几何参数对逆流矢量喷管性能的影响研究

采用数值模拟研究了逆流矢量喷管中主要几何参数（二次流道高度G与外套管轴向长度L、横向高度C、出口边缘斜切角θ）对气动性能的影响。结果表明,L或G的增加均提高了矢量角,减少了合成推力系数,但较小的G（如0.2）更容易发生主流附体。当C=H（主喷管出口高度）时气动性能达到最佳,所对应的矢量角最大。θ对气动性能的影响较小,但对矢量角的最大值起到限制作用。     

轨/姿控火箭发动机推力矢量动态测试系统测量原理与动态性能

 基于国防和航天对轨/姿控火箭发动机脉冲推力矢量动态测试的重大需求,以压电石英为力敏,研制了压电式推力矢量动态测试系统。在探讨推力矢量描述参数及计算的基础上,提出了一种推力矢量测量方案。根据静力平衡原理,推导了求解推力矢量的一般方程。改进了非线性模态分析方法,以所获取的实际动态响应曲线为基础,建立了测试系统的理论动力学模型,利用拉普拉斯变换与逆变换、卷积定理,研究了系统的动态性能和脉冲推力测量性能。针对脉冲推力测量过程中所产生的误差,提出了一种基于理论动力学模型的加速度补偿算法。实验结果证明了测量方案和加速度补偿算法的可行性。     

基于奇异值差的转静件碰摩故障诊断方法研究

针对目前奇异值分解方法在航空发动机碰摩故障诊断处理中的不足,在基于矩阵分析推导奇异值残差重构信号能量成分的基础上,提出了利用奇异值残差重构突变信息的方法并建立了诊断流程.利用仿真信号对提出的方法进行了验证,得出了该方法与理论分析相符合.最后将其应用于某型航空发动机实测数据的处理,成功地判断出该发动机碰摩的时刻和碰摩故障的延展,结果表明该方法对航空发动机碰摩故障的诊断具有良好的效果.      

Direct Optimization of Low-thrust Many-revolution Earth-orbit Transfers

Low-thrust Earth-orbit transfers with 10^?5-order thrust-to-weight ratios involve a large number of orbital revolutions which poses a real challenge to trajectory optimization. This article develops a direct method to optimize minimum-time low-thrust many-revolution Earth-orbit transfers. A parameterized control law in each orbit, in the form of the true optimal control, is proposed, and the time history of the parameters governing the control law is interpolated through a finite number of nodal values. The orbital averaging method is used to significantly reduce the computational workload and the trajectory optimization is conducted based on the orbital averaging dynamics expressed by nonsingular equinoctial elements. Furthermore, Earth's shadowing and perturbation effects are taken into account. The optimal transfer problem is thus converted to the parameter optimization problem that can be solved by nonlinear programming. Taking advantage of the mapping between the parameterized control law and the Lyapunov control law, a technique is proposed to acquire good initial guesses for optimization variables, which results in enlarged convergence domain of the direct optimization method. Numerical examples of optimal Earth-orbit transfers are presented.     

一种电动飞机电推进系统的能效优化方法

电动飞机依靠电推进系统为飞机提供所需的动力,而电动飞机蓄电池的能量密度制约了飞机续航能力的提升。在蓄电池能量密度受限的条件下,进行电推进系统能效优化,提高电推进系统效率,降低电推进系统损耗,对增加飞机的续航时间具有重要意义。以某双座可调定桨距螺旋桨电动飞机电推进系统为例,依据飞机的飞行任务剖面搭建了飞机电推进系统在起飞及巡航阶段的系统损耗模型,以可调定桨距螺旋桨桨矩角为优化变量,以飞机完成一次飞行任务剖面能耗最小为目标,提出一种适于可调定桨距螺旋桨电动飞机电推进系统的能效优化方法。为了验证该方法的有效性,搭建样机测试平台,进行了样机试验,试验结果表明：该能效优化方法能够有效提高飞机电推进系统效率,使飞机完成一次飞行任务剖面的系统能耗降低了8%以上。     

一种航天器用先导级电磁阀的新型结构设计

提出了一种新型两位三通结构的先导级电磁阀设计方案,由2组永磁体和3组控制线圈构造3条永磁锁位磁路和2条电磁偏置磁路,不仅实现了阀门的小型化结构和无功耗位置保持,而且提高了阀门的密封可靠性.这种阀门可以作为大推力发动机推进剂主阀的先导级控制阀,能够满足在轨长期应用的需求.通过电磁场有限元分析和产品样机试验的方法,对设计方案的可行性进行验证,验证结果表明新型先导级电磁阀的各项性能指标均达到设计目标.     

超燃冲压发动机推阻力特性研究综述

超燃冲压发动机由进气道、燃烧室和尾喷管等部件构成,推阻力是其最重要的特性参数。回顾了超燃冲压发动机部件级推阻力特性和整体推阻力特性研究现状,介绍了超燃冲压发动机推阻力特性研究方法和测量技术。建议今后研究过程中关注以下几个问题：研究精确的自由射流试验测量技术,研究流场均匀性对发动机性能的影响,开发高精度仿真平台。     

基于膨胀度可控的SERN设计及试验验证

单边膨胀喷管（SERN）是超燃冲压发动机的关键部件,由于其几何非对称,在发动机点火/熄火瞬间,SERN会产生较大的冷热态俯仰力矩差,影响飞行器的稳定性。现有解决方法主要是利用几何/气动调节方式,但都有不利影响。本文提出了基于膨胀度可控的SERN设计的新方法,将采用该方法得到的喷管模型B与基准喷管模型A进行了对比研究,并对模型B进行缩比冷流试验,试验与数值模拟结果吻合良好。研究结果表明：飞行马赫数为4.5时,模型B的推力系数比模型A仅仅下降了0.1%,而模型B比模型A的冷热态俯仰力矩差减小了80.49%;飞行马赫数为6.5时,模型B的推力系数比模型A不仅上升1.1%,同时模型B比模型A冷热态俯仰力矩差还下降12.73%,验证了设计思想的正确性,为提高SERN俯仰力矩性能提供了一种新的思路。     

Numerical investigation of the nonreacting and reacting flow fields in a transverse gaseous injection channel with different species

The mixing and combustion process has an important impact on the engineering realization of the scramjet engine. The nonreacting and reacting flow fields in a transverse injection channel have been investigated numerically, and the predicted results have been compared with the available experimental data in the open literature, the wall pressure distributions, the separation length, as well as the penetration height. Further, the influences of the molecular weight of the fuel and the jet-to-crossflow pressure ratio on the wall pressure distribution have been studied. The obtained results show that the predicted results show reasonable agreement with the experimental data, and the variable trends of the penetration height and the separation distance are almost the same as those obtained in the experiment. The vapor pressure model is suitable to fit the relationship between the penetration height, the separation distance and the jet-to-crossflow pressure ratio. The combustion process mainly occurs upstream of the injection port, and it makes a great difference to the wall pressure distribution upstream of the injection port, especially when the jet-to-crossflow pressure ratio is large enough, namely 17.72 and 25.15 in the range considered in the current study. For hydrogen, the combustion downstream of the injection port occurs more intensively, and this may be induced by its smaller molecular weight.     

Dawn′s exploration of Vesta

On 16 July 2011, after completing nearly four years of interplanetary flight, Dawn entered orbit around (4) Vesta, the second most massive body in the main asteroid belt. Dawn used solar electric propulsion to spiral to six different orbits to accomplish its science campaign. Although the transfers to progressively lower orbits presented significant challenges, all were executed smoothly. During its nearly 14 months in orbit, Dawn spiraled down to 210 km above the surface and back up before initiating the gradual departure to travel to dwarf planet (1) Ceres for a 2015 rendezvous. Dawn′s exploration of Vesta has shown it to be geologically complex and fascinating, resembling terrestrial planets more than typical asteroids. Among the principal features is a 500-km-diameter impact basin within which is the second tallest mountain known in the solar system. This paper presents Dawn′s operations at Vesta and summarizes the principal findings.