LDA测量方截面U型旋转通道速度分布

为了深入了解旋转涡轮叶片内冷通道中的流动特性，用激光多谱勒测速仪(LDA)测量了旋转U型通道中的平均速度分布。通道的横截面积为50mm×50mm，弯管的平均半径与水利直径的比值为0.65，旋转轴与弯管的曲率轴平行。在Re＝105时分别测量了转动数Ro＝0，0.2和-0.2三种旋转状态下的速度分布。在这三种情况下弯管内侧θ＝90°至下游一定范围内都有流动的分离出现。由于不同的旋转状态二次流的方向和强弱不同，导致了分离区大小和通道中速度分布的不同。     

High resolution studies of intermediatedrift bursts

We report high resolution observations of the Intermediate Drift (IMD) bursts in decimetric band (ν = 950 – 2650 MHz). With a time resolution of 20 – 50 ms and a frequency resolution of 4 – 10 MHz, we are able to estimate the characteristics of IMD bursts such as the bandwidth and duration of the emission. Frequency drift rate and its dependence on the frequency are derived for individual IMD structures. All IMD bursts analyzed show negative drift rate. The values are of the order of −28 – −274 MHz s⁻¹. The drift rates normalized by the mean frequency are ranged between −0.20 s⁻¹ and −0.02 s⁻¹. Both the frequency drift rate and its frequency dependence provide important clues to the emission mechanisms of IMD. A comparison and a critique of the existing models based on the plasma and the maser emissions with modulation by Alfvén solitons as well as the whistler wave model are presented.     

The search for extraterrestrial artifacts (SETA)

The rationale for the use of interstellar artifacts by intelligent life in the universe is described. The advantages of using interstellar probes as a means of exploration and communication are presented and shown to be significant enough to counter the time, energy, and technology arguments generally raised against contact via extraterrestrial artifacts. Four classes of artifacts are defined: Those seeking contact, those seeking to avoid contact, those intended to provide a passive technological threshold for detection, and those for which detection is irrelevant. The Search for Extraterrestrial Artifacts (SETA) is based on the latter two classes. Under the assumption that an extraterrestrial probe will be interested in life in our solar system, a near-Earth search space is defined. This search space is accessible to us now with ground and satellite observing facilities. The current observational status of SETA is reviewed and contrasted with the achievable detection limits for the different parts of the search space.     

Rapid impactor sample return (RISR) mission scenario

Due to the long lead time and great expense of traditional sample return mission plans to Mars or other astronomical bodies, there is a need for a new and innovative way to return materials, potentially at a lower cost. The Rapid Impactor Sample Return (RISR) mission is one such proposal. The general mission scenario involves a single pass of Mars, a Martian moon or an asteroid at high speeds (7 km/s), with the sample return vehicle skimming just 1 or 2 m above a high point (such as a top ridge on Olympus Mons on Mars) and releasing an impactor. The impactor strikes the ground, throwing up debris. The debris with roughly the same forward velocity will be captured by the sample return vehicle and returned to Earth. There is no delay or orbit in the vicinity of Mars or the asteroid: RISR is a one-pass mission. This paper discusses some of the details of the proposal. Calculations are presented that address the question of how much material can be recovered with this technique. There are concerns about the effect of Mars tenuous atmosphere. However, it will be noted that such issues do not occur for RISR style missions to Phobos, Deimos, or asteroids and Near Earth Objects (NEOs). Recent test results in the missile defense community (IFTs 6–8 in 2001, 2002) have scored direct hits at better than 1 m accuracy with closing velocities of 7.6 km/s, giving the belief that accuracy and sensing issues are developed to a point that the RISR mission scenario is feasible.     

旋转方截面U型通道分离流二阶相关分量测量

为了深入了解旋转涡轮叶片内冷通道中的紊流特性，并为CFD研究提供实验数据，用激光多普勒测速仪（LDA）测量了旋转U型通道中分离流的雷诺应力分量。通道的转轴与弯道的曲率轴平行，测量是在与转轴垂直的对称平面中进行的，流动状态为Re=100,000,Ro=0,0.2和－0．2。直接测量的分量为ux^2^-,Ux^2^-和uxux^-，结果表明旋转对紊流分布的形式有很强的影响。在测量的三种旋转状态中Ro=0.2的正转和Ro=0.2的负转分别具有最低和最高的紊流强度。根据测量到的信息估算了雷诺应力uiuj^-的产生率，结果显示负转的产生率比正转时高。