圆锥形喷管的脉冲激光推进能量相似律数值模拟

 为了验证理论分析得到的圆锥形喷管在单脉冲条件下的激光推进能量相似律,用2维轴对称辐射流体动力学方法,计算得到了不同构形的推进性能参数,分析了锥角、长度、无量纲因子、入射激光能量对冲量、冲量耦合系数的影响。计算揭示的激光推进能量相似律合理,在理论模型可以描述的范围内,其定性规律与理论分析、实验结果之间相互印证。结果表明：当锥角固定时,冲量和冲量耦合系数随无量纲因子先增大后减小,极大值对应的无量纲因子仅与气体比热比相关;当无量纲因子固定时,冲量随入射激光能量增加而增大,冲量耦合系数受激光能量的影响很小,冲量和冲量耦合系数均随锥角增大而单调减小。     

带延长圆柱形喷管激光推力器推进性能数值研究北大核心CSCD

针对抛物形喷管与圆柱形喷管相组合的带延长圆柱形喷管激光推力器模型,通过求解含激光能量源项的流体力学方程组,计算得到了不同单脉冲激光能量条件下3种构形参数对冲量耦合系数和推力的影响。结果显示带延长圆柱形喷管可获得高于600N/MW的冲量耦合系数,同时表明冲量耦合系数随圆柱喷管长度的增加而增大并趋于饱和,圆柱喷管饱和长度与激光能量呈线性关系。冲量耦合系数随抛物形喷管张角的增大先增大后减小,对于总长度为100mm的喷管,半张角在33°左右时取得最大值且受激光能量的影响很小。冲量耦合系数随点火位置的增大也存在最大值,最大值对应的点火位置与激光能量成线性关系。     

悬摆法测量气体推进剂激光推进冲量耦合系数

 给出了悬摆法测量激光推进冲量耦合系数的原理，分别以空气、氩气、氮气和氦气为推进剂，用悬摆法测量了抛物形推力器在能量不同的单脉冲TEA CO₂激光辐照下的冲量耦合系数。实验结果表明：氩气的冲量耦合系数最高，氦气的冲量耦合系数最低；在实验测试的激光能量范围内，4种推进剂气体的激光推进冲量耦合系数基本上都随着激光能量的增加而线性增大，冲量耦合系数的相对误差为5.4%~6.4%。实验结果与国外相关实验结论一致。     

线性喷管构形对激光推力器冲量耦合系数的影响

 喷管是激光推力器的重要组成部分。在设计喷管构形时，可以使其与聚光系统一体化设计，也可以把聚光系统和喷管分离设计。针对聚光系统与喷管分离设计的工作模式，建立了一种辅助聚焦系统的点火模型。通过改变喷管的构形，分析了圆锥形、圆台形喷管的冲量耦合系数与喷管顶部直径与出口直径之比以及喷管长度与出口直径之比之间的关系。通过对推力曲线的分析，阐述了喷管结构参数对其性能影响的原因。研究结果显示，圆台形喷管的推进性能优于圆锥形和圆筒形。     

单脉冲能量对吸气式激光推进冲量耦合系数的影响

 利用透镜聚焦,抛物面喷管约束,结合复摆和光指针测量系统研究了单脉冲能量对吸气式激光推进冲量耦合系数的影响,实验中通过调节激光器工作电压和硅片衰减实现了脉冲能量5~70 J范围的有效拓展;进一步采用纳秒分幅高速相机拍摄了24 J能量下的流场纹影照片。结果表明：在4~9 J低能量和32~70 J较高能量区间,冲量耦合系数均较稳定;9~32 J能量下冲量耦合系数呈线性增长趋势,变化范围(6.5~21.0)×10^-5 N·s·J^-1;纹影照片显示流场演化经历了激光支持爆轰波、爆燃波和激波3个阶段,耦合系数的变化规律源于不同单脉冲能量对应不同的能量沉积效率。     

激光烧蚀冲量耦合系数解析计算模型

利用激光清除空间碎片被认为是一种可行手段,冲量耦合系数是数值计算空间碎片清除效果的重要参数。建立了激光烧蚀冲量耦合系数解析计算模型,引入电离度参数,将气化机制与等离子体机制两种机制下的冲量耦合系数解析计算模型联系起来,建立统一的耦合系数解析模型。以空间碎片常见材料Al为例,计算得到冲量耦合系数、电离度、激光功率密度三者之间的变化关系。随着激光功率密度的增加,气化机制逐渐向等离子体机制过渡,电离度增加,直至完全电离,冲量耦合系数先增加后减少,并且在等离子机制占主导情况下达到最优冲量耦合。     

激光推进冲量耦合系数测量方法比较

 针对测量冲量耦合系数的水平导轨法和冲击摆法,分别进行了误差计算和实验研究。计算结果表明:水平导轨测量法的相对误差（4.6%）略小于冲击摆测量法的相对误差（6.1%）,其中位移参数和最大摆角的测量精度对于相对误差的影响最大。实验结果表明:两种方法的测量结果基本一致,冲量耦合系数均随着入射脉冲能量的增大而增大,且两组数据相差在6%以内,在入射脉冲能量为3~14 J时,冲量耦合系数最高可达260 N·MW^-1。     

采用靶摆式探头测量软X射线辐射材料产生的喷射冲量

 采用靶摆旋转运动式冲量探头，在“强光一号”加速器上，测量了脉冲软X射线辐射材料产生的喷射冲量。实验结果表明，在平均能量为0.21 keV、平均半高宽为36 ns和平均能注量为143 J/cm²的软X射线辐射下，测得一种复合材料的喷射冲量耦合系数为0.70 Pa·s/(J·cm^-2)。     

声子色散对量子点中弱耦合磁极化子声子平均数的影响

利用线性组合算符和幺正变换相结合的方法,研究了声子色散对抛物量子点中弱耦合磁极化子电子周围光学声子平均数的影响。计及纵光学（ LO）声子色散,在抛物近似下导出了基态能量与量子点有效受限长度、声子色散系数、回旋共振频率以及电子－声子耦合常数之间的关系,电子周围光学声子平均数与声子色散系数以及电子－声子耦合常数的关系。数值计算结果表明在弱耦合情况下抛物量子点中磁极化子的基态能量随声子色散系数的增大而减小;电子周围光学声子平均数随声子色散系数增大而增大,随电子－声子耦合常数的增大而增大。     

声子色散对量子点中弱耦合磁极化子声子平均数的影响

利用线性组合算符和幺正变换相结合的方法,研究了声子色散对抛物量子点中弱耦合磁极化子电子周围光学声子平均数的影响．计及纵光学(LO)声子色散,在抛物近似下导出了基态能量与量子点有效受限长度、声子色散系数、回旋共振频率以及电子-声子耦合常数之间的关系,电子周围光学声子平均数与声子色散系数以及电子-声子耦合常数的关系．数值计算结果表明在弱耦合情况下抛物量子点中磁极化子的基态能量随声子色散系数的增大而减小;电子周围光学声子平均数随声子色散系数增大而增大,随电子-声子耦合常数的增大而增大．     

Influence of the opening angle of a conical supersonic nozzle on the structure of initial interval of non-isobaric jet

The ideal gas exhaustion from an infinite volume into a gas at rest through a supersonic conical Laval nozzle is considered. The problem was solved numerically by steadying in time in a unified formulation for the regions inside the nozzle and in the ambient environment. In such a statement, the nozzle outlet section is no internal boundary of the region under consideration, and there is no need of specifying the boundary conditions here. Local subsonic zones arising in the flow lie inside the region under consideration, which eliminates the possibility of using a marching technique along one of the coordinates. The numerical solution is constructed by a unified algorithm for the entire flow region, which gives a possibility of obtaining a higher accuracy. The computations are carried out in the jet initial interval, where, according to monograph [1], the wave phenomena predominate over the viscous effects. The exhaustion process is described by the system of gas dynamics equations. Their solution is constructed with the aid of a finite difference Harten’s TVD (Total Variation Diminishing) scheme [2], which has the second approximation order in space. The second approximation order in time is achieved with the aid of a five-stage Runge-Kutta method. The solution algorithm has been parallelized in space and implemented on the multi-processor computer systems of the ITAM SB RAS and the MVS-128 of the Siberian Supercomputer Center of SB RAS. The influence of the semi-apex angle of the nozzle supersonic part and the pressure jump between the nozzle outlet section and the ambient environment on the flow in the initial interval of a non-isobaric jet is investigated in the work. A comparison with experimental data is presented. The computations are carried out for the semi-apex angles of the nozzle supersonic part from 0 (parallel flow) to 20 degrees. For all considered nozzles, the Mach number in the nozzle outlet section, which was computed from the one-dimensional theory, equaled three. Computations showed that in the case of flow acceleration in a conical supersonic nozzle, its geometry is one of the main factors determining the formation of the jet initial interval in ambient environment.     

喷管构形和聚焦位置对雾化水滴推进性能的影响

以抛物形和锥形喷管为研究对象,开展了雾化水滴的脉冲式TEA CO<,2>激光推进性能的实验研究.冲营的大小由压电传感器测量得出的推力随时间的变化关系曲线得出.雾化水滴的能量转化效率达到了26.1%,比冲达到了102 s.对于较短的喷管而言,聚焦位置距离喷管顶部越近,推进性能参数越高.喷管构形对推进性能的影响比较明显,抛...     

Design and characterization of nozzles and solid propellants for IR laser propulsion

In this article, we present an experimental study of the effect of conical section nozzles coupled to solid targets on laser ablation propulsion. The impulse produced on the target by laser ablation was measured in terms of the coupling coefficient C _m using a piezoelectric (PZT) sensor. The standard deviation of the PZT signal was used as an estimator of the transferred impulse. The ablation was performed with a TEA CO₂ laser at room temperature and atmospheric pressure. The targets were pellets of 90/10 % w/w Zn/CaCO₃ concentration ratio. Aluminum nozzles with conical section were coupled to these propellant pellets. A comparative study of the variation of C _m using nozzles of different inlet and outlet diameters of the ejected material as well as of different heights was made. The results demonstrate that for the pellet composition analyzed, as the nozzle’s height increases and its diameter decreases improvements up to 250 % respect to the target without nozzle are obtained. These are promising results for the potential development of laser ablation microthrusters.     

任意长度喷管型面设计方法在气动激光器喷管设计中的应用

 将一种新的任意长度喷管型面设计（ALN）方法应用于气动激光器喷管型面设计,在相同的喷管出口设计马赫数、喷管喉部高度及喷管扩张段长度条件下,设计了4条ALN方法喷管型面,并和一条最短长度（MLN）喷管型面作对比,采用2维气动激光器增益场仿真方法对5个喷管的小信号增益场进行仿真。计算结果表明:ALN方法可以有效地实现增益场分布的控制,选择合理的设计参数得到的喷管长度比MLN喷管更短,小信号增益更大。     

Experimental study of the influence of annular nozzle on acoustic characteristics of detonation sound wave generated by pulse detonation engine

Acoustic characteristics of the detonation sound wave generated by a pulse detonation engine with an annular nozzle, including peak sound pressure, directivity, and A duration, are experimentally investigated while utilizing gasoline as fuel and oxygen-enriched air as oxidizer. Three annular nozzle geometries are evaluated by varying the ratio of inner cone diameter to detonation tube exit diameter from 0.36 to 0.68. The experimental results show that the annular nozzles have a significant effect on the acoustic characteristics of the detonation sound wave. The annular nozzles can amplify the peak sound pressure of the detonation sound wave at 90° while reducing it at 0° and 30°. The directivity angle of the detonation sound wave is changed by annular nozzles from 30° to 90°. The A duration of the detonation sound wave at 90° is also increased by the annular nozzles. These changes indicate that the annular nozzles have an important influence on the acoustic energy distribution of the detonation sound wave, which amplify the acoustic energy in a direction perpendicular to the tube axis and weaken it along the direction of the tube axis.     

激光推力器喷管热防护实验研究

 基于激光推力器喷管热烧蚀因素分析，初步提出了反射式和吸收式两种喷管热防护方法，并相应设计了两种喷管。以10 kW级脉冲式CO₂激光器为光源，三次反射激光推力器为对象，进行了两种方式下两种喷管的热防护初步实验研究。结果表明：两种喷管均发生不同程度烧蚀，与相对聚焦位置和激光作用时间有关；反射式热防护通过喷管光学表面对透射激光能量进行二次聚焦，以及良好的循环冷却，可能成为将来激光推力器喷管热防护的备选方案之一。     

不同气体工质对激光推力器冲量耦合系数的影响

通过冲击摆实验,测量了激光推力器在不同气体工质(氩气,氦气)、不同工作压力条件下的冲量耦合系数,比较了不同气体对激光推力器冲量耦合系数的影响.实验结果表明:冲量耦合系数随着环境压力的下降而下降,并且下降趋势越来越快;在氩气中测量的冲量耦合系数比氦气的高;实验产生误差的主要因素是摆角的测量误差.