Numerical investigation on properties of attack angle for an opposing jet thermal protection system

The three-dimensional Navier Stokes equation and the k-ε viscous model are used to simulate the attack angle characteristics of a hemisphere nose-tip with an opposing jet thermal protection system in supersonic flow conditions. The numerical method is validated by the relevant experiment. The flow field parameters, aerodynamic forces, and surface heat flux distributions for attack angles of 0°, 2°, 5°, 7°, and 10° are obtained. The detailed numerical results show that the cruise attack angle has a great influence on the flow field parameters, aerodynamic force, and surface heat flux distribution of the supersonic vehicle nose-tip with an opposing jet thermal protection system. When the attack angle reaches 10°, the heat flux on the windward generatrix is close to the maximal heat flux on the wall surface of the nose-tip without thermal protection system, thus the thermal protection has failed.

Innovative Design and Additive Manufacturing of Regenerative Cooling Thermal Protection System Based on the Triply Periodic Minimal Surface Porous Structure

The new regenerative cooling thermal protection system exhibits the multifunctional characteristics of load-carrying and heat exchange cooling,which are fundamental for the lightweight design and thermal protection of hypersonic vehicles.Triply periodic minimal surface(TPMS)is especially suitable for the structural design of the internal cavity of regenerative cooling structures owing to its excellent structural characteristics.In this study,test pieces were manufactured using Ti6Al4V lightweight material.We designed three types of porous test pieces,and the interior was filled with a TPMS lattice(Gyroid,Primitive,I-WP)with a porosity of 30%.All porous test pieces were manufactured via selective laser melting technology.A combination of experiments and finite element simulations were performed to study the selection of the internal cavity structure of the regenerative cooling thermal protection system.Hence,the relationship between the geometry and mechanical properties of a unit cell is established,and the deformation mechanism of the porous unit cell is clarified.Among the three types of porous test pieces,the weight of the test piece filled with the Gyroid unit cell was reduced by 8.21%,the average tensile strength was reduced by 17.7%compared to the solid test piece,while the average tensile strength of the Primitive and I-WP porous test pieces were decreased by 30.5%and 33.3%,respectively.Compared with the other two types of unit cells,Gyroid exhibited better mechanical conductivity characteristics.Its deformation process was characterised by stretching,shearing,and twisting,while the Primitive and I-WP unit cells underwent tensile deformation and tensile and shear deformation,respectively.The finite element predictions in the study agree well with the experimental results.The results can provide a basis for the design of regenerative cooling thermal protection system.

Establishment and Optimization of Ablation Surrogate Model for Thermal Protection Material

The temperature response calculation of thermal protection materials,especially ablative thermal protection materials,usually adopts the ablation model,which is complicated in process and requires a large amount of calculation.Especially in the process of optimization calculation and parameter identification,the ablation model needs to be called many times,so it is necessary to construct an ablation surrogate model to improve the computational efficiency under the premise of ensuring the accuracy.In this paper,the Gaussian process model method is used to construct a thermal protection material ablation surrogate model,and the prediction accuracy of the surrogate model is improved through optimization.

Numerical Estimation of the Thermal Response of Thermal Protective Clothing-Air Gap-Human Skin Micro-system

Thermal protective clothing has been recognized as the primary shielding against emergency fire hazard and inflammable gas leakage. Therefore,the thermal response of human covered with thermal protective clothing under high temperature is the key work to investigate the thermal insulation of thermal protective clothing. A coupling model composed of thermal protective clothing,air gap and human skin is established and the temperature of the micro-system is numerically solved via the finite element method( FEM).Especially,the heat transfer of air gap located between clothing and human skin considering conduction and radiation is established while the human skin layers involve the effect of blood perfusion. Then the effect of thermophysical properties( thermal conductivity and volumetric capacity) of fabric and thickness of fabric and air on the thermal response of the micro-system is elucidated and compared.The results indicate that the volumetric heat capacity of fabric is the key parameter to affect the thermal shielding performance of thermal protective clothing,and the thicker fabric thickness and air gap thickness can improve the thermal protective properties of the micro-system.

Self-actuating protection mechanisms for safer lithium-ion batteries

Safety issue is still a problem nowadays for the large-scale application of lithium-ion batteries(LIBs)in electric vehicles and energy storage stations.The unsafe behaviors of LIBs arise from the thermal run-away,which is intrinsically triggered by the overcharging and overheating.To improve the safety of LIBs,various protection strategies based on self-actuating reaction control mechanisms(SRCMs)have been proposed,including redox shuttle,polymerizable monomer additive,potential-sensitive separator,thermal shutdown separator,positive-temperature-coefficient electrode,thermally polymerizable addi-tive,and reversible thermal phase transition electrolyte.As build-in protection mechanisms,these meth-ods can sensitively detect either the temperature change inside battery or the potential change of the electrode,and spontaneously shut down the electrode reaction at risky conditions,thus preventing the battery from going into thermal runaway.Given their advantages in enhancing the intrinsic safety of LIBs,this paper overviews the research progresses of SRCMs after a brief introduction of thermal runaway mechanism and limitations of conventional thermal runaway mitigating measures.More importantly,the current states and issues,key challenges,and future developing trends of SRCTs are also discussed and outlined from the viewpoint of practical application,aiming at providing insights and guidance for developing more effective SRCMs for LIBs.

Two Degree-of-Freedom Dynamic Theoretical Model on Tile Thermal Protection System

In order to study the dynamic behaviors of the thermal protection system(TPS)and dynamic strength of the strain-isolation-pad(SIP),a two degree-of-freedom dynamic theoretical model is presented under the acoustic excitation and base excitation. The tile and SIP are both considered as the elastic body and simplified as a mass point,a linear spring and a damping element. The theoretical solutions are derived,and the reasonability of theoretical model is verified by comparing the theoretical results with the numerical results. Finally,the influences on the dynamic responses of TPS by the structural damping coefficient of TPS,elasticity modulus and thickness of SIP are analyzed.The results show that the material with higher damping,and SIP with thicker size and lower elastic modulus should be considered to reduce the dynamic responses and intensify the security of TPS. The researches provide a theoretical reference for studying the dynamic behaviors of TPS and the dynamic strength of SIP. Besides,the dynamic theoretical model can be used as a quick analysis tool for analyzing the dynamic responses of TPS during the initial design phase.

Porous Ultra-high Temperature Ceramics for Ultra-high Temperature Thermal Protection System

Ultra-high temperature ceramics(UHTCs)are a family of borides,carbides and nitrides of transition elements such as hafnium,zirconium,tantalum and niobium.They exhibit the highest known melting points,good mechanical strength,good chemical and thermal stability under certain conditions.In last decade,researchers dedicated to characterize porous UHTCs aiming to develop novel thermal insulating materials that could withstand temperatures over 2000℃.In this article,the preparation and characteristics of porous UHTCs were reviewed.Dry processing,colloidal processing and solution processing routes have been used to prepare porous UHTCs with porosities ranging from 5%to 97%and pore sizes ranging from hundreds of nanometers to hundreds of micrometers.The obtained porous UHTCs are chemically and dimensionally stable at temperatures up to 2000℃ during static state high-temperature thermal aging.

Experimental demonstration of a new concept of drag reduction and thermal protection for hypersonic vehicles

A new idea of drag reduction and thermal protection for hypersonic vehicles is proposed based on the combination of a physical spike and lateral jets for shockreconstruction. The spike recasts the bow shock in front of a blunt body into a conical shock, and the lateral jets work to protect the spike tip from overheating and to push the conical shock away from the blunt body when a pitching angle exists during flight. Experiments are conducted in a hypersonic wind tunnel at a nominal Mach number of 6. It is demonstrated that the shock/shock interaction on the blunt body is avoided due to injection and the peak pressure at the reattachment point is reduced by 70% under a 4° attack angle.

Research progress on thermal protection materials and structures of hypersonic vehicles

Hypersonic vehicles represent future trends of military equipments and play an important role in future war. Thermal protection materials and structures, Which relate to the safety of hypersonic vehicles, are one of the most key techniques in design and manufacture of hypersonic vehicles. Among these materials and Structures, such as metallic temperature protection structure, the temperature ceramics and carbon/carbon composites are usually adopted in design. The recent progresses of research and applica- tion of ultra-high temperature materials in preparation, oxidation resistance, mechanical and physical characterization are summarized.

Editorial: Special subject on the mechanical behavior of thermal protection materials and structures

The thermal protection materials and structures are widely used in hypersonic vehicles for the purpose of thermal insulation, and their mechanical behavior is one of the key issues in design and manufacture of hypersonic vehicles. It is our great pleasure to present the seven papers in this special subject of Theoretical ＆ Applied Mechanics Letters （TAML） and introduce the recent progresses on the mechanical behavior of thermal protection materials and structures by the authors.

Effect of Phase Change Materials on the Thermal Protective Performance of the Multi-layered Fabrics Examined by TPP Tester under Flash Fire

Cotton fabrics treated with phase change materials( PCMs)were used in multi-layered fabrics of the fire fighter protective clothing to study its effect on thermal protection. The thermal protective performance( TPP) of the multi-layered fabrics was measured by a TPP tester under flash fire. Results showed that the utilization of the PCM fabrics improved the thermal protective performance of the multi-layered fabrics. The fabric with a PCM add on of 41. 9% increased the thermal protection by 50. 6% and reduced the time to reach a second degree burn by 8. 4 s compared with the reference fabrics( without PCMs). The employment of the PCM fabrics also reduced the blackened areas on the inner layers. The PCM fabrics with higher PCM melting temperature could bring higher thermal protective performance.

Effect of Air Gap under Fabric on Thermal Protective Performance Using an Improved Apparatus

The bench top test is one of the most important and effective methods to evaluate the total thermal protective performance(TPP) of firefighters' protective clothing,which is greatly influenced by the air gaps entrapped.In this paper,to investigate the effect of air gap width on TPP,a new improved apparatus with two height changeable buttons to hold the thermal sensor was developed to get a series of air gap sizes from 0 mm to 40 mm.The TPP of two types of flame-resistant outer fabrics was measured with TPP test apparatus respectively.Analysis of temperature rise with each air gap width was made to determine the effects of different air gaps on protective performance.It was indicated that air gap size had great effect on TPP of fabrics in the bench top test.An air gap width above 8 mm was suggested for the thermal protective clothing design.

Comparison of Thermo-Structural Responses for Integrated Thermal Protection Panels with Different Corrugated Core Configurations

To explore new light-weight integrated thermal protection system panel configuration and gain good insight into the responses mechanism,heat transfer and structural field analysis for one single-layer and four double-layer corrugated core panels were performed. The obtained the temperature,buckling,stress and deflection responses were compared,and the deflection and stress distributions as well as thermal buckling mode at the time were discussed for the considered configurations when the temperature difference between the top and bottom face sheet was maximum. The results demonstrated that the non-orthogonal and hat-stiffened double-layer structures provide superior performance to resist thermal buckling deformation in comparison with other configurations. The useful information is provided for the forthcoming optimization in which thermal buckling is considered as critical design driver.

高温界面接触热阻试验

飞行器组件之间不可避免地存在接触热阻,接触热阻的准确获取对热结构细节设计至关重要。针对高温、高压同时作用下接触热阻测量的难题,基于静态热流法自主研制了高温界面接触热阻测量装置。该装置能够有效测得给定界面压力、最高热面温度1500℃固体结构界面间的接触热阻。利用该装置,成功开展了三类热结构组件高温界面接触热阻测量试验,获得了压力、温度和界面粗糙度对结构界面接触热阻的影响规律。试验结果表明,测量装置稳定可靠、温度和压力载荷模拟精度高、试验易实施,试验结果可以为飞行器热结构设计与工程应用提供依据。

A novel predictive braking energy recovery strategy for electric vehicles considering motor thermal protection

Braking energy recovery(BER)aims to recover the vehicle's kinetic energy by coordinating the motor and mechanical braking torque to extend the driving range of the electric vehicle(EV).To achieve this goal,the motor/generator mode requires frequent switching and prolonged operation during driving.In this case,the motor temperature will unavoidably rise,potentially triggering motor thermal protection(MTP).Activating MTP increases the risk of motor component failure,and the EV typically disables the BER function.Thus,maximizing BER while reducing the risk of motor overheating is a challenging problem.To address this issue,this article proposes a predictive BER strategy with MTP using the non-smooth Pontryagin Minimum Principle(NSPMP)for EVs.Firstly,a Markov long short-term memory(MLSTM)model is designed to obtain future velocity information.Secondly,the BER problem with MTP in the studied EV is embedded in a model predictive control(MPC)framework.Then,under the MPC framework,the NSPMP strategy is proposed to resolve the problem of MTP.Finally,the performance of the proposed strategy is verified through simulation and a hardware-in-loop test.The results show that in two real-world driving cycles,compared to the rule-based strategy,the proposed strategy reduced power consumption by 1.24%and0.96%,respectively,and effectively limited motor temperature.Additionally,under global cycle conditions,this strategy demonstrated better MTP control performance compared to other benchmark strategies.

电厂热控系统中热控保护装置故障研究

热控保护装置是电厂热控系统的重要组成部分,在多重因素的影响下,可能出现误动或拒动、软件程序故障等问题,严重影响电厂的安全、稳定运行。基于此,针对热控保护装置的常见故障,分析故障原因并提出具体的处理措施。此外,为确保热控保护装置性能稳定,还提出了定期检测维修、完善故障报警系统等保护措施,以期为相关从业人员提供借鉴与参考。

基于关联规则的火电厂热工保护用机电系统故障分析方法

传统火电厂热工保护用机电系统故障分析方法直接对故障信号高维特征进行解析,未对系统故障微弱信号进行高效解耦提取,造成传统方法故障识别率低,因此提出基于关联规则的火电厂热工保护用机电系统故障分析方法。对系统故障微弱信号进行高效解耦提取,并在此基础上基于关联规则进行故障信号高维特征解析,设计火电厂热工保护用机电系统故障自动检测流程,实现系统故障自动检测。实验结果表明,该研究方法故障识别率更高,故障识别效果更好。

某火电厂集控室消防细水雾抑制火灾模拟分析

以某火电厂建设工程集控室消防系统设计为例,利用PyroSim火灾模拟软件建立试验模型,模拟研究在不同压力和角度下细水雾对T^(2)模式自由火的抑制过程,对比分析细水雾在喷头角度为45°、60°、90°和喷头压力为1 MPa、2 MPa、5 MPa时的火焰温度变化曲线,模拟空间内的CO、O_(2)浓度变化、灭火时间和灭火用水量等情况。结果表明:灭火过程可以分为喷雾初期的抑制阶段、火焰强化膨胀阶段和细水雾再次抑制阶段3个阶段;水雾压力越大,灭火效果越明显;喷射角度为90°的细水雾灭火过程中火焰温度变化平稳,适合作为集控室的自动灭火喷头参数;垂直布设的中压细水雾具有更好的实用价值。

火电厂热控保护系统故障分析与预防措施研究

为了解决火电厂热控保护系统故障问题,提高火电机组的安全可靠性和经济效益,分析控制主机硬件故障、外围元件故障、软件系统故障等常见故障,提出具体的故障处理措施及预防对策。期望本研究能够为相关从业人员提供借鉴,为火电厂热控保护系统的故障分析和预防提供参考,进而提高火电机组的运行效率和安全性。