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A Simple Solution of the Laminar Dam Break Wave
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Pages :
1-10
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Authors :
H. Chanson,
The sudden release of a mass of fluid in a channel generates a highly unsteady flow motion, called dam break
wave. While industrial fluids exhibit sometimes non-Newtonian behaviours, the viscous fluid flow assumption
remains a useful approximation for simplified analyses. In this study, new solutions of laminar dam break wave
are proposed for a semi-infinite reservoir based upon the method of characteristics. The solutions yield simple
explicit expressions of the wave front location, wave front celerity and instantaneous free-surface profiles that
compare favourably with experimental observations. Both horizontal and sloping channel configurations are
treated. The simplicity of the equations may allow future extension to more complicated fluid flows.
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Energetics of the Beamed Zombie Turbulence Maser Action Mechanism for Remote Detection of Submerged Oceanic Turbulence
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Pages :
11-42
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Authors :
C. H. Gibson,
V. G. Bondur,
R. Norris Keeler,
P. T. Leung,
Sea surface brightness spectral anomalies from a Honolulu municipal outfall have been detected from space
satellites in 200 km2 areas extending 20 km from the wastewater diffuser (Leung and Gibson 2004, Bondur
2005, Keeler et al. 2005, Gibson et al. 2006). Dropsonde and towed body microstructure measurements show
greatly enhanced viscous and temperature dissipation rates above the outfall trapping-layer. Fossil-turbulencewaves
(FTWs) and secondary zombie-turbulence-waves (ZTWs) break as they propagate near-vertically and
then break again near the surface to produce wind-ripple smoothing with narrow-wavelength λ patterns from the
soliton-like internal waves that supply turbulence energy to advected outfall fossils and to the ZTWs they
radiate. The λ = 30-250 m solitons reflect an efficient maser-action conversion of horizontal tidal and current
kinetic energy by bottom boundary layer turbulence events to near-vertical FTWs with λ the Ozmidov scale of
the events at fossilization. Secondary (zombie) turbulence amplifies, channels in chimneys, and near-vertically
beams ambient internal wave energy at scales λ just as energized metastable molecules amplify and beam
quantum wavelengths in astrophysical lasers and masers around stars. Kilowatts of buoyancy power from the
treatment plant produce fossil turbulence patches trapped below the thermocline. Beamed zombie turbulence
maser action (BZTMA) in mixing chimneys amplifies these kilowatts into the megawatts of surface turbulence
dissipation required to affect brightness on wide sea surface areas. The BZTMA vertical mixing mechanism
appears critical to vertical oceanic transport of information, heat, mass and momentum, and to the conversion of
barotropic tides to baroclinic tides.
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Determination of Settling Tanks Performance Using an Eulerian- Lagrangian Method
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Pages :
43-54
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Authors :
A. Tamayol,
B. Firoozabadi,
G. Ahmadi,
Circulation regions always exist in settling tanks. These regions reduce the tank’s performance and decrease its
effective volume. The recirculation zones would result in short-circuiting and high flow mixing problems. The
inlet position would also affect the size and location of the recirculation region. Using a proper baffle
configuration could substantially increase the performance of the settling tanks. A common procedure for the
comparison of the performances of different tanks has been using the Flow Through Curves (FTC) method.
FTC, however, neglects tendencies for particles sedimentation. In this work, a new method for evaluation of the
settling tanks performance is presented. The new method which is referred to as the particle Tracking Method
(PTM) is based on an Eulerian-Lagrangian approach. In this paper, by using FTC and PTM the effects of the
inlet position and the baffle configuration on the hydraulic performance of the primary settling tanks were
studied and results were compared. Then, shortcomings of the FTC approach were stated. The optimal
positioning of the baffles was also determined though a series of computer simulations.
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Effects of Air Entrainment on Fluid Transients in Pumping Systems
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Pages :
55-61
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Authors :
T. S. Lee,
H. T. Low,
D. T. Nguyen,
In pumping installations, fluid transient computations are necessary to achieve safety, efficiency and
economy in design and operation. In some systems, where air content and air entrainment exist, such
computations become highly inaccurate when constant wave speed is assumed. In this paper, a numerical
model and a computational procedure have been developed to investigate the effects of air entrainment on
the pressure transient in pumping systems. Free gas in the fluid and cavitation at the fluid vapour pressure
were modeled in the form of variable wave speed model, which was numerically solved by the method of
characteristics. This model was tested for the case of pump trips due to power failures. The pressure
transient results obtained by this variable wave speed model were analyzed and compared with those results
obtained by constant wave speed model and with the experimental results of other investigators.
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Numerical Modelling of Tracer Transport in Unsaturated Porous Media
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Pages :
62-70
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Authors :
T. Bunsri,
M. Sivakumar,
D. Hagare,
Many types of chemical substances have been used as tracers to estimate the migration of contaminant in a porous media.
Inorganic ionic compounds have been applied extensively as hydrogeologic tracers. Sodium chloride is generally used as a
tracer since this common salt does not degrade or get removed from the system. Movement of tracer could be described as
migration of a non-reactive constituent. A tracer transport numerical model was developed according to the advectivedispersive
contaminant transport equation in unsaturated porous media. The governing equation was solved numerically and
coded in MATLAB program. The objectives of this study were to develop a model for estimating the non-reactive
constituent transport in the unsaturated porous media and to determine the impact of ionic strength of tracer and the effect of
the thickness of porous media. The experiments were conducted with two different sodium chloride tracer concentrations
(low strength-200 mg/L and high strength-500 mg/L) and for two different soil depths (5 and 20 cm). The observation and
simulation data indicate that the interference from soil background concentration is significant, provided that the high
strength tracer is applied. As expected, the tracer transport in the thick layer took longer elapse time than in the thin layer.
The simulation results using the developed model corresponded very well with the observed data.
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Turbulent Separated Flows: Near-Wall Behavior and Heat and Mass Transfer
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Pages :
71-77
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Authors :
A. Gorin,
This paper was presented at the Eleventh Asian Congress of Fluid Mechanics as an invited/keynote lecture. The lecture
summarizes development of physical model for transfer processes in turbulent separated flows. Attention is focused on the
factors that have led to significant advances in understanding of the mechanisms of transfer processes in separated flows,
which differs from those in traditional attached turbulent flows in channels and zero pressure gradient turbulent flows. The
physical model of transfer processes in the near-wall region of turbulent separated and reattached flows based on the
assumption of the governing role of generated local pressure gradient that takes place in the immediate vicinity of the wall in
separated flow as a result of intense instantaneous accelerations induced by large-scale vortex flow structures is discussed.
Similarity laws for mean velocity and temperature profiles and spectral characteristics of the transfer processes resulting in
the physical model are confirmed by the available experimental data. The physical model has provided explanations of the
well-known empirical heat and mass transfer correlations for turbulent separated flows and other types of flows close in their
structure to those of turbulent separated flows.
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Mixed Convection in an Enclosure with Different Inlet and Exit Configurations
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Pages :
78-93
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Authors :
S. Saha,
A. Hasan Mamun,
M. Zakir Hossain,
A. K. M. Sadrul Islam,
A numerical analysis is carried out to study the performance of mixed convection in a rectangular enclosure. Four different
placement configurations of the inlet and outlet openings were considered. A constant flux heat source strip is flush-mounted
on the vertical surface, modeling an integrated circuit chips affixed to a printed circuit board, and the fluid considered is air.
The numerical scheme is based on the finite element method adapted to triangular non-uniform mesh elements by a nonlinear
parametric solution algorithm. Results are obtained for a range of Richardson number from 0 to 10 at Pr = 0.71 and
Re = 100 with constant physical properties. At the outlet of the computational domain a convective boundary condition
(CBC) is used. The results indicate that the average Nusselt number and the dimensionless surface temperature on the heat
source strongly depend on the positioning of the inlet and outlet. The basic nature of the resulting interaction between the
forced external air stream and the buoyancy-driven flow by the heat source is explained by the heat transfer coefficient and
the patterns of the streamlines, velocity vectors and isotherms.
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