• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.2
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• pp.202-212
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• 1985

Numerical and experimental studies are presented for turbulent flows and heat transfer in annular channel with circumferential fins on the inner tube in a double pipe heat exchanger. Flow and heat transfer characteristics are periodically fully developed, and complex flow patterns are shown. Numerical calculations are executed by using modified TEACH-2E computer program based on the standard k-.epsilon. turbulence model. Mean velocity, turbulent kinetic energy, and Reynolds stress distributions are measured with the hot wire anemometer. Static pressures on the outer wall of the pipe are measured for three pitch-height ratios and several Reynolds numbers. Numerical predictions generally show reasonable results in comparison with experimental results. When the pitch-height ratio is about 5.0 and other geometric parameters are fixed in this paper, maximum heat transfer is achieved. Reattaching flow patterns appeared in this region. As the pitch between fins is increased beyond 5.0, mean Nusselt numbers are decreased and the pressure drop through one pitch almost remains.

• Journal of Power System Engineering
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• v.4 no.4
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• pp.25-31
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• 2000

This paper represents the vector fields and three dimensional mean velocities in the X-Y plane of cone type swirl gas burner measured by using X-probe from the hot-wire anemometer system. This experiment is carried out at flowrate 350 and $450{\ell}/min$ respectively in the test section of subsonic wind tunnel. The vector plot shows that the maximum axial mean velocity component is focused in the narrow slits distributed radially on the edge of a cone type swirl burner, for that reason, there is some entrainment of ambient air in the outer region of the burner and the rotational flow can be shown in the inner region of the burner because mean velocity W is distributed about twice as large as mean velocity V due to inclined flow velocity ejecting from the swirl vanes of a cone type baffle plate of burner. Moreover, the mean velocities are largely distributed near the outer region of burner within $X/R{\fallingdotseq}1.5$, hence, the turbulent characteristics are anticipated to be distributed largely in the center of this region due to the large inclination of mean velocity and swirl effect.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.4
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• pp.21-28
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• 2009

Most of domestic shipyards are located at coastal regions which are affected by typhoons nearly every year. For effectiveness of shipbuilding, shipyards contain many facilities which are light-weighted and affected dominantly by wind. In the present paper, we analyze various wind fields over a shipyard including surrounding topology and structures to evaluate the structural safety of the facilities posed in the strong wind. Extreme wind speed for a study region was estimated by typhoon Monte Carlo simulation and then used for inlet wind speed for CFD analysis for wind load on the facilities. Considering geometrical wind effects, we assess the surface pressure of the elements as the pressure factor, the ratio of surface pressure to dynamic pressure. The results show that the simulated wind speed is greater than the design wind speed for the some facilities because of the shipyard's geometry. It also shows that surrounding topography in coastal area is needed to be considered and adjustment for design wind speed at wind load standard application is necessary for mooring ship and industry facilities.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.3
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• pp.444-453
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• 1987

In the present study, a new computational closure model is proposed in order to contain physical models in the k- and .epsilon.- equations. The time scale of the third-order diffusive transport of turbulent kinetic energy in a curved streamline flow field is assumed as a function of a velocity time scale and a curvature time scale, the latter being derived from the analogy between buoyancy and streamline curvature effects on turbulence. The curvature time scale is represented by a combination of Brunt-Vaisala frequency of the curvature instability and the velocity time scale. Besides the modification of diffusive transport time scale, the destruction term in the dissipation rate equation is modeled to incorporate the streamline curvature effect on the dissipation rate of turbulent kinetic energy as a function of the ratio between velocity time scale and curvature time scale. The new curvature dependent 2-equation model is found to yield very good prediction accuracy for the various turbulent recirculating flows. Particurarly, the recovery of the mean velocity profile in the redeveloping region after the reattachment is correctly simulated by the present model.

• Korean Journal of Remote Sensing
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• v.36 no.5_1
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• pp.679-692
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• 2020

We coupled a CFD model to the WRF-Chem model (WRF-CFD model) and investigated the characteristics of flows and carbon monoxide (CO) distributions in a building-congested district. We validated the simulated results against the measured wind speeds, wind directions, and CO concentrations. The WRF-Chem model simulated the winds from southwesterly to southeasterly, overestimating the measured wind speeds. The statistical validation showed that the WRF-CFD model simulated the measured wind speeds more realistically than the WRF-Chem model. The WRF-Chem model significantly underestimated the measured CO concentrations, and the WRF-CFD model improved the CO concentration prediction. Based on the statistical validation results, the WRF-CFD model improved the performance in predicting the CO concentrations by taking complicatedly distributed buildings and mobiles sources of CO into account. At 04 KST on May 22, there was a downdraft around the AQMS, and airflow with a relatively low CO concentration was advected from the upper layer. Resultantly, the CO concentration was lower at the AQMS than the surrounding area. At 15 KST on May 22, there was an updraft around the AQMS. This resulted in a slightly higher CO concentration than the surroundings. The WRF-CFD model transported CO emitted from the mobile sources to the AQMS measurement altitude, well reproducing the measured CO concentration. At 18 KST on May 22, the WRF-CFD model simulated high CO concentrations because of high CO emission, broad updraft area, and an increase in turbulent diffusion cause by wind-shear increase near the ground.

• Journal of the Korean Society of Marine Environment & Safety
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• v.15 no.3
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• pp.165-171
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• 2009

In order to illustrate the effects of water temperature inversion on the stratification variation in the South Sea of Korea, water temperature, salinity, and density measured in October and December 1999 by National Fisheries Research and Development Institute were reviewed. In October and December of 1999, temperature inversion occurred mainly between 25m and 75m, and in particular in depth of water, in December temperature inversion layer also was formed in the surface layer. In case of October and December, the Tsushima Warm Current (TWC), warm and saline water, was one of motors, and in December, influence of surface cold water was added Although northerly wind prevails in October and December, in October, expanding of the South Korean Coastal Waters (SKCW) towards offshore is not clear, but in December when wind speed is relatively greater than that in October and strength of the TWC become weak, the SKCW spreads towards offshore through the upper layer. Stratification variation was higher along the area where temperature inversion occurred.

• Korean Journal of Agricultural and Forest Meteorology
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• v.2 no.3
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• pp.80-86
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• 2000

Eddy covariance method is widely used in measuring vertical fluxes of mass and energy between the atmosphere and the biosphere. In this method, scalar concentration is measured with either open-path or closed-path sensors. For the latter, fluctuations of scalar concentration are attenuated as the sample travels through a long tube, resulting in flux loss. To quantify this tube attenuation, water vapor concentrations measured with both closed-path and open-path sensors were analyzed. Our statistical analysis showed that the power spectral density obtained from the closed-path sensor was different from that from the open-path sensor in the frequency range of > 0.5 Hz. The loss of water vapor flux due to tube attenuation was < 5% during midday. At nighttime, however, the flux loss increased significantly because of the low wind speeds and the weak turbulence sources. Theoretical calculation for the tube attenuation showed a small bias in high frequency range probably because of the interaction of sticky water vapor with a tube wall.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.1
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• pp.157-164
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• 2021

Wind and temperature were measured with a three-dimensional ultrasonic anemometer and the carbon dioxide concentration was measured using an infrared sensor in the tidal flat of Suncheon Bay. In general, as the temperature increases, the concentration of carbon dioxide increases, and as the temperature decreases, the carbon dioxide also decreases in the atmosphere. However, since photosynthesis declined immediately after the sunset, the concentration of carbon dioxide increased as the temperature decreased. In addition, near the high tide when the tidal flat is covered with seawater, the atmospheric turbulence was strong despite an increase in temperature, resulting in a decrease in carbon dioxide concentration. It is necessary to quantitatively evaluated the effects of photosynthesis, respiration and atmospheric turbulence on the change of carbon dioxide concentration over tidal flat ecosystems.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2A
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• pp.371-382
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• 2006

A buffeting analysis is utilized for the estimation of aerodynamic vulnerability of a cable-stayed bridge due to upcoming wind turbulences. The buffeting analysis requires several input parameters such as structural parameters, aerodynamic parameters, and aero-elastic parameters. This study is motivated to estimate the sensitivity of these parameters on buffeting responses. The Seohae bridge is selected as an example bridge. The investigated parameters consist of the inclination of lift and drag coefficient of stiffening girder section, exponential decay factors of span-wise distributed wind turbulences, roughness length, spectra of wind velocity fluctuation, and structural damping. The buffeting response showed high dependency on the input parameters. As conclusions, the importance of parameter selection is emphasized. A further study is also proposed for more general conclusions.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2923-2928
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• 2007

The study of model for velocity and turbulence within the urban canopy was carried out. To evaluate existing urban model we conducted wind tunnel experiment and large-eddy simulation (LES). Mean velocity profile and turbulence are measured within simple three different obstacle arrays. To obtain supplemental data and to verify morphological model large-eddy simulation was performed. Several methods have been used to achieve embodying the flow field in urban area. Recently, morphological method obtaining flow parameters from the statistical or physical representation of obstacle elements is a arising method. It was found that all morphological model, evaluated in this study, over predict the friction velocity, most sensitive one among the flow parameters. Velocity and turbulence in the urban canopy layer were improved by the correction using 'true' friction velocity.