叶轮机平面叶栅的气动设计及统流计算

通过全速势方程的数值积分，利用ＡＦ２格式，给出了一种用于叶轮机中叶栅型面的气动设计和绕流计算的便捷方法，对于稳态亚音速、跨音速及超音速流动均适用。与目前普及很广的、在超音区应用人工压缩性的方案相比，该算法有明显的优势。     

涡轴八发动机的发展问题研究

根据涡轴8发动机的生产、使用现状，以及我国加入WT0后所面临的竞争压力，从技术潜力和市场前景两个方面分析了涡轴8发动机发展的有利因素，并从多方面提出了涡轴8发动机发展的可行途径。     

带顶盖的半球形静电分析器的计算机模拟

从解带顶盖的半球形90°静电分析器关于势分布的Laplace方程开始,建立了荷电粒子在分析器中的运动方程,确定了以时间为参量的粒子运动轨道,引出了传输函数和几何因子的表达式,从而提供了一套适用于带顶盖的半球形90°静电分析器的模拟方法.为了使用方便,给出了传输函数和几何因子的尺度性质.所编制的程序特别地被应用于Sablik等的分析器原型,在现在的模拟结果和Sablik等的结果的对比中,评估了本文描述的模拟技术的精确性.      

Impact of local and global factors and meteorological parameters in temporal variation of atmospheric potential gradient

In this research work, we have performed comparative diurnal variations of atmospheric Potential Gradient (PG) of fair-weather days by using the data of three stations installed in Northern, Pakistan for the year 2018. We investigated the impact of both local and global factors and meteorological parameters in the diurnal variation of atmospheric Potential Gradient on the annual and seasonal time scale. We observed two peaks, primary and secondary. This is because of the land-based measurements of annual and seasonal variations. The annual average curve of Potential Gradient of all three stations: Islamabad (CES), Muzaffarabad (MZF), and Balakot (BKT) demonstrated a notable deviation from the standard oceanic Carnegie curve. The atmospheric Potential Gradient variations are due to numerous meteorological factors e.g., air pollution, humidity, aerosol particles, fog, and temperature. Among three stations, the MZF station is located in highland (mountainous) and it demonstrated a higher atmospheric Potential Gradient. We further differentiate the results of our three stations with global results for authenticity and observed coherence between them. In addition, a positive correlation of fair-weather Potential Gradient is observed with temperature and a notable correlation between relative humidity and atmospheric Potential Gradient for all the three observatories.     

电位法测量微缺口试样的数值分析

疲劳寿命受到材料内部缺陷的制约,可以通过电位法试验获得微缺口试样的疲劳裂纹扩展规律,进而分析缺陷对材料疲劳寿命的影响。在试验前,需要预先研究试验的主要影响因素。利用COMSOL有限元软件,研究了电流输入点位置和电势差测点位置对试验精度和试验复现性的影响,计算得到不同裂纹前缘形状对应的电位法校核曲线。结果表明:(1)电流输入点位置位于试样平行于裂纹面的上下表面时,可以保证试验的复现性。(2)当测点位于裂纹面的垂直对称面上,且测点距离裂纹面垂直距离为0.06～0.1倍试样宽度时,可以同时满足测试精度和复现性。(3)当裂纹宽度和裂纹深度的比值3时,可以不考虑裂纹前缘形状对校核曲线的影响,当裂纹宽度和裂纹深度的比值≤3时,裂纹前缘形状对校核曲线的影响较大。     

Preliminary results of fair-weather atmospheric electric field in the proximity of Main Boundary Thrust,Northern Pakistan

The atmospheric electric Potential Gradient (PG) variation of fair-weather days at Muzaffarabad (MZF, Northern Pakistan) station is presented for the period of January 2015–October 2017. The present investigations focus on the diurnal variation of atmospheric PG on the seasonal and annual time scale. The fair-weather seasonal and annual average PG variation has revealed two peaks, i.e. a primary maximum peak and a secondary maximum peak. The average maximum PG value found is ～410?Vm^?1. The results are then compared with the well-known standard oceanic Carnegie curve. The diurnal curve of PG is found to deviate from the Carnegie curve. The seasonal PG variation at MZF shows lower values during the summer (monsoon) and autumn (post-monsoon) as compared to the winter and spring (pre-monsoon) which could be due to local aerosol concentration. Global comparison of PG (%) values of the annual mean at different longitude, with MZF observatory, shows local morning and evening peaks depicting local sunrise and sunset effects on the PG. The overall outcomes will certainly contribute to further investigate the Global Electric Circuit (GEC).     

Three-dimensional path planning for unmanned aerial vehicle based on interfered fluid dynamical system

This paper proposes a method for planning the three-dimensional path for low-flying unmanned aerial vehicle(UAV) in complex terrain based on interfered fluid dynamical system(IFDS) and the theory of obstacle avoidance by the flowing stream. With no requirement of solutions to fluid equations under complex boundary conditions, the proposed method is suitable for situations with complex terrain and different shapes of obstacles. Firstly, by transforming the mountains, radar and anti-aircraft fire in complex terrain into cylindrical, conical, spherical, parallelepiped obstacles and their combinations, the 3D low-flying path planning problem is turned into solving streamlines for obstacle avoidance by fluid flow. Secondly, on the basis of a unified mathematical expression of typical obstacle shapes including sphere, cylinder, cone and parallelepiped, the modulation matrix for interfered fluid dynamical system is constructed and 3D streamlines around a single obstacle are obtained. Solutions to streamlines with multiple obstacles are then derived using weighted average of the velocity field. Thirdly, extra control force method and virtual obstacle method are proposed to deal with the stagnation point and the case of obstacles’ overlapping respectively. Finally, taking path length and flight height as sub-goals, genetic algorithm(GA) is used to obtain optimal 3D path under the maneuverability constraints of the UAV. Simulation results show that the environmental modeling is simple and the path is smooth and suitable for UAV. Theoretical proof is also presented to show that the proposed method has no effect on the characteristics of fluid avoiding obstacles.     

一种火箭发射场坪流场的环形线汇描述方法

针对火箭发射场坪流场分布规律，基于势流法提出环形线汇描述方法，推导了环形线汇流场的速度势和速度的计算公式，建立了流场的FLUENT仿真模型并进行计算，将环形线汇理论计算结果与仿真结果进行对比。结果表明，不同火箭半径和入口流速对环形线汇和FLUENT仿真两种方法计算结果的相关性没有影响，随着箭井间隙增大，两种方法计算结果的相关度减小；环形线汇方法能够描述发射场坪流场变化趋势，在箭井间隙较小且误差允许时可以作为发射场坪流场的简化描述方法。     

Study on effects of thickness on airfoil-stall at low Reynolds numbers by cusp-catastrophic model based on GA(W)-1 airfoil

The phenomena of an airfoil stall present the behaviors of catastrophe and hysteresis at low Reynolds numbers. Numerical simulation results of two-dimensional airfoil GA(W)-1 show that the width of the hysteresis loop of airfoil stall will gradually decrease and even disappear with the decrease of thickness ratio. These nonlinear characteristics are in accordance with the topological features of the cusp catastrophic model. According to the topological invariant principle, a novel topological mapping method is developed to establish the mapping relationship between cusp catastrophic model and stall characteristics of the airfoil, then the effect of thickness ratio on airfoil stall is successfully described quantitatively by cusp catastrophic model. Further, based on the established topological mapping relationship, combined with the mean flow field of the airfoil stall, potential function approach of cusp catastrophic model is first introduced to interpret the catastrophe and hysteresis of the airfoil stall, and it is found that as the thickness ratio decreases, the system's maximal potential energy gradually disappears, and the short separation bubble at the leading edge of the airfoil changes to long separation bubble, so the airfoil stall changes from a bistable system to a monostable system.     

中间轨道实用化的进一步探讨

对于受摄二体问题,通常都是处理成一个变化椭圆轨道问题。而对于强摄动情况,椭圆变化太快,人们希望能找到另一种更接近真实运动的所谓中间轨道来代替椭圆轨道。特别针对一些环绕大行星(包括地球)或小行星运行的低轨卫星(探测器),因中心天体的扁率影响较大,给出了几类中间轨道。如Vinti型中间轨道,它可完整地包含扁率项的摄动影响。但它毕竟不能完全反映中心天体的非球形引力作用,在此基础上再去求各种剩余摄动是否简单,人们作了一些有益的探讨。本文就是在此背景下对Vinti型中间轨道的实用化作进一步的深入探讨。结果表明,对一些特殊的中心天体,中间轨道还是有一定实用价值的。