超声速气流中液体横向射流一次破碎过程

发展显微成像方法获得空间分辨率为1.57 μm/pixel的近场射流瞬态图像,分析超声速气流中液体横向射流表面波演化规律。采用流体体积法获得射流的三维形态及近场流场特征,研究近场流场结构及气液作用。射流的一次破碎过程主要有表面破碎和液柱破碎。其中表面破碎由气液剪切引起的K-H不稳定主导,液柱破碎由气液加速引起的R-T不稳定主导;射流柱表面局部压力的脉动是诱导产生射流迎风面表面波并促使其沿射流方向发展的主要原因;射流柱与超声速气流作用形成背风面回流,近壁面液雾主要由表面破碎及背风面回流输运的液滴组成。     

Numerical simulation of the blast wave of a multilayer composite charge

The numerical simulation of a blast wave of a multilayer composite charge is investigated. A calculation model of the near-field explosion and far-field propagation of the shock wave of a composite charge is established using the AUTODYN finite element program. Results of the near-field and far-field calculations of the shock wave respectively converge at cell sizes of 0.25–0.5 cm and 1–3 cm. The Euler––flux-corrected transport solver is found to be suitable for the far-field calculation after mapping. A numerical simulation is conducted to study the formation, propagation, and interaction of the shock wave of the composite charge for different initiation modes. It is found that the initiation mode obviously affects the shock-wave waveform and pressure distribution of the composite charge. Additionally, it is found that the area of the overpressure distribution is greatest for internal and external simultaneous initiation, and the peak pressure of the shock wave exponentially decays, fitting the calculation formula of the peak overpressure attenuation under different initiation modes, which is obtained and verified by experiment. The difference between numerical and experimental results is less than 10%, and the peak overpressure of both internal and external initiation is 56.12% higher than that of central single-point initiation.     

Experimental research on the instability propagation characteristics of liquid kerosene rotating detonation wave

In order to study the instability propagation characteristics of the liquid kerosene rotating detonation wave (RDW), a series of experimental tests were carried out on the rotating detonation combustor (RDC) with air-heater. The fuel and oxidizer are room-temperature liquid kerosene and preheated oxygen-enriched air, respectively. The experimental tests keep the equivalence ratio of 0.81 and the oxygen mass fraction of 35% unchanged, and the total mass flow rate is maintained at about 1000 g/s, changing the total temperature of the oxygen-enriched air from 620 K to 860 K. Three different types of instability were observed in the experiments: temporal and spatial instability, mode transition and re-initiation. The interaction between RDW and supply plenum may be the main reason for the fluctuations of detonation wave velocity and pressure peaks with time. Moreover, the inconsistent mixing of fuel and oxidizer at different circumferential positions is related to RDW oscillate spatially. The phenomenon of single-double-single wave transition is analyzed. During the transition, the initial RDW weakens until disappears, and the compression wave strengthens until it becomes a new RDW and propagates steadily. The increased deflagration between the detonation products and the fresh gas layer caused by excessively high temperature is one of the reasons for the RDC quenching and re-initiation.     

Analysis of the stress wave and rarefaction wave produced by hypervelocity impact of sphere onto thin plate

Shock wave is emitted into the plate and sphere when a sphere hypervelocity impacts onto a thin plate. The fragmentation and phase change of the material caused by the propagation and unloading of shock wave could result in the formation of debris cloud eventually. Propagation models are deduced based on one-dimensional shock wave theory and the geometry of sphere, which uses elliptic equations (corresponding to ellipsoid equations in physical space) to describe the propagation of shock wave and the rarefaction wave. The “Effective thickness” is defined as the critical plate thickness that ensures the rarefaction wave overtake the shock wave at the back of the sphere. The “Effective thickness” is directly related to the form of the debris cloud. The relation of the “Effective thickness” and the “Optimum thickness” is also discussed. The impacts of Al spheres onto Al plates are simulated within SPH to verify the propagation models and associated theories. The results show that the wave fronts predicted by the propagation models are closer to the simulation result at higher impact velocity. The curvatures of the wave fronts decrease with the increase of impact velocities. The predicted “Effective thickness” is consistent with the simulation results. The analysis about the shock wave propagation and unloading in this paper can provide a new sight and inspiration for the quantitative study of hypervelocity impact and space debris protection.     

高频地波超视距雷达述评

高频(HF)地波超视距雷达(GW-OTHR)利用雷达波束绕地表面衍射作用,能探测视距外的舰船、低空飞机和巡航导弹,不仅覆盖面积大、费用低,能弥补常规微波雷达低空盲区和天波超视距雷达的近距盲区,也无需注意电离层的变化,且可反隐身、抗反辐射导弹(ARM),因而在许多国家的国民经济和国防领域中得到了广泛的应用。论述了地波沿海面传播的特性和探测能力,并对超视距雷达的发展和应用进行了介绍。     

高速方尾水面舰船兴波问题计算方法研究

将Dawson型兴波阻力计算方法推广用于高速方尾水面舰船兴波问题计算,在计算中同时计入了尾封板0静压力、尾倾与下沉等因素的影响.以两高速方尾水面舰船为例计算了兴波问题,将兴波阻力计算值与剩余阻力模型试验值进行了比较,求出了相应的相关系数.结果表明,本方法可较好地求解高速方尾水面舰船的兴波问题,兴波阻力相关系数可用于修正理论计算结果,以提高计算精度.     

雷电回击地面水平电场的解析求解

假定大地为良导电平面 ,基于DU模型计算了雷电回击地面电磁场 ,并探讨了地面水平电场的求解。对于雷电回击水平电场的两种近似求解方法———大地表面阻抗法和斜波法 ,进行了解析推导 ,并从数学上证明了两种方法在远区场的等价法。     

利用简并V型原子与光场的非共振作用隐形传送未知原子态

根据简并V型三能级原子与光场的远离共振相互作用系统的改进型有效哈密顿量 ,通过矩阵方法 ,推导出系统随时间演化的波函数 ,提出一种未知原子态的隐形传态方案。     

火炮射击声信号AR模型特征研究

针对现代炮兵战场上的目标识别问题,阐述了火炮射击声信号数据—发射波、弹道波和爆炸波的特征,介绍了火炮射击声信号AR模型谱估计的方法和步骤,利用MATLAB信号处理工具箱具体实现了三种不同类型火炮发射波的AR模型谱估计,并对一批样本成功进行了分类识别实验,探讨了火炮射击声信号AR模型特征在现代战场火炮目标识别中的意义和应用价值。     

某新型主战坦克超越射击时至友军的安全距离

在分析影响坦克超越射击时至友军安全距离主要因素的基础上,结合某新型主战坦克炮口冲击波超压试验数据,通过运用M athem atica软件对数据进行统计处理和理论分析计算,提出了某新型主战坦克超越射击时至友军的安全距离,为我军新型主战坦克安全地实施超越射击提供了可靠的理论依据。