Special Issue / Special Column

Review of low-frequency unsteadiness in shock wave/turbulent boundary layer i...

FAN Xiaohua, TANG Zhigong, WANG Gang, YANG Yanguang

doi:10.7527/S1000-6893.2021.25917

2022, (1): 625917-625917.

Abstract

Shock wave/Turbulent Boundary Layer Interaction(STBLI) is ubiquitous in internal and external of supersonic and hypersonic flow. The physical mechanism of low-frequency unsteadiness, which is found in shock-induced separation and appears as low-frequency shock motion accompanied with the expansion and contraction of the separation bubble, has been disputed. This research field has been widely concerned and studied. The driving mechanism of low-frequency unsteadiness could be generally divided into three categories. Some researchers believed that the source of the low-frequency unsteadiness originated in the upstream boundary layer. On the contrary some scholars held the opinion that the low-frequency dynamics was dominated by intrinsic nature of downstream separation flow. However, some recent researches trended to reconcile these two opposite views, believing that the upstream and downstream mechanisms co-existed with a weighting function depending on the state of the STBLI. The coupl...

Flow control technique for shock wave/turbulent boundary layer interactions

SHI Xiaotian, LYU Meng, ZHAO Yuan, TAO Shancong, HAO Le, YUAN Xiangjiang

doi:10.7527/S1000-6893.2021.25929

2022, (1): 625929-625929.

Abstract

Shock wave/Turbulent Boundary Layer Interaction(STBLI) is ubiquitous presence in aircraft engineering. Occurring in the case from transonic to hypersonic, the complex linear and nonlinear mechanisms in the STBLI such as the flow separation, peak heating and low frequency pressure fluctuating can heavily affect the vehicle, inlet and component geometry, structural integrity, material selection, fatigue life and the design of thermal protection systems. Therefore, the flow control is considered as a key issue to adjust the flow field of STBLI. To deepen the understanding of STBLI and its flow control, the present paper conducted a comprehensive review on the important knowledge, mostly the flow control techniques such as vortex generator, plasma and magnetohydrodynamics for STBLI to improve the flow control design and troubleshooting of STBLI in engineering, especially in the case of hypersonic.

Experimental study on unsteadiness characteristics of shock wave/turbulent bo...

WANG Hongyu, YANG Yanguang, HU Weibo, CHEN Zhi, FENG Liming, ZHOU Youtian

doi:10.7527/S1000-6893.2021.25905

2022, (1): 625905-625905.

Abstract

Wind tunnel experiments are carried out to control a ramp induced shock wave/turbulent boundary layer interaction with high-frequency microsecond pulse discharge in a Mach 2.5 supersonic flow. The discharge is generated between 6 pairs of electrodes arranged in the streamwise direction upstream of the ramp, and the discharge frequency f=14 kHz is adopted, which is close to the characteristic frequency of the incoming boundary layer. High-speed schlieren imaging technology is used to record the dynamic flows. The recorded schlieren images are statistically processed by average, root-mean-square, proper orthogonal decomposition, dynamic mode decomposition, and Fourier transform methods based on their spatial gray values, and the unsteady characteristics of the shock wave/turbulent boundary layer interaction with and without control are compared and studied. The results show that for the baseline flow without control, the low-frequency characteristics are shown as the oscillation of the s...

An extension of hybrid kinetic WENO method

HE Kang, LI Xinliang, LIU Hongwei

doi:10.7527/S1000-6893.2021.25909

2022, (1): 625909-625909.

Abstract

An extension of the high-order WENO methods based on the gas-kinetic theory is carried out. The hybrid kinetic WENO method proposed inInt.J.Numer.Meth. Fluids79(6),290-305(2015) is further extended to the 7th-order and the 9th-order cases. Within the framework of the 5th-order hybrid kinetic WENO method, the computational accuracy and efficiency of different shock detection techniques are compared. The TVD Runge-Kutta method is used for temporal integration, and the hybrid kinetic WENO method is employed for spatial discretization. Both one-dimensional and two-dimensional numerical examples are presented to show that the extended hybrid kinetic methods have higher resolution and less numerical dissipation than the traditional flux vector splitting technique, and can also have good shock-capturing ability. It is also found that the shock detection technology proposed by Ohwada et al. has good shock-detection ability and computational efficiency.

Decomposition of mean friction drag in compression-expansion turbulent bounda...

DUAN Junyi, TONG Fulin, LI Xinliang, LIU Hongwei

doi:10.7527/S1000-6893.2021.25915

2022, (1): 625915-625915.

Abstract

The interaction between the shock wave with Mach number 2.9 and the turbulent boundary layer in the configuration of 24° compression-expansion corners is investigated by using direct numerical simulation. The influence of normal height of the expansion corner on the shock wave interaction region and downstream boundary layer is analyzed. It is found that when the height is large enough, the shock wave interaction region is not affected by the downstream expansion wave, and the characteristics are consistent with those of the traditional compression corner configuration. While the height is small, the reattachment process of the detached shear layer is accelerated by the downstream expansion wave, which causes the reattachment point to move upstream and the separation bubble to shrink dramatically. The decomposition of mean friction drag is applied to the turbulent boundary layer of the upstream and downstream plates, and the difference between the turbulent boundary layer in equilibriu...

Influence of spanwise width on reflection types of oblique shock wave inciden...

ZHANG Zhigang, ZHAO Jinshan, WANG Chengpeng, LUO Wanqing, LIAO Junhao, XIAO Yu, CHEN Ting, SU Siyao

doi:10.7527/S1000-6893.2021.25927

2022, (1): 625927-625927.

Abstract

Shock wave interference is a local interference phenomenon that needs to be considered in the pneumatic layout of hypersonic vehicle and the design of scramjet. When this phenomenon occurs, complex wave structures will be generated to affect the behavior characteristics of the flow field and then significantly affect the planeload and engine performance. Numerical simulation is used to study the problem of incident shock wave of a plate. Under the condition of constant Mach number 5 and unit Reynolds number 7.12×106m-1, the types of shock reflection in six different states are studied by changing the transverse width of the upper and lower plates. The results show that the influence of lateral overflow on the reflection types of shock wave must be considered in the restricted space. With the broadening of the transverse width of the plate, the shock reflection type gradually changes from regular reflection to Mach reflection, and the length of Mach stem becomes longer and moves forward...

Statistical characteristics of skin friction of shock wave/turbulent boundary...

SHEN Pengfei, LIU Pengxin, SUN Dong, YUAN Xianxu

doi:10.7527/S1000-6893.2021.26005

2022, (1): 626005-626005.

Abstract

To examine the statistical characteristics of skin friction of shock wave/turbulent boundary layer interaction, the direct numerical simulation method was used to obtain the exact flow field of the shock wave/turbulent boundary layer in a hollow cylinder-flare configuration at Mach 6. The decomposition formula of averaged skin friction was derived and studied together with the convection item, streamwise inhomogeneity item, molecular viscous item, curvature effect item, and turbulent kinetic energy dissipation item. The statistical characteristics of fluctuating skin friction and averaged skin friction were explored. Probability density functionresults indicate that the fluctuating skin friction deviates from the normal distribution in the interaction region with distinct intermittency. Power Spectrum Density results show that energy of skin friction plays the main role in middle frequency zone whose peal location is 0.14 before interaction while it does in higher frequency zone after ...

Structure of shock-induced separation in confined flow

XIE Zhuxuan, YANG Yanguang, WANG Gang

doi:10.7527/S1000-6893.2021.26042

2022, (1): 626042-626042.

Abstract

To study the flow separation caused by the shock wave/boundary layer interaction in the inner flow channel, RANS method is used to calculate the flow in a rectangular channel with a 20° wedge angle of different widths and heights under Mach 6 inflow. Studies on the separation structure of the inner flow channel are carried outby focusing on the structural characteristics of the separation in the center region of the bottom wall, comparing the flow structures under different geometric parameters, and summarizing the variation rules as well as discussing the influence mechanism of each parameter. The results show that the separation induced by shock wave in the inner channel has a complex three-dimensional structure; the vortex structure in the center separation zone of the bottom wall is "Ω"-shaped; the mass exchange with the separation near the side wall occurs through the cyclone vortex of "Ω" vortex. Under the condition of given inflow state parameters, the separation structure of ...

Experiment on interaction between supersonic turbulent boundary layer and cyl...

GANG Dundian, YI Shihe, MI Qi, NIU Haibo

doi:10.7527/S1000-6893.2021.26104

2022, (1): 626104-626104.

Abstract

The flow field of interactions between the turbulent boundary layer and cylinders was studied in a supersonic wind tunnel with the Mach numbers 3.4 and 3.8 respectively. The cylinder was mounted on the floor of the test section, and the boundary layer was fully developed at the installation position. Besides, the influence of the diameter and height of the cylinders on the flow field structure and pressure fluctuations was studied, and the fine structures of the flow field in the streamwise and the spanwise plane were obtained using Nano-tracer Planar Laser Scattering(NPLS) technique. The shock system and the horseshoe vortex structure could be clearly distinguished. It could be found that the interactions between the shock wave and the turbulence structures presented unsteady characteristics through images of the spanwise plane. The dynamic pressure transducers were used to measure the pressure pulsation characteristics of the interaction region in front of the cylinder. In the shock ...

Time evolution process of high resolution shock wave/turbulent boundary layer...

LU Xiaoge, YI Shihe, HE Lin, QUAN Pengcheng, GANG Dundian

doi:10.7527/S1000-6893.2021.26147

2022, (1): 626147-626147.

Abstract

In this paper, a test system based on the Nano-tracer Planar Laser Scattering(NPLS) technique for studying time evolution of unsteady flow structures is developed to solve the problems of stability and beam combination after parallel connection of multiple monopulse lasers, the overall design and layout of array CCD cameras, and the synchronous and accurate control of the test system. Based on this system, the experimental study on the interactions between the incident shock wave ofθ=20° shock generator and the turbulent boundary layer of the incoming wall was performed. The experiments are performed in a Mach number 3.4 supersonic low-noise wind tunnel at the unit Reynolds number of 6.30×106/m. For the first time, eight frames of temporal-correlated fine structure images of transient flow field with shock wave/turbulent boundary layer interaction are obtained under the experimental conditions, and the spatio-temporal evolution characteristics of the flow structure are analyzed.

Technical development of variable camber wing: Review

WANG Binwen, YANG Yu, QIAN Zhansen, WANG Zhigang, LYU Shuaishuai, SUN Xiasheng

doi:10.7527/S1000-6893.2020.24943

2022, (1): 24943-024943.

Abstract

The Variable Camber Wing(VCW) remains a research hot-spot as it aims to ensure that aircraft acquire optimal aerodynamic efficiency in various flight conditions. The benefits brought by VCWs are firstly presented, and the demands of VCWs from different types of aircraft are classified and thoroughly described. The developing process of VCWs in the past decades are then reviewed in terms of the leading edge and the trailing edge, respectively, and the current major obstacles in application are listed. Further research directions are finally suggested.

Review on chatter stability in robotic machining for large complex components

LIAO Wenhe, ZHENG Kan, SUN Lianjun, DONG Song, ZHANG Lei

doi:10.7527/S1000-6893.2021.26061

2022, (1): 26061-026061.

Abstract

Industry robots are widely applied to the manufacturing and assembly of large complex components. Its machining stability is the prerequisite and basis for accomplishing the high-precision, high-efficiency and high-quality production. Chatter suppression is an important way to realize the stable processing of robots. Unlike the single chatter type in CNC machine tools, robotic machining instability involves regenerative chatter and mode couple chatter mainly. As a result, the combined effect of the two increases the complexity of chatter stability analysis greatly. Currently, scholars at home and abroad have carried out theoretical and experimental research on robotic processing chatter formation mechanism, chatter prediction and control, and have achieved many results. However, it is still in its infancy. For example, the chatter mechanism is not clear, the analysis methods of stability are not comprehensive enough and engineering applications are not yet popular. Apart from this, the...

Development and applications of airport avian radar: Review

CHEN Weishi, HUANG Yifeng, CHEN Xiaolong, LU Xianfeng, ZHANG Jie

doi:10.7527/S1000-6893.2020.24758

2022, (1): 24758-024758.

Abstract

Avian radar has become an important bird situation observation tool in airport bird strike avoidance. The origin of avian radar technology is first introduced, followed by analysis of the target characteristics of flying birds in terms of the target echo amplitude, flight speed, flight height, trajectory characteristics and micro-Doppler characteristics. Four typical airport avian radar systems, including Merlin radar, Accipiter radar, Robin radar and Aveillant radar, and the research status of the domestic avian radar technology are then introduced. Key radar technologies such as antenna, radar waveform, target detection and tracking, target recognition and classification are analyzed, and the performance of typical avian radar systems compared. In addition, the applications of avian radar are discussed with respect to the fusion of radar and photoelectric technologies, the linkage of bird detection and repellent, and the bird information analysis. Conclusions are finally drawn and pr...

Survey on multi-task learning for object classification and recognition

LI Hongguang, WANG Fei, DING Wenrui

doi:10.7527/S1000-6893.2021.24889

2022, (1): 24889-024889.

Abstract

Multi-Task Learning(MTL) aims to enhance the model performance by jointly leveraging supervisory signals and sharing useful information among multiple related tasks. This paper comprehensively summarizes and analyzes the mechanism and mainstream methods of multi-task learning for object classification and recognition applications. First, we review the definitions, principles and methods of MTL. Second, taking the representative and widely used fine-grained classification and object re-identification as examples, we emphatically introduce two types of multi-task learning for object classification and recognition: task-based multi-task learning and feature-based multi-task learning, and further categorize each type and analyze the design ideas, and advantages and disadvantages of different MTL algorithms. Third, we compare the performance of various MTL algorithms reviewed in this paper on common datasets. Finally, prospects on development trends of MTL algorithms for object classificati...

Aircraft tire hydroplaning behavior based on real texture of surface runway m...

YANG Yang, ZHU Xingyi, ZHAO Hongduo

doi:10.7527/S1000-6893.2020.24813

2022, (1): 124813-124813.

Abstract

Aircraft landing safety under wet conditions has been the focus of research in the field of aviation safety. Based on the main wheel of Airbus A320 aircraft, a aircraft tire model with different tread pattern characteristics and the refined tread pattern model were developed. Using optical scanning and 3D reconstruction, a runway surface model with gradation of SMA-13 asphalt mixture was constructed. Combined with Heinrich contact algorithm between rubber and rough runway surface was obtained, and the contact model between tread rubber and runway surface was developed. The Coupled-Eulerian-Lagrange (CEL) algorithm was used to solve the fluid-solid interaction between water film and runway surface and aircraft tire. Based on the proposed finite element model, the influence of aircraft landing speed, water film thickness, tire load, tread pattern and tire pressure on the hydroplaning was analyzed by the contact force between the runway surface and the tire and the hydroplaning speed.

Effects of ignition on initiation characteristics of hollow rotating detonati...

ZHAO Minghao, WANG Ke, WANG Zhicheng, ZHU Yiyuan, YU Xiaodong, FAN Wei

doi:10.7527/S1000-6893.2020.24870

2022, (1): 124870-124870.

Abstract

To investigate the initiation process and operating characteristics of rotating detonation waves in the hollow combustor, the initiation and propagation of rotating detonation waves of three ignition methods, i.e., spark plug ignition, vertical pre-detonation tube ignition, and tangential pre-detonation tube ignition, were studied. Ethylene and oxygen-enriched air were used as fuel and oxidizer, respectively. Experimental results indicate that the rotating detonation waves were able to be initiated and propagated steadily with the three ignition methods, which seem to have little influence on the propagating direction of rotating detonation waves. Compared with the results of spark plug ignition, stable detonations were available with a wider range of mass flow rate when adopting vertical and tangential pre-detonation tube ignition. The obtained average propagating velocities of rotating detonations were almost consistent for all the three cases. When the pre-detonation tube was used, ...

Direct numerical simulation of high-temperature turbulent boundary layer with...

LIU Pengxin, YUAN Xianxu, SUN Dong, FU Yalu, LI Chen

doi:10.7527/S1000-6893.2020.24877

2022, (1): 124877-124877.

Abstract

Under specific flying conditions, interaction between turbulence and chemical nonequilibrium will occur on hypersonic vehicle surfaces; however, related research is limited. Choosing the flow state after the leading shock of a cone and utilizing two gas models, i.e. the calorically perfect gas and the chemical reaction gas, we conduct a Direct Numerical Simulation (DNS) study to analyze the effects of chemical nonequilibrium on the turbulence statistics and fluctuations, and investigate the scaling law. The results show that the endothermic dissociated reaction is dominant in the boundary layer, significantly reducing the average temperature and temperature fluctuation. However, chemical nonequilibrium only have a small influence on the average streamwise velocity, velocity fluctuation and Reynold stress. In the log-region, the Extended Self-Similarity(ESS) of the fluctuations is still consistent with the scaling law.

Dynamic modeling and simulation analysis of LOX/RP1 variable thrust engines u...

CUI Peng, SONG Jie, LI Qinglian, CHEN Lanwei, LIANG Tao, SUN Jun

doi:10.7527/S1000-6893.2021.24884

2022, (1): 124884-124884.

Abstract

LOX/RP1 variable thrust liquid rocket engines using a motor pump have been widely studied in recent years because of their environmentally friendly performance, adjustable throttling depth and convenient adjustment. As a kind of variable thrust rocket engine, its system response characteristics are critical in directly determining the spacecraft maneuverability. However, previous research on the LOX/RP1 variable thrust engine using a motor pump mainly focuses on the system scheme design, and the dynamic analysis is relatively preliminary. In this paper, the response characteristics of the throttling system under different conditions and the variation of system performance parameters with the thrust level are studied by establishing a simulation platform of the LOX/RP1 variable thrust engine using a motor pump in consideration of the influence of the battery, motor and cooling channel. The results show that, although the response speed of the motor pump is fast, that of the cooling chan...

Efficient robust aerodynamic design optimization method for high-speed NLF ai...

ZHAO Huan, GAO Zhenghong, XIA Lu

doi:10.7527/S1000-6893.2020.24894

2022, (1): 124894-124894.

Abstract

The advanced high-speed and high-lift Natural-Laminar-Flow (NLF) airfoil has played an important role in improving the aerodynamic performance of the new generation of High-Altitude Long Endurance (HALE) Unmanned Air Vehicles (UAV). However, shock waves and separation bubbles are likely to occur on the surface of this kind of airfoil, which are very sensitive to the aerodynamic characteristics such as fluctuation of Mach number and angle of attack. The aerodynamic shape designed with the traditional method has low robustness, and is thus difficult to be used in engineering practice. Although the Robust Aerodynamic Design Optimization (RADO) method is a very promising solution, it encounters the difficulty of large computational cost. In this paper, we study the key technologies affecting the efficiency of RADO and develop a sparse PC reconstruction algorithm based on the Adaptive Forward-Backward Selection (AFBS) method, greatly improving the efficiency of Uncertainty Quantification (U...

High-order scheme discretization of sonic boom propagation model based on aug...

WANG Di, QIAN Zhansen, LENG Yan

doi:10.7527/S1000-6893.2021.24916

2022, (1): 124916-124916.

Abstract

The sonic boom prediction is one of the key technologies in the development of the new generation low-boom supersonic transport aircraft. In view of the low accuracy of the numerical scheme for the far-field propagation model of sonic boom based on the augmented Burgers equation, we study the discretization method for high-order scheme. After the physical properties of each effect term in the model is analyzed, an appropriate high-order accuracy scheme is used to discretize each term, and the classical geometric acoustic ray tracing method is adopted to calculate the propagation path of sonic boom, so as to realize the accurate prediction of ground waveform. The reliability of the high-order discrete method used in this paper is verified by the numerical simulation of the sonic boom flight test of F-5E aircraft and the standard numerical examples of the 2nd AIAA Sonic Boom Prediction Workshop on sonic boom prediction. Further results show that the high-order scheme has lower dissipatio...

Unsteadiness of flow separation in an asymmetric supersonic nozzle

HE Chengjun, LI Jianqiang, HUANG Jiangtao, LI Yaohua, CHEN Xian

doi:10.7527/S1000-6893.2020.24930

2022, (1): 124930-124930.

Abstract

Using flow visualization and dynamic pressure measurement technology, the shock structure and dynamic pressure on the wall in an asymmetric supersonic nozzle with flow separation were experimentally measured. The time and frequency domain features of the wall pressure were analyzed to obtain the characteristics of the unsteady flow in different modes of flow separation inside the nozzle. The results show that when the Nozzle Pressure Ratio (NPR) increased from 1.8 to 12.70, the flow field structure inside the nozzle shifted from the downward to upward pattern. On the upper wall of the nozzle, there were three different modes of flow separation: Restricted Shock Separation (RSS), end effect, and Free Shock Separation (FSS). On the lower wall, the main mode of flow separation was FSS. In the RSS mode, the separation data began to deviate from the Schmucker’s criterion. In both the RSS and end effect modes, the wall in the intermittence region was under low-frequency pressure and the sho...

Longitudinal stability of blended-wing-body aircraft based on experimental bi...

FU Junquan, SHI Zhiwei, GENG Xi, ZHU Jiachen, WANG Lishuang, WU Dawei, PAN Lijun

doi:10.7527/S1000-6893.2020.24931

2022, (1): 124931-124931.

Abstract

Bifurcation analysis and the catastrophe theory are used to study the longitudinal stability of Blended-Wing-Body (BWB) aircraft. Equilibrium branches of the angle of attack with the elevator are obtained, and stability of the branches and the catastrophe points analyzed. Then bifurcation analysis is introduced into the virtual flight tests to physically track the equilibrium branches, enabling the experimental bifurcation analysis research in the wind tunnel. A pseudo-linear controller based on the nonlinear dynamic inverse is designed, with the open-loop and closed-loop experimental bifurcation diagrams obtained and analyzed. The comparative analysis shows that the theoretical bifurcation analysis and the open-loop experimental bifurcation analysis are basically consistent in the range of small angles of attack, verifying the feasibility and accuracy of the experimental bifurcation analysis method. The longitudinal instability of the BWB aircraft is mainly caused by the sudden change...

Coupling method for stability improvement for transonic compressor at variabl...

ZHAO Le, WANG Wei, ZHANG Lefu, WANG Weichao, LU Jinling, CHU Wuli

doi:10.7527/S1000-6893.2021.24942

2022, (1): 124942-124942.

Abstract

To explore an effective method to improve the stall margin of a transonic compressor at different operating speeds, this study couples the slot casing treatment and tip injection to enhance the compressor stability. The effects of the number, length, width of the slots and the nozzle circumferential width on the compressor performance are studied parametrically, and the mechanism of stability enhancement is revealed using unsteady numerical simulations. The results show that the stall margin increases by 9.31%, 8.26% and 8.68% at 100%, 80% and 60% speed, respectively, while the compressor efficiency at the design point is decreased correspondingly by 0.77%, 0.23% and 0.41%. The number, length and width of the slots have significant effects on the stall margin and the efficiency of the compressor, while the circumferential width of the nozzle has little effect on the compressor performance. A flow cycle composed of suction and injection is formed in the coupled casing treatment. The inc...

Gust response analysis and verification of elastic aircraft based on nonlinea...

SHI Yan, WAN Zhiqiang, WU Zhigang, YANG Chao

doi:10.7527/S1000-6893.2021.25474

2022, (1): 125474-125474.

Abstract

For low-speed aircraft, gust is more likely to lead to the generation of nonlinear aerodynamic force and nonlinear aeroelastic response, consequently causing flight safety problems. To study these nonlinear problems, the classical panel method cannot meet the accuracy requirements, and the Computational Fluid Dynamics (CFD)/Computational Structure Dynamics (CSD) full order coupling analysis is inefficient. Therefore, it is necessary to establish a flight dynamics analysis model with high precision and high efficiency to satisfy the engineering requirements. A nonlinear aerodynamic Reduced-Order Model (ROM) is proposed in this paper to predict the nonlinear aerodynamic force of low-speed aircraft under high amplitude gusts. Taking a flying wing aircraft model in a wind tunnel test as an example, we obtain the aerodynamic data of the model with the CFD method. A linear aerodynamic ROM and a nonlinear aerodynamic correction ROM of the flying wing aircraft model are established by the Auto...

Laminated acoustic metamaterial for improving low-frequency broadband sound i...

GU Jintao, WANG Xiaole, TANG Youheng, ZHOU Jie, HUANG Zhenyu

doi:10.7527/S1000-6893.2020.24785

2022, (1): 224785-224785.

Abstract

Aiming at the problem of low-frequency broadband noise control in the aircraft cabin, a laminated acoustic metamaterial, which is suitable for sound insulation enhancement of aircraft wall panels, is proposed. The laminated acoustic metamaterial is composed of two membrane-constrained acoustic metamaterial panels with different composition parameters in the front and the back, and a porous sound-absorbing material filled in them. By establishing the sound insulation calculating finite element model of laminated acoustic metamaterials, analyzing the relationship between the sound insulation characteristics of each layer of membrane-constrained acoustic metamaterials and the laminated acoustic metamaterials composed of them. And focusing on the mechanism of negative mass effect of laminated acoustic metamaterials on its sound insulation characteristics. Based on the four-microphone acoustic impedance tube test system, the normal incident sound insulation of the laminated acoustic metamat...

Impact of seatbelts on impact characteristics of aviation seats and occupants

FENG Zhenyu, LIU Xu, LIN Lanhui, YANG Yongpan, XIE Jiang, SHI Xiaopeng, XIAO Pei, LI Leizi, YI Pengf

doi:10.7527/S1000-6893.2020.24808

2022, (1): 224808-224808.

Abstract

A finite element model for the aviation seat/seat belt is established and validated based on typical triple passenger seats, and the influence of seat belt parameters such as seat belt anchor position, seat belt stiffness and seat belt type on the dynamic response of the seat system is invistigated. Under horizontal impact loading, the position of belt’s anchor has significant effect on the occupant’s motion trajectory and loads on seat legs. The load on the rear left leg and front left leg in theZdirection decreases with the increase of the seat belt angle. Meanwhile, the position of the belt’s anchor has small influence on the seat belt load. Seat belt stiffness has significant effect on the occupant’s motion trajectory, seat belt load and seat leg load. As the stiffness increases, the seat belt load increases, while the occupant's forward movements and seat leg load decrease. Besides, compared with the two-point seat belt, the Y-belt restraint the occupant better, and can reduce...

Fatigue experiments and lifetime for post-impact sheets of aluminum-alloys(AA...

ZHANG Yibo, CHEN Di, CHENG Zhengqiang, SHEN Peiliang, XIONG Junjiang

doi:10.7527/S1000-6893.2020.24811

2022, (1): 224811-224811.

Abstract

Tests of low velocity impact are performed on the sheets of AAs 2524-T3 and 7075-T62, respectively, with four different impact forces, and static and fatigue experiments are conducted on the intact and post-impact sheets under static tensile, constant amplitude and block spectrum loading. The impact-dent size, static and fatigue properties, and spectrum-loading life are determined, with the effect of impact on fatigue characteristics and damage mechanism analyzed and discussed from fractographic and experimental observations. AnS-N-Ktsurface model is proposed to depict fatigue characteristics for fatigue lifetime prediction of post-impact sheets subjected to block spectrum loading. A new concept is applied for experimental data and a reasonable agreement obtained between the theoretical and experimental results, demonstrating the effective and practical use of the developed surface model. A nonlinear elastic-plastic FE model based on the Johnson-Cook constitutive equation is generated ...

Analysis of primary resonance characteristics of dual-rotor system in maneuve...

CHEN Yi, HOU Lei, LIN Rongzhou, YANG Yang, CHEN Yushu

doi:10.7527/S1000-6893.2020.24841

2022, (1): 224841-224841.

Abstract

This paper focuses on the primary resonance analysis of a dual-rotor system considering the two rotor imbalanced excitations with different rotating speeds, the radial clearance of the inter-shaft bearing and the maneuver load. The vibration equations of the dual-rotor in the hover flight environment are formulated using the Lagrange equation. The primary resonance responses are then obtained by numerical methods, followed by the investigation into the primary resonance characteristics under the influence of the maneuver load and the clearance of inter-shaft bearing. The results reveal that the dual-rotor system has some typical nonlinear dynamic behaviors, such as vibration jump and bi-stable phenomenon. The maneuver load exerts a "stiffness enhancement effect" while the inter-shaft bearing clearance a "stiffness weakening effect" on the dual rotor system.

Design implementation and error analysis of mass and centroid measurement of ...

LIN Chuang, ZHENG Yu, GUANG Chenhan, WANG Yan, YANG Yang

doi:10.7527/S1000-6893.2020.24893

2022, (1): 224893-224893.

Abstract

To solve the problem that the traditional centroid measurement system based on three-sensor cannot be applied to the aerocraft with large wingspan, a mass centroid measurement system based on three-point is proposed, which has no requirements for the aerocraft rotation angle. To improve the measurement accuracy of system, the comprehensive influence of random errors on the system measurement accuracy is analyzed by the response surface method. Firstly, the mass and centroid measurement system of the aerocraft with wingspan is designed. Then, the mathematical derivation between random error and system measurement accuracy is given by using the random error transfer formula. Using the response surface method and the Latin hypercube sampling method, the quadratic term relational model between the random error and system measurement accuracy is obtained. Based on the quadratic term relational model and system accuracy index, the accuracy requirements of each component are obtained, and the...

Analysis method for flutter mode indicator based on principle of work and pow...

WANG Xinjiang, LIU Ziqiang, GUO Li, FU Zhichao, LYU Jinan

doi:10.7527/S1000-6893.2020.24920

2022, (1): 224920-224920.

Abstract

Flutter boundaries and flutter coupling mechanisms are of high significance for aircraft design and flutter tests. The flutter boundary is determined by the distinguishing characteristic of the generalized coordinate of modes, which often depends on the experience of designers and therefore it is difficult to guarantee the quantitative uniformity of discriminant standards. This paper proposes a new method for the flutter mode indicator analysis based on the principle of work and power. The analysis is realized through energy accumulation of generalized force work on modal coordinates. Rational function approximation and the CFD/CSD method are used respectively in the AGARD445.6 flutter mode indicator analysis to verify the proposed method. Then, the ‘frequency drifting’ phenomenon of twin-fuselage aircraft is explained logically by the proposed method, highlighting the advantage of the proposed method. The results show that the proposed method well reflects the flutter coupling mecha...

Distributed power allocation method for netted radar based on cooperative gam...

JIN Biao, KUANG Xiaofei, PENG Yu, ZHANG Zhenkai

doi:10.7527/S1000-6893.2020.24776

2022, (1): 324776-324776.

Abstract

Due to the existence of network topology switching and information transmission delay in the decentralized radar network, the global resource allocation scheme given by each radar node may be inconsistent. To solve this problem, the cooperative game theory is applied to the power allocation of netted radar nodes in multi-target tracking Scenario. Firstly, the Signal to Interference Noise Ratio(SINR) is described as a function of the target spatial position and radar transmitting power. Then, the problem of radar node power allocation in the decentralized network is regarded as a cooperative game model with SINR as the characteristic function. The weighted graph is used to improve the calculation method of the Shapley value of the cooperative game to reduce the computational complexity. A fast algorithm for solving the cooperative game model is then proposed. The proposed method does not need to use the complex optimization algorithm, and has good real-time performance. Simulation resul...

Guidance method for maneuvering target interception based on virtual look ang...

WANG Yaning, WANG Hui, LIN Defu, YUAN Yifang

doi:10.7527/S1000-6893.2020.24799

2022, (1): 324799-324799.

Abstract

To enable the missile to intercept one maneuvering target with a certain terminal attack angle, a guidance method for interception of the maneuvering target with terminal virtual look angle and terminal line-of-sight angle constraints is proposed. According to the transform relationship between the motion vectors in the velocity coordinates system, the nonlinear model of relative motion in the virtual coordinates system is established. Then, the thought of polynomial guidance in the linear model is introduced into the nonlinear model creatively. Through the constraints of the terminal virtual look angle and the terminal line-of-sight angle, the solution of the polynomial virtual control variable of the distance between the missile and the target is derived. Finally, according to the transformation relation between the virtual vectors and the motion vectors, the acceleration command expression in the velocity coordinates system is obtained. Simulations under the conditions of different ...

Electromagnetic shielding principles and technologies of cavity grille

YU Longzhou, CHEN Xian, HUANG Jiangtao, ZHONG Shidong, QUE Xiaofeng

doi:10.7527/S1000-6893.2020.24803

2022, (1): 324803-324803.

Abstract

Inlet grilles can prevent electromagnetic waves from entering the cavity to form strong scattering sources, improve the surface discontinuousness of air vehicles, and thereby reduce their scattering characteristics. Taking the leaning rectangular straight cavity as the research object, this study illustrates the principle of electromagnetic shield using the theory of waveguide mode propagation based on the algorithm of fast multi-pole method. The relationship between the size of the grille and the Radar Cross Section (RCS) is analyzed as well as that between the polarization angle and the direction of the grille. The inhomogeneous grille in the longitudinal and horizontal dimensions is designed based on the principle of destructive interference. Numerical simulations indicate that: compared with that of the homogeneous grille, the RCS of the inhomogeneous grille in the horizontal dimension is reduced beyond 8 dB within the range of ±15° in the front direction. The RCS of the inhomogene...

Cooperative guidance method based on impact time and angle control

TANG Yang, ZHU Xiaoping, ZHOU Zhou, YAN Fei

doi:10.7527/S1000-6893.2020.24844

2022, (1): 324844-324844.

Abstract

Suicide-attack UAVs need to adopt cooperative guidance to simultaneously attack the target from different directions under strong confrontation conditions. Therefore, a cooperative guidance law based on impact time and angle control is proposed. Firstly, an auxiliary phase is introduced to a two-phase guidance law to enhance its time control ability. On this basis, the switching conditions of the two-phase guidance law with an auxiliary phase are modified to simultaneously control the impact time and angle. With the desired impact time and angle taken within their permissible sets, the constraints on the acceleration and field-of-view will be satisfied during the engagement with the proposed algorithms, which can be used to realize cooperative guidance. Finally, the effectiveness of the methodology is verified by numerical simulations.

Measurement of sea surface height using airborne global navigation satellites...

WANG Feng, YANG Dongkai, ZHANG Guodong, ZHANG Bo

doi:10.7527/S1000-6893.2020.24852

2022, (1): 324852-324852.

Abstract

This paper studies the measuring model of sea surface height using the airborne GNSS reflectometry, the estimation method of the delay between direct and reflected signals based on point tracking and model fitting, and error calibration. For the problem of high computational complexity of Z-V model fitting, a new fitting model named as 7-β model is proposed used to compute the delay between direct and reflected GNSS signal. In addition, an error calibration method is developed using the looking-up table and weighted averaging to correct the delay bias caused by the sea state. The validation is implemented utilizing the experimental data acquired by CSIC-IEEC in the Baltic Sea on December 3rd, 2015. The results show that the decimeter-level sea surface height can be obtained by using the existing and proposed methods to estimate the delay between direct and reflected GPS L1 and Galileo E1 signals and then using the proposed approach to correct the delay bias caused by the sea state.

Cooperative object detection in UAV-based vision-guided docking

WANG Hui, JIA Zikai, JIN Ren, LIN Defu, FAN Junfang, XU Chao

doi:10.7527/S1000-6893.2020.24854

2022, (1): 324854-324854.

Abstract

Autonomous aerial recovery of UAV is a future development trend, and automatic detection of aerial vehicles is one of the key technologies to realize vision-guided recovery. At present, the research on the detection of aerial related objects is limited to individual objects, and the information between correlated objects is not fully utilized. For the problem of related object detection in high-dynamic aerial docking, this paper proposes a single-stage fast cooperative algorithm for detection of the master and the mount, including detection of sibling independent head of related category, detection of mask enhancement of related category, and constraints on consistency of features of related categories. These modules can improve the detection performance jointly. Experiments show that in the test dataset, the algorithm can obtain a 4.3% increase of the average precision of compared with YOLOv4, and can obtain a 31.6% increase of the average precision compared with YOLOv3-Tiny. At the s...

Voltage drop in composite aircraft grounding and current return network

YANG Zhangang, SUI Zheng, ZHANG Qihao, LIU Jianying

doi:10.7527/S1000-6893.2021.24859

2022, (1): 324859-324859.

Abstract

To ensure normal operation of onboard electrical equipment, a metal grounding and current return network should be added to the composite aircraft fuselage to meet the grounding requirements of the onboard electrical system. For calculation of the pressure drop in the composite aircraft grounding and current return network, the conductor-based volumetric partial element equivalent circuit method is used to model the grounding and current return network installed on the composite aircraft. We analyze the voltage drop of partial distribution unit loads which belong to 28 VDC, 115 VAC bus along the path in the grounding grid under the cruising condition, and consider the influence of large fault current injection and contact impedance between components on the voltage drop of the grounding and current return network. The voltage drop in the network is analyzed by establishing a simplified model. The proposed calculation method and simulation calculation results of the voltage drop in the ...

Improved aeronautical telemetry channel sounding

LI Sai, DANG Xiaoyu, HAO Chongzheng, LI Jie

doi:10.7527/S1000-6893.2020.24881

2022, (1): 324881-324881.

Abstract

Sliding correlators are widely used in the measurement of channel characteristics, but large delay fading in the aeronautical telemetry channel severely limits the performance of the measurement system, and even cause the system to be unable to complete the measurement. To measure aeronautical telemetry channels more accurately, this paper proposes a sliding correlator based on Zadoff-Chu(ZC) sequences. The channel sounding ability of the correlator in the measurement system of aeronautical telemetry channels is studied. Different from traditional analysis methods, the analytical expression of each interference component in the measurement system is first given from the frequency domain. Second, the average dynamic range in the multipath environment is given. Finally, the influence of each interference component on the measurement performance is analyzed based on the simulation of the ZC sequence root, normalized sliding factor, Signal-to-Noise Ratio(SNR) and measurement sequence lengt...

Energy-balanced communication topology generation of three-dimensional optima...

LUO He, LI Xiaoduo, WANG Guoqiang

doi:10.7527/S1000-6893.2021.24922

2022, (1): 324922-324922.

Abstract

The optimization of communication topology of persistent formation is to minimize the communication energy consumption between agents on the basis of ensuring that the multi-agents use the persistent formation control method to maintain formation. The existing methods can minimize the total communication energy consumption of agents, but do not consider balancing communication energy consumption between agents, which will lead to early withdrawal of some agents from the formation. To solve this problem and maximize the formation keeping time, a communication topology generation method of 3D optimally persistent formation considering energy consumption balance is proposed. First, an offline optimization mechanism of communication topology is designed, including selecting a suitable cycle, calculating the communication topology of each cycle before formation movement, and adjusting the communication topology periodically during the formation keeping process, so as to avoid additional com...

k-terminal reliability analysis of satellite network based on QoS guarantee

CAI Ruiyan, LIU Yanhong, WEI Debin

doi:10.7527/S1000-6893.2021.26020

2022, (1): 326020-326020.

Abstract

Existing reliability analysis methods cannot solve the problem of low calculation accuracy due to prolonged information transmission time in the satellite network and diverse service requirements. Considering the multi-state characteristics of satellite operation, reliability of satellite network in multi-states is studied, and a k-terminal reliability analysis algorithm is proposed based on Quality of Service(QoS). Firstly, the nodes are fused, and the non-fused elements are set to zero; the network topology adjacency matrix is transformed to get the path connecting K nodes. Compared with the traditional method, the matrix transformation is effectively reduced and the redundant links are avoided. Then, to improve the accuracy of reliability calculation, according to the QoS constraints of different services and the current state of the link, the available paths satisfying the conditions in the network are determined. Finally, the k-terminal path reliability for different services is c...

Design and research of two-dimensional fuel pump with balanced inertia force

WANG Heyuan, LI Sheng, RUAN Jian

doi:10.7527/S1000-6893.2020.24696

2022, (1): 424696-424696.

Abstract

A new concept named two-dimensional fuel pump with balanced inertia force balanced is proposed. The pump integrates the flow distribution mechanism on the piston and the piston ring, eliminating the independent flow distribution mechanism of the traditional piston pump, and simplifying the structure of the fuel pump. The axial reciprocating movement of the piston and the piston ring in the opposite direction increases the discharge stroke of the pump without changing the volume, and further improves the power density ratio of the fuel pump. The guide surface of the fuel pump adopts equal acceleration and deceleration curved surfaces, and uses the balancing group to perform reciprocating motion with the same acceleration and opposite direction as that of the driving group to balance the inertial force generated by the driving group at high speed, providing a kind of possibility of high-speed fuel pump. Based on the principle of the pump, the effects of internal leakage, external leakage...

Experimental identification for rotordynamic coefficients of labyrinth seal b...

ZHANG Wanfu, WANG Yingfei, ZHANG Xiaobin, YANG Xingchen, LI Chun

doi:10.7527/S1000-6893.2020.24719

2022, (1): 424719-424719.

Abstract

An experimental facility is established and improved to identify rotordynamic coefficients of the labyrinth seal. The impedance method is employed to identify the rotordynamic coefficient of the labyrinth seal. Effects of rotational speed, inlet pressure and whirling frequency on the dynamic characteristics are studied. The identification method for the dynamic characteristics of the seal based on the infinitesimal theory is applied for numerical analysis of the experimental seal. Results of numerical analysis are compared with the experimental results. The comparison shows that the rotordynamic characteristics of the labyrinth seal identified from the experiment are slightly higher than those from numerical analysis, but their varying trends are in good agreements. Particularly, the results of the effective damping coefficient, which characterizes the stability of the system, has good consistency. The dynamic coefficient of the labyrinth seal shows a frequency dependence when the roto...

Prediction of dangerous point of thermal barrier coating by biaxial stress st...

YAO Yudong, AI Yanting, SONG Chun, GUAN Peng, TIAN Jing

doi:10.7527/S1000-6893.2021.24937

2022, (1): 424937-424937.

Abstract

The spallation life cycle of thermal barrier coat (TBC) is a key factor for failure in one operating period of the aircraft engine. Research on the thermal fatigue life (TFL) of TBC has great significance for prolonging the service life of engine. An effective failure analysis method for TBC is performed using biaxial stress state analysis, finite element method, phenomenology theory, and linear cumulative damage model. It is demonstrated that with the increase of thermally grown oxide layer thickness, the position of the maximum thermal stress moves from peak to valley along the cosine curve of the top coat. Comparing with the traditional stress analysis method, the biaxial stress state analysis method is more suitable to predict the accurate position of the risk point, because the position of the normal stress peak and shear stress peak calculated by biaxial stress state analysis method is closer to each other. Based on the phenomenology theory and linear cumulative damage model, the...

On-line damage monitoring of composites based on carbon nanotube films

QU Shuxuan, GONG Wenbin, SUN Xiaozhu, ZHANG Dongxing, LIANG Zhiqiang, GAO Limin, LYU Weibang

doi:10.7527/S1000-6893.2020.24949

2022, (1): 424949-424949.

Abstract

Considering that fiber-reinforced polymeric composites would be damaged due to impact, compression, fatigue and other factors during service, a composite with on-line damage self-sensing capabilities was developed based on carbon nanotube films, which possess desirable mechanical and electrical properties. Using the conductive network formed by carbon nanotubes, the damage of composites will destroy the conductive path and greatly increase the resistance of carbon nanotube films. The on-line self-sensing of composite damages was realized by measuring the boundary voltage of the composite, and then solving/imaging the conductivity distribution within the composite through the Electrical Resistance Tomography. Both damages of through-hole and model-I interlaminar fracture were investigated, and the results show that for these two damage modes, the obtained composite can realize on-line damage localization as well as damage display through EIT image reconstruction. For the through hole da...