带用横向射流的三维超声速湍流流场分析

应用显式的五阶WENO格式，结合k-ω湍流模型，求解三维Favre平均N－S方程，计算了从方孔横向喷出的声速气流与马赫数为3．0的超声速气流的干扰流场。结果表明，在射流上游，射流的阻碍便超声速气流产生分离，形成两个主要的回流区域，主回流导致在方孔射流两侧形成马蹄涡区域，射流下游存在低压区域，形成较小的回流以及一对螺流形旋涡。     

射电星系双源结构的磁射流理论

本文利用太阳风的二维加速理论,来讨论射电星系的射电束加速。用分析的方法得到了射流束的流动特征,基本的流动是沿射流方向的运动。文中给出了从亚声速一直加速到超声速流动的机制,同时,还解释了射电星系双源的某些精细结构。     

激波在变截面管道中的传播及新激波的产生与发展

由于爆炸或各种不同的原因在介质中引起的压缩作用,如以超声速传播就形成激波。当一个强激波进入变截面管道后,由于管道截面积的变化,激波强度也发生变化,其后面形成不定常气流。为了探讨激波及其后面的不定常气流的变化规律,我们用三种方法进行数值计算,即:一维特征线法,一维两步二阶差分法及轴对称二维两步二阶差分法。计算结果,三种方法相辅相成,并弄清了管内的流场。计算表明,第一个激波过后在连续流中很快出现了新的激波,并逐渐增强。二维不定常方法还算出了三叉波的形成。     

超声速气流中含灰气体点源流动特性

采用Lagrange方法，研究了超声速气流中含灰气体点源的流动特性，求得了对称轴附近激波层内的流动参数．计算数值模拟结果揭示了大惯性颗粒在激波层内沿着相互交叉的振荡轨迹运动，颗粒分布形成了高、低密度层交错出现的“多层结构”，而且粒子在轨迹包络线附近急剧聚集．     

高浓度悬浮固粒对射流界面的粘性稳定性影响

该文首次利用双流体模型和扰动速度势理论,推得含高浓度悬浮固粒的射流界面粘性稳定性方程和对应的固气扰动速度比值方程．通过数值计算,得到了不同雷诺数及固粒属性的射流界面粘性稳定性曲线和对应的固气扰动速度比值曲线．在分析和比较所得的粘性稳定性曲线的基础上,得到了流场雷诺数及固粒特性对射流界面粘性稳定性影响的结论．同时,通过分析所得的固气扰动速度比值曲线,得到了流场雷诺数及固粒等效斯托克斯数对固粒跟随气流的扰动 性能的影响的结论．这些结论是首次在计入气流的粘性的条件下得到的,不同于文献［８］和文献［１０］相关的囿于无粘情形的研究,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．     

静水中正方形孔口的有障碍浮射流(Ⅱ)——流场特性分析

在数值计算成果的基础上,对正方形阻力盘浮力射流的流场进行了分析和总结,基于轴线流速的变化规律将盘后流场分为3个区域:回流区、过渡区和自相似区．验证了竖直方向流速自相似性的存在．根据给出的轴线流速的变化图也可以区分盘后3个区域的位置,同时发现各工况在自相似区域的轴线流速沿同一规律曲线变化,采用Chen和Rodi对流速的表示方法,得到了所有工况下自相似区域轴线流速的分布公式．给出了典型工况下阻力盘后不同高度位置处的压强场等值线变化过程,发现盘后各负压中心区域的产生、膨胀、破裂和消失．     

HF化学激光放大器的交叉弛豫动力学研究

在低气压超声速cwHF化学激光放大器中 ,假设平动和转动非平衡交叉弛豫同时起作用 .对于气流介质的层流和湍流扩散混合两类流动模型 ,分别导出了饱和增益谱的表示式 ,并进行了数值计算 .计算结果表明 ,湍流扩散混合模型与实验结果符合得更好 .     

流动环境中高浓度射流扩散实验研究

通过流动显示和定量测量对浅水流动环境条件下,高浓度流体垂体向抛射入水后形成的射流运动扩散及浓度分布特征进行了水槽实验研究。实验分析了射流入水后与环境水流条件的相互作用,通过数据分析给出了射流中心线着底点与横向扩散角的拟合公式。实验结果表明高浓度射流在近区呈现出不同于一般淹没射流的复杂流动形态及扩散特征,以异重流的形式向下游推移。     

论超声速燃烧

论述了超声速燃烧概念 ,提出了对超声速燃烧的两种不同理解 ,论述了超声速燃烧与亚声速燃烧的不同 ,指出了超声速燃烧传播机制的特点和等截面超声速燃烧加热量的限制 .通过超声速流动中的燃烧分析 ,表明定常爆燃产物的熵增和总压损失随燃烧速度的增加而减少 .还论述了在欠驱动弱斜爆轰解条件下 ,波角不受斜劈角控制 ,只决定于燃烧速度 ,因此此解可能变成常波角的自持斜爆轰 .     

大速差同向射流——一种新型火焰稳定与强化燃烧的空气动力学原理

本文介绍了一种稳定火焰和强化燃烧的新型空气动力学原理——大速差同向射流技术。单股或多股高速小射流(空气、蒸汽或其它气体)与低速的主气流(燃料和空气混合物)同方向射入燃烧室,可以产生高湍流强度的大回流区,从而可以使可燃混合物与高温回流烟气有效地混合,以维持燃烧室内稳定而强化地燃烧,甚至对于着火性能很差的燃料也是如此。这是继传统的旋流燃烧器和钝体燃烧器之后又一种新型的有效而实用的火焰稳定方法。基于这种原理研制的煤粉燃烧器更具有优良的性能,并且在结构上也很简单。这种类型的煤粉预燃室,已经在电站和工业锅炉上安装使用。目前,使用这种预燃室可以在冷风条件下成功地启动贫煤(V^f<15％,A^f>30％)锅炉及低负荷情况下仍能维持燃烧。这项新技术所展示的火焰稳定和强化燃烧原理在燃烧界引起了广泛的关注和兴趣。     

Generation of large-scale vortex dislocations in a three-dimensional wake-type flow

Numerical study of three-dimensional evolution of wake-type flow and vortex dislocations is performed by using a compact finite diffenence-Fourier spectral method to solve 3-D incompressible Navier-Stokes equations. A local spanwise nonuniformity in momentum defect is imposed on the incoming wake-type flow. The present numerical results have shown that the flow instability leads to three-dimensional vortex streets, whose frequency, phase as well as the strength vary with the span caused by the local nonuniformity. The vortex dislocations are generated in the nonuniform region and the large-scale chain-like vortex linkage structures in the dislocations are shown. The generation and the characteristics of the vortex dislocations are described in detail.     

Dynamics of Vortex Rossby Waves in Tropical Cyclones,Part 1: Linear Time‐Dependent Evolution on an f‐Plane

Analyses of observational data on hurricanes in the tropical atmosphere indicate the existence of spiral rainbands which propagate outward from the eye and affect the structure and intensity of the hurricane. These disturbances may be described as vortex Rossby waves. This paper describes the evolution of barotropic vortex Rossby waves in a cyclonic vortex in a two‐dimensional configuration where the variation of the Coriolis force with latitude is ignored. The waves are forced by a constant‐amplitude boundary condition at a fixed radius from the center of the vortex and propagate outward. The mean flow angular velocity profile is taken to be a quadratic function of the radial distance from the center of the vortex and there is a critical radius at which it is equal to the phase speed of the waves. For the case of waves with steady amplitude, an exact solution is derived for the steady linearized equations in terms of hypergeometric functions; this solution is valid in the outer region away from the critical radius. For the case of waves with time‐dependent amplitude, asymptotic solutions of the linearized equations, valid for late time, are obtained in the outer and inner regions. It is found that there are strong qualitative similarities between the conclusions on the evolution of the vortex waves in this configuration and those obtained in the case of Rossby waves in a rectangular configuration where the latitudinal gradient of the Coriolis parameter is taken into account. In particular, the amplitude of the steady‐state outer solution is greatly attenuated and there is a phase change of across the critical radius, and in the linear time‐dependent configuration, the outer solution approaches a steady state in the limit of infinite time, while the amplitude of the inner solution grows on a logarithmic time scale and the width of the critical layer approaches zero.     

Numerical simulation of the interaction between vortex ring and bubble plume

In present paper a three-dimensional Vortex-In-Cell method with two-way coupling effect was developed to study the bubble plume entrainment by a vortex ring. In this method the continuous flow was calculated by the three-dimensional Vortex-In-Cell method and the bubbles are tracked through bubble motion equation. Two-way coupling effect between continuous flow and dispersed bubbles is considered by introducing a vorticity source term, which is induced by the change of void fraction gradient in each computational cell. After validated by the comparison between experimental measurements and simulation results for the motion of vortex rings and the rising velocity of bubble plume, present method is implemented to simulate the interaction between an evolving vortex ring and a rising bubble plume. It was found that there is little effect of the bubble entrainment to the total circulation of vortex ring while the effect of bubble entrainment to the vortex ring structure is quite obvious. The bubble entrainment by the vortex ring not only changed the vorticity distribution in the vortex structure, but also displaced the positions of the vortex cores. The vorticity in the lower vortex core of the vortex ring decreases more than that in the upper vortex core of the vortex ring while the vortex core in the upper part of the vortex ring is displaced to the center of vortex ring by the entrained bubbles. Smaller bubbles are easier to be entrained by the large scale vortex structure and the transportation distance is in inverse proportion to bubble diameter.     

Dynamic Depletion of Vortex Stretching and Non-Blowup of the 3-D Incompressible Euler Equations

We study the interplay between the local geometric properties and the non-blowup of the 3D incompressible Euler equations. We consider the interaction of two perturbed antiparallel vortex tubes using Kerr's initial condition . We use a pseudo-spectral method with resolution up to 1536 × 1024 × 3072 to resolve the nearly singular behavior of the Euler equations. Our numerical results demonstrate that the maximum vorticity does not grow faster than doubly exponential in time, up to t = 19, beyond the singularity time t = 18.7 predicted by Kerr's computations , . The velocity, the enstrophy, and the enstrophy production rate remain bounded throughout the computations. As the flow evolves, the vortex tubes are flattened severely and turned into thin vortex sheets, which roll up subsequently. The vortex lines near the region of the maximum vorticity are relatively straight. This local geometric regularity of vortex lines seems to be responsible for the dynamic depletion of vortex stretching.     

Rossby Waves on a Shear Flow with Recirculation Cores

Large-amplitude Rossby waves riding on a background flow with a weak shear can be calculated up to a critical amplitude for which the meridional velocity, in a frame traveling with the wave, approaches zero at some point. Here we consider waves with an amplitude slightly greater than the critical amplitude by incorporating a region of recirculating fluid (vortex core) near this critical point. The effect of the vortex core is to introduce an extra nonlinear term into the equation for the wave amplitude proportional to the 3/2 power of the difference between the wave amplitude and the critical amplitude. The main effect due to the vortex core is a broadening of the wave profile. Furthermore, we show that the vortex core family has a limiting amplitude, with the limiting amplitude corresponding to a semi-infinite bore.     

激波在异种气体中传播及诱导的剪切混合研究

利用二阶迎风TVD格式求解多组分,层流全N－S方程,针对直通道和突扩直通道,研究了马赫数为2和4的激波在H2和空气界面上的传播及诱导的燃料剪切混合,计算结果表明：（1）直通道中,剪切层中的激波阵面要发生畸变,存在对混合起主要作用的卷吸涡,激波马赫数不同,卷吸涡结构和横向混合的尺寸也不同,激波马赫数低,剪切混合效果好,（2）在突扩直通道中,马赫数为2和4的激波在H2中产生不同强度激波,在剪切层中都能产生顺时针,尺度较大的卷吸涡,后台阶增强了剪切层的混合。     

Computational study of decaying annular vortex flow using the Rε/k − ε turbulence model

In this article, we present three dimensional CFD study of turbulent vortex flow in an annular passage using OpenFOAM 1.6. The vortex flow is generated by introducing the flow through a tangential entry to the passage. For the analysis presented in this article, turbulence was modeled using the R_ε/k − ε model, in addition, a comparison between such model with the standard k − ε model was conducted and discussed. The main characteristics of the flow such as vortex structure and recirculation zone were investigated. It was found that flow is subjected to Rankine vortex structure with three forced vortex regimes and a free vortex region near to the outer wall. The phenomenon of vortex decay was investigated by depicting the swirl number trend along the axial direction of the flow domain. It was found that the vortex decay is subjected to an exponential decay behavior. New coefficients for the exponential decay correlation were derived based on local values of velocity components in different radial planes.     

The structure of fully nonlinear Taylor vortices

The structure of nonlinear short-wavelength Taylor vorticesin the flow between rotating concentric cylinders is considered.In the short-wavelength limit, the nonlinear vortex motion isgoverned by a mean-flow-first-harmonic interaction problem.The initial structure of the nonlinear vortex state is shownto be governed by a multilayer structure in which the vortexis constrained to lie between the inner cylinder and a positioninternal to the flow regime. This position is dependent uponthe Taylor number and it is found that there is a critical valueof the Taylor number at which the vortex first impinges on theouter boundary. The vortex field then develops a double boundarylayer structure at both the inner and outer boundary as theTaylor number is increased past this critical Taylor number.     

三角翼大迎角流场结构和气动力特性的计算分析研究

采用数值计算方法对亚音速三角翼纵向及带有小侧滑和横侧小扰动情况下的流场结构进行了计算,利用数值计算所得到的大迎角流动流场数据,结合相关的实验研究结果,建立了对大迎角旋涡流场结构进行定量分析的方法．给出了三角翼大迎角情况下相应的气动力、力矩系数,以及机翼前缘分离涡轴线位置和旋涡破裂位置随迎角的变化规律,并对带有小侧滑和横侧小扰动情况下对横侧力矩的影响进行了计算与分析．计算结果表明,在前缘分离涡破裂前的上游旋涡区内,前缘分离涡轴线基本保持为直线,且随着迎角增加,前缘分离涡轴线位置愈靠近翼根,并远离翼面;在前缘分离涡破裂的初始阶段,于旋涡轴线处,压力系数会迅速增加,沿涡轴线方向速度迅速减小,在垂直于流向的截面内,愈靠近涡轴线处,沿涡轴线方向速度愈小,甚至出现负值,说明沿涡轴线方向出现回流．当绕机翼上表面前缘分离涡破裂后,将会导致横侧运动不稳定,如果受到小扰动,将产生横侧力矩发散．     

浅水横流中异重冲击射流的大尺度涡结构

采用RNG湍流模型对浅水横流中异重冲击射流的大尺度涡结构进行了详细的数值研究．分析了冲击区滞止点上游壁面涡结构和近区Scarf涡结构的尺度、形成机理和演化特征．计算得到了上游壁面涡的特征尺度,结果表明上游壁面涡具有高度的三维性,其特征尺度依赖于流速比和环境水深．近区Sarf涡结构对横流冲击射流的横向浓度分布具有重要的影响．当流速比相对较小时,在底层壁射流与环境横流的横向边界附近出现明显的高浓度聚集现象,计算结果表明Scarf涡结构对这一高浓度聚集区的形成起主导作用．