Electro-osmotic flow and heat transfer of a non-Newtonian fluid in a hydrophobic microchannel with Navier slip

In this paper, we investigate the implications of electro-osmosis on electrohydrodynamic transport of a non-Newtonian fluid on a hydrophobic micro-channel by developing a suitable analytical method. Velocity-slip and temperature-jump conditions are paid due attention. An attempt has been made to examine the effects of rheological and electro-osmotic parameters on the kinematics of the fluid. The nonlinear Poisson-Boltzmann equation governing the formation of the electrical double layer and the body force that is generated by the applied potential are accounted for in the study. Perturbation solutions are presented. In order to exhibit the applicability of the analysis, the problem of electro-osmotic flow and heat transfer of blood in an arteriole has been taken up as an illustrative example of a real-life problem. An intensive quantitative study has been made through numerical computation of the physical variables involved in the analysis, which are of special interest in the study. The computational results are presented graphically. The study reveals that the temperature of blood can be controlled by increasing/decreasing the Joule heating parameter.     

Flow of a micropolar fluid in a micro-channel under the action of an alternating electric field: Estimates of flow in bio-fluidic devices

The paper is devoted to a study of the electro-osmotic flow of a micropolar bio-fluid, when the flow takes place between two plates that are in a state of periodic vibrations. Considering blood as a micropolar fluid, it is found that the amplitude of oscillation of the microparticles of blood increases when the micropolar effect is pronounced more and more and that a rise in DebyeHückel parameter enhances both the velocity and microrotation gradient. The results provide guidelines for the improvement of design of bio-sensing and micro-fluidic devices. The study leads to the conclusion that electrical double layers formed in the vicinity of the wall can significantly alter the flow dynamics of physiological fluids in micro-bio-fluidic devices.     

双筒流变仪中Burger流体流动分析

该文研究了双筒流变仪中Burger流体非稳态流动,应用Hankel变换得到了双筒流变仪中Burger流体非稳态流动的解析解,据此可分析环管内旋转速度和切应力分布与变化特征。利用Laplace变换数值反演Stehfest方法分析了流变仪中Burger流体的动态特征,结果表明速度场和应力场分布对Burger流体参数非常敏感。Navier-Stokes流体的著名解,像Maxwell流体、二阶流体和Oldroyd-B流体的解都是本文解的特殊情况.     

多孔介质中粘弹性液体广义流动分析

将分数阶导数引入渗流力学建立了多孔介质中具有松驰特性的非牛顿粘弹性液体的含有分数阶导数的不稳定渗流模型，利用离散逆Laplace变换技巧和广义Mittag-Eeffler函数研究了多孔介质中非牛顿松弛粘弹性液分数阶流动特征。对任意的分数阶导数得到了精确解，并先求出了长时和短时渐进解，然后用拉普拉斯数值反演Stehfest方法分析无限大地层粘弹性液的流动。结果表明粘弹性流体对分数导数的阶数具有极强的敏感性。     

Stability of fluid flow in a Brinkman porous medium–A numerical study

The stability of fluid flow in a horizontal layer of Brinkman porous medium with fluid viscosity different from effective viscosity is investigated. A modified Orr-Sommerfeld equation is derived and solved numerically using the Chebyshev collocation method. The critical Reynolds number cRe, the critical wave number αc and the critical wave speed cc are computed for various values of porous parameter and ratio of viscosities. Based on these parameters, the stability characteristics of the system are discussed in detail. Streamlines are presented for selected values of parameters at their critical state.     

二层流体浅水波演化模型

本文在Boussinesq的浅水波假定下，采用各层内任意点ziα速度水平分量代替传统的垂向平均速度，推导出了各层速度的三个分量及压力由各层内点ziα速度水平分量表示的沿垂向分布，将三维问题简化为二维问题，建立了二层流体浅水波演化模型，即二层流体的改进Boussinesq方程组。在该方程组中，随ziα距交界面距离不同，该二层流体浅水波演化模型具有不同的色散特性和非线性。作者证明文中参数αi皆取-0.393时，该方程组具有最佳的色散特性。该方程组不仅适于模拟波浪沿水平方向从深水域向浅水域传播时的折射、绕射和反射问题，而且也适用于研究在浅水或中等水深的水域中波浪传播问题。     

Diffusion of chemically reactive species in Casson fluid flow over an unsteady permeable stretching surface

In this paper we investigate the two-dimensional flow of a non-Newtonian fluid over an unsteady stretching permeable surface. The Casson fluid model is used to characterize the non-Newtonian fluid behavior. First-order constructive/destructive chemical reaction is considered. With the help of a shooting method, numerical solutions for a class of nonlinear coupled differential equations subject to appropriate boundary conditions are obtained. For the steady flow, the exact solution is obtained. The flow features and the mass transfer characteristics for different values of the governing parameters are analyzed and discussed in detail.     

两层黏性流体中直立圆柱体绕流的三维数值模拟

研究了两层流体中直立贯底圆柱体的三维黏性绕流问题.以不可压缩Navier-Stokes方程为控制方程,应用VOF方法追踪两层流体的内界面,建立了该问题的数值模拟方法.成功地数值模拟了两层流体中圆柱体黏性绕流产生的三维尾涡特征,表明了流体的密度分层效应对直立贯底圆柱体的尾涡特性和阻力系数都是有影响的.在海洋立管涡激振动的研究中,考虑流体的密度分层效应是重要的.     

幂律流体在圆管内湍流流动剪切率的近似计算

根据剪切率和能量耗散率的定义，建立了幂律流体湍流剪切率与能量耗散率的关系式。参照文献上对不可压缩牛顿流体湍流能量耗散率的近似算法，提出了一种幂律流体管内湍流能量耗散率的近似算法，从而得到了幂律流体管内湍流剪切率的实用近似算式，再利用湍流剪切率与脉动流剪切率的关系即可得到脉动流剪切率。计算得到的湍流剪切率分布及其随流动特性指数变化的特征与已知规律相符。     

Pressure distribution on the wall of the inner cylinder reciprocating axially to the unsteady flow of viscoelastic fluid in eccentric annulus

1. INTRODUCTION During the oil production process, the produced fluid flows in the eccentric annulus between the tube and the sucker-rod reciprocating axially. In this article, the pressure distribution on the wall of the inner cylinder for the unsteady flow of the flowing fluid, which can be regarded as viscoelastic fluid, in the eccentric annulus with the inner cylinder reciprocating axially, is studied and the results are of significance in practical engineering for analyzing the mechan…     

Homotopy-based analytical approximation to nonlinear short-crested waves in a fluid of finite depth

A nonlinear short-crested wave system, consisting of two progressive waves propagating at an oblique angle to each other in a fluid of finite depth, is investigated by means of an analytical approach named the homotopy analysis method(HAM). Highly convergent series solutions are explicitly derived for the velocity potential and the surface wave elevation. We find that, at every value of water depth, there is little difference between the kinetic energy and the potential energy for nonlinear waves. The nonlinear short-crested waves with a larger angle of incidence always contain the more potential wave energy. With the aid of the HAM, we obtain the dispersion relation for nonlinear short-crested waves. Furthermore, it is shown that the wave elevation tends to be smoothened at the crest and be sharpened at the trough as the water depth increases, and the wave pressure crests and troughs become steeper with increasing incident wave steepness.     

改进的时间序列模型在非汛期水沙预报中的应用

从ARMA模型出发，对传统的误差实时修正方法进行改进，用服从正态分布的纯随机序列代替，延长了时间序列预测时域．用这两种方法对黄河潼关水文站水沙序列进行了预测，经计算表明，改进的时间序列方法有效地提高了预测精度。     

Efficacy of increasing discharge to reduce tow-mediated fish passage across an electric dispersal barrier system in a confined channel

The Electric Dispersal Barrier System (EDBS) in the Chicago Sanitary and Ship Canal (CSSC) was built to limit the interbasin transfer of aquatic invasive species between the Mississippi River Basin and the Great Lakes Basin. Commercial barge traffic, or tows, moving downstream through the EDBS can facilitate the upstream passage of small fish through the barrier by reducing the voltage gradient of the barrier and causing localized upstream return currents. This study tested whether it is possible to prevent upstream passage of small fish across the barrier by preventing upstream return currents. Measurements of water velocity, voltage gradient, and tow speed, as well as sonar-based observations of resident fish, were made as a tow transited the EDBS moving downstream. The results indicate that upstream return currents can be prevented for typical flow conditions in the CSSC (ambient velocity = 0.15 to 0.23 m/s) when tow speeds are <0.46 m/s. Similarly, increasing the ambient velocity above typical values can prevent upstream return currents for faster tow speeds and larger tows. Additionally, preventing upstream return currents at the EDBS may reduce, but does not prevent, tow-mediated upstream fish passages because tows also cause a temporary reduction in the streamwise voltage gradient at the EDBS. These results have implications for the management of invasive bigheaded carps in the Illinois Waterway.     

The potential role of tributaries as seed sources to an impoundment in Northern Sweden: a field experiment with seed mimics

Fragmentation and flow regulation of rivers by large dams are known to obstruct the longitudinal dispersal of waterborne plant propagules between impoundments, and to affect plant community composition. However, even several decades after a dam has been built, impoundments may still have a relatively species‐rich riparian flora. We hypothesized that free‐flowing tributaries act as the major gene pools for such impoundments, thus alleviating the fragmenting effect large dams have on the main channel. The importance of tributaries as seed sources was tested by releasing wooden seed mimics in three different‐sized (0.22–6.93 m³ s^?1) tributaries of an impoundment in the Ume River in Northern Sweden. In each tributary seed mimics were released, during the spring flood peak, from three points approximately 1, 2 and 3 km upstream the outlet in the impoundment. The importance of a tributary as a seed source increased with tributary size. Of the 9000 released seed mimics 1.5% reached the impoundment; 1.2% of the 9000 originated from the largest tributary and 0.3% from the middle‐sized one. The smallest tributary retained all its mimics. Copyright © 2007 John Wiley & Sons, Ltd.