Direct Numerical Simulation Of Hypersonic Boundary-Layer Transition Over A Blunt Cone

Direct numerical simulation of transition How over a blunt cone with a freestream Mach number of 6, Reynolds number of 10,000 based on the nose radius, and a 1-deg angle of attack is performed by using a seventh-order weighted essentially nonoscillatory scheme for the convection terms of the Navier-Stokes equations, together with an eighth-order central finite difference scheme for the viscous terms. The wall blow-and-suction perturbations, including random perturbation and multifrequency perturbation, are used to trigger the transition. The maximum amplitude of the wall-normal velocity disturbance is set to 1% of the freestream velocity. The obtained transition locations on the cone surface agree well with each other far both cases. Transition onset is located at about 500 times the nose radius in the leeward section and 750 times the nose radius in the windward section. The frequency spectrum of velocity and pressure fluctuations at different streamwise locations are analyzed and compared with the linear stability theory. The second-mode disturbance wave is deemed to be the dominating disturbance because the growth rate of the second mode is much higher than the first mode. The reason why transition in the leeward section occurs earlier than that in the windward section is analyzed. It is not because of higher local growth rate of disturbance waves in the leeward section, but because the growth start location of the dominating second-mode wave in the leeward section is much earlier than that in the windward section.

Direct numerical simulation of hypersonic boundary layer transition over a blunt cone with a small angle of attack

The direct numerical simulation of boundary layer transition over a 5° half-cone-angle blunt cone is performed. The free-stream Mach number is 6 and the angle of attack is 1°. Random wall blow-and-suction perturbations are used to trigger the transition. Different from the authors’ previous work [Li et al., AIAA J. 46, 2899(2008)], the whole boundary layer flow over the cone is simulated (while in the author’s previous work, only two 45° regions around the leeward and the windward sections are simulated). The transition location on the cone surface is determined through the rapid increase in skin fraction coefficient (Cf). The transition line on the cone surface shows a nonmonotonic curve and the transition is delayed in the range of 0° ≤ θ ≤ 30° (θ = 0° is the leeward section). The mechanism of the delayed transition is studied by using joint frequency spectrum analysis and linear stability theory (LST). It is shown that the growth rates of unstable waves of the second mode are suppressed in the range of 20° ≤ θ ≤ 30°, which leads to the delayed transition location. Very low frequency waves VLFWs� are found in the time series recorded just before the transition location, and the periodic times of VLFWs are about one order larger than those of ordinary Mack second mode waves. Band-pass filter is used to analyze the low frequency waves, and they are deemed as the effect of large scale nonlinear perturbations triggered by LST waves when they are strong enough.The direct numerical simulation of boundary layer transition over a 5° half-cone-angle blunt cone is performed. The free-stream Mach number is 6 and the angle of attack is 1°. Random wall blow-and-suction perturbations are used to trigger the transition. Different from the authors’ previous work [ Li et al., AIAA J. 46, 2899 (2008) ], the whole boundary layer flow over the cone is simulated (while in the author’s previous work, only two 45° regions around the leeward and the windward sections are simulated). The transition location on the cone surface is determined through the rapid increase in skin fraction coefficient (Cf). The transition line on the cone surface shows a nonmonotonic curve and the transition is delayed in the range of 20° ≤ θ ≤ 30° (θ = 0° is the leeward section). The mechanism of the delayed transition is studied by using joint frequency spectrum analysis and linear stability theory (LST). It is shown that the growth rates of unstable waves of the second mode are suppressed in the range of 20° ≤ θ ≤ 30°, which leads to the delayed transition location. Very low frequency waves (VLFWs) are found in the time series recorded just before the transition location, and the periodic times of VLFWs are about one order larger than those of ordinary Mack second mode waves. Band-pass filter is used to analyze the low frequency waves, and they are deemed as the effect of large scale nonlinear perturbations triggered by LST waves when they are strong enough.

Property studies of optical waveguide formed by 6.0 MeV carbon ion implantation into Nd : silicate glass

Nd:silicate glass was implanted at room temperature by 6.0 MeV C3+ ions with a dose of 2.0 x 10(15) ions cm(-2). A waveguide with thickness of about 6.3 mu m was formed. The prism-coupling method was used to observe the dark modes of the waveguide at 633 nm and 1539 nm, respectively. There are three dark modes at 633 nm, of which one is the enhanced-index mode. The propagation loss of the enhanced-index mode in the waveguide measured at 633 nm is 0.42 dB cm(-1) after annealing at 217 degrees C for 35 min. The reflectivity calculation method was applied to simulate the refractive index profiles in the waveguide. The mode optical near-field output at 633 nm was presented.

树鼩(Tupaia belangeri chinensis)消化系统解剖和组织学观察

该文对云南产中国树鼩的消化系统作了大体解剖和组织学观察, 在此基础上描述了树鼩消化系统的主要特征, 并与其他有关种类作了比较和讨论。

同一源区半导体光放大器、电吸收调制器集成器件

Submitted by zhangdi (zhangdi@red.semi.ac.cn) on 2009-06-04T08:36:34Z No. of bitstreams: 1 dspace.cfg: 33388 bytes, checksum: ac9630d3fdb36a155287a049e8b34eb7 (MD5)

gcs-ma: a group communication system for mobile agents

Reliable messaging is a key component necessary for mobile agent systems. Current researches focus on reliable one-to-one message delivery to mobile agents. But how to implement a group communication system for mobile agents remains an open issue, which is a powerful block that facilitates the development of fault-tolerant mobile agent systems. In this paper, we propose a group communication system for mobile agents (GCS-MA), which includes totally ordered multicast and membership management functions. We divide a group of mobile agents into several agent clusters,and each agent cluster consists of all mobile agents residing in the same sub-network and is managed by a special module, named coordinator. Then, all coordinators form a ring-based overlay for interchanging messages between clusters. We present a token-based algorithm, an intra-cluster messaging algorithm and an inter-cluster migration algorithm to achieve atomicity and total ordering properties of multicast messages, by building a membership protocol on top of the clustering and failure detection mechanisms. Performance issues of the proposed system have been analysed through simulations. We also describe the application of the proposed system in the context of the service cooperation middleware (SCM) project.

不同施肥制度下农田生态系统微量元素分布及其特征

本研究以潮棕壤一组进行了18年的长期定位试验（开始于1990年）为平台，以室内分析为主要手段，研究不同施肥制度下农田生态系统Fe、Mn、Zn、Cu、Pb5种微量元素的分布及转化情况。该长期定位试验涵盖了中国颇具代表性的八种施肥模式，此处选择其中的四种施肥模式：不施肥（CK）、单施循环猪圈肥（M）、施氮磷钾化肥（NPK）和氮磷钾化肥与循环猪圈肥配施（NPK+M）。结果表明： 施肥对土壤全量微量元素浓度没有显著影响，但对有效态的浓度影响显著，施肥导致土壤有效态微量元素浓度增加，具体表现为NPK+M处理微量元素有效态最高，NPK处理次之，M处理更低，CK处理最低。 不同施肥处理下不同作物中微量元素浓度变化各异，但多由作物产量的变化而引起，玉米籽实和秸秆及大豆籽实中Mn浓度随产量的升高而升高，大豆籽实中Fe浓度也随产量的升高而升高，玉米秸秆中Zn浓度和大豆秸秆中Cu浓度均随着产量的增加而降低。年际间作物体内Fe、Zn、Cu浓度相对稳定，Mn的浓度出现波动。大豆籽实中所测微量元素浓度均显著高于玉米籽实中对应元素浓度，较玉米具有更高的营养价值。 不同施肥处理间作物收获物中微量元素含量有极显著差异，表现为：NPK+M>NPK>M>CK。且作物收获物中微量元素的含量与作物籽实产量（或秸秆产量）间有极显著的相关关系。不同作物收获物中微量元素的分配也不相同，玉米收获物中微量元素主要分配在秸秆中，而大豆主要分配在籽实中。 有机肥和化肥均可向农田生态系统输入微量元素，其中以有机肥形式输入农田的微量元素远大于以化肥形式输入的量，且微量元素的输入量随有机肥用量的增加而增加。 不同元素在饲喂-堆腐过程中的循环率差异较大，Zn的循环率最低，但也能超过70%，而Fe、Mn、Cu、Pb的循环率均可超过80%，其中Fe、Mn、Pb的循环率均接近90%，且微量元素的循环率随着投料量的增加有增加的趋势。 各处理土壤微量元素收入均小于支出，不同处理间收支差额NPK+M＜M＜CK＜NPK，单施化肥加剧土壤微量元素赤字化，养分循环利用可弥补土壤微量元素的损失，减小收支差额。

CSR电子冷却段磁场造成闭轨畸变及校正

电子冷却的应用提高了重离子储存环的束流品质,也为重离子储存环的运行带来了新的课题．电子冷却段的横向磁场在引导约束强流电子束的同时也不可避免影响了多次经过的离子轨道．为了保证束流的安全运行,必须将离子轨道的畸变部分限制在局部范围,并保证轨道畸变量对储存环接收度的影响可以容忍．讨论在建的兰州重离子储存环HIRFL-CSR电子冷却段磁场及其造成闭轨畸变和校正方案．

偏最小二乘回归方法在土地利用结构研究中的应用

针对当前LUCC研究中存在的数据间多重相关性和样本量不足的问题,论文将一种新型的多元统计数据分析方法———偏最小二乘回归引入到研究中。该方法可以有效地克服上述缺陷,并能实现多种数据分析方法的综合应用。为检验方法的功能及实用性,论文以苏锡常地区为例,对区域的土地利用结构及其影响因子进行了定量分析。结果表明,偏最小二乘回归是进行土地利用结构研究的一种十分有效的工具,在地学领域有广阔的应用前景。