转子叶尖引射式射流的数值研究

转子叶尖射流能够有效地提高压气机的稳定工作裕度, 但是现有的各种射流器结构复杂, 并使发动机的重量增加. 研究目的在于探索一种新型的射流方式, 以方便在压气机中的实现,并且不增加发动机的重量. 采用对转子叶尖前缘位置机匣进行局部修型的方法, 提高了转子叶尖前缘附近流场的轴向速度, 从而产生类似转子叶尖射流的效果. 在Rotor37上的数值分析发现, 该方法能够提高转子的失速裕度约6.7%, 并能使转子的效率与压比有较小的提升. 对比不同机匣修型方案发现, 修型位置对压气机裕度的影响最为明显. 对转子叶尖流场的分析表明, 该方法能够提高转子叶尖前缘的轴向速度, 并将叶尖泄露涡向下游推移, 减小了转子叶尖的流动堵塞, 从而拓宽了转子的失速裕度.      

The leakage current mechanisms in the Schottky diode with a thin Al layer insertion between Al0.245Ga0.755N/GaN heterostructure and Ni/Au Schottky contact

This paper investigates the behaviour of the reverse-bias leakage current of the Schottky diode with a thin Al inserting layer inserted between Al0.245Ga0.755 N/GaN heterostructure and Ni/Au Schottky contact in the temperature range of 25-350°C. It compares with the Schottky diode without Aluminium inserting layer. The experimental results show that in the Schottky diode with Al layer the minimum point of I-V curve drifts to the minus voltage, and with the increase of temperature increasing, the minimum point of I-V curve returns the 0 point. The temperature dependence of gate-leakage currents in the novelty diode and the traditional diode are studied. The results show that the Al inserting layer introduces interface states between metal and Al0.245Ga0.755N. Aluminium reacted with oxygen formed Al2O3 insulator layer which suppresses the trap tunnelling current and the trend of thermionic field emission current. The reliability of the diode at the high temperature is improved by inserting a thin Al layer.     

UNSTEADY STATE DISPERSION OF AIR POLLUTANTS UNDER THE EFFECTS OF DELAYED AND NONDELAYED REMOVAL MECHANISMS

Abstract In this paper, we present a two‐dimensional time‐dependent mathematical model for studying the unsteady state dispersion of air pollutants emitted from an elevated line source in the atmosphere under the simultaneous effects of delayed (slow) and nondelayed (instantaneous) removal mechanisms. The wind speed and coefficient of diffusion are taken as functions of the vertical height above the ground. The deposition of pollutants on the absorptive ground and leakage into the atmosphere at the inversion layer are also included in the model by applying appropriate boundary conditions. The model is solved numerically by the fractional step method. The Lagrangian approach is used to solve the advection part, whereas the Eulerian finite difference scheme is applied to solve the part with the diffusion and removal processes. The solutions are analyzed to observe the effects of coexisting delayed and nondelayed removal mechanisms on overall dispersion. Comparison of delayed and nondelayed removal processes of equal capacity shows that the latter (nondelayed) process is more effective than the former (delayed removal) in the removal of pollutants from the atmosphere.     

Existence and global stability of almost automorphic solutions for shunting inhibitory cellular neural networks with time-varying delays in leakage terms on time scales

In this paper, shunting inhibitory cellular neural networks(SICNNs) with time-varying delays in leakage terms on time scales are investigated. With the aid of the existence of the exponential dichotomy of linear dynamic equations on time scales, fixed point theorem and the theory of calculus on time scales, we establish some sufficient conditions to ensure the existence and exponential stability of almost automorphic solutions for the model. An example with its numerical simulations is given to illustrate the feasibility and effectiveness of the theoretical findings.     

Existence and global exponential stability of almost periodic solutions for BAM neural networks with distributed leakage delays on time scales

In this paper, we deal with a class of BAM neural networks with distributed leakage delays on time scales. Some sufficient conditions which ensure the existence and exponential stability of almost periodic solutions for such class of BAM neural networks are obtained by applying the exponential dichotomy of linear differential equations, Lapunov functional method and contraction mapping principle. An example is given to illustrate the effectiveness of the theoretical predictions. The obtained results in this paper are completely new and complement the previously known publications.     

低速轴流压气机中工况变化对动叶顶部泄漏流波动频率的影响

本文利用数值方法研究了某两级低速轴流压气机第二级动叶在存在前后静叶扰动时,工况变化对其顶部非定常泄漏流波动频率的影响。结果显示其波动主要集中在泄漏涡轨迹附近,并且随着流量减小而增强。在大流量工况,其波动频率为转子通道频率。在中等流量工况,其波动频率为0.59倍通道频率。在小流量工况,其波动频率为0.51倍通道频率。并且其波动频率与前后静叶扰动强度无关。     

超导变压器绕组环流及漏磁场计算

高温超导变压器的漏磁场降低绕组中的临界电流并增加交流损耗;超导材料的零电阻特性使得绕组限制环流的能力极低.因此,在设计超导变压器时,进行磁场分析和环流计算显得尤其重要.本文采用场-路结合的方法,即在用ANSYS求得反映变压器各支路之间电磁耦合的电感矩阵的基础上列出电路方程,计算了变压器低压绕组5种不同形式的各支路电流分布,并进而分析了磁场.同时提出了减小环流和改善磁场分布的一些措施.     

椭圆微孔端面机械密封泄漏率与几何收敛点的关系

采用解析法和数值计算相结合的方法,解释椭圆微孔端面机械密封的方向角所引起的几何特性改变如何影响到泄漏率.首先,得到了不同方向角下,椭圆沿速度方向上的几何收敛点的解析解.然后,基于质量守恒的JFO空化边界条件建立数值计算模型,分析了液膜的压力分布,并使用最高压力点的坐标来近似表征高压区的位置,得到了方向角与最高压力点的关系.接着,通过对比,发现几何收敛点和最大压力点位置一致,并分析了原因.最后,分析了在不同结构参数和操作参数下方向角对泄漏率的影响规律,通过分析得到,方向角的改变,使几何收敛点的位置发生改变,从而改变高低压区的分布,当高压区靠近泄漏出口时,泄漏率大;当高压区远离泄漏出口时,泄漏率小.     

氧空位缺陷对PbTiO_3铁电薄膜漏电流的调控

基于非平衡格林函数及密度泛函理论第一性原理计算方法,计算了Fe, Al, V和Cu四种阳离子掺杂对氧空位缺陷引起的PbTiO_3铁电薄膜漏电流的调控.研究表明:Fe和Al离子掺杂将会增大由其中氧空位缺陷导致的铁电薄膜的漏电流,而Cu和V离子掺杂对该漏电流的大小具有明显抑制作用.这是因为Cu和V掺杂对氧空位缺陷有明显的钉扎作用.相比于半径更大的Cu离子,由于V的离子半径更小,且更接近于PbTiO_3铁电薄膜中Ti的离子半径,可以预言V离子更可能被掺杂进入薄膜,从而抑制氧空位缺陷引起的漏电流.研究结果对铁电薄膜器件的电学性能控制和优化有一定的理论指导意义.     

混合制冷剂泄漏试验研究与模拟分析

1研究背景目前在制冷和空调系统中，绝大多数采用混合制冷剂作为R502与HCFC－22等的替代物。但混合物的特殊问题，即在贮存、使用时因泄漏而引起的成分变化、特别是成分变化而导致制冷剂可燃性或系统性能的变化，引起了人们的普遍重视。英国I.C.I公司对R407C（HFC－32／125／134a）系统进行测试表明，由于泄漏后成分变化而引起的性能变化在10％以内。日本DAIKIN公司研究HFC－32／134a混合物时发现：其临界可燃配比为56Wt％，即HFC－32重量比超过56％时可燃；使用名义配比30／70wt％的HFC－32／134a混合物并不可燃，但发生泄漏后…