Effects of Navier slip on unsteady flow of a reactive variable viscosity non-Newtonian fluid through a porous saturated medium with asymmetric convective boundary conditions

A study on the effects of Navier slip, in conjunction with other flow parameters, on unsteady flow of reactive variable viscosity third-grade fluid through a porous saturated medium with asymmetric convective boundary conditions is presented. The channel walls are assumed to be subjected to asymmetric convective heat exchange with the ambient, and exothermic chemical reactions take place within the flow system. The heat exchange with the ambient obeys Newton's law of cooling. The coupled equations, arising from the law of conservation of momentum and the first law of thermodynamics, then the derived system are nondimensionalised and solved using a semi-implicit finite difference scheme. The lower wall slip parameter is observed to increase the fluid velocity profiles, whereas the upper wall slip parameter retards them because of backflow at the upper channel wall. Heat production in the fluid is seen to increase with the slip parameters. The wall shear stress increases with the slip parameters while the wall heat transfer rate is largely unaltered by the lower wall slip parameter but marginally increased by the upper wall slip parameter.     

Thermodynamic analysis for a third grade fluid through a vertical channel with internal heat generation

This paper makes the thermodynamic analysis in forced convective flow of a third grade fluid through a vertical channel. Due to the reactive nature of the fluid, the effect of internal heat generation is considered and assumed to be a linear function of temperature. The coupled nonlinear dimensionless ordinary differential equations governing the fluid flow are solved by using the Adomian decomposition method(ADM). The effects of various physical parameters such as third grade material parameter, buoyancy parameter and heat generation parameter on the thermal structure of flow are presented and discussed.     

Numerical simulation of self-similar thermal convection from a spinning cone in anisotropic porous medium

Self-similar steady natural convection thermal boundary layer flow from a rotating vertical cone to anisotropic Darcian porous medium is investigated theoretically and numerically. The transformed non-dimensional two-point boundary value problem is reduced to a system of coupled, highly nonlinear ordinary differential equations, which are solved subject to robust surface and free stream boundary conditions with the MAPLE 17 numerical quadrature software. Validation with earlier non-rotating studies is included, and also further verification of rotating solutions is achieved with a variational finite element method(FEM). The rotational(spin) parameter emerges as an inverse function of the Grashof number. The influence of this parameter, primary Darcy number, secondary Darcy number and Prandtl number on tangential velocity and swirl velocity, temperature and heat transfer rate are studied in detail. It is found that the dimensionless tangential velocity increases whilst the dimensionless swirl velocity and temperature decrease with the swirl Darcy number, tangential Darcy number and the rotational parameters. The model finds applications in chemical engineering filtration processing, liquid coating and spinning cone distillation columns.     

Effects of space and temperature dependent internal heat generation/absorption on MHD flow of a nanofluid over a stretching sheet

In this paper we analyzed the effects of space and temperature dependent internal heat generation/absorption(non-uniform heat source/sink) on magnetohydrodynamic boundary layer flow of water based nanofluid over a stretching sheet with different nanoparticles. The flow is generated due to linear stretching of the sheet and influenced by uniform magnetic field, which is applied normally to the stretching sheet. A scaling group of transformation is used to reduce the governing momentum and energy equations into non-linear ordinary differential equations. The resulting differential equations are solved analytically using hypergeometric functions and numerically by the fourth order Runge-Kutta method with shooting technique. The influence of nanoparticle volume fraction, magnetic field, Prandtl number, non uniform heat source/sink, local skin friction coefficient and reduced Nusselt number are investigated for different nanoparticles.     

Theoretical analysis of slip flow on a rotating cone with viscous dissipation effects

This paper is concerned with the mutual effects of viscous dissipation and slip effects on a rotating vertical cone in a viscous fluid. Similarity solutions for rotating cone with wall temperature boundary conditions provides a system of nonlinear ordinary differential equations which have been treated by optimal homotopy analysis method(OHAM). The obtained analytical results in comparison with the numerical ones show a noteworthy accuracy for a special case. Effects for the velocities and temperature are revealed graphically and the tabulated values of the surface shear stresses and the heat transfer rate are entered in tables. From the study it is seen that the slip parameter ? enhances the primary velocity while the secondary velocity reduces. Further it is observed that the heat transfer rate 1/2xNu Re? increases with Eckert number Ec and Prandtl number Pr.     

The effect of variable viscosity on the flow and heat transfer of a viscous Agwater and Cu-water nanofluids

A numerical study is carried out to study the effects of the temperature dependent viscosity on the flow and heat transfer of a nanofluid over a flat surface in the presence of viscous dissipation. The governing nonlinear partial differential equations are transformed into nonlinear ordinary differential equations, and are solved numerically by the Keller-box method. The numerical results indicate that the effect of nanoparticle volume fraction is to increase the heat transfer and hence enhance the thermal boundary layer thickness. This is true even in the presence of variable viscosity and the viscous dissipation. Furthermore, the results obtained for heat transfer characteristics with nanoparticles reveal many interesting behaviors that warrant further study on the effects of the "nano-solid-particles".     

Effects of variable fluid properties on the thin film flow of Ostwald-de Waele fluid over a stretching surface

We investigate, in this paper, the effects of thermo-physical properties on the flow and heat transfer in a thin film of a power-law liquid over a horizontal stretching surface in the presence of a viscous dissipation. The fluid properties, namely the fluid viscosity and the fluid thermal conductivity, are assumed to vary with temperature. Using a similarity transformation, the governing partial differential equations with a time dependent boundary are converted into coupled non-linear Ordinary Differential Equations (ODEs) with variable coefficients. Numerical solutions of the coupled ODEs are obtained by a finite difference scheme known as the Keller-box method. Results for the velocity and temperature distributions are presented graphically for different values of the pertinent parameters. The effects of unsteady parameter on the skin friction, the wall temperature gradient and the film thickness are presented and analyzed for zero and non-zero values of the temperature-dependent thermo-physical properties. The results obtained reveal many interesting features that warrant further study on the non-Newtonian thin film fluid flow phenomena, especially the shear-thinning phenomena.     

引水流量对引水渠道中水内冰演变影响的数值模拟

水电站引水渠道中的冰害会影响水电站的安全运行,危害当地人民的人身安全。为开展引水渠道中水内冰演变的研究,建立了三维非稳态欧拉两相流模型,动量方程考虑了相间曳力、升力、虚拟质量力,热量传递方程中考虑了冰水之间的热量传递以及太阳辐射、有效辐射、蒸发热损失、水面对流热损失等。模拟分析了不同引水流量下温度及冰体积分数的沿程分布,结果表明：冰温沿程逐渐升高;水温沿程先降低后升高、沿程出现最低点。冰体积分数沿程存在突变点,且突变点在水温最低点附近。随着引水流量减小,产冰起始位置向渠道上游移动,但最终的产冰量和冰体积分数逐渐减小。通过与黄河上游河道中水内冰演变计算结果对比,验证了模型的可靠性。     

Flow,thermal criticality and transition of a reactive third-grade fluid in a pipe with Reynolds' model viscosity

Neglecting the consumption of the material, a steady incompressible flow of an exothermic reacting third-grade fluid with viscous heating in a circular cylindrical pipe is numerically studied for both cases of constant viscosity and Reynolds' viscosity model. The coupled ordinary differential equations governing the flow in cylindrical coordinates, are transformed into dimensionless forms using appropriate transformations, and then solved numerically. Solutions using Maple are presented in tabular form and given in terms of dimensionless central fluid velocity and temperature, skin friction and heat transfer rate for three parametric values in the Reynolds' case. The numerical results for the velocity and temperature fields are also presented through graphs. Bifurcations are discussed using shooting method. Comparisons are also made between the present results and those of previous work, and thus verify the validity of the provided numerical solutions. Important properties of thermal criticality are provided for variable viscosity parameter and reaction order. Further numerical results are presented in the form of tables and graphs for transition of physical parameters, while varying certain flow and fluid material parameters. Also, the flow behaviour of the reactive fluid of third-grade is compared with those of the Newtonian reactive fluid.     

明渠大扩散角过渡段水流特性及偏流机理研究

明渠大扩散角过渡段水流偏流特性是影响输水工程设计的重要问题。在室内水槽试验中采用旋桨流速仪和PIV两种手段,在不同缓流条件下对明渠大扩散角过渡段开展了流速场测量,并对扩散段边界层分离、主流偏移和回流区水流运动特性等问题进行了分析研究。结果表明：水流经过扩散段后发生边界层分离、主流挤压在小范围弱回流区一侧,而另一侧则形成大范围强势回流区,随机形成偏流,流速横向分布不均匀,动量不能均衡扩散;水流特性沿垂向分布具有差异性,明渠扩散段水流的底层和中层受侧壁和底部边界影响较大,水流流向产生偏移,而上层水流边界层分离不明显,水流产生的偏流程度较小。     

通量差分分裂上风差分格式求解船舶粘性流动

本文阐述了采用人工可压缩方法计算不可压缩粘性流体的流动问题。对一般曲线坐标系下的流动控制方程采用了通量差分分裂上风差分格式和二阶中心差分格式离散。在隐式求解格式下，代数方程组用线松弛方法求解。本文计算了Ｍ维圆柱绕流和Ｗｉｇｌｅｙ船的绕流问题，计算结果同试验相当吻合，这说明本文所采用的方法是处理不可压缩流动的可靠方法。     

Analytical approach to entropy generation and heat transfer in CNT-nanofluid dynamics through a ciliated porous medium

The transportation of biological and industrial nanofluids by natural propulsion like cilia movement and self-generated contraction-relaxation of flexible walls has significant applications in numerous emerging technologies. Inspired by multi-disciplinary progress and innovation in this direction, a thermo-fluid mechanical model is proposed to study the entropy generation and convective heat transfer of nanofluids fabricated by the dispersion of single-wall carbon nanotubes(SWCNT) nanoparticles in water as the base fluid. The regime studied comprises heat transfer and steady, viscous, incompressible flow, induced by metachronal wave propulsion due to beating cilia, through a cylindrical tube containing a sparse(i.e., high permeability) homogenous porous medium. The flow is of the creeping type and is restricted under the low Reynolds number and long wavelength approximations. Slip effects at the wall are incorporated and the generalized Darcy drag-force model is utilized to mimic porous media effects. Cilia boundary conditions for velocity components are employed to determine analytical solutions to the resulting non-dimensionalized boundary value problem. The influence of pertinent physical parameters on temperature, axial velocity, pressure rise and pressure gradient, entropy generation function, Bejan number and stream-line distributions are computed numerically. A comparative study between SWCNT-nanofluids and pure water is also computed. The computations demonstrate that axial flow is accelerated with increasing slip parameter and Darcy number and is greater for SWCNT-nanofluids than for pure water. Furthermore the size of the bolus for SWCNT-nanofluids is larger than that of the pure water. The study is applicable in designing and fabricating nanoscale and microfluidics devices, artificial cilia and biomimetic micro-pumps.     

THE EXPERIMENTAL STUDY FOR NATURAL CONVECTIVE HEAT AND MASS TRANSFER IN POROUS MEDIA

An electrochemical method is employed to study experimentally natural convection driven by combined thermal and solutal buoyant forces in a fluid-saturated porous enclosure. The horizontal temperature and concentration gradients are imposed in such a way that their effects on the flow are either opposing or augmenting. The inside temperature profiles and heat and mass transfer characteristics on the vertical walls are experimentally determined. The effects of dimensionless parameter Ra, Le, N on flow, heat and mass transfer are discussed in details.     

垂向一维水温模型在东江水库中的应用研究

针对现有垂向一维水温模型研究中缺少对模型关键参数和边界条件敏感性的系统分析,以东江水库为例,开展了垂向一维模型在湖泊型水库水温模拟中的适用性研究。研究结果表明:东江水库库区斜温层变化主要受气象条件控制,年内下泄水温过程稳定,模型能够较好模拟出垂向水温结构演变及下泄水温过程特征,与实测结果吻合良好;表层水温计算对水气热通量参数较为敏感,垂向扩散系数是影响垂向水温结构模拟的关键参数;同时,不同精度系列的气象过程不改变水库的整体热量收支,对水温结构基本无影响。     

基于热示踪的饱和层状介质水热参数反演

多孔介质的水热运移参数是影响介质中水热运动过程的主要因素。本文基于热示踪方法,开展了稳定流场条件下饱和层状石英砂的热示踪实验,分别采用热电偶与热成像两种方法测定了砂箱内部和表面的温度,同时结合HYDRUS模型的反问题算法对层状石英砂的水热运移参数进行了反演。研究结果表明:当介质中存在细粒夹层时,热成像图像能反映非均匀流场中热流峰面在分层界面处出现的"收束"现象;层状介质中的细颗粒夹层可导致热流锋面沿水流方向迁移速率下降、热量沿垂直于水流方向运移范围加大、温度分布更均匀。同时对于热源持续输入的系统,热成像温度在前期能较好的反映层状介质对水流运动的影响。将热示踪与HYDRUS模型相结合可较好地用于反演介质水热运移参数,反演所得的饱和导水率估值随粒径的减小显著降低,纵向热弥散度随粒径的减小而增大,而横向热弥散度变化趋势与之相反;纵横弥散比变化范围在10~120之间,且纵横弥散比随粒径减小而逐渐增大。对细砂饱和导水率的估计不足及热量损失是造成水流通量估计误差的主要原因,在模拟模型中增加细砂层测点数量可显著降低水流通量的估计误差。本研究可为非均质介质中水热迁移过程模拟与参数反演提供相应的方法。     

Numerical simulation of flow and bed morphology in the case of dam break floods with vegetation effect

The purpose of this study is to establish a depth-averaged 2-D hydrodynamic and sediment transport model for the dambreak flows with vegetation effect. The generalized shallow water equations are solved using an explicit finite volume method with unstructured quadtree rectangular grid, and in the hydrodynamic model, a Harten-Lax-Van Leer(HLL) approximate Riemann solver is used to calculate the intercell flux for capturing the dry-to-wet moving boundary. The sediment transport and bed variation equations in a coupled fashion are calculated by including the bed variation and the variable flow density in the flow continuity and momentum equations. The drag force of vegetation is modeled as the sink terms in the momentum equations. The developed model is tested against lab experiments of the dam-break flows over a fix bed and a movable bed in vegetated and non-vegetated channels. The results are compared with experimental data, and good agreement is obtained. It is shown that the reduced velocity under vegetated conditions leads to a decrease of the peak discharge and a rise of the water level of rivers and also an enhancement of the sediment deposition.     

裂隙岩体水-岩传热分析

水-岩传热机理研究是有着重要应用背景的新研究领域。通过对裂隙岩体热传递过程的分析,发现流体力学与传热学中的边界层理论可用于水-岩传热研究;结合传热学相关理论,归结出裂隙岩体中水-岩传热机理。通过分析单一裂隙面与水流对流传热机理,得出了求解裂隙水流微元体温度增量的3种方法。     

某水库泄洪明渠末端扩散段急流控导试验研究

通过对某水库泄洪排沙系统的水力模型进行试验研究,发现陡槽明渠末端扩散过渡段水流流态不稳,主流贴岸冲刷严重,为了保证泄流系统的正常运行与堤防安全,必须协调好扩散过渡段前后的水流衔接。基于急流控导理论,提出了边岸导流、水下潜没控制两个控导方案。模型试验研究表明在扩散段加设管桩坝,可以将扩散段主流导向扩散段中央,边岸流速有所减小;采用创新性的组合潜没三角翼在均衡水流和抑制边界层分离都有很好的效果,实现了主流居中稳定、大大减轻了扩散段末端护坦冲刷和右边岸堤防冲刷,研究成果对解决同类型工程问题有一定的借鉴意义。     

三峡水库近坝区三维流场及温度场的数值模拟

基于三维不可压缩流动的N-S方程建立水流水温模型,模型在动量方程中考虑浮力作用并取消了静水压力假定,采用大涡模拟紊流模型计算紊动扩散,并考虑水面散热及其太阳辐射的影响因素,适合于对复杂流态及其有密度分层流动的数值模拟。应用所建立的数学模型对三峡近坝区从庙河至坝前水域的三维流场及温度场进行了数值模拟,计算出的水温分布与坝前观测的水温分布二者符合良好。模拟结果表明,三峡水库在蓄水至139 m水位时,垂向没有明显的水温分层,与实测结果相符。     

扩散作用对静水湖泊水质浓度空间分布的影响

根据水域开阔的中小型浅水湖泊的水动力特征,建立了加入扩散项的湖泊移流模式,分析了污染物对流输移、降解作用、扩散作用对污染物浓度空间分布的影响。研究发现:在静风条件下,对流输移、降解作用是湖泊水质浓度空间分布的主要影响因素,扩散作用对湖泊水质浓度空间分布的影响居次要地位。但当排污流量较小且污染物浓度较高时,扩散作用对预测结果有一定的影响。在进行湖泊水质空间分布精确预测时,应综合考虑对流输移、降解及扩散作用等因素的综合影响。