高重频激光控制IV型激波干扰方法研究

在实验和数值分析IV型激波干扰特性及其对飞行器表面压力和热流影响的基础上,提出采用脉冲激光能量控制IV型激波干扰的方法,以降低飞行器波阻、驻点压力和热流。采用实验和数值方法,研究了100m J单脉冲激光能量与马赫5.0条件下IV型激波干扰的相互作用过程,揭示了单脉冲激光能量控制IV型激波干扰的机理。数值研究了频率为150k Hz的激光能量注入后,激光空气锥的形成及其与IV型激波干扰的相互作用过程,得到了钝头体表面压力、热流和波阻的演化过程。结果表明,沉积高重频的激光沉积方式可以利用相对较少的激光能量形成比较稳定的准静态波结构,进而利用准静态波与IV型激波干扰的相互作用将高能区脱离钝头体表面。在马赫数为5.0的流场中沉积频率为150k Hz、单脉冲能量为5m J的激光能量可使峰值压力、热流和波阻分别降低40%,33%和23%。     

飞行器阵风响应的CFD-6DOF仿真分析

飞行器在大气中飞行,不可避免地受到阵风的影响。阵风所附加的气动载荷引发飞行器飞行状态的改变,过大幅值的阵风影响飞行的性能与安全。针对这种状况,首先采用改进的Lamb-Ossen涡模型,建立尾涡形式的阵风场;然后采用基于CFD技术的非定常N-S方程求解,并在计算网格中引入"网格速度"来模拟阵风,对SWIM(Subsonic Wall Interference Model)尾涡中的定常气动特性进行验证;最后通过CFD-6DOF的耦合,对SWIM俯冲穿越尾涡场的飞行轨迹进行研究。结果表明:计算结果与实验值符合较好;SWIM在尾涡中飞行时出现抖动、下沉、改变飞行状态、剧烈翻转的现象,与实际飞行器进入尾涡中的轨迹特性类似。     

浅谈《航空发动机原理》课程教学方法改革

结合《航空发动机原理》课程的教学实践,针对其涉及多门学科,并且实践性比较强的课程特点,阐述了如何运用分类模块式教学法、研究讨论式教学法、模拟式现场教学法和作业自由化教学法等多种方法来进行教学改革,培养学生对课程的浓厚兴趣,从而提高课程教学质量。     

High-order compact finite volume methods on unstructured grids with adaptive mesh refinement for solving inviscid and viscous flows

In the present paper, high-order finite volume schemes on unstructured grids developed in our previous papers are extended to solve three-dimensional inviscid and viscous flows. The high-order variational reconstruction technique in terms of compact stencil is improved to reduce local condition numbers. To further improve the efficiency of computation, the adaptive mesh refinement technique is implemented in the framework of high-order finite volume methods. Mesh refinement and coarsening criteria are chosen to be the indicators for certain flow structures. One important challenge of the adaptive mesh refinement technique on unstructured grids is the dynamic load balancing in parallel computation. To solve this problem, the open-source library p4est based on the forest of octrees is adopted. Several two- and three-dimensional test cases are computed to verify the accuracy and robustness of the proposed numerical schemes.     

Thermospheric Density: An Overview of Temporal and Spatial Variations

Neutral density shows complicated temporal and spatial variations driven by external forcing of the thermosphere/ionosphere system, internal dynamics, and thermosphere and ionosphere coupling. Temporal variations include abrupt changes with a time scale of minutes to hours, diurnal variation, multi-day variation, solar-rotational variation, annual/semiannual variation, solar-cycle variation, and long-term trends with a time scale of decades. Spatial variations include latitudinal and longitudinal variations, as well as variation with altitude. Atmospheric drag on satellites varies strongly as a function of thermospheric mass density. Errors in estimating density cause orbit prediction error, and impact satellite operations including accurate catalog maintenance, collision avoidance for manned and unmanned space flight, and re-entry prediction. In this paper, we summarize and discuss these density variations, their magnitudes, and their forcing mechanisms, using neutral density data sets and modeling results. The neutral density data sets include neutral density observed by the accelerometers onboard the Challenging Mini-satellite Payload (CHAMP), neutral density at satellite perigees, and global-mean neutral density derived from thousands of orbiting objects. Modeling results are from the National Center for Atmospheric Research (NCAR) thermosphere-ionosphere-electrodynamics general circulation model (TIE-GCM), and from the NRLMSISE-00 empirical model.     

基于VPX架构的遥测采集平台设计

当今世界各航天大国都在大力发展航天测控通信技术,但现有测控设备间连接关系复杂,不利于系统小型化、低功耗设计,很难满足新型飞行器的设计需要。针对现阶段测控通信系统提出的一体化、小型化,高可靠性等要求,对VPX总线架构进行研究,并应用于遥测采集平台设计。提出了基于VPX架构的遥测采集平台设计方案,经试验验证,可满足目前测控通信系统提出的小体积、高速率以及高可靠性共存的设计需求,在航天领域具有广阔的发展前景。     

Fuzzy norm method for evaluating random vibration of airborne platform from limited PSD data

For random vibration of airborne platform, the accurate evaluation is a key indicator to ensure normal operation of airborne equipment in flight. However, only limited power spectral density（PSD） data can be obtained at the stage of flight test. Thus, those conventional evaluation methods cannot be employed when the distribution characteristics and priori information are unknown. In this paper, the fuzzy norm method（FNM） is proposed which combines the advantages of fuzzy theory and norm theory. The proposed method can deeply dig system information from limited data, which probability distribution is not taken into account. Firstly, the FNM is employed to evaluate variable interval and expanded uncertainty from limited PSD data, and the performance of FNM is demonstrated by confidence level, reliability and computing accuracy of expanded uncertainty. In addition, the optimal fuzzy parameters are discussed to meet the requirements of aviation standards and metrological practice. Finally, computer simulation is used to prove the adaptability of FNM. Compared with statistical methods, FNM has superiority for evaluating expanded uncertainty from limited data. The results show that the reliability of calculation and evaluation is superior to 95%.     

钛基稀土激光熔覆层组织细化机制及性能

采用通快TruDisk 4002光纤激光器在TC4合金表面分别制备了0wt% Y₂O₃和3wt% Y₂O₃的TC4+Ni45+Co-WC钛基耐磨复合涂层。利用XRD、SEM、EDS、EPMA、显微硬度计和摩擦磨损试验机等分析了涂层组织、显微硬度和摩擦学性能。结果表明，两种涂层表面均无裂纹孔隙等缺陷，且生成相一致，主要包括TiC、TiB₂、Ti₂Ni、WC和α-Ti；0wt% Y₂O₃涂层组织存在明显偏析，析出相尺寸粗大且方向性明显；3wt% Y₂O₃涂层组织呈均匀弥散状态分布，细化特征明显；经Bramfitt二维点阵错配度计算，（100）_Y2O3和（100）_Ti2Ni、（111）_Y2O3和（110）_TiC、（110）_Y2O3和（1010）_TiB2间的错配度分别为5.75%、6.72%和10.10%，Y₂O₃作为异质形核核心对Ti₂Ni、TiC和TiB₂的细化能力依次为Ti₂Ni > TiC > TiB₂；0wt% Y₂O₃和3wt% Y₂O₃涂层显微硬度分别为600~630 HV_0.5和470~480 HV_0.5，较基材分别提高了约62%和26%；3wt% Y₂O₃涂层耐磨减摩性最优，其磨损体积和摩擦系数较0wt% Y₂O₃涂层分别下降了约47.8%和5.0%，磨损机制主要为磨粒磨损。     

如何运用微博发展电视新闻

利用微博发布新闻已成为当今社会信息发布的一个平台,由于微博新闻有着信息短小、快捷、图片资料真实,话语权公开可信,与政府、媒体沟通及时,迅速等特点,利用微博发展电视新闻,愈来愈受到各主流媒体的重视.通过运用微博发展电视新闻的阐述,不仅进一步确立了电视新闻的主流媒体地位,而且会拥有巨大的发展空间和庞大的受众.     

大学英语大班教学方法探索

大班教学已是我国大学英语公共外语教学的普遍形式,而班级规模的扩大给英语教学带来了许多新的问题。为了培养合格的英语人才,适应新形势下社会的需求,详细地、有针对性地做了一系列研究,提出解决的对策和建议。