Magnetohydrodynamics Nanofluid Flow Containing Gyrotactic Microorganisms Propagating Over a Stretching Surface by Successive Taylor Series Linearization Method

Nanofluid dynamics with magnetohydrodynamics has tremendously contributed in industrial applications recently since presence of nanoparticle in base fluids enhances the specific chemical and physical properties. Owing to the relevance of nanofluid dynamics, we analyze the nanofluid flow in the presence of gyrotactic microorganism and magnetohydrodynamics through a stretching/shrinking plate. The impacts of chemical reaction and thermal radiation on flow characteristics are also studied. To simplify the governing equations of microorganisms, velocity, concentration and temperature, the similarity transformations are employed. The couple governing equations are numerically solved using Successive Taylor Series Linearization Method (STSLM). The velocity profile, motile microorganism density profile, concentration profile, temperature profile as well as Nusselt number, skin friction coefficient, Sherwood number and density number of motile microorganisms are discussed using tables and graphs against all the sundry parameters. A numerical comparison is also given for Nusselt number, Sherwood number, skin friction, and density number of motile microorganisms with previously published results to validate the present model. The results show that Nusselt number, Sherwood number and density number diminish with increasing the magnetic field effects.     

Entropy Generation for Flow and Heat Transfer of Sisko-Fluid Over an Exponentially Stretching Surface

In the present study, the effects of the magnetic field on the entropy generation during fluid flow and heat transfer of a Sisko-fluid over an exponentially stretching surface are considered. The similarity transformations are used to transfer the governing partial differential equations into a set of nonlinear-coupled ordinary differential equations. Runge-Kutta-Fehlberg method is used to solve the governing problem. The effects of magnetic field parameter M, local slip parameter λ, generalized Biot number γ, Sisko fluid material parameter A, Eckert number Ec, Prandtl number Pr and Brinkman number Br at two values of power law index on the velocity, temperature, local entropy generation number N_G and Bejan number Be are inspected. Moreover, the tabular forms for local skin friction coefficient and local Nusselt number under the effects of the physical parameters are exhibited. The current results are helpful in checking the entropy generation for Sisko-fluid. It is found that, an extra magnetic field parameter makes higher Lorentz force that suppresses the velocity. For shear thinning fluids (n < 1), the temperature dominates and the velocity rises. Local entropy generation number is more for larger generalized Biot number, magnetic field parameter and Brinkman number. The local skin friction coefficient increases as magnetic field parameter and material parameter are increase and it decreases as local slip parameter increases. The local Nusselt number decreases as magnetic field parameter, local slip parameter and Eckert number are increase, while it increases as material parameter, generalized Biot number and Prandtl number are increase.     

A Finite Difference Method and Effective Modification of Gradient Descent Optimization Algorithm for MHD Fluid Flow Over a Linearly Stretching Surface

Present contribution is concerned with the construction and application of a numerical method for the fluid flow problem over a linearly stretching surface with the modification of standard Gradient descent Algorithm to solve the resulted difference equation. The flow problem is constructed using continuity, and Navier Stoke equations and these PDEs are further converted into boundary value problem by applying suitable similarity transformations. A central finite difference method is proposed that gives third-order accuracy using three grid points. The stability conditions of the present proposed method using a Gauss-Seidel iterative procedure is found using VonNeumann stability criteria and order of the finite difference method is proved by applying the Taylor series on the discretised equation. The comparison of the presently modified optimisation algorithm with the Gauss-Seidel iterative method and standard Newton’s method in optimisation is also made. It can be concluded that the presently modified optimisation Algorithm takes a few iterations to converge with a small value of the parameter contained in it compared with the standard descent algorithm that may take millions of iterations to converge. The present modification of the steepest descent method converges faster than Gauss-Seidel method and standard steepest descent method, and it may also overcome the deficiency of singular hessian arise in Newton’s method for some of the cases that may arise in optimisation problem(s).     

Pseudolaminar Boundary Layer on a Blunt Body Subjected to a Heterogeneous Flow

The distributions of the velocities of air and solid particles in a pseudolaminar boundary layer developing on the surface of a cylinder with a hemispherical end face are experimentally investigated. The experiments reveal a significant rise of fluctuations of the particle velocity in the wall region of the boundary layer. Data are obtained on the decrease in the particle concentration in the vicinity of the model wall compared to its value in the external flow.     

Numerical Treatment of MHD Flow of Casson Nanofluid via Convectively Heated Non-Linear Extending Surface with Viscous Dissipation and Suction/Injection Effects

This paper introduces the effect of heat absorption (generation) and suction (injection) on magnetohydrodynamic (MHD) boundary-layer flow of Casson nanofluid (CNF) via a non-linear stretching surface with the viscous dissipation in two dimensions. By utilizing the similarity transformations, the leading PDEs are transformed into a set of ODEs with adequate boundary conditions and then resolved numerically by (4–5)^th-order Runge-Kutta Fehlberg procedure based on the shooting technique. Numerical computations are carried out by Maple 15 software. With the support of graphs, the impact of dimensionless control parameters on the nanoparticle concentration profiles, the temperature, and the flow velocity are studied. Other parameters of interest, such as the skin friction coeffi- cient, heat, and mass transport at the diverse situation and dependency of various parameters are inspected through tables and graphs. Additionally, it is verified that the numerical computations with the reported earlier studies are in an excellent approval. It is found that the heat and mass transmit rates are enhanced with the increasing values of the power-index and the suction (blowing) parameter, whilst are reduced with the boosting Casson and the heat absorption (generation) parameters. Also, the drag force coefficient is an increasing function of the powerindex and a reduction function of Casson parameter.     

Control of Velocity Profiles in a Boundary Layer

The control of average velocity in the turbulent boundary layer of a flat plate is investigated theoretically and experimentally. The control is exercised by injecting jets of air into the incident flow. Interpolation expressions are derived for the distribution of average velocities, dependent on the control parameters.     

Active Control of Laminar Boundary Layer Using Various Wall Motions

In this study, three types of surface motion of wall motion actuators were proposed and used to control the Tollmien-Schlichting (T-S) wave in the laminar boundary layer of a plate. These three types of motion are standing transverse wave (with out-of-plane displacement), traveling transverse wave (with out-of-plane displacement) and standing longitudinal wave (with in-plane displacement). The length of a wall motion actuator was set to 1, 2 or 3 cycles of waveform. Numerical simulation was performed on the generation of T-S wave and its suppression with the three types of surface motion of the wall motion actuator and the dependence of control effect on the amplitude and the phase of the surface motion, and the number of waveform was investigated.     

表面层型半导体陶瓷电容器的开发及产业化

表面层型半导体陶瓷电容器的开发成功,是我国新型元件领域中的一项高新技术及其产业化的突破。重点介绍了表面层型半导体陶瓷电容器的基本结构和原理。本项目开发创新成果,隧道式气氛烧组合炉,还原气氛的获取,半导化及再氧化技术,工程中设计参数及氧化层厚度观察及量测技术等。     

平行平板微通道流场在双电层和边界滑移条件下的解析解

讨论了双电层和边界滑移对微通道液体流动系统的影响.利用双电层动电效应理论对控制方程进行修正,同时引入Navier滑移边界条件考虑边界滑移现象,建立了两种壁面效应同时存在时微流动控制模型,得到了流场的解析解.结果显示,双电层效应抑制流动的发展,使流体在固/液边界附近区域产生回流;边界滑移虽能促进流动发展,但当这两种效应同时存在时,边界滑移的作用变为加强抑制流动,使回流现象更加显著.     

压力梯度作用下相干结构的演化

采用共振三波的一个周期作为湍流边界层近壁区相干结构的初值，用直接数值模拟方法对有压力梯度，包括定常压力梯度和变压力梯度作用下相干结构的演化进行了研究，得出其各种特性的变化与实验观测到的结果一致。压力梯度对相干结构初始扰动波的选择以及演化过程都起作用，相比之下对前者的作用更大。条纹结构和流向涡之间有某种内在的紧密的联系，可能是产生流向涡的起因。     

逆压梯度下近壁湍流的喷射和扫掠

采用Fourier谱展开和紧致有限差分格式，选用两组共振三波为相干结构的初值，计算了其在零压和逆压梯度作用下的演化。对演化后期流场的2，4象限的运动进行了详细的分析。结果发现，在逆压梯度下，扫掠对雷诺应力的贡献要强于喷射。无论是在零压梯度还是逆压梯度下，uv和u2在法向的输运主要是靠Q2和Q4这两种运动来完成的。零压梯度下喷射部分对输运的贡献大于扫掠的部分。而在逆压梯度下喷射部分对输运的贡献明显减少，扫掠的作用要强于喷射。     

带化学反应的边界层流动问题中一类弱奇异Volterra积分方程的近似解

研究带化学表面反应的边界层流动问题导出的一类弱奇异Volterra积分方程的近似解。以一些化学反应的阶数为例求出解在零点的分数阶级数展开式及其■有理逼近。通过将发散积分解释为Hadamard有限部分积分,并借助数值积分方法导出解在无穷远点的带高阶对数项的渐近展开式。实际计算表明,给出的解在零点和无穷远点展开式的联合使用可以在整个半无限区间上高效地求解这类带化学表面反应的边界层流动问题。     

A Novel Approach to Identify the Thermal Conductivities of a Thin Anisotropic Medium by the Boundary Element Method

A common difficulty arises in characterizing the anisotropic properties of a thin sheet of anisotropic material, especially in the transverse direction. This difficulty is even more phenomenal for measuring its mechanical properties on account of its thickness. As the prelude of such investigation, this paper proposes a novel approach to identify the thermal conductivities of an unknown thin layer of anisotropic material. For this purpose, the unknown layer is sandwiched in isotropic materials with known conductivities. Prescribing proper boundary conditions, one may easily measure temperature data on a few sample boundary points. Therefore, the anisotropic thermal conductivities can be calculated inversely. For the inverse analysis, the boundary element method (BEM) is employed to combine with the conjugate gradient method (CGM). For verifying our analysis, numerical experiments were carried out. The obtained results have shown great computational efficiency and accuracy in identifying the thermal conductivities of the thin anisotropic layer.