激光武器发射转塔尺寸对飞机作战效能的影响

机载激光武器可以主动防御来袭导弹,大幅提升作战飞机的生存能力。为了具备更远的打击距离,激 光武器需要尽可能大的发射镜直径,但几何尺寸较大的发射转塔会对飞机的气动和隐身性能产生不利影响,降低飞机的战场生存能力。利用计算流体力学和物理光学法,分析发射转塔直径对飞机的气动性能和隐身性能 的影响,并采用基于agent的作战仿真方法研究发射转塔直径对飞机在突防作战中作战效能的影响。结果表 明:飞行速度随着发射转塔直径的增大有小幅度降低,降低幅度在2%以内;30、50和70cm 的发射转塔直径分别导致飞机的头向 RCS64%、173%和282%的增加;对于作战效能而言,激光武器发射转塔的尺寸并非越大越 好,相对于无防御措施的无人机执行突防任务,50cm的发射转塔直径可以提高77.2%的任务成功率,是三种 方案中最高的。     

转子倾斜对交错式迷宫密封动静特性的影响

建立了交错式迷宫密封数值分析模型,并通过基于微元理论的密封动力特性系数理论识别方法研究了转子倾斜对密封动静特性的影响。结果表明：转子倾斜可降低交错式迷宫密封泄漏量,倾斜角为0.6°时泄漏量降低约2.5%,且进出口压比越大,效果越显著;转子倾斜带来的交错式密封腔室几何形状与齿径向间隙变化使得腔室在周向存在压力分布不均,且随倾斜角增加而增大;密封各腔室对系统稳定性影响规律不同,与交错式迷宫密封腔室的几何特性有关,密封腔室进口靠近转子、出口远离转子的腔室局部出现逆转动方向的速度场,能提高密封系统稳定性,而密封腔室进口远离转子、出口靠近转子的腔室则降低系统稳定性;整个密封段的有效阻尼随倾斜角增大而增大,转子在密封段中心倾斜不会降低交错式迷宫系统的稳定性。     

基于CFD的某减速器飞溅润滑仿真分析与验证

为评估飞溅润滑减速器的储油结构是否合理,基于计算流体动力学方法,建立了包含机匣、螺旋锥齿轮等构件的某减速器飞溅润滑动态仿真模型,开展了气液两相流飞溅润滑流体仿真计算与分析,获得了减速器内部的滑油运动轨迹及分布云图。通过仿真分析可以发现:输入端油兜收集到的滑油量为531 mL,大于输出端收集到的滑油量65 mL;4号油兜收集到的滑油量为0 mL,结构设计存在不合理之处,并进行了飞溅润滑试验验证。仿真分析结果与试验结果的趋势一致,验证了仿真分析方法的准确性,为飞溅润滑减速器储油结构设计提供了指导。     

多维虚拟振动试验系统设计及应用

虚拟振动试验能在产品设计阶段对其进行结构动力学分析和振动环境预评估,缩短产品研制周期,节省研制费用.本文完成了振动台机电耦合建模、刚体建模、试件有限元建模和闭环控制系统设计,建立了三维虚拟振动试验系统,开展了一维和三维正弦扫描虚拟振动试验技术研究.仿真结果表明：振动台机电耦合模型的频率特性与实际振动台的试验数据吻合;激振方向会对试件的加速度响应产生显著影响;与一维振动试验结果相比,多维虚拟振动试验不仅能明显提高故障激发效率,而且可以激发试件的高阶局部模态,使其高频段内的最大动应力曲线出现多个较高峰值且幅值增幅明显.     

Numerical analysis on noise of rotor with unconventional blade tips based on CFD/Kirchhoff method

A solver is developed aiming at efficiently predicting rotor noise in hover and forward flight. In this solver, the nonlinear near-field solutions are calculated by a hybrid approach which includes the Navier-Stokes and Euler equations based on a moving-embedded grid system and adaptive grid methodology. A combination of the third-order upwind scheme and flux-difference splitting scheme, instead of the second-order center-difference scheme which may cause larger wake dissipation, has been employed in the present computational fluid dynamics (CFD) method. The sound pressure data in the near field can be calculated directly by solving the Navier-Stokes equations, and the sound propagation can be predicted by the Kirchhoff method. A harmonic expansion approach is presented for rotor far-field noise prediction, which gives an analytical expression for the integral function in the Kirchhoff formula. As a result, the interpolation process is simplified and the efficiency and accuracy of the interpolation are improved. Then, the high-speed impulsive (HIS) noise of a helicopter rotor at different tip Mach numbers and on different observers is calculated and analyzed in hover and forward flight, which shows a highly directional characteristic of the rotor HIS noise with a maximum value in the rotor plane, and the HSI noise weakens rapidly with the increasing of the directivity angle. In order to investigate the effects of the rotor blade-tip shape on its aeroacoustic characteristics, four kinds of blade tips are designed and their noise characteristics have been simulated. At last, a new unconventional CLOR-II blade tip has been designed, and the noise characteristics of the presented CLOR-II model rotor have been simulated and measured compared to the reference rotors with a rectangular or swept-back platform blade tip. The results demonstrate that the unconventional CLOR-II blade tip can significantly reduce the HSI noise of a rotor.     

民机直接维修成本系统动力学仿真研究

以民用飞机直接维修成本为研究对象,分析了成本产生的因果关系,绘制了存量流量图,建立了存量、流量、辅助变量、常量之间的关联方程以及确定其初始值;在确定模型合理的基础上,分析了模型的计算结果,并通过调整模型的参数来观察模型结果的变化以确定最优策略,为决策者提供决策支持。分析结果表明,仿真方法具有一定的实用性。     

An in situ laser induced breakdown spectroscope (LIBS) for Chandrayaan-2 rover: Ablation kinetics and emissivity estimations

A miniaturized in situ laser induced breakdown spectroscope-LIBS is one of the two lunar rover payloads to be flown in India’s next lunar mission Chandrayaan-2, with an objective to carry-out a precise qualitative and quantitative elemental analyses of lunar regolith at the proximity of the landing region. As per the imposed mission constraints and the executed design optimization studies, a compact and light-weight LIBS prototype model is developed at our premises. This paper mainly concerns with the estimation of theoretical aspects; especially on evaluation of elemental ablation parameters and signal-to-noise ratio (SNR) calculations for the designed instrument. Theoretical estimations and simulations yielded an incident laser power density of the order of 5 × 10¹⁰ W/cm² on the target surface at a defined lens-to-surface distance (LTSD) of 200 mm and revealed an SNR > 100 for most of the elements under consideration. This paper also addresses the impact of LTSD variation on detection capability. The estimation of plasma-temperatures was carried out utilizing the emission spectra obtained under high vacuum environments employing the LIBS laboratory model. Experimental investigations and the performed theoretical estimations asserted the successful operation of the configured LIBS instrument for in situ elemental analyses on lunar surface.     

Modeling solar proton access to geostationary spacecraft with geomagnetic cutoffs

Solar energetic particle (SEP) cutoffs at geosynchronous orbit are sensitive to moderate geomagnetic activity and undergo daily variations due to the day–night asymmetry of the magnetosphere. At geosynchronous orbit, cutoff rigidity also has a large directional dependence, with the highest cutoff rigidity corresponding to ions arriving from magnetic east and lowest cutoff rigidity corresponding to ions incident from the west. Consequently, during geomagnetically quiet periods, the SEP flux observed by an eastward facing particle detector is significantly lower than observed by a westward facing particle detector. During geomagnetically disturbed periods the cutoff is suppressed allowing SEPs access well inside of geosynchronous, so that the east–west SEP flux ratio approaches unity. Variations in the east–west SEP flux ratio observed by GOES Energetic Particle Sensors (EPS) have recently been reported by Rodriguez et al. (2010). In NOAA’s operational processing of EPS count rates into differential fluxes, the differential flux is treated as isotropic and flat over the energy width of the channel. To compare modeled SEP flux with GOES EPS observations, the anisotropy of the flux over the EPS energy range and field of view must be taken into account. A technique for making direct comparisons between GOES EPS observations and SEP flux modeled using numerically computed geomagnetic cutoffs is presented. Initial results from a comparison between modeled and observed flux during the 6–11 December 2006 SEP event are also presented. The modeled cutoffs reproduce the observed flux variations well but are in general too high.     

无人机伞降回收过程动力学建模与仿真

文章以无人机的降落伞回收系统为研究对象,通过对伞降回收过程中各阶段动力学特性的分析,推导了便于编程实现的矢量形式降落伞-飞行器二体系统动力学模型。在此基础上,给出了利用MAT-LAB环境的面向对象和并行计算特性搭建无人机回收过程蒙特卡罗仿真环境的一种实现方案。最后,根据仿真计算的结果对某无人机在不同条件下的回收安全性、落点散布特性等进行了计算分析,为后续总体设计方案的验证、改进和优化提供了参考依据。     

S形进气道/JT15D-4涡扇发动机地面实验与数值模拟

为进一步研究所设计的S形进气道与涡扇发动机共同工作时对发动机性能和稳定性的影响,制作了S形进气道1∶1玻璃钢模型,安装在小型涡扇发动机JT15D-4上,观察发动机在地面台架条件下的工作状态,并进行了相关数据的测量.利用CFD(Computational Fluid Dynamics)方法进行同样条件下的进气道数值仿真计算.将计算结果与实验结果相比较,结果表明:两种方法得到的数据相吻合,一方面说明所设计的S形进气道与发动机匹配良好,能够保证发动机的正常运转;另一方面说明,CFD方法可用于进气道的设计验证.