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1.
研究了平行板微管道中二维磁流体(MHD)电渗流(EOF)在zeta电势调制下的流动.流体的流动是由两个外加水平电场和垂直磁场所产生的Lorentz力和电场力的组合驱动的.在滑移边界条件下,得到了流函数以及速度分布的解析解.详细讨论了速度随Hartmann数Ha、滑移长度B、电动宽度K等相关的无量纲参数量级变化的变化规律.结果表明,调制的壁面电势会产生一个垂直速度分量,从而导致涡旋的形成.此外,可以观察到,速度的大小随着滑移长度B和电动宽度K的增大而增大.值得注意的是,速度的大小随着Ha值的增大而减小,这与一维流动中Ha值存在临界值的情况不同.  相似文献   

2.
Numerical modelling of acousto-microfluidic particle manipulation systems cannot only be used to explain the complex phenomena observed in experiments, but can also be applied to optimise their performances. In this work, we present numerical simulations of continuous-flow-based two-stage acoustic microparticle separations with a reduced-fluid model, which is consisted of three main parts: (1) an acoustic focusing zone; (2) a transition zone; and (3) an acoustic separation zone. The acoustophoresis of microparticles of various sizes in the fluid channel was modelled based on Newton's second law, where the acoustic radiation forces and the flow-induced drag forces, the main driving terms for particle motion, were solved from the Gorkov equation and the Navier-Stokes equations, respectively. It was found that an acoustic focusing process configured with appropriate force amplitudes can focus all particles to the same flow vector before entering the separation zone and thus can improve the separation efficiency, and that a sheath flow injected from the transition zone can push the sample flow onto the side boundaries, which can broaden the effective separation range for more robust separations. Based on the mechanism analyses, we here numerically demonstrated acoustofluidic separation of 5 different particle fractions simultaneously in a continuous microfluidic channel ending with 9 equally spaced outlets. We also predicted here that, with carefully designed acoustic and flow fields, it is capable to acoustically separate two different particle fractions with a diameter difference of 4% (difference in acoustic mobility of only ~1.08).  相似文献   

3.
We consider the long-time behavior of the mean curvature flow in heterogeneous media with periodic fibrations, modeled as an additive driving force. Under appropriate assumptions on the forcing term, we show existence of generalized traveling waves with maximal speed of propagation, and we prove the convergence of solutions to the forced mean curvature flow to these generalized waves.  相似文献   

4.
In local radial gravitational force fields there is no viable flow of the force itself, and if divergence of a vector is constructed within the field, then it actually requires time-based radial gravitational potentials rather than the usual distance-based radial potentials. When cast in structural relationships of multispatial hyperspace, the new multispatial representation of the usual, Newtonian radial gravity term suggests thus that the allegedly missing mass-energy of the known universe may be the result of inappropriate accounting methods rather than cosmic mass deficiency, as some used to believe. More detailed analysis of local radial gravitational field reveals that the allegedly universal gravitational constant hides fairly compound functional of locally constant value and therefore the radial force depends on more variables than are explicitly displayed in the Newton's inverse square law of gravitation.  相似文献   

5.
The interaction of an externally imposed magnetic and electric field on the laminar flow of a conducting fluid in a channel is studied using computational techniques. The Navier-Stokes equations and the equations describing the electromagnetic field are solved simultaneously in a single control volume-type computational fluid dynamic code, in a moderate Hartmann number and interaction parameter regime. The flow considered is two-dimensional, with an imposed magnetic field acting in the third dimension over the central region of the channel and decaying exponentially in the remainder. A pair of electrodes placed at right angles to the magnetic field exercises control over the resultant Lorentz force and hence the velocity profile shape. This configuration has application in direct-current electromagnetic pumps or, conversely, electromagnetic brakes. The initial parabolic flow profile acquires an M-shape / W-shape mode in the magnetic field fringe regions, corresponding to a pump / brake. A novel coupled procedure is described to model magnetohydrodynamic phenomena and is used to explore the effects of the Reynolds number, interaction parameter, and applied voltage on the pump / brake configuration.  相似文献   

6.
Two methods of consideration of surface energy were compared by the author in the case of variational problems on phase transitions in continuous-medium mechanics and problems on phase transitions in thermoelasticity. In this paper, these methods are compared for problems on phase transitions in large force fields. Bibliography: 5 titles. Translated fromProblemy Matematicheskogo Analiza, No. 19, 1999, pp. 182–192.  相似文献   

7.
Electromagnetic fields are often used industrially to controlthe flow of liquid metal, and in particular this review is concernedwth applications of alternating fields. An alternating fieldinduces eddy currents in liquid metal which interact with thefield to give a Lorentz body force which is generally rotationaland which must therefore drive fluid motion. We derive generalexpressions for the Lorentz force, showing that it consistsof both steady and oscillatory components. The flow in a circularcylinder due to a rotating field is discussed in detail, sincethis problem is simple to analyse and illustrates several importantgeneral principles. In the high-frequency limit, the field isconfined to a narrow layer on the surface of the conductor,and we derive approximate methods for calculating the surfacemagnetic pressure andthe induced flow. We also examine the otherextreme of slowly alternating fields. As each problem is studied,we discuss practical applications.  相似文献   

8.
In this work a two phase 3D mathematical model was developed using the volume of fluid (VOF) algorithm, which is able to accurately describe the cavity geometry and size as well as the liquid flow patterns created when a gas jet that impinges on a liquid free surface. These phenomena are commonly found in steelmaking operations such as in the Electric Arc Furnace (EAF) and the Basic Oxygen Furnace (BOF) where oxygen jets impinge on a steel bath and they control heat, momentum and mass transfer. The model was successfully validated with measurements made on a physical model through velocity fields obtained by Particle Image Velocimetry (PIV) and high speed camera images of the cavity. Agreement between model predictions and experimental measurements is excellent in both x-velocity component of the liquid and cavity sizes. The cavity formed in the liquid by the impinging jet depends on a force balance at the free surface where the inertial force of the jet governs this phenomena, while the liquid circulation depends on also the jet inertial force of the jet, but its angle plays an important role, being the lowest angle the best choice to shear the bath and promote stronger circulation and better mixing in the liquid.  相似文献   

9.
In this paper we use computational fluid dynamics (CFD) to study the effect of contact angle on droplet shape as it moves through a contraction. A new non-dimensional number is proposed in order to predict situations where the deformed droplet will form a slug in the contraction and thus have the opportunity to interact with the channel wall. It is proposed that droplet flow into a contraction is a useful method to ensure that a droplet will wet a channel surface without a trapped lubrication film, and thus help ensure that a slug will remain attached to the wall downstream of the contraction. We demonstrate that when a droplet is larger than a contraction, capillary and Reynolds numbers, and fluid properties may not be sufficient to fully describe the droplet dynamics through a contraction. We show that, with everything else constant, droplet shape and breakup can be controlled simply by changing the wetting properties of the channel wall. CFD simulations with contact angles ranging from 30° to 150° show that lower contact angles can induce droplet breakup while higher contact angles can form slugs with contact angle dependent shape.  相似文献   

10.
We consider the dynamics of vector fields on three-manifolds which are constrained to lie within a plane field, such as occurs in nonholonomic dynamics. On compact manifolds, such vector fields force dynamics beyond that of a gradient flow, except in cases where the underlying manifold is topologically simple (i.e., a graph-manifold). Furthermore, there are strong restrictions on the types of gradient flows realized within plane fields: such flows lie on the boundary of the space of nonsingular Morse-Smale flows. This relationship translates to knot-theoretic obstructions for the link of singularities in the flow. In the case of an integrable plane field, the restrictions are even finer, forcing taut foliations on surface bundles. The situation is completely different in the case of contact plane fields, however: it is easy to realize gradient fields within overtwisted contact structures (the nonintegrable analogue of a foliation with Reeb components). Received: December 9, 1997.  相似文献   

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