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Issue 1, Volume 3,
January 2008
Title of the Paper: Effect of a Thin
Floating Fluid Layer in Parametrically Forced Waves
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Authors: Elena B. Martin, Jose M. Vega
Abstract: In order to describe correctly on-board experiments, where residual
acceleration can have a significant impact in the fluid motion, we consider
the effect of a thin immiscible fluid layer on top of a liquid substrate in
incrementing the damping and promoting drift instabilities in spatially
uniform standing Faraday waves. It is seen that the effective surface
viscosity of the newtonian liquid film enhances drift instabilities that lead
to various steadily travelling and standing and travelling oscillatory
patterns, among others. In particular, travelling waves appear to be the
primary instability of the basic standing wave for deep water problems.
Keywords: Faraday
instability, weakly nonlinear analysis, oscillatory boundary layers,
streaming flow, immiscible liquid film, surface viscosity, on-board
experiments, vertically vibrated container.
Title of the Paper: Comparison of
Surrogate Models for Turbomachinery Design
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Authors: J. Peter, M. Marcelet
Abstract: This article addresses the issue of selecting surrogate models
suitable for the global optimization of turbomachinery flows. As a first step
towards this goal the analysis of a family of 2D flows on a two-parameter
design space is presented. Four types of surrogate models are considered:
least square polynomials, artificial neural networks (multi-layer perceptron
and radial basis function) and Kriging. Discussed is the ability of these
surrogate functions to give a satisfactory description of the exact function
of interest on the design space, during a global optimization. The number of
CFD evaluations for an adequate description of the exact function is
presented.
Keywords: Turbomachinery,
global optimization, surrogate model
Title of the Paper: A Boundary Layer
Inspection on a Wing Profile through High Resolution Thermography and
Numerical Methods
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Authors: M. Malerba, M. Argento, A.
Salviuolo, G. L. Rossi
Abstract: In fluid-dynamic phenomena the boundary layer plays a fundamental
role. It also affects the drag and lift force of a body immersed in a fluid.
Reynolds analogy introduces the possibility to correlate fluidynamic to
thermal field. By using high sensitivity thermographic systems, temperature
pattern on the surface of solid bodies immersed into a fluid can be analysed.
Temperature distribution depends on many combined effects, such as:
conversion of kinetic energy of the flow into thermal energy, flow
temperature variation in time and space, convection heat transfer phenomena
between flow and body, conduction phenomena inside the body, and radiation
heath exchange. A numerical approach is used to compare results of the
proposed procedure. A transient simulation with increasing inlet fluid
temperature is carried out to evaluate the thermal exchange between the
airstream and the body. The effect of the different thermal exchange due to
the local flow peculiarity is modelled.
Keywords: Boundary layer,
Infrared thermography, Subsonic flow, Passive technique, Wing profile, CFD
Title of the Paper: Different
Approaches for the Characterization of a Fractured Karst Aquifer
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Authors: Claudia Cherubini, Nicola
Pastore, Vincenzo Francani
Abstract: Karstic aquifers contain dissolution-generated cavities whose
geometry is characterized by high variability; their cross-sections may range
from uniform elliptical shapes, to high and narrow fissures, to irregular
shapes partly filled with rock fragments and terra rossa deposits. In these
conduits turbulent groundwater flow conditions may occur; in other cases no
flow conditions may be due to the existence of lenses of terra rossa. In the
examined site, located in the city of
Bari,
characterized by a fractured and karstic aquifer, an hydrogeological
reconstruction of the heterogeneities is carried out, in order to simulate
subterranean draining conditions that prove to be as near as possible to the
real ones. Two different approaches are applied; the first one, aimed at only
reconstructing the level of fracturation by means of geostatistical
interpolation, and the second one, more complete, where multiple realizations
are generated and conditioned to borehole data (RQD population), in order to
obtain a three-dimensional distribution of fracture frequency, cavities and
terra rossa lenses in the aquifer.
Keywords: heterogeneity,
fractures, cavities, geostatistics, simulations
Title of the Paper: Analysis of
Zero-Net-Mass-Flux Synthetic Jets using DNS
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Authors: Declan Hayes-Mccoy, Xi Jiang, Duncan Lockerby
Abstract: Axisymmetric direct numerical simulations (DNS) are performed to
study the formation criterion and evolution of zero-net-mass-flux synthetic
jets. Jet formation is characterised by an oscillating streamwise jet
centreline velocity, showing net momentum flux away from the orifice. This
momentum flux away from the orifice takes the form of a series of vortical
structures, often referred to as a vortex train. Simulation of the jet
actuator consists of a modified oscillating velocity profile applied to a
wall boundary. The jet issues into quiescent air, and the Reynolds numbers
used vary from 85 < Re < 1000. Variations to the input simulation
parameters are carried out in order to determine the overall effects on the
flow field. From these results the conditions necessary for the formation of
the synthetic jet along with the input parameters that provide an optimal jet
output are deduced. Jet optimisation is defined by both the vortical strength
and longevity of the vortex train as it travels downstream. This study
examines the vortical structures, the jet centreline velocities along with
other flow characteristics in order to deduce and visualise the effects of
the input parameters on the jet performance. The results attained on altering
the oscillation frequency of the jet actuator indicated that synthetic jets
with zero mean velocity at the inflow behave significantly differently from
jets with non-zero mean velocity at the inflow. An evolution study into the
formation of the train of vortical structures associated with the formation
of a synthetic jet is performed. This study is accompanied with a time
history of the jet centreline velocity, showing the net momentum flux of the
fluid away from the orifice of a fully developed synthetic jet. Further
details on the jet centreline velocity for all cases are also presented;
along with a study on the effect on the vortical structures of altering the
Reynolds number of the flow.
Keywords: Synthetic jet,
DNS, axisymmetric, vortical structures
Title of the Paper: Film Cooling and
Hub Disk Leakage Flow Experiments in a Fully Rotating HP Turbine Stage
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Authors: M. Pau, A. De
La Loma, G. Paniagua, D. Delhaye
Abstract: This paper describes the experimental methodology, test conditions,
and uncertainty analysis concerning a novel rim seal film cooling experiments
on a fully rotating HP transonic turbine stage under engine representative
conditions. A complex secondary air system has been designed in order to feed
the cooled turbine. The rotor blade has been heavily instrumented at the
platform, 7% and 15% of the blade height with fast response pressure sensors
and double-layer thin film gauges, allowing a complete aero-thermal
characterization of the flow field. The hub disk leakage and platform cooling
blowing ratios have been varied independently in order to assess their impact
individually. Furthermore, tests have been performed at two different
rotational speeds. The presented study should help designers improve the
protection of the rotor platform and minimize the amount of coolant used.
Keywords: Gas turbine,
leakage flows, film cooling.
Title of the Paper: Analysis of Nonlinear
Isentropic Sound Wave-Propagation in a Cylindrical Tube Filled with
Fluid-Saturated Porous Media
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Authors: Hazim M. Dwairi
Abstract: A theory of sound waves propagation in porous media that includes
the nonlinear effects of Forchheimer type with nonzero radial velocity
effects is laid out utilizing variational solutions technique. It is shown
that the main parameters governing the propagation of sound waves are shear
wave number, reduced frequency number, porosity, Darcy number, and
Forchheimer number. The manner in which the flow influences the attenuation
and the phase velocities of forward and backward propagating isentropic
acoustic waves is deduced. It is found that increasing Darcy number and
Forchheimer number increased wave’s attenuation and phase velocity for both
forward and backward sound waves, whereas increasing the porosity decreased
attenuation and phase velocity for both waves. The effect of increasing the
reduced frequency is found to increase attenuation of the forward waves and
decrease attenuation and phase velocity of the backward sound waves.
Moreover, the effect of the steady flow is found to decrease the attenuation
and phase velocities for forward sound waves and enhance them for the
backward sound waves.
Keywords: sound waves,
porous medium, fluid flow, noise isolator.
Issue 2, Volume 3,
April 2008
Title of the Paper: Modelling the
Zero-Inertia, Horizontal Viscous Dam-Break Problem
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Authors: B. Nsom, W. Ndong, B. Ravelo
Abstract: This paper considers the dam-break problem in a horizontal smooth 1D
channel, for hydrogeological hazards purpose. The fluid is muddy and it can
be described by a Newtonian model, provided that the inertial effects be
neglected versus the viscous ones in the momentum balance. Assuming the
shallow water approximation, a non dimensional equation is built from the
continuity and the Navier-Stokes equations in the limit of zero-inertia and
solved analytically in two limits: short time and long time. These solutions
are then combined into a single, universal model. Limitations of the model
are examined by comparison to a converged finite difference numerical
solution of the flow equation.
Keywords: Dam failure,
Finite difference method, Flow regimes, Numerical models, One dimensional
flow, Shallow water approximation, Similar solution
Title of the Paper: Wall Shear Stress
and Atherosclerosis: Numerical Blood Flow Simulations in the Mouse Aortic
Arch
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Authors: P. Ruengsakulrach, A. K. Joshi,
S. Fremes, S. Foster, J. Butany, B. Wiwatanapataphee, Y. Lenbury
Abstract: The aims of this study were (1) to demonstrate the feasibility of
computational fluid dynamic (CFD) modelling of realistic blood flow in the
mouse aortic arch, and (2) to determine the relation of wall shear stress and
atherosclerosis in the mouse aortic arch. ApoE knockout mice were chosen for
this study. The blood flow fraction in the major branches of the mouse aortic
arch was measured by ultrasound biomicroscopy. The geometry of the aortic
arch was captured by plastic casting and micro CT imaging. Mouse blood
viscosities were measured by rheometry. A pathological examination was
performed. A well-validated in-house finite element code, which solves the
three dimensional Navier-Stokes equations, was used to compute the wall shear
stress and velocity patterns in the ascending aorta and the aortic arch. The
distribution of the wall shear stress was correlated with the distribution of
the atherosclerosis from the pathological examination in order to investigate
the effect of wall shear stress on atherosclerosis. It is concluded that CFD
modeling of hemodynamics in the mouse aortic arch is feasible. Qualitative
impressions show that atherosclerosis was related with the region of low wall
shear stress in mouse aortic arch.
Keywords: Blood Flow,
Mouse, Aortic Arch, Wall Shear Stress, Atherosclerosis
Title of the Paper: Dynamic Behaviour
of Plates Subjected to a Flowing Fluid
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Authors: Y. Kerboua, A. A. Lakis
Abstract: Elastic structures subjected to a flowing fluid undergo a
considerable change in their dynamic behaviour and can lose their stability.
In this article we describe the development of a fluid-solid finite element
to model plates subjected to flowing fluid under various boundary conditions.
The mathematical model for the structure is developed using a combination of
a hybrid finite element method and Sanders’ shell theory. The membrane
displacement field is approximated by bilinear polynomials and the
transversal displacement by an exponential function. Fluid pressure is
expressed by inertial, Coriolis and centrifugal fluid forces, written
respectively as function of acceleration, velocity and transversal displacement.
Bernoulli’s equation for the fluid-solid interface and a partial differential
equation of potential flow are applied to calculate the fluid pressure. The
impermeability condition ensures contact between the system of plates and the
fluid. Mass and rigidity matrices for each element are calculated by exact
integration. Calculated results are in reasonable agreement with other
analytical theories.
Keywords: Vibration,
Finite element, Plates, Potential flow, Fluid structure interaction, Critical
velocity.
Title of the Paper: Preparation of
Flood Reduction Plan for Surat
City and Surrounding Region (India)
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Authors: Prasit G. Agnihotri, Jayantilal N. Patel
Abstract: Floods affect Suart city situated on river Tapi in India
many times, which creates damage to the people and properties. In this paper
the study of floods at Surat city in general
and the study of flood occurred at Surat
during 2006 in
particular has been made. Certain preventive and curative measures are
suggested for reducing the effects of flood in the study area. Flood
reduction plan for the study area has been also prepared and presented in
this paper.
Keywords:
Surat, River Tapi,
Flood, Submergence, Flood Level, Desilting, Diversion, Protection Wall, Flood
Reduction Plan
Title of the Paper: Rainfall – Runoff
Modeling: Comparison and Combination of Simple Time-Series, Linear
Autoregressive and Artificial Neural Network Models
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Authors: A. Jagan Mohan
Reddy, Ch. Suresh Babu,
P. Mallikarjuna
Abstract: Runoff simulation and forecasting is essential for planning,
designing and operation of water resources projects. In the present study,
the rainfall – runoff process is modeled using empirical methods such as
simple time - series (STS) and linear autoregressive (ARX) models and
compared with Artificial Neural Networks (ANNs). It also explores the
improvement in the performance of neural networks by combing them with
empirical methods. The study uses the monthly data at Sriramsagar, Mancherial
and Polavaram gauging sites of Godavari
basin of India.
The ANN models, because of their nonlinear modeling capability, outperformed
the empirical approaches. The study also reveals that the performance of ANN
models in the simulation and forecasting of monthly runoff during monsoon
period can be improved considerably by including the residuals derived from
STS and ARX models as additional inputs together with rainfall.
Keywords: Simple
time-series model, Linear autoregressive model, Artificial neural network,
Comparison and combination, Performance evaluation
Title of the Paper: Heat and Water Management
in a PEM Fuel Cell
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Authors: Ebrahim Afshari, Seyed Ali
Jazayeri
Abstract: Proton exchange membrane (PEM) fuel cells are promising
power-generation sources for mobile and stationary applications. In this
paper a non-isothermal, single-domain and two-dimensional computational fluid
dynamics model is presented to investigate heat and water transfer in a PEM
fuel cell. A set of governing equations, conservation of mass, momentum,
species, energy and charge for gas channels, gas diffusion layers, catalyst
layers and the membrane regions are considered. These equations are solved
numerically in a single domain, using finite-volume-based computational fluid
dynamics technique. This model accounts for the major transport phenomena in
a PEM fuel cell: convective and diffusive heat and mass transfer, electrode
kinetics, and potential fields. The results are shown to be in good agreement
with previous work and it is validated with recent experimental data
available.
Keywords: PEM Fuel cell;
Heat; Non-isothermal, Single-Domain; CFD
Title of the Paper: On
Coherent Structures in a Separated/Reattached Flow
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Authors: Zhiyin Yang, Ibrahim E.
Abdalla
Abstract: It is well known that large-scale organised motions, usually called
coherent structures, exist in many transitional and turbulent flows. The
topology and range of scales of coherent structures change widely in
different flows. However, it is not well established what kind of large-scale
coherent structures exists in separated/reattached transitional flows. Large
Eddy Simulation (LES) with a dynamic subgrid-scale model is employed to
investigate a separated boundary layer transition under 2% free stream
turbulence level and without free stream turbulence on a flat plate with a
blunt leading edge. Flow visualization is employed to show the entire
transition process leading to breakdown to turbulence and large-scale
coherent structures have been identified at various stages of the transition
process. However, there are some noticeable difference between the flow case
with and without free stream turbulence. The Kelvin-Helmholtz rolls, which
are clearly visible under no free stream turbulence (NFST), are not so
clearly visible under 2% free steam turbulence (FST) case. The Lambda-shaped
vortical structures which can be clearly seen in the NFST case can hardly be
identified in the FST case. Generally speaking, the effects of free-stream
turbulence have led to an early breakdown of the separated boundary layer and
hence increased the randomisation in the vortical structures, degraded the
spanwise coherence of those large-scale structures.
Keywords: Large-eddy
simulation; large-scale coherent structures; free stream turbulence;
transition
Title of the Paper: Flow Analysis of
Annular Jets by Proper Orthogonal Decomposition. Active Control on in the
Initial Zone of Large Diameter Ratio Annular Instabilities with Acoustic
Excitations
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Authors: A. Danlos, E. Rouland, B. Patte-Rouland
Abstract: Proper Orthogonal Decomposition (P.O.D.) is a technique used for
analysis of vortex structures in a turbulent flow. In this study, complex
shear flows are observed by P.I.V. measurements (Particle Image Velocimetry)
of a large diameter ratio annular jet. The annular jet is an example of
complex shear flow situations. Two axisymmetric shear layers, originating at
the jet exit, one at the nozzle lip and the other at the centre body,
eventually meet downstream or interact with each other. The main aim of this
study is to observe and analyze the effects of active control using acoustic
waves on an annular jet with a great diameter ratio (r= 0.91), in order to
find a new way to reduce jet instabilities. This contribution discusses the application
of Proper Orthogonal Decomposition to the P.I.V. (Particle Image Velocimetry)
velocity fields of an annular jet and on a statistic of time resolved
tomographic images of the initial zone of the annular jet. Acoustic waves are
then applied on the annular jet with different frequencies (fundamental,
first harmonic…). Measurements are conducted with a Reynolds number
ReDo=107800. The fluctuation frequency of the stagnation point is known for
this Reynolds number. The Strouhal number corresponding to this frequency is
StDo = 0.27. The P.O.D. analysis applied on a natural annular jet and an
excited annular jet enables us to see the importance of the triggering of the
acoustic wave with the stagnation point motion. An active control is
therefore necessary to use acoustic excitation to reduce instabilities in the
initial zone of these turbulent jets. Active control has already been used
with round jets and has given promising results, but only a few studies have
been conducted on annular jets in this field. This work will permit us
essentially to have a better knowledge of annular jets and to meet
manufacturers' needs.
Keywords: Particle Image
Velocimetry, Proper Orthogonal Decomposition, annular jet, control, acoustics
excitations
Title of the Paper: Flow Field and
Oscillation Frequency of a Rotating Liquid Droplet
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Authors: Tadashi Watanabe
Abstract: Oscillations and rotations of a liquid droplet are simulated
numerically using the level set method, and the combined effects of
oscillation amplitude and rotation rate on the drop-shape oscillation is
studied. The oscillation frequency is shown to decrease as the amplitude of
oscillation increases. The oscillation frequency increases, in contrast to
the effect of amplitude, as the rotation rate increases. The pressure
distribution in the droplet corresponds to the frequency shift, and it is
shown that the oscillations without frequency shift are possible. It is found
that the relation between the amplitude and the rotation rate is linear both
for the frequency shift of zero and for the pressure difference of zero even
though the fluid properties are different. The flow fields in and around the
droplet are visualized, and it is shown that the vortices formed by the
oscillation are not affected by the rotation. Parallel computations are
performed with satisfactory high efficiency for the calculations of the
pressure field, and the importance of the communication rate is demonstrated.
Keywords: Droplet,
Oscillation, Amplitude, Rotation, Frequency, Level Set Method, Parallel
Computation
Title of the Paper: Optimal Design of
Hydraulic Turbine Distributor
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Authors: Ahmed Alnaga, Jean-Louis Kueny
Abstract: This work concerns the development of an automatic iterative
procedure for optimal design of hydraulic turbine distributors. This
procedure based on the geometry parameterization of the distributor to
facilitate the fully automatic generation of the design by modifying the
geometry parameters, and Evolutionary Algorithms to define the best design
parameters using optimal functions (regrouped fixed objectives) evaluated from
CFD results to decide the design quality. This procedure is successfully
applied in two examples of Francis turbine distributors, the first with a
specific speed equal to 81 and the second with a specific speed equal to 48.
We obtained two new geometries with better efficiency and performance
compared to the initial designs.
Keywords: Hydraulic
turbines, geometry parameterization, flow simulation, evolutionary
algorithms.
Title of the Paper: Comparing Various
Methods for Topology and Shape Optimization of Floating Breakwaters
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Authors: Ghassan Elchahal, Pascal
Lafon, Rafic Younes
Abstract: In this paper, structural optimization of a floating breakwater is
addressed through several methods concerning its topology and shape, which
constitutes a new application. Three methods are introduced to handle the
optimization problem. The first one discusses the shape optimization of a
simple predefined geometrical form. The second, studies the topological
optimization based on bit array representation of a triangular mesh using
genetic algorithms. An attempt to overcome the limitations of bit-array was
developed through several steps (new partition element, mesh distinguishing
between the representation type and finite element analysis, varying finite
element problem size, creating a density vector to control the presence or
absence of the boundaries, generating initial population representing void
domains instead of void elements). The third method concerns shape
optimization, based on a variable number of points creating a structural
domain. In contrary to traditional methods where the variable points are
indicated by the user, it searches for the optimum number of points to create
the optimum shape. Finally, a comparison between these methods for the case
of the floating breakwater is discussed.
Keywords: Wave modelling;
Floating breakwaters; Shape and topology optimization.
Issue 3, Volume 3,
July 2008
Special Issue: Sustainable Energy and Environmental Fluid
mechanics
Guest Editor: Dr. Mohammad Rasul
Title of the Paper: The Influence of
Freshwater Biofilms on Drag in Hydroelectric Power Schemes
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Authors: J. M. Andrewartha, J. E.
Sargison, K. J. Perkins
Abstract: Freshwater biofilms are currently being studied to determine their
effect on the capacity of hydroelectric power scheme canals and the structure
of their turbulent wall layers. Mean velocity boundary layer profiles and
total drag measurements have been conducted in a purpose built recirculating
water tunnel on freshwater biofilms grown in a hydroelectric canal. Two
different fouled surfaces were compared with a smooth painted surface to
determine the effects of the physical characteristics of a biofilm on skin
friction drag. A 310% increase in local skin friction coefficient was
measured for a biofilm dominated by long filamentous algae streamers, and a
50% increase was measured for a biofilm dominated by a low-form gelatinous
diatom.
Keywords: biofilm,
biofouling, boundary layer, drag, hydroelectric, skin friction, water tunnel
Title of the Paper: Experimental and
Computational Investigation of Flow Around a 3-1 Prolate Spheroid
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Authors: D. B. Clarke, P. A. Brandner,
G. J. Walker
Abstract: The flow around a 3-1 prolate spheroid near the critical Reynolds
number is investigated experimentally and numerically. This work was
conducted as part of a larger project to examine the flow around Unmanned
Underwater Vehicles. The experimental investigation has been performed in a
water tunnel at the Australian
Maritime College.
Fast response pressure probes and a 3-D automated traverse have been
developed to investigate the state of the boundary layer. A commercial CFD
code has been modified to allow the experimentally determined boundary layer
state to be included in the computation. Qualitative and quantitative
comparisons between the measured and calculated results are discussed. The
tests on the spheroid were conducted within a Reynolds numbers range of 0.6 ×
106 to 4 × 106. The results presented here are for an incidence of 10o.
Keywords: spheroid,
boundary layer, transition, computational, experimental, pressure, flow
visualisation
Title of the Paper: A Numerical
Prediction of the Hydrodynamic Torque acting on a Safety Butterfly Valve in a
Hydro-Electric Power Scheme
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Authors: A. D. Henderson, J. E.
Sargison, G. J. Walker, J. Haynes
Abstract: A numerical study of the flow through a safety butterfly valve used
in a hydro-electric power scheme to stop water supply to a downstream
penstock is reported. Computational fluid dynamics applied in a quasi-steady
manner is used to predict the variation in hydrodynamic torque coefficient
with opening angle during a constant head test. Factors influencing these
results, such as Reynolds number and unsteady flow effects, are found to be
significant. The predicted results are compared with field measurements of
the full-size valve. Issues associated with applying the numerical results to
predict valve characteristics at higher Reynolds numbers are discussed.
Further computational and experimental studies are recommended.
Keywords: Numerical,
Safety, Butterfly valve, Torque, Hydro-electric power
Title of the Paper: A Scalar
Concentration (Komori) Probe for Measuring Fluctuating Dye Concentration in
Water
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Authors: J. T. Madhani, R. J. Brown
Abstract: The scalar (dye) concentration probe of Komori has been used at QUT
to measure the mixing and dispersion of pollutants in rivers from outboard
motors and in a gross pollutant trap (GPT). Although usages have been
documented in literature, little is known of the Komori (dye) probe’s
frequency response characteristics and the quality of data sampled. In this
work, the frequency response characteristic of the Komori probe is determined
by injecting methylene blue dye over a range of water flow velocities.
Despite some noise and drift, the data collected from the probe is useful
because of its high frequency response in comparison to regular commercial
concentration probes. The rise and fall times are reported and the
theoretical response time is also determined. It is found that the frequency
response is a strong function of flow velocity and a maximum of 100 Hz is
noted under typical operating conditions. Comparison between rise and fall
data show that the rise time is generally shorter than half the fall time.
Keywords: Concentration
probe, dye measurement, frequency response, Komori probe, tracer, rise time
and fall time
Title of the Paper: Flow Field
Phenomena about Lift and Downforce Generating Cambered Aerofoils in Ground Effect
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Authors: J. W. Vogt, T. J. Barber,
E. Leonardi
Abstract: A Computational Fluid Dynamics investigation was conducted to ascertain
and highlight the different ways in which ground effect phenomena are present
around both an upright (lift generating) and inverted (downforce generating)
cambered aerofoil when in close proximity to the ground. The trends in force
and flow field behaviour were observed at various ground clearances, while
the angle of attack was held constant at 6 degrees. The different mechanisms
by which ground effect influences the two different configurations were
highlighted through observation of the pressure coefficient plots, contour
maps of velocity and turbulence intensity and their effect on the normal and
drag forces. The primary contributing factor to the increase in normal force
for the lifting aerofoil, as the ground was approached, was a constriction
and rise in pressure of the flow. For the downforce aerofoil, a significantly
sped up flow increased suction and enhanced downforce. Also discussed is the
observation of a reduction in lift for the upright aerofoil as its ground
clearance is reduced through high and medium clearances.
Keywords: Aerodynamics,
Ground Effect, Computational Fluid Dynamics, Aerofoil
Title of the Paper: Evaluation of a
Proposed and an Existing Dust Ventilation/Collection System in an Underground
Mine Crushing Plant
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Authors: J. Naser, F. Alam, M. Khan
Abstract: Computational Fluid Dynamics (CFD) modeling of two alternative dust
collection systems in an underground mine-crushing plant was carried out. In
the proposed system, dust was collected/absorbed through the holes along the
top edge of the Run of Mine (ROM) bin. In the existing conventional approach,
the outgoing dust laden air is collected through an exit in the ceiling. The dust
collection performances of both systems were summarized. Detail results are
presented in the form of velocity vectors and dust concentration iso-surface
contours. Dust was found to be well contained within the crusher bin for the
proposed system and stands out as a viable option. However, the velocity
magnitudes were found to be high in and around the hole exits, which has the
potential to lead to undesirable pressure drop and generation of noise.
Keywords: Dust, modeling,
CFD, multiphase, ventilation.
Title of the Paper: Numerical Modelling
of Reverse Flow Phenomena in a Channel with Obstruction Geometry at the Entry
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Authors: M. A. Kabir, M. M. K. Khan,
M. G. Rasul
Abstract: Numerical modelling and simulation of the reverse flow phenomenon
in a channel with obstruction geometry at the entry were performed using
CFD-ACE+ simulation solver. Obstruction geometries used for simulation were
triangle, circle, semicircle and flat plate. Simulations were performed for
different gap to width ratio, for different gap between the test channel and
obstruction geometry, and for different Reynolds number. The simulated
results are discussed and compared with flow visualization images.
Simulations results predicted the occurrence of reverse flow and existence of
other flow features such as vortex shedding at both ends. The numerically
predicted results of the flow phenomena are generally in good agreement with
the experimentally observed flow visualization images.
Keywords: Reverse Flow,
Test Channel, Obstruction, Flow Visualization and Simulation
Title of the Paper: A Study of Bubble
Trajectory and Drag Co-efficient in Water and Non-Newtonian Fluids
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Authors: N. M. S. Hassan, M. M. K.
Khan, M. G. Rasul
Abstract: A new experimental set-up was used to analyze the characteristics
of the bubbles rising in water and three different concentrations of xanthan
gum solutions for higher Reynolds number. The bubble size, bubble rise
velocity, and bubble trajectory were measured using a combination of
non-intrusive-high speed photographic method and digital image processing.
The results of bubble trajectory for various bubbles in water and different
xanthan gum solutions are presented and discussed. In trajectory analysis, it
is seen that the smaller bubbles show helical or zigzag motion and larger
bubbles follow spiral motion for water. In xanthan gum solutions, small
bubbles experience less horizontal motion than that in water. Larger bubbles
produce more spiral motion with the increase in xanthan gum concentration.
Drag coefficients for air bubbles at higher Reynolds number are reported. It
is seen that the experimental drag coefficient increases with the increase in
xanthan gum concentration corresponding to the same bubble volume.
Keywords: Bubble
trajectory, bubble volume, drag co-efficient, Reynolds number, polymer
solution, non-intrusive method
Title of the Paper: A Study of Spin
Effects on Tennis Ball Aerodynamics
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Authors: Firoz Alam, Aleksandar Subic,
Jamal Naser, M. G. Rasul, M. M. K. Khan
Abstract: Due to complex surface structure, the aerodynamic behaviour of a
tennis ball is significantly different compared to other sports balls. This
difference is more obvious when spin is involved. Although several studies
have been conducted on drag and lift in steady state condition (no spin
involved) by the authors and others, little or no studies have been conducted
on spin effect. It is known that the spinning can affect aerodynamic drag and
lift of a tennis ball thus the motion and flight of the ball. The primary
objective of this work was to study the effect of spin using experimental and
computational methods. Several new tennis balls were used in experimental
study as function of wind speed, seam orientation and spins. A simplified
model of a tennis ball was used in computational study using commercial
software ‘FLUENT’. The simulation results were compared with the experimental
findings. The study shows that the spin has significant effects on the drag
and lift of a new tennis ball, and the averaged drag coefficient is
relatively higher compared to the non- spin condition. The study has also
found a significant variation between CFD and EFD results as the complex
tennis ball with fuzz elements was difficult to model in CFD.
Keywords: Drag
coefficient, lift coefficient, spin, wind tunnel, EFD, CFD
Title of the Paper: An Experimental and
Computational Study of Aerodynamic Properties of Rugby
Balls
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Authors: Firoz Alam, Aleksandar Subic,
Simon Watkins, Jamal Naser, M. G. Rasul
Abstract: The aerodynamic properties of rugby balls as a function of wind
speeds and yaw angles were measured using experimental and computational
methods. The average drag and side forces coefficients for all speeds and yaw
angles were computed and compared. The flow pattern around the rugby ball was
visualized using wool tuft and smoke. No significant variation in Reynolds
numbers was found in CFD results, however, some variations were noted in
experimental findings. The average drag coefficient of a rugby ball at zero
yaw was 0.18 and 0.14 in
experimental and computational studies and this rose to about 0.60 and 0.50
when yawed at 90 degrees respectively.
Keywords: Drag
coefficient, side force, wind tunnel, EFD, CFD
Title of the Paper: Sustainability in
Building Environment: A Review and Analysis on Mould Growth in a Subtropical
Climate
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Authors: M. M. Rahman, M. G. Rasul, M. M. K. Khan
Abstract: A review on mould growth in buildings in a subtropical climate and
the characteristics of moulds in a subtropical Central Queensland University
(CQU), Rockhampton campus, Australia,
buildings are presented and analysed. The mould (fungal spore) concentrations
indoors and outdoors are compared and correlations between mould
concentrations and environmental parameters such as temperature and humidity
are developed. Specific genera of moulds and total spores were identified and
recovered colonies were counted from the airborne samples. The SPSS
(Statistical Product and Service Solutions) software was used for
nonparametric data analysis. Total airborne mould concentrations were found
highest in the dry season and lowest in the wet season and were positively
correlated with relative humidity and temperature. Further studies are
recommended for controlling mould growth in buildings in a subtropical
climate.
Keywords: Airborne fungal
spores, a subtropical climate, total fungal spores, Burkard spore trap,
Spearman correlation coefficient.
Title of the Paper: Modelling of Flow
and Tracer Dispersion over Complex Urban Terrain in the Atmospheric Boundary
Layer
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Authors: A. T. Skvortsov, P. D. Dawson,
M. D. Roberts, R. M. Gailis
Abstract: A new mathematical model of polutant plume dispersion in an urban
environment is presented. The model uses parameters that explicitly take into
account turbulent flow close to the ground and the urban canopy parameters
enabling an analytic calculation of the plume concentration profiles and
concentration fluctuations. Model predictions are compared with some recent
experimental data, showing a close match. The model developed can be used as
an analytical tool for predicting CBR plume behaviour in complex urban
environments, or as a prototype and performance check for a new generation of
dispersion models.
Keywords: Plume,
Pollutant, Dispersion, Tracer, Urban Canopy, Concentration Fluctuations,
Intermittency, Model.
Issue 4, Volume 3, October 2008
Title of the Paper: Using
GIS Buffer Technique to Improve Rainfall-Radar Reflectivity Relationship
Estimation
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Authors: Sarintip Tantanee, Saman
Prakarnrat
Abstract: In Past decade, Thailand
has regularly faced the problem of flash flood and landslides, especially
over the lower Northern part of the country. This area is mountainous area
where there is the problem of raingage scarcity and absence. In order to
construct the effective warning system, the appropriate rainfall estimation
should be first developed. Thus, this research was implemented based on the
concept of using information from radar to detect rainfall in order to solve
the problem of information lacking over ungaged area. This research was setup
under the collaboration among Naresuan
University, Thai
Meteorological Department and Royal Irrigation Department. The objective of
the research is to estimate the rainfall (R) from Z-R relationship by using
the measured reflectivity (Z) from radar station located at the middle of
flash flood risky area in Lower Northern Thailand. Coupling GIS technique
with probability matching, the Spatial Probability Technique (SPT) and Buffer
Probability Technique (BPT) were developed to evaluate the appropriate Z-R
pair for Z-R relationship analysis. From both techniques, the obtained Z-R
relationship can be expressed in form of, where are Function Parameters, as
the previous studies. Comparing between these two techniques on rainfall
detecting from reflectivity, the obtained R Z=aRb a,b2 from both processes
are slightly difference, whereas, BPT provided less standard error of
estimation. However, this study emphasized only on the Z-R relationship, the
further study should be done with the other parameters to support the
disaster warning system in the future.
Keywords: Rainfall,
Radar, Reflectivity, Z-R Relationship, Buffer, Spatial, Ungauged area
Title of the Paper: Modelling Muddy Flash Floods and Debris Flows
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Authors: B. Nsom, B. Ravelo, W. Ndong,
N. Latrache, K. Bouchlaghem, S. Elouragini
Abstract: After long
and intense rains in a mountainous region, large quantities of water flow in
the torrents. For some reason, this flow can be obstructed by cross-linked
branches and debris (natural dam). When the hydrostatic pressure exerted by
the fluid exceeds a given yield value, the dam collapses and the fluid is
released inside and outside the torrent bed, as well. Such scenario which is
known as a dam-break flow can describe the initiation of certain geological
flows, (debris flows, mudflows, etc.). As for any gravity current, the flow
description depends on the time scale. Immediately after the dam collapse,
the inertial forces are the dominant ones and this configuration can model a
flah flood. Flash floods develop at time and space scales that conventional
observation systems are not able to monitor, so reliable modelling remains a
crucial step. At larger time scale, a viscous regime takes place where the
viscous forces become the dominant ones and this configuration can model a
classical debris flow. Debris floods develop in a long domain, i.e. a domain
of space that is much longer than it is wide. They generally erode their bed
and transport much energy and can move rocks and boulders upon very long
distances. Both, the flash flows and the debris floods constitute dangerous
phenomena for public safety and quality of life. The originality of the
present approach is to consider these two flood waves as special cases of a
single global model of a dam-break flow of a muddy fluid, depending on the
time scale. The study was experimental, analytical and numerical, as well.
The experimental study performed in previous work consisted in designing
model fluids to be used in the laboratory experiments, characterizing these
synthetic muds and monitoring the corresponding dam-break flows in the
laboratory. The corresponding results agreed with the theoretical study
presented here and which consists in stating the equations of motion
governing the different flows studied, and solving them in their non
dimensional form, both analytically and numerically.
Keywords: Dam failure, Finite
difference method, Herschel-Bulkley fluid, Inertial regime, Numerical models,
One dimensional flow, Shallow water approximation, Similar solution, Viscous
regime.
Title of the Paper: Calculus of Indicated Power by Mathematical Modeling Method of
Compression Process and Study of
Exegetic Efficiency of the Helical Screw Compressor with Oil Injection
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Authors: Petrilean
Dan Codrut, Dosa Ion
Abstract: The first
part of the article studies the problem of establishing a mathematical model
that ensures the calculus of the output power for the helical screw
compressor with oil injection. In the second part the problem of establishing
the equation of exegetic efficiency for helical screw compressors with oil
injection is further explored. The obtained results are checked by carrying
out case studies on real compressors.
Key words: indicated power,
exergy, helical screw compressor, mathematical modeling method, exegetic
efficiency, modeling of working conditions.
Title of the Paper: Von Karman Vortices Formation at the Trailing Edge of a Turbine Blade
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Authors: Daniele
Simoni, Marina Ubaldi, Pietro Zunino
Abstract: - The paper
presents the results of an experimental investigation of the von Karman
vortices formation at the blade trailing edge of a large scale turbine
cascade. The mean and time varying characteristics of the flow in the
trailing edge region were measured by means of a two-component fiber-optic
laser Doppler velocimeter over an experimental grid very close to the blade
trailing edge. A phase locked ensemble averaging technique has been applied
to separate coherent and incoherent contributions in the instantaneous LDV
data. The trailing edge of the central blade of the cascade has been
instrumented with a multisensor surface mounted hot-film probe. The probe
outputs proportional to the instantaneous wall shear stress were sampled
simultaneously with a filtered reference signal from a hot-wire probe located
in the wake and sensitive to the vortex periodicity. Organised periodic
structures have been clearly identified in the flow and their evolution in
time has been documented through a sequence of instantaneous pictures of the
periodic flow field during a cycle of the vortex shedding. Time-averaged and
time-resolved ensemble averaged wall shear stresses on the blade trailing
edge help to identify the positions where the boundary layers separate and to
analyze the effects of the vortex shedding on the wall shear stress along the
trailing edge.
Key-Words: - Turbine blade
boundary layers, Turbine blade wakes, Von Karman vortices, Wall shear stress,
Hot-film measurements.
Title of the Paper: Experimental and Computational Aerodynamic Investigations of a Car
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Authors: Manan Desai, S. A. Channiwala,
H. J. Nagarsheth
Abstract:- In the
recent times, CFD simulations [1], with the advent of computer architectures
with superfast processing capabilities are rapidly emerging as an attractive
alternative to conventional wind tunnel tests which are either too
restrictive or expensive, for aerodynamic styling of a car. The paper
describes comparative assessment of two distinct experimental strategies of
aerodynamic predictions by conventional wind tunnel approach and its
subsequent validation with advanced computational procedures, carried out as
a part of design process of a small hybrid car proposed to be named as
ADRENe. The experimental investigations were performed on an open circuit
suction type wind tunnel having a 30cm x 30cm x 100cm test section, on a
geometrically similar, reduced scale (1:15) clay model, while the three
dimensional computational analysis was carried out using Gambit as the
preprocessing software and Fluent as the solver and post processor. A good agreement
between performance values obtained independently by two experimental
methods, suggests their reliability and suitability for further
experimentation purposes. The comparison with computational approach shows
that the computed drag forces and pressure distributions agree well with the
experimental values over the entire range of air velocities, however, the
agreement with the data for drag coefficient varies, which appears to suggest
a higher degree of dependency on the grid quality and elements selection.
Key-Words: - Car design,
Aerodynamics, Wind tunnels, CFD.
Title of the Paper: Void
Fraction Fluctuations in Two Phase Flow: Theoretical Models
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Authors: G.
B. Roston, M. E. Ascheri, M. C. Martin, R. Pizarro
Abstract: The knowledge
on the structure and dynamical behavior of the two phase flow is important
for a great number of processes, including the coolant behavior in a nuclear
power reactor. Previous studies performed on gas liquid phase or in
experimental devices specially designed for that purpose, have introduced
theoretical models that describe the void fraction fluctuations in a two
phase flow. Nevertheless, they only partially explained the measured effects
or have a doubtful applicability. In this work, from data obtained from a BWR
nuclear power plant, we apply different mathematical models in order to study
the change of the intensity of the void fraction fluctuations along the
channel. By comparing these models, we conclude that the bimodal twophase
flow model is a more realistic one for void fraction estimation. This model
can be applied for high void fraction rate and converges to the Poisson model
for low void fraction rate. The expected contribution of this work is, by
means of a proper use of neutron signal analysis, to obtain a better
understanding of the dynamics and structure of the two phase flow in a
nuclear power reactor.
Key-Words: Two phase flow, Bimodal
model, Neutron noise, Coolant, Nuclear reactor.
Title of the Paper: Simulation of Viscous
Flows with a Gridless Particle Method
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Authors: Fotios
G. Stamatelos, John S. Anagnostopoulos
Abstract: The aim of
this paper is to present the numerical simulation of the evolution of the
viscous, low Reynolds flows in two-dimensional cases with the use of the
Smoothed Particle Hydrodynamics (SPH) method. This work is considered as the
first step towards the simulation of complex three-dimensional flows, which
occur in impulse water turbines. The method was originally developed for
solving problems of astrophysical nature and belongs to the mesh less
methods, as it does not require any computational grid. A set of discrete
fluid particles is used to represent the continuous fluid, and their
trajectories are being calculated in a Lagrangian sense through time. The 2-D
test cases examined in this paper are the Couette and the Poiseuille Flow,
and the basic problem of the liquid column collapse (Dam Break). For the
first two test cases the numerical results were tested against analytical
solutions from the literature, while for the third test case experimental
measurements were used for the validation of the calculations. The agreement
of the numerical results with the corresponding analytical and experimental
data is quite good and encouraging towards the use of the SPH method in
modelling of more complex, unsteady and multiphase flow fields, while the
performance of the algorithm referring to the speed of the calculations and
the qualitative results is remarkable.
Key-Words: - Smoothed Particle
Hydrodynamics (SPH), Dam Break, Couette and Poiseuille Flow, Numerical
Modelling
Title of the Paper: Nonlinear
Behavior of Pile-Soil Subjected to Torsion due to
Environmental Loads on
Jacket Type Platforms.
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Authors: M.
R. Emami Azadi, S. Nordal, M. Sadein
Abstract: - In the present study,
the torque-twist behavior of non-linear pile-soil system related to the
wavecurrent loading on Jacket type offshore platform is investigated. The
non-linearities of pile-soil with respect to both depth and the twist angle
of pile are considered. The basic differential equilibrium equations of the
pilesoil system are derived based on hyper- elasticity theory of soil. A
numerical central finite difference method is applied based on simplification
of stress field around the pile elements which takes into account changes in
the s e co nd a r y shear stress components and also non-linearities due to
non-homogeneous soil condition. This method uses a one-dimensional mesh along
pile-soil interface. It also takes into account the changes in G of soil with
respect to the twist angle of pile. In a separate work, the simulated
torque-twist behavior of pile-soil system based on this analysis approach is
compared with the results of more refined finite element analysis by using
continuum mechanics theory and also full scale pile-soil test results
(Emami,2002). The torque-twist results by using the proposed approach have
been used to study the behavior of two jacket-pile-soil systems under sea
environmental and accidental loading.
Key-Words: - Pile-Soil interaction,
Jacket-Pile-Soil system, Pile-Soil Non-linearities, Disk Model of Soil,
Torque-Twist (t-t) transfer curves
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