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    • Collection Down  7 Views  22
      Autonomous maneuver decision is a key technology in air-to-air confrontation, and the study of autonomous maneu-ver decision involves an optimal maneuver solution method. Through the study of autonomous maneuver decision method, the real-time and accuracy of autonomous maneuver decision of Unmanned Combat Aerial Vehicle (UCAV) in an aerial combat engagement can be improved, which has important theoretical research significance and application value in the promotion of UCAV's autonomous aerial combat and manned/unmanned aircraft cooperative aerial com-bat. Currently, a large number of researches have been conducted around the theories of mathematical solution, data-driven, intelligent optimization and their applications, which have given a greater impetus to the research of autono-mous maneuver decision methods and their applications. Firstly, the basic concept of autonomous maneuver decision of UCAV is elaborated, then the research progress of maneuver decision methods is reviewed, several methods commonly used in maneuver decision research are introduced, the maneuver decision methods are classified and summarized and the performance of several typical maneuver decision methods in air combat simulation is compared. Finally, the difficulties and prospects of autonomous maneuver decision research are pointed out.
    • Collection Down  1 Views  10
      Carbon fiber reinforced polymer (CFRP) are widely used as an advanced composite material. Traditional cutting methods for processing CFRP are prone to forming machining defects such as delamination, burrs, and cracks, and have the problem of severe tool wear. Laser processing and water jet processing of CFRP are prone to generating the processing defects such as the heat affected zones, impact damage, and stepped delamination. As a non-contact machining method, electrical discharge machining (EDM) can machine any conductive material regardless of the strength, hardness, and stiffness of the workpiece material. Therefore, EDM has a great potential in solving the difficult machining problem of large CFRP components. However, the EDM of CFRP faces challenges such as the contamination of the CFRP compo-nents by the liquid medium and the limited size of the CFRP components. Therefore, this study proposes to perform the CFRP EDM in an aerosol medium and builds an EDM milling machine tool based on a six degree of freedom serial robot. The experiments on planar and spatial EDM milling of the CFRP components were conducted and the action mechanism of the droplet in EDM of CFRP material in aerosol medium was revealed, verifying the feasibility of the EDM milling of CFRP in aerosol medium. This study has a great significance for the low-cost, green, and efficient process of large and complex CFRP thin-walled structural components.
    • Collection Down  2 Views  10
      When establishing a strain-load relationship model for aircraft structures, ground calibration tests can obtain high-fidelity data but are trapped with limited test ranges, while finite element simulations are not limited by test ranges but the data fidelity is low. This leads to difficulties in achieving win-win situation of accuracy and applicability based solely on either ground calibration test data or finite element simulation data. To address above issue, two multi-level neural network models fusing real data and virtual data were put forward, respectively called mapping-based model and a compensation-based model; a method for measuring the model's cognitive degree based on the variance of sub-learners is established and embedded into the compensation-based model. A neural network model with high accuracy, wide applicability, and the capability to forewarn of unreliable prediction results was therefore developed. This developed model was validated using a scaled-down wing. Compared with complete reliance on real data from ground calibration tests, the load models based on fusion of multi-source data demon-strate superior capabilities, and the compensating-based model is better than the mapping-based one. Moreover, the compensating-based model can effectively identify data samples with poor cognitive degree of the load model after embedding the base learner variance method and thereby provide warnings for unreliable prediction results.
    • Collection Down  1 Views  10
      A variable chord wing based on composite material elastic periodic structure is designed using NACA0014 profile. The finite element model of the wing is built, and the maximum chord morphing amplitude is given based on static strength analysis. The aerodynamic analysis model of the wing is established, and the aerodynamic performance of the wing is calculated under different morphing status. The pre-morphing analysis is done according to stiffness requirement in normal direction. The strength, stiffness and stability of the morphing wing structure are checked under heavy load case and economical cruise case. The wing structure initial damage mode and ultimate load factor is predicted through overload calculation. The normal mode and transient analysis of the morphing wing is completed, and the basic dynamic performance is given. It is shown that the variable chord wing based on symmetrical double ripple elastic periodic structure has simple structure and activation mechanism. The streamline and smooth wing surface are maintained during chord morphing. The strength, stiffness and stability of the morphing wing meet the design requirements. The maximum stretch amplitude of the elastic periodic structure is 140mm, which is 58.33% of the initial chord length of periodic structure and 23.33% of the wing initial chord length. The maximum safety angle of attack of the wing initial and maximum morphing status is 12°, and the optimum angle of attack is 8°. The lift of maximum morphing status is higher than that of the initial status by 22.89%. The stiffness issue in Y direction is satisfied through the pre-stressed silicon rubber skin with pre-chord-morphing of 16mm. The initial damage of the periodic structure occurs when the aerodynamic load increases up to 1.96 times of the static strength heavy load case, and the damage mode is fiber tensile failure. The first and second order normal modes of the maximum morphing status are vertical and horizontal bending. The displacement kinetic convergence of the morphing wing occurs in 2 seconds when gust load is engaged during level flight.
    • Collection Down  3 Views  17
      Evaluating propulsion system performance accurately is an important part of the aircraft/engine integrated design process, which determines the potential performance of the aircraft. Optimizing installation performance and reducing installation losses are effective ways to improve aircraft performance potential. Adaptive cycle engine can ensure engine inlet airflow constant during throttling process, which decreases inlet outflow drag and promotes installation performance. However, optimization design only involves in engine itself in early engine overall scheme demonstration. The inlet/exhaust system’s effect on engine matching is neglect. And the consistency of optimal conditions between propulsion system and engine is hard to be ensured, which determines model complexity and optimization priority during design process. Based on these problems, research on overall performance optimization method of propulsion system is carried out and adaptive cycle engine that has multiple control variables and working modes is taken as research object. Firstly, overall performance calculation model of adaptive cycle engine and installation performance calculation model are established. Secondly, key design parameters’ effect on installation loss and installation performance estimation are developed by using different configurations of inlets and nozzles. The optimal configurations and suitable parameters of inlets and nozzles are chosen. Finally, optimization method of propulsion system overall performance based on random search algorithm and regression analysis is developed. And two fast optimization methods to gain propulsion system performance are established: one is optimizing engine performance and then calculating installation performance, the other is optimizing installation performance directly. The comparisons of optimal performance between two optimization methods are conducted in the cruise throttling conditions and velocity-altitude characteristic conditions. By regression fitting precision analysis and coincidence comparison optimal throttling characteristics in cruise conditions and maximum thrust characteristics in different velocities and altitudes, the maximum root mean square error is about 0.01 in cruise conditions, and 0 in velocity-altitude characteristic conditions, which means that optimal working conditions of engine can represent optimal working conditions of propulsion system. Therefore, it is unnecessary to consider the effect on inlet/exhaust system to ensure the optimality of the propulsion system in the scheme demonstration stage, which greatly simplifies the model complexity of the scheme design. This design method is suitable for different configurations of adaptive cycle engines to conduct fast optimization design of propulsion system performance, which has strong engineering guidance significance and application value.

    • Research on safety judgment method of forward separation of protective shield

      Abstract

      Dong-Yang Zou An-Ping WU Jing-Zhou LIN

      doi: 10.7527/S1000-6893.2024.31005

      Full text:

      PDF [1604KB]（1）   

      Collection Down  1 Views  9
      The purpose of the research on safety boundary of multi-body separation is to find suitable safety design criterion or system analysis method, and to provide reference for relevant professional design, so as to provide optimization basis and solution for safety separation design. In this paper, the safety boundary of high Mach number forward separation of protective shield is studied, and the criterion of safety boundary of typical forward separation between protective shield and projectile and the inequality of back-pursuing collision of protective shield are put forward. The judge criterion of safety boundary can be used to research on the safety of shields during the axial direction separation stage. It can also provide a basis for the design of separation schemes and the selection of engine types. The back-pursuing collision inequality establishes the relationship between the motion parameters at the initial moment of free motion and the motion acceleration of the protective shield, which provides a reference for predicting the later motion of the protective shield. According to the initial state, the safety of the separation process of the protective cover can be judged by using the safety boundary criterion and the back-pursuing collision inequality, which provides reference for the separation design related majors.
    • Collection Down  2 Views  13
      In order to land a fixed-wing UAV on a moving platform, serval problems should be addressed. For example, the rapid movement of the landing platform, the UAV has to maintain high speed to generate sufficient lift while it can-not brake in mid-air at will. A segmented guidance strategy based on action planning is proposed. The autonomous shipborne landing process is divided into two stages: transition guidance and approach guidance. During the transi-tion guidance stage, a finite state machine is utilized to guide the fixed-wing UAV from any initial state to a specific distance behind the moving deck. In the approach guidance stage, action sampling based method is used to adjust the trajectory in real-time to guide the UAV to touch the deck accurately. Numerical simulation and FlightGear based semi-physical simulation demonstrate that the proposed segmented guidance strategy can effectively guide a fixed-wing UAV from any initial state to the center of aircraft carrier with different speeds, and the landing error is within 2m.
    • Collection Down  10 Views  26
      In the traditional yaw-steering mode, spacecraft swings back and forth around the yaw axis within a certain angle range, causing the spacecraft's front or back to always be exposed to direct sunlight, resulting in additional weight and power consumption costs for the thermal design of extravehicular equipment. The yaw-steering attitude control strategy with front and back pointing to the sun alternately has been proposed, providing spacecraft with a uniformly exposed thermal environment. This not only simplifies the thermal design of extravehicular equipment, but also improves the reliability of equipment sensitive to temperature range fluctuations in orbit. Three attitude control strategies for yaw-steering with front and back pointing to the sun alternately are compared in terms of power generation and propellant consumption. The optimal comprehensive index of the complementary-angle control strategy has been successfully applied to the Tianzhou-1 cargo spacecraft.
    • Collection Down  7 Views  20
      The behavior of helicopter brownout endangers flight safety, induces rotor blade erosion, and reduces its performance. An analyzed method of helicopter blade erosion in brownout condition is then proposed. In this method, variations of the sand cloud are simulated by a helicopter brownout model based on a viscous vortex particle method and a discrete element method, a collision and erosion models between blade and sand cloud are coupled, and the characteristics of blade erosion with high velocity is also considered. It compares with experimental data of plane erosion with different impact velocities, impact angles, and materials, including stainless steel (SS304), nickel, titanium (Ti-6Al-4V), glass fiber reinforced epoxy (CF/EP), bidirectional carbon fiber reinforced epoxy (GF/EP), and polyurethane (PU), to validate the method. The characteristics of blade erosion for the EH-60L helicopter in brownout condition is then analyzed, and the influence of flight speed on the blade erosion is also investigated. The results show that the predicted erosion rate by the present method agrees well with the experiment. As time increases, the collision between the blade and the sand cloud, the blade erosion, and the rotor erosion zone significantly increases in helicopter brownout condition. Furthermore, the erosion in blade tip is obvious worse than inner blade due to the longer time period, larger impact velocity and angle. Additionally, the blade erosion and the rotor erosion zone increase firstly and then reduce with increasing flight speed.
    • Collection Down  9 Views  23
      In order to investigate the performance of a fuel thermal management system (FTMS) with expendable heat sink under multiple temperature limit points, and to extend the system’s longest normally working time (thermal endurance) by optimizing the utili-zation of expendable heat sink, a simulation flow path using liquid methane (LM) as the expendable heat sink was constructed. Initially, the characteristics of hot fuel return were analyzed. The results indicate that the fuel heat sink consumption rate increas-es with increasing supply pump flow rate during normal operations. When the ram air is insufficient, the fuel return temperature to the fuel tank becomes the main limit temperature of the FTMS, and to meet the temperature requirement of hot fuel return, the system optimal supply pump flow rate is too large during working, resulting in a poor heat dissipation. In this case, the use of LM can not only cool the hot fuel return, but also further reduce the fuel heat sink consumption by reducing the optimal supply pump flow rate. Subsequently, the effect of the middle fuel return branch (MFRB) on system heat dissipation performance was explored. The results show that once the ram air is insufficient, the MFRB can not only increase the heat dissipation through combustion fuel, but also further enhance the system heat dissipation capability by decreasing the optimal supply pump flow rate as well. The fuel heat sink consumption rate under the standard condition without LM can be reduced by 17.62% in the new flow path. Next, the characteristics of LM supply flow were analyzed. The results demonstrate that the LM supply flow rate can be divided into the high efficiency, general, and low efficiency zones for LM according to the effect of using LM. Finally, a new dynamic supply strategy of LM was proposed. Under the standard condition, the thermal endurance can be improved by 9.21% and 27.44% compared to the constant low flow and high flow LM supply strategies, respectively.
    • Collection Down  11 Views  27
      In the pursuit of a carbon-neutral society, hydrogen, as a zero-carbon fuel, has gained significant attention in the aviation propulsion systems. Hydrogen has a higher flame propagation speed and a thinner flame thickness, which increases the risk of flashback in the design and operation of hydrogen-fueled combustor. The widely used micro-mixer nozzle effectively prevents core flow flashback by increasing axial velocity. However, the boundary layer flashback remains a challenging issue in hydrogen-fueled combustor. This paper investigates the boundary layer flashback of hydrogen-fueled combustor, examining the flame propagation characteristics and unique molecular transport properties of hydrogen. It reviews experimental and numerical simulations for non-swirling and swirling boundary layer flashback, summarizes classical critical velocity gradient theory for boundary layer flashback, and outlines laminar and turbulent boundary layer flashback criteria developed over recent decades. Finally, this work introduces fast flashback prediction method, discusses the current challenges in boundary layer flashback research in hydrogen-fueled combustor, and outlooks the future development of boundary layer flashback for premixed hy-drogen flames.

    • Active Disturbance Rejection Load Relief Control for Launch Vehicle Con-sidering Elastic Effects

      Abstract

      Zi-Bo LIU Ran Zhang Wenchao Xue Hui-Feng LI

      doi: 10.7527/S1000-6893.2024.30319

      Full text:

      PDF [1261KB]（5）   

      Collection Down  5 Views  18
      The load relief control of launch vehicles reduces aerodynamic loads by decreasing the angle of attack. However, ex-isting active disturbance rejection control (ADRC) methods for load relief do not fully account for elastic effects, which may lead to reduced disturbance estimation accuracy and even compromise system stability. To address this, this paper analyzes the impact of elastic vibration on disturbance estimation and observer gain, and proposes an im-provement to suppress elastic vibration. By isolating elastic motion from rigid-body motion, the measured input of the extended state observer (ESO) is made to match the observation model, thereby reducing the influence of elasticity on disturbance estimation. Based on this, the open-loop transfer function of the active disturbance rejection load relief control system considering elastic vibration is derived, and a set of parameter tuning rules is provided. By properly configuring the bandwidths of the load relief feedback control and the ESO, the tuning process is simplified while ensuring sufficient stability margins. Simulation and experimental results demonstrate that this method enhances system stability while achieving effective disturbance suppression and load relief. Finally, the algorithm's feasibility was vali-dated through hardware-in-the-loop simulations and flight tests on a rocket.
    • Collection Down  0 Views  15
      A suppression methodology based on the high voltage energy storage system and bidirectional energy conversion is proposed in this paper to solve the stability problem caused by the transient power demand of the radar/direct energy weapon and the bidirectional power flow of four-quadrant electric actuator. Firstly, a bidirectional energy control topology based on high-voltage battery and bidi-rectional power conversion is proposed, which uses the instantaneous charging and discharging of high-voltage battery to cut peaks and fill valleys to achieve the bidirectional transient power control. Secondly, a comprehensive power supply management strategy based on bus voltage-load current and battery SOC is proposed to realize rapid detection of system load disturbance and fast config-uration of power supply mode. Thirdly, a voltage stabilizing control method based on differential tracker and load current feedfor-ward is proposed to improve the voltage performance of the converter under various load. The simulation and experimental results show that the proposed method can effectively suppress the voltage fluctuation caused by high-power bidirectional transient load disturbance, and improve the robustness and quality of aerospace HVDC power supply system.
    • Collection Down  2 Views  14
      In order to enhance the performance of the nozzle in a wide airspace (0~24km) and wide speed domain (Ma0~5), a two-stage expansion nozzle design methodology has been investigated by utilizing altitude compensation and inverse design concepts. Firstly, the design method and steps of the two-stage expansion nozzle were introduced. The two-stage ex-pansion nozzle profiles are divided into the base section and extension section profiles, in which the base section profiles are generated by the reverse design method based on the wall pressure, which is used to shorten the negative thrust surface of the nozzle by changing the position and strength of the shock wave and to improve the thrust performance of the nozzle under the low-speed flight condition; The nozzle extension profile adopts the maximum thrust nozzle design method based on strong geometric constraints to meet the purpose of hypersonic vehicle afterbody integration design. Secondly, in order to verify the validity of the proposed design methodology, the proposed design methodology was inves-tigated using numerical simulation, in which the numerical calculation methodology was introduced and verified. Further-more, the grid resolution was determined. One step further, the design method of controlling the wall pressure distribution reverse designing the nozzle base section profiles was validated and the goal of forward/backward shifting of the shock wave was achieved. At the same time, a study was conducted on the influence of the two key design parameters, i. e. , the position control factor and the pressure control factor, on the the performance of the nozzle. Finally, comparative analysis of the proposed method and the maximum thrust nozzle design method with full geometric constraints was per-formed to verify the effectiveness and superiority of the new method. The results show that the nozzle improves the thrust performance by 7.86% in the over-expansion state and decreases the thrust performance by only 0.75% in the under-expansion state relative to the fully geometrically constrained maximum-thrust nozzle under typical design condi-tions, which provides a theoretical basis for the exhaust system of hypersonic vehicles.
    • Collection Down  2 Views  18
      The drag ball de-orbiting method is an effective solution for addressing the problem of space debris in low-Earth orbit (LEO). Utiliz-ing a high-performance fiber integrated weaving process to produce drag ball de-orbiting structures can effectively improve the curved surface irregularities of the spliced structure. During the de-orbiting cycle, the high-performance fiber material will be ex-posed to environmental factors such as temperature fluctuations and atomic oxygen (AO) erosion in LEO for extended periods. To investigate the effects of these two major space environment factors—temperature fluctuations and atomic oxygen erosion—on the structure and performance of high-performance fibers in the LEO environment, fibers with good adaptability to the space environ-ment were selected for weaving. The mechanical properties, surface morphology, and chemical properties of three types of organic high-performance fibers, namely polyimide fiber, polyaramid fiber Vectran?, and polyaramid fiber Yokolar?, were tested and ana-lyzed after undergoing temperature fluctuation treatment and atomic oxygen erosion treatment. The results showed that the strength of all three fibers decreased after the temperature fluctuation treatment, but the strength retention rate remained higher than 70%. Mi-nor defects such as particles and grooves were observed on the surface of the fibers; however, there was no significant change in the infrared spectra's characteristic peaks, indicating that the chemical structure was largely stable. In contrast, the mechanical properties of all three fibers experienced more than a 40% loss after atomic oxygen erosion, leading to increased hardness and reduced flexibil-ity. The polyimide fiber surface exhibited numerous concave and convex undulations, uneven thickness, and noticeable erosion holes. The surfaces of the two types of polyaramid fibers showed original fibrillated cleavage and stripping. New characteristic peaks appeared in the fiber infrared spectroscopy after treatment, and some original peaks weakened or disappeared, indicating that the chemical structures of all three fibers were damaged. While the three high-performance fibers demonstrated good resistance to tem-perature fluctuations, atomic oxygen erosion caused severe damage to their structure and performance. Thus, further investigation into atomic oxygen protection methods for high-performance fibers is necessary.
    • Collection Down  12 Views  47
      In order to explain and analyze the opponent’s air combat strategy, an Explicit Opponent Modeling (EOM) method for one-on-one Beyond Visual Range (BVR) air combat is proposed to address the lack of existing tools of strategy cogni-tion. The BVR problem is regarded as an imperfect information game, the space-time continuous process of BVR is discretized, different types of air combat actions are abstracted, the concept of decision point is introduced to aggre-gate the information sets conforming to the same distribution, the key decision variables are defined to examine the key factors affecting the actions, and the non-parametric machine learning approach is used to construct an easy-to-understand opponent strategy model (i.e., the model of the action probability distribution varies with the key decision variable in decision points). The post-game analysis of the simulated BVR air combat shows that the constructed strat-egy model by the proposed method can explain the opponent’s actions and analyze the opponent’s weak points more comprehensively than existing methods, and can provide suggestions for strategy optimization and equipment devel-opment.
    • Collection Down  8 Views  28
      In the deployment process of the Venus balloon probe, the balloon needs to be decelerated by the parachute to inflate in the air. The aerodynamic drag of the parachute-balloon combination is a factor that needs to be considered in the scheme design. For this issue, a fluid-structure interaction numerical model is established for the parachute-balloon combination. In this model, the flow field is solved using the ALE (Arbitrary Lagrange-Euler) method, and the fluid mesh follows the motion of the parachute-balloon combination. The penalty function method is used to handle the fluid-structure interaction between the flow field and the parachute and balloon, as well as the structural self-contact of the parachute and balloon. The internal pressure and volume changes of the balloon are solved by the CV (Control volume) method. The partially inflated balloon shape is obtained through compression by setting the initial internal pressure of the balloon. The buoyancy of the balloon is achieved by applying a pressure difference that varies with height on the surface of the balloon. Using this model, simulations are conducted on the process of partially inflated balloon parachute descending in the atmospheric environment of Venus, and the impact of changes in balloon inflation rates on the calculation results is analyzed. The calculation results indicate that the balloon shape undergoes slight changes over time under the influence of the flow field, and the balloon rotates. The drags of the balloon and para-chute fluctuate significantly over time, and their fluctuation frequencies are basically the same. The inflation rate change has no significant effect on the fluctuation frequency. As the inflation rate increases, the average drag of the balloon increases, while the average drag of the parachute remains basically unchanged. The areas of the balloon sorted in order of stress from high to low are as follows: flange fringes and wrinkles of the balloon, the filled area at the top of the balloon, depressed areas of the balloon.
    • Collection Down  38 Views  111
      Small object detection in UAV (Unmanned Aerial Vehicle) aerial images based on deep learning has a wide range of applications in military intelligence reconnaissance, battlefield surveillance and assessment, military object cap-ture and verification, intelligent traffic management, infrastructure inspection and maintenance, disaster prevention and control, search and rescue, crop management and analysis, ecological protection and monitoring and other fields, and has become a current research hotspot in recent years. However, no review on this topic has been found, so a comprehensive and in-depth investigation is conducted on small object detection in UAV aerial images based on deep learning in the past five years. First of all, the definition and challenges of small object detection in UAV aerial images are introduced. Secondly, focus on discriminative feature learning, super-resolution technology, real-time lightweight detection, and other improvement ideas to summarize the drone aerial image small object detection methods in detail. Then systematically summarize the small object detection datasets of UAV aerial images, and analyze the performance of different algorithms based on the VisDrone Challenge. Finally, comprehensively present the specific applications of small object detection in UAV aerial images in the military and civilian fields, discuss its potential future development directions, and point out some concerns about UAV aerial photography. It is expected that this review would inspire relevant researchers to further promote the development of small object detection in UAV aerial images based on deep learning.
    • Collection Down  11 Views  37
      In multidisciplinary coupled calculations represented by aeroelastic calculations, structural deformation will lead to deformation of the fluid solution domain. It is necessary to develop a mesh deformation technology with good versa-tility, high computational efficiency and strong applicability to meet the calculation needs of aerodynamic forces. The dynamic mesh technology based on the radial basis function (RBF) interpolation method has strong deformation ability and is applicable to the deformation calculation of any type of mesh. It is considered to be a dynamic mesh technology with good application prospects. This article introduces the basic theory of dynamic mesh technology based on RBF, analyzes the selection scheme of basis function and compact radius of RBF, summarizes the re-search progress of acceleration algorithm and accuracy improvement method for mesh deformation technology based on RBF, introduced the hybrid dynamic mesh technology based on RBF, and finally made a brief summary of the current research status of RBF-based dynamic mesh technology in aeroelastic calculations.
    • Collection Down  5 Views  22
      Impact of liquid nitrogen droplets on superheated wall is a fundamental phenomenon in liquid nitrogen spray cooling of cryogenic wind tunnels. The impact characteristics of droplets affect the advancement of liquid nitrogen spray field and the cooling performance of gas flow. In this study, a visualization experimental platform was designed and established to realize wall-impact of a single liquid nitrogen droplet with controllable size and impact velocity. Various dynamic behaviors and transition criteria of liquid nitrogen droplets impacting superheated wall were obtained. In different boiling modes, the maximum spreading coefficient of liquid nitrogen droplets impacting wall was investigated. During the generation of liquid nitrogen droplets, surface tension works against gravity, resulting in three stages of accumulation, necking, and breakup. As the wall temperature increases, the droplets successively exhibit contact boiling, atomization boiling and film boiling upon impact. The two corresponding critical temperatures are not affected by the Weber number (We). The droplet spreading process involves the conversion of impact kinetic energy to surface energy. With an increase in We, droplets transition from non-splashing to splashing during the spreading process, and the corresponding critical We is not affected by the wall temperature. Furthermore, the spreading characteristics of droplets are associated with the Leidenfrost temperature. Below the Leidenfrost temperature, droplets spread on the wall, and an increase in the wall temperature leads to intensified boiling bubbles, causing the maximum spreading coefficient to decrease. Above the Leidenfrost temperature, droplets spread on a vapor film, and the maximum spreading coefficient is independent of the wall temperature. This study deepens the understanding of the dynamic characteristics of liquid nitrogen droplets impacting superheated surfaces and provides a theoretical basis for improving the spray cooling performance of liquid nitrogen in cryogenic wind tunnels.
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Total visits: 6658907 Today visits: 1341All copyright © editorial office of Chinese Journal of Aeronautics

All copyright © editorial office of Chinese Journal of Aeronautics

Total visits: 6658907 Today visits: 1341