叶片尾缘掠型对离心压气机特性影响研究

针对叶片尾缘掠型对离心压气机特性影响开展了数值仿真与试验验证的研究工作,详细分析了尾缘掠型对压气机特性的影响规律和压气机叶轮内部流动特征,研究结果表明:尾缘掠型能够提升压气机出口的总压,使离心压气机压比变高,自由掠叶型相比于斜掠叶型,压比会进一步提升。叶片尾缘掠型能够有效抑制尾缘流动分离与叶间泄漏效应的结合效果,降低流动分离强度和分离区域,提升叶轮的稳定工作范围与效率。试验验证结果表明采用自由掠型尾缘叶轮,压比随着转速的升高提升幅度变大,最多提升了9.14%,喘振线明显向左偏移,运行流量范围拓宽。尾缘掠型能够有效提升压气机压比和稳定工作范围,是改善压气机特性的有效手段。     

超跨声涡轮叶栅尾缘激波系流动研究

本文通过分析超跨声涡轮尾缘波系的流动机理给出了详细的尾缘激波系流动图画,强调了尾缘分离激波的重要作用。经过分析,认为基底区压力是通过影响基底区宽度来影响涡轮叶栅尾缘激波强度的。最后将上述机理应用到某叶栅S1计算程序的改进工作中,数值计算和叶栅试验结果表明,改进工作有效提高了该程序对超跨声涡轮叶栅尾缘激波流动的模拟能力。     

“强光一号”Al丝阵Z箍缩产生K层辐射实验研究

在“强光一号”加速器开展了Al丝阵Z箍缩产生K层辐射的实验研究,固定Al丝线径20 μm、丝阵直径12 mm,丝根数为8和12的负载获得K层产额分别为0.9 kJ/cm和1.1 kJ/cm,明显高于16和24根丝负载.辐射功率波形和时间分辨的X射线图像显示,低丝数负载存在拖尾质量引起的多次内爆现象.在60%—80%的内爆时间内,丝阵几乎停留在初始位置;主体内爆在随后的25—30 ns内完成,将部分等离子体留在初始位置,形成质量的拖尾分布;内爆后期驱动电流向外围的拖尾质量迁移,引 关键词： Al丝阵 Z箍缩 K层辐射')" href="#">K层辐射 拖尾质量     

声学回波统计的鱼群密度评估方法*

与传统的回波积分法相比，回波统计鱼群数量密度评估方法具有无需回波信号绝对量和鱼群中个体鱼的平均目标强度先验知识的优点。对该方法在鱼群数量密度评估上的应用问题进行了实验研究，并针对其中鱼群密度分布的不均匀性及统计样本量偏少导致评估结果偏差的问题，提出了一种基于能量阈值的鱼群回波数据预处理方法和统计样本的改进抽样方法，有效提高了该方法鱼群密度评估的精确度。与传统的回波积分法评估结果的对比分析表明，该评估方法适用于低密度鱼群的评估。     

Simple modeling of dipolar coupled Li spins and stimulated-echo spectroscopy of single-crystalline β-eucryptite

Stimulated-echo spectroscopy has recently been applied to study the ultra-slow dynamics of nuclear spin-3/2 probes such as 7Li and 9Be in solids. Apart from the dominant first-order quadrupolar interaction in the present article also the impact of the homonuclear dipolar interactions is considered in a simple way: the time evolution of a dipole coupled pair of spins with I = 3/2 is calculated in an approximation, which takes into account that the satellite transitions usually do not overlap. Explicit analytical expressions describing various aspects of a coupled quadrupolar pair subjected to a Jeener-Broekaert pulse sequence are derived. Extensions to larger spin systems are also briefly discussed. These results are compared with experimental data on a single-crystalline Li ion conductor.     

Rollup region of a turbulent trailing vortex issued from a blade with flow separation

This paper presents the results of an experimental investigation on the near field of a tip vortex generated by a blade at moderate incidence. The experiments were conducted at Re=15 000 and the boundary layer over the blade separated around midchord on the upper surface. Laser-Doppler measurements of the turbulent flow (Tu=1.5%) were performed at various stations downstream of the blade. The three components of the mean velocity field and turbulent attributes were quantified at cross-planes, characterizing both the blade wake and the tip vortex structure. This allowed the analysis of the rollup and initial stages of decay of the tip vortex in the light of known theories and models. The axial velocity defect at the center of the vortex core evolved as x⁻¹ log x, without displaying any significant outgrowth imposed by the separated flow upstream. Momentum balances were also carried out at a station downstream to the conclusion of vortex rollup. The approximate axisymmetry of the flow field in the trailing vortex was used to formulate the balances in a cylindrical coordinate system. Among other observations, it was seen that an adverse axial pressure gradient developed in the vortex core, which reinforced the tenacity of the axial velocity defect. In contrast, an area influenced by a favorable pressure gradient was found outside the core.     

叶片尾缘内冷通道中最佳强化传热的针肋排列结构研究

本文应用湍流模型对涡轮叶片尾缘针肋通道的换热与流动进行了二维数值模拟研究。为了研究通道内针肋排列 方式对换热与流动的影响,对三种不同的针肋排列方式的通道进行了数值模拟计算。比较了顺排和叉排的区别,并提出了 一种沿流向叉排的针肋排列方式,且对各种排列的传热和阻力特性进行了综合分析和比较。     

Coherent tunneling of lithium defect pairs in KCl crystals

The tunneling of two lithium ion impurities on next-nearest neighbor sites in potassium chloride are investigated both experimentally and theoretically. The strong dipolar interaction leads to coherent tunneling motion of the two defect ions between degenerate off-center positions. Comparing data of rotary echo experiments for impurity pairs ⁷Li—⁷Li, ⁶Li—⁶Li, and ⁷Li—⁶Li with theory permits a thorough investigation of the isotope effect and of the effect of the interaction on the tunnel states. Our findings confirm the tunneling model with <111> off-center states to be valid even for strongly interacting impurities. Using degenerate perturbation theory in terms of two-particle states, we obtain essentially exact expressions for the tunneling spectrum and the dynamical susceptibility which agree well with the measured data.     

Can a ground-based vehicle hear the shape of a room?

Assume that a ground-based vehicle moves in a room with walls or other planar surfaces. Can the vehicle reconstruct the positions of the walls from the echoes of a single sound event? We assume that the vehicle carries some microphones and that a loudspeaker is either also mounted on the vehicle or placed at a fixed location in the room. We prove that the reconstruction is almost always possible if (1) no echoes are received from floors, ceilings, or sloping walls and the vehicle carries at least three noncollinear microphones, or if (2) walls of any inclination may occur, the loudspeaker is fixed in the room and there are four noncoplanar microphones. The difficulty lies in the echo-matching problem: How to determine which echoes come from the same wall. We solve this by using a Cayley–Menger determinant. Our proofs use methods from computational commutative algebra.