Effects of casing treatment on behavior of tip leakage flow in an isolated axial compressor rotor blade row

This article deals with enhancement in aerodynamic performance of an isolated axial compressor rotor blade row while applying treated casing. Three dimensional unsteady flow is assumed and a flow solver, utilizing Large Eddy Simulation (LES), is undertaken for the numerical calculations. Unsteady tip leakage flow and its propagation trajectory are simulated in detail for both smooth and treated casings. Oscillatory nature of tip leakage flow is depicted and its frequency is calculated by the calculation of pressure distribution along the rotor blade tip, for smooth and treated casings. For the smooth casing and in comparison with experimental data, results showed that in contrast with the Reynolds Averaged Navier–Stokes method, the LES realizes dependency of frequency characteristics of the tip leakage flow on the blade tip clearance size, and also can recognize different frequency characteristics of the tip leakage flow along the blade chord. Results also demonstrated that performing casing treatment causes the amplitude of unsteadiness of tip leakage flow to reduce and its frequency to get closer to the blade passing frequency. This in turn, causes flow blockages and losses in total pressure to reduce.     

Propagation of optical vortices embedded with multiple wavefront singularities

Optical vortices with the embedded wavefront singularities have attracted intensive attentions in many branches of modern physics, due to their important applications in optical tweezers, quantum entangles, optical testing, atmospheric propagations, etc. In this paper, optical vortices are generated by new types of custom designed wavefronts and their propagation in free-space is reported. Huygens–Fresnel diffraction integral is directly solved using the Gauss–Legendre quadrature method to estimate the diffraction pattern at some arbitrary plane. The variation of vorticity is demonstrated under diffraction. Evolution of phase singularities in wavefronts as the wavefront propagate is predicted for various near field distances. Simulations reveal that the exchange of the nature of topological charge occurs at a finite distance. Experimentally, the wavefronts have been generated using the phase-only spatial light modulator and their far-field diffraction patterns are recorded. The experimental result has been validated with the numerical simulation.     

弯管压降随迪恩涡的变化规律及数值模拟

从弯管内二次流及其影响因素出发,在不同主流速度下对不同弯曲程度的、长500mm的Φ50弯管压降变化规律进行数值模拟,并对模拟结果进行实验验证。为了精确地描述二次流对压降的影响,借助有限体积法模拟管内流场,并采用带旋流修正的realizable k-e双方程模型和SIMPLE算法来求解控制方程组。通过分析对比模拟结果和实验结果发现:弯管压降受到主流速度v、弯管弯曲程度(r/Rc)等因素的共同影响,在完全湍流区之前可用迪恩数Dn来衡量,并根据实验结果和模拟结果得出弯管压降与迪恩数的拟合关系。     

Energy Resolution of a Superconducting Nanowire Single-Photon Detector

An energy resolution of 0.6 eV was achieved with an NbN superconducting nanowire single-photon detector for near infrared photons in the energy range from 1.2 eV to 0.8 eV. The detector operates at 6 K and is read out with a room-temperature amplifier. The photon-energy dependent response of the detector is associated with the change of the detection scenario from the hot-spot formation to unbinding of paired magnetic vortices.      

Unsteady Heat Transfer in HeII in Cylindrical and Spherical Geometries

The problem of evolution of strong heat pulses in superfluid helium interacting with quantum vortices induced by these pulses is investigated numerically on the basis of equations of hydrodynamics of superfluid turbulence. The “discontinuity decay” method (Godunov method) is used for the calculations. In order to study nonlinear effects, the initial equations are expanded to the second order in the amplitudes of pulses. The influence of the main flow parameters—heat flux and rest time—on temperature evolution is reported. The numerical investigations are carried out at the bath temperature of 1.4 K. The obtained results are compared with experimental data.      

膜过程中防治膜污染强化渗透通量技术进展(Ⅱ)膜组件及膜系统的结构设计

通过膜组件和膜系统的结构设计减轻浓差极化和膜污染的方法，如设置流道内构件、旋转滤器、弯曲流道等进行了介绍和评述     

军用直升机旋翼尾迹在火箭弹道上的诱导流动计算

建立了旋翼升力线模型和广义尾迹模型，在计算尾迹涡线诱导速度时，采用了快速收敛方法。以ＡＨ－１Ｇ“眼镜蛇”直升机悬停旋翼在火箭轨道上的诱导速度分布为算例，数值结果与Ｌａｎｄｇｅｂｅ的预定尾迹旋翼入流模型分析结果作了对比，两者吻合较好。     

大跨平屋盖表面锥形涡流动模型研究

基于大跨平屋盖表面旋涡流动显示试验,对兰金涡模型进行改进,在其涡核区与势流区之间添加过渡区,建立简化的二维锥形涡流动模型,给出旋涡上部流速、旋涡内部流线曲率以及屋面涡核吸力之间的定量关系。据此流动模型分析表明,旋涡内部流线曲率越大,旋涡转速越快,旋涡强度越高,且后者的影响更为显著。根据流动显示试验结果,量化各风向下大跨平屋盖表面锥形涡强度。通过考虑旋涡效应对准定常理论进行修正,给出旋涡涡核吸力的计算式,并将计算值与大跨平屋盖刚性模型风洞测压试验数据进行对比,验证锥形涡流动模型对于预测旋涡涡核吸力的有效性。     

Experimental investigations of superconductivity in quasi-two-dimensional epitaxial copper oxide superlattices and trilayers

Epitaxial trilayer and superlattice structures grown by pulsed laser ablation have been used to study the superconducting-to-normal transition of ultrathin (one and two c-axis unit cells) YBa₂Cu₃O_7−x layers. The normalized flux-flow resistances for several epitaxial structures containing two-cell-thick YBa₂CU₃O,_7−x films collapse onto the “universal” curve of the Ginzburg-Landau Coulomb gas (GLCG) model. Analysis of normalized resistance data for a series of superlattices containing one-cell-thick YBa₂Cu₃O_7−x layers also is consistent with the behavior expected for quasi-two-dimensional layers in a highly anisotropic, layered three-dimensional superconductor. Current-voltage measurements for one of the trilayer structures also are consistent with the normalized resistance data, and with the GLCG model. Scanning tunneling microscopy, transmission electron microscopy, and electrical transport studies show that growth-related steps in ultrathin YBa₂Cu₃O_7−x layers affect electrical continuity over macroscopic distances, acting as weak links. However, the perturbation of the superconducting order parameter can be minimized by utilizing hole-doped buffer and cap layers, on both sides of the YBa₂Cu₃O_7−x layer, in trilayers and superlattices. These results demonstrate the usefulness of epitaxial trilayer and superlattice structures as tools for systematic, fundamental studies of high-temperature superconductivity.