The mixing of a viscous fluid in a layer between rotating eccentric cylinders

The motion of an incompressible viscous fluid in a thin layer between two circular cylinders, inserted into one another, with parallel axes is investigated. The cylinders rotate relative to one another about an axis parallel to the axes of the cylinders. The stream function of the unsteady plane-parallel flow that occurs is found by solving the boundary-value problem for the equations of hydrodynamic lubrication theory. The motion of the fluid particles is found from the solution of a non-autonomous time-periodic Hamiltonian system with a Hamiltonian equal to the stream function. The positions of fluid particles over time intervals that are a multiple of the period of rotation (Poincaré points) are calculated. The set of points is investigated using a Poincaré mapping on the phase flow. The observed transition to chaotic motion is related to the mixing of the fluid particles and is investigated both numerically and using a mapping, calculated with an accuracy up to the third power of the small eccentricity. The optimum mode of motion is observed when the area of the mixing (chaos) region reaches its highest value.     

前后排列旋转圆柱体对流热交换的格子Boltzmann方法解

用格子Boltzmann方法,数值研究流过前后排列两旋转圆柱体的二维层流．用二阶精度的速度场和温度场,数值化涉及运动的曲线边界．在Reynolds数为100,Prandtl数为0.71时,研究旋转速度比的变化和不同间距的影响．在4种不同间距(3, 1.5, 0.7, 0.2)下,研究旋转速度比的不同范围．结果表明,当间距取大数值时,第1个圆柱体的升力和阻力系数,与单个圆柱体相类似;对所有间距(除间距3以外),第2个圆柱体的升力系数,随着角速度的增加而减小,而阻力系数反而增加．圆柱体表面平均周期Nusselt数的结果表明,当两圆柱体间距小且角速度又低时,热传导是主要的传热机理,而当间距大且角速度又高时,对流是主要的传热机理．     

两个非同心旋转圆柱间粘性流动的广义雷诺方程及其基本流

运用张量分析方法及修正双极坐标系,建立了轴承润滑流动所应满足的广义Reynolds方程.应用薄流层中的Navier-Stokes方程的渐近分析方法和张量分析工具,得到了两个非同心旋转圆柱之间粘性流动的基本流所应满足的方程.这个基本流可以表示为两个同心旋转圆柱之间的Taylor流加上一个扰动项,并且给出了数值计算例子.     

Numerical study of a transverse streamlined flow of an infinite series of cylinders

The problem of transverse streamlined flow of an infinite series of cylinders by a flow of viscous incompressible liquid is considered. The problem is solved numerically by using the method of difference approximation of the Navier-Stokes equations with use of Arakawa scheme of the second degree of accuracy. Computations were given for a series of cylinders with the step L=2.2, 2.8, 3.2, 3.6 and with Reynolds numbers Re equal to 40, 100, 200, 400. Relations between the hydrodynamic characteristics of the series and the distance between the axes of the cylinders are obtained for different Reynolds numbers.Translated from Dinamicheskie Sistemy, No. 7, pp. 53–57, 1988.     

Flow separation behind ellipses at Reynolds numbers less than 10

Flow separation behind two-dimensional ellipses with aspect ratios ranging from 0, a flat plate, to 1, a circular cylinder, were investigated for Reynolds numbers less than 10 using both a cellular automata model and a commercial computational fluid dynamics software program. The relationship between the critical aspect ratio for flow separation and Reynolds number was determined to be linear for Reynolds numbers greater than one. At slower velocities, the critical aspect ratio decreases more quickly as the Reynolds number approaches zero. The critical Reynolds numbers estimated for flow separation behind a flat plate and circular cylinder agree with extrapolations from experimental observations. Fluctuations in the values of the stream function for laminar flow behind the ellipses were found at combinations of Reynolds number and aspect ratio near the critical values for separation.     

On an extremal property of the Poiseuille flow between two coaxial cylinders

Some extremal property is established of the axial stationary flow of a Newtonian fluid between two concentric cylinders. It is shown that the ratio of the flow rate through the cross-section of an eccentric gap to the pressure drop (along the axis) reaches its minimum when the eccentricity equals zero; i.e., the minimum of the ratio is realized for the Poiseuille flow.     

The hydromagnetic flow between eccentric cylinders with velocity slip at the cylinder walls

The hydrodynamic flow between two eccentric cylinders is examined for small values of modified Reynolds number, porosity parameter and the non-dimensional slip velocity parameter in the presence of a radial magnetic field.The stream function and the pressure distribution are calculated and the results are presented graphically.     

Oscillatory flow about a cylinder pair

Oscillatory flow about a pair of circular cylinders is considered.The distance between the cylinders can be varied as can theangle that the undisturbed oscillatory flow makes with the linejoining the cylinder centres. In common with other fluid flowsdominated by oscillatory flow, a time-independent, or steadystreaming, motion develops. Attention is focused on the caseof high streaming Reynolds numbers and the resulting jets thaterupt from the surfaces of the cylinders.     

Peristatcally induced MHD slip flow in a porous medium due to a surface acoustic wavy wall

The influences of Hall current and slip condition on the MHD flow induced by sinusoidal peristaltic wavy wall in two dimensional viscous fluid through a porous medium for moderately large Reynolds number is considered on the basis of boundary layer theory in the case where the thickness of the boundary layer is larger than the amplitude of the wavy wall. Solutions are obtained in terms of a series expansion with respect to small amplitude by a regular perturbation method. Graphs of velocity components, both for the outer and inner flows for various values of the Reynolds number, slip parameter, Hall and magnetic parameters are drawn. The inner and outer solutions are matched by the matching process. An interesting application of the present results to mechanical engineering may be the possibility of the fluid transportation without an external pressure.     

Pulsating magnetohydrodynamic flow in an annular channel

Pulsating laminar flow of a viscous incompressible electrically conducting fluid in an annular channel between two infinitely long circular cylinders under a radial impressed magnetic field is considered. The solutions of magnetohydrodynamic equations have been obtained on the assumption that the space between two cylinders is small compared to their mean radius. The solutions were also obtained on the assumption of small magnetic Reynolds number with special consideration of those for low and high frequencies.     

Flow between torsionally oscillating noncoaxial cylinders

The flow of an incompressible viscous fluid between two torsionally oscillating noncoaxial cylinders has been investigated. Closed form solutions for symmetric and first order asymmetric flow are obtained for the cases when the gap between the cylinders is finite. Solutions of the governing equations under the geometrical restriction of narrow gap are also presented. These solutions coincide with the solutions of the finite gap by incorporating in them the condition of narrow gap. The components of the force acting on the inner cylinder are calculated.     

A Suggested Mechanism for Nonlinear Wall Roughness Effects on High Reynolds Number Flow Stability

The interactions between an uneven wall and free stream unsteadiness and their resultant nonlinear influence on flow stability are considered by means of a related model problem concerning the nonlinear stability of streaming flow past a moving wavy wall. The particular streaming flows studied are plane Poiseuille flow and attached boundary-layer flow, and the theory is presented for the high Reynolds number regime in each case. That regime can permit inter alia much more analytical and physical understanding to be obtained than the finite Reynolds number regime; this may be at the expense of some loss of real application, but not necessarily so, as the present study shows. The fundamental differences found between the forced nonlinear stability properties of the two cases are influenced to a large extent by the surprising contrasts existing even in the unforced situations. For the high Reynolds number effects of nonlinearity alone are destabilizing for plane Poiseuille flow, in contrast with both the initial suggestion of earlier numerical work (our prediction is shown to be consistent with these results nevertheless) and the corresponding high Reynolds number effects in boundary-layer stability. A small amplitude of unevenness at the wall can still have a significant impact on the bifurcation of disturbances to finite-amplitude periodic solutions, however, producing a destabilizing influence on plane Poiseuille flow but a stabilizing influence on boundary-layer flow.     

Noncoaxial vibration of fluid-filled multi-walled carbon nanotubes

This paper is concerned with the free vibration of the fluid-filled multi-walled carbon nanotubes (MWCNTs) with simply supported ends. Based on simplified Donnell’s cylindrical shell model and potential flow theory, the effect of internal fluid on the coupling vibration of the MWCNTs-fluid system is discussed in detail. The results show that the resonant frequencies are decreased due to the effect of the fluid, and the fluid has only a little influence on the associated amplitude ratio in MWCNTs corresponding to the natural resonant frequency (frequency of the innermost tube), while plays a significant role in the associated amplitude ratios corresponding to the intertube resonant frequency. For the natural resonant frequency, the vibration mode is coaxial. However, for the intertube resonant frequency, the system shows complex noncoaxial vibration, which plays a critical role in electronic and transport properties of carbon nanotubes (CNTs).     

Deformation of a drop in a viscous stream and conditions of existence of its equilibrium form

The difference method is used for obtaining a solution of the problem of unsteady motion of a drop in a stream, taking into account its deformation under conditions of axial symmetry. The fluid inside and outside the drop is assumed viscous and incompressible. The stable forms of drop are represented for various Reynolds and Weber numbers of external stream. By analyzing the conditions for normal stresses at the drop boundary, the critical Weber number was obtained, which establishes the conditions of existence of equilibrium form of the drop.     

Fluid flows around cascades

Flows induced by the small-amplitude and high frequency harmonic oscillations of a cascade of bodies in an unbounded fluid which is otherwise at rest are investigated theoretically. In the theoretical study we separate the flow into inner and outer regions. The flow in the inner region is governed by the Stokes boundary-layer equation. The first-order outer flow is governed by the potential solution which is found by using a conformai mapping technique. The second-order outer flow is governed by the full Navier-Stokes equation and the steady streaming flow has been obtained using a modified central-difference scheme for cascades with square cylinders and flat plates for values of the streaming Reynolds number,R _s , up to 70. These results show a complicated flow structure.     

Longitudinal permeability of spatially periodic rectangular arrays of circular cylinders II. An arbitrary distribution of cylinders inside the unit cell

We study the longitudinal permeability of unidirectional disjoint circular cylinders, when a Newtonian fluid is flowing at low Reynolds number along these cylinders; the longitudinal velocity satisfies the Poisson equation. The cylinders are arranged according to a doubly periodic structure. The number of cylinders in each rectangle can be arbitrary as well as their positions and radii. The method of functional equations yields analytical formulae for permeability in terms of these quantities. These formulae are written also in continuous form to study the flow for large numbers of cylinders. Special attention is paid to the case of the square unit cell, equal radii and lognormal distribution of radii.     

Viscoelastic flow in a curved channel: A similarity solution for the Oldroyd-B fluid

A similarity solution is used to analyse the flow of the Oldroyd fluid B, which includes the Newtonian and Maxwell fluids, in a curved channel modelled by the narrow annular region between two circular concentric cylinders of large radius. The solution is exact, including inertial forces. It is found that the non-Netonian kinematics are very similar to the Newtonian ones, although some stress components can become very large. At high Reynolds number a boundary layer is developed at the inner cylinder. The structure of this boundary layer is asymptotically analysed for the Newtonian fluid. Non-Newtonian stress boundary layers are also developed at the inner cylinder at large Reynolds numbers.     

Circular oscillations of a cylinder in a viscous fluid

Summary The steady streaming velocity induced by the circular motion of a cylinder of elliptic cross-section in a viscous fluid is considered. The amplitude of this circular motion is supposed small compared with a typical diameter of the cylinder, which maintains a fixed orientation throughout the motion. Outside the Stokes shear-wave layer Reynolds stresses contribute to the induced steady streaming. The outer flow is calculated in the case of large streaming Reynolds numbers for two particular cylinders.

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Zusammenfassung Es wird die stationäre Strömung untersucht, die durch die kreisförmige Bewegung eines Zylinders mit elliptischem Querschnitt in einer zähen Flüssigkeit induziert wird. Die Amplitude dieser Kreisbewegung wird als klein angenommen gegenüber den Halbachsen der Ellipse, deren Orientierung während der Bewegung unverändert bleibt. Ausserhalb der Stokes-Schicht tragen die Reynolds-Spannungen zur Induzierten stationären Strömung bei. Die äussere Strömung wird im Falle von grossen Reynolds-Zahlen der Strömung für zwei besondere Zylinder berechnet.

     

Numerical stability analysis of the Taylor-Couette flow in the two-dimensional case

The stability of the laminar flow between two rotating cylinders (Taylor-Couette flow) is numerically studied. The simulation is based on the equations of motion of an inviscid fluid (Euler equations). The influence exerted on the flow stability by physical parameters of the problem (such as the gap width between the cylinders, the initial perturbation, and the velocity difference between the cylinders) is analyzed. It is shown that the onset of turbulence is accompanied by the formation of large vortices. The results are analyzed and compared with those of similar studies.     

Homotopy analysis method for the heat transfer in a asymmetric porous channel with an expanding or contracting wall

The flow of a viscous incompressible fluid between two parallel plates due to the normal motion of the porous upper plate is investigated and an analysis is made to determine the heat and mass transfer. The unsteady Navier–Stokes equations are reduced to a generalization of the Proudman–Johnson equation retaining the effect of wall motion using a suitable similarity transformation. The analytical solution for stream function and heat transfer characteristics are obtained by employing homotopy analysis method. The effects of various physical parameters like expansion ratio, Prandtl number, Reynolds number on various momentum and heat transfer characteristics are discussed in detail.