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Issue 1, Volume 4,
January 2009
Title of the Paper: Laboratory
Investigations and Theoretical Analysis of Axial Thrust Problem in High
Rotational Speed Pumps
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Authors: Andrzej Wilk
Abstract: Theoretical analysis of the influence of the increase of the
rotational speed of the rotodynamic pump on axial thrust is made in the paper.
The algorithm of the designing of the axial thrust relieving system by means
of the relieving holes and relieving blades is presented. The calculation
examples for pump working at low and high rotational speed are included. The
conclusions concerning with both axial thrust relieving systems for high
rotational speed are presented. The laboratory tests of rotodynamic pump
working at rotational speed 6000 rpm are presented. The purpose of the tests
was to determine the pump operation characteristics and pressure distribution
around the impeller.
Keywords: Pump, high
rotational speed, axial thrust, open impeller, radial blades, pressure
distribution
Title of the Paper: Numerical Modeling
of Extended Mild Slope Equation with Modified Mac Cormack Method
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Authors: Asu Inan, Lale
Balas
Abstract: The transformation of waves is one of the important subjects in
coastal engineering studies. Refraction, diffraction, shoaling, reflection can
be analysed with the mild slope equation over mild sloped topographies. But
the extended mild slope equation can be applied to the rapidly varying
topographies since it includes higher order bottom effects such as square of
bottom slope and bottom curvature. In this study, extended mild slope equation
has been solved with finite difference method using Mac Cormack and Point
Gauss Seidel Methods together. The nonlinear wave celerity and group velocity
have been used. The numerical model has been tested on elliptic shoaling area
and compared with the physical experiment measurements given in literature.
The predictions are in consistency with the measurements. As a result of error
analysis, it is decided that the numerical can be used for the simulation of
wave propagation. Numerical model has been applied to a coastal area in the
Kocaeli Bay in the Marmara Sea in Turkey.
Keywords: Extended mild
slope equation, Mac Cormack Method, Point Gauss Seidel Method, wave
refraction, diffraction, finite difference method, CFD
Title of the Paper: An Unstructured Grid
Generation Approach for Inviscid Flow Solutions
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Authors: Bahrainian
Seyed Saied, Daneh Dezfuli Alireza
Abstract: The unsteady and inviscid compressible flow around a circular
cylinder and airfoil has been solved using a cell-centered finite volume
method. A new algorithm for the generation of unstructured triangular grids
was used to discretize the computational flow domain. Automatic grid
generation, cell size distribution, and geometry treatment are some of the
grid algorithm capabilities. Euler flow solutions have been obtained for
subsonic and transonic flow conditions. The subsonic solution of flow around a
circular cylinder grid verified the unstructured grid techniques, and was
compared with an analytical solution. Transonic solution over the same grid
fully converged after only 2791 iterations. The grid quality resulted in
smooth pressure contours. Transonic flow solutions were also obtained for
airfoil at free stream Mach number of 0.8 and attack angle of 1.25. The true
position of the shock is illustrated in the pressure coefficient plots, and
shows the shock capturing capability of the solution method. The convergence
history obtained, points to the accuracy of the numerical solution.
Keywords: Unsteady,
Inviscid, Geometry Movement, Unstructured Grid, Edge Swapping
Issue 2, Volume 4,
April 2009
Title of the Paper: Hot-Film and LDV
Investigation of the Boundary Layer Transition on a Turbine Profile at
Different Reynolds Numbers
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Authors: Daniele Simoni,
Marina Ubaldi, Pietro Zunino
Abstract: An experimental investigation of the suction side boundary layer of
a large scale turbine cascade has been performed to study the effect of
Reynolds number on the boundary layer transition process at large (1.6x106)
and moderate (5.9x105) Reynolds numbers. The boundary layer development has
been investigated by means of a two-component laser Doppler velocimeter. Time
traces of the instantaneous velocities and boundary layer velocity and
turbulence fields provide a physical insight of the different transition
processes for the two Reynolds numbers. Surface mounted hot-film gauges were
used to measure the quantity qτw, which is proportional to the wall shear
stress. Statistical analysis of the instantaneous qτw data, including
statistical moments, probability density function and intermittency function
distributions, provides quantitative information on the state of advancement
of the transition process at the two different Reynolds numbers.
Keywords: Boundary layer
transition, Turbine profile, Hot-film probes, Wall shear stress, Intermittency
detection technique, LDV measurements
Title of the Paper: Comparison of
Different 2nd Order Formulations for the Solution of the 2D Groundwater Flow
Problem over Irregular Triangular Meshes
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Authors: Costanza Arico,
Tullio Tucciarelli
Abstract: Mixed and Mixed Hybrid Finite Elements (MHFE) methods have been
widely used in the last decade for simulation of groundwater flow problem,
petroleum reservoir problems, potential flow problems, etc. The main advantage
of these methods is that, unlike the classical Galerkin approach, they
guarantee local and global mass balance, as well the flux continuity between
inter-element sides. The simple shape of the control volume, where the mass
conservation is satisfied, makes also easier to couple this technique with a
Finite Volume technique in the time splitting approach for the solution of
advection-dispersion problems. In the present paper, a new MHFE formulation is
proposed for the solution of the 2D linear groundwater flow problem over
domain discretized by means of triangular irregular meshes. The numerical
results of the modified MHFE procedure are compared with the results of a
modified 2nd spatial approximation order Finite Volume (FV2) formulation [2],
as well as with the results given by the standard MHFE method. The FV2
approach is equivalent to the standard MHFE approach in the case of isotropic
medium and regular or mildly irregular mesh, but has a smaller number of
unknowns and better matrix properties. In the case of irregular mesh, an
approximation is proposed to maintain the superior matrix properties of the
FV2 approach, with the consequent introduction of a small error in the
computed solution. The modified MHFE formulation is equivalent to the standard
MHFE approach in both isotropic and heterogeneous medium cases, using regular
or irregular computational meshes, but has a smaller number of unknowns for
given mesh geometry.
Keywords: Groundwater,
finite elements method, mixed hybrid finite elements method, finite volumes
method, positive-definite matrix, M-property, Raviart-Thomas basis function
Title of the Paper: Air Curtains
Integrity when Misusing the Refrigerated Display Cabinets
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Authors: Samir R.
Traboulsi, Ali Hammoud, M. Farid Khalil
Abstract: Tilted air curtains are used as barriers between two environments of
different temperature, humidity and quality and are the core elements in
Refrigerated display cabinets. Energy consumption and performance became the
concern of end users of cabinets as the Entrainment of one environment Fluid
(air) into the curtain by shear layer mixing contributes to both the sensible
and the latent heat load on the other environment and the impingement of the
air curtain formed. Obstructions of any type on the path of the air curtain
endanger its integrity. Protrusion present in the direction of the flow
impacts the performance of the air curtain and defeats its purpose of
existence. Computational Fluid Dynamics (CFD) software method is used to
evaluate the impact of such intentional and non intentional obstructions, on
the performance of the air curtain formed by the tilted jet plane and is also
validated by comparing the CFD calculations results with experimental results.
Qualitative design combination of various geometrical parameters and various
levels of obstruction in the direction of the flow(s) are proposed in order to
guarantee the existence of the air curtain.
Keywords: Display Cabinet,
Simulation, Velocity, Turbulence, Infiltration Rate, Air Curtain
Title of the Paper: Pre-mixed and
Diffusion Flames Assessment using CFD Tool for Natural Gas and Biogas Fuels in
Gas Turbine Combustion Chambers
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Authors: Lucilene De
Oliveira Rodrigues, Marco Antonio Rosa Do Nascimento
Abstract: In the past few years, with the development of advanced numerical
computational codes, numerical simulation became a promising option to develop
and improve technology in different fields. The results obtained through
simulations are used to gather important information during the design phase
or optimization of industrial equipment. Its employment generates reliable
results at low cost due to the reduced number of experiments as well as the
opportunity to develop new products and perform many simulations before
construction of a new product. With the recent energy shortage and the
reduction of the fossils fuel reserves, the industrial sector starts to
develop more compact equipment that can be fed with different fuels, attending
a wide range of heat and power demand. The aim of the work is to assess
thermal-aerodynamics and emission using numerical simulation (Computational
Fluid Dynamics CFD) of a 600kW simple cycle gas turbine combustion chamber.
The thermal-aerodynamics assessment of the combustion chamber will be
presented, showing the profiles of temperature and emissions, when used the
premixed and diffusion flame for the natural gas and biogas fuels,
respectively.
Keywords: Combustion
Chamber, Flame, Premixed, Diffuse, Different Fuels, Gas Turbine
Issue 3, Volume 4,
July 2009
Title of the Paper: Hydrodynamics of
Vertical Semi-Immersed Slotted Barrier
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Authors: E. V. Koutandos
Abstract: In the present study, wave interaction with fixed, vertical,
semi-immersed, slotted barriers is investigated numerically. Numerical results
are obtained with the use of the COBRAS (Cornell breaking Wave and Structures)
wave model for regular waves, revealing the effects of relative depth d/L (d:
water depth, L: wave length) and the porosity of the barrier on the
hydrodynamic characteristics (wave transmission, reflection, dissipation,
velocity field, turbulence kinetic energy field). Numerical results concerning
wave transmission, reflection, dissipation against the porosity of the
structure, are well compared with experimental results by Isaacson et al.
[13], revealing the credibility of the wave model. Detailed computed
velocities and turbulence kinetic energy in the vicinity of the structure
indicate the effects of the special breakwater on the flow pattern and the
turbulence structure.
Keywords: Slotted barrier,
Permeable barrier, Special breakwater
Title of the Paper: Universal Solutions
of Unsteady Two-Dimensional MHD Boundary Layer on the Body with Temperature
Gradient along Surface
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Authors: Zoran Boricic,
Dragisa Nikodijevic, Bratislav Blagojevic, Zivojin Stamenkovic
Abstract: In this paper, we consider multi-parametric method for solution of
unsteady temperature twodimensional MHD laminar boundary layer. Outer magnetic
field induction is assumed as function of longitudinal coordinate and time
with force lines perpendicular to the body on which boundary layer forms.
Temperature varies along body surface with longitudinal coordinate, but not
with time. Further, electric field is neglected and value of magnetic Reynolds
number is significantly less then one i.e. problem is considered in
induction-less approximation. According to temperature differences under 50oC
physical properties of fluid are constant. Introducing new variables and then
similarity parameters, starting equations are transformed into universal form.
Obtained universal equations and corresponding boundary conditions do not
contain explicit characteristics of particular problems. Appropriate
approximations of obtained equations are solved numerically in this paper, and
a part of obtained results is given in the form of figures and corresponding
conclusions.
Keywords: MHD,
multi-parametric method, boundary layer, similarity parameters, temperature,
universal solutions
Issue 4, Volume 4,
October 2009
Title of the Paper: Investigation into
LBM Analysis of Incompressible Laminar Flows at High Reynolds Numbers
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Authors: A. C. Benim, E.
Aslan, I. Taymaz
Abstract: The Lattice Boltzmann Method is applied to incompressible, steady,
laminar flows at high Reynolds numbers varying in a range form 50 to 2000. The
developing channel flow and the lid driven cavity flow are analyzed. The
effect of the model Mach number on accuracy is investigated by performing
computations at different Mach numbers in the range 0.1 - 0.4 and comparing
the results with finite-volume predictions of the incompressible Navier-Stokes
equations. It is observed that the Mach number does not effect the results
within this range, and the results agree perfectly well with the finite-volume
solution of the incompressible Navier-Stokes equations. An important purpose
of the study has been to explore the stability limits of the method. It is
observed that the maximum allowed collision frequency decreases with
increasing Reynolds and Mach numbers, and this dependency is more predominant,
and the limiting collision frequencies are lower for the channel flow compared
to the lid driven cavity flow.
Keywords: Lattice
Boltzmann Method, Computational Fluid Dynamics, Incompressible Flow, Laminar
Flow, High Reynolds Number
Title of the Paper: Computational
Analysis of Gas Turbine Preswirl System Operation Characteristics
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Authors: M. Cagan, A. C.
Benim, D. Gunes
Abstract: Gas turbine engine efficiency can be increased by the improvements
of the cooling air system. In this study, gas turbine preswirl cooling system
is computationally analyzed using a validated three-dimensional quasi-steady
model. In the first phase of the study, the system is analyzed with respect to
different operating conditions, for understanding its behavior. In this part,
the dependence of the discharge coefficient and the temperature drop on the
inverse of the swirl ratio parameter are employed to characterize the system.
In the second phase of the analysis, the possibilities of improving the system
performance is investigated by implementing different modifications on the
system geometry.
Keywords: Gas turbine
cooling, Preswirl system, Discharge coefficient, Performance, CFD
Title of the Paper: The Analysis of the
Influence of the Initial Impeller on the Discharge and the Delivery Head of
High Speed Pump with Radial Blades
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Authors: Andrzej Wilk
Abstract: The article discusses a theoretical analysis of fluid flow through
the initial impeller which is mounted at the inlet to the centrifugal impeller
in the impeller pump. The article presents the results of laboratory tests for
the influence of various initial impellers in the impeller pump with an
open-flow impeller and rectilinear radial blades on the pump operating
parameters and the course of performance characteristics. The research has
been performed at the rotational speed from 3000 to 7000 rpm.
Keywords: High-speed pump,
open-flow impeller, radial blades, initial impeller, performance
characteristics
Title of the Paper: Estuarine
Hydrodynamic as a Key-Parameter to Control Eutrophication Processes
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Authors: Antonio A. L.
S. Duarte, Jose M. P. Vieira
Abstract: Estuaries and coastal lagoons are commonly subjected to intensive
anthropogenic stress due to massive pollutant loading from urbanised riparian
areas. Nutrient enrichment is a key-factor for habitat degradation, leading to
sensible structural changes in estuarine ecosystems with the consequent
occurrence of eutrophication processes. The influence of hydrodynamics must
not be neglected on estuarine eutrophication vulnerability assessment. In
fact, flushing time affects the transport and the permanence of water and its
constituents inside an estuary, so the increase of estuarine flushing capacity
can be seen as a management measure to mitigate or to invert eutrophication
processes, like the one observed in the Mondego River estuary (Portugal),
during the last two decades. In this work, an integrated 2-DH water quality
model was applied to calculate water residence time values, at different
simulated management scenarios of the Mondego estuary. The results of the
performed simulations illustrate the strong asymmetry of flood and ebb
duration time at the inner sections of this estuary, a keyparameter for a
correct tidal flow estimation, as the major driving force of the southern arm
flushing capacity, as well as a spatial and temporal variability of calculated
RT values. The conclusions of this work confirm the crucial influence of
hydrodynamics on estuarine water quality status and the usefulness of this
hydroinformatic tool as contribution to support the design of a sustainable
management plan, based on nutrient loads reduction and hydrodynamic
circulation improvement. So, the proposed methodology, integrating
hydrodynamics and water quality, constitutes a powerful hydroinformatic tool
for enhancing estuarine eutrophication vulnerability assessment, in order to
contribute for better water quality management practices and to achieve a true
sustainable development.
Keywords: Water
sustainable management, estuarial modelling, eutrophication, hydroinformatics,
residence time, Mondego estuary
Title of the Paper: Is a Flat Inlet
Profile Sufficient for WSS Estimation in the Aortic Arch?
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Authors: J. Renner, D.
Loyd, T. Lanne, M. Karlsson
Abstract: Atherosclerosis is one of the main reasons for cardivascular disease
which cause many deaths every year especially in the Western world. The
development of atherosclerosis is strongly believed to be influenced by
hemodynamic forces in the arteries e.g. wall shear stress (WSS). Estimations
of WSS are therefore very important. By combining magnetic resonance imaging (MRI),
image processing and computational fluid dynamic (CFD) simulations, it is
possible to estimate subject specific WSS in the human arteries. The framework
for performing such work includes i.e. using inlet boundary conditions which,
however, will influence the final result i.e. the WSS distribution. This paper
aims to investigate the influence of the inflow boundary condition in the
human aorta with comparing two settings for the inflow: 1) subject specific
inlet profile measured with MRI and 2) uniform profile with the subject
specific mass flow rate. The analysis of WSS will be performed both on spatial
location along the artery as well as on the temporal location in the cardiac
cycle. Subject specific data have been used for geometry, inflow velocity
profile and blood viscosity. The recommendation due to our findings from nine
healthy subjects, is that a measured subject specific inlet boundary condition
must be used in order to get a subject specific WSS distribution; the
difference in WSS is 8-34% compared to using a mass-flow correct uniform
profile. Temporal variations were clearly seen in the WSS differences due to
the different inflow velocity profiles used. The lowest influence of the inlet
boundary condition was found at peak velocity in the cardiac cycle. The aortic
geometry does not form the flow in such extent (compared to the influence by
inlet boundary condition) to obtain a more correct WSS distribution further
away from the inlet at the systolic parts of the cardiac cycle. The shape of
the vessel has only a significant influence at low velocities i.e. the
diastolic phase of the cardiac cycle.
Keywords: Wall Shear
Stress – Aorta - CFD - Subject Specific - Inlet Boundary Condition - Uniform
Velocity Profile
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