• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.69.3-69.3
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• 2019

The CHIMPS2 survey is to extend the JCMT HARP $^{13}CO/C^{18}O$ J=3-2 Inner Milky-Way Plane Survey (CHIMPS) and the ${12}^CO$ J=3-2 survey (COHRS) into the inner Galactic Plane, the Central Molecular Zone (CMZ), and a section of the Outer Plane. When combined with the complementary $^{12}CO/^{13}CO/C^{18}O$ J=1-0 survey at the Nobeyama 45m (FUGIN) at matching 15" resolution and sensitivity, and other current CO surveys, the results will provide a complete set of transition data with which to calculate accurate column densities, gas temperatures and turbulent Mach numbers. These will be used to: analyze molecular cloud properties across a range of Galactic environments; map the star-formation efficiency (SFE) and dense-gas mass fraction (DGMF) in molecular gas as a function of position in the Galaxy and its relation to the nature of the turbulence within molecular clouds; determine Galactic structure as traced by molecular gas and star formation; constrain cloud-formation models; study the relationship of filaments to star formation; test current models of the gas kinematics and stability in the Galactic center region and the flow of gas from the disc. It will also provide an invaluable legacy data set for JCMT that will not be superseded for several decades. In this poster, we will present the current status of the CHIMPS2.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.8 no.4
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• pp.213-220
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• 1979

A number of methods has been developed for calculation of heat transfer in the vertical round tube under conditions of forced convection with uniform heat flux at wall. I would like to express hereby one of applications of this study in the design of heat exchanger instruments for water flow at $15.8^{\circ}C(p_r=8)$ used frequently in our daily life. Also all the results are investigated for forced convective heat transfer in the case of heated water-flow at uniform wall heat flux in the vortical round copper tube, where the ratio of length to diameter will be 44. They are well in agreement with Gratz and Kraussold equation respectively in laminar and transition flow range. In turbulent flow in the range from Re=10,000 to 65,000, the experimental formula Is show as follows ; Nu=0.023 $R_e^{0.814}\;P_r^{0.4}$. And this is agreed with Dittus - Boelter equation when Reynolds number exponent increases from 0.80 to 0.814.

• Journal of the Korean Society of Visualization
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• v.21 no.2
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• pp.24-33
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• 2023

This work is to observe the wake flow generated behind a ramp. We have conducted a large eddy simulation with two ramp models having different heights with two different inflow conditions. Reynolds number based on the height of the large ramp (LR) and small ramp (SR) are Re_h = 2.8×10⁴ and 1.4×10⁴ respectively. The wake flow visualization shows the formation of streamwise counter-rotating vortices pairs at the downstream of the obstacle. These primary vortices are stretched and lifted up when moving downstream. In order to observe the effect of the inflow condition on the wake transition, two different inlet flow conditions are given on the inlet section as an inlet boundary condition. Induced counter-rotating vortices pairs due to sharp-edged triangular ramp obstacles are developed and propagated downstream. In the result, the large ramp shows a more complicated wake structure of the boundary layer than the small ramp.

• Journal of Korea Water Resources Association
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• v.53 no.1
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• pp.1-13
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• 2020

The most common approach for computing engineering flow problems at high Reynolds number is still the Reynolds-averaged Navier-Stokes (RANS) computations based on turbulence models with wall functions. The recently developed generalized wall functions blending between the wall-limiting viscous and the outer logarithmic relations ensure a smooth transition of flow quantities across two regions. The performances and convergence properties of widely used turbulence models with wall functions that are applicable for turbulence kinetic energy (TKE), turbulent and specific dissipation rates, and eddy viscosity are presented through a series of near wall flow simulations. The present results show that RNG k-𝜖 model should be carefully applied with small tolerance to get the stable solution when the first grid lies in the buffer layer. The standard k-𝜖 and RNG k-𝜖 models are not sensitive to the selection of wall functions for both TKE and eddy viscosity, while the k-ω SST model should be applied together with kL-wall function for TKE and nutUB-wall functions for eddy viscosity to ensure accurate and stable boundary conditions. The applications to a backward-facing step flow at Re=155,000 reveal that the reattachment length is reasonably well predicted on appropriately refined mesh by all turbulence models, except the standard k-𝜖 model which about 13% underestimates the reattachment length regardless of the grid refinement.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6B
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• pp.641-649
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• 2006

The behavior of a three-dimensional pure rectangular water jet with aspect ratio of 10 was experimentally investigated based on the results of the mean velocity field obtained by PIV. The saddle back distribution was observed in the lateral distribution along the major axis. The theoretical centerline velocity equation derived from the point source concept using the spreading rate for the axisymmetric jet was in good agreement with the measured centerline velocity and gave the division of the potential core region, two-dimensional region, and axisymmetric region. The range of the two-dimensional region divided by the criterion of the theoretical centerline velocity decay for the aspect ratio of 10 was observed to be smaller than that of the transition region. The applicability of the two-dimensional model to the behavior of the rectangular jet with low aspect ratio or the wastewater discharged from a multiport diffuser in the deep water of real ocean may result in significant error in the transition and axisymmetric regions after the two-dimensional region. In the two-dimensional region, the Gaussian constant tended to be conserved, and the spreading rate slightly decreased at the end of the two-dimensional region. The normalized turbulent intensity along the centerline of the jet initially abruptly increased and showed relatively higher intensity for higher Reynolds number.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.285-292
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• 2013

The purpose of this research is to investigate how the boundary layer separation caused by a tripping wire installed in front of the flat plate affects the transition from laminar to turbulent flow, and consequently mass transfer. A naphthalene sublimation technique is used to measure the local mass transfer coefficients on the flat plate, and two boundary conditions for the developed and developing flow are considered to evaluate the effects of the flow boundary. The local mass transfer data for a flat plate with a tripping wire are compared with the data for a flat plate without a tripping wire. The variation trends of the local heat transfer coefficients for the plates with and without the tripping wire are similar to each other in the case of the developing flow, but are quite different for the developed flow. The average Sherwood number for the flat plate with a tripping wire is much higher than that without a tripping wire because of the boundary layer separation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.10
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• pp.941-951
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• 2013

A three dimensional numerical simulation of laminar flow and heat transfer in fully developed curved pipe flow has been performed to study the effects of Dean number and pipe curvature on the flow and temperature fields under the thermal boundary condition of axially uniform wall heat flux. The Reynolds number under consideration ranges from 100 to 4000, and the Prandtl number is 0.71. The curvature ratios are 0.01, 0.025, 0.05 and 0.1. The axial velocity and temperature profiles and the local Nusselt number obtained from the present study are in good agreement with the previous numerical and experimental results currently available. To show the effects of pipe curvature on the flow and heat transfer, the resistance coefficients and heat transfer coefficients are computed and compared with the results of the previous theoretical and experimental studies. The averaged Nusselt number is correlated with Dean and Prandtl numbers. Furthermore, the critical Reynolds number for transition to turbulent flow is observed to depend upon the curvature ratio.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2010.04a
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• pp.59-63
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• 2010

Seven different size of orifice were applied in a constant volume combustion chamber for evaluating the effects of torch-ignition on combustion. The initial flame development and flame propagation were analyzed by the mass fraction burn and combustion enhancement rate. The combustion pressures were measured to calculate the mass fraction burn and the combustion enhancement rates. In addition, the flame propagations were visualized by the shadowgraph method for the qualitative comparison. The result showed that the combustion pressure and mass burned fraction were increased when using the torch-ignition device. The combustion enhancement rates of torch-ignition cases were improved in comparison with conventional spark ignition. Finally, the visualization results showed that the torch-ignition induced faster burn than conventional spark ignition due to the earlier transition to turbulent flame and larger flame surface, during the initial stage.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.5
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• pp.477-485
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• 2012

Fluid flow and heat transfer in horizontal ducts are strongly coupled with large changes in thermodynamic and transport properties near the critical region as well as the gravity force. Numerical analysis has been carried out to investigate convective heat transfer in horizontal rectangular ducts for water near the thermodynamic critical point. Convective heat transfer characteristics, including velocity, temperature, and the properties as well as local heat transfer coefficients along the ducts are compared with the effect of proximity on the critical point. When there is flow acceleration because of a density decrease, convective heat transfer characteristics in the ducts show transition behavior between liquid-like and gas-like phases. There is a large variation in the local heat transfer coefficient distributions at the top, side, and bottom surfaces, and close to the pseudocritical temperature, a peak in the heat transfer coefficient distribution resulting from improved turbulent transport is observed. The Nusselt number distribution depends on pressure and duct aspect ratio, while the Nusselt number peak rapidly increases as the pressure approaches the critical pressure. The predicted Nusselt number is also compared with other heat transfer correlations.

• Journal of computational fluids engineering
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• v.20 no.4
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• pp.14-20
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• 2015

Without electirc power to cool down the hot reactor core, passive systems utilizing natural circulation are becoming a big specialty of recent neculear systems after the severe accident in Fukusima. When we consider the natural circulation in a pool, thermal mixing phenomena may start from single phase circulation and can continue to two phase condition. Since the CUPID code, which has been developed for two-phase flow analysis, can deal with the phase transition phenomena, the CUPID would be pertinent to natural convection problems in single- and two-phase conditions. Thus, the CUPID should be validated against single- and two-phase natural circulation phenomena. For the first step of the validation process, this study is focused on the validation of single-phase natural circulation. Moreover, the CUPID code solves the fluid properties by the relationship to pressure and temperature from the steam table considering non-condensable gas effects, so that the effects from variable properties are included. Simple square thermal cavity problems are tested for laminar and turbulent conditions against numerical and experimental data. Throughout the investigation, it is found that the variable properties can affect the flow field in laminar condition, but the effect becomes weak in turbulence condition, and the CUPID code implementing steam table is capable of analyzing single phase natural circualtion phenomena.