Numerical investigation of the effect of inlet condition on self‐excited oscillation of wet steam flow in a supersonic turbine cascade

Self‐excited oscillation can be induced due to the interaction between condensation process and local transonic condition in condensing flow, which is an important problem in wet steam turbine. With an Eulerian/Eulerian numerical model, the self‐excited oscillation of wet steam flow is investigated in a supersonic turbine cascade. Owing to supercritical heat addition to the subsonic flow in the convergent part of the cascade, the oscillation frequency decreases with increased inlet supercooling. Mass flow rate increases in the oscillating flow due to the greater supersaturation in condensation process, while the increase will be suppressed with the flow oscillation. Higher inlet supercooling leads to the fact that the condensation process moves upstream and the loss increases. Moreover, some predictions of oscillation effects on outflow angle and aerodynamic force are also presented. Finally, heterogeneous condensations with inlet wetness and periodic inlet conditions, as a result of the interference between stator and rotor, are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Nonlinear resonances and self-excited oscillations of a rotor caused by radial clearance and collision

This paper investigates oscillations in a flexible rotor system with radial clearance between an outer ring of the bearing and a casing by experiments and numerical simulations. The mathematical model considers the collisions of the bearing with the casing. The following phenomena are found: (1) Nonlinear resonances of subharmonic, super-subharmonic and combination oscillation occur. (2) Self-excited oscillation of a forward whirling mode occurs in a wide range above the major critical speed. (3) Entrainment phenomena from self-excited oscillation to nonlinear forced oscillation occur at these nonlinear resonance ranges. Moreover, this study analyzes periodic solutions of the mathematical model by the Harmonic Balance Method (HBM). As the results, the nonlinear resonances of subharmonic oscillation and its entrainment phenomenon can be explained theoretically by investigating the stability of the periodic solutions. The influence of the static force and the bearing damping on these oscillation are also clarified.     

Matrix characterization of oscillation for double sequences

The notion of oscillation for ordinary sequences was presented by Hurwitz in 1930. Using this notion Agnew and Hurwitz presented regular matrix characterization of the resulting sequence space. The primary goal of this article is to extend this definition to double sequences, which grants us the following definition: the double oscillation of a double sequence of real or complex number is given P-lim sup_{(m,n)→∞;(α,β)→∞}|S _m,n -S _α,β |. Using this concept a matrix characterization of double oscillation sequence space is presented. Other implication and variation shall also be presented.      

二阶时标非线性中立型动力学方程的振动性

运用广义Riccati变换给出时标上二阶非线性中立型动力学方程振动的充分条件,进一步研究了具扰动项的动力学方程解的性态.所得结论推广和改进了已知文献的部分结果.     

一类具有连续变量的二阶非线性阻尼差分方程的振动准则

考虑了一类具有连续变量的二阶非线性阻尼差分方程,利用积分变换和广义R iccati变换,给出了此类方程的振动准则.     

二阶非线性阻尼微分方程解的振动性质

本文研究了一类二阶非线性阻尼微分方程解的振动性,利用分类讨论和分析的方法,建立了两个新的振动性定理,推广和改进了已有的结果.     

外力驱动下耦合弹簧振子的法诺共振

法诺共振是物理体系中普遍存在的一种非对称共振现象,它最早起源于量子物理,其微观图像是原子谱线中窄的分离态与宽的连续态之间的相干干涉.本文利用经典力学体系中两个弹簧振子的耦合,使其中一个弹簧振子受到周期性外力的驱动,成功类比了量子力学中的法诺共振现象.通过分析每个弹簧振子的动力学方程,严格求解它们的振动公式,从而得到每个弹簧振子的振幅和位相与外部驱动力频率之间的关系.结果表明,耦合体系中受外力驱动的那个弹簧振子既可以发生非对称的法诺共振,又可以发生对称的洛仑兹共振,而另一个弹簧振子只能发生洛仑兹共振.本文的推导与分析能够使读者更好地理解法诺共振现象及其激发条件.     

超疏水表面液滴的振动特性及其与液滴体积的关系

超疏水表面液滴的振动特性与接触线的移动、液滴体积、基底振幅等因素密切相关.本文在基底振幅较小且恒定的条件下,研究了超疏水表面液滴的共振振幅、模式区间、共振频率等振动特性及其与液滴体积(20—500μL)的关系.此外,将基于一般性疏水表面建立的Noblin共振频率计算模型应用于超疏水表面,并提出“虚驻点”的概念,借此对模型进行了误差分析和修正.研究表明:1)共振时,液滴高度变化率即比振幅随体积增大而增大,随阶数增大而减小;2)各模式区间的起止频率首尾相接,其范围随体积增大而减小;3)液滴体积越大,共振频率越小,随着阶数增大,共振频率f与体积V的关系趋于f-V^–0.4,不同于一般性疏水表面上的f-V^–0.5;4)直接应用Noblin模型计算共振频率会产生较大误差,主要原因在于液滴表面波波段数量统计存在较大偏差,而修正后的模型可以准确计算超疏水表面大体积液滴的共振频率.     

基于压电振荡原理的微阵列点样系统的研制

针对基于电磁微阀原理的非接触点样方式存在操作过程复杂、点样量偏大,以及压电喷墨原理的非接触点样方式存在点样针不易清洗、造价昂贵等不足,研制了一种基于压电振荡原理的新型非接触点样装置,实现了微量液体点样.在本装置中,毛细管点样针与压电驱动装置为两个独立单元,可以单独对毛细管点样针进行更换和清洗.采用激光拉制法制备的玻璃毛细管点样针具有内径可调、成本低等优点.此点样方式通过改变压电陶瓷的振幅和频率,可在10Symbolm@@_10～10Symbolm@@_9 L之间调控点样体积.以此为基础,结合三维精密位移控制技术,研制了一种基于压电振荡原理的微阵列生物芯片点样系统.对点样系统的点样体积、点样密度、点样精度等参数进行了测试,结果表明,此点样系统的最小点样体积可达320 pL,点样密度可达4000 点/cm2,并能够实现界面图案化制备.     

气泡振动的非线性耦合模型

我们推广了Longuet-Higgins关于各向同性气泡的非各向同性模式激发的二阶理论。着重注意“呼吸”模式和“变形”模式之间的相互作用,两个模式之间的能量交换足够强,以致于两个模式有同量级的振幅。文中指出:模式耦合的方程组类似于其他物理领域(如非线性光学、水波)所研究的方程组,并讨论了二种特解,考虑了平衡点及其稳定性。