Abstract: In this study, a 3D combustion chamber was simulated
using FLUENT 6.32. Aims to obtain accurate information about the
profile of the combustion in the furnace and also check the effect of
oxygen enrichment on the combustion process. Oxygen enrichment is
an effective way to reduce combustion pollutant. The flow rate of air
to fuel ratio is varied as 1.3, 3.2 and 5.1 and the oxygen enriched
flow rates are 28, 54 and 68 lit/min. Combustion simulations
typically involve the solution of the turbulent flows with heat
transfer, species transport and chemical reactions. It is common to
use the Reynolds-averaged form of the governing equation in
conjunction with a suitable turbulence model. The 3D Reynolds
Averaged Navier Stokes (RANS) equations with standard k-ε
turbulence model are solved together by Fluent 6.3 software. First
order upwind scheme is used to model governing equations and the
SIMPLE algorithm is used as pressure velocity coupling. Species
mass fractions at the wall are assumed to have zero normal
gradients.Results show that minimum mole fraction of CO2 happens
when the flow rate ratio of air to fuel is 5.1. Additionally, in a fixed
oxygen enrichment condition, increasing the air to fuel ratio will
increase the temperature peak. As a result, oxygen-enrichment can
reduce the CO2 emission at this kind of furnace in high air to fuel
rates.
Abstract: Understanding of how and where NOx formation
occurs in industrial burner is very important for efficient and clean
operation of utility burners. Also the importance of this problem is
mainly due to its relation to the pollutants produced by more burners
used widely of gas turbine in thermal power plants and glass and steel
industry.
In this article, a numerical model of an industrial burner operating
in MILD combustion is validated with experimental data.. Then
influence of air flow rate and air temperature on combustor
temperature profiles and NOX product are investigated. In order to
modification this study reports on the effects of fuel and air dilution
(with inert gases H2O, CO2, N2), and also influence of lean-premixed
of fuel, on the temperature profiles and NOX emission.
Conservation equations of mass, momentum and energy, and
transport equations of species concentrations, turbulence, combustion
and radiation modeling in addition to NO modeling equations were
solved together to present temperature and NO distribution inside the
burner.
The results shows that dilution, cause to a reduction in value of
temperature and NOX emission, and suppresses any flame
propagation inside the furnace and made the flame inside the furnace
invisible. Dilution with H2O rather than N2 and CO2 decreases further
the value of the NOX. Also with raise of lean-premix level, local
temperature of burner and the value of NOX product are decreases
because of premixing prevents local “hot spots" within the combustor
volume that can lead to significant NOx formation. Also leanpremixing
of fuel with air cause to amount of air in reaction zone is
reach more than amount that supplied as is actually needed to burn
the fuel and this act lead to limiting NOx formation
Abstract: This paper presents a numerical investigation of the
unsteady flow around an American 19th century vertical-axis
windmill: the Stevens & Jolly rotor, patented on April 16, 1895. The
computational approach used is based on solving the complete
transient Reynolds-Averaged Navier-Stokes (t-RANS) equations: a
full campaign of numerical simulation has been performed using the
k-ω SST turbulence model. Flow field characteristics have been
investigated for several values of tip speed ratio and for a constant
unperturbed free-stream wind velocity of 6 m/s, enabling the study of
some unsteady flow phenomena in the rotor wake. Finally, the global
power generated from the windmill has been determined for each
simulated angular velocity, allowing the calculation of the rotor
power-curve.
Abstract: The process for predicting the ballistic properties of a liquid rocket engine is based on the quantitative estimation of idealized performance deviations. In this aim, an equilibrium chemistry procedure is firstly developed and implemented in a Fortran routine. The thermodynamic formulation allows for the calculation of the theoretical performances of a rocket thrust chamber. In a second step, a computational fluid dynamic analysis of the turbulent reactive flow within the chamber is performed using a finite volume approach. The obtained values for the “quasi-real" performances account for both turbulent mixing and chemistryturbulence coupling. In the present work, emphasis is made on the combustion efficiency performance for which deviation is mainly due to radial gradients of static temperature and mixture ratio. Numerical values of the characteristic velocity are successfully compared with results from an industry-used code. The results are also confronted with the experimental data of a laboratory-scale rocket engine.
Abstract: Effective cooling of electronic equipment has emerged
as a challenging and constraining problem of the new century. In the
present work the feasibility and effectiveness of jet impingement
cooling on electronics were investigated numerically and
experimentally. Studies have been conducted to see the effect of the
geometrical parameters such as jet diameter (D), jet to target
spacing (Z) and ratio of jet spacing to jet diameter (Z/D) on the heat
transfer characteristics. The values of Reynolds numbers considered
are in the range 7000 to 42000. The results obtained from the
numerical studies are validated by conducting experiments. From the
studies it is found that the optimum value of Z/D ratio is 5. For a
given Reynolds number, the Nusselt number increases by about 28%
if the diameter of the nozzle is increased from 1mm to 2mm.
Correlations are proposed for Nusselt number in terms of Reynolds
number and these are valid for air as the cooling medium.
Abstract: This paper investigates experimental and numerical study of the airflow characteristics for vortex, round and square ceiling diffusers and its effect on the thermal comfort in a ventilated room. Three different thermal comfort criteria namely; Mean Age of the Air (MAA), ventilation effectiveness (E), and Effective Draft Temperature (EDT) have been used to predict the thermal comfort zone inside the room. In experimental work, a sub-scale room is set-up to measure the temperature field in the room. In numerical analysis, unstructured grids have been used to discretize the numerical domain. Conservation equations are solved using FLUENT commercial flow solver. The code is validated by comparing the numerical results obtained from three different turbulence models with the available experimental data. The comparison between the various numerical models shows that the standard k-ε turbulence model can be used to simulate these cases successfully. After validation of the code, effect of supply air velocity on the flow and thermal field could be investigated and hence the thermal comfort. The results show that the pressure coefficient created by the square diffuser is 1.5 times greater than that created by the vortex diffuser. The velocity decay coefficient is nearly the same for square and round diffusers and is 2.6 times greater than that for the vortex diffuser.
Abstract: This study presents the numerical simulation of
optimum pin-fin heat sink with air impinging cooling by using
Taguchi method. 9 L ( 4 3 ) orthogonal array is selected as a plan for
the four design-parameters with three levels. The governing
equations are discretized by using the
control-volume-based-finite-difference method with a power-law
scheme on the non-uniform staggered grid. We solved the coupling of
the velocity and the pressure terms of momentum equations using
SIMPLEC algorithm. We employ the k −ε two-equations
turbulence model to describe the turbulent behavior. The parameters
studied include fin height H (35mm-45mm), inter-fin spacing a , b ,
and c (2 mm-6.4 mm), and Reynolds number ( Re = 10000- 25000).
The objective of this study is to examine the effects of the fin
spacings and fin height on the thermal resistance and to find the
optimum group by using the Taguchi method. We found that the fin
spacings from the center to the edge of the heat sink gradually
extended, and the longer the fin’s height the better the results. The
optimum group is 3 1 2 3 H a b c . In addition, the effects of parameters are
ranked by importance as a , H , c , and b .
Abstract: The objective of this study is to investigate fire
behaviors, experimentally and numerically, in a scaled version of an
underground station. The effect of ventilation velocity on the fire is
examined. Fire experiments are simulated by burning 10 ml
isopropyl alcohol fuel in a fire pool with dimensions 5cm x 10cm x 4
mm at the center of 1/100 scaled underground station model. A
commercial CFD program FLUENT was used in numerical
simulations. For air flow simulations, k-ω SST turbulence model and
for combustion simulation, non-premixed combustion model are
used. This study showed that, the ventilation velocity is increased
from 1 m/s to 3 m/s the maximum temperature in the station is found
to be less for ventilation velocity of 1 m/s. The reason for these
experimental result lies on the relative dominance of oxygen supply
effect on cooling effect. Without piston effect, maximum temperature
occurs above the fuel pool. However, when the ventilation velocity
increased the flame was tilted in the direction of ventilation and the
location of maximum temperature moves along the flow direction.
The velocities measured experimentally in the station at different
locations are well matched by the CFD simulation results. The
prediction of general flow pattern is satisfactory with the smoke
visualization tests. The backlayering in velocity is well predicted by
CFD simulation. However, all over the station, the CFD simulations
predicted higher temperatures compared to experimental
measurements.
Abstract: The present paper develops and validates a numerical procedure for the calculation of turbulent combustive flow in converging and diverging ducts and throuh simulation of the heat transfer processes, the amount of production and spread of Nox pollutant has been measured. A marching integration solution procedure employing the TDMA is used to solve the discretized equations. The turbulence model is the Prandtl Mixing Length method. Modeling the combustion process is done by the use of Arrhenius and Eddy Dissipation method. Thermal mechanism has been utilized for modeling the process of forming the nitrogen oxides. Finite difference method and Genmix numerical code are used for numerical solution of equations. Our results indicate the important influence of the limiting diverging angle of diffuser on the coefficient of recovering of pressure. Moreover, due to the intense dependence of Nox pollutant to the maximum temperature in the domain with this feature, the Nox pollutant amount is also in maximum level.
Abstract: This is the second part of the paper. It, aside from the
core subroutine test reported previously, focuses on the simulation of
turbulence governed by the full STF Navier-Stokes equations on a
large scale. Law of the wall is found plausible in this study as a model
of the boundary layer dynamics. Model validations proceed to
include velocity profiles of a stationary turbulent Couette flow, pure
sloshing flow simulations, and the identification of water-surface
inclination due to fluid accelerations. Errors resulting from the
irrotational and hydrostatic assumptions are explored when studying
a wind-driven water circulation with no shakings. Illustrative
examples show that this numerical strategy works for the simulation
of sloshing-shear mixed flow in a 3-D rigid rectangular base tank.
Abstract: In the present paper, a numerical investigation has
been carried out to classify and clarify the effects of paramount
parameters on turbulent impinging slot jets. The effects of nozzle-s
exit turbulent intensity, distance between nozzle and impinging plate
are studied at Reynolds number 5000 and 20000. In addition, the
effect of Mach number that is varied between 0.3-0.8 at a constant
Reynolds number 133000 is investigated to elucidate the effect of
compressibility in impinging jet upon a flat plate. The wall that is
located at the same level with nozzle-s exit confines the flow. A
compressible finite volume solver is implemented for simulation the
flow behavior. One equation Spalart-Allmaras turbulent model is
used to simulate turbulent flow at this study. Assessment of the
Spalart-Allmaras turbulent model at high nozzle to plate distance,
and giving enough insights to characterize the effect of Mach number
at high Reynolds number for the complex impinging jet flow are the
remarkable results of this study.
Abstract: This paper examines the depiction of Muslim militants in Thai newspapers in 2004. Stuart Hall-s “representation" and “public idioms" are used as theoretical frameworks. Critical Discourse Analysis is employed as a methodology to examine 240 news articles from two leading Thai language newspapers. The results show that the militants are usually labeled as “southern bandits." This suggests that they are just a culprit of the violence in the deep south of Thailand. They are usually described as people who cause turbulence. Consequently, the military have to get rid of them. However, other aspects of the groups such as their political agenda or the failures of the Thai state in dealing with the Malay Muslims were not mention in the news stories. In the time of violence, the researcher argues that this kind of newspaper coverage may help perpetuate the discourse of Malay Muslim, instead of providing fuller picture of the ongoing conflicts.
Abstract: Dense slurry flow through centrifugal pump casing
has been modeled using the Eulerian-Eulerian approach with
Eulerian multiphase model in FLUENT 6.1®. First order upwinding
is considered for the discretization of momentum, k and ε terms.
SIMPLE algorithm has been applied for dealing with pressurevelocity
coupling. A mixture property based k-ε turbulence model
has been used for modeling turbulence. Results are validated first
against mesh independence and experiments for a particular set of
operational and geometric conditions. Parametric analysis is then
performed to determine the effect on important physical quantities
viz. solid velocities, solid concentration and solid stresses near the
wall with various operational geometric conditions of the pump.
Abstract: The present study is concerned with the effect of
exciting boundary layer on cooling process in a gas-turbine blades.
The cooling process is numerically investigated. Observations show
cooling the first row of moving or stable blades leads to increase
their life-time. Results show that minimum temperature in cooling
line with exciting boundary layer is lower than without exciting.
Using block in cooling line of turbines' blade causes flow pattern and
stability in boundary layer changed that causes increase in heat
transfer coefficient. Results show at the location of block,
temperature of turbines' blade is significantly decreased. The k-ε
turbulence model is used.
Abstract: The present work compares the performance of three
turbulence modeling approach (based on the two-equation k -ε
model) in predicting erosive wear in multi-size dense slurry flow
through rotating channel. All three turbulence models include
rotation modification to the production term in the turbulent kineticenergy
equation. The two-phase flow field obtained numerically
using Galerkin finite element methodology relates the local flow
velocity and concentration to the wear rate via a suitable wear model.
The wear models for both sliding wear and impact wear mechanisms
account for the particle size dependence. Results of predicted wear
rates using the three turbulence models are compared for a large
number of cases spanning such operating parameters as rotation rate,
solids concentration, flow rate, particle size distribution and so forth.
The root-mean-square error between FE-generated data and the
correlation between maximum wear rate and the operating
parameters is found less than 2.5% for all the three models.
Abstract: Today-s manufacturing companies are facing multiple and dynamic customer-supplier-relationships embedded in nonhierarchical production networks. This complex environment leads to problems with delivery reliability and wasteful turbulences throughout the entire network. This paper describes an operational model based on a theoretical framework which improves delivery reliability of each individual customer-supplier-relationship within non-hierarchical production networks of the European machinery and equipment industry. By developing a non-centralized coordination mechanism based on determining the value of delivery reliability and derivation of an incentive system for suppliers the number of in time deliveries can be increased and thus the turbulences in the production network smoothened. Comparable to an electronic stock exchange the coordination mechanism will transform the manual and nontransparent process of determining penalties for delivery delays into an automated and transparent market mechanism creating delivery reliability.
Abstract: The objective of this work is to show a procedure for
mesh generation in a fluidized bed using large eddy simulations
(LES) of a filtered two-fluid model. The experimental data were
obtained by [1] in a laboratory fluidized bed. Results show that it is
possible to use mesh with less cells as compared to RANS turbulence
model with granular kinetic theory flow (KTGF). Also, the numerical
results validate the experimental data near wall of the bed, which
cannot be predicted by RANS.model.
Abstract: This paper presents a CFD analysis of the flow field
around a thin flat plate of infinite span inclined at 90° to a fluid
stream of infinite extent. Numerical predictions have been compared
to experimental measurements, in order to assess the potential of the
finite volume code of determining the aerodynamic forces acting on a
bluff body invested by a fluid stream of infinite extent.
Several turbulence models and spatial node distributions have
been tested. Flow field characteristics in the neighborhood of the flat
plate have been investigated, allowing the development of a
preliminary procedure to be used as guidance in selecting the
appropriate grid configuration and the corresponding turbulence
model for the prediction of the flow field over a two-dimensional
vertical flat plate.
Abstract: Turbulence modeling of large-scale flow over a vegetated surface is complex. Such problems involve large scale computational domains, while the characteristics of flow near the surface are also involved. In modeling large scale flow, surface roughness including vegetation is generally taken into account by mean of roughness parameters in the modified law of the wall. However, the turbulence structure within the canopy region cannot be captured with this method, another method which applies source/sink terms to model plant drag can be used. These models have been developed and tested intensively but with a simple surface geometry. This paper aims to compare the use of roughness parameter, and additional source/sink terms in modeling the effect of plant drag on wind flow over a complex vegetated surface. The RNG k-ε turbulence model with the non-equilibrium wall function was tested with both cases. In addition, the k-ω turbulence model, which is claimed to be computationally stable, was also investigated with the source/sink terms. All numerical results were compared to the experimental results obtained at the study site Mason Bay, Stewart Island, New Zealand. In the near-surface region, it is found that the results obtained by using the source/sink term are more accurate than those using roughness parameters. The k-ω turbulence model with source/sink term is more appropriate as it is more accurate and more computationally stable than the RNG k-ε turbulence model. At higher region, there is no significant difference amongst the results obtained from all simulations.
Abstract: This research paper presents the CFD analysis of
oscillating airfoil during pitch cycle. Unsteady subsonic flow is
simulated for pitching airfoil at Mach number 0.283 and Reynolds
number 3.45 millions. Turbulent effects are also considered for this
study by using K-ω SST turbulent model. Two-dimensional unsteady
compressible Navier-Stokes code including two-equation turbulence
model and PISO pressure velocity coupling is used. Pressure based
implicit solver with first order implicit unsteady formulation is used.
The simulated pitch cycle results are compared with the available
experimental data. The results have a good agreement with the
experimental data. Aerodynamic characteristics during pitch cycles
have been studied and validated.