle of sideslip with high accuracy. Full article
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23 pages, 19427 KiB  
Article
An Experimental Study on Rotor Aerodynamic Noise Control Based on Active Flap Control
by Zhiyuan Hu, Yang Liu, Yongjie Shi and Guohua Xu
Aerospace 2023, 10(2), 121; https://doi.org/10.3390/aerospace10020121 - 27 Jan 2023
Cited by 1 | Viewed by 2005
Abstract
Reducing rotor aerodynamic noise is an important challenge in helicopter design. Active flap control (AFC) on rotors is an effective noise reduction method. It changes the segment airfoil shape, aerodynamic load distribution, and the wake path of the rotor flow by adding trailing [...] Read more.
Reducing rotor aerodynamic noise is an important challenge in helicopter design. Active flap control (AFC) on rotors is an effective noise reduction method. It changes the segment airfoil shape, aerodynamic load distribution, and the wake path of the rotor flow by adding trailing edge flaps (TEFs). Although AFC noise reduction control is easily simulated, the relevant experiments have not been widely conducted due to test technical problems and limited financial support. The acoustic characteristics of the AFC-equipped rotor, such as the placement of TEFs for noise reduction and whether multiple winglets can provide a better effect than single winglets, have not been verified in previous experiments. In this work, an AFC-equipped rotor with two TEFs was designed, and its acoustic properties were tested in the FL-17 acoustic wind tunnel with microphone arrays in the far field. The results showed that the noise reduction effect of AFC was closely related to the control frequency and phase. Increasing the control phase could move the reduction region toward the azimuth-decreasing region for far-field noise. The noise reduction in a single outboard TEF was better than that in a single inboard TEF, while the dual-TEF model performed better. In this experiment, the average noise reduction in the observation point at the lower front of the rotor could be more than 3 dB, and the maximum noise reduction could be 6.2 dB. Full article
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20 pages, 21380 KiB  
Article
Numerical Simulation of Microscale Oblique Droplet Impact on Liquid Film
by Yan Cao, Jingxin Wang and Chunling Zhu
Aerospace 2023, 10(2), 119; https://doi.org/10.3390/aerospace10020119 - 26 Jan 2023
Cited by 1 | Viewed by 1422
Abstract
The oblique impact of microscale water droplets on liquid film is numerically investigated. Two-phase flow problems are simulated using three-dimensional incompressible Navier-Stokes equations, and the level-set method is employed for capturing the gas-liquid interface. The numerical model is verified using experimental results from [...] Read more.
The oblique impact of microscale water droplets on liquid film is numerically investigated. Two-phase flow problems are simulated using three-dimensional incompressible Navier-Stokes equations, and the level-set method is employed for capturing the gas-liquid interface. The numerical model is verified using experimental results from a normal and oblique impact via the qualitative comparison of crown profile features and quantitative contrast of the crown height and radius varying with time. The article discusses the influence of tangential impact velocity, water film thickness, Reynolds number, and Weber number on the shape characteristics, tangential momentum, and kinetic energy of the annular crown. The results show that the decreasing momentum in the tangential direction can be divided into three clear stages: rapid decrease, slight increase, and continuous decrease. In addition, film thickness and Weber number have significant effects on the momentum decay rate. Full article
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26 pages, 7362 KiB  
Article
An EMD-LSTM Deep Learning Method for Aircraft Hydraulic System Fault Diagnosis under Different Environmental Noises
by Kenan Shen and Dongbiao Zhao
Aerospace 2023, 10(1), 55; https://doi.org/10.3390/aerospace10010055 - 5 Jan 2023
Cited by 8 | Viewed by 2610
Abstract
Aircraft hydraulic fault diagnosis is an important technique in aircraft systems, as the hydraulic system is one of the key components of an aircraft. In aircraft hydraulic system fault diagnosis, complex environmental noises will lead to inaccurate results. To address the above problem, [...] Read more.
Aircraft hydraulic fault diagnosis is an important technique in aircraft systems, as the hydraulic system is one of the key components of an aircraft. In aircraft hydraulic system fault diagnosis, complex environmental noises will lead to inaccurate results. To address the above problem, hydraulic system fault detection methods should be capable of noise resistance. Previous research has mainly focused on noise-free conditions and many effective approaches have been proposed; however, in real-world aircraft flying conditions, the aircraft hydraulic system often has strong and complex noises. The methods proposed may not have good fault detection results in such a noisy environment. According to the situation, this work focuses on aircraft hydraulic system fault classification under the influence of a hydraulic working environment with Gaussian white noise. In order to eliminate the noise interference and adapt to the actual noisy environment, a new aircraft hydraulic fault diagnostic method based on empirical mode deposition (EMD) and long short-term memory (LSTM) is presented. First, the hydraulic system is constructed by AMESIM. One normal state and five fault states are considered in this paper. Eight-channel signals of different states are collected for network training and testing. Second, the EMD method is used to obtain the different intrinsic mode functions (IMFs) of the signals. Third, principal component analysis (PCA) is used to obtain the main component of the IMFs. Fourth, three different LSTM methods are chosen to compare and the best structure that is chosen is the gate recurrent unit (GRU). After that, the network parameters are optimized. The results under different noise environments are given. Then, a comparison between the EMD-GRU with several different machine learning methods is considered, and the result shows that the method in this paper has a better anti-noise effect. Therefore, the proposed method is demonstrated to have a strong ability of fault diagnosis and classification under the working noises based on the simulation results. Full article
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14 pages, 2612 KiB  
Article
Modelling of Parachute Airborne Clusters Flight Dynamics and Parachute Interactions
by Yanjun Li, Congyuan Qu, Jun Li and Li Yu
Aerospace 2023, 10(1), 51; https://doi.org/10.3390/aerospace10010051 - 4 Jan 2023
Viewed by 2087
Abstract
With the need for more condensed airborne clusters in a shortened time, there are increased risks of parachute collision and other interactions in the air. In this paper, the flight dynamics model of the parachute system is proposed for the whole deplaning airborne [...] Read more.
With the need for more condensed airborne clusters in a shortened time, there are increased risks of parachute collision and other interactions in the air. In this paper, the flight dynamics model of the parachute system is proposed for the whole deplaning airborne process, including parachute deployment, inflation, and the steady descent stages. The trajectories and velocities of the typical parachute airborne system are simulated, and the results are validated against the experimental measurement. To understand the potential interactions between parachutes, the flight dynamics of parachute airborne clusters, are then studied based on this model. The main parameters include the airborne altitudes, deplaning velocities, and airborne mass. The results show that the flight characteristics of parachutes are determined by the competence of the inertia effect and aerodynamic drags. The flight interactions of parachute clusters are most likely to occur at the moment of deployment, where the distance between parachutes is at a minimum. This critical distance increases with deplaning velocities and is insensitive to airborne altitudes. Adjusting the airborne order or using adaptive time periods by airborne mass can also avoid the potential interactions. The results of this paper can provide support for airborne strategies and help increase the safety and efficiency of airborne systems. Full article
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16 pages, 7572 KiB  
Article
Numerical Investigations of Precise Wind Field in Main Landing Area during the Landing Phase of “Shen Zhou” Series Spacecraft Mission
by Yilei Song, Guolin Ma, Linlin Tian, Ning Zhao and Xiyun Lu
Aerospace 2023, 10(1), 37; https://doi.org/10.3390/aerospace10010037 - 1 Jan 2023
Cited by 1 | Viewed by 1185
Abstract
Wind is one of the main factors raising errors in the spacecraft’s landing phase. As a result, an accurate description of incoming wind conditions is supposed to be a prerequisite for reliable parafoil trajectory planning. This work utilizes the Weather Research Forecast (WRF) [...] Read more.
Wind is one of the main factors raising errors in the spacecraft’s landing phase. As a result, an accurate description of incoming wind conditions is supposed to be a prerequisite for reliable parafoil trajectory planning. This work utilizes the Weather Research Forecast (WRF) model system with efficient parameterization schemes to reproduce the wind field in the main landing area during the landing phase of the “Shen Zhou” series spacecraft mission. In comparison with observational data from several cases, it is validated that the WRF model has the potential to give an accurate imitation of wind behaviors and is expected to be an alternative technique for costly and time-consuming experimental undertakings. Based on the numerical results, a linear model is proposed in the current work, which is applicable to the altitude range, specifically for parafoil trajectory planning. It is validated by comparisons with observational wind properties from radio-sounding stations. In addition, a sixth-order polynomial model is introduced for comparison as well. The results show that the current proposed model has both the characteristics of a simple form and good accuracy. It shows overall better consistency with observational data than the sixth-order polynomial model. Full article
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18 pages, 6478 KiB  
Article
Numerical Study on Parameters of the Airborne VLF Antenna by Quasi-Stationary Model
by Jiangfeng Cheng, Xueqiang Liu and Feng Deng
Aerospace 2023, 10(1), 29; https://doi.org/10.3390/aerospace10010029 - 29 Dec 2022
Cited by 1 | Viewed by 1593
Abstract
When a Very-Low-Frequency (VLF) antenna is towed in a circular flightpath at a constant altitude, the spatial configuration of the antenna can become relatively stationary with the orbiting aircraft. Accordingly, a quasi-stationary model of the towed antenna is established based on the force [...] Read more.
When a Very-Low-Frequency (VLF) antenna is towed in a circular flightpath at a constant altitude, the spatial configuration of the antenna can become relatively stationary with the orbiting aircraft. Accordingly, a quasi-stationary model of the towed antenna is established based on the force balance, which can efficiently solve a large number of parameter optimization problems. This work studies the influence law of all relevant parameters, including the physical properties of the drogue and the towline, the flight conditions, the wind profile, and the phase of the flight. The results show that the towline verticality and towing force are highly sensitive to the flight conditions, wind profile, and the phase of the flight; followed by sensitivity to the towline itself, and slight sensitivity to the drogue. The flight conditions of the aircraft can change the verticality of the towline from 15% to 80% or more. In addition, as the maximum monthly average wind speed exceeds 7 m/s, the antenna system in hover will oscillate seriously, resulting in a range of up to 50% variation in towline verticality between different positions. Full article
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16 pages, 9176 KiB  
Article
Experimental Study on the Effect of Porous Media on the Aerodynamic Performance of Airfoils
by Wenjie Kong, Hao Dong, Jie Wu, Yidi Zhao and Zhou Jin
Aerospace 2023, 10(1), 25; https://doi.org/10.3390/aerospace10010025 - 27 Dec 2022
Cited by 2 | Viewed by 2023
Abstract
Porous media has potential applications in fluid machinery and in aerospace science and engineering due to its excellent drag-reduction properties. We carried out experimental time-resolved particle image velocimetry (TR-PIV) research, laying porous media with different pore densities on the suction side of an [...] Read more.
Porous media has potential applications in fluid machinery and in aerospace science and engineering due to its excellent drag-reduction properties. We carried out experimental time-resolved particle image velocimetry (TR-PIV) research, laying porous media with different pore densities on the suction side of an airfoil in the low-turbulence recirculation wind tunnel of Nanjing University of Aeronautics and Astronautics to study the effects and mechanisms of porous media on airfoil aerodynamic performance. We also used a smooth airfoil model in the experiment for comparison. Comparing the aerodynamic forces, pressure distributions, and the airfoil’s suction side flow field, we found that the porous media with different pore densities had different effects on the airfoil’s aerodynamic performance. Although the porous media with 20PPI (pores per inch) increased the pressure drag and reduced the airfoil lift, it considerably reduced the friction drag, thus significantly improving the airfoil’s aerodynamic force. The flow visualization results indicated that, although the porous media with 20PPI reduced the circulation of flow velocity around the suction side of airfoil, it also destroyed the vortex structure, broke the low-frequency large-scale vortex into a high-frequency granular vortex, inhibited the amplitude of vortex fluctuation, reduced the shear stress on the airfoil surface, weakened the vortex energy of different modes, and accelerated the vortex’s spatio-temporal evolution. Full article
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12 pages, 16023 KiB  
Article
Experimental Study on Ice Accretion of Aviation Jet Fuel Tube
by Chengxiang Zhu, Jingxin Wang, Qingyong Bian, Chunyang Liu, Ning Zhao and Chunling Zhu
Aerospace 2023, 10(1), 22; https://doi.org/10.3390/aerospace10010022 - 26 Dec 2022
Viewed by 1467
Abstract
Ice accretion on the inner surface of a fuel tube can fall off and potentially block the filters and small orifices, which thereby restricts the fuel flow to the engines during the long flying of the aircraft in cold conditions. This might cause [...] Read more.
Ice accretion on the inner surface of a fuel tube can fall off and potentially block the filters and small orifices, which thereby restricts the fuel flow to the engines during the long flying of the aircraft in cold conditions. This might cause the engines to shut down and pose a catastrophic safety threat. In this pursuit, the present study evaluates the effects of fuel temperature, entrained water concentration, and duration on the accretion of ice in flowing super-saturated RP-3 aviation jet fuel. A methodology for the quantitative mixing of water mist with fuel for accurately controlling water concentration was proposed. The different kinds of accreted ice, ‘fluffy’ and ‘pebbly’, were observed. As the distance of flow increased, a non-uniform distribution of ice on the cross-sectional area was noted. The amount of ice accretion increased with a decrease in the temperature from −2 °C and −12 °C, and with an increase in entrained water concentration. Besides, the amount of ice accretion showed an increasing trend as time went on and became stable after 2 h. Our experimental results can assist to gain a better understanding of the ice accretion process in flowing super-saturated fuels and may serve as a basis for the design of the aircraft fuel system and airworthiness certification. Full article
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19 pages, 9774 KiB  
Article
Numerical Study on Tandem-Rotor Autorotation in Forward Flight
by Jiayu Wen, Yanguo Song, Huanjin Wang and Dong Han
Aerospace 2023, 10(1), 15; https://doi.org/10.3390/aerospace10010015 - 24 Dec 2022
Cited by 1 | Viewed by 1677
Abstract
This work presents a systematic approach to analyzing the aerodynamic characteristics of tandem rotor forward autorotation considering rotor-to-rotor interference. The single-rotor computational model trimmed from a generic helicopter flight dynamics analysis program was used as the baseline model. The effectiveness of the baseline [...] Read more.
This work presents a systematic approach to analyzing the aerodynamic characteristics of tandem rotor forward autorotation considering rotor-to-rotor interference. The single-rotor computational model trimmed from a generic helicopter flight dynamics analysis program was used as the baseline model. The effectiveness of the baseline model is demonstrated by a comparison with data from wind tunnel tests performed in this work. The rotor disk angle of attack and driven moment distribution obtained by the modified model indicate the fact that the rotor acceleration is primarily caused by the higher angle of attack region of the disk. This is of great significance in the rotor blade design, in terms of the drag-to-lift ratio characteristics of the airfoil under different angle-of-attack ranges. The influence of wind speed, rotor shaft angle, and collective pitch on the steady-state rotor speed was then studied. The results show a nonlinear nature of the variation of steady rotor speed with collective pitch, which can cause a thrust control reverse problem during flight operations. To reveal the flow field details of rotor-to-rotor interference, the flow field Navier–Stokes equations of tandem rotor autorotation were solved. Computational results of both rotors’ inflow velocities were considered when deriving the empirical model of interference. The refined interference model was compared to the wind tunnel test data of the tandem rotor autorotation and showed good performance. This synthetical methodology, which combines mechanism analysis with CFD-aided refinement and experiment verification, achieves a balance between computational costs and accuracy and thus can be readily applied to engineering practices. Full article
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11 pages, 5085 KiB  
Article
Thermal Protection Mechanism of a Novel Adjustable Non-Ablative Thermal Protection System for Hypersonic Vehicles
by Bin Chang, Jie Huang and Wei-Xing Yao
Aerospace 2023, 10(1), 1; https://doi.org/10.3390/aerospace10010001 - 20 Dec 2022
Cited by 2 | Viewed by 1795
Abstract
In order to improve the thermal protection performance of the active thermal protection system (TPS) based on the spike and jet, an adjustable non-ablative thermal protection system, of which the spike can be rotated in the direction of the free stream, is proposed [...] Read more.
In order to improve the thermal protection performance of the active thermal protection system (TPS) based on the spike and jet, an adjustable non-ablative thermal protection system, of which the spike can be rotated in the direction of the free stream, is proposed in this paper. The thermal protection mechanism and the optimal installation angle are analyzed by adopting the numerical method. The results show that the angle of attack has great influence on the peak heat flux of hypersonic vehicles, the dangerous point is on the windward side of the vehicles at the non-zero angle of attack. With the increase in angle of attack, the heat flux of the windward side of the vehicles rises rapidly, leading to the decrease in the global thermal protection efficiency. The adjustable non-ablative TPS in this paper greatly reduces the aeroheating of the windward side through the installation angle between the spike and nose cone, thus improving the global thermal protection efficiency. The optimal installation angle can be obtained by numerical or experimental methods in engineering design, and the difference between the angle of attack and the optimal installation angle is about 2.4° for the proposed model. Therefore, the installation angle can be automatically adjusted based on the angle of attack to achieve the highest thermal protection efficiency. Full article
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18 pages, 3115 KiB  
Article
Reverse Design of a Novel Coupling Strut for Vibration Attenuation in the Helicopter Cabin
by Ming Ding, Jinhui Jiang, Fang Zhang, Xiao Liang and Nansun Shen
Aerospace 2022, 9(12), 843; https://doi.org/10.3390/aerospace9120843 - 18 Dec 2022
Viewed by 1303
Abstract
Helicopter gearbox support strut is one of the main research objects in the field of vibration and noise control in helicopter cabins. Aiming to further widen the vibration attenuation range of traditional Bragg periodic struts, a novel type of Local resonance (LR)/Bragg coupling [...] Read more.
Helicopter gearbox support strut is one of the main research objects in the field of vibration and noise control in helicopter cabins. Aiming to further widen the vibration attenuation range of traditional Bragg periodic struts, a novel type of Local resonance (LR)/Bragg coupling periodic strut with graded parameters as well as the reverse design method is proposed. Combined with the spectral element method (SEM) and the transfer matrix method (TMM), the analytical expression of the transform relationship of longitudinal vibrations through the coupling strut is yielded. The impacts of different parameters on the boundaries of bandgaps are explored according to the results of simulation analysis. On this basis, the gradient of parameters is determined, and then all unknown structural parameters can also be determined. Compared with the traditional Bragg periodic struts and the LR/Bragg coupling periodic strut with non-graded parameters, the presented strut has an obvious advantage of widening the low-frequency bandgaps below 500 Hz. Full article
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17 pages, 6510 KiB  
Article
Study on the Leading Edge of a Hypersonic Vehicle Using the Aero-Thermoelastic Coupling Method
by Long Chen and Jian Xia
Aerospace 2022, 9(12), 835; https://doi.org/10.3390/aerospace9120835 - 15 Dec 2022
Cited by 1 | Viewed by 1591
Abstract
The characteristics of aero-thermoelastic coupling are important for the design of the leading edge in hypersonic vehicles. Herein, a fluid–structure interaction analysis is performed to study the leading edge of a hypersonic vehicle using aero-thermoelastic coupling methods. The results show that the maximum [...] Read more.
The characteristics of aero-thermoelastic coupling are important for the design of the leading edge in hypersonic vehicles. Herein, a fluid–structure interaction analysis is performed to study the leading edge of a hypersonic vehicle using aero-thermoelastic coupling methods. The results show that the maximum heat flux and temperature of the optimized Bézier curve leading edge are reduced to a certain extent, compared with a hemi-cylindrical leading edge, and the lift–to–drag ratios of the two models are close. The Bézier curve leading-edge model can reduce the blunt radius of the leading edge of the hypersonic vehicle and increase the aerodynamic performance without losing thermal performance. Full article
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12 pages, 3698 KiB  
Article
Experimental and Numerical Study on the Influence of Rubbing Force on Radial Crack Initiation in Labyrinth Seal Fins
by Yicheng Yang, Jiaqi Chang, Zhaoguo Mi and Weihua Yang
Aerospace 2022, 9(12), 831; https://doi.org/10.3390/aerospace9120831 - 15 Dec 2022
Cited by 1 | Viewed by 1466
Abstract
Radial cracks appear in the labyrinth seal fins of the shrouded turbine blade of an aero-engine during service. To clarify the influence rule of rubbing force on crack initiation, a high-speed rubbing test bench and a numerical calculation model are established, and the [...] Read more.
Radial cracks appear in the labyrinth seal fins of the shrouded turbine blade of an aero-engine during service. To clarify the influence rule of rubbing force on crack initiation, a high-speed rubbing test bench and a numerical calculation model are established, and the research is carried out through experiment and numerical calculation. It is found that cracks can be initiated when the rubbing force is greater than 20 N with a high rubbing temperature at high speed. It is verified by numerical calculation and shows that pure mechanical load will not cause crack initiation, while the thermal load is the main reason for the radial crack initiation of fins. With the increase of rubbing force, the time of crack initiation increases, and the number and length of cracks decrease. At high rubbing temperatures, rubbing force will lead to radial crack initiation, which mainly affects the position of crack initiation. Full article
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20 pages, 8723 KiB  
Article
Image Quality Enhancement with Applications to Unmanned Aerial Vehicle Obstacle Detection
by Zhaoyang Wang, Dan Zhao and Yunfeng Cao
Aerospace 2022, 9(12), 829; https://doi.org/10.3390/aerospace9120829 - 15 Dec 2022
Viewed by 1418
Abstract
Aiming at the problem that obstacle avoidance of unmanned aerial vehicles (UAVs) cannot effectively detect obstacles under low illumination, this research proposes an enhancement algorithm for low-light airborne images, which is based on the camera response model and Retinex theory. Firstly, the mathematical [...] Read more.
Aiming at the problem that obstacle avoidance of unmanned aerial vehicles (UAVs) cannot effectively detect obstacles under low illumination, this research proposes an enhancement algorithm for low-light airborne images, which is based on the camera response model and Retinex theory. Firstly, the mathematical model of low-illumination image enhancement is established, and the relationship between the camera response function (CRF) and brightness transfer function (BTF) is constructed by a common parameter equation. Secondly, to solve the problem that the enhancement algorithm using the camera response model will lead to blurred image details, Retinex theory is introduced into the camera response model to design an enhancement algorithm framework suitable for UAV obstacle avoidance. Thirdly, to shorten the time consumption of the algorithm, an acceleration solver is adopted to calculate the illumination map, and the exposure matrix is further calculated via the illumination map. Additionally, the maximum exposure value is set for low signal-to-noise ratio (SNR) pixels to suppress noise. Finally, a camera response model and exposure matrix are used to adjust the low-light image to obtain an enhanced image. The enhancement experiment for the constructed dataset shows that the proposed algorithm can significantly enhance the brightness of low-illumination images, and is superior to other similar available algorithms in quantitative evaluation metrics. Compared with the illumination enhancement algorithm based on infrared and visible image fusion, the proposed algorithm can achieve illumination enhancement without introducing additional airborne sensors. The obstacle object detection experiment shows that the proposed algorithm can increase the AP (average precision) value by 0.556. Full article
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14 pages, 6291 KiB  
Article
Nonlinear Tunability of Elastic Waves in One-Dimensional Mass-Spring Lattices Attached with Local Resonators
by Nansun Shen, Jinhui Jiang, Fang Zhang and Ming Ding
Aerospace 2022, 9(12), 818; https://doi.org/10.3390/aerospace9120818 - 12 Dec 2022
Cited by 1 | Viewed by 1185
Abstract
Vibration propagates in the form of elastic waves. The tuning of elastic waves is of great significance for vibration and noise reduction. The elastic metamaterials (EMs), which can effectively prohibit elastic wave propagation in the band gap frequency range, have been widely studied. [...] Read more.
Vibration propagates in the form of elastic waves. The tuning of elastic waves is of great significance for vibration and noise reduction. The elastic metamaterials (EMs), which can effectively prohibit elastic wave propagation in the band gap frequency range, have been widely studied. However, once the structures of the EMs are determined, the band gap is also determined. In this paper, a discrete nonlinear elastic metamaterial is proposed. The harmonic balance method is used to derive the nonlinear dispersion relation combined with Bloch’s theorem. The low frequency band gap near the linear natural frequency of local resonators is obtained. The theoretical results show that the nonlinearity will change the starting and ending frequencies of the band gap. In addition, amplitude can also influence the band gap. This means that the amplitude can be changed to achieve the tunability of elastic waves in nonlinear elastic metamaterials. Finally, the theoretical results are verified by numerical simulation, and the results are in good agreement with each other. Full article
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17 pages, 6851 KiB  
Article
Stealthy Configuration Optimization Design and RCS Characteristics Study of Microsatellite
by Hanqing Sun and Yuantian Qin
Aerospace 2022, 9(12), 815; https://doi.org/10.3390/aerospace9120815 - 12 Dec 2022
Cited by 1 | Viewed by 1567
Abstract
Firstly, the radar cross section (RCS) test results of the stealthy microsatellite of TianXun-1(TX-1) in the anechoic chamber are compared with the RCS numerically simulated by the physical optics method, and the accuracy of the physical optical method is verified. On this basis, [...] Read more.
Firstly, the radar cross section (RCS) test results of the stealthy microsatellite of TianXun-1(TX-1) in the anechoic chamber are compared with the RCS numerically simulated by the physical optics method, and the accuracy of the physical optical method is verified. On this basis, in order to improve the radar stealth performance of the microsatellite, a satellite stealth configuration optimization design method is proposed with the multi-prismatic stealth configuration of TX-1 as the initial configuration, and two olive stealth satellite configurations are obtained. By comparing the RCS simulation and radar detection probability of the optimized Olive-A and Olive-B satellite stealth configurations in multiple directions, it is demonstrated that the stealth performance of the Olive-B configuration is better. Finally, the anechoic chamber test is conducted on the metallic Olive-B model, and the test results show that the test results and simulation results of Olive-B are in good agreement, which again verifies that the stealth performance of Olive-B is better than that of TX-1 and Olive-A. Full article
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13 pages, 6672 KiB  
Article
Reynolds Number Effect on Aerodynamic and Starting Characteristics of a Two-Dimensional Hypersonic Inlet
by Jun Liu, Jingzhe Chen and Huacheng Yuan
Aerospace 2022, 9(12), 811; https://doi.org/10.3390/aerospace9120811 - 9 Dec 2022
Cited by 4 | Viewed by 1145
Abstract
The Reynolds number effect induced by model scaling and inflow conditions will affect the aerodynamic and starting characteristics of a two-dimensional hypersonic inlet. This effect is investigated through a numerical simulation method. First, the numerical simulation method is validated through experimental data. The [...] Read more.
The Reynolds number effect induced by model scaling and inflow conditions will affect the aerodynamic and starting characteristics of a two-dimensional hypersonic inlet. This effect is investigated through a numerical simulation method. First, the numerical simulation method is validated through experimental data. The static pressure from the numerical simulation method agreed well with wind tunnel tests. Then, this simulation method is used to study the Reynolds number effect on a two-dimensional hypersonic inlet caused by the model scaling and inflow conditions. The numerical simulation results indicate that as the Reynolds number decreases from 4.86 × 106 to 9.71 × 104 with model scaling increases from 1 to 1/50, the relative boundary layer thickness at the entrance of the inlet increases from 10.4% to 21.2%; as the flight altitude increases from 25.5 km to 36.5 km, which causes the Reynolds number to decrease from 5.67 × 106 to 1.07 × 106, the relative boundary layer thickness at the entrance of the inlet increases from 9.8% to 13.2%. Finally, the Reynolds number effect on the aerodynamics and starting characteristics caused by these two different factors are compared. The results show that the effect of scaling the model is similar to the effect of changing the altitude. As the relative boundary layer thickness increased by 1.0%, the total pressure recovery at the throat section decreased by 0.8%, and the inlet starting Mach number increased by 0.1. Full article
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15 pages, 5616 KiB  
Article
Study of Brake Disc Friction Characteristics Effect on Low Frequency Brake Induced Vibration of Aircraft Landing Gear
by Songyang Zhang, Qiaozhi Yin, Xiaohui Wei, Jiayi Song and Hong Nie
Aerospace 2022, 9(12), 809; https://doi.org/10.3390/aerospace9120809 - 9 Dec 2022
Cited by 2 | Viewed by 1837
Abstract
During aircraft braking, the change of ground adhesion forces can cause forward and backward vibration of the landing gear, and the performance of the brake disc may exacerbate this vibration. In order to solve this problem, a rigid–flexible coupling dynamic model of a [...] Read more.
During aircraft braking, the change of ground adhesion forces can cause forward and backward vibration of the landing gear, and the performance of the brake disc may exacerbate this vibration. In order to solve this problem, a rigid–flexible coupling dynamic model of a two-wheel strut landing gear considering the friction characters of brake discs with different materials and a hydraulic brake system model is established in this paper. The brake disc friction characteristics effect on the low-frequency brake-induced vibration of the landing gear given different brake disc materials and ambient temperatures is studied. It is shown that the C/SiC brake disc has a “negative slope” phenomenon between the friction coefficient of the brake disc and the wheel speed, and this variable friction characteristic has a great effect on the low-frequency braking-induced vibration of the landing gear. In addition, the variable friction characteristics of the C/SiC brake disc are easily affected by ambient temperature, while the friction coefficient of the C/C brake disc changes stably. Full article
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19 pages, 10006 KiB  
Article
A Numerical Study on the Water Entry of Cylindrical Trans-Media Vehicles
by Feng Deng, Xiaoyuan Sun, Fenghua Chi and Ruixue Ji
Aerospace 2022, 9(12), 805; https://doi.org/10.3390/aerospace9120805 - 8 Dec 2022
Viewed by 1463
Abstract
In recent years, more attention has been paid to vehicles that can travel between air and water, known as trans-media vehicles. They are often designed as cylindrical bodies in order to reduce the impact load during water entry. In this paper, the water-entry [...] Read more.
In recent years, more attention has been paid to vehicles that can travel between air and water, known as trans-media vehicles. They are often designed as cylindrical bodies in order to reduce the impact load during water entry. In this paper, the water-entry processes of small-sized cylindrical trans-media vehicles, with a characteristic length of 1 m, were investigated numerically by solving the unsteady Reynolds-averaged Navier–Stokes equations using the volume-of-fluid method, the dynamic grid method and the six degrees of freedom solver. The numerical methods were first validated by comparing the numerical results with the existing experimental data. Then, the effects of the body mass, the diameter-to-length ratio, the water-entry angle and the head shape on the water-entry process were investigated. The results show that the peak impact load, measured by the peak force exerted by water on the body, can be significantly reduced by decreasing the body mass, decreasing the diameter, entering the water at an optimum water-entry angle or installing an ellipsoidal head. In particular, the peak impact load was found to be approximately proportional to the square of the body mass or the cube of the cylinder diameter. Furthermore, installing an ellipsoidal head can reduce about 94% of the peak impact load experienced by a cylindrical body. Full article
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15 pages, 2649 KiB  
Article
Whirl Flutter Suppression of Tiltrotor Aircraft Using Actively Controlled Aileron
by Linghua Dong and Qiyu Li
Aerospace 2022, 9(12), 795; https://doi.org/10.3390/aerospace9120795 - 4 Dec 2022
Cited by 1 | Viewed by 1718
Abstract
Whirl flutter of a tiltrotor aircraft is a complex aeroelastic phenomenon and it can result in catastrophic consequences. The deflection of an aileron mounted on a wing has the potential to solve this fatal problem. Whirl flutter suppression using an actively controlled aileron [...] Read more.
Whirl flutter of a tiltrotor aircraft is a complex aeroelastic phenomenon and it can result in catastrophic consequences. The deflection of an aileron mounted on a wing has the potential to solve this fatal problem. Whirl flutter suppression using an actively controlled aileron is studied in this study. Firstly, a semi-span aeroelastic model is established for the whirl flutter problem using the Hamilton principle. This model is composed of three parts: a rigid rotor, a rigid nacelle and a flexible wing, and the effect of the aileron deflection on the aeroelastic responses is also taken into consideration through a quasi-steady aerodynamic model. In addition, the accuracy of this aeroelastic model is validated with the results of two different wind-tunnel tests. Then, an LQR controller is developed to control the dynamic deflection of the aileron, and a full-dimensional state observer is built to estimate the state of the time-invariant system of a tiltrotor aircraft. Finally, simulations are carried out using the aeroelastic model and the LQR controller at different flight conditions to study the influence of the aileron deflection on whirl flutter. The simulation results demonstrate that the flutter boundary speed can be improved by 18.1% with the active deflection of the aileron, compared with the uncontrolled condition. Full article
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19 pages, 6083 KiB  
Article
Mesh Adaptation for Simulating Lateral Jet Interaction Flow
by Shuling Tian and Zongzi Peng
Aerospace 2022, 9(12), 781; https://doi.org/10.3390/aerospace9120781 - 1 Dec 2022
Cited by 1 | Viewed by 1398
Abstract
Under the condition of supersonic incoming flow, a missile lateral jet flow field has complex flow structures, such as a strong shock wave, an unsteady vortex and flow separation. In order to improve ability to capture complex flow structures in numerical simulation of [...] Read more.
Under the condition of supersonic incoming flow, a missile lateral jet flow field has complex flow structures, such as a strong shock wave, an unsteady vortex and flow separation. In order to improve ability to capture complex flow structures in numerical simulation of lateral jets, this paper proposes a combined-grid adaptive method. When combined with finite volume approximation of second-order and h-type adaptive technology, our method was verified by numerical experiments, which shows that wave structure and vortex structure in the jet flow field can be effectively captured at the same time. In comparison of uniformly refined mesh results, it was found that accuracy of computed results and resolution of characteristic flow structures were significantly improved after mesh adaptation. In comparison of the pressure coefficient, it was found that the error between the adaptive mesh and the uniformly refined mesh was smaller, and the maximum errors of the base grid, adaptive grid and uniformly refined grid were 92.1% and 12.3%. Full article
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14 pages, 3334 KiB  
Article
Research on Landing Stability of Four-Legged Adaptive Landing Gear for Multirotor UAVs
by Xinlei Ni, Qiaozhi Yin, Xiaohui Wei, Peilin Zhong and Hong Nie
Aerospace 2022, 9(12), 776; https://doi.org/10.3390/aerospace9120776 - 30 Nov 2022
Cited by 3 | Viewed by 2194
Abstract
Rotorcraft Unmanned Aerial Vehicles (UAVs) often need to take off and land under complex working conditions. The rugged terrains may cause the UAV to tilt during takeoff and landing and even cause rollover and other accidents in severe cases. In this paper, a [...] Read more.
Rotorcraft Unmanned Aerial Vehicles (UAVs) often need to take off and land under complex working conditions. The rugged terrains may cause the UAV to tilt during takeoff and landing and even cause rollover and other accidents in severe cases. In this paper, a new four-legged landing gear of multirotor UAVs with a passive cushioning structure is designed, aiming at the landing stability requirement of rotorcraft UAVs in complex terrains. The mathematical model of the landing gear dynamics is established in MATLAB/Simulink, and the drop test simulation is carried out under different landing terrain conditions. By comparing the simulation results of the drop test multibody dynamic model in Simcenter3D dynamics software, the adaptive landing and cushioning capacity of the landing gear and the accuracy of the mathematical model are verified. Combined with the landing stability criterion and control strategy of adaptive landing gear adjustment, the landing stability of adaptive landing gear under different slope angles of landing surface and horizontal velocities is studied. The landing stability boundary under different combinations of these two parameters is found. Full article
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13 pages, 5818 KiB  
Article
Numerical Research on the NS-SDBD Control of a Hypersonic Inlet in Off-Design Mode
by Yilun Yan and Jiangfeng Wang
Aerospace 2022, 9(12), 773; https://doi.org/10.3390/aerospace9120773 - 30 Nov 2022
Cited by 1 | Viewed by 1278
Abstract
The overall performance of a scramjet inlet will decline while entering off-design mode. Active flow control using nanosecond surface dielectric barrier discharge (NS-SDBD) can be a novel solution to such inlet–unstart problems. NS-SDBD actuators are deployed on the surface of the internal compression [...] Read more.
The overall performance of a scramjet inlet will decline while entering off-design mode. Active flow control using nanosecond surface dielectric barrier discharge (NS-SDBD) can be a novel solution to such inlet–unstart problems. NS-SDBD actuators are deployed on the surface of the internal compression section, controlling the shock waves and the separation area. Numerical simulations of hypersonic flows are carried out using the compressible Reynolds average Navier–Stokes equation (RANS), along with the plasma phenomenological model which is added in as the energy source term. Flow structures and the evolution of performance parameters are analyzed. Results show that NS-SDBD actuators are able to increase the static pressure behind the cowl shock, boosting the downstream total pressure. The compression effect becomes stronger while raising the frequency or shortening the spacing between the actuators. Under the inlet–unstart conditions, the compression wave generated by the actuator pushes the reattachment point forward, making the separation bubble longer in length and shorter in height, which reduces the strength of the separation shock. The results provide a numerical basis for the state control of a hypersonic inlet. Full article
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20 pages, 7487 KiB  
Article
Quantitative Measurement Method for Ice Roughness on an Aircraft Surface
by Yuan Wang, Yang Zhang, Yan Wang, Dongyu Zhu, Ning Zhao and Chunling Zhu
Aerospace 2022, 9(12), 739; https://doi.org/10.3390/aerospace9120739 - 22 Nov 2022
Cited by 5 | Viewed by 1764
Abstract
When an aircraft passes through clouds containing supercooled water droplets, the leading edge’s surface will gradually accumulate ice. Ice surface roughness is an important parameter affecting the local convective heat transfer coefficient and the water collection coefficient, which in turn affect the ice’s [...] Read more.
When an aircraft passes through clouds containing supercooled water droplets, the leading edge’s surface will gradually accumulate ice. Ice surface roughness is an important parameter affecting the local convective heat transfer coefficient and the water collection coefficient, which in turn affect the ice’s shape. However, because the surface roughness of aircraft icing is a transient value varying in time and space, it is extremely difficult to measure with existing methods in real time. In this study, a noncontact ultrasonic pulse-echo (UPE) technique is applied to characterize the ice roughness of an airfoil model’s surface. A multilayer model with equivalent bead-like roughness profiles is established to study the effects of changes in ice roughness on ultrasonic echo signals. A series of simulations indicated that ice roughness can be measured quantitatively and effectively in the range of [11.6, 120] μm. Based on these simulations, an experimental UPE device was developed to measure echo signals on top of the ice corresponding to surface roughness. The results show that for both the regular and irregular surface roughness samples, the maximum relative error in the roughness is less than 15%. Meanwhile, we designed and supplemented the experiment with the NACA-0012 airfoil model to realize the online measurement of ice roughness in an icing research tunnel. Full article
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