二维可压缩流体Kelvin-Helmholtz不稳定性

利用高精度数值格式,研究了二维可压缩流体中的Kelvin-Helmholtz不稳定性,主要研究了可压缩性对Kelvin-Helmholtz稳定性增长率的影响.模拟定量的给出低Mach和高Mach数两种情况下,初始静压和对流Mach数以及Kelvin-Helmholtz不稳定性线性增长率的关系.模拟结果和自由剪切层以及混合层的实验结果以及理论分析一致.模拟表明,对流Mach数是描述流体可压缩性的合适参数,对流Mach数越小流体越不可压,Kelvin-Helmholtz不稳定性的线性增长率随对流Mach数的增加而减小. 关键词： Kelvin-Helmholtz不稳定性 可压缩流体 Mach数 超音速流体     

用NND格式模拟Kelvin-Helmholtz不稳定性

使用局部Steger-Warming通量分裂方法,利用NND有限差分格式求解守恒型流体力学方程组,实现对Kelvin-Helmholtz不稳定性的数值模拟.数值模拟给出的线性增长率与线性稳定性分析给出的结果相符合,得到锐利的界面变形图像.     

二维不可压流体Kelvin-Helmholtz不稳定性的弱非线性研究

通过将扰动速度势展至三阶,提出了Kelvin-Helmholtz（KH）不稳定性的弱非线性理论.在模耦合过程中观察到一个重要的共振现象,共振使得模耦合过程变得相当复杂,单模扰动很快进入非线性区,产生大量高次谐波,共振加强了非线性作用.分析了单模扰动中二次和三次谐波产生效应,以及对基模指数增长的非线性校正.模拟结果支持了解析理论.利用该理论,分析了KH不稳定的非线性阈值问题. 关键词： Kelvin-Helmholtz不稳定性 弱非线性理论 非线性阈值     

流向磁场抑制Kelvin-Helmholtz不稳定性机理研究

采用CTU + CT (corner transport upwind + constrained transport)算法对磁流体动力学方程组进行求解, 分别对有无磁场控制条件下开尔文-赫姆霍兹(Kelvin-Helmholtz, KH)不稳定性的演化过程进行数值模拟. 数值结果分析了磁场(MA=3.33)对混合层流...     

二维不可压缩流体Kelvin-Helmholtz不稳定性的二次谐波产生

推导了Kelvin-Helmholtz(KH)不稳定性二次谐波产生的理论公式,利用该公式得到的二次谐波增长的弱非线性结果与LARED-S程序的模拟结果符合.二维模拟定出了KH不稳定性单模非线性增长的阈值. 关键词： Kelvin-Helmholtz不稳定性 二次谐波产生 非线性阈值     

可压缩流体的Rayleigh-Taylor和Kelvin-Helmholtz不稳定性

可压缩流体界面不稳定性的小扰动研究中，往往首先规定具体的状态方程形式，然后给出色散关系。这使得所给出的结果仅适用于该状态方程的具体形式，具有特殊性。由于这种特殊性，使得某些机理的讨论变得复杂，且结论相互矛盾。     

高精度有限差分法模拟Kelvin-Helmholtz不稳定性

WENO有限差分格式有较高的分辨精度,适合复杂流场的计算,在国际上被广泛采用。本文利用WENO有限差分格式求解2维守恒型欧拉方程,实现了对无粘流体中Kelvin-Helmholtz不稳定性的数值模拟。速度剪切方向采用周期边界条件;扰动增长方向采用嵌边出流边界条件,一个不稳定波长分布64个网格。数值模拟给出的扰动幅值线性增长率与线性稳定性分析给出的结果很好符合,显示了该格式的有效性和精度。数值模拟给出了清晰的密度等值线,表明该方法还具有较好的界面变形捕捉能力。     

可压缩Kelvin-Helmholtz不稳定性低耗散锐界面方法直接模拟

采用低耗散WENO(weighted essential non-oscillatory)格式及锐界面方法模拟可压缩Kelvin-Helmholtz不稳定性问题.由于物质界面被描述成一种接触间断, 该方法可精确求解切向速度间断.基于优化模板对原始光滑指标进行正规化后, 得到一种低耗散WENO格式.修正后的方法显著降低了普通流动区域的过衰减问题, 保持了良好的激波捕捉性能, 并可获得与混合格式相当的求解精度.不同于以往求解单一流体或易混界面时, 通过初始设定有限宽度的剪切层或快速数值耗散以抑制高波数模态, 该方法允许高波数扰动的发展.计算结果表明, 高波数扰动展现出与以往理想Kelvin-Helmholtz不稳定性问题数值模拟或线化理论结果不同的特征, 但与有限厚度的剪切层结果相符.      

磁场对激光驱动Kelvin-Helmholtz不稳定性影响的二维数值研究

Kelvin-Helmholtz不稳定性(KHI)是流体和等离子体的基本物理过程,广泛存在于自然、天体物理以及高能量密度物理现象中.本文提出一种新的实验方案产生磁化KHI.利用开源的FLASH模拟程序对激光驱动调制靶产生的KHI进行了二维的数值模拟,考察和比较了KHI涡旋在毕尔曼自生磁场、外加磁场和无磁场情况下的演化.模拟结果表明自生磁场在KHI演化过程中基本不会改变KHI涡旋的形貌,而平行于流体方向的外加磁场对剪切流有致稳作用,主要稳定长波扰动.该研究结果可为在高能量密度激光装置中开展强磁环境下KHI实验提供理论指导.     

热传导对横截面不同的直管道中Kelvin-Helmholtz不稳定性的影响

Kelvin-Helmholtz不稳定性(KHI)增长的动力学分析是一个活跃的研究领域.本文解析研究了流体在横截面不同的直管道中流动时,热传导对KHI的影响.结果表明:管道中上下流体的界面相对切向速度会随着波数的增加先增加后减小,并且小的界面热传导系数导致相对切向速度随波数的减小更多,不同于横截面相同的直管道结果.另外,热传导会提高KHI的增长率,与横截面相同的直管道一致.研究结果可以为实际管道中流体不稳定性的分析以及管道的通风设计和供暖等工程研究提供一定参考.     

Magnetohydrodynamic Kelvin-Helmholtz instability for finite-thickness fluid layers

We have derived the analytical formulas for the Kelvin-Helmholtz instability (KHI) of two superposed finite-thickness fluid layers with the magnetic field effect into consideration. The linear growth rate of KHI will be reduced when the thickness of the fluid with large density is decreased or the thickness of fluid with small density is increased. When the thickness and the magnetic field act together on the KHI, the effect of thickness is more obvious when the magnetic field intensity is weak. The magnetic field transition layer destabilizes (enforces) the KHI, especially in the case of small thickness of the magnetic field transition layer. When considering the effect of magnetic field, the linear growth rate of KHI always decreases after reaching the maximum with the increase of total thickness. The stronger the magnetic field intensity is, the more obvious the growth rate decreases with the total thickness. Thus, it should be included in applications where the effect of fluid thickness on the KHI cannot be ignored, such as in double-cone ignition scheme for inertial confinement fusion.     

黏性各向异性磁流体Kelvin-Helmholtz不稳定性:二维数值研究

利用corner transport upwind和constrained transport算法求解非理想磁流体动力学方程组,对匀强平行磁场作用下,黏性各向异性等离子体自由剪切层中的Kelvin-Helmholtz不稳定性进行了数值模拟.从流动结构、涡结构演化、磁场分布、横向磁压力、抗弯磁张力等角度对各向同性和各向异性黏性算例结果进行了讨论,分析了黏性各向异性对Kelvin-Helmholtz不稳定性的影响.结果表明,黏性各向异性比黏性各向同性更利于流动的稳定.其稳定性作用是由于磁感线方向上剪切速率降低导致界面卷起程度和圈数的降低,并使卷起结构中小涡产生增殖、合并,破坏了涡的常规增长,从而导致流动的稳定.黏性各向异性对横向磁压力的影响比对抗弯磁张力更大.     

Kelvin-Helmholtz instability in a rotating ideally conducting inhomogeneous plasma

The Kelvin-Helmholtz instability in sheared magnetohydrodynamic flow of an ideally conducting rotating inhomogeneous compressible plasma is investigated. The asymptotic behaviour inx of the Kelvin-Helmholtz eigenfunctions for the case of finite compressibility in the presence of rotation is discussed and instability condition is derived. In the incompressible limit, a dispersion relation is derived which has been solved numerically and discussed in detail. It is found that the inhomogeneous system is unstable in an incompressible plasma.     

Phase Effect on Mode Coupling in Kelvin-Helmholtz Instability forTwo-Dimensional Incompressible Fluid

This paper studies the phase effect in mode coupling of Kelvin-Helmholtzinstability in two-dimensional incompressible fluid. It is found that thereis an important growth phenomenon of every mode in the mode couplingprocess. The growth changes periodically with phase difference and in thecondition of our simulation the period is about 0.7π. The periodcharacteristic is apparent in all stage of the mode coupling process,especially in the relatively later stage.     

Kinetic Simulation of Nonequilibrium Kelvin-Helmholtz Instability

The recently developed discrete Boltzmann method(DBM), which is based on a set of uniform linear evolution equations and has high parallel efficiency, is employed to investigate the dynamic nonequilibrium process of Kelvin-Helmholtz instability(KHI). It is found that, the relaxation time always strengthens the global nonequilibrium(GNE), entropy of mixing, and free enthalpy of mixing. Specifically, as a combined effect of physical gradients and nonequilibrium area, the GNE intensity first increases but decreases during the whole life-cycle of KHI. The growth rate of entropy of mixing shows firstly reducing, then increasing, and finally decreasing trends during the KHI process. The trend of the free enthalpy of mixing is opposite to that of the entropy of mixing. Detailed explanations are:(i) Initially,binary diffusion smooths quickly the sharp gradient in the mole fraction, which results in a steeply decreasing mixing rate.(ii) Afterwards, the mixing process is significantly promoted by the increasing length of material interface in the evolution of the KHI.(iii) As physical gradients are smoothed due to the binary diffusion and dissipation, the mixing rate reduces and approaches zero in the final stage. Moreover, with the increasing Atwood number, the global strength of viscous stresses on the heavy(light) medium reduces(increases), because the heavy(light) medium has a relatively small(large) velocity change. Furthermore, for a smaller Atwood number, the peaks of nonequilibrium manifestations emerge earlier, the entropy of mixing and free enthalpy of mixing change faster, because the KHI initiates a higher growth rate.     

倾斜壁面中Kelvin-Helmholtz不稳定性演化数值分析

基于FTM（Front Tracking Method）对倾斜壁面下的二维不混溶、不可压缩流体的Kelvin-Helmholtz（K-H）不稳定性进行数值模拟.研究壁面倾角,速度梯度层厚度以及理查德森数对K-H不稳定性发展的影响.研究表明,壁面倾角越大,K-H不稳定性发展越快,卷起的液体越多;倾斜壁面下速度梯度层厚度的增加对界面卷起表现出抑制作用.理查德森数重力项越大,界面卷起越缓慢,而理查德森数表面张力项对界面卷起高度的影响较小.