• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.2
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• pp.195-203
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• 2000

The local heat/mass transfer coefficients for arrays of impinging circular air jets on a plane surface are determined by means of the naphthalene sublimation method. Fluid from the spent jets is constrained to flow out of the system in one direction. Therefore, the spent fluid makes a crossflow in the confined space. The present study investigates effects of jet-orifice-plate to impingement-surface spacing and jet Reynolds number. The spanwise- and overall-averaged heat/mass transfer coefficients are obtained by numerical integrating the local heat transfer coefficients. The local maximum heat/mass transfer coefficients move further in the downstream direction due to the increase of crossflow velocity. At the mid-way between adjacent jets, the heat/mass transfer coefficients have a small peak owing to the collision of the adjacent wall jets and are affected strongly by the crossflow. The effect of the crossflow occurs strongly at the small orifice-to-impingement surface distance.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.113-118
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• 2004

This paper presents a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method (FDLBM). We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing the conventional FDLBM, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of $\alpha=23^0$. At a stand-off distance $\omega$, the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and th propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips. The lattice BGK model for compressible fluids is shown to be one of powerful tool for computing sound generation and propagation for a wide range of flows.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.209-212
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• 2006

Insect and birds in nature flap their wings to generate fluid dynamic forces that are required for the locomotion. Most of the previous published papers discussed mainly on the effect of flapping parameters such as flapping frequency and amplitude on the thrust at a fixed Reynolds number. However, it is not much known on the values of the flapping parameters that the flapping wing requires to generate the thrust at the low Reynolds number flow. In this paper, the onset of the thrust generation is investigated using the lattice Boltzmann method. The wake patterns and velocity profiles behind a flat plate in heaving oscillation are investigated for the heaving amplitude of 0.5C. The time-averaged thrust coefficient value is investigated by changing the reduced frequency from 0.125 to 3.0 for three values of heaving amplitude (h/C=0.25, 0.325, 0.50). It is also found that the critical Strouhal number over which the flat plate starts to produce the thrust is around 0.1 and the thrust is an exponential function of the Strouhal number.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.208-214
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• 2008

The equilibrium molecular-dynamic simulations have been performed to estimate the properties of the three kinds of fluids (the Lennard-Jones fluid, water and aqueous sodium-chloride solution) confined between two plates that are separated by 1.086 nm; included in the equilibrium properties are the density distribution and the static structure, and the diffusivity in the dynamic property. Three kinds of fluids considered in this study are. The water molecules are modeled by using the SPC/E model and the ions by the charged Lennard-Jones particle model. To treat the water molecules, we combined the quaternion coordinates with Euler angles. We also proposed a plausible algorithm to assign the initial position and direction of molecules. The influence of polarization of water molecules as well as the presence of ions in the solution on the properties will be addressed in this study. In addition, we performed the non-equilibrium molecular-dynamic simulation to compute the flow velocity for the case with the gravitational force acting on molecules.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.208-214
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• 2008

The equilibrium molecular-dynamic simulations have been performed to estimate the properties of the three kinds of fluids (the Lennard-Jones fluid, water and aqueous sodium-chloride solution) confined between two plates that are separated by 1.086 nm; included in the equilibrium properties are the density distribution and the static structure, and the diffusivity in the dynamic property. Three kinds of fluids considered in this study are. The water molecules are modeled by using the SPC/E model and the ions by the charged Lennard-Jones particle model. To treat the water molecules, we combined the quaternion coordinates with Euler angles. We also proposed a plausible algorithm to assign the initial position and direction of molecules. The influence of polarization of water molecules as well as the presence of ions in the solution on the properties will be addressed in this study. In addition, we performed the non-equilibrium molecular-dynamic simulation to compute the flow velocity for the case with the gravitational force acting on molecules.

• Journal of computational fluids engineering
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• v.14 no.3
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• pp.56-62
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• 2009

In this study, the heat transfer and flow field of a condenser used for a Kim-chi refrigerator is analysed with numerical method. Main objective is to present the basic data for designing a new condenser model with improvement of heat transfer performance. For CFD analysis, a commercial code, STAR CCM+ was used. The water was used for the inner working fluid and the air was used for the outer fluid. The condenser type used in this study is a flat plate fin-and-tube heat exchanger. As analysis parameters, the effect of condenser geometry and air velocity was investigated. For validation of the numerical calculations, the results were compared with the experimental ones. The heat transfer rates for both results were consistent with each other by maximum 5 % error. Based on this comparison, the numerical analysis was done with some modifications. As a result, it has been observed that there is a suitable fin pitch with which heat transfer performance of condenser is maximized.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.2-5
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• 2008

This study describes the numerical simulation of three-dimensional droplet formation and the following motion in a cross-junction microchannel by using the Lattice Boltzmann Method (LBM). Our aim is to develop the three-dimensional binary fluids model, consisting of two sets of distribution functions to represent the total fluid density and the density difference, which introduces the repulsive interaction consistent with a free-energy function between two fluids. We validated the LBM code with the velocity profile in a 3-dimensional rectangular channel. Then, we applied our code to the numerical simulation of a binary fluid flow in a cross-junction channel focusing on the investigation of the droplet formulation. Due to the pressure and interfacial-tension effect, one component of the fluids which is injected from one inlet is cut off into many droplets periodically by the other component which is injected from the other inlets. We considered the effect of the boundary conditions for density difference (order parameter) on the wetting of the droplet to the side walls.

• The KSFM Journal of Fluid Machinery
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• v.8 no.4 s.31
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• pp.20-26
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• 2005

When the pumps are started or stopped for the operation or tripped due to the power failure, the hydraulic transients occur as a result of the sudden change in velocity. The field tests on the waterhammer were carried out for Pangyo booster pumping station in which had six booster pumps and two in-line pumps with the motor of output 1,700 kW, respectively. The booster pumping station was equipped with the pump control valve as the main surge suppression device, and the surge relief valve as auxiliary one. But the pump control valve had not early controlled in the planned closing mode, the slamming occurred to the valve of which abruptly closed during the large reverse flow. Because the positive pressure wave caused by the pump failure was superposed on the slam surge, the upsurge increased so extremely that the pump control valve was damaged. After the air chambers were additionally installed in the booster pumping station, it was preyed that the water supply system acquire the safety and reliability on the pressure surge.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.2
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• pp.190-196
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• 2014

Exhaust system by reinforcement of environment regulation came to the foe study necessity. And Exhaust system has necessary to increase the engine performance and silence. From this cause, Automobile has significantly considered production expense. this study makes process for checking the characteristics about Exhaust variable valve within muffler. Variable valve might reduce the baffle within muffler, It was possible to remove the front muffler. Therefor, To miniaturize a size of muffler might be increased by performance through cost-cutting effect and controling of back pressure. Because the Study on Variable valve installed within muffler, to measure the real data was hardly resulted one of the assignments. From manufactured conduct device, might measure data one of piece which was up-graded of problem. Considering to these point, stressed pressure distribution has analyzed on cross section, floating characteristics about velocity distribution around variable valve using analysis as computational fluid dynamics of Ansys with completed measurement data.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.341-349
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• 2001

Heat distortion of the non-contacting mechanical face seal is affected by friction heat between primary seal and seal sheet. The fluid or gas in mechanical face seal maintains operating gap, cooling friction heat and lubricates at the face of seal. So we designed face of seal for inclined face. inclined face of seal improves fluid or gas flow at the face of seal and it increases circumferential velocity at outer radius of the seal so temperature of the seal is decreased by low heat transfer coefficient at there. In this paper, inclined face seal are analysed numerically using finite element method for proof improve inclined face seal performance. Angle of the incline face used for FEA is from 50$^{\circ}$to 90$^{\circ}$and for explaining the effects of inclined face in seal, we get temperature, face distortion, and stress in the seal with variable operating gap and rotating speeds. Result of analysis shows that angle of the incline face is 60$^{\circ}$come to good thermal distortion characteristics.