Slow viscous flow around two particles in a cylinder

This article describes the motion of two arbitrarily located free moving particles in a cylindrical tube with background Poiseuille flow at low Reynolds number. We employ the Lamb’s general solution based on spherical harmonics and construct a framework based on cylindrical harmonics to solve the flow field around the particles and the flow within the tube, respectively. The two solutions are performed in an iterated framework using the method of reflections. We compute the drag force and torque coefficients of the particles which are dependent on the distances among the cylinder wall and the two particles. In addition, we provide detailed flow field in the vicinity of the two particles including streamlines and velocity contour. Our analysis reveals that the particle–particle interaction can be neglected when the separation distance is three times larger than the sum of particles radii when the two particles are identical. Furthermore, the direction of Poiseuille flow, the particle position relative to the axis and the particle size can make the two particles attract or repel. Unlike the single particle case, the two particles can move laterally due to the hydrodynamic interaction. Such analysis can give insights to understand the mechanisms of collision and aggregation of particles in microchannels.     

圆管绕流旋涡脱落诱导振动的数值模拟

利用计算流体力学软件Ansys／Flotran CFD,首先对粘性不可压缩流体的固定圆管绕流进行了数值模拟,然后结合逐步积分法完成了同时考虑纵横两向弹性支撑圆管绕流旋涡脱落诱导振动的数值模拟,并通过快速傅立叶变换,得到了弹性支撑圆管和固定圆管的升力及弹性支承圆管横向位移响应的功率谱．通过计算结果分析,得出了一些有价值的结论,可供从事具有圆管绕流构件设备设计的工程技术人员参考．     

Calculating viscous incompressible flow past an elliptical cylinder on a parallel computer

An algorithm developed for a parallel computer is described. The algorithm has been simulated on an ES-1060 machine, and the results are compared with those obtained on BÉSM-6 computer.Translated from Kibernetika, No. 1, pp. 64–68, January–February, 1990.     

An optimal analysis of radiated nanomaterial flow with viscous dissipation and heat source

Microsystem Technologies - The present work explores the analytical study of nanofluid flow above a stretching medium with the heat source and viscous dissipation. Additional radiative effects are...     

Solute dispersion in oscillating electro-osmotic flow with boundary mass exchange

Mass transfer in an oscillatory electro-osmotic flow (EOF) is theoretically studied, for the case of a cylindrical tube with a reactive wall. An expression for the dispersion coefficient, reflecting the time-averaged mass flux of an electrically neutral solute, is derived analytically. Under the influence of a reversible solute-wall mass exchange, the dispersion coefficient exhibits a complex dependence on the various parameters representing the effects of the electric double-layer thickness, oscillation frequency, solution transport properties, solute partitioning, and reaction kinetics. Our results suggest that, in the presence of a reversible mass exchange at the wall, an oscillatory EOF may be used for separation of species. It is found that optimal conditions for separation are achieved for a thin double-layer, where an inert solute, or one with slow exchange kinetics, experiences virtually no dispersion while the dispersion is maximized for the reactive solute exhibiting fast kinetics.     

Simulation of a viscous compressible flow past a circular cylinder with high-order discontinuous Galerkin methods

This paper is devoted to the simulation of viscous compressible flows with high-order accurate discontinuous Galerkin methods on bidimensional unstructured meshes. The formulation for the solution of the Navier–Stokes equations is due to Oden et al. [An hp-adaptive discontinuous finite element method for computational fluid dynamics. PhD thesis, The University of Texas at Austin, 1997; J Comput Phys 1998;146:491–519]. It involves a weak imposition of continuity conditions on the state variables and on fluxes across interelement boundaries. It does not make use of any auxiliary variables and then the cost for the implementation is reasonable. The method is coupled with a limiting procedure recently developed by the authors to suppress oscillations near large gradients. The limiter is totally free of problem dependence and maintains the convergence order for errors measured in the L¹-norm. This paper presents detailed numerical results of a viscous compressible flow past a circular cylinder at a Reynolds number of 100 for the cases of subsonic and supersonic regimes. The proposed simulations suggest that the method is very robust and is able to produce very accurate results on unstructured meshes.     

Computer acquisition and analysis of skin temperature and heat flow data from heat flux transducers

A computer-controlled system for the collection and analysis of skin temperature and heat flow data originating from an array of heat flux transducers is describe. The systems is based on a program (‘THERMAL’) that reads, stores, prints and displays skin temperatures and heat flow data every 2 min for up to 4 h. It also simultaneously calculates important environmental physiology parameters such as mean skin and mean body temperatures as well as mean heat flow according to four different combinations of transducers such as the established 3-, 4-, 7- and 12-point (site) formulae. Core temperature, heart rate and environmental condition indices such as dry bulb, wet bulb and globe temperatures are also continuously monitored.     

Two-dimensional nonsteady viscous flow simulation on the Navier-Stokes Computer miniNode

The needs of large-scale scientific computation are outpacing the growth in performance of mainframe supercomputers. In particular, problems in fluid mechanics involving complex flow simulations require far more speed and capacity than that provided by current and proposed Class VI supercomputers. To address this concern, the Navier-Stokes Computer (NSC) was developed. The NSC is a parallel-processing machine, comprised of individual Nodes, each comparable in performance to current supercomputers. The global architecture is that of a hypercube, and a 128-Node NSC has been designed. New architectural features, such as a reconfigurable many-function ALU pipeline and a multifunction memory-ALU switch, have provided the capability to efficiently implement a wide range of algorithms. Efficient algorithms typically involve numerically intensive tasks, which often include conditional operations. These operations may be efficiently implemented on the NSC without, in general, sacrificing vector-processing speed. To illustrate the architecture, programming, and several of the capabilities of the NSC, the simulation of two-dimensional, nonsteady viscous flows on a prototype Node, called the miniNode, is presented.     

Time-dependent solutions of the viscous incompressible flow past a circular cylinder by the method of series truncation

Semi-analytic solutions of the Navier-Stokes equations are calculated for two-dimensional, symmetrical, viscous incompressible flow past a circular cylinder. The stream and vorticity functions are expanded in the finite Fourier series and then substituted in the Navier-Stokes equations. This led to a system of coupled parabolic partial differential equations which are solved numerically. More terms of the series are required as Reynolds number increases and the present calculations were terminated at Reynolds number 600 with 60 terms of Fourier series. The results are compared with similar calculations and experimental data for Reynolds numbers 60, 100, 200, 500, 550 and 600. At the termination of the calculations for Reynolds numbers 60 and 100, the separation angle, the wake length, the drag coefficient, and the vorticity distributions around the surface were very close to their steady-state values. A secondary vortex appeared on the surface of the cylinder in the case of Reynolds numbers 500, 550 and 600. The wake length, the drag coefficient and the separation angle differ slightly at a given instant in the case of Reynolds numbers 500, 550 and 600.     

Estimation of heat transfer in oscillating annular flow using artifical neural networks

In this study, the prediction of heat transfer from a surface having constant heat flux subjected to oscillating annular flow is investigated using artificial neural networks (ANNs). An experimental study is carried out to estimate the heat transfer characteristics as a function of some input parameters, namely frequency, amplitude, heat flux and filling heights. In the experiments, a piston cylinder mechanism is used to generate an oscillating flow in a liquid column at certain frequency and amplitude. The cycle-averaged values are considered in the calculation of heat transfer using the control volume approach. An experimentally evaluated data set is prepared to be processed with the use of neural networks. Back propagation algorithm, the most common learning method for ANNs, is used for training and testing the network. Results of the experiments and the ANN are in close agreements with errors less than 5%. The study showed that the ANNs could be used effectively for modeling oscillating flow heat transfer in a vertical annular duct.     

Non-coaxial rotating flow of viscous fluid with heat and mass transfer

Heat and mass transfer in unsteady non-coaxial rotating flow of viscous fluid over an infinite vertical disk is investigated. The motion in the fluid is induced due to two sources. Firstly, due to the buoyancy force which is caused because of temperature and concentration gradients. Secondly, because of non-coaxial rotation of a disk such that the disk executes cosine or since oscillation in its plane and the fluid is at infinity. The problem is modeled in terms of coupled partial differential equations with some physical boundary and initial conditions. The dimensionless form of the problem is solved via Laplace transform method for exact solutions. Expressions for velocity field, temperature and concentration distributions are obtained, satisfying all the initial and boundary conditions. Skin friction, Nusselt number and Sherwood number are also evaluated. The physical significance of the mathematical results is shown in various plots and is discussed for several embedded parameters. It is found that magnitude of primary velocity is less than secondary velocity. In limiting sense, the present solutions are found identical with published results.

     

On the use of several compact methods for the study of unsteady incompressible viscous flow round a circular cylinder

Fourth order accurate methods of mehrstellen type are compared to second order accurate methods for the solution of the unsteady incompressible Navier-Stokes equations in their vorticity stream function formulation. These methods are applied to the study of separated flow around a circular cylinder at several Reynolds numbers. The impulsively started cylinder at Re = 200 and 550, is considered without symmetry restrictions. The features illustrated include the bulge phenomenon at Re = 200, the occurrence of secondary vortices depending on the schemes used at Re = 550, and of twin secondary vortices at Re = 3000. The Karman vortex street is investigated at Re = 200 with a uniform flow in the far field and with superimposed motions of the cylinder. In this last case, a frequency analysis has allowed a critical examination of results pertaining to locked-in situations with respect to confinement effects.     

Finite element analysis of viscous fluid flow

A finite element model for the analysis of two dimensional viscous flows is formulated using the virtual work method. The model is in part based on a finite element shell model, using the same reduced integration of quadratic interpolations for all variables[1]. Differences from preceding formulations are that integration by parts is applied to the continuity equation, yielding different loading terms which are more easily defined in some problems, and a new approach is used for the convective inertia terms, giving a clearer interpretation of their effects which are distributed to both sides of the nonlinear recurrence relation. In the case of compressible flow, for which comparatively few formulations have been proposed to date, the thermal energy equation is used to form a two stage solution and here this seems the most natural and economical approach.     

CFD analysis of viscous non-Newtonian flow under the influence of a superimposed rotational vibration

The effects of a superimposed sinusoidal rotational vibration on the flow of non-Newtonian fluids in a tube are studied numerically by computational fluid dynamics (CFD). Inelastic time-independent fluids of the power law, Herschel-Bulkley, Bingham plastic, and Newtonian types are investigated. Newtonian flow is unchanged by any superimposed oscillations but the flow of non-Newtonian fluids is greatly affected. The flow of shear-thinning fluids and viscoplastic fluids is enhanced, whilst the flow of shear-thickening fluids is retarded. The effects of the various rheological as well as vibration parameters are studied in detail. Flow is affected by both vibration frequency and amplitude, but different amplitude-frequency combinations which correspond to the same peak acceleration result in the same effect. Mechanical vibration in the sonic range generates substantial flow enhancements in low to moderately viscous fluids, but has limited scope for highly viscous fluids. Mechanical vibration in the ultrasound range, however, has a good potential for the processing of highly viscous materials, being able to generate orders of magnitude enhancement in flow. The extent of flow enhancement achieved is also dependent on the nature of the superimposed vibration: a rotational oscillation produces more flow enhancement than a transversal oscillation, but less than a longitudinal oscillation.     

Computer simulation and discrete-event models in the analysis of a mammography clinic patient flow

OBJECTIVE: This work develops a discrete-event computer simulation model for the analysis of a mammography clinic performance. MATERIAL AND METHODS: Two mammography clinic computer simulation models were developed, based on an existing public sector clinic of the Brazilian Cancer Institute, located in Rio de Janeiro city, Brazil. Two clinics in a total of seven configurations (number of equipment units and working personnel) were studied. Models tried to simulate changes in patient arrival rates, number of equipment units, available personnel (technicians and physicians), equipment maintenance scheduling schemes and exam repeat rates. Model parameters were obtained by direct measurements and literature reviews. A commercially-available simulation software was used for model building. RESULTS: The best patient scheduling (patient arrival rate) for the studied configurations had an average of 29 min for Clinic 1 (consisting of one mammography equipment, one to three technicians and one physician) and 21 min for Clinic 2 (two mammography equipment units, one to four technicians and one physician). The exam repeat rates and equipment maintenance scheduling simulations indicated that a large impact over patient waiting time would appear in the smaller capacity configurations. CONCLUSIONS: Discrete-event simulation was a useful tool for defining optimal operating conditions for the studied clinics, indicating the most adequate capacity configurations and equipment maintenance schedules.     

An investigation of oscillating motions in a miniature pulsating heat pipe

A mathematical model for predicting the oscillating motion in a pulsating heat pipe is presented. The model considers the thermal energy from the temperature difference between the evaporator and condenser as the driving force for the oscillating motion, which will overcome both the frictional force and the force due to the deformation of compressible bubbles. The results show that the oscillating motion depends on the temperature difference between the condensing section and evaporating section, the working fluid, the operating temperature, the dimensions, and the filled liquid ratio. The results of this investigation will assist in the development of miniature pulsating heat pipes capable of operating at increased power levels.     

Numerical analysis of dual-phase-lag heat transfer in a layered cylinder with nonlinear interface boundary conditions

To accommodate the micro-structural effect, this work analyzes the heat transfer induced by a pulsed surface heating in a two-layered solid cylinder with the dual-phase-lag model. The interface thermal resistance is specified with the radiation boundary condition model. Due to the difference in the relaxation times between two dissimilar materials, the strong nonlinearity of the interfacial boundary condition, and the singularity at the center axis, it introduces the complexity and causes some mathematical difficulties to analyze the present problem. Thus a numerical scheme is developed. Results show the lagging thermal behavior is affected with the geometry effect and the interface thermal resistance and depends on the magnitude of the relaxation times more than the ratio value between the relaxation times. The microstructure effect would destroy the structure of thermal wave. The propagation speed of thermal wave is independent of the interface thermal resistance and the microstructure effect.     

Transient flow and heat transfer mechanism for Williamson-nanomaterials caused by a stretching cylinder with variable thermal conductivity

The utilization of nanometre-sized solid particles in working fluids has been seriously recommended due to their enhanced thermal characteristics. This suspension of solid particles in base fluids can significantly enhance the physical properties, such as, viscosity and thermal conductivity. They are widely used in several engineering processes, like, heat exchangers, cooling of electronic equipment, etc. In this exploration, we attempt to deliver a numerical study to simulate the nanofluids flow past a circular cylinder with convective heat transfer in the framework of Buongiorno’s model. A non-Newtonian Williamson rheological model is used to describe the behavior of nanofluid with variable properties (i.e., temperature dependent thermal conductivity). The leading flow equations for nanofluid transport are mathematical modelled with the assistance of Boussinesq approximation. Numerical simulation for the system of leading non-linear differential equations has been performed by employing versatile, extensively validated, Runge–Kutta Fehlberg scheme with Cash–Karp coefficients. Impacts of active physical parameters on fluid velocity, temperature and nanoparticle concentration is studied and displayed graphically. It is worth to mention that the temperature of non-Newtonian nanofluids is significantly enhanced by higher variable thermal conductivity parameter. One major outcome of this study is that the nanoparticle concentration is raised considerably by an increasing values of thermophoresis parameter.