Increase In Skin Friction Coefficient Research Articles

Heat transfer analysis in ferromagnetic viscoelastic fluid flow over a stretching sheet with suction

In this article, an investigation has been performed to explore the two-dimensional boundary layer flow problem and heat transfer characteristic of ferromagnetic viscoelastic fluid flow over a stretching surface with a linear velocity under the impact of magnetic dipole and suction. The governing PDEs are converted into a system of nonlinear ODEs by applying appropriate similarity approach. The modelled equations are then solved numerically by utilizing efficient Runge–Kutta–Fehlberg procedure based on shooting algorithm. Influence of pertinent flow parameter involved, such as ferromagnetic interaction parameter, suction parameter, viscoelastic parameter, Prandtl number on dimensionless velocity, temperature, skin friction, and Nusselt inside the boundary layer, are portrayed graphically and discussed. The results show that pressure profile and skin friction coefficient increase with the variation of ferromagnetic interaction parameter and opposite behaviour is noted for local Nusselt number.

Effect of viscous dissipation and suction/injection on MHD nanofluid flow over a wedge with porous medium and slip

The purpose of present study is to identify the effects of viscous dissipation and suction/injection on MHD flow of a nanofluid past a wedge with convective surface in the appearance of slip flow and porous medium. The basic non-linear PDEs of flow and energy are altered into a set of non-linear ODEs using auxiliary similarity transformations. The system of equations together with coupled boundary conditions have been solved numerically by applying Runge-Kutta-Fehlberg procedure via shooting scheme. The influence of relevant parameters on non-dimensional velocity and temperature profiles are depicted graphically and investigated in detail. The results elucidate that as enhance in the Eckert number, the skin friction coefficient increases, while heat transfer rate decreases. The outcomes also specify that thermal boundary layer thickness declines with an increase in suction parameter. Moreover, it is accelerated with augment in injection parameter. The results are analogized with the study published earlier and it creates a fine concord.

Heat and Mass Transfer in Three Dimensional Free Convective Oscillatory Flow in Porous Medium with Constant Heat and Mass Flux in Presence Radiation for an optically Thin Fluid

A theoretical analysis of free convective flow of viscous incompressible fluid through a porous medium bounded by a flat porous plate subject to periodic suction and constant heat and mass flux has been presented. The flow becomes three dimensional due to variation of suction velocity in transverse direction. Analytical expression for velocity, temperature, concentration and skin friction are obtained using perturbation technique. Numerical solutions are obtained for different values Grash of number (G r ), mass Grashof number(Gc), Prandtl number (Pr), Schmidt number (Sc) and Radiation (R). It is found that non-dimensional velocity increases with increase of Gr, Gc and Sc and decreases with increase of R, non-dimensional temperature decreases with increasing of R, Concentration decreases with increase of Sc. and skin friction co-efficient increases with increase of Gr and R but effect of Gr is more than R.

Mixed convection boundary layer flow over a horizontal elliptic cylinder with constant heat flux

Mixed convection boundary layer flow of a viscous fluid over a horizontal elliptic cylinder with a constant heat flux is investigated numerically. The governing partial differential equations are transformed to non-dimensional form and then are solved by an efficient implicit finite different scheme known as Keller-box method. The solutions are expressed in the form of skin friction and Nusselt number, which are plotted against the eccentric angle. The effect of pertinent parameters such as mixed convection parameter, aspect ratio (ratio of lengths of minor axis to major axis), and Prandtl number on skin friction and Nusselt number are illustrated through graphs for both blunt and slender orientations. The increase in the value of mixed convection parameter results in increase in skin friction coefficient and Nusselt number for blunt as well as slender orientations.

Effect of radiation on heat and mass transfer of fluid flow across a horizontal cylinder

The free convective boundary layer flow, heat and mass transfer across an isothermal cylinder in the diffusing species is investigated. The partial differential conservation equations are non-dimensionalized and solved numerically by using an implicit iterative tridiagonal finite-difference method. The effects of radiation parameters on dimensionless velocity, temperature and species concentration distributions are studied, for the case of water (Pr = 7.0), concentration is slightly affected by radiation parameter; Temperatures are however increased by an increase in radiation parameter. Furthermore, the local skin friction, local Nusselt number and local Sherwood number have been analyzed for various parametric conditions. It is found that as the thermal radiation parameter increases the skin-friction coefficient increases and the local Nusselt number decreases. Excellent agreement is obtained with the earlier studies for the purely fluid.

Computational study of a turbulent wall jet flow on an oblique surface

Purpose – The purpose of the present study is to investigate the flow and turbulence characteristics of a turbulent wall jet flowing over a surface inclined with the horizontal and to investigate the effect of variation of the angle of inclination of the wall on the flow structure of the wall jet. Design/methodology/approach – The high Reynolds number two-equation κ− model with standard wall function is used as the turbulence model. The Reynolds number considered for the present study is 10,000. The Reynolds averaged Navier-Stokes (RANS) equations are used for predicting the turbulent flow. A staggered differencing technique employing both contravariant and Cartesian components of velocity has been applied. Results for distribution of wall static pressure and skin friction, decay of maximum streamwise velocity, streamwise variation of integral momentum and energy flux have been compared for the cases of α=0°, 5°, and 10°. Findings – Flow field has been represented in terms of streamwise and lateral velocity contours, static pressure contour, vorticity contour and streamwise velocity and static pressure profiles at different locations along the oblique offset plate. Distribution of Reynolds stresses in terms of spanwise, lateral and turbulent shear stresses, and turbulent kinetic energy and its dissipation rate have been presented to describe the turbulent characteristics. Similarity of streamwise velocity and the velocity parallel to the oblique wall has been observed in the developed region of the wall jet flow. A decaying trend is observed in the variation of total integral momentum flux in the developed region of the wall jet which becomes more evident with increase in oblique angle. Developed flow region has indicated trend of similarity in profiles of streamwise velocity as well as velocity component parallel to the oblique wall. A depression in wall static pressure has been observed near the nozzle exit when the wall is inclined and the depression increases with increase in inclination. Effect of variation of oblique angles on skin friction coefficient has indicated that it decreases with increase in oblique angle. Growth of the outer and inner shear layers and spread of the jet shows linear variation with distance along the oblique wall. Decay of maximum streamwise velocity is found to be unaffected by variation in oblique angle except in the far downstream region. The streamwise variation of spanwise integral energy shows increase in oblique angle and decreases the magnitude of energy flux through the domain. In the developed flow region, streamwise variation of centreline turbulent intensities shows increased values with increase in oblique angle, while turbulence intensities along the jet centreline in the region X<12 remain unaffected by change in oblique angles. Normalized turbulent kinetic energy distribution highlights the difference in turbulence characteristics between the wall jet and reattached offset jet flow. Near wall velocity distribution shows that the inner region of boundary layer of the developed oblique wall jet follows a logarithmic profile, but it shows some difference from the standard logarithmic curve of turbulent boundary layers which can be attributed to an increase in skin friction coefficient and a decrease in thickness of the wall attached layer. Originality/value – The study presents an in-depth investigation of the interaction between the jet and the inclined wall. It is shown that due to the Coanda effect, the jet follows the nearby wall. The findings will be useful in the study of combined flow of wall jet and offset jet and dual offset jet on oblique surfaces leading to a better design of some mechanical jet flow devices.

The effect of step height of microscale backward-facing step on mixed convection nanofluid flow and heat transfer characteristics

Simulation of laminar mixed convective flow over a 3-D horizontal microscale backward-Facing step (MBFS) is presented to explore the effect of step height on the flow and heat transfer characteristics. The momentum and energy equations were discretized by means of a finite volume method (FVM). The SIMPLE algorithm scheme was used to link the pressure and velocity fields in the entire domain. Three values of step height were considered S=350μm, S=450μm and S=550μm. EG-SiO2 nanofluid was considered as the working fluid with 25nm nanoparticle diameter, 0.04 volume fraction. The results revealed that the Nusselt number and skin friction coefficient increase with the increase of the step height. The Reynolds number and pressure drop were found to decrease with the increase of the step height.

Numerical analysis of the combustion and fluid flow in a carbon monoxide boiler

Poor performance of a carbon monoxide (CO) boiler can have a detrimental influence on the operation and production of petrochemical industry, steel and iron industry and relevant industries. In this paper, the combustion and fluid flow in a carbon monoxide boiler is examined. Influences of some important parameters related to the geometry and operation of a CO boiler are discussed, including refractory thickness, insertion of an ellipsoidal cone, inlet air flowrate and inlet flue gas flowrate. It is found that when the refractory is thickened, the skin friction coefficient in the DeNOx section increases and arises later in the flow direction. Temperature and NO concentration increase in the DeNOx section and the larger the ellipsoidal cone angle is, the larger the skin friction coefficient will be. Compared with the original CO boiler, refractory thickening alleviates the temperature and NO rise in the DeNOx section. For moderate ellipsoidal cone angles, insertion of an ellipsoidal cone can alleviate the temperature rise in the DeNOx section and this leads to a lower NO emission. On the other hand, as the ellipsoidal cone angle becomes very large, the temperature rise in the DeNOx section is severer than for smaller ellipsoidal cone angles, leading to higher NO emission. A lower excess air flowrate can reduce the skin friction coefficient, NO formation and CO concentration, but the temperature increases. A higher flue gas flowrate can reduce the NO formation and the CO concentration, but the temperature and the skin friction coefficient increase. On the other hand, when the flue gas flowrate is reduced, the temperature and the skin friction coefficient decrease, but the NO formation and CO concentration in the product increase.

Micropolar Fluid Flow and Heat Transfer over a Nonlinearly Stretching Plate with Viscous Dissipation

The flow and heat transfer of a micropolar fluid past a nonlinearly stretching plate is studied numerically, by taking into account the viscous dissipation effect. It is assumed that the plate is stretched nonlinearly from the slot where it is issued. The governing system of partial differential equations is transformed into ordinary differential equations, which are then solved numerically using a finite-difference scheme known as the Keller-box method. The effects of the governing parameters, namely, the material parameterK, the Eckert number Ec, the Prandtl number Pr, and the nonlinear stretching parametern, on the flow field and the heat transfer characteristics are obtained and discussed. The velocity and the temperature profiles are also illustrated to aid the validity of the numerical results obtained. It is found that both the local Nusselt number and the magnitude of the skin friction coefficient increase with the nonlinear stretching parametern, and the opposite trend occurs asKincreases for fixedn.

Analytical solutions of the boundary layer flow of power-law fluid over a power-law stretching surface

This article discusses analytical solutions for a nonlinear problem arising in the boundary layer flow of power-law fluid over a power-law stretching surface. Using perturbation method analytical solution is presented for linear stretching surface. This solution covers large range of shear thinning and shear thickening fluids and matches excellently with the numerical solution. Furthermore, some new exact solutions are found for particular combination of m (power-law stretching index) and n (power-law fluid index). This leads to generalize the case of linear stretching to nonlinear stretching surface. The effects of fluid index n on the boundary layer thickness and the skin friction for nonlinear stretching surface is analyzed and discussed. It is observed that the boundary layer thickness and the skin friction coefficient increase as non-linear parameter n decreases. This study gives a new dimension to obtain analytical solutions asymptotically for highly nonlinear problems which to the best of our knowledge has not been examined so far.

Numerical Investigation of Transient Natural Convection of Viscoelastic Fluid Due to a Nonlinearly Stretching Surfaces with a Power-Law Surface Temperature

Transient boundary layer flow and heat transfer of a viscoelastic fluid due to non-linearly stretching surface subject to a power-law surface temperature are investigated numerically. The dimensionless unsteady, coupled and nonlinear partial governing differential equations are solved by an implicit finite difference scheme of Crank-Nicolson type. The effects of various parameters entering into the problem on the flow and heat transfer transient characteristics are studied. It was found that, the velocity inside the boundary layer increases as the viscoelastic parameter increases, and accordingly the skin friction coefficient increases. Meanwhile, an opposite behavior is observed for the temperature profiles. The power-law index has significant influences on the temperature profiles and the Nusselt. The computed numerically results are compared with previously reported work and were found to be in excellent agreement. This paper is the first attempt in introducing the heat transfer of a viscoelastic fluid due to non-linearly stretching surface subject to a power-law surface temperature and this model is essential in many patents based on drawing devices for viscoelastic fluid over a non-linearly stretching surface subject to a power-law surface temperature.

CFD Simulation of Flow in an Abrasive Water Suspension Jet: The Effect of Inlet Operating Pressure and Volume Fraction on Skin Friction and Exit Kinetic Energy

Abrasive particles in the suspension mixture in an abrasive water suspension jet (AWSJ) machining causes acute skin friction effect thereby effectively changing the jet diameter due to wear, which in turn influences jet exit kinetic energy. This results in lowering the life of the jet for effective machining. In consideration of this aspect, the present work examines the effect of inlet pressure on skin friction coefficient and jet exit kinetic energy. It is inferred from the analysis that an increase in inlet pressure causes a significant increase in skin friction coefficient and also results in proportional increase in the exit kinetic energy of the jet. Further, it is revealed from the analysis that an increase volume fraction of abrasive (abrasive concentration) in water results in significant decrease in the skin friction coefficient and jet exit kinetic energy.

A numerical study on unsteady natural convection of air with variable viscosity over an isothermal vertical cylinder

The present study deals with the boundary layer flow and heat transfer of unsteady laminar free convection flow past a semi-infinite isothermal vertical cylinder immersed in air. The fluid viscosity is assumed to vary with the temperature. An implicit finite-difference method has been employed to solve the governing non-dimensional boundary layer equations. A parametric study is performed to illustrate the influence of variable viscosity on the velocity and temperature profiles. The numerical results reveal that the viscosity has significant influences on the transient velocity and temperature profiles, average skin-friction coefficient and the average heat transfer rate. The results indicate that as the viscosity parameter increases, the temperature and the skin-friction coefficient increase, while the velocity near the wall and the Nusselt number decrease.

The effects of variable viscosity and thermal conductivity on heat transfer for hydromagnetic flow over a continuous moving porous plate with Ohmic heating

A numerical study of heat transfer from boundary layer flow driven by a continuous moving porous plate is proposed. The flow with electrically fluid due to the plate in the presence of a transverse magnetic field and Ohmic heating was molded as a steady, viscous, and incompressible. Both viscosity and thermal conductivity were variable and considered only a function of temperature. Similar analysis with Chebyshev finite difference method (ChFD) was developed to solve the governing equations for momentum and energy and determine the skin-friction coefficient and heat transfer rate. As the magnetic parameter and variable viscosity parameter increase, the fluid temperature and skin-friction coefficient increase and the fluid velocity and heat transfer rate decrease. The fluid temperature increases and heat transfer rate decreases with an increasing Eckert number and thermal conductivity parameter. The skin-friction coefficient and heat transfer rate increase, whereas the fluid velocity and temperature decrease as the wall suction velocity increase.

Large eddy simulation of magnetohydrodynamic turbulent channel flows with local subgrid-scale model based on coherent structures

For turbulent channel flows with a uniform magnetic field perpendicular to insulated walls, the performance of the coherent structure Smagorinsky model (CSM) is investigated in comparison to the Smagorinsky model (SM) and the dynamic Smagorinsky model (DSM). The Lorentz force acts against a streamwise flow. The effect of the Hartmann flattening leads to an increase in the wall shear stress, so that the skin friction coefficient increases. In contrast, the turbulence suppression by the magnetic field results in a decrease of the Reynolds shear stress near the wall, so that the skin friction coefficient decreases. As the magnetic field increases, a turbulent magnetohydrodynamic (MHD) flow transits to a laminar MHD flow at a critical Hartmann number. The CSM predicts a higher transition Hartmann number than the DSM and SM, because the model parameter of the CSM is locally determined based on coherent structures and the fluctuations are reflected in the shear stress. On the other hand, the model parameter of the DSM is averaged in the homogeneous directions, so that the shear stress is somewhat underestimated for the subcritical Hartmann number. The SM with a model constant and a wall damping function of the Van Driest type reproduces the laminar MHD flow at the lowest transition Hartmann number, because the model parameter (which does not change in the magnetic field) provides significant energy dissipation. Moreover, the CSM and DSM can reproduce properly the laminar MHD flow at high Hartmann number, because the model parameters of the CSM and DSM are drastically damped near the wall and the Reynolds shear stresses are suppressed to zero. The skin friction coefficients predicted by the CSM and DSM agree with the “two-dimensional” laminar solution, whereas the SM gives higher values than the laminar solution. The coherent structures become large and align themselves along the magnetic field in the transition to the laminar MHD flow.

Mixed convection boundary layer flow on inclined wavy plates including the magnetic field effect

A coordinate transformation and the spline alternating-direction implicit method are applied to study the mixed convection boundary layer flow along an inclined wavy plate in the presence of a transverse magnetic field. A numerical solution of the transformed boundary layer equation has been carried out for different values of magnetic field, buoyancy, wavy geometry and material parameters. Results demonstrate that the heat transfer rate and the skin-friction coefficient increase with the inclined angle. As the Prandtl number increases, the heat transfer rate and its amplitude will increase, but the skin-friction coefficient and its amplitude will decrease. The action of the magnetic field tends to accelerate the flow near the leading edge of the wavy surface and decelerate the flow far downstream of the leading edge. However, the total mixed convection heat flux along a wavy plate is higher than that of a flat plate under all circumstances.

Forced convection in a wavy-wall channel

The rates of heat transfer for flow through a sinusoidally curved converging–diverging channel has been analyzed using a simple coordinate transformation method and the spline alternating-direction implicit method. The effects of the wavy geometry, Reynolds number and Prandtl number on the skin-friction and Nusselt number have been studied. Results show that the amplitudes of the Nusselt number and the skin-friction coefficient increase with an increase in the Reynolds number and the amplitude–wavelength ratio. The heat transfer enhancement is not significant at smaller amplitude wavelength ratio, however, at a sufficiently larger value of amplitude wavelength ratio the corrugated channel will be seen to be an effective heat transfer device, especially at higher Reynolds numbers.

The effect of extrusion slit on the flow and heat-transfer characteristics from a continuously moving material with suction or injection

Abstract The flow and heat-transfer characteristics over a continuously moving horizontal material with suction or injection are studied very close and far away downstream from the extrusion slit. The finite-volume method is used to map out the solutions in the nonsimilar and similar regions subject to uniform surface velocity and temperature. The effects of Prandtl number (Pr), suction/injection parameter (d) and Reynolds number ( Re x ) on the friction and heat-transfer coefficients are studied. Comparisons with the similarity method solutions downstream at high Re x are made. Critical Reynolds numbers to distinguish between the self-similar and nonsimilar regions are obtained. The region very close to the slit is characterized by: (i) a rapid increase in skin-friction coefficient with increasing suction, or with increasing injection above d ≈ 0.45; the lowest friction coefficient is attained at an injection parameter d ≈ 0.45, and (ii) large heat-transfer coefficient which increases with increasing Prandtl number and suction, and decreases with increasing injection. On the other hand, downstream where the similarity solution is valid both the skin-friction and heat-transfer coefficients reach asymptotic values depending on d and, for the latter, on Pr.

INVESTIGATION OF TURBULENT WAKE-BOUNDARY LAYER INTERACTION WITH INJECTION

The present paper is concerned with experimental study of the interaction between a wake, with injection at its begining,and a boundary layer. The wake is developed downstream a finite length and thickness plate inside an open-type wind tunnel test section while the boundary layer is developed over the wall of the test section. The measurements are carried out at Reynolds number 1.8 x 105 and injection to Main stream velocity ratios (A) of (0 < A< 0.7). In the experiments the mean velocity pro-files, the wall static pressure distrubtion and the local skin friction coefficient are measured. The results indicate that, for a certain velocity ratio, moving downstream from the trai-ling edge of the thick plate the wake decays while the bound-arey layer grows gradually. Also, the wake depth decreases,the wake width increases and the position of maximum velocity moves into the inner layer. On the other hand-at a certain distance from the trailing edge-as the velocity ratio increases the wall pressure coefficient, the momentum thickness Reynolds number and the shape factor decrease while the skin friction coeffic-ient increases. Also-as the velocity ratio increases the rate of wake decay, the wake center line velocity and the wake width increase while the wake depth decreases.

Boundary layers on an electrode wall

The analysis deals with the interaction of electric and viscous boundary layers and its effects on the flow phenomenon near the electrode wall of a MHD channel. Using a local nonsimilarity solution method, the problem is solved numerically. It is found that the skin-friction coefficient increases, and the potential drop across the boundary layer decreases, as the applied potential at the electrode wall and ion to electron temperature ratio increases.