Abstract: This paper investigates the aerodynamic characters of a model ducted fan system, analyses the basic principle of the effect of thrust promotion and torque reduction, discovers the relationship between the revolutions per minute(RPM) of the fan and the characters of thrust, as well as system torque. Firstly a model ducted fan has been designed and manufactured according to the specific structure of flow field, then CFD simulation has been carried out to analyze such aerodynamics, finally bench tests have been used to validate the simulation results and system configuration.
Abstract: In this study, direct numerical simulation for the bubble condensation in the subcooled boiling flow was performed. The main goal was to develop the CFD modeling for the bubble condensation and to evaluate the accuracy of the VOF model with the developed CFD modeling. CFD modeling for the bubble condensation was developed by modeling the source terms in the governing equations of VOF model using UDF. In the modeling, the amount of condensation was determined using the interfacial heat transfer coefficient obtained from the bubble velocity, liquid temperature and bubble diameter every time step. To evaluate the VOF model using the CFD modeling for the bubble condensation, CFD simulation results were compared with SNU experimental results such as bubble volume and shape, interfacial area, bubble diameter and bubble velocity. Simulation results predicted well the behavior of the actual condensing bubble. Therefore, it can be concluded that the VOF model using the CFD modeling for the bubble condensation will be a useful computational fluid dynamics tool for analyzing the behavior of the condensing bubble in a wide range of the subcooled boiling flow.
Abstract: An exploratory computational investigation using
RANS & URANS was carried out to understand the aerodynamics
around an isolatedsingle rotating wheel with decreasing ground
proximity. The wheel was initially modeled in free air conditions,
then with decreasing ground proximity and increased yaw angle with
rotational speeds. Three speeds of rotation were applied to the wheel
so that the effect of different angular velocities can be investigated. In
addition to rotation, three different yaw angles were applied to the
rotating wheel in order to understand how these two variables
combined affect the aerodynamic flow field around the wheel.
Abstract: In order to investigate a PROX microreactor
performance, two-dimensional modeling of the reacting flow
between two parallel plates is performed through a finite volume
method using an improved SIMPLE algorithm. A three-step surface
kinetics including hydrogen oxidation, carbon monoxide oxidation
and water-gas shift reaction is applied for a Pt-Fe/γ-Al2O3 catalyst
and operating temperatures of about 100ºC. Flow pattern, pressure
field, temperature distribution, and mole fractions of species are
found in the whole domain for all cases. Also, the required reactive
length for removing carbon monoxide from about 2% to less than 10
ppm is found. Furthermore, effects of hydraulic diameter, wall
temperature, and inlet mole fraction of air and water are investigated
by considering carbon monoxide selectivity and conversion. It is
found that air and water addition may improve the performance of
the microreactor in carbon monoxide removal in such operating
conditions; this is in agreement with the pervious published results.
Abstract: The aim of this work is to investigate on the internalflow
patterns in a plate heat exchanger channel, which affect the
rate of sedimentation fouling on the heat transfer surface of the
plate heat exchanger. The research methodologies were the
computer simulation using Computational Fluid Dynamics (CFD)
and the experimental works. COMSOL MULTIPHYSICS™
Version 3.3 was used to simulate the velocity flow fields to verify
the low and high flow regions. The results from the CFD technique
were then compared with the images obtained from the
experiments in which the fouling test rig was set up with a singlechannel
plate heat exchanger to monitor the fouling of calcium
carbonate. Two parameters were varied i.e., the crossing angle of
the two plate: 55/55, 10/10, and 55/10 degree, and the fluid flow
rate at the inlet: 0.0566, 0.1132 and 0.1698 m/s. The type of plate
“GX-12" (the surface area 0.12 m2, the depth 2.9 mm, the width of
fluid flow 215 mm and the thickness of stainless plate of 0.5 mm)
was used in this study. The results indicated that the velocity
distribution for the case of 55/55 degree seems to be very well
organized when compared with the others. Also, an increase in the
inlet velocity resulted in the reduction of fouling rate on the surface
of plate heat exchangers.
Abstract: This work has been carried out in order to provide an understanding of the physical behaviors of the flow variation of pressure and temperature in a vortex tube. A computational fluid dynamics model is used to predict the flow fields and the associated temperature separation within a Ranque–Hilsch vortex tube. The CFD model is a steady axisymmetric model (with swirl) that utilizes the standard k-ε turbulence model. The second–order numerical schemes, was used to carry out all the computations. Vortex tube with a circumferential inlet stream and an axial (cold) outlet stream and a circumferential (hot) outlet stream was considered. Performance curves (temperature separation versus cold outlet mass fraction) were obtained for a specific vortex tube with a given inlet mass flow rate. Simulations have been carried out for varying amounts of cold outlet mass flow rates. The model results have a good agreement with experimental data.
Abstract: Majority of pepper farmers in Malaysia are using the
open-sun method for drying the pepper berries. This method is time
consuming and exposed the berries to rain and contamination. A
maintenance-friendly and properly enclosed dryer is therefore
desired. A dryer design with a solar collector and a chimney was
studied and adapted to suit the needs of small-scale pepper farmers in
Malaysia. The dryer will provide an environment with an optimum
operating temperature meant for drying pepper berries. The dryer
model was evaluated by using commercially available computational
fluid dynamic (CFD) software in order to understand the heat and
mass transfer inside the dryer. Natural convection was the only mode
of heat transportation considered in this study as in accordance to the
idea of having a simple and maintenance-friendly design. To
accommodate the effect of low buoyancy found in natural convection
driers, a biomass burner was integrated into the solar dryer design.
Abstract: Tread design has evolved over the years to achieve the common tread pattern used in current vehicles. However, to meet safety and comfort requirements, tread design considers more than one design factor. Tread design must consider the grip and drainage, and the manner in which to reduce rolling noise, which is one of the main factors considered by manufacturers. The main objective of this study was the application the computational fluid dynamics (CFD) technique to simulate the contact surface of the tire and ground. The results demonstrated an air-Pumping and large pressure drop effect in the process of contact surface. The results also revealed that the pressure can be used to analyze sound pressure level (SPL).
Abstract: In this work, study the location of interface in a stirred vessel with Rushton impeller by computational fluid dynamic was presented. To modeling rotating the impeller, sliding mesh (SM) technique was used and standard k-ε model was selected for turbulence closure. Mean tangential, radial and axial velocities and also turbulent kinetic energy (k) and turbulent dissipation rate (ε) in various points of tank was investigated. Results show sensitivity of system to location of interface and radius of 7 to 10cm for interface in the vessel with existence characteristics cause to increase the accuracy of simulation.
Abstract: This article discusses stress analysis and the shape characteristics of the inflatable wing, and then introduces the design method of inflatable wing, in order to accurately approximate a standard airfoil. It specifically analyses the aerodynamic characteristics of the inflatable wing with the method of CFD, along with comparing to standard airfoil, afterwards we carries out the manufacture of inflatable wing and the flight test.
Abstract: The purpose of this study was to explore the complex
flow structure a novel active-type micromixer that based on concept of
Wankle-type rotor. The characteristics of this micromixer are two
folds; a rapid mixing of reagents in a limited space due to the
generation of multiple vortices and a graduate increment in dynamic
pressure as the mixed reagents is delivered to the output ports.
Present micro-mixer is consisted of a rotor with shape of triangle
column, a blending chamber and several inlet and outlet ports. The
geometry of blending chamber is designed to make the rotor can be
freely internal rotated with a constant eccentricity ratio. When the
shape of the blending chamber and the rotor are fixed, the effects of
rotating speed of rotor and the relative locations of ports on the mixing
efficiency are numerical studied. The governing equations are
unsteady, two-dimensional incompressible Navier-Stokes equation
and the working fluid is the water. The species concentration equation
is also solved to reveal the mass transfer process of reagents in various
regions then to evaluate the mixing efficiency.
The dynamic mesh technique was implemented to model the
dynamic volume shrinkage and expansion of three individual
sub-regions of blending chamber when the rotor conducted a complete
rotating cycle. Six types of ports configuration on the mixing
efficiency are considered in a range of Reynolds number from 10 to
300. The rapid mixing process was accomplished with the multiple
vortex structures within a tiny space due to the equilibrium of shear
force, viscous force and inertial force. Results showed that the highest
mixing efficiency could be attained in the following conditions: two
inlet and two outlet ports configuration, that is an included angle of 60
degrees between two inlets and an included angle of 120 degrees
between inlet and outlet ports when Re=10.
Abstract: In this work study the location of interface in a stirred vessel with a Concave impeller by computational fluid dynamic was presented. To modeling rotating the impeller, sliding mesh (SM) technique was used and standard k-ε model was selected for turbulence closure. Mean tangential, radial and axial velocities and also turbulent kinetic energy (k) and turbulent dissipation rate (ε) in various points of tank was investigated. Results show sensitivity of system to location of interface and radius of 7 to 10cm for interface in the vessel with existence characteristics cause to increase the accuracy of simulation.
Abstract: This paper presents a numerical analysis of the
performance of a five-bladed Darrieus vertical-axis water turbine,
based on the NACA 0025 blade profile, for both bare and shrouded
configurations. A complete campaign of 2-D simulations, performed
for several values of tip speed ratio and based on RANS unsteady
calculations, has been performed to obtain the rotor torque and power
curves. Also the effect of a NACA-shaped central hydrofoil has been
investigated, with the aim of evaluating the impact of a solid
blockage on the performance of the shrouded rotor configuration.
The beneficial effect of the shroud on rotor overall performances
has clearly been evidenced, while the adoption of the central
hydrofoil has proved to be detrimental, being the resulting flow slow
down (due to the presence of the obstacle) much higher with respect
to the flow acceleration (due to the solid blockage effect).
Abstract: Numerical analysis for the aerodynamic characteristics
of the WIG (wing-in ground effect) craft with highly cambered and
aspect ratio of one is performed to predict the ground effect for the
case of with- and without- lower-extension endplate. The analysis is
included varying angles of attack from 0 to10 deg. and ground
clearances from 5% of chord to 50%. Due to the ground effect, the lift
by rising in pressure on the lower surface is increased and the
influence of wing-tip vortices is decreased. These two significant
effects improve the lift-drag ratio. On the other hand, the endplate
prevents the high-pressure air escaping from the air cushion at the
wing tip and causes to increase the lift and lift-drag ratio further. It is
found from the visualization of computation results that two wing-tip
vortices are generated from each surface of the wing tip and their
strength are weak and diminished rapidly. Irodov-s criteria are also
evaluated to investigate the static height stability. The comparison of
Irodov-s criteria shows that the endplate improves the deviation of the
static height stability with respect to pitch angles and heights. As the
results, the endplate can improve the aerodynamic characteristics and
static height stability of wings in ground effect, simultaneously.
Abstract: Due to the stringent legislation for emission of diesel
engines and also increasing demand on fuel consumption, the
importance of detailed 3D simulation of fuel injection, mixing and
combustion have been increased in the recent years. In the present
work, FIRE code has been used to study the detailed modeling of
spray and mixture formation in a Caterpillar heavy-duty diesel
engine. The paper provides an overview of the submodels
implemented, which account for liquid spray atomization, droplet
secondary break-up, droplet collision, impingement, turbulent
dispersion and evaporation. The simulation was performed from
intake valve closing (IVC) to exhaust valve opening (EVO). The
predicted in-cylinder pressure is validated by comparing with
existing experimental data. A good agreement between the predicted
and experimental values ensures the accuracy of the numerical
predictions collected with the present work. Predictions of engine
emissions were also performed and a good quantitative agreement
between measured and predicted NOx and soot emission data were
obtained with the use of the present Zeldowich mechanism and
Hiroyasu model. In addition, the results reported in this paper
illustrate that the numerical simulation can be one of the most
powerful and beneficial tools for the internal combustion engine
design, optimization and performance analysis.
Abstract: This paper presents a means for reducing the torque
variation during the revolution of a vertical-axis water turbine
(VAWaterT) by increasing the blade number. For this purpose, twodimensional
CFD analyses have been performed on a straight-bladed
Darrieus-type rotor. After describing the computational model and
the relative validation procedure, a complete campaign of
simulations, based on full RANS unsteady calculations, is proposed
for a three, four and five-bladed rotor architectures, characterized by
a NACA 0025 airfoil. For each proposed rotor configuration, flow
field characteristics are investigated at several values of tip speed
ratio, allowing a quantification of the influence of blade number on
flow geometric features and dynamic quantities, such as rotor torque
and power. Finally, torque and power curves are compared for the
three analyzed architectures, achieving a quantification of the effect
of blade number on overall rotor performance.
Abstract: Periodic vortex shedding in pulsating flow inside wavy
channel and the effect it has on heat transfer are studied using the
finite volume method. A sinusoidally-varying component is superimposed
on a uniform flow inside a sinusoidal wavy channel and
the effects on the Nusselt number is analyzed. It was found that a
unique optimum value of the pulsation frequency, represented by the
Strouhal number, exists for Reynolds numbers ranging from 125 to
1000. Results suggest that the gain in heat transfer is related to the
process of vortex formation, movement about the troughs of the wavy
channel, and subsequent ejection/destruction through the converging
section. Heat transfer is the highest when the frequencies of the
pulsation and vortex formation approach being in-phase. Analysis of
Strouhal number effect on Nu over a period of pulsation substantiates
the proposed physical mechanism for enhancement. The effect of
changing the amplitude of pulsation is also presented over a period
of pulsation, showing a monotonic increase in heat transfer with
increasing amplitude. The 60% increase in Nusselt number suggests
that sinusoidal fluid pulsation can an effective method for enhancing
heat transfer in laminar, wavy-channel flows.
Abstract: In this paper, computational fluid dynamics (CFD) is utilized to characterize a prototype biolistic delivery system, the biomedical device based on the contoured-shock-tube design (CST), with the aim at investigating shocks induced flow instabilities within the contoured shock tube. The shock/interface interactions, the growth of perturbation at an interface between two fluids of different density are interrogated. The key features of the gas dynamics and gas-particle interaction are discussed
Abstract: Considering non-ideal behavior of fluids and its effects on hydrodynamic and mass transfer in multiphase flow is very essential. Simulations were performed that takes into account the effects of mass transfer and mixture non-ideality on hydrodynamics reported by Irani et al. In this paper, by assuming the density of phases to be constant and Raullt-s law instead of using EOS and fugacity coefficient definition, respectively for both the liquid and gas phases, the importance of non-ideality effects on mass transfer and hydrodynamic behavior was studied. The results for a system of octane/propane (T=323 K, P =445 kpa) also indicated that the assumption of constant density in simulation had major role to diverse from experimental data. Furthermore, comparison between obtained results and the previous report indicated significant differences between experimental data and simulation results with more ideal assumptions.
Abstract: In the present work flow past circular cylinder and
cylinder with rectangular and triangular wake splitter is studied to
improve aerodynamic parameters. The Comparison of drag
coefficient is tabulated for bare cylinder, cylinder with rectangular
and triangular wake splitters. Flow past circular cylinder and cylinder
with triangular and rectangular wake splitter is performed at
Reynoldsnumber 5, 20, 40, 50,80, 100.An incompressible PISO finite
volume code employing a non-staggered grid arrangement is used, a
second order upwind scheme is used for convective terms. The time
discretization is implicit and a Second order Crank-Nicholson scheme
is employed. Length of wake splitter in both configurations is taken
to be equal to diameter of cylinder. Wake length is found to be less
with rectangular wake splitter when compared to bare cylinder and
cylinder with triangular wake splitter. Coefficient of drag is found to
be less for triangular wake splitter when compared to bare cylinder &
cylinder with rectangular wake splitter.