Implications of scale effect for the prediction of high angle of attack aerodynamics

Scale effect is of significance in all experimental aerodynamics testing. At high angles of attack such issues as Reynolds and Mach number scaling are further complicated by the presence of complex, unsteady separated flow structures. The understanding and quantification of such flow effects remains a substantial challenge to the combat aircraft designer. The challenge, especially during conceptual and preliminary design stages, is to obtain sufficiently accurate information to make relevant design decisions, addressing potential weaknesses before proceeding to detail design. The focus in the present review is on the application of the water tunnel in such cases. The combination of qualitative and quantitative data obtainable from the water tunnel provides a useful complement to other tools during the early design stages. The effect of Reynolds number in particular is however critical; and appreciation of its effects are critical to the effective use of such a tool. It is shown however that for certain configurations such effects can be small in comparison to other experimental effects.     

微细管道内流体流动的黏性耗散分析

目前,还没有实验数据和理论分析可以得出在微细管道内流体的黏性对流体流动及换热的影响,而在微细管道(微米级)内流体高速流动中黏性耗散是不能够忽略的,但是没有合理的计算公式进行理论计算。因此,这里对粘性耗散在微细管道流中的影响进行了分析和理论验证。根据已有的分析给定了一个粘性耗散在微细管道流中造成明显影响的最小标准值。     

英语学习者语篇模式研究

以国外学者对英语特有的语篇模式的论述为依据,试图探索中国英语学习者所应用的英语语篇模式,分析中国学生构建出的英语语篇的组织结构特点。调查结果表明,少数中国英语学习者以类似英语的语篇模式组织语篇,但绝大多数使用不同于英语的语篇模式,这给英语教学带来新的启示。     

Analysis of queuing behavior of automatic ESM systems

Radar electronic support measures (ESM) systems detect active emitters in a given area and determine their identities and bearings. The high arrival rate of radar pulses in dense emitter environments demands fast automatic processing of arriving pulses so that the ESM system can fulfill its functions properly in real time. Yet, the performance analysis of automatic ESM system in real life Is difficult since both pulse arrivals and widths can be specified only probabilistically. The success of queuing theory in many applications such as computer communication networks and flow-control has encouraged designers to utilize queuing theory in qualifying and judging the performance of automatic ESM systems in dense emitter environments. The queuing behavior of these systems is analytically evaluated under different service disciplines and elaborate computer simulations validate the results. The analysis involves statistical modeling of arrival and departure processes as well as distribution of service times. It permits estimating the blocking probability due to high arrival rates of intercepted radar pulses or due to limited speed of the deinterleaver processor. Queuing analysis is shown to be quite useful to quantitatively assess tradeoffs in ESM systems design     

近地轨道卫星太阳电池阵功率衰减估计

针对LEO(Low Earth Orbit,近地轨道)卫星的太阳电池阵输出功率衰减问题,在分析卫星轨道半长轴、太阳入射角、日地距离等参数变化与影响的基础上,提出按照轨道衰减快慢来区分太阳活动高年与低年,进而通过区分高年与低年,再根据不同季节分别进行太阳电池阵输出功率的衰减估计,而无须做功率归一化。同时,重点关注了夏至前后的最低输出功率的衰减情况,以此作为在轨卫星长期管理中的能源参考,建立平均电流和功率衰减因子估计模型,并结合实际工程数据进行了衰减估计。结果表明,太阳电池阵输出功率的年衰减因子约为-0.012,年衰减率约为1.2%。该结果可应用于在轨卫星长期管理的遥测诊断辅助。     

航空发动机风扇叶片结构损伤识别研究

航空发动机风扇叶片常常因为疲劳裂纹而引起整个结构的损坏,导致重大的安全事故。基于此,提出基于BP神经网络研究航空发动机风扇叶片结构损伤识别的方法,采用有限元法计算出的结构固有频率平方的变化量为标识量进行网络仿真,通过对仿真数据的分析,比较准确地识别出结构损伤的位置和程度,为及时地发现损伤并且进行针对性的维修提供依据。     

波瓣高宽比对波瓣强迫混合排气系统性能影响

在保证波瓣强迫混合排气系统内外涵流道面积不变的情况下,建立了某型涡扇发动机不同波瓣高宽比波瓣强迫混合排气系统的几何模型,基于Navier-Stokes方程进行了数值模拟研究,得到了波瓣强迫混合排气系统中,在涵道比和内外涵面积不变的条件下,波瓣高宽比对波瓣强迫混合排气系统的流场、热混合效率、总压恢复系数和推力系数的影响规律.结果表明:当涵道比不变时,在波瓣高宽比为2~4.5的变化范围内,在排气系统出口处,混合效率随波瓣高宽比的增加呈现出增大-减小-增大的趋势,其中波瓣高宽比为3和3.21分别为曲线的两个拐点.而随着波瓣高宽比的增加,总压恢复系数、推力系数均不断减小.      

Estimate of the climate impact of cryoplanes

The climate impact of cryoplanes (i.e. hydrogen-powered aircraft) is estimated in terms of radiative forcing (RF). We compare two scenarios: the conventional (i.e. kerosene-powered aircraft) scenario assumes a growth of the fleet until 2015 and a constant fleet thereafter. In the cryoplane scenario, the whole conventional fleet is instantaneously replaced by cryoplanes in 2015 and does not change thereafter. The resulting direct and indirect effects of aircraft emissions of H₂O (direct RF and RF due to contrails) and NO_x (RF due to O₃ production and CH₄ destruction), as well as aviation-induced atmospheric CO₂ are investigated for both scenarios.Whereas in case of conventional air traffic the components CO₂, O₃, CH₄ and contrails cause a similar RF, in case of cryoplanes, contrails are by far the most climatic relevant component. In 2015, total RF due to the cyoplane scenario is larger than total RF due to the conventional scenario. This changes with time and in 2100 the climate impact due to the cryoplane scenario is smaller. Due to large uncertainties regarding the optical properties of cryoplane contrails, the RF of contrails, and the impact of aviation on `natural' cirrus, our present knowledge is not sufficient to decide whether a substitution of the conventional fleet by a fleet of cryoplanes is of environmental benefit. Further research is necessary in order to faciliate a more precise approach to this question.     

Excitation of instabilities in the wake of an airfoil by means of active winglets

Strong wake vortices that develop behind every aircraft as a byproduct of lift production pose a threat where aircraft fly in close staggering such as in the vicinity of airports. One approach to alleviate these vortex wakes is the use of high lift systems or control surfaces of the wing to create an unstable vortex system. The inherent instability of this vortex system shall then lead to an accelerated decay of the vortex wake, triggered for example by a periodic motion of the control surfaces. In the work presented here a simple wing model with winglets able to produce a vortex system of up to six distinct vortices is investigated in towing tank experiments. Theoretical studies show that these vortex systems potentially have a high degree of instability. By means of active oscillation of rudders integrated into the winglets, these vortex systems are to be excited to initiate an accelerated decay of the vortices. It is shown that configurations exist which exhibit strong instabilities, that lead to a significantly lower hazard level behind the vortex generating wing, even when not actively excited. However, an additional oscillation does not seem to accelerate decay of these vortex systems in relation to the statical reference case.     

海拔高度对转子发动机性能影响的模拟试验

随着海拔高度增加,三角转子发动机的功率会下降.为测试不同海拔高度下三角转子发动机性能,建立了三角转子发动机电控汽油喷射系统,并在发动机台架上通过模拟不同海拔高度下的进气压强,测试了不同进气压强下208 cm3排量电控汽油喷射三角转子发动机的性能,实现了发动机在空中运行时的实时监控和调节,进而提出了海拔补偿措施,为其在空中更好地运行提供了可能.      

叶片摩擦阻尼器的优化设计方法研究

为减小叶片振动应力 ,防止叶片出现大应力的疲劳破坏 ,在叶片上设计干摩擦阻尼结构是最常用的方法之一。本文对叶片缘板摩擦阻尼器的工程优化设计方法进行了研究。研究了摩擦阻尼器参数对叶片响应的影响规律并提出了设计时应采取的措施。在阻尼器的材料和摩擦面结构已确定的情况下 ,优化设计的最主要的一个参数就是接触面的法向正压力 ,基于实际发动机中叶片激振力和粘性阻尼不易精确确定的实际 ,研究了激振力和粘性阻尼对法向正压力优化的影响 ,并提出了一种法向正压力的优化方法。由于这一优化方法对激振力和粘性阻尼值并不敏感 ,因此为工程上进行法向正压力的优化提供了理论方法     

超声速燃烧凹槽火焰稳定的研究动态

高超声速气流在燃烧室的停留时间非常短，使得超燃冲压发动机燃烧室内燃料与气流的混合及其燃烧变得非常困难。目前集燃料喷射、混合及火焰稳定为一体的凹槽有望改进这一情况而受到了普遍关注。介绍了超声速气流流过凹槽的自激振荡及其控制、停留时间和阻力等特性，总结、分析了近几年凹槽在超声速气流中增强混合及燃烧的实验与数值研究，指出了在把凹槽用于提高超燃冲压发动机性能方面存在的问题和进一步研究的方向。     

Detection of Changes in the Characteristics of a Gauss-Markov Process

By an extension to the theory of sequential detection with dependent measurements, it is possible to develop a sequential probability ratio test (SPRT) to detect changes in regime in a Gauss-Markov process rather than detecting which of the two regimes exists. It is shown how a posterior form of this extended SPRT may be simplified to reduce computational complexity. The simplified SPRT's are in fact modifications of the original SPRT detecting the regime and not the change. The tests are applied to the problem of fault detection in a gyro navigational system; the results of a detailed computer simulation are given.     

武警初级指挥院校学员人文素质的培养

武警初级指挥院校作为培养武警部队高素质人才的重要基地,由于主客观方面的原因,学员人文素质的培养一直相对较弱.要适应现代教学的发展,武警初级指挥院校必须在课程体系、课堂教学、教员职责、校园环境等多个方面采取有效措施,尽快提高学员的人文素质.     

Interdisciplinary Aspects of Engineering: The Environment of Concept Engineering

Involvement in concept engineering forces the individual as well as corporations to consider aspects and disciplines concerned with public utility, taste, and convenience. The marketplaces are varied and in a state of flux. Nevertheless, personal entrepreneurship as exemplified by high technology efforts in the aerospace, computer, and electronics industries is essential and identified as a basic American characteristic. Individuals and corporations are challenged to channel their efforts and organization to attack broad social objectives, currently recogned but awaiting clarification and polarization of the environment, to allow technology, via effective concept engineering, to participate in the achievement of successes equal to those attained in consumer products, defense engineering, and space exploration.     

旋转盘腔瞬态响应特性的研究

为保证发动机在飞行包线内正常运转,需研究旋转盘腔的瞬态响应特性。采用1-D模型方法和计算流体力学(CFD方法对旋转盘腔进口压力突升的情况进行非稳态数值计算,所得结果与文献中的结果进行对比,提出1-D模型方法的一些缺点,并证明了CFD计算的正确性。然后用CFD方法并通过用户自定义函数(UDF编程研究了进口压力渐增、正弦变化以及盘腔尺寸对旋转盘腔流动瞬态响应特性的影响。结果表明:1-D模型的计算结果不能显示出CFD模型计算结果的一个高阶震荡;进口压力以不同方式变化,瞬态响应存在不同程度的滞后;进口压力突增和进口压力渐增响应的特征时间比进口压力正弦变化的特征时间分别增加56.0%和106.4%盘腔宽径比由0.2变化到0.39时,腔内均压变高,出口质量流量变低,特征响应时间缩短至40%当宽径比由0.2变化到0.58时,特征响应时间缩短至25%。     

波动图法在槽液动态管理中的应用

针对以往表面处理过程中槽液管理方面存在的弊端,介绍了质量管理中常用的统计工具——波动图法的应用情况;并摸索、制定了一整套标准化的具有可操作性的槽液管理方法,从而实现了表面处理“槽液动态管理”及其控制程序化。     

Detection of obstacles in the flight path of an aircraft

The National Aeronautics and Space Administration (NASA), along with members of the aircraft industry, recently developed technologies for a new supersonic aircraft. One of the technological areas considered for this aircraft is the use of video cameras and image-processing equipment to aid the pilot in detecting other aircraft in the sky. The detection techniques should provide high detection probability for obstacles that can vary from subpixel to a few pixels in size, while maintaining a low false alarm probability in the presence of noise and severe background clutter. Furthermore, the detection algorithms must be able to report such obstacles in a timely fashion, imposing severe constraints on their execution time. Approaches are described here to detect airborne obstacles on collision course and crossing trajectories in video images captured from an airborne aircraft. In both cases the approaches consist of an image-processing stage to identify possible obstacles followed by a tracking stage to distinguish between true obstacles and image clutter, based on their behavior. For collision course object detection, the image-processing stage uses morphological filter to remove large-sized clutter. To remove the remaining small-sized clutter, differences in the behavior of image translation and expansion of the corresponding features is used in the tracking stage. For crossing object detection, the image-processing stage uses low-stop filter and image differencing to separate stationary background clutter. The remaining clutter is removed in the tracking stage by assuming that the genuine object has a large signal strength, as well as a significant and consistent motion over a number of frames. The crossing object detection algorithm was implemented on a pipelined architecture from DataCube and runs in real time. Both algorithms have been successfully tested on flight tests conducted by NASA.     

Formation of the Cores of the Outer Planets

The formation of the giant planets seems to be best explained by accretion of planetesimals to form massive cores, which in the case of Jupiter and Saturn were able to capture nebular gas. However, the timescale for accretion of such cores has been a problem. Accretion in the outer solar system differs qualitatively from planetary growth in the terrestrial region, as the larger embryo masses and lower orbital velocities make bodies more subject to gravitational scattering. The planetesimal swarm in the outer nebula may be seeded by earlier-formed large bodies scattered from the region near the nebular “snow line”. Such a seed body can experience rapid runaway growth undisturbed by competitors; the style of growth is not oligarchy, but monarchy.     

悬停状态旋翼尾迹研究及气动特性计算

本文用试验的方法显示了悬停状态旋翼的尾迹几何形状，并以试验结果为依据对现有的尾迹几何模型进行了修正。最后以两个模型旋翼为例，分别用修正前的修正后的尾迹几何模型计算它们在悬停的气动特性和桨中处的诱导速度分布。所得结果表明用修正后的尾迹几何模型来计算悬停状态旋翼的气动特性能有效地改善计算结果的准确性。