• 한국항공우주학회지
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• 제30권6호
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• pp.53-60
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• 2002

단일 분사 노즐을 갖는 연소기 내부의 혼합과정에 대한 이해를 바탕으로 연료 분사 노즐을 이중으로 갖는 연소기의 혼합과정에 대한 수치연구를 수행하였다. 수치연구를 위하여 3차원 Navier-Stokes 방정식과 k-$\omega$ SST난류 모델을 이용하여 연료 이중 분사 유동을 모사하였다. 이중 분사구 사이의 거리 변화에 따른 혼합특성의 변화를 살펴보기 위하여 파라메터 연구를 수행하였다. 연료 이중 수직분사에서 두 분사기의 유동 및 혼합특성은 서로 상당히 다른 경향을 보이며, 후방 분사기의 유동 및 혼합특성은 전방 분사류의 영향을 받아 더 크게 팽창하고 침투거리가 증가하는 것으로 나타났다. 어떤 특정 거리가 되기 전까지 분사기 사이의 거리가 증가할수록 전체적인 혼합률과 침투거리가 증가하는 등 혼합특성이 개선되지만, 특정 거리보다 크게되면 오히려 혼합특성이 악화되는 것으로 나타났다. 이는 이중분사기에서 최적인 혼합특성을 위한 두 분사기 사이의 거리가 존재함을 의미하는 것으로 판단된다.

• 천문학회보
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• 제36권2호
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• pp.103.1-103.1
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• 2011

Recent observations by Hinode show weakly-attenuated coronal loop oscillations in the presence of background flow (Ofman & Wang 2008, A&A, 482, L9). We study the vertical kink oscillations in solar coronal loops, considering field aligned flows inside the loops as well as surrounding the loops environment. The two dimensional numerical model of straight slab is used to explore the excitation and attenuation of the impulsively triggered fast magnetosonic standing kink waves. A full set of time dependent ideal magnetohydrodynamics equations is solved numerically taking into account the value of flow of the order of observed flows detected by SOT/Hinode. We find that relaxing the assumption of the limited flows within the loops enhances the damping rate of the fundamental mode of the standing kink waves by 2 - 3 % as compared to flow pattern which is basically localized within the loops. We further notice that extending the flow pattern beyond the loop thickness also enhances the strength of the shock associated with slow magnetoacoustic waves, recognized as an addition feature detected in the numerical simulation. The wider out-flow pattern destroys the oscillation patterns early as compared to narrower flow pattern, in other words we can say that it affects the durability of the oscillation. However, for the typical coronal loops parameters we find that the observed durability periods of the SOT/Hinode observation can be achieved with an out-flow Gaussian patterns for which half-width is not greater than factor 2.0 of the loop-half-width. explain a possible relation between electric current structure and sigmoid observed in a preflare phase.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2018년도 학술발표회
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• pp.325-325
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• 2018

The main purpose of this study is to suggest the more reliable flow direction methods within the framework of DEM by investigating the existing methodologies. To this end SFD(single flow direction method), MFD(multiple flow direction method) and IFD(Infinite flow direction method) are applied to determination of flow direction for water particles in Jeonjeokbigyo basin, and then assessed with respect to the variation of flow accumulation. As the main results the different patterns of flow accumulation are found out from each application of flow direction methods. As the flow dispersion increases on DEM contributing areas to outlet grow in sequence of SFD, IFD, MFD but contribution of individual pixels into outlet decreases. Especially MFD and IFD tend to make additional hydrologic abstraction from rainfall excess due to the flow dispersion within flow paths on DEM. Based on parameter estimation for power law distribution by maximum likelihood flow accumulation can be thought of as scale invariance factor. Combination of several flow direction methods could give rise to the more realistic water flow on DEM through separate treatment of flow direction methods for dispersion and aggregation effects of water flow within different topographies.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3197-3202
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• 2007

An analysis program for pedestrian flow has been developed to investigate the flow patterns of passenger in railway stations. Analysis algorithms for pedestrian flow based on DEM(Discrete Element Method) are newly developed. There are lots of similarity between particle-laden two phase flow and passenger flow. The velocity component of 1st phase corresponds to the unit vector of calculation cell, each particle to passenger, volume fraction to population density and the particle velocity to the walking velocity, etc. And, the walking velocity of passenger is also represented by the function of population density. Key algorithms are developed to determine the position of passenger, population density and numbering to each passenger. By using the developed program, we compared the simulation results of the effects of the location and size of exit and elapsed time.

• 한국해양공학회지
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• 제15권3호
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• pp.35-42
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• 2001

The characteristics of tidal circulation with the flow-control structures using the three-dimensional numerical model (POM, Princeton Ocean Model) of Chinhae Bay, Korea were investigated. To confirm th efficiencies of flow-control structures, the training wall and submerged training wall were constructed at the mouth and narrow channel in Chinhae Bay. On the basis of the present investigation, the tidal circulation induced by the construction of flow-control structures could enhance the water exchange improvement appropriately. And, th training wall at the central is more dominated than the other structures for the efficient of water exchange. The sites and types of structure and flow patterns seem to be very sensitive in tidal simulation and changes in flow fields.

• 한국유체기계학회 논문집
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• 제2권3호
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• pp.37-44
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• 1999

In a screw-type centrifugal pump, the pump head deteriorates from single-phase flow to the choke due to an increased air entrainment at a wide tip clearance compared to that of a narrow tip clearance. Moreover, at a narrow tip clearance, the pump head became partially higher in a two-phase flow than that of a single-phase flow near the best efficiency point in low void fraction region. Therefore, we observed the internal flow pattern by using a stroboscope and we measured the mean size of bubbles from the images obtained with a high speed camera. Then, we investigated the influences of the mean size of bubbles, tip clearances and flow patterns on pump performance.

• 한국유체기계학회 논문집
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• 제3권1호
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• pp.28-36
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• 2000

For the improvement of the pump characteristics in the partial capacity range, it must be verified that the influence of the impeller design factor on the internal flows and the influence of the impeller internal flows on the pump characteristics. In this paper, in order to understand the influence of outlet angles on flow conditions and characteristics of a mixed flow pump, experiments were carried out for four kinds of impeller, which have the same inlet angle distributions and meridional section shapes. Results shown that separation and stall in the partial capacity range were enlarged by the outlet angles. The relationship between the separation and the stall at the impeller and the discharge flow conditions were clarified.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.374-377
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• 2009

The operating temperature of Proton Exchange Membrane Fuel Cell (PEMFC) usually has to be limited under $100^{\circ}C$ to maintain the proper ionic conductivity. Therefore, the only product from reaction, water, is in the liquid phase. Two-phase flow makes the flow phenomenon in the channel difficult to understand and predict. Water blocking in the PEMFC channel or the pore of Gas Diffusion Layer (GDL), called flooding, is known as the main effect of PEMFC degradation. To analyze two-phase flow, the PEMFC with transparent acrylic plate was used. Two-phase flow patterns were observed by varying the current density. When the PEMFC is mounted horizontally, water in the cathode is mainly transported on the interface between the channel and GDL.

• 한국자동차공학회논문집
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• 제9권3호
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• pp.1-8
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• 2001

The flow field inside a cylinder of four-valve Sl engine was investigated quantitatively using a three-dimensional Laser Doppler Velocimetry system, to determine how stroke changes affect the flow field. The purpose of this work was to develop quantitative methods which correlate in-cylinder flows to engine performance. For this study, the sane intake manifold, engine head, cylinder, and the piston were used to examine the flow characteristics in different strokes. Quantification of the flow field was done by calculating three major parameters which are believed to adequately characterize in cylinder motion. These quantities were TKE, tumble and swirl ratios. The LDV results reveal that flow patterns are similar, the flow velocities scale with piston speed but another parameters such as TKE, and tumble and swirl numbers are not the same for different stroke systems.

• 한국유체기계학회 논문집
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• 제10권4호
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• pp.47-54
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• 2007

Simultaneous 3-D LDV measurements of the in-cylinder flows of three different engine setups were summarized for the quantification of the flow characteristics in each vertical or horizontal plane, and in entire cylinder volume. The ensemble averaged-velocity, tumble and swirl motions, and turbulent kinetic energy during the intake and compression strokes were examined from the measured velocity data (approximately 2,000 points for each engine setup). The better spatial resolution of the 3-D LDV allows measurements of the instantaneous flow structures, yielding more valuable information about the smaller flow structures and the cycle-to-cycle variation of these flow patterns. Tumble and swirl ratios, and turbulent kinetic energy were quantified as planar and volumetric quantities. The measurements and calculation results were animated for the visualization of the flow, and hence ease to analysis.