可压缩流向涡与激波轴对称干扰的数值模拟

用ＮＳ方程数值模拟了可压缩流向涡和激波轴对称相互作用现象。数值模拟包括定常和非定常两种情况,计算结果分别与相应的实验进行了比较,结果表明数值模拟成功地捕捉到了激波和旋涡相互作用过程中发生的激波波面变形,激波振荡,涡核变大以及激波波后出现驻点、回流区等流场特征。提出了判断流向涡与运动激波相互作用中旋涡破碎的准则。     

可压缩流向涡与激波轴对称干扰的数值模拟1)

用NS方程数值模拟了可压缩流向涡和激波轴对称相互作用现象.数值模拟包括定常和非定常两种情况,计算结果分别与相应的实验进行了比较.结果表明数值模拟成功地捕捉到了激波和旋涡相互作用过程中发生的激波波面变形,激波振荡,涡核变大以及激波波后出现驻点、回流区等流场特征.提出了判断流向涡与运动激波相互作用中旋涡破碎的准则.     

可压缩流向涡与激波轴对称干扰的数值模拟

用ＮＳ方程数值模拟了可压缩流向涡和激波轴对称相互作用现象．数值模拟包括定常和非定常两种情况,计算结果分别与相应的实验进行了比较．结果表明数值模拟成功地捕捉到了激波和旋涡相互作用过程中发生的激波波面变形,激波振荡,涡核变大以及激波波后出现驻点、回流区等流场特征．提出了判断流向涡与运动激波相互作用中旋涡破碎的准则     

混合层流动拟序结构的大涡模拟

采用大涡模拟方法对空间发展的二维平面混合层进行了数值模拟 ,动量方程采用分步投影法求解 ,亚格子项采用标准Smagorinsky亚格子模式模拟 ,压力泊松方程采用修正的循环消去法快速求解 ,同时求解了标志物输运方程以实现数值流场显示。模拟结果给出了混合层流动的瞬态发展过程以及流动中拟序结构的发展演变过程 ,成功地模拟了混合层发展中的各种瞬态细节过程 ,如涡的卷起、增长 ,涡与涡之间的配对、合并过程 ,以及大涡破碎为小涡的级联过程 ,为各种以混合层流动为原型流动的射流、尾流等工业流动的控制和优化提供了理论基础。     

激波与涡对相互作用的实验研究

在方截面激波管中进行了平面运动激波和涡对的二维相互作用实验，研究了激波与同向涡对、激波与反向涡对相互作用的非定常过程．根据实验照片，分析讨论了作用过程中激波的变形，二次激波和三波点的形成、演变，激波与激波的相互作用，以及旋涡结构的变化等．实验表明，激波通过涡核时，激波发生剧烈变形，旋涡强度增大，涡核形状改变．     

可压缩流向涡与反向运动激波相互作用的实验

对可压缩流向涡与反向运动激波相互作用的现象进行了实验研究．实验在９４ｍｍ×９４ｍｍ的方截面激波管中进行．在实验段上游安装了一个有限翼展平直机翼．当入射激波通过机翼后，波后２区气流在模型翼尖诱导出一条流向涡．入射激波在激波管端壁反射后，形成的反射激波在观察窗处和流向涡发生作用．实验中拍摄了激波与流向涡作用全过程的纹影照片，观察到了一些和定常激波与旋涡相互作用不同的现象，并与数值计算结果进行了初步比较     

低对流马赫数平面混合层的声波产生机理

为了详细揭示低对流马赫数下平面混合层的声波产生机理,基于高精度混合格式,对空间发展的平面混合层的流场结构及其声场特性进行了直接模拟.数值结果描述了对流马赫数为0.4时混合层失稳产生的涡串以及涡发展过程中所存在的各种声源,其中包括常规的单涡四极子声源、双涡以及多涡合并过程产生的四极子声源,另外,还发现因K-H不稳定引起混合层振动而产生的偶极子声源,声波以平面波的形式向周围传播.     

二维混合层拟序结构的直接数值模拟

本文是在文[1]的基础上,引用Cain等人(1981)提出的映射函数将无穷远的边界变换到有限距离处,用伪谱方法对N-S方程组进行直接数值模拟,研究时间发展的二维混合层的不稳定性,再现了大涡的卷起,涡对的合并与撕裂以及三个涡、四个涡之间的相互作用过程,并将过程进行了动态显示。     

激波诱导环形SF6气柱演化的机理

基于可压缩多组分Navier-Stokes控制方程,结合5阶加权本质无振荡格式以及网格自适应加密技术和level-set方法,数值模拟了平面激波(Ma=1.23)与环形SF₆气柱(内外半径分别为8和17.5 mm)界面的相互作用过程。相比于之前的实验结果,数值模拟结果揭示了入射激波在界面内4次透射过程中的复杂波系结构,观察到透射激波在内部界面传播时形成自由前导折射结构并向自由前导冯诺依曼折射结构转换的波系演变过程;另外,界面内的复杂激波结构诱导内部下游界面上的涡量发生了3次反向;在界面演化后期,内部界面形成的“射流”结构与下游界面相互作用,诱导界面形成一对主涡、一对次级涡以及一个反向“射流”结构。定量分析了环形界面长度、宽度、位移、环量以及混合率的变化情况,结果表明,内部气柱的存在减弱了前期小涡结构合并形成大涡结构过程中对界面高度与长度的影响,同时提高了重质气体与环境气体的混合率。     

超声速中等欠膨胀冲击射流的涡声关系研究

使用大涡模拟方法对冲击面为平面的超声速中等欠膨胀冲击射流进行了数值模拟. 利用三阶迎风和四阶对称紧致格式对无量纲化轴对称可压缩滤波N-S方程进行空间离散，时 间上推进采用的是三阶精度的TVD型Rugge-Kutta法. 通过与经典的冲击射流实验比较，证 实了程序的可靠性. 数值模拟得到了流场中不同尺度的涡结构和激波结构，观察到了上行 声波和反射波以及流场中不同位置的声源，分析了冲击区剪切层附近区域的压强和涡旋转强 度变化的频率、冲击平板上的压强变化频率以及射流剪切层中不同位置的涡合并出现的频率， 发现冲击区剪切层附近区域的压强和涡强度变化以及射流剪切层中的涡合并现象和离散频率 的冲击单音有重要关联.     

超声速混合层中扰动增强混合实验

以基于纳米技术的平面激光散射(nano-based planar laser scattering,NPLS)流动显示技术定性研究了隔板扰动对超声速混合层(Mc=0.5)的混合增强效果.首先通过系列实验优化设计了扰动参数.实验结果表明,超声速混合层对于从隔板引入的扰动非常敏感.二维扰动的混合强化机制是提前混合层失稳位置,增厚混合层;而三维扰动的混合强化机制主要是通过诱导流向涡和展向运动,促进流动三维性质的发展.总体而言,三维扰动的混合强化效果优于二维扰动.由于是超声速混合层,隔板上的扰动片虽然很薄,但同样会引起激波的产生,是该方法中总压损失的主要原因.     

Evolution of a 2-D disturbance in a supersonic boundary layer and the generation of shocklets

Through direct numerical simulation, the evolution of a 2-D disturbance in a supersonic boundary layer has been investigated. At a chosen location, a small amplitude T-S wave was fed into the boundary layer to investigate its evolution. Characteristics of nonlinear evolution have been found. Two methods were applied for the detection of shocklets, and it was found that when the amplitude of the disturbance reached a certain value, shocklets would be generated, which should be taken into consideration when nonlinear theory of hydrodynamic stability for compressible flows is to be established.     

Effect of Streamline Curvature on Intensity of Streamwise Vortices in the Mixing Layer of Supersonic Jets

The structure of supersonic nonisobaric jets with Mach numbers M_a = 1 and 2 is considered experimentally to find the effect of streamline curvature on the evolution of streamwise vortices in the mixing layer. The spatial development of steady streamwise vortices in the mixing layer of supersonic jets is considered. A method for generation of steady streamwise vortices by applying microroughness elements of controlled size onto the inner surface of the nozzle is developed. Radial profiles and azimuthal variations of total pressure are obtained; the mixinglayer thickness and the curvature of streamlines in supersonic jets are determined. A significant effect of microroughness elements of prescribed shape located on the nozzle surface on the behavior of total pressure in the mixing layer of supersonic jets, as compared to natural disturbances, is obtained.     

Features of a Turbulent Jet at High Supersonic Velocities

The results of modeling a turbulent supersonic jet at M = 5 using large-eddy simulation (LES) are presented. The structural features of turbulence formed in this flow are analyzed. The possibilities of the large-eddy simulation method and the complexities of simulation of the compressibility effects in jet flows at high Mach numbers are considered. Such features of the supersonic jet as the local turbulent shocklets and Mach waves are reproduced numerically. It is shown that in the neighborhood of the jet the trajectories of ejection flow are located along the front of Mach waves. Anisotropic turbulent structures whose longitudinal scale is greater than the transverse scale by an order of magnitude are revealed in the jet. An estimate of the baroclinic effects shows their weak influence on the vorticity generation in the jet flow considered.     

化学反应对超音速混合层发展的影响分析

超音速混合层流动发展的研究对于了解超音速燃烧过程具有重要意义.基于耦合详细化学反应动力学机理的高精度数值模拟，分析了化学反应对超音速混合层发展过程的影响.主要分析了在两种燃烧状态下化学反应对混合层的演化过程和混合层厚度的影响.此外从涡动力学角度，分析了化学反应对混合层厚度的影响机理.     

用格子Boltzmann方法数值模拟混合层中旋涡的合并过程

用格子Boltzmann方法计算混合层中的流动问题。在流场的入口处加不同频率、振幅和相位的小扰动,观察混合层中旋涡的演进机理,模拟二维混合层中旋涡合并现象。在基本扰动波的基础上,又加入频率为基本波频率一半的亚谐波,得到了两个涡合并的计算结果,当加入的亚谐波频率为基本波频率的三分之一时,得到了三个涡合并的计算结果。这些计算结果与已有文献的结果基本一致,显示用格子Boltzmann方法模拟混合层问题是可行的。     

超音速混合层稳定性分析及增强混合的研究

利用流动稳定性提高超音速混合层的混合效率,对于提高超音速流的高效混合是一个有效途径。研究结果表明,有展向曲率的三维混合层中,三维扰动的增长率很大,且法向的掺混能力也较强,可以有效地增强混合。对于高马赫数来流的超音速混合层,这一特性依然存在,这将有利于提高高超音速混合层的混合能力。     

Mixing Characteristics in a Supersonic Combustor with Gaseous Fuel Injection Upstream of a Cavity Flameholder

Non-reacting experiments and numerical simulations have been performed to investigate the mixing characteristics in a supersonic combustor with gaseous fuel injection upstream of a flameholding cavity in a supersonic vitiated air flow with stream Mach number 1.7. Using helium as simulated fuel, the acetone vapor is adulterated into the fuel jet. The fuel distribution in spanwise and streamwise direction is imaged by the planar laser-induced fluorescence (PLIF) measurement. According to the similarity of experimental observations with different cavities, the typical L/D = 7 cavity with aft wall angle 45° is chosen and the flowfield with the injection is calculated by Large Eddy Simulation. Experimental and numerical results have shown that most of the fuel flow away upon the open cavity with the lifting counter-rotating vortex structures induced by the transverse jet. Only a small portion of the fuel is convected into the cavity shear layer by the vortex interaction of the jet with cavity shear layer, and then transported into the cavity due to the cavity shear layer motion and the interaction of the shear layer with the cavity trailing edge.     

Suppression of embedded shocks in supersonic free-shear-layer structures

Although the suppressed instability of supersonic free shear layer flow has been documented by many investigators, the underlying physics are still ambiguous. In the present study, numerical simulations were performed to cast physical insight into the two-dimensional large-scale structure which is organized in a supersonic free shear layer. It is found that an acoustic interaction of the disturbed shear layer with a flow channel wall or another shear layer is indispensable to generate the organized structure. The undisturbed vorticity layer is deformed into a traveling wavy one. As the flow Mach number increases, its degree of deformation decreases so that the formation of shock waves embedded in the structure is avoided. Received 4 August 1995 / Accepted 6 March 1996     

Shocklets in compressible flows

The mechanism of shocklets is studied theoretically and numerically for the stationary fluid, uniform compressible flow, and boundary layer flow. The conditions that trigger shock waves for sound wave, weak discontinuity, and Tollmien-Schlichting （T-S） wave in compressible flows are investigated. The relations between the three types of waves and shocklets are further analyzed and discussed. Different stages of the shocklet formation process are simulated. The results show that the three waves in compressible flows will transfer to shocklets only when the initial disturbance amplitudes are greater than the certain threshold values. In compressible boundary layers, the shocklets evolved from T-S wave exist only in a finite region near the surface instead of the whole wavefront.