• 한국산학기술학회논문지
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• 제14권1호
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• pp.485-492
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• 2013

일반과 변형구조의 싸이클론에서 입자흐름의 체류시간분포 특성을 통해 선회강도, 난류성 에디, 벽면 바운싱에 의한 고체흐름의 역혼합과 2단 선회류 약화기의 직경이 집진효율에 미치는 영향을 고찰하였다. 변형구조 싸이클론(S = 13, 15cm)에서 플라이애쉬의 집진효율이 일반 싸이클론보다 높게 나타났다. 변형구조의 싸이클론에서 집진효율은 2단 선회류 약화기의 직경(S)이 13cm에서 가장 높게 나타내었다. 글라스비드의 체류시간분포에 대한 분산과 평균 체류시간은 선회강도와 난류성 에디로 인해서 2단 선회류 약화기의 직경이 증가할수록 증가하였다. 변형구조의 싸이클론에서 고체 흐름의 역혼합은 기체 유입속도가 증가할수록 증가하였고 일반 싸이클론보다 높게 나타났다.

• 한국환경과학회지
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• 제15권12호
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• pp.1141-1154
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• 2006

Orographic effect is one of the important factors to induce Local circulations and to make atmospheric turbulence, so it is necessary to use the exact topographic data for prediction of local circulations. In order to clarify the sensitivity of the spatial resolution of topography data, numerical simulations using several topography data with different spatial resolution are carried out under stable and unstable synoptic conditions. The results are as follows: 1) Influence of topographic data resolution on local circulation tends to be stronger at simulation with fine grid than that with coarse grid. 2) The hight of mountains in numerical model become mote reasonable with high resolution topographic data, so the orographic effect is also emphasized and clarified when the topographic data resolution is higher. 2) The higher the topographic resolution is, the stronger the mountain effect is. When used topographic data resolution become fine, topography in numerical model becomes closer to real topography. 3) The topographic effect tends to be stronger when atmospheric stability is strong stable. 4) Although spatial resolution of topographic data is not fundamental factor for dramatic improvement of weather prediction accuracy, some influence on small scale circulation can be recognized, especially in fluid dynamic simulation.

• 한국환경과학회지
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• 제3권3호
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• pp.241-252
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• 1994

Meteorological parameters In the atmospheric boundary layer and the vertical and horizontal dispersion parameters were determined by analyzing the data obtained by the special upper-air observations of one clear day for each season from October 1991 to August 1992. The concentration of the aklospheric pollutants over Taegu was analyzed by using the application of the Gaussian diffusion model. In the diurnal variation of diffusion of atmospheric pollutants, vertical diffusion due to turbulence is active in daytime while horizontal diffusion due to wind is active in nighttime. The mean concentration of pollutants in the side of downwind is higher during the daytime than the nighttime. Thus, the height of the mixed-layer at the nighttime considered as the most important parameter of the mean concentration of pollutants. In the seasonal variation of diffusion of atmospheric pollutants, vertical diffusion due to strong solar radiation is active in summer case day, and horizontal diffusion due to strong wind is active in winter case day. In winter case day, the mean concentration of pollutants in the side of downwind is maximum in the daytime. However, in summer case day, that is maximum in the nighttime.

• 한국환경과학회지
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• 제10권5호
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• pp.337-342
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• 2001

The Rondonia Boundary Layer Experiment (RBLE-II) was conceived to collect data the atmospheric boundary layer over two representative surface in the Amazon region of Brazil; tropical forest and a deforested, pasture area. The present study deals with the observations of atmospheric boundary layer growth and decay. Although the atmospheric boundary layer measurements made in RBLE-II were not made simultaneously over the two different surface types, some insights can be gained from analysing and comparing with their structure. The greater depth of the nocturnal boundary layer at the forest site may be due to influence of mechanical turbulence. The pasture site is aerodynamically smoother and so the downward turbulent diffusion will be much pasture than over the forest. The development of the convective boundary layer is stronger over the pasture than over the forest. The influence of the sensible heat flux is important but may be not enough to explain the difference completely. It seems that energy advection may occur from the wet and colder(forest) to the dry and warmer area(pasture), rapidly breaking up the nocturnal inversion. Such advection can explain the abrupt growth of the convective boundary layer at the pasture site during the early morning.

• 한국대기환경학회지
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• 제23권2호
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• pp.214-224
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• 2007

A three-dimensional computational fluid dynamics (CFD) model with the renormalization group (RNG) $k-{\varepsilon}$ turbulence model is used to examine the effects of difference in building height on flow and pollutant dispersion in asymmetric street canyons. Three numerical experiments with different street canyons formed by two isolated buildings are performed. In the experiment with equal building height, a portal vortex is formed in the street canyon and a typical recirculation zone is formed behind the downwind building. In the experiment with the downwind building being higher than the upwind building, the ambient flow comes into the street canyon at the front of the downwind building and incoming flow diverges strongly in the street canyon. Hence, pollutants released therein are strongly dispersed through the lateral sides of the street canyon. In the experiment with the upwind building being higher than the downwind building, a large recirculation zone is formed behind the upwind building, which is disturbed by the downwind building. Pollutants are weakly dispersed from the street canyon and the residue concentration ratio is largest among the three experiments. This study shows that the difference in upwind and downwind building height significantly influences flow and pollutant dispersion in and around the street canyon.

• 한국환경과학회지
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• 제21권2호
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• pp.145-152
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• 2012

The mean wind speed and turbulence intensity profiles in the atmospheric boundary layer were extracted from a LIDAR remote sensing campaign in order to apply for CFD validation. After considering the semi-steady state field data requirements to be used for CFD validation, a neutral atmosphere campaign period, in which the main wind direction and the power-law exponent of the wind profile were constantly maintained, was chosen. The campaign site at the Pohang Accelerator Laboratory, surrounded by 40~50m high hills, with an apartment district spread beyond the hills, is to be classified as a semi-complex terrain. Nevertheless, wind speed profiles measured up to 100m above the ground fitted well into a theoretical-experimental logarithmic-law equation. The LIDAR remote-sensing data of the sub-layer of the atmospheric boundary layer has been proven to be superior to the data obtained by conventional extrapolation of the wind profile with 2 or 3 anemometer measurements.

• 한국수소및신에너지학회논문집
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• 제26권4호
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• pp.386-392
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• 2015

Flow characteristics inside a 10 inch ball valve have been analyzed using three-dimensional numerical analysis and experiments. Continuity and three-dimensional Reynolds-averaged Navier-Stokes equations have been used as governing equations for the numerical analysis. The numerical model has been constructed through the grid dependency test and validation with the results of experiments to ensure reliability and numerical effectiveness. The shear stress transport (SST) model has been used as the turbulence closure. The experimental test-rig has been constructed to measure pressure, temperature and flow rate along the pipeline. Some valve opening angles have been tested to evaluate the flow characteristics inside the ball valve and pipeline. The results show that the rapid pressure variations is observed while the valve opening angle decreases, which caused by flow separation at the downstream of the ball valve.

• 한국수소및신에너지학회논문집
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• 제25권2호
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• pp.191-199
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• 2014

Effects of design variables on the performance of a double-inlet centrifugal blower have been analyzed based on the three-dimensional flow analysis. Two design variables, blade inlet and outlet angles, are introduced to enhance a blower performance. General analysis code, ANSYS-CFX13, is employed to analyze internal flow and a blower performance. SST turbulence model is employed to estimate the eddy viscosity. Throughout the shape optimization of an impeller at the design flow condition, the blower efficiency and pressure are successfully increased by 4.7 and 1.02 percent compared to reference one. It is noted that separated flow observed near cut-off region can be reduced by optimal design of blade angles, which results in stable flow pattern in the blade passage and increase of a blower performance. The stable flow at the impeller also makes good effects at the outlet of a volute casing.

• Wind and Structures
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• 제27권2호
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• pp.123-136
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• 2018

The effects of steep and shallow hills on a stationary tornado-like vortex with a swirl ratio of 0.4 are simulated and quantified as Fractional Speed Up Ratios (FSUR) at three different locations of the vortex with respect to the crests of the hills. Steady state Reynolds Averaged Naiver Stokes (RANS) equations closed using Reynolds Stress Turbulence model are used to simulate stationary tornadoes. The tornado wind field obtained from the numerical simulations is first validated with previous experimental and numerical studies by comparing radial and tangential velocities, and ground static pressure. A modified fractional speed-up ratio (FSUR) evaluation technique, appropriate to the complexity of the tornadic flow, is then developed. The effects of the hill on the radial, tangential and vertical flow components are assessed. It is observed that the effect of the hill on the radial and vertical component of the flow is more pronounced, compared to the tangential component. Besides, the presence of the hill is also seen to relocate the center of tornadic flow. New FSUR values are produced for shallow and steep hills.

• International Journal of Fluid Machinery and Systems
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• 제7권3호
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• pp.86-93
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• 2014

This paper describes performance enhancement of a regenerative blower used for a 20 kW fuel cell system. Two design variables, bending angle of an impeller and blade thickness of an impeller tip, which are used to define an impeller shape, are introduced to enhance the blower performance. Internal flow of the regenerative blower has been analyzed with three-dimensional Navier-Stokes equations to obtain the blower performance. General analysis code, CFX, is introduced in the present work. SST turbulence model is employed to estimate the eddy viscosity. Throughout the numerical analysis, it is found that the thickness of impeller tip is effective to increase the blower efficiency in the present blower. Pressure is successfully increased up to 2.8% compared to the reference blower at the design flow condition. And efficiency is also enhanced up to 2.98 % compared to the reference one. It is noted that low velocity region disturbs to make strong recirculation flow inside the blade passages, thus increases local pressure loss. Detailed flow field inside the regenerative blower is also analyzed and compared.