Computational Fluid Dynamics 2020

This book presents a collection of works published in a recent Special Issue (SI) entitled “Computational Fluid Dynamics”. These works address the development and validation of existent numerical solvers for fluid flow problems and their related applications. They present complex nonlinear, non-Newtonian fluid flow problems that are (in some cases) coupled with heat transfer, phase change, nanofluidic, and magnetohydrodynamics (MHD) phenomena. The applications are wide and range from aerodynamic drag and pressure waves to geometrical blade modification on aerodynamics characteristics of high-pressure gas turbines, hydromagnetic flow arising in porous regions, optimal design of isothermal sloshing vessels to evaluation of (hybrid) nanofluid properties, their control using MHD, and their effect on different modes of heat transfer. Recent advances in numerical, theoretical, and experimental methodologies, as well as new physics, new methodological developments, and their limitations are presented within the current book. Among others, in the presented works, special attention is paid to validating and improving the accuracy of the presented methodologies. This book brings together a collection of inter/multidisciplinary works on many engineering applications in a coherent manner

Unsteady electromagnetic radiative nanofluid stagnation-point flow from a stretching sheet with chemically reactive nanoparticles, Stefan blowing effect and entropy generation

The present article investigates the combined influence of nonlinear radiation, Stefan blowing and chemical reactions on unsteady EMHD stagnation point flow of a nanofluid from a horizontal stretching sheet. Both electrical and magnetic body forces are considered. In addition, the effects of velocity slip, thermal slip and mass slip are considered at the boundaries. An analytical method named as homotopy analysis method is applied to solve the non-dimensional system of nonlinear partial differential equations which are obtained by applying similarity transformations on governing equations. The effects of emerging parameters including Stefan blowing parameter, electric parameter, magnetic parameter etc. on the important physical quantities are presented graphically. Additionally, an entropy generation analysis is provided in this article for thermal optimization. The flow is observed to be accelerated both with increasing magnetic field and electrical field. Entropy generation number is markedly enhanced with greater magnetic field, electrical field and Reynolds number, whereas it is reduced with increasing chemical reaction parameter

Multiple solutions for slip effects on dissipative magneto-nanofluid transport phenomena in porous media : stability analysis

The present paper considers a numerical investigation of transport phenomena in electricallyconducting nanofluid flow within a porous bed utilizing Buongiorno’s transport model and Runge-Kutta-Fehlberg fourth-fifthorder method. Induced flow by non-isothermal stretching/shrinking sheet along with magnetic field impact, dissipation effect and slip conditions at the surface are also included. The numerical results show the existence of two branches of the solution for a selected range of the governing parameters. The physical significance of both branches of solutions is ensured by performing a stability analysis in which a linearized eigenvalue problem is solved. The multiple regression analysis with help of MALTAB LinearModel.fitpackage has also been conducted to estimate the dependency of the parameters on Nusselt number

Unsteady flow of a nanofluid past a permeable shrinking cylinder using Buongiorno’s model

The unsteady laminar boundary layer flow of a nanofluid and heat transfer over a permeable shrinking cylinder using the Buongiorno’s nanofluid model is investigated. Using a similarity transformation, the governing partial differential equations are transformed into a system of ordinary differential equations and then solved numerically using a shooting method. The numerical results are obtained for velocity, temperature and concentration profiles as well as the skin friction coefficient, the local Nusselt number and the local Sherwood number. Dual solutions are found to exist in a certain range of the suction and unsteadiness parameters. It is observed that suction parameter increase both the skin friction coefficient and the heat transfer rate at the surface, whereas the opposite trend is obtained for the Sherwood number. It is also observed that suction widens the range of the unsteadiness parameter for which the solution exists

Similarity solutions of boundary layer flows in a channel filled by non-newtonian fluids

Similarity solutions of non-Newtonian fluids are getting much attention to researchers because of their practical importance in the field of science and engineering. Currently, most of researchers focus their work on non-Newtonian fluids over a sheet. However, only a few of them pay their attention towards the geometry of channel due to the complexity of governing equations. Therefore, this study attempts to investigate the numerical solutions of new problems of laminar incompressible Nanofluids, Casson fluids and Micropolar fluids under various fluid flow conditions. Each considered fluid involves porous channel walls, stretching or shrinking walls, and expanding or contracting walls with the influence of various physical parameters. Mathematical formulations such as the law of conservation, momentum or angular momentum, heat and mass transfer are performed on the new problems. After the mathematical formulation is developed, the governing fluid flow equations of partial differential equations are then transformed into boundary value problems (BVPs) of nonlinear ordinary differential equations (ODEs) by using the suitable similarity transformations. After converting high order BVPs into the equivalent first order system of BVPs, shootlib function in Maple 18 software is employed to obtain the similarity solutions of nonlinear ODEs. The numerical results in this study are compared with the existing solutions in literature for the purpose of validation. The results are found to be in good agreement with the existing solutions. Multiple solutions of some of the problems particularly in porous channel with expanding or contracting walls also exist for the case of strong suction. This study has successfully find the numerical solutions of the new problems for various fluid flow conditions. The results obtained from this study can serve as a theoretical reference in related fields

Numerical solution of the stagnation point flow and heat transfer with several effects

Problems related to boundary layer flow and heat transfer is important due to its various practical applications in engineering and industrial area. Cooling systems, nuclear reactor, electronic, hydrodynamics process, paper production and the boundary layer in liquid film condensation process are some of the example of various applications related to boundary layer flow and heat transfer. Present thesis solved numerically three problems of boundary layer flow on stagnation point over a stretching by considering the Newtonian fluid (viscous fluid) and non-Newtonian fluid (Williamson fluid). Besides, this thesis concern of the influence of slip flow, thermal radiation, magnetohydrodynamic (MHD) and viscous dissipation effects associated with constant wall temperature as boundary conditions. All gorvening equations in the form partial differential equations are transformed into ordinary differential equations by employing the suitable similarity transformation. The transformed ordinary differential equations obtained are solved numerically using a Shooting method in Maple software. Numerical solutions are obtained for the local Nusselt number and skin friction coefficient as well as the temperature and velocity profiles. The features of the flow and heat transfer characteristics for various values of eight pertinent parameters which are the Prandtl number, the stretching parameter, the Eckert number, the velocity slip parameter, the thermal slip parameter, the radiation parameter, the magnetic parameter and the nonNewtonian Williamson fluid parameter are analyzed and discussed. The comparison is also done by verifying through existing research so that the results obtained are a good agreement and reliable. As conclusion, the increases of Prandtl number, stretching parameter, dimensionless thermal and velocity slip parameter result to the decreasing in the wall temperature and also thermal boundary layer thickness. Meanwhile, increasing the non-Newtonian Williamson fluid parameter and thermal radiation parameter, the thermal boundary layer also increases

Beberapa masalah aliran lapisan sempadan olakan dengan kesan gelinciran dan tanpa gelinciran pada permukaan

Fenomenon kesan gelinciran pada permukaan boleh berlaku pada permukaan bendalir-pepejal dan pada permukaan lapisan bendalir-bendalir, terutama bagi sesetengah bendalir berskala kecil dalam mikroaliran. Dalam kebanyakan kajian aliran lapisan sempadan yang telah dilakukan oleh para penyelidik, didapati kesan gelinciran adalah baik bagi meningkatkan kadar pemindahan haba pada permukaan yang diperlukan dalam suatu proses penyejukan. Bagi aliran tanpa gelinciran, ciri-ciri pemindahan haba bergantung pada masalah aliran yang dikaji. Dalam tesis ini, model matematik dibina untuk mengkaji ciri-ciri aliran dan pemindahan haba bagi lima masalah aliran lapisan sempadan yang dihadkan kepada aliran mantap dua matra dalam bendalir likat tak mampat. Masalah pertama dan kedua masing-masing mempertimbangkan aliran berdekatan titik genangan dan aliran hidromagnet, keduaduanya pada helaian tegak meregang. Masalah ketiga dan keempat mempertimbangkan syarat sempadan gelinciran, masing-masing bagi aliran terhadap titik genangan pada permukaan tegak dan aliran terhadap helaian telap mengecut. Sementara itu, masalah kelima melibatkan aliran pada permukaan meregang/mengecut di bawah aliran ricih luar dengan syarat sempadan permukaan olakan. Formulasi model matematik diperoleh dengan menurunkan persamaan pembezaan separa tak linear kepada persamaan pembezaan biasa menggunakan penjelmaan keserupaan. Analisis kepada sistem persamaan yang terhasil dimulakan dengan menyelesaikan masalah secara berangka menggunakan kaedah kotak Keller atau kaedah tembakan. Kaedah kotak Keller diatur cara menggunakan perisian MATLAB 7, manakala kaedah tembakan menggunakan atur cara “bina dalam” dalam perisian Maple 12. Seterusnya, nilai-nilai berangka bagi pekali geseran kulit dan nombor Nusselt setempat serta profil-profil halaju dan suhu diperoleh untuk pelbagai nilai parameter menakluk seperti parameter nisbah halaju, parameter keapungan, parameter magnet, parameter gelinciran halaju dan terma, nombor Prandtl, parameter olakan, parameter sedutan/semburan dan parameter regangan/kecutan. Keputusan berangka yang diperoleh dipersembahkan dalam bentuk jadual dan graf. Didapati gelinciran halaju mengurangkan pekali geseran kulit tetapi meningkatkan kadar pemindahan haba pada permukaan, manakala kesan gelinciran terma adalah sebaliknya. Suhu permukaan pula didapati bertambah dengan kehadiran medan magnet dan dengan syarat sempadan permukaan olakan. Selain itu, parameter-parameter menakluk yang lain turut mempengaruhi pekali geseran kulit dan nombor Nusselt setempat, di samping kewujudan penyelesaian dual atau unik, bagi masalah-masalah yang dikaji

MHD STAGNATION POINT FLOW WITH THERMAL RADIATION AND SLIP EFFECT OVER A LINEAR STRETCHING SHEET

This research investigates the flow of stagnation point magnetohydrodynamic (MHD) and heat transfer along the stretched sheet in the existence of radiation and slip effects. With the help of similarity variables, the governing partial differential equations (PDEs) are transformed into ordinary differential equations (ODEs). The BVP4C technique in Matlab function has been used to simplify the governing ODEs. The numerical outcomes for temperature and velocity profiles, coefficient of skin friction and Nusselt Number have been achieved and matched with the findings in literature. The findings are compared to previously reported results. In addition, the impacts of numerous related parameters on the profiles of velocity and temperature are shown, and the results of every related parameter are presented using graphs. The velocity profile decreases as the magnetic force, suction, and permeability parameters rise

Axisymmetric stagnation-point flow over a stretching/shrinking plate with second-order velocity slip

AbstractThe axisymmetric stagnation point flow over a stretching/shrinking surface with second-order slip and temperature jump is studied numerically. The governing partial differential equations are transformed into ordinary (similarity) differential equations. These equations along with the corresponding boundary conditions are solved numerically using a boundary value problem solver bvp4c in Matlab software. It is observed that dual (first and second) solutions exist for the similarity equations. The effects of different parameters on the velocity and the temperature distributions as well as the skin friction coefficient and the Nusselt number are analyzed and discussed

Mathematical models for heat and mass transfer in nanofluid flows.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.The behaviour and evolution of most physical phenomena is often best described using mathematical models in the form of systems of ordinary and partial differential equations. A typical example of such phenomena is the flow of a viscous impressible fluid which is described by the Navier-Stokes equations, first derived in the nineteenth century using physical approximations and the principles of mass and momentum conservation. The flow of fluids, and the growth of flow instabilities has been the subject of many investigations because fluids have wide uses in engineering and science, including as carriers of heat, solutes and aggregates. Conventional heat transfer fluids used in engineering applications include air, water and oil. However, each of these fluids has an inherently low thermal conductivity that severely limit heat exchange efficiency. Suspension of nanosized solid particles in traditional heat transfer fluids significantly increases the thermophysical properties of such fluids leading to better heat transfer performance. In this study we present theoretical models to investigate the flow of unsteady nanofluids, heat and mass transport in porous media. Different flow configurations are assumed including an inclined cylinder, a moving surface, a stretching cone and the flow of a polymer nanocomposite modeled as an Oldroyd-B fluid. The nanoparticles assumed include copper, silver and titanium dioxide with water as the base fluid. Most recent boundary-layer nanofluid flow studies assume that the nanoparticle volume fraction can be actively controlled at a bounding solid surface, similar to temperature controls. However, in practice, such controls present significant challenges, and may, in practice, not be possible. In this study the nanoparticle flux at the boundary surface is assumed to be zero. Unsteadiness in fluid flows leads to complex system of partial differential equations. These transport equations are often highly nonlinear and cannot be solved to find exact solutions that describe the evolution of the physical phenomena modeled. A large number of numerical or semi-numerical techniques exist in the literature for finding solutions of nonlinear systems of equations. Some of these methods may, however be subject to certain limitations including slow convergence rates and a small radius of convergence. In recent years, innovative linearization techniques used together with spectral methods have been suggested as suitable tools for solving systems of ordinary and partial differential equations. The techniques which include the spectral local linearization method, spectral relaxation method and the spectral quasiliearization method are used in this study to solve the transport equations, and to determine how the flow characteristics are impacted by changes in certain important physical and fluid parameters. The findings show that these methods give accurate solutions and that the speed of convergence of solutions is comparable with methods such as the Keller-box, Galerkin, and other finite difference or finite element methods. The study gives new insights, and result on the influence of certain events, such as internal heat generation, velocity slip, nanoparticle thermophoresis and random motion on the flow structure, heat and mass transfer rates and the fluid properties in the case of a nanofluid