【作者】 黄波；

【导师】 陈雄； 李映坤；

【作者基本信息】 南京理工大学 ， 飞行器设计， 2020， 硕士

【摘要】 双脉冲发动机解决了固体火箭发动机推力不可调整和间断的问题,采取具有阻燃隔热功能的脉冲隔离装置,将燃烧室分隔成两个拥有独立点火系统的燃烧室,控制点火间隔,精确分配推力,具有机动性佳、有效射程远、飞行末速度大、隐身效果好等优点。本文以轴径混合式双脉冲发动机为研究背景,针对双脉冲发动机软质隔层热载荷下烧蚀特性展开研究,结合实验分析与数值模拟,编制了绝热材料传热烧蚀过程仿真程序,深入探究了Ⅰ脉冲工作环境下EPDM软质隔层材料的热解烧蚀过程,对发动机热防护结构设计具有重要的参考价值。(1)模拟计算了轴径混合隔层式双脉冲发动机Ⅰ脉冲工作时的两相流内流场,得到了流场流动特性参数和软质隔层工作热载荷参数。结果表明,颗粒相热惯性大,温度降幅小,气固相之间存在温度和速度滞后,导致喷管轴线处温度比同截面其它位置高,马赫数却更低。颗粒随流性很好,被气流带着朝喷管运动,未进入燃烧室上游。部分颗粒与收敛段碰撞反弹后喷出。随着燃面后移,颗粒运动起点离轴线越远,碰撞位置越靠收敛段上端,轨迹更为集中。整个过程鲜有颗粒向上游运动,对隔层未产生显著烧蚀冲刷作用。(2)采取热失重实验和激光烧蚀炭化实验对EPDM材料进行了研究。对热失重数据分析,获得了材料的热解动力学参数。观测激光烧蚀炭化过程和分析烧蚀炭化前后形貌,得到了材料烧蚀炭化结构及元素含量变化。热失重质量损失分三个阶段:样品脱水期;主要热失重区间,损失速率快,质量损失多;热解结束。激光烧蚀炭化后,呈原始材料层、热解层和炭化层三层烧蚀结构,热解层孔隙分布不均,存在大块基体。炭化层为疏松多孔介质结构,基体充分炭化,空洞无规则排列。(3)针对热解炭化类绝热材料烧蚀过程,提出了一种材料比热容、热导率等参数随时间和温度变化的数学模型,并编制了变热物性烧蚀计算程序。推导建立了热解气体变热物性模型、材料密度模型和材料比热容及热导率模型。采取基于格心的有限体积法对控制方程离散,温度偏导数通过Jacobian变换计算,时间推进采用三阶龙格库塔法,编制了变热物性烧蚀程序。通过两个热传导算例,及与经典烧蚀实验结果和常热物性计算结果对比,表明对热解炭化类热防护材料热解烧蚀过程仿真具有较高的准确性,充分验证了该程序的可靠性,为模拟Ⅰ脉冲工作下隔层烧蚀过程提供了求解平台和理论依据。(4)结合模拟得到的Ⅰ脉冲工作两相流内流场特性参数及热载荷参数,和建立的变热物性模型,研究了给定热流作用下芳纶/EPDM绝热材料能量扩散过程、热解炭化过程和热失重过程,并对影响隔层热解烧蚀过程的三个因素燃气热流密度、软质隔层厚度和Ⅰ脉冲工作时间展开了探究。获得了材料内部温度、密度分布,热导率、比热容变化历程,热解层、炭化层厚度-时间曲线等热解烧蚀热响应特性参数。热流作用初期,材料上表面升温迅速,能量不断向内扩散,因热解吸热、热解气体逸出携带能量和向外辐射能量导致扩散速率下降,温度推进速率降低。热流持续作用,炭化层厚度前期增加较快,而后减慢近似成线性增长。温度对热解反应速率的影响呈指数变化趋势,直接导致近上表面部分热解反应速率极快,而离上表面越远则越慢,且趋势较为明显,当地热解气体生成率随距离下降极快。更多还原

【Abstract】 The dual pulse motor(DPM)solves the inherent problems of solid rocket engine that the thrust can not be adjusted and interrupted.DPM adopts the pulse isolation device with the functions of flame-retardant and heat insulation,which divides the combustion chamber into two combustion chambers with independent ignition systems.The ignition interval is controlled and accurately distributed.It has the advantages such as excellent maneuverability,long effective range,high speed at the end of flight,and good stealth effect.In this dissertation,the application of axial-diameter hybrid DPM is the research background.The ablation characteristics of the soft compartment wrapping a Ⅱ pulse grain under thermomechanical loadings were studied.The experimental analysis and numerical simulation are combined to establish a more accurate thermal insulation predictive model of material during heat transfer and ablation process to deeply study of the pyrolysis and ablation process of EPDM soft compartment material under Ⅰpulse working environment,which contribute a lot for the design of thermal protection structure of DPM.The main contents of this dissertation are as follows:(1)The internal flow field of the two-phase flow of the axial-diameter hybrid DPM duringⅠ pulse operation was simulated and the parameters of the flow field and the working environment of the soft compartment are obtained.The results reveal that the particle phase has a large thermal inertia,a small temperature drop,and a temperature and velocity lag between the gas-solid phase,resulting in the nozzle axis temperature being higher than other locations on the same section,while Mach number is lower.The particles follow the flow very well,and are carried by the airflow towards the nozzle,without entering the upstream of the combustion chamber.Part of the particles collided with the convergence section and bounced out.As the burning surface moves backward,the farther the particle’s starting point is from the axis,the closer the collision position is to the upper end of the convergence section,and the trajectory becomes more concentrated.During the whole process,few particles moved upstream,and there was no significant ablation and erosion effect on the soft compartment.(2)Experimental studies on the thermal weight loss and laser ablation carbonization were used to study the EPDM soft barrier material.By analyzing the thermal weight loss data,the pyrolysis kinetic parameters of the soft barrier material were obtained.By observing the laser ablation and carbonization process and analyzing the morphology before and after the ablation carbonization,the changes in the structure and element content of the material were obtained.Thermal weightlessness and mass loss are divided into three stages: the sample dehydration period;the main thermal weightlessness interval,with rapid loss rate,and large mass loss;the pyrolysis ends.After laser ablation and carbonization,the three-layer ablation structure of the original material layer,the pyrolysis layer and the carbonization layer was observed.The carbonized layer has a fully pyrolyzed and carbonized matrix,and randomly arranged cavities,which confirms the correctness of the three-layer pyrolysis layer model.(3)In view of the heat transfer and ablation process of pyrolytic carbonized thermal insulation model materials,a mathematical model of the specific heat capacity and thermal conductivity of the materials with time and temperature is proposed.The variable thermal properties of pyrolysis gas,material density model,material specific heat capacity and thermal conductivity model are established.A finite volume method based on the lattice center is adopted to discretize the governing equations.The temperature partial derivative is calculated by the Jacobian transformation.The time advancement is performed by the third-order Runge-Kutta method.Compared with the results of classical ablation experiments and the calculation results of normal thermal properties,it shows that the prediction of the pyrolysis process of EPDM insulation materials has higher accuracy,which fully verifies the reliability and credibility of the proposed model.(4)Combined with the simulated Ⅰ pulse working two-phase flow field characteristic parameters and the established variable thermal properties model,the energy diffusion process,pyrolysis carbonization process and thermal weight loss process of aramid / EPDM insulation material under a given heat flow were studied.The internal temperature,density distribution,thermal conductivity,specific heat capacity change history,thickness-time curve of pyrolysis layer and carbonized layer,and other thermal response characteristic parameters were obtained.In the initial stage of heat flow,the upper surface of the material heats up rapidly,and the energy continuously diffuses inward.Due to the heat of thermal desorption,the escape of the pyrolysis gas and the energy of radiation,the diffusion rate decreases and the temperature advancement rate decreases.The heat flow continues,and the thickness of the carbonized layer increases rapidly at the early stage,and then decreases almost linearly.The effect of temperature on the pyrolysis reaction rate changes exponentially,directly leading to the extremely fast pyrolysis reaction rate near the upper surface,and the slower the distance from the upper surface,and the trend is more obvious,the local pyrolysis gas generation rate decreases with distance rapidly.更多还原