

Intermittency in the Transition to Turbulence for a ShearThinning Fluid in HagenPoiseuille Flow


Pages :
16


Authors :
Seyed Amir BAHRANI,
ChÃ©rif NOUAR,
Since Reynolds original experiments in 1883, very few studies have been carried out on the transition to turbulence for shear thinning fluid in HagenPoiseuille. Compared to the Newtonian fluids, the results showed two interesting phenomenon: a delay in transition to turbulence and the appearance of an asymmetry in the mean axial velocity profiles. In this study, we measured experimentally the fraction factor and axial velocity profiles using Laser Doppler Velocimetry system (LDV) at different Reynolds numbers. It is shown an axisymmetric in the mean axial velocity profiles for laminar and turbulent regimes and an increasing asymmetry profile with increasing Rew for transition regime. Two different stages are clearly identified during transition to turbulence. The first stage which we called it pretransition, took place only in the non Newtonian fluids while the second stage correspond to the appearance of turbulent puffs. Another objective of this study is the statistical analysis of the axial velocity fluctuation. In the transition regime, power spectra identified the existence of a weak turbulence. It is generated by the shearthinning character of the fluid, which follows a power law with an exponent close to 3 (f 3).
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Joule Heating Effects on MHD Natural Convection Flows in Presence of Pressure Stress Work and Viscous Dissipation from a Horizontal Circular Cylinder


Pages :
713


Authors :
A.S. Bhuiyan, NHM.,
Mohammed Azim,
M. K. Chowdhury,
The effects of joule heating on MHD natural convection flow from a horizontal circular cylinder along the outer
surface from the lower stagnation point to the upper stagnation point in presence of pressure stress work and viscous
dissipation is investigated. The results have been obtained by transforming the governing boundary layer equations
into a system of nondimensional equations and by applying implicit finite difference method together with Newton’s
linearization approximation. Numerical results for different values of the magnetic parameter, joule heating parameter
and Prandtl number have been obtained. The velocity profiles, temperature distributions, skin friction coefficient and
the rate of heat transfer have been presented graphically for the effects of the aforementioned parameters. Results are
compared with previous investigation.





Effect of Radiation on Boundary Layer Flow and Heat Transfer over a Stretching Sheet in the Presence of Free Stream Velocity


Pages :
1524


Authors :
S Manjunatha,
. Dr. B.J. Gireesha,
C.S Bagewadi,
Aim of the paper is to study an unsteady boundary layer flow and heat transfer analysis of a viscous, incompressible dusty fluid over a porous stretching surface in the presence of time dependent free stream. The governing partial differential equations are reduced to coupled nonlinear ordinary differential equations by similarity transformation. Numerical solutions of these equations are obtained by using RKF45 method. The solution obtained is dependent on governing parameters like Hartman number (M), unsteadiness parameter (A), Prandtl number (Pr), dust interaction parameter (Î²), suction parameter (R), Eckert number (Ec), the ratio of free stream velocity parameter and stretching parameter (Î») and thermal radiation parameter (Nr). Some important findings reported in this work reveals that the effect of radiation have significant impact in controlling the rate of heat transfer in the boundary layer region.





Heat and Mass Transfer in the Boundary Layer Flow along a Vertical Isothermal Reactive Plate near Stagnation Point: Existence of Dual Solution


Pages :
2533


Authors :
Gurminder Singh,
P.R. Sharma,
Heat and mass transfer in a steady stagnation point boundary layer flow of viscous incompressible fluid through
highly porous media along a vertical isothermal plate is investigated. The plate surface reacts with the flowing fluid
and inert specie is produced that diffuses inside the boundary layer. The mass flux of the specie at the plate is taken
directly proportional to specie concentration at the plate. The governing equations of continuity, momentum, energy
and specie diffusion are transformed into ordinary differential equation using the similarity transformation and solved
numerically using RungeKutta method along with shooting technique. It is found that the system of ordinary
differential equations possesses dual solution. The velocity, heat and specie concentration distribution are obtained
for different parameters and presented through figures. Skinfriction coefficient, Nusselt number and Sherwood
number at plate for various physical parameters are discussed numerically and presented through tables.





NonLinear Oberbeck Convection in Chiral Fluid through a Vertical Permeable Channel in the Presence of a Transverse Magnetic Field


Pages :
3541


Authors :
N. Rudraiah,
B.M. Rajaprakash,
. Nagaraju,
Nonlinear oberbeck convection in a chiral incompressible Boussinesq fluid flowing through a vertical channel
bounded by rigid permeable isothermal boundaries kept at different temperatures is investigated in this paper in the
presence of a uniform transverse magnetic field, under the influence of viscous dissipation. The nonlinearcoupled
momentum and energy equations are solved analytically using a regular perturbation method valid for small values of
buoyancy parameter N. To validate the results obtained from the analytical solutions of the nonlinear equations,
which are also solved numerically using a finite difference method supplemented with the successive over recreation
(SOR) technique. The velocity, temperature, skin friction, mass flow rate and the rate of heat transfer are computed
for various values of electromagnetic thermal number Wemt, buoyancy parameter N, and suction Reynolds Number
Re. The results obtained are represented graphically and found that an increase in Wemt, increases the velocity and
temperature. Physically, we attributes this to setting up of small scale turbulence by magnetic filed. The effect of
perturbation parameter N is shown to increases the skin friction, heat transfer and the mass flow rate.





Oscillatory Mixed Convection in a Porous Medium


Pages :
4350


Authors :
S.K Ghosh,
Oscillating mixed convection on the fully developed flow between two infinitely long vertical walls heated
asymmetrically in a porous medium, has been studied. It experiences g jitter force associated with microgravity in
the field of space science with reference to crystal growth in space. Our present study can be exposed to a real life
situation of a microgravity field. The time varying gravity field generates oscillatory free convection velocity field.
This is combined with the forced oscillating flow driven by a pressure gradient.





Effects of Thermophoresis, Viscous Dissipation and Joule Heating on Steady MHD Flow over an Inclined Radiative Isothermal Permeable Surface with Variable Thermal Conductivity


Pages :
5161


Authors :
Machireddy Gnaneswara Reddy,
A twodimensional mathematical model is presented for the laminar heat and mass transfer of an electricallyconducting, viscous and Joule (Ohmic) heating fluid over an inclined radiate isothermal permeable surface in the presence of the variable thermal conductivity, thermophoresis and heat generation. The Talbot ChengSchefferWillis formulation (1980) is used to introduce a thermophoretic coefficient into the concentration boundary layer equation. The governing partial differential equations are nondimensionalized and transformed into a system of nonlinear ordinary differential similarity equations, in a single independent variable . The resulting coupled nonlinear equations are solved under appropriate transformed boundary conditions using the RungeKutta fourth order along with shooting method. Comparisons with previously published work are performed and the results are found to be in very good agreement. Computations are performed for a wide range of the governing flow parameters, viz., magnetic field parameter, thermophoretic coefficient (a function of Knudsen number), Eckert number (viscous heating effect), angle of inclination, thermal conductivity parameter, heat generation parameter and Schmidt number. The present problem finds applications in optical fiber fabrication, aerosol filter precipitators, particle deposition on hydronautical blades, semiconductor wafer design, thermoelectronics and magnetohydrodynamic energy generators.





MHD Pulsatile Flow through a Porous Medium


Pages :
6374


Authors :
Rajnish Kumar,
B.G. Prasad,
This paper develops a mathematical model with an aim to compute the analytic solution for the MHD pulsatile flow driven by an unsteady pressure gradient between permeable beds of a viscous incompressible Newtonian fluid saturated porous medium. The dimensionless governing equations for this investigation are solved analytically after separating into a steady part and an unsteady part. The influence of pertinent parameters on the flow is delineated and appropriate conclusions are drawn. The results presented in this work constitute an innovative way to describe correctly the boundary conditions at both the walls. Favorable comparisons with previously published work authenticate a remarkable accuracy of the results investigated in the paper.
Mathematics Subject Classification 2010: 76D05, 76D10, 76S05, 76W05.





Parametric Study of Exhaust Pattern in Cold Spray Using CFD and ParticleWall Impact Analysis


Pages :
7587


Authors :
M. Karimi,
G. W. Rankin,
A. Fartaj,
A numerical simulation of a cold gas dynamic spray process using a computational fluid dynamic (CFD) technique is presented. Distribution of particulate matter in the immediate surroundings of spray application site is of interest. The flow field inside an oval shaped supersonic nozzle and the surroundings of the nozzle is simulated. Particle trajectories along their flight in the nozzle as well as before and after impact with the target plane are calculated. Fluent is used for the purpose of flow field simulation. A discretephase Lagrangian particle trajectory model is used for particle trajectory calculation. A model uses the principles of motion and impact dynamics to predict particle behavior upon impacting the substrate. The locations and concentrations of particle exhaust patterns around the impact location are determined and presented graphically. The dependence of these patterns to variations in the jettarget tilting angle, standoff distance, upstream temperature and particle material is investigated.





A MultiRelaxationTime Lattice Boltzmann Method on Non Uniform Grids for Large Eddy Simulation of RayleighBénard Convection Using Two SubGrid Scale Models


Pages :
89102


Authors :
Ahmad Reza Rahmati,
Mahmud Ashrafizaadeh,
E. Shirani,
In the present work, for the first time, the application of a MultiRelaxationTime Lattice Boltzmann (MRTLB) model
for largeeddy simulation (LES) of turbulent thermally driven flows on nonuniform grids is considered. A Taylor series
expansion and Least square based Lattice Boltzamnn method (TLLBM) has been implemented in order to use a nonuniform
mesh. It permits to reduce the required mesh size and consequently the computational cost to simulate the
turbulent buoyant flow fields. The implementation is discussed in the context of a MRTLB model in conjunction with
both Smagorinsky and mixed scale viscosity subgrid models. At first, to validate the code, a multirelaxation–time lattice
Boltmann method on nonuniform grid is utilized to simulate a liddriven cavity flow .Then large eddy simulation of this
model is applied to simulate a turbulent RayleighBénard convection at different Rayleigh numbers in ranging 104 to 1015
for Prantdl number of 0.71. The simulation results show that lattice Boltzmann method is capable to simulate turbulent
convection flow problems at high Rayleigh numbers.





Pulsatile Flow in a Tapered UTube


Pages :
103110


Authors :
M. Sumida,
An experimental investigation of pulsatile flow through a tapered 180 curved tube, i.e., a Utube, was performed to study the blood flow in the aorta. The experiments were carried out in a Utube with a curvature radius ratio of 3.5 and a 50 reduction in the crosssectional area from the entrance to the exit of the curved section. Velocity measurements were conducted by a laser Doppler velocimetry (LDV) for a Womersley number of 10, a mean Dean number of 400 and a flow rate ratio of 1. Additionally, flow was visualized to qualitatively investigate the nature of the flow, complementing the quantitative LDV measurements. The velocity profiles for steady and pulsatile flows in the tapered Utube were compared with the corresponding results in a Utube having a uniform crosssectional area. The striking effects of the tapering on the flow are exhibited in the axial velocity profiles in the section from the latter half of the bend to the downstream tangent immediately behind the bend exit. A depression in the velocity profile appears at a smaller turn angle in the case of tapering, although the magnitude of the depression relative to the crosssectional average velocity decreases. Near the bend exit, strong secondaryflow motion occurs, leading to a weak depression in the velocity profile in the downstream tangent immediately behind the bend exit. The value of , which indicates the uniformity in the velocity profile over the cross section, decreases with increasing , whereas it rapidly increases immediately behind the bend exit.





Fluid Flow and Heat Transfer over a Permeable Stretching Cylinder


Pages :
111120


Authors :
K Vajravelu,
k. V. Prasad,
S.R. Santhi,
In this paper, we analyze the effects of thermophysical properties on the axisymmetric flow of a viscous fluid
induced by a stretching cylinder in the presence of internal heat generation/absorption. It is assumed that the
cylinder is stretched in the axial direction with a linear velocity and the surface temperature of the cylinder is
subjected to vary linearly. Here, the temperature dependent thermophysical properties namely, the fluid
viscosity and the fluid thermal conductivity are respectively assumed to vary as an inverse function of the
temperature and a linear function of the temperature. The governing system of partial differential equations is
converted into a system of coupled nonlinear ordinary differential equations with variable coefficients. The
resulting system is solved numerically using a second order finite difference scheme known as the Kellerbox
method. The governing equations of the problem show that the flow and heat transfer characteristics depend
on six parameters, namely the curvature parameter, fluid viscosity parameter, injection/suction parameter,
variable thermal conductivity parameter, heat source/sink parameter and the Prandtl number. The numerical
values obtained for the velocity, temperature, skin friction, and the Nusselt number are presented through
graphs and tables for several sets of values of the pertinent parameters. The results obtained for the flow and
heat transfer characteristics reveal many interesting behaviors that warrant further study on the axisymmetric
flow phenomena. Comparisons with the available results in the literature are presented as special cases.





A Criterion for QuasiSteadiness of the Laminar Diffusion Flamelet Model


Pages :
121124


Authors :
Hu Bing,
The laminar diffusion flamelet model is a wellestablished approach to modeling turbulent nonpremixed combustion. Its quasisteady version, referred to as the steady flamelet model, is very useful in engineering CFD calculations due to its low computational cost. However, previous studies have shown that unsteadiness of flamelets needs to be taken into account under certain circumstances. In this study, we derive a flamelet time scale, which is a characteristic time period needed for a flamelet structure to reach its quasisteady state, and we use this time scale to propose a criterion to test quasisteadiness of the flamelet. Although this criterion is rather conservative in that the predicted steadyflamelet regime tends to be smaller than it should be, the criterion is easy to use because it only requires the information from the mixing field.





Boundary Layer Flow and Heat Transfer over a Permeable Exponentially Shrinking Sheet in the Presence of Thermal Radiation and Partial Slip


Pages :
125134


Authors :
Rajesh Sharma,
Ishak Anuar,
Roslinda Nazar,
Ioan Pop,
The steady boundary layer flow of a viscous fluid with heat transfer over an exponentially shrinking sheet in the presence of thermal radiation with mass suction is studied. Velocity and temperature slip is considered on the boundary. Using a similarity transformation, the governing boundary layer equations are transformed into a system of nonlinear ordinary differential equations, which are then solved numerically using MATLAB routine solver. Dual solutions exist for a certain range of mass suction parameter. It is also found that the range of mass suction parameter for obtaining the steady solution is enhanced with the increase of velocity slip parameter and is independent of the thermal slip parameter as well as the radiation parameter.





An HAM Analysis of StagnationPoint Flow of a Nanofluid over a Porous Stretching Sheet with Heat Generation


Pages :
135145


Authors :
Amir Malvandi,
F. Hedayati,
M. R. H. Nobari,
Steady twodimensional stagnation point flow and heat transfer of a nanofluid over a porous stretching sheet investigated analytically using the Homotopy Analysis Method (HAM). The employed model for nanofluid includes twocomponent fourequation nonhomogeneous equilibrium model that incorporates the effects of Brownian diffusion and thermophoresis simultaneously. The basic partial boundary layer equations have been reduced to a twopoint boundary value problem via similarity variables. The effects of thermophoresis number ( ), Brownian motion number ( ), suction/injection parameter ( ), source/sink parameter ( ), permeability parameter ( ), stretching parameter and Lewis number ( ) on the temperature and nanoparticle concentration profiles are studied in detail. Moreover, special attention is paid on the variations of reduced Nusselt and Sherwood number on the affects of physical parameters. The obtained results indicate that for , reduced Sherwood number remains constant however, corresponds to negative Sherwood number, i.e. concentration rate is reversed.





On Exchange of Stabilities in Ferromagnetic Convection in a Rotating Ferrofluid Saturated Porous Layer


Pages :
147154


Authors :
Jyoti Prakash,
In the present paper, first of all, it is proved that the ‘principle of the exchange of stabilities’ is not, in general valid, for the case of free boundaries and then a sufficient condition is derived for the validity of this principle in ferromagnetic convection, for the case of free boundaries, in a horizontal ferrofluid saturated porous layer in the presence of a uniform vertical magnetic field and uniform rotation about the vertical axis.





Numerical Solution of ThreeDimensional Flow over Angled BackwardFacing Step with Raised Upper Wall


Pages :
155167


Authors :
S. Bayraktar,
In the present study, results obtained from threedimensional incompressible flow over backwardfacing step in a rectangular duct using Realizable k turbulence model are reported. Effects of step inclination angle have been investigated for =30, 45, 90 while upper wall of duct kept parallel to the bottom wall and then rose to =6. Reynolds number based on freestream velocity and step height is examined by varying its magnitude in the range of 15,00064,000. Simulated results are presented for revealing the general flow features and reattachment lengths after a successful validation of the present work with the experimental data of Driver and Seegmiller (1985). It is found that turbulence kinetic energy increases suddenly after the step for both straight and raised upper walls and reaches its maximum at x/h=5 that consistent with the published literature. The size of reattachment lengths increases with the step inclination angle, i.e., maximum reattachment length occurs at 90 for both straight and raised upper walls. It is seen that raising the upper wall leads to longer reattachment lengths.





MHD Flow and Heat Transfer of an Exponential Stretching Sheet in a BoussinesqStokes Suspension


Pages :
169176


Authors :
P.G. Siddheshwar,
G. N. Sekhar,
A. S. Chethan,
An analysis is carried out to study the flow and heat transfer due to an exponentially stretching sheet in a Boussinesq
Stokes suspension. Two cases are studied in heat transfer, namely (i) the sheet with prescribed exponential order
surface temperature (PESTcase) and (ii) the sheet with prescribed exponential order heat flux (PEHFcase). The
governing coupled, nonlinear, partial differential equations are converted into coupled, nonlinear, ordinary differential equations by a similarity transformation and are solved numerically using shooting method. The classical explicit RungeKuttaFehlberg 45 method is used to solve the initial value problem by the shooting technique. The effects of various parameters such as the couple stress parameter, Reynolds number and Prandtl number on velocity and temperature profiles are presented and discussed. The results have possible technological applications in the liquidbased systems involving stretchable materials.





Homotopy Perturbation Method for MHD Boundary Layer Flow with Low Pressure Gradient over a Flat Plate


Pages :
177185


Authors :
JHANKAL ANUJ,
Using He’s Homotopy Perturbation Method (HPM), the system of nonlinear partial differential equations governing the MHD boundary layer equations with low pressure gradient over a flat plate are solved. The main advantage of HPM is that it does not require the small parameters in the equations and hence the limitations of traditional perturbation can be eliminated. The influence of various relevant physical characteristics are presented and discussed.





