Direct Numerical Simulation Of Three-Dimensional Richtmyer-Meshkov Instability

Direct numerical simulation (DNS) is used to study flow characteristics after interaction of a planar shock with a spherical media interface in each side of which the density is different. This interfacial instability is known as the Richtmyer-Meshkov (R-M) instability. The compressible Navier-Stoke equations are discretized with group velocity control (GVC) modified fourth order accurate compact difference scheme. Three-dimensional numerical simulations are performed for R-M instability installed passing a shock through a spherical interface. Based on numerical results the characteristics of 3D R-M instability are analysed. The evaluation for distortion of the interface, the deformation of the incident shock wave and effects of refraction, reflection and diffraction are presented. The effects of the interfacial instability on produced vorticity and mixing is discussed.

Vertically forced surface wave in weakly viscous fluids bounded in a circular cylindrical vessel

Two-time scale perturbation expansions were developed in weakly viscous fluids to investigate surface wave motions by linearizing the Navier-Stokes equation in a circular cylindrical vessel which is subject to a vertical oscillation. The fluid field was divided into an outer potential flow region and an inner boundary layer region. A linear amplitude equation of slowly varying complex amplitude, which incorporates a damping term and external excitation, was derived for the weakly viscid fluids. The condition for the appearance of stable surface waves was obtained and the critical curve was determined. In addition, an analytical expression for the damping coefficient was determined and the relationship between damping and other related parameters (such as viscosity, forced amplitude, forced frequency and the depth of fluid, etc.) was presented. Finally, the influence both of the surface tension and the weak viscosity on the mode formation was described by comparing theoretical and experimental results. The results show that when the forcing frequency is low, the viscosity of the fluid is prominent for the mode selection. However, when the forcing frequency is high, the surface tension of the fluid is prominent.

Waverider configurations derived from general conical flowfields

A method based on the computational fluid dynamics (CFD) is presented for a flexible waverider's design. The generating bodies of this method could be any cones. In addition, either the leading edge or the profile of the scramjet's inlet is used as the waverider's definition curve, parameterized by the quadric function, the sigmoid function or the B-spline function. Furthermore, several numerical examples are carried out to validate the method and the relevant codes. The CFD results of the configurations show that all the designs are successful. Moreover, primary suggestions are proposed for practical design by comparing the geometrical and aerodynamic performances of the cone-derived waveriders at Mach 6.

三维湍流高速进气道内外流场的高效高分辨率解

提出一种高效、高分辨率求解三维复杂流场的隐式算法,并成功地用于求解高速进气道内外流场的三维、可压缩、雷诺平均Navier-Stokes方程组，获得了三个工况五种流场的三维数值解；与有关实验数据比较，结果令人满意。

用空间推进法来解钝锥三维粘性绕流

本文将文献［１］中提出的方法推广应用于三维可压缩Ｎ－Ｓ方程，文中给出了钝锥超声速三维粘性绕流的结果。得到了背风面分离的流动图画，计算结果与实验相吻合。

超声速和高超声速进气道的数值模拟

本文讨论超声速和高超声速进气道的数值模拟问题,其中包括国内外对进气道问题的一些主要进展、方向和今后预研的动态,目的在于弄清流场形成的机理,为高速飞行器进气道的气动设计提供理论依据。

解不可压缩流体力学问题的降阶法——Ⅱ.空间V~h的基函数和误差估计

本文对于一大类数值求解二维Navier-Stokes方程边值问题的有限元格式给出了零散度空间V~h的一组简单基函数,讨论了速度的数值误差对压力的数值解的影响,并提出一个改进算法。

扩散型连续波HF化学激光器小信号增益的计算

应用层流边界层二维简化模型计算了扩散型连续波HF化学激光器的小信号增益。研究了气流速度、温度、组份对增益的影响,得到一些有用的结果。计算结果与二维Navier-Stokes方程组的计算结果相符,但计算方法较简单。

高温空气的热力学性质

<正> 自从第二次世界大战末德国发明V-2火箭,特别是1957年苏联发射第一个人造地球卫星以后,航空和宇航技术高速发展,现在,飞行体的速度已远远超过第一宇宙速度(7.8公里/秒)。随着速度剧增,带来了低速飞行时不曾出现的特殊问题:一是高M数效应,一是高温对飞行介质的影响。高M数效应使得通常的Navier-Stokes方程失效。研究这方面问题,属于高速空气动力学范围。在实际问题中,高速必然伴随着产生高温,这两方面的效应交织在一起。热效应比起单纯的速度效应更本质,这使得高速高温流动现象及其介质性质的研究成为高温气体物理力学的一个最重要方面。

利用有限差分法求解扩散混合化学反应二维平行流动

利用隐式有限差分方法,对两股平行流的扩散混合、化学反应问题进行了计算。计算中,使用了层流压缩边界层方程并考虑了HF化学激光器的化学反应。计算结果表明:HF(2)振动激发态的浓度要比HF(1),HF(3)、HF(0)的浓度都高,从而获得了粒子数反转条件。另外,在计算中不需要混合长度的假设,就可以求得主流(无化学反应区)与化学反应区的两条界面曲线。当然,本文的计算方法要比直接求解二维Navier-stokes方程要简单得多。

多孔介质中流体流动的细观-宏观模拟

阐述了如何用体积平均化方法推导具有非线性吸附效应的多孔介质中的 Forchhermer方程和对流 -扩散方程。这两个方程对分析多孔介质中质量输运有着极大的应用价值。在分析 Navier- Stokes方程中 ,我们发现非滑移条件在平均化过程中并不扮演重要的角色 ,而吸附边界条件对体积平均化输运方程作出了重要贡献。所以 ,在推导多相输运方程时对平均化方法和边界条件的处理必须非常小心。

激波-涡干扰声场的数值研究

采用高精度差分格式求解非定常可压缩Navier-Stokes方程,对激波-单涡/双涡相互干扰产生的声场进行了直接数值模拟。详细研究了波-涡干扰声场结构的早期发展阶段,将激波-单涡的计算结果和相应实验进行了对比,并给出近场声压的衰减规律。在此基础上模拟较为复杂的激波-双涡干扰,给出不同旋涡旋转方向下的声场结构。

可压剪切层线性稳定性特征直接数值模拟

基于伪随机数生成技术促生白噪声扰动，以高精度迎风/对称紧致混合差分算法求解二维/三维非定常可压Navier-Stokes方程，揭示了可压自由剪切层初始剪切过程中扰动的线性演化特征，以及该过程对扰动波数方向的内在选择性。验证了所用算法的有效性，表明线性理论同数值模拟相结合是可压剪切层研究的合理途径之一。

可压缩双组分混合层的直接数值模拟研究

通过数值求解可压缩Navier-Stokes方程模拟了三维可压缩双组分混合层问题,着重研究了双组分密度比和可压缩效应对混合层发展演化的影响.研究表明,随着密度比的增大,混合层扰动增长率降低.在混合层发展初期,可压缩性作用尤其是斜压效应对旋涡的发展起主导作用;在混合层发展后期,可压缩性影响减弱,旋涡的拉伸扭转效应占主导作用.同时,还分析讨论了可压缩混合层中湍流的转捩及拟序结构的演化过程.

可压涡卷空间演化的迎风紧致差分数值模拟

从数值算法的耗散和色散特征的时空全离散Fourier分析出发，通过直接求解二维非定常可压Navier-Stokes方程，将发展的5阶迎风紧致差分格式用于无约束可压平面受迫剪切层中基频涡卷空间演化过程的数值模拟。采用被动守恒标量等方法显示了基频涡卷的饱和、一次对并、二次对并等现象，据此探讨了入口来流亚谐扰动引起的初值效应问题，表明可压大尺度涡结构空间演化形态与受迫扰动方式之间存在关联。