【作者】 杨乐；

【导师】 周进；

【作者基本信息】 国防科学技术大学 ， 航空宇航科学与技术， 2007， 博士

【摘要】 电推进装置以其优越的性能广泛应用于空间飞行任务。脉冲等离子体推力器(Pulsed Plasma Thruster,PPT)是一种比冲高、功耗低、结构简单、重量轻的电磁推力器,可应用于微小卫星的位置保持、姿态控制、编队飞行等任务,成为当前国际上电推进研究的热点之一。通过理论分析、实验研究和数值模拟等多种手段,本文系统研究了平行板电极固体推进剂PPT的工作过程,分析了影响推力器性能的因素,探讨了提高推力器性能的途径。建立了PPT实验系统,包括模拟航天器飞行条件的真空系统、PPT微推力测量系统以及放电参数测量系统等。详细分析了各子系统的技术要求、指标与特性。采用电磁灭甲结构研制了微推力测量装置,解决了PPT研究中推力测量的关键技术问题。采用机电模型对PPT的性能参数进行了预估,针对不同电参数(电容器容量、初始电压、电路电阻、电子温度等)和结构参数(电极间距、电极宽度及推进剂烧蚀剖面高宽比)进行了计算分析,研究了这些参数的变化对推力器性能的影响。研制了一种平行板电极尾部馈送型PPT,在不同工况下对推力器进行了点火实验,测量获得了放电电流和电压波形、脉冲平均烧蚀质量、平均推力等工作参数,计算得到了不同工况下元冲量、比冲、推力效率等性能参数,分析了不同电参数和结构参数对推力器性能的影响。实验研究表明:在相同的放电能量情况下,采用小容量电容器、提高电容器初始电压可以有效提高推力器元冲量、比冲和推力效率;在合理的范围内增加电极长度可以提高推力器元冲量、比冲和推力效率;在相同的放电能量下,降低推进剂烧蚀剖面面积有利于提高比冲和推力效率;对于相同的烧蚀剖面面积,提高推进剂的高宽比,元冲量、比冲和效率都会提高。以局部热力学平衡和等离子体宏观电中性为基本假设,建立了基于磁流体动力学(Magnetohydrodynamic,MHD)的PPT工作过程一维非定常数学模型。模型描述了PPT内部多种重要的物理机制及其相互间的耦合作用,反映了对流和扩散产生的物质、能量和动量的输运、洛伦兹力的作用及欧姆加热、磁场扩散等物理过程。对理想MHD方程进行了特征分析,推导了其特征矩阵,采用二阶MacCormack显式格式对带欧姆加热源项的MHD方程组进行了求解。数值计算表明:电离气体主要来自于脉冲前期,经洛伦兹力加速后获得高的喷射速度,是推力的主要来源;在一次脉冲周期内,推力器放电结束后,推进剂烧蚀表面温度较长时间仍处在Teflon分解温度之上,导致推进剂的滞后蒸发,是PPT推进剂的利用效率及推力效率低的主要原因。更多还原

【Abstract】 Electric propulsion devices have been used widely in space flight mission for its superior performance. Pulsed plasma thruster (PPT) is a kind of electromagnetic thruster, which has characters of high specific impulse, low power, simplicity, light weight and so on. It can be applied in station-keeping, attitude control and formation flying requirements of micro-satellites, which has become a highlight of electric propulsion research internationally currently. By means of theoretical analysis, experimental investigation and numerical simulation, working process of parallel-plate solid-propellant PPT was studied, factors affecting thrust performance were analyzed, the way to improving thrust performance was explored.PPT experimental system was established, which includes vacuum system, micro-thrust measure system and electric parameters measure system. Technique requirements, targets and characters of experimental system were analyzed in detail. Based on electromagnetism balance micro-thrust measurement device was developed, which resolved key technique problem in PPT research.Electromechanical model was used to predict PPT performance parameters. Influences of variations of electric parameters (capacitor capacitance, initial voltage, circuit resistance and electron temperature) and configuration parameters (electrodes distance, electrode width and electrode ratio of height to width) on thruster performance were studied by numerical simulation.A breech-fed parallel-plate PPT was designed and manufactured. Ignition experiments were performed under different working conditions. Performance parameters such as discharge voltage and current waveform, ablation mass per pulse and thrust per pulse were measured, and performance parameters such as impulse bit, specific impulse, thruster efficiency were calculated. Influence of variations of electric parameters and configuration parameters on thruster performance was analyzed. The experimental results showed, at the same discharge energy smaller capacitance and higher initial voltage can effectively improve thruster impulse bit, specific impulse and thrust efficiency, within reasonable range increasing electrode length can improve impulse bit, specific impulse and thrust efficiency, at the same discharge energy smaller propellant ablation area is of advantage to specific impulse and thrust efficiency, and to the same ablation area, increasing the ratio of height to width of propellant can improve impulse bit, specific impulse and thrust efficiency.On the assumption of local thermodynamic equilibrium and quasi-neutral plasma, 1 -D PPT working process unsteady mathematic model based on magnetohydrodynamic was established, which described physics mechanisms and couple effects of mechanisms in PPT, reflected the physics progress of convection, energy and momentum transportation, Lorentz force, ohmic heating and magnetic field diffusion, etc. The eigenvalues and eigenvectors of the ideal MHD equations were analyzed and deduced. MHD equations with ohmic heating source were solved by second order MacCormack scheme. Calculation results showed, ionized gases mostly come out at the pulsed time, exhaust velocity accelerated by Lorentz force is primary source of thrust, propellant ablation surface temperature is above Teflon decompose temperature in a pulse time after discharge for a long time, which lead to late ablation of propellant to reduce the use efficiency of propellant.更多还原