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A Numerical Simulation of Turbulence Flow around a Blade Profile of HAWT Rotor in Moving Pulse
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Pages :
1-9
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Authors :
N. Belkheir,
R. Dizene,
S. Khelladi,
A computation of three-dimensional flow past an isolated NACA0012 airfoil using Reynolds-averaged Navier -stokes
equations (RANS) method is conducted. Tow closure models k-ε and SST are applied to the numerical prediction of
the turbulent flow. A two-dimensional numerical simulation of oscillatory movement of the profile, based on solving
URANS equations is then studied for the dynamic stall prediction. FlUENT's software is used for the numerical
solution. Flow methodology for modelling 2-D unsteady viscous flow is presented and based on the incidence angle
variation taken as a pulse using Gaussian function and oscillation forms. Results compared with experiment, show a
very satisfactory agreement and highlight the need to take into account the unsteady flow and loads induced by
movement of the structure.
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The Lateral Migration of a Drop under Gravity between Two Parallel Plates at Finite Reynolds Numbers
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Pages :
11-21
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Authors :
A. Nourbakhsh,
S. Mortazavi,
A finite difference / front tracking method is used to examine the lateral migration of a three-dimensional deformable
drop in plane Poiseuille flow at a finite-Reynolds-number. The computations are based on an improved
implementation of the front tracking method at finite Reynolds numbers that include convective terms. The elliptic
pressure equation is solved by a multigrid method. Both neutrally buoyant and non-neutrally buoyant drop are
studied. The computation is performed within a unit cell which is periodic in the direction along the channel. A
neutrally buoyant drop lags the fluid slightly, and the wall effect balances the effect of the curvature of the velocity
profile, giving rise to an equilibrium lateral position about halfway between the wall and the centerline (the Segre-
Silberberg effect). Results are presented over a range of density ratios. In the non-neutrally buoyant case, the gravity
force is imposed along the flow direction. Non-neutrally buoyant drops have more complicated patterns of migration,
depending upon the magnitude of the buoyancy force. When the density difference is small, the equilibrium position is
either near the wall or near the centerline, depending on whether the drop leads or lags the local fluid. When the
density difference is large enough, the equilibrium position shifts towards the centerline, irrespective of whether the
drop is lighter or heavier than the fluid. The effect of Reynolds number and capillary number on the non-neutrally
buoyant drops is investigated. The accuracy of the method is assessed by comparison with the other simulations and
experiments.
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Numerical Investigation of Head-on Binary Drop Collisions in a Dynamically Inert Environment
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Pages :
23-37
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Authors :
M. D. Saroka,
N. Ashgriz,
M. Movassat,
The results of three-dimensional numerical simulations of drop collisions without the effect of a surrounding
environment are presented. The numerical model is based on an Eulerian, finite-difference, Volume-of-Fluid method.
Surface tension is included using the Continuum Surface Force method. Head-on collisions using equal size drops
with three different fluid properties of water, mercury and tetradecane are presented. Various drop diameters
ranging from 200 μm to 5 mm are considered. A separation criterion based upon deformation data is found. The
lower critical Weber numbers are found for mercury and water drops while tetradecane drops did not result in
separation for the range of Weber numbers considered. The effect of Reynolds number is investigated and regions of
permanent coalescence and separation are plotted in the Weber-Reynolds number plane. The role of viscosity and its
effect on dissipation is also investigated. Finally, the validity of the assumptions made in some of the collision
models is assessed.
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Numerical Simulations of Morphology, Flow Structures and Forces for a Sonic Jet Exhausting in Supersonic Crossflow
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Pages :
39-47
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Authors :
S. B. H Shah,
S. Zahir,
X. Y. Lu,
A numerical study is performed for a sonic jet issuing from a blunted cone to provide possible directional control in
supersonic crossflow by solving the unsteady Reynolds-averaged Navier-Stokes (RANS) equations with the twoequation
k −ω turbulence model. Results are presented in the form of static aerodynamic coefficients, computed at
a free stream Mach number 4.0, with varying pressure ratios, incidence angle and keeping zero yaw and roll angles.
The morphology and flow structure for the jet exhausting in crossflow at various pressure ratios is described in
detail. The Flight control of the projectile can be accomplished by taking advantage of a complex shock-boundary
layer interaction produced by jet interacting with the oncoming crossflow by altering pressure distribution in vicinity
of the jet, a net increase in the net force can be utilized for maneuvering of vehicle and possible flight control.
Computed static aerodynamic coefficients and pressure distribution using CFD analyses is with an accuracy of ± 5%
in the supersonic range.
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Effect of Non-Uniform Temperature Gradients on the Onset of Convection in a Couple-Stress Fluid-Saturated Porous Medium
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Pages :
49-55
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Authors :
I. S. Shivakumara,
S. Sureshkumar,
N. Devaraju,
The effect of different forms of basic temperature gradients on the criterion for the onset of convection in a layer of
an incompressible couple-stress fluid-saturated porous medium is investigated. It is shown that the principle of
exchange of stability is valid, and the eigenvalue problem is solved numerically using the Galerkin technique. The
parabolic and inverted parabolic basic temperature profiles have the same effect on the onset of convection and
similar is the case between piecewise linear temperature profiles heating from below and above. Amongst the various
basic temperature profiles, the linear temperature profile is found to be more stabilizing on the onset of instability.
In addition, the influence of thermal depth on the criterion for the onset of convection is assessed in the case of
piecewise linear temperature profiles. Moreover, an increase in the value of couple-stress parameter is found to
delay the onset of convection and to increase the width of convection cells. It is also noted that the critical wave
numbers are slightly affected by the nature of basic temperature profiles.
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Control of the Separation Flow in a Sudden Enlargement
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Pages :
57-66
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Authors :
A. Abdel-Fattah,
In the present paper, an experimental and numerical investigation of fluid flow and heat transfer in the case of wall
injection besides main flow through a circular sudden enlargement are studied. The injected flow is achieved through
an annular slot placed around the inner side wall of the step. The static pressure variation along the sudden
enlargement length is measured and calculated at different values of injection ratio (Q) and injection flow angles.
The average heat transfer with Reynolds number (ReJ) of injected flow at different values of the inlet flow angle is
obtained. The velocity, turbulent kinetic energy and temperature contours are presented in this study. Reynolds
number of injected flow is varied between 320 and 840, Reynolds number of main flow is between 5895 and 8450 and
the injection flow angles are 0o, 15o, 30o, 45o and 60o. In the injection case, the results indicate that, the pressure
recovery coefficient increases by decreasing the injection ratio and increasing the flow angle. The average heat
transfer coefficient increases as both injection Reynolds number and the injection flow angle increase. The numerical
results showed that two recirculation zones generate behind the step between the injection flow and the main flow.
The size of these recirculation zones decreases by increasing the injection flow rate. The turbulent kinetic energy
increases within region between the recirculation zones and main zone also, it decays by injecting flow in the
recirculation zone. The length for higher value of flow temperature decreases by injecting flow in the recirculation
zone, and that length increases as the injection flow rate increases. The comparison between the experimental results
and the numerical results gives good agreement using the k-ε model with Leschziner and Rodi correction.
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On the Reliability of Eddy Viscosity Based Turbulence Models in Predicting Turbulent Flow past a Circular Cylinder Using URANS Approach
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Pages :
67-79
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Authors :
B. N. Rajani,
A. Kandasamy,
S. Majumdar,
Turbulent flow past circular cylinder at moderate to high Reynolds number has been analysed employing an secondorder
time accurate pressure-based finite volume method solving two-dimensional Unsteady Reynolds Averaged
Navier Stokes (URANS) equations for incompressible flow, coupled to eddy-viscosity based turbulence models. The
major focus of the paper is to test the capabilities and limitations of the present turbulence model-based 2D URANS
procedure to predict the phenomenon of Drag Crisis, usually manifested in reliable measurement data, as a sharp
drop in the mean drag coefficient around a critical Reynolds number. The computation results are compared to
corresponding measurement data for instantaneous aerodynamic coefficients and mean surface pressure and skin
friction coefficients. Turbulence model-based URANS computations are in general found to be inadequate for correct
prediction of the mean drag coefficients, the Strouhal number and also the coefficients of maximum fluctuating lift
over the range of flow Reynolds number varying from 104 to 107.
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Influence of Thermal Radiation on a Transient MHD Couette Flow through a Porous Medium
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Pages :
81-87
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Authors :
I. G. Baoku,
C. Israel-Cookey,
B. I. Olajuwon,
The paper examines transient MHD Couette flow of an electrically conducting fluid in the presence of an applied
transverse magnetic field and thermal radiation through a porous medium. The dimensionless governing equations of
the flow are coupled non-linear partial differential equations and are solved by an efficient and unconditionally
stable finite difference scheme of Crank–Nicolson type. The influence of the medium permeability is also assessed.
The velocity and temperature profiles for the flow are studied for various interesting parameters of Prandtl number,
Nahme number and Hartmann number, and are presented graphically. The results show that the thermal radiation
has appreciable influence on the flow.
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Active and Passive Flow Control around Simplified Ground Vehicles
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Pages :
89-93
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Authors :
C. H. Bruneau,
E. Creusé,
D. Depeyras,
P. Gilliéron,
I. Mortazavi,
The aim of this work is to control the flow around ground vehicles by active or/and passive strategies. The active
control is achieved by steady, pulsed or closed-loop jets located at the backof the simplified car model. The passive
control is performed using porous layers between the solid body and the fluid in order to modify the shear forces. The
two previous control methods can be coupled to improve the drag reduction.
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Syngas Treatment Unit for Small Scale Gasification - Application to IC Engine Gas Quality Requirement
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Pages :
95-103
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Authors :
L. C. Laurence,
D. Ashenafi,
Gasification is a process that converts carbonaceous materials (coal, biomass, organic waste) into carbon monoxide
and hydrogen by reacting the raw material at high temperatures with a controlled amount of oxygen and/or steam.
The resulting gas mixture: syngas, can be used in energy production process. Syngas may be burned directly in
internal combustion engines, used to produce methanol and hydrogen, or converted via the Fischer-Tropsch process
into synthetic fuel. In addition, the high-temperature combustion refines out corrosive ash elements (chloride,
potassium) allowing clean gas production after flying ash removal. Therefore, the main issue to syngas use in
internal combustion engine is the removal of tarry product, ash and corrosive gaseous compounds. This paper
consists in a state of the art on the composition of gaz from gazeifier considering the gasification operating
conditions and the gazeified waste composition. The literature survey considers processes available to remove tarry
products and particles from syngas produced in small scale gazeifier and to purify gas from unwanted gazeous
compouds.
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On Heat Conduction with Phase Change: Accurate Explicit Numerical Method
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Pages :
105-112
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Authors :
N. Sadoun,
E. K. Si-Ahmed,
J. Legrand,
The one phase Stefan problem is discussed using the Goodman HBI method and an explicit numerical method
including modified boundary immobilization scheme. The main advantage of the HBI method lie in the remarkable
association of simplicity, flexibility and acceptable accuracy which an error less than 2.5% in predicting the moving
front location for Stefan number less than unity which covers most usual isothermal phase change material. An
accurate explicit numerical model to track the moving front in Stefan-like problems is provided. The scheme is
obtained using the variable space step method based on variable domain. The method is developed using central
difference approximations to replace spatial and temporal derivatives. Furthermore, iterative procedure, in
numerical calculation, is avoided by introducing simple assumptions. The numerical results show that the accuracy
of the method has been considerably improved without additional computational cost.
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Effects of Inclination and Magnetic Field on Natural Convection Flow Induced by a Vertical Temperature
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Pages :
113-120
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Authors :
M. N. Kherief,
K. Talbi,
F. Berrahil,
A numerical program is been developed to simulate the natural convection in a rectangular cavity in presence of a
magnetic field. The cavity in filled with mercury with a Prandtl number equal to 0.024. The flow is induced by a
vertical temperature gradient. This type of configuration concerns the crystal growth using the Bridgman vertical
method. The mass, momentum and energy equations, adopting the Boussinesq approximation, are solved numerically
using the finite-volume method in conjunction with the SIMPLER algorithm the flow under consideration is steady,
laminar and two-dimensional. The temperature gradients are assumed to be weak. The results show that the dynamic
and temperature fields are strongly affected by variations of the magnetic field intensity and the angle of inclination.
Numerical simulations have been carried out considering different combinations of Grashof and Hartmann numbers
to study their effects on the streamlines, the isotherms and the Nusselt number.
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