含悬浮固粒射流界面稳定性研究

利用气固两相耦合模型,理论推导出含悬浮固粒射流的稳定性方程,通过数值计算得到了两相射流稳定性特征曲线、固气扰动速度比值幅值曲线及固气相位差曲线,进而得到了关于固粒对流场中扰动增长和传播的影响及失稳过程中固粒扰动特性的结论。这些结论对于两相射流发展的认识和工程实际中实施对两相射流场的人工控制有重要意义。     

含高浓度悬浮固粒运动射流稳定性研究

首先用连续介质耦合模型推导出含高浓度悬浮固粒运动射流的空间稳定性方程,然后借助渐进分析法和欧拉守恒差分格式,用有限差分数值解法得到不同流向位置、流场雷诺数、固粒属性和喷射装置运动速度时流场的稳定性特征曲线,说明喷射装置的反向运动使不稳定扰动频率范围扩大,正向运动则相反。固粒抑制流场的不稳定性,随着固粒等效斯托克斯数的减小,这种效应增强。这些结论,对于两相运动射流发展的认识有重要意义。     

悬浮固粒对二维混合层流动失稳特性的影响*

本文在不可压缩二维混合层流动方程的基础之上,通过添加固粒的作用项,推导得到了修正的瑞利方程;然后用数值计算方法解其特征方程,得到了悬浮固粒的质量密度、固粒和气流的速度比值以及Stokes数不同时二维混合层流动中扰动频率与空间增长率的关系曲线,给出了关于悬浮固粒对流场失稳特性影响的几个重要结论。     

气固两相固射流场涡结构影响固粒扩散的研究

用三维离散涡丝方法模拟轴对称圆射流场涡结构的发展,所得结果在某个周向位置上与用二维点涡方法计算的结果符合较好。然后采用单向淹合模型模拟固粒在圆射流中的运动,说明当固粒Ｓｔ数远小于１时,固粒受流场的作用较明显,当Ｓｔ数为１时,固粒主要分布在涡结构的周围,分布较均匀;当Ｓｔ数远大于１时,固粒受流场的影响较弱,当对涡环沿周向施以五个波长的扰动时,固粒扩散的范围较宽,固粒的扩散与扰动的振幅成正比,中所得     

气固两相圆射流场涡结构影响固粒扩散的研究

用三维离散涡丝方法模拟轴对称圆射流场涡结构的发展·所得结果在某个周向位置上与用二维点涡方法计算的结果符合较好·然后采用单向耦合模型模拟固粒在圆射流中的运动,说明当固粒Ｓｔ数远小于１时,固粒受流场的作用较明显,当Ｓｔ数为１时,固粒主要分布在涡结构的周围,分布较均匀;当Ｓｔ数远大于１时,固粒受流场的影响较弱·当对涡环沿周向施以五个波长的扰动时,固粒扩散的范围较宽·固粒的扩散与扰动的振幅成正比·文中所得结论与一些实验结果相符,对实际应用有指导意义     

两相流中柱状固粒对流体湍动特性影响的研究

对含柱状固粒的两相流场,建立了包含柱状固粒对流场影响的流体脉动速度方程,在求解脉动速度方程的基础上,经平均得到流体的湍流强度和雷诺应力.将该方法用于槽流湍流场的求解,并与单相流实验结果进行了比较.计算中变化柱状固粒的参数,给出了固粒的体积分数、长径比、松驰时间对流场湍动特性的影响,说明粒子对流场的湍动特性起着抑制作用,其抑制的程度与粒子的体积分数、长径比成正比,与粒子的松弛时间成反比.     

均匀格子气Boltzmann方程的稳定性研究

１．引言格子气的基本方程是在几何空间、速度空间和时间上都是离散的Ｂｏｌｔｚｍａｎｎ方程（Ｂ方程）．这是一个有限差分方程．在离散速度气体运动论中［１］,Ｂ方程在速度空间上是离散的,在几何空间和时间上是连续的．这是一个偏微分方程．人们对离散速度气体Ｂ方程的稳定性和渐近特性的研究已经取得了很多结果．Ｍａａｓｓ~［２］通过构造Ｌｙaｐｕｎｏｖ函数族,在分布函数在空间上均匀的条件下,证明了平衡分布的渐近稳定性．信息函数Ｈ是该函数族的一员．Ｂｅｌｌｏｍｏｅｔａｌ~［３］．采用小扰动线性化方法在初值距离平衡解足…     

一类双曲方程自由边界问题的稳定性

锅炉炉管中汽水界面的稳定性是一个重要的开问题［１］，本文以此问题为模型，讨论了近似带域上双曲方程自由边界问题，利用小参数法和能量不等式，得到了解的渐近稳定性与平均稳定性．所得的稳定性条件，定性地看与工业试验结果相一致．     

数值求解Euler方程的UCGVC差分格式的注记

１．引言 近年来高精度差分格式的研究引起国内外的普遍重视,目的是更准确地模拟复杂流场的流动．众所周知,传统的二阶ＴＶＤ类格式虽然能较好地捕捉激波,但却存在局部极值点降阶的问题,而且由于一些格式的数值粘性过大,当用该格式计算粘性流特别是高雷诺数问题时,格式本身的数值粘性可能掩盖了流场的物理粘性,从而降低了格式对边界层的分辨率,因而无法正确计算热流值。文献［３］指出,采用高精度格式可适当放松对网格雷诺数的要求,因此发展三阶或三阶以上的格式是需要的。近年来,人们已经发展了一些无伪振荡的高阶格式,如ＥＮ…     

二维气固两相混合层中固粒对流场影响的研究

采用双向耦合模型对含有固粒的二维气固两相混合层流场进行了研究。流场采用拟谱方法直接数值模拟,固粒采用颗粒-轨道模型,在考虑流场对固粒作用的同时,考虑固粒对流场的反作用。结果发现固粒的浓度和Stokes数对流场影响明显。固粒的作用使涡量扩散加快,并阻碍流场的变化,减弱了流场中拟序结构的强度,缩短涡的生存期;固粒在流场中的分布规律与单相耦合所得结果相似。     

Existence of shocklets in a two-dimensional supersonic mixing layer and its influence on the flow structure

The spatial evolution of a T-S wave and its subharmonic wave, introduced at the inlet in a 2-D supersonic mixing layer, was investigated by using DNS. The relationship between the amplitude of the disturbance wave and the strength of the shocklet caused by the disturbance was investigated. We analyzed the shape of the disturbance velocity profile on both sides of the shocklet, and found that the existence of shocklet affected appreciably the disturbance velocity. The effects on the high speed side and low speed side of the mixing layer were found to be different     

The Inviscid Initial Value Problem for a Piecewise Linear Mean Flow

The time evolution of a small disturbance on a piecewise linear mean flow, approximating a parabolic profile, is calculated using Fourier transform methods. The solution is found to consist of two parts: one dispersive, incorporating the spreading of waves; one convective, characterized by a convection of the disturbance with the local mean velocity. Two dispersive modes are found: one symmetric with respect to the channel center line and one antisymmetric. The dispersivity of the symmetric mode is in fair agreement with the symmetric mode obtained for inviscid parabolic flow, whereas the antisymmetric mode is misrepresented. One of the parts of the solution to the horizontal velocities is found to be purely three-dimensional. This results from fluid elements retaining part of their horizontal momentum as they are lifted up by the time integrated effect of the vertical velocity. Calculations of the development of a particular disturbance modeling two vortex pairs are also made. The results show that the dispersive part, although decaying, is largest for the vertical velocity. For the horizontal velocity the three-dimensional lift-up effect provides the largest amplitudes. This part does not show any sign of decay, in agreement with earlier analysis by Gustavsson [8] and Landahl [16]. This last effect partly explains the sensitivity to three-dimensional disturbances seen in transition experiments and calculations. Comparison of the solution to a full numerical simulation using the Navier-Stokes equations shows good agreement for short times.     

Nonlinear Evolution of Singular Disturbances to the Bickley Jet

We consider the nonlinear evolution of a disturbance to the Bickley jet, and the critical layer for the disturbance is located very close to the nose of the jet rather than at the inflection points. Using a nonlinear critical layer analysis, equations governing the evolution of the disturbance are derived and discussed. When the critical layer is located exactly at the nose of the jet, we find that the disturbance cannot exist on a linear basis, even with weak viscosity present, but that nonlinear effects inside the critical layer do permit the disturbance to exist if both modes are present. However, when the phase velocity of the disturbance is perturbed sufficiently away from unity, so that we have a pair of critical layers slightly above and below the nose rather than a single critical layer, we find that the waves can exist on a linear basis, and again we derive equations governing the nonlinear evolution of the disturbance.     

Adaptive Robust Tracking for Flexible Spacecraft in Presence of Disturbances

The paper deals with trajectory tracking for a flexible spacecraft, subject to a gravity-gradient disturbance, under parameter uncertainties. The controls are gas jets and reaction wheels, and the measured variables describe the attitude and angular velocity of the rigid part. The flexible dynamics is treated as an additional disturbance acting on a rigid structure. First, an adaptive control is designed with only the gravity-gradient disturbance acting on the spacecraft; second, it is proved to be effective also in the presence of disturbance due to the flexibility, provided that appropriate robustness conditions on the controller gains are satisfied. These conditions use partial knowledge of the parameters describing the elastic dynamics. Simulations show the good performance of such control scheme and demonstrate its applicability even in the presence of input saturation.     

旋转流体中圆球沿旋转轴运动产生的扰动

本文用线化理论分析了整体旋转的理想流体中有一个圆球沿旋转轴作匀速运动时流体的扰动,基于旋轴对称流动的假设导出了决定运动稳定性的扰动压力方程和扰动流函数方程.用简正模法分析了扰动流函数方程,得出了非平凡中性扰动的波数与波速必须满足的约束条件,并求出了扰动的精确表达式.文中得出结论,中性扰动共有三种可能的形式.     

Äquivalenzsatz, Ähnlichkeitssätze für schallnahe Geschwindigkeiten und Widerstand nicht angestellter Körper kleiner Spannweite

Summary In transonic flow the velocity disturbance on low aspect ratio wings can be reduced to the velocity disturbance on bodies of revolution with the same distribution of cross-sectional area. This law of equivalence has been proved in another paper and is stated here from the physical point of view. By the similarity law for bodies of revolution corresponding similarity laws for low aspect ratio wings are given. Further the law of equivalence for the pressure drag is given for bodies of revolution and pointed low aspect ratio wings with any cross-section at the end, if the end lies sufficiently far in the supersonic flow. The last one is a generalisation for transonic flow of a formula ofWard originally valid for linearized supersonic equations only.     

Concentrated force acting in an inviscid and incompressible parallel flow

The paper discusses the steady disturbance velocity field induced by a concentrated force acting at a fixed point of space in a parallel flow of an inviscid and incompressible fluid. Force and parallel flow have the same direction. The induced velocity field, its pressure field and its acceleration field are described by means of generalized functions (distributions). Copyright © 2000 John Wiley & Sons, Ltd.     

A stability of the steady flow of compressible viscous fluid with respect to initial disturbance (v∞ ≠ 0)

We consider a compressible viscous fluid with the velocity at infinity equal to a strictly non‐zero constant vector in ?³. Under the assumptions on the smallness of the external force and velocity at infinity, Novotny–Padula (Math. Ann. 1997; 308 :439– 489) proved the existence and uniqueness of steady flow in the class of functions possessing some pointwise decay. In this paper, we study stability of the steady flow with respect to the initial disturbance. We proved that if H³‐norm of the initial disturbance is small enough, then the solution to the non‐stationary problem exists uniquely and globally in time, which satisfies a uniform estimate on prescribed velocity at infinity and converges to the steady flow in L_q‐norm for any number q? 2. Copyright © 2006 John Wiley & Sons, Ltd.     

Some Inviscid “Cat's Eye” Flows

Some inviscid flows with the combined shear and periodic disturbance characteristic of the Kelvin “eat's eye” pattern are presented. The solutions have constant vorticity in each region of closed streamlines, with discontinuities in vorticity (but not velocity) allowed across boundaries.