Numerical investigation of the interaction between upstream cavity purge flow and main flow in low aspect ratio turbine cascade

In modern gas turbines, rim seal located between the stator-disc and rotor-disc is used to prevent hot-gas ingestion into the inner stage-gap of high pressure turbine. However, the purge flow supplied to the cavity through the rim seal interacts with the main flow, producing additional aerodynamic loss due to the mixing process which plays a significant role in the formation, development and evolution of downstream secondary flow. In this paper, a set of cascade representative of low aspect ratio turbine is selected to numerically investigate the influence of upstream cavity purge flow on the hub secondary flow structure and aerodynamic loss. Cascade with/without upstream cavity and four different purge mass flow rates are all taken into account in this simulation. Then, a deep insight into the loss mechanism of interaction between purge flow and main flow is gained. The results show that the presence of cavity and purge flow has a significant impact on the main flow which not only changes the vortex structure in both the passage and upstream cavity, but also alters the cascade exit flow angle distribution along the spanwise. Moreover, aerodynamic loss in the cascade rises with the increase of purge flow rate while the sealing effect is also enhanced. Therefore, the effect of upstream cavity purge flow must be considered in the process of turbine aerodynamic design. What is more, it is necessary to minimize the purge flow rate in order to reduce aerodynamic loss on the premise of satisfying cooling requirements.     

高校体育行政管理信息系统的开发

介绍笔者开发的《高校体育行政管理信息系统》的基本特点、系统结构和主要功能，以及系统运行效果和应用前景。     

基于89C51的低速无线串行通信

在一些相对较复杂的单片机应用系统中,仅仅一个单片机资源是不够的,往往需要两个或多个单片机系统协同工作,论文介绍一种实现双机无线串行通信的方法。     

Active collision avoidance maneuver under constant thrust

In this paper, the relative position parameters of the target spacecraft are obtained by using the vision measurement and the target maneuver positions are calculated through the isochronous interpolation method. Furthermore, new switch control laws under constant thrust are designed for active collision avoidance maneuver of the chaser along a specified trajectory. The switch control laws are obtained based on the acceleration sequences and the working times of thrusters in three axes which can be respectively computed by the time series analysis method. The perturbations and fuel consumptions are addressed during the computation of the working times.     

Assessment of the sensitivity of vegetation to El-Niño/Southern Oscillation events over China

This research explores the sensitivity of vegetation in China to El-Niño/Southern Oscillation (ENSO) events from 1982 to 2006. The ENSO events are defined by the Multivariate ENSO Index (MEI), and variation in vegetation cover is captured by the Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI). Pearson’s χ2 test was used to identify the areas where the variation in vegetation was sensitive to El Niño and La Niña events. The difference in the sensitivity of various ecosystems was investigated using the Moderate Resolution Imaging Spectroradiometer (MODIS) land cover product in 2000. Composite NDVI graphs during El Niño, La Niña and non-ENSO years were also produced to investigate the ENSO relationship with the six vegetation ecosystems during El Niño, La Niña and normal phases. The results show that most of the ENSO-sensitive land in China is only affected by one of the two phases of ENSO events, and the area of El Niño-sensitive vegetation is much larger than that of La Niña-sensitive vegetation. North China and the Hengduan Mountains are the two cores of the El Niño-sensitive areas, while the La Niña-sensitive areas are mainly distributed in the central, northwest and northeast regions of China. The sensitivity of vegetation varies across ecosystems: grassland and shrubland had the largest share of El Niño-sensitive areas, and sparse vegetation and savanna were the most sensitive to La Niña events. Overall, the impacts of El Niño events on vegetation in China had regular seasonal variation, while the impacts of La Niña events had regular zonal distribution.     

基于聚偏二氟乙烯(PVDF)压电薄膜的密封舱壁穿孔损伤识别技术

日益恶化的空间碎片环境将严重威胁空间站及航天员的在轨安全。文章基于聚偏二氟乙烯（polyvinylidene fluoride,PVDF）压电薄膜设计了一种密封舱壁穿孔损伤识别技术方案,用于识别空间碎片超高速撞击对航天器密封舱壁造成的损伤模式,可为航天员合理选择应急措施提供依据。首先,发射超高速弹丸穿透铝合金靶板以模拟密封舱壁被击穿损伤的情况,形成的碎片云撞击PVDF压电薄膜探头,利用信号采集设备获取高速撞击引起的去极化效应信号,识别该信号的频率特征;其次,对PVDF压电薄膜探头及其支撑结构进行敲击试验,模拟在轨运行时因碰撞产生的干扰信号,掌握此类干扰信号的频率特征。试验结果表明,当系统采样频率为20 MHz时：1）所获得的探头去极化效应信号具有极为陡峭的上升沿,且上升沿的时长为亚μs量级;2）去极化效应信号主要由1 MHz以下的信号组成,但也包含少量的3～10 MHz高频成分;3）敲击探头及其支撑结构所产生的干扰信号频率在20 kHz以下。可根据频率差异进行两种信号的识别。     

发动机台架点的自动化测量

针对外场测量台荼量大、准确度低的问题，进行了分析研究，将单片机技术引入到发动机检测领域，实现了发动机台架点的自动化测量，大大减以了试车工作人员的测试工作量，提高了台架点测试精度，具有重要的军事价值。     

简论工厂的规划,建设与改造

简要论述了工厂规划的重要性和必要性，及其对工厂建设与改造的指导作用，并就方面存在的某些问题，进行了剖析，明确提出了加强规划工作的基本原则，要求和任务。     

ML─2900吨蒙皮拉形机的改造

介绍了大型航空专用设备ML─2900t蒙皮拉形机改造基本做法及其所取得的成效。阐述了采用先进技术改造老设备，对加速企业技术改造，促进企业技术进步，具有重要意义和作用。     

激光自动跟踪空间坐标测量系统的发展（一）

介绍了近十年来国外在激光跟踪空间坐标动态测量方面的研究成果，它集多种现代先进技术于一体，目前多应用于机器人领域，但应用的前景非常广阔，代表了计量学新的发展方向。下面将介绍球坐标法，三角法，多边法等多种测量方法，讨论单站，多站（双站、三站和四站）的测量原理及系统结构，还分析了各系统可能或已经达到到的精度及优缺点。