菱形口射流与超音主流的相互作用

基于在不同射流角(10°, 27.5°, 45°, 90°)和射流总压(0.1 MPa, 0.46 MPa)下,对音速次膨胀射流通过菱形口喷射到马赫5横穿主流的实验及圆形射流器的对比实验,研究了次膨胀射流与超音横穿主流相互作用流场, 实验包括横截面流场的Pitot和锥静压力, 获得横截面马赫数、 压力分布．结果表明近壁面低马赫数半圆区为尾区,尾区附近边界层减薄．脱体激波高度向自由流扩展,激波形状更弯曲, 低马赫数区较大．高射流压力和射流角增加羽流涡度,激波位置较高．90°菱形和圆形喷射器有更强的羽流涡度,但圆形喷射器的低马赫数区较小．前沿渐细的变壁面的斜面物增加羽流涡度,反之,双变壁面的斜面物减弱羽流涡度．通过表面激波形状、中心平面激波及横截面激波模化三维激波形状,激波总压损失用正激波关系式通过马赫数法向分量估计．激波总压损失随射流角和动压比的减小而减小,最大损失发生在90°圆形和菱形喷射器．     

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。     

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。     

带有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-ε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30的超声速气流的干扰流场。结果表明,在射流上游,射流的阻碍使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旋形旋涡。     

平行双射流场纳米颗粒的形成与凝聚的研究

对平行双射流中H2SO4蒸气扩散进行了大涡模拟,给出了硫酸/水系统成核生成纳米颗粒及颗粒的凝聚过程中颗粒的分布特性,分析了燃料中硫的浓度、环境相对湿度以及射流Reynolds数对于颗粒浓度和粒径分布的影响．结果表明,硫酸/水系统会成核生成大量的纳米颗粒,在双管射流的中间和射流场周围,颗粒具有较高的浓度;颗粒的凝聚过程使颗粒的数量减少、直径变大;随着硫的浓度的增加,流场中的颗粒浓度有明显增加,而成核后形成的颗粒直径减小;环境湿度和Reynolds数的增大,有利于成核过程,因而导致形成更多的颗粒．     

湍流边界层内准流向发卡涡生成的数值模拟

采用根据共振三波理论模型建立的初始准二维流场和直接数值模拟方法,对湍流边界层近壁区流向涡的生成进行了研究．计算得到了准流向发卡涡和次生准流向涡结构的生成过程及其主要特征,讨论了它们的产生机理．作为相干结构的主要特征,利用共振三波理论模型对流向涡结构生成与演化过程的研究为湍流边界层内相干结构的研究与流动控制提供了新的途径和思路．     

用子波谱分析壁湍流多尺度结构的能量传递

测量了壁湍流不同法向位置的流向速度.用子波变换研究湍流能谱,表明子波全局谱是Fourier谱按子波尺度加权平均的结果,高阶消失矩的子波变换能够表征湍谱的衰减特性;子波局部谱显示边界层内涡的变形、破碎等现象与边界层法向位置有关,含能涡结构呈多尺度分布,随着测点远离壁面,含能涡的尺度增大;在缓冲区出现更高频的小尺度含能涡,在外区能量集中在低频大尺度涡结构中,含能涡的频带变窄.     

圆形垂直浮力射流的稳定性与混合特性研究

建立浅水静止环境中圆形轴对称垂直浮力射流的k-ε模型,采用混合有限分析方法进行了数值计算．针对两种不同的流动形态:近区的混合流体以浮力表面层的形式沿径向扩散的稳定排放;近区产生旋涡,浮力热水对混合热水形成二次挟带的非稳定排放,并对稳定性判据进行了验证,最后对两种不同流动结构下的远区的混合特性进行了数值模拟,结果同Lee和Jirka的试验和理论资料均十分吻合．     

锯齿射流与圆射流流场和远场噪声特性的对比研究

采用大涡模拟研究了高亚音速、基于直径Reynolds(雷诺)数为Re=105的圆喷管构型射流和6齿喷管与4齿喷管构型的锯齿射流.将圆射流的计算结果与前人已有的实验和大涡模拟结果进行了对比,验证了当前计算结果的可靠性.对比研究了锯齿射流与圆射流特征,结果显示锯齿射流在近喷口附近具有更大的径向扩张率和更短的势核区长度;锯齿射流的总声压级在低辐射角度上相比于圆射流可低4 dB,而在侧边辐射方向噪声没有明显升高.分析了锯齿射流和圆射流远场压力脉动的前三阶周向Fourier(傅里叶)模态m=0,1,2,结果显示三组算例在同一周向模态上呈现出相似的声压级分布,然而4齿锯齿射流的第零阶和第一阶周向模态在高辐射角度上相较于圆射流具有更高的噪声水平.将POD分解技术用于提取特定周向模态上的最具能量的大尺度结构,在与大尺度结构相关的波包特征角度部分解释了锯齿射流和圆射流远场噪声特性的不同.     

湍动尺度的模糊聚类分析

湍流运动可看成是大小不同尺度的涡体运动的叠加.定量地确定湍动尺度的分类,对于更好地描述不同尺度的涡体运动,探讨不同尺度涡体之间的相互作用,建立较好的湍流模式都具有重要的意义. 对事物按一定要求进行分类的数学方法,叫做聚类分析.由于湍动尺度的分类具有一定程度的模糊性,因而本文采用模糊聚类的方法,对壁面光滑及租糙两种边界条件下的湍动尺度进行了分类,并对各类结构的特性及其相互作用进行了探讨.     

Robin-type wall functions and their numerical implementation

The paper is devoted to numerical implementation of the wall functions of Robin-type for modeling near-wall turbulent flows. The wall functions are based on the transfer of a boundary condition from a wall to some intermediate boundary near the wall. The boundary conditions on the intermediate boundary are of Robin-type and represented in a differential form. The wall functions are formulated in an analytical easy-to-implement form, can take into account the source terms, and do not include free parameters. The relation between the wall functions of Robin type and the theory of Calderon–Ryaben'kii's potentials is demonstrated. A universal robust approach to the implementation of the Robin-type wall functions in finite-volume codes is provided. The example of an impinging jet is considered.     

用时变雷诺方程模型模拟孤立波与半圆型防波堤的相互作用

以时变雷诺方程为控制方程,用k-ε模型封闭该方程,采用体积函数(VOF)方法来跟踪波动自由表面,建立了二维垂向波浪数学模型,并用已有的实验资料进行了验证．随后用该模型模拟了半圆型防波堤与孤立波在淹没、平顶水位、完全露顶且不越浪3种典型工况下的相互作用过程．得到了半圆堤附近的流场、压强场和波面的变形过程．结果表明,在淹没状态下,半圆堤背浪面的底部会产生涡旋;平顶水位时,由于越浪的冲击作用,在半圆堤的背浪面将逐渐形成一对较大的涡旋,而半圆堤背浪面的底部,速度始终相对较小;而在露顶不越浪时,半圆堤的迎浪面会出现波浪的二次爬升的现象．为进一步研究结构物附近的污染物的输移扩散和泥沙运动提供基础．     

针对壁面旋转变径管内螺旋流的压力应变项研究

通过壁面旋转变径圆管内螺旋湍流流动特征的分析，确定其切向速度场内涡流区为微团旋转主导的椭圆形流动，外涡流区为微团变形主导且受壁面旋转影响的双曲形流动.进而利用张量的不变量理论，引入旋转率张量与应变率张量的综合不变量作为模型系数，将适用于微团旋转主导的旋转湍流Reynolds应力压力应变项修正模型拓展到了非旋转效应主导的双曲形流动中.将修正压力应变项应用于壁面旋转变径圆管流场的模拟，并将结果与实测结果进行了对比，验证了修正模型的改进效果.     

环形扩压通道内有旋绕流动的研究

本文计算了环形截面的扩压通道内带进气旋绕的流动.在小横向流假定下.用三维边界层积分方程法求解内外壁面附近的流动.通过对子午面上与流线子午投影准正交方向的速度梯度方程和流量不变方程的迭代求解得出边界层外的势流场.计算与实验结果基本符合.本研究可用于分析环形扩压器内带进气予旋的流动.     

Nonsimilar solutions for double-diffusion boundary layers on a sphere in micropolar fluids with constant wall heat and mass fluxes

This work presents nonsimilar boundary layer solutions for double-diffusion natural convection near a sphere with constant wall heat and mass fluxes in a micropolar fluid. A coordinate transformation is employed to transform the governing equations into nondimensional nonsimilar boundary layer equations and the obtained boundary layer equations are then solved by the cubic spline collocation method. Results for the local Nusselt number and the local Sherwood number are presented as functions of the vortex viscosity parameter, Schmidt number, buoyancy ratio, and Prandtl number. Higher vortex viscosity tends to retard the flow, and thus decreases the local convection heat and mass transfer coefficients, raising the wall temperature and concentration. Moreover, the local convection heat and mass transfer coefficients near a sphere in Newtonian fluids are higher than those in micropolar fluids.     

Flow Structure in a Technical Scale Reactor with an Internal Reboiler

In this contribution, results of experimental flow investigations in a technical scale cylindrical reactor with centrally located internal reboiler are presented. The fluid motion in the kettle is induced by natural circulation. Two different geometrical configurations are considered. First, the liquid level is set below the evaporator's outlet. Thus, only the liquid phase penetrates the liquid surface. The second configuration characterizes the a direct injection of the two phase mixture into bulk liquid. In both cases the liquid leaves the evaporator radially and horizontally towards the cylindrical wall. Gathered results reveal the presence of the big, toroidal vortex in the kettle annulus. Independently on the boundary conditions, self similarity of velocity profiles in the near wall region is observed. In contrast, investigations of the momentum transfer between the jet and the bulk liquid reveal strong dependency on the geometrical configuration of the setup. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The topology of the sectional streamlines

The unsteady, three-dimensional full Navier-Stokes equations are solved using a Beam-Warming implicit algorithm in this paper. Computations of the flow over a 76° sweep delta wing at 36.5° angle of attack is presented. The sectional streamlines are depicted and the evolution of the instantaneous crossflow topology of the leading-edge vortex is analyzed. It is found that, along the axis, the topology of the primary vortex alters several times starting from stable focus near the apex to unstable focus, and lasts back to stable focus near wake edge; The stable limit cycle and unstable limit cycle are shown in this evolution. These various altering topologies stem from the stretching and compression of the vortex core.     

Analytical solutions of laminar swirl decay in a straight pipe

In this work, the laminar swirl flow in a straight pipe is revisited and solved analytically by using prescribed axial flow velocity profiles. Based on two axial velocity profiles, namely a slug flow and a developed parabolic velocity profiles, the swirl velocity equation is solved by the separation of variable technique for a rather general inlet swirl velocity distribution, which includes a forced vortex in the core and a free vortex near the wall. The solutions are expressed by the Bessel function for the slug flow and by the generalized Laguerre function for the developed parabolic velocity. Numerical examples are calculated and plotted for different combinations of influential parameters. The effects of the Reynolds number, the pipe axial distance, and the inlet swirl profiles on the swirl velocity distribution and the swirl decay are analyzed. The current results offer analytical equations to estimate the decay rate and the outlet swirl intensity and velocity distribution for the design of swirl flow devices.     

The wall jet flow of a conducting gas over a permeable surface in the presence of a variable transverse magnetic field

The effects of the magnetic field, Mach number and the permeability parameter on the wall jet flow (radial or plane) of an electrically conducting gas spreading over a permeable surface have been investigated. Taking the Prandtl number of the fluid as unity and assuming a linear relationship between viscosity and temperature, it is found that similar solutions for the velocity distribution exist for a specified distribution of the normal velocity along the wall and the corresponding distribution of the transverse magnetic field. Previous non-magnetic flow results have been improved by adopting a new and simple transformation of variables.