• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.687-690
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• 2008

Currently, Stream flow analysis has been accomplished by one or two dimensional equations and was applied by simple momentum equations and fixed energy conservations which contain many reach uppermost limit. In this study, FLOW-3D using CFD(Computational Fluid Dynamics) was applied to stream flow analysis which can solve three dimensional RANS(Reynolds Averaged Navier-Stokes Equation) control equation to find out physical behavior and the effect of hydraulic structures. Numerical simulation accomplished those results was compared by using turbulence models such as $k-\varepsilon$, RNG(Renomalized Group Theory) $k-\varepsilon$ and LES(Large Eddy Simulation). Numerical analysis results have been illustrated by the turbulence energy effects, velocity of flow, water level pressure and eddy flows around the side overflow type structures at Jangwall bridge in urban stream.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.4
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• pp.419-425
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• 2014

The current work investigated the variation of numerical solutions according to the grid number, the distance of the first grid point off the ship surface, turbulence modeling and discretization. The subject vessel is KVLCC. A commercial code, Gridgen V15 and FLUENT were used the generation of the ship hull surface and spatial system and flow computation. The first part of examination, the effect of solutions were accessed depending on the grid number, turbulence modeling and discretization. The second part was focus on the suitable selection of the distance of the first grid point off the ship surface: $Y_P+$. When grid number and discretization were fixed the same value, the friction resistance showed differences within 1 % but the pressure resistance showed big differences 9 % depending on the turbulence modeling. When $Y_P+$ were set 30 and 50 for the same discretization, friction resistance showed almost same results within 1 % according to the turbulence modeling. However, when $Y_P+$ were fixed 100, friction resistance showed more differences of 3 % compared to $Y_P+$ of 30 and 50. Whereas pressure resistance showed big differences of 10 % regardless of turbulence modeling. When turbulence modeling and discretization were set the same value, friction, pressure and total resistance showed almost same result within 0.3 % depending on the grid number. Lastly, When turbulence modeling and discretization were fixed the same value, the friction resistance showed differences within 5~8 % but the pressure resistance showed small differences depending on the $Y_P+$.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.233-237
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• 2007

Recent experimental data shows that an irregular fuel surface pops up during the combustion test. This may contribute to the agitated boundary layer due to blowing effect of fuel vaporization. Blowing effect can be of significance in determining the combustion characteristics of solid fuel within the oxidizer flow. LES was implemented to investigate the flow behavior on the fuel surface and turbulence evolution due to blowing effect. Simple channel geometry was used for the investigation instead of circular grain configuration without chemical reactions. This may elucidate the main mechanism responsible for the formation of irregular isolated spots during the combustion in terms of turbulence generation. The interaction of turbulent flow with blowing mass flus causes to breakup turbulent coherent structures and to form the small scale isolated eddies near the fuel surface. This mechanism attributes to the formation of irregular isolated sopt on the fuel surface.

• Journal of computational fluids engineering
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• v.9 no.2
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• pp.30-35
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• 2004

A numerical study of underexpanded jet and impingement on a wall mounted at various distances from the nozzle exit is presented. The 3-dimensional Wavier-Stokes equations and κ-ω turbulence equations are solved. The grids are constructed as overlapped grid systems to examine the distance effect. The DADI method is applied to obtain steady-state solutions. To avoid numerical instability such as the carbuncle phenomena that sometimes accompany approximate Riemann solver, the HLLE+ scheme is employed for the inviscid flux at the cell interfaces. A goal of this work is to apply a number of two-equation turbulence models based on the w equation to the impinging jet problem.

• Wind and Structures
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• v.15 no.6
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• pp.463-480
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• 2012

The effects of Reynolds number (Re), freestream turbulence intensity (Tu) and integral length scale (${\Lambda}$) on the drag coefficient ($C_d$) of a circular cylinder in cross flow were experimentally studied for $6.45{\times}10^3$ < Re < $1.82{\times}10^4$. With the help of orificed plates, Tu was fixed at approximately 0.5%, 5%, 7% and 9% and the normalized integral length scale (L/D) was varied from 0.35 to 1.05. Our turbulent results confirmed the general trend of decreasing $C_d$ with increasing Tu. The effectiveness of Tu in reducing $C_d$ is found to lessen with increasing ${\Lambda}$/D. Most interestingly, freestream turbulence of low Tu (${\approx}5%$) and large ${\Lambda}$/D (${\approx}1.05$) can increase the $C_d$ above the corresponding smooth flow value.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1749-1757
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• 1995

The structure of turbulence of fully developed flow through three concentric annuli with both rough inner and outer walls was investigated experimentally for Reynolds number range Re=15000-93000. Turbulence intensities were measured in three (u, v, w) directions, and turbulence shear stresses in annuli of radius ratios .alpha.= 0.26, 0.4 and 0.56, respectively. The result showed that the structure of turbulence for these asymmetric flows was not the same as that for the annulus with smooth walls. The velocity fluctuations of all three components (u, v, and w-directions) showed little discernible variation with Reynolds numbers, but became apparent with the influence of radius ratio (.alpha.) The experimental results for an annulus with the roughened outer wall and a smooth annulus were shown in the figures as a reference. The eddy diffusivities and friction factors were also presented and discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.9 s.252
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• pp.891-897
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• 2006

The SRS method is applied to a turbulent flame with radiation/turbulence interaction to invert the temperature and concentration profile. The flame is conditioned as optically thin per each fluctuation length and the flame spectral intensity is measured for inversion. From inversion result, we find that SRS can successfully invert the coupled temperature/concentration fluctuation amplitudes. For two cases of experiments, inverted values are within approximately 1% over the full range of fluctuation amplitude. However, SRS cannot find the detailed local fluctuation parameters such as pattern and phase, etc. as far as they do not affect the resulting radiation intensity. Important available parameters are the mean temperature and the temperature fluctuation amplitude. The radiation/turbulence interaction effect is verified to play an important role in the radiation.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.294-296
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• 1988

The tomographic imaging that employs ultrasonic echos has achieved outstanding advances in recent years, and today, ultrasonic diagnostic equipment has become the tool that is absolutely indispensible for clinical operations. Meanwhile, the feasility of measuring blood flow in the heart and vessels by the use of Doppler effect in ultrasonic waves is a well known fact. With respect to the method of blood flow measurment, there are two kinds which employ continous wave and pulse wave doppler system. In this paper, we describe the measurment of Blood flow-turbulence using general purpose Digital Signal Processing Board which had been implemented for the purpose of real-time spectrum analyser. Blood flow-turbulence means the blood-flow behavior. And it's value proportional to the spectrum variance. Therefore mean frequency of blood signal and variance provide useful diagnostic information. We have applied to the major arteries and vein, obtained the information about the time dependent blood-flow behavior.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2396-2400
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• 2008

The motion of small heavy particles in homogeneous isotropic turbulence in the present of gravity is investigated using Direct Numerical Simulations (DNS) at moderate Reynolds number. The Lagrangian velocity and acceleration statistics of particles and of flow for a wide range of Stokes number, defined as the ratio of the particle response time to Kolmogorov time scale of turbulence, were obtained for the direction of the gravity and normal direction, respectively. It is found that particles lose their correction faster than the case without gravity. Then, a significant increase in the average settling velocity was observed for a certain range of Stokes number. Our focus is placed on gravitational effect on very small particles. Our simulations show that as the Stokes number reduces to zero, their mean settling velocity approaches the terminal velocity in still fluid.

• International Journal of Air-Conditioning and Refrigeration
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• v.11 no.2
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• pp.51-60
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• 2003

In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can occur due to coolant leaking in the check valve. The thermal stratification produces excessive thermal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, effects of turbulence penetration on the thermal stratification into T-branches with square cross-section in the modeled ECCS are analysed numerically. Standard k-$\varepsilon$ model is employed to calculate the Reynolds stresses in momentum equations. Results show that the length and strength of thermal stratification are primarily affected by the leak flow rate of coolant and the Reynolds number of duct. Turbulence penetration into the T-branch of ECCS shows two counteracting effects on the thermal stratification. Heat transport by turbulence penetration from main duct to leaking flow region may enhance thermal stratification while the turbulent diffusion may weaken it.