•The first formulation and implementation of the compressible wall function of Han and Reitz in the framework of hybrid wall treatment.•The model is validated against spark ignition (SI) engine heat ...transfer measurements (“pancake” engine benchmark). Predicted wall heat flux evolutions on the cylinder head exhibit very good agreement with the experimental data, being superior to similar numerical predictions available in the published literature.•The present work demonstrates potential advantages of the hybrid wall heat transfer approach in conjunction with the advanced turbulence model.
Recent developments in the engine heat transfer modeling tend to improve existing wall heat transfer models (temperature wall functions) which mostly rely on the standard or low-Re variants of k-ε turbulence model. Presently applied mesh resolutions already allow for first near-wall computational cells reaching the buffer or locally even viscous/conductive sub-layer, thus increasing the importance of more sophisticated modeling approach. As temperature gradient-induced density and fluid property variations become significant, wall heat transfer is strongly influenced by property variations (viscous/conductive sub-layer) and predictive capability of the turbulence model (buffer region), standard wall laws being inadequate anymore, even for attached boundary layers. The present approach relies on the k-ζ-f turbulence model and formulates a compressible wall function of Han and Reitz in the framework of hybrid wall treatment. The model is validated against spark ignition (SI) engine heat transfer measurements. Predicted wall heat flux evolutions on the cylinder head exhibit very good agreement with the experimental data, being superior to similar numerical predictions available in the published literature.
Display omitted
This study comprehensively explores the generalized form of two-dimensional peristaltic motions of incompressible fluid through temperature-dependent physical properties in a non-symmetric channel. ...Generation of entropy in the system, carrying Joule heat and Lorentz force is also examined. Viscous dissipation is not ignored, for viewing in-depth, effects of heat transmission and entropy production. The modeling of equations is tracked first in fixed and then in wave frame. The resultant set of coupled non-linear equations are solved numerically by utilizing NDSolve in Mathematica. Comparison between NDSolve and the numerical results obtained through bvp4c MATLAB is made for the validation of our numerical codes. The attained results are found to be in excellent agreement. The impact of control parameters on the velocity profiles, pressure gradient, heat transfer, streamlines and entropy production are studied and discussed graphically. It is witnessed that entropy production and heat transfer are increased significantly subject to the enhancement of Hartman number, Brinkman number and electrical conductivity parameter. Hence, choosing appropriate values of physical parameters, performance and efficiency of flow structure and system can be improved. The results reported provide a virtuous insight into bio energy systems providing a useful standard for experimental and extra progressive computational multiphysics simulations.
This article deals with the nanofluid flow and heat transfer of the MHD free stream over an exponentially radiating stretching sheet accompanied by constant and variable fluid characteristics ...together. The underlying governing partial differential equations (PDEs) have been translated into nonlinear ordinary differential equations (ODEs) by incorporating adequate similarity transformations. By using the shooting method and the MATLAB built-in solver bvp4c, the corresponding ODEs are effectively solved. The impact on the skin friction coefficient (quantifying resistance), the local Nusselt number (heat transfer rate) and the local Sherwood number (mass transfer rate) on the surface due to the flow field variables has been computed against various parameters i.e., magnetic parameter M, Prandtl number Pro, Lewis number Le, thermophoresis parameter Nt, Brownian motion parameter Nb, velocity parameter λ, radiation parameter Rd and thermal conductivity parameter ϵ. Graphs are also plotted to study the impact of distinct parameters on velocity, temperature and concentration profiles. It has been noted by raising the values of ϵ, the heat transfer rate reduces for variable fluid properties. On the other hand, raising Pro increases the heat transfer rate.
•Flow and heat transfer of a generalized fractional Maxwell fluid in porous medium are studied.•Temperature dependent fluid viscosity and thermal conductivity are taken into account.•Modified ...fractional Fourier's law and Darcy's law are proposed in constitutive relations.•Solutions are obtained by implicit difference method based on non-shifted Grünwald formula.•Effects of involved parameters on the velocity and temperature fields are analyzed.
We present an investigation for coupled flow and heat transfer of a generalized fractional Maxwell fluid in a porous medium between two infinite parallel plates. Unlike most classical works, the temperature dependent fluid properties (variable fluid viscosity and thermal conductivity) are taken into account by modified fractional Fourier's law and Darcy's law to describe the constitutive relations in highly coupled velocity and temperature fields in porous medium. The fractional governing equations are solved numerically using implicit finite difference method based on non-shifted Grünwald formula. The effects of pertinent physical parameters on the velocity and temperature fields are presented graphically and analyzed.
The objective of this paper comprises two key aspects: to establish descriptive mathematical models for constant and variable fluid flows over a variable thickness sheet by inducting applied electric ...and magnetic fields, porosity, radiative heat transfer, and heat generation/absorption, and to seek their solution by constructing a novel numerical method, the Simplified Finite Difference Method (SFDM). We resort to similarity transformations to implicate partial differential equations (PDEs) into a set of ordinary differential equations (ODEs). Optimal results for a pair of ODEs obtained from SFDM are assessed by drawing a comparison with bvp4c and existing literature values. SFDM has been implemented in MATLAB for both constant and variable fluid properties. Tabulated numerical values of the skin friction coefficient and local Nusselt and Sherwood numbers are measured and analyzed against different parameters. The influence of distinct parameters on velocity, temperature, and nanoparticle volume fraction are explained in great detail via diagrams. The skin friction coefficient for variable fluid properties is greater than for constant fluid properties. However, the local Nusselt number is lower for variable fluid properties than with constant fluid properties. Surprisingly, high-precision computational results are achieved from the SFDM.
•A model of tube laminar forced convection with internal heat generation is developed.•Varying fluid properties is taken into account to investigate axial heat conduction.•Variable-property effects ...alleviate the reduction in Nu due to axial heat conduction.•Variable properties affect velocity and temperature profiles at different parts.
In this article, a theoretical model is developed to investigate the effects of the axial heat conduction on the laminar forced convection in a circular tube with uniform internal heat generation in the solid wall. In the current work, three different fluids, i.e. water, n-decane and air, are selected on purpose since their thermophysical properties show different behavior with temperature. The effects of the axial heat conduction with varying dynamic viscosity and/or varying thermal conductivity are investigated in a systematic manner. Results indicate that the variable-property effects could alleviate the reduction in Nusselt number (Nu) due to the axial heat conduction. For the case of Peclet number (Pe) equal to 100, wall thickness to inner diameter ratio of 1 and solid wall to fluid thermal conductivity ratio of 100, the maximum Nu deviation between constant and variable properties are up to 7.33% at the entrance part for water in the temperature range of 50°C, and 4.45% at the entrance part for n-decane in the temperature range of 120°C, as well as 2.20% at the ending part for air in the temperature range of 475°C, respectively. In addition, the average Nu deviation for water, n-decane and air is 3.24%, 1.94% and 1.74%, respectively. Besides, Nu decreases drastically with decreasing Pe when Pe⩽500 and with increasing solid wall to fluid thermal conductivity ratio (ksf) when ksf⩽100. It is also found that variable properties have more obvious effects on the velocity profile at the upstream part while more obvious effects on the temperature profile at the downstream part.
A non-Newtonian Williamson fluid flow due to a stretching sheet with radiation, magnetic field, and viscous dissipation effects is described using variable conductivity and variable diffusivity. The ...Cattaneo-Christov model is used to correctly compute the physical properties of a heat and mass flux model. Both the chemical reaction phenomenon and the slip velocity have an impact on the heat and mass mechanism. The physical problem is represented mathematically as a nonlinear coupled differential system. After that, the shooting method is used to solve the mathematical model numerically. To gain a better understanding of the behavior of governing emergent factors on dimensionless velocity, concentration, and temperature profiles, physical interpretations are created and discussed utilizing graphical and tabular representations. The results show that the Sherwood number and the Nusselt number are both decreased by the magnetic, viscosity, and slip velocity parameters. Also, according to the findings it has been observed that the concentration outlines enhances for the magnetic number, the viscosity parameter, and the slip velocity parameter, but they dwindle for expanding reaction rate values. Finally, after confirmation of our numerical results, the theoretical results show good agreement with previously published work.
In this paper, the effects of variable fluid properties and thermophoresis on unsteady forced convective boundary layer flow along a permeable stretching/shrinking wedge are studied numerically. The ...analysis accounts for temperature dependent viscosity and thermal conductivity. The governing time dependent nonlinear partial differential equations are reduced to a set of nonlinear ordinary differential equations by the similarity transformations. The resulting local similarity equations are solved numerically by Nachtsheim–Swigert shooting iteration technique with sixth order Runge–Kutta integration scheme. Comparison with previously published work is performed and the results are found to be in excellent agreement. Numerical results for the non-dimensional velocity, temperature and concentration profiles as well as the variable Prandtl number and the variable Schmidt number are displayed graphically for several sets of material parameters. The effects of the model parameters on the local skin friction coefficient, the rate of heat and mass transfer, and the thermophoretic particle deposition velocity are also tabulated. The results show that for the flow with variable thermal conductivity, the Prandtl number as well as the Schmidt number varies significantly within the boundary layer. Thus, in any physical model where fluid transport properties are temperature dependent, the Prandtl number and the Schmidt number within the boundary layer should be considered as variables rather than constants.
•Effects of variable fluid properties are investigated on the unsteady convective boundary layer flow.•The Prandtl and Schmidt numbers must be treated as variable when fluid properties are temperature dependent.•Unsteadiness significantly controls the heat and mass transfer characteristics.•Thermophoretic particle depositions are influenced by the concentration ratio and the thermophoretic parameter.
PDF
