Effect of concentration of vortices on streakline patterns

This investigation addresses simulation of flow visualization of vortical structures, accounting for both the circulation and the degree of concentration of vorticity of the vortices via the exact nonlinear solution of Stuart for an unsteady mixing layer. At a fixed value of circulation, an increased concentration of vorticity (which corresponds to decrease in the area containing most of the vorticity) actually spreads the visualization marker over an increased area of the flow. Moreover, different combinations of vorticity concentration and circulation give essentially the same flow patterns.     

Flow of a viscous fluid past an array of spheres

The Stokes flow of a viscous incompressible fluid through a periodic array of impenetrable spheres with linear friction on the boundary is considered. A solution and an expression for the drag are obtained to terms of order c^5/3 compared with unity (c is the volume concentration of the spheres). The proposed algorithm permits solution with any required degree of accuracy. The solution contains as limits the cases of perfect slip and no-slip on the surfaces of the spheres. In the problem with the no-slip condition, an asymptotically exact lower bound for the drag, which is valid for all values of the concentration c, is constructed.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 37–44, July–August, 1981.     

On the refracted patterns produced by liquid vortices

A theoretical analysis of the refracted shadows produced by steady and time-decaying liquid vortices under uniform illumination from above is given in this article. An expression for the induced shadow intensity is derived and found to be a function of the vortex’s free surface profile, i.e., function of the static pressure distribution. The patterns for different focusing depth are given and compared with previous visualization results from the literature. The phenomenon is examined and illustrated as a bench mark case by using both steady and time-decaying algebraic vortex models. However, this study can be extended to check the feasibility of recovering the main flow properties by analyzing the luminous image intensity of the refracted patterns. The present analysis is valid only when the swirl velocity is order of magnitude higher than the meridional flow components and the vorticity is concentrated within the core region and of intense conditions.     

Flow instability and transient flow patterns inside intercrossed silicon microchannel array in a micro-timescale

The objective of this study is to visualize the transient flow patterns and heat transfer behaviors at low mass fluxes and high heat fluxes. The silicon chip consists of the intercrossed microchannel array with 10 triangular microchannels with the hydraulic diameter of 155.4 μm, and five transverse trapezoid microchannels, separating the triangular microchannels into six independent zones. The chip is horizontally positioned. Liquid acetone is used as the working fluid. Tests were performed in the range of mass flux 40–80 kg/m² s and heat flux 107–216 kW/m².     

Shedding patterns of the near-wake vortices behind a circular cylinder

The unsteady incompressible Navier-Stokes equations have been accurately solved for the laminar flow past a circular cylinder in the Reynolds number range 50–200. A direct elliptic solver called the SEVP is used to rapidly advance the streamfunction in time, facilitating the overall convergence to the fully periodic or quasi-steady state. A new integral-series method is developed for the far-field streamfunction condition on a finite two-dimensional computational domain. The use of fourth-order Hermitian relations for the convection terms in the conservation-form vorticity transport equation has also contributed to the good comparison of the present results with the earlier experimental data. The vortex-shedding patterns visualized by the experimentalist are numerically reproduced here in the given Reynolds number range. Discussions that may be helpful in interpreting the behaviour of the shedding frequency are presented in the main text.     

Theory of nonstationary vortices in an ideal fluid

Equations that describe the evolution of a region with nonzero vorticity are formulated. These equations are solved on a bounded time interval for regions having the shape of a sphere or a circular cylinder at the initial time. It is shown that a spherical vortex formed in a medium at rest begins to move, and is stretched in the direction of the motion; a cylindrical vortex, under the influence of the nonuniform intensity of the vorticity on its boundary, changes both the magnitude and direction of its velocity, and describes a curvilinear trajectory. Expressions are obtained which describe the initial evolution of a fluid sphere of one density in a fluid medium of another density.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 3–11, November–December, 1980.     

Secondary steady-state and time-periodic flows from a basic flow with square array of odd number of vortices

In a magnetohydrodynamic(MHD) driven fluid cell, a plane non-parallel flow in a square domain satisfying a free-slip boundary condition is examined. The energy dissipation of the flow is controlled by the viscosity and linear friction. The latter arises from the influence of the Hartmann bottom boundary layer in a three-dimensional(3D)MHD experiment in a square bottomed cell. The basic flow in this fluid system is a square eddy flow exhibiting a network of N² vortices rotating alterna...     

Flow patterns in vertical two-phase flow

This paper is concerned with the flow patterns which occur in upwards gas-liquid two-phase flow in vertical tubes. The basic flow patterns are described and the use of flow pattern maps is discussed. The transition between plug flow and churn flow is modelled under the assumption that flooding of the falling liquid film limits the stability of plug flow. The resulting equation is combined with other flow pattern transition equations to produce theoretical flow pattern maps, which are then tested against experimental flow pattern data. Encouraging agreement is obtained.     

Problem of the motion of annular vortices in an ideal fluid

The study discusses problems in the numerical modeling of axisymmetric flows of an incompressible fluid induced by a continuous vortex region or vortex sheet by means of a discrete system of vortex rings.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 68–75, May–June, 1987.     

Flow of wormlike micelle solutions through a periodic array of cylinders

Solutions of self-assembled wormlike micelles are used with ever increasing frequency in a multitude of consumer products ranging from cosmetic to industrial applications. Owing to the wide range of applications, flows of interest are often complex in nature; exhibiting both extensional and shear regions that can make modeling and prediction both challenging and valuable. Adding to the complexity, the micellar dynamics are continually changing, resulting in a number of interesting phenomena, such as shear banding and extensional flow instabilities. In this paper, we present the results of our investigation into the flow fields generated by a controllable and idealized porous media: a periodic array of cylinders. Our test channel geometry consists of six equally spaced cylinders, arranged perpendicular to the flow. By systematically varying the Deborah number, the flow kinematics, stability and pressure drop were measured. A combination of particle image velocimetry in conjunction with flush mount pressure transducers were used to characterize the flow, while flow induced birefringence measurements were used to determine micelle deformation and alignment. The pressure drop was found to decrease initially due to the shear thinning of the test fluid, and then exhibit a dramatic upturn as other elastic effects begin to dominate. We present evidence of the onset of an elastic instability in one of the test fluids above a critical Deborah number manifest in fluctuating transient pressure drop measurements and asymmetric streamlines. We argue that this disparity in the two test fluids can be attributed to the measurable differences in their extensional rheology.     

Quantitative comparison of cellular patterns of stable and unstable mixtures

This study describes a comparison of smoked foils from five different mixtures \(({\hbox {C}}_{2}{\hbox {H}}_{2}+2.5{\hbox {O}}_{2}+85\,\%{\hbox {Ar}}, 2{\hbox {H}}_{2}+{\hbox {O}}_{2}+50\,\%{\hbox {Ar}}, {\hbox {C}}_{2}{\hbox {H}}_{2}+2.5{\hbox {O}}_{2}+70\,\%{\hbox {Ar}}, \hbox {C}_{2}{\hbox {H}}_{2}+5{\hbox {N}}_{2}{\hbox {O}}\), and \({\hbox {CH}}_{4}+2{\hbox {O}}_{2})\) that produced transverse waves of regular and irregular spacing. Histograms, variance, and the autocorrelation function (ACF) were used to quantify the spacing irregularity. Each smoked foil was first digitized then separated into left-running and right-running waves for subsequent analysis. The five mixtures showed different degrees of irregularity in the analysis of the histograms and the ACF of the spacing of the transverse waves. The dominant mode was readily found from the peak in the histogram and the first peak in the ACF result. The spacing of the main transverse waves provided by the histogram and the first peak of the ACF were much closer to the spacing of the transverse waves measured by eye for stable mixtures than for unstable ones due to their stronger dominant mode. In certain cases, other modes besides the dominant one were observed, such as two peaks in the histogram and other large peaks in the ACF result. Variance was used as a quantitative measurement of the cellular pattern irregularity level.     

基区无吹氦环柱型高超音速低温喷管流场分析

设计了小基区、基区不吹He的环柱型高能化学激光器环形HYLTE喷管 阵列,并使用数值模拟的方法对环形HYLTE喷管阵列流场的气动性能和光学性能进行了分 析. 结果表明,该设计有利于形成ν= 1 →ν = 0之间振转跃迁谱线,不利 于ν = 2→ν =1之间振转跃迁谱线的形成,由于光腔区绝大多数的HF(2)分 子碰撞去激活后成为HF(1)分子,从而使1P谱线的小信号增益倍增,无基 区吹He的设计有利于提高高能化学激光 器的效率. 采用小基区的设计可以增大喷管阵列的功率流密度,无基区吹He的设计不但可 以使复杂的环形高超音速低温喷管叶片的加工与装配得到简化,而且降低了激光器工作 气体的消耗. 因此该设计不但有利于实现高能激光器的紧凑化设计,还有利于节省高能 激光器建造和运行的成本.     

旋转爆轰胞格结构的实验和数值研究

对爆轰波在环形圆管(预混气体为2H2/O2/Ar)内的传播分别进行了实验和数值研究。实验研究 采用烟迹板记录了环形圆管内爆轰波的胞格结构。数值计算利用二阶附加半隐的Runge-Kutta法和五阶 WENO格式分别离散欧拉方程的时间和空间导数项,采用基元反应简化模型描述化学反应过程,得到了旋转 爆轰的流场及数值胞格结构。实验和数值模拟结果表明:爆轰波在圆环管中传播时,由于圆环的内壁发散、外 壁收敛,圆环内侧爆轰强度小于外侧,胞格尺寸较大;内侧OH 的分布区域大于外侧,浓度较低。旋转爆轰的 这种性质,使爆轰波能以稳定的角速度绕轴旋转。     

Interaction of helical vortices

A characteristic feature of atmospheric vortices of a convective nature is the powerful radial motions of the medium at their base. In order to take these motions into account in analytical and numerical modeling, it is necessary to use point or distributed vortex sinks (vortex sources), which we will call helical vortices (from the shape of the streamlines of the flows produced) [1]. It seems likely that the interaction of point helical vortices was first considered in the until recently little-known study [2] which was included in the collection [3] and partially overlaps with the more recent studies [4, 5].Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 183–185, July–August, 1995.     

Chains of axisymmetric vortices

Chains of coaxial vortex formations of the “vortex breakdown“ type in axisymmetric swirling incompressible viscous and ideal fluid flows are represented in analytic form. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 174–176, March–April, 1998.     

Flow of gas with a cellular vortical structure through a nozzle

The operation of rocket motors is often accompanied by the development of powerful secondary vortices in the combustion chamber [1–3], The superposition of the secondary vortices on the main flow leads to the formation of a cellular flow structure. Each of the cells represents a three-dimensional vortical circulation of the gas, and this causes a change in the working conditions of the nozzle. The model of helical motion [4] is used in this paper in considering the influence of the three-dimensional behavior of an adiabatic flow on the flow and traction characteristics of the nozzle.