变工况非定常叶栅绕流数值仿真

采用离散涡方法数值仿真了不同来流攻角下,固定与动边界叶栅绕流。在设计工况时流动接近定常流动。而变 工况时流动具有明显的非定常特征。特别是当攻角较大时,流场中存在着激烈分离,流动具有不稳定性。分离流动与旋涡 的分布息息相关。当来流角从20°到60°逐渐增大时,前驻点从背面经前缘点向腹面移动。固定叶栅与振动叶栅时的绕流 有明显的不同。振动叶栅绕流,流体决不是简单地随叶栅作同样的振动。     

Dynamics of radiation induced quasiparticles in superconducting tunnel junction detectors

In order to achieve a high resolution in the spectroscopy of low energy X-rays, detectors based on superconducting tunnel junctions as sensors are presently investigated. The knowledge of the processes affecting the signal generation in such sensors is essential for the interpretation of the detector response. Starting from a diffusion model including decay and tunneling of excess quasiparticles in the metal layers of a superconducting tunnel junction detector, the detector response is determined as a function of absorption position and of rate constants. Model predictions agree very well with experimental data. The advantages of a detector employing quasiparticle trapping are pointed out and the parameters determining the signal gain are deduced. The linearity of the detector signal is much more affected by pair recombination of the quasiparticles during their tunneling rather than during their diffusive propagation into the tunneling region.     

降低风机动叶尖间隙涡流噪声研究

气流流过动叶叶尖引起的不规则流动产生的间隙涡流噪声是轴流风机涡流噪声的主要组成部分，采用减小动叶叶尖间隙方法不仅可抑制和减小间隙涡流的产生，有效地降低轴流风机的涡流噪声，而且可改善气动性能。同时可预测、该方法也有利于减小间隙涡流产生的二次流及流动尾迹时下静叶的干扰噪声     

Interference of intersecting singular beams

A vorticity of the light field created by interference of two intersecting Laguerre–Gaussian singular beams is analysed. It is demonstrated that the number and location of the vortices present in the field depend on the propagation length as well as on the topological charges of the individual beams, their intersection angle and amplitude ratio.     

The similarities in loss creation in LTS and HTS cables

The coupling current losses represent an essential contribution to AC losses in most practical superconducting conductors. The origin of this loss type is well known, being caused by induced currents in different loops consisting of superconducting and non-superconducting parts. However, the ‘current pattern' in different conductor types (strands, flat or round cables, more complicated cable structures, CICC) varies appreciably. These differences are mainly due to geometrical effects (size and shape of filaments and/or strands, their spatial distribution, conductor aspect ratio, demagnetization effects). Although the general knowledge about AC losses in low temperature cable structures is by far not complete (mainly at higher frequencies, in inhomogeneous fields and for inhomogeneous cable structure), an attempt is made to summarize those results which can be adopted to high T_c conductors and some remarks are made about new features of AC losses in these conductor types.     

叶轮机械中的泄漏流与泄漏涡

本文基于非正交曲线坐标及非正交速度分量下完全守恒型的N-S方程,采用整体H型网格,用数值方法研究叶轮机械中的泄漏流动。对于不同的间隙尺寸,对于环壁静止与旋转的不同壁面条件,揭示了泄漏流与通道二次涡相互作用的细节,揭示了泄漏涡的生成与发展过程。     

电力系统动模实验用50kJ高温超导储能磁体的设计研究

介绍了 2 0 K下对电力系统动模实验用 5 0 k J高温超导储能磁体的设计步骤 ,给出了用 Bi- 2 2 2 3单根超导带进行5 0 k J磁体线圈的设计和优化结果 ,分析了高温超导体的各向异性对磁体临界电流的影响和磁体漏磁的分布 ,并讨论了用单根高温超导带组成的超导体和用多根高温超导带组成的超导体设计的储能磁体的特性参数对改善电力系统动态特性的能力的影响。     

Correlations between microstructure and a.c. magnetic response of bulk superconducting YBa2Cu3O7−x

Summary The magnetic response of granular superconducting YBCO samples with different grain sizes is reported. The analysis is carried out by measuring the low-frequency a.c. magnetic susceptibility as a function of the temperature with an applied magnetic field of amplitude ranging between 0.4 and 800 A/m. The observed magnetic behaviour is interpreted in terms of grain size and weak-links properties. The experimental results evidence the influence of the sample microstructure on the magnetic susceptibility. The intergranular and intragranular onset temperatures are compared with the critical temperature of the samples obtained by means of electrical-resistivity measurements. The temperature dependence of the intergranular critical current density is derived from the susceptibility data.     

Simulations of the unsteady separated flow past a normal flat plate

Well-resolved two-dimensional numerical simulations of the unsteady separated flow past a normal flat plate at low Reynolds numbers have been performed using a fractional step procedure with high-order spatial discretization. A fifth-order upwind-biased scheme is used for the convective terms and the diffusive terms are represented by a fourth-order central difference scheme. The pressure Poisson equation is solved using a direct method based on eigenvalue decomposition of the coefficient matrix. A systematic study of the flow has been conducted with high temporal and spatial resolutions for a series of Reynolds numbers. The interactions of the vortices shed form the shear layers in the near-and far-wake regions are studied. For Reynolds numbers less than 250 the vortices are observed to convect parallel to the freestream. However, at higher Reynolds numbers (500 and 1000), complex interactions including vortex pairing, tearing and deformations are seen to occur in the far-wake region. Values of the drag coefficient and the wake closure length are presented and compared with previous experimental and numerical studies.