• Journal of Advanced Marine Engineering and Technology
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• 제18권3호
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• pp.17-25
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• 1994

Fully developed turbulent flow through three concentric annuli with both the rough inner and outer walls was experimentally investigated for a Reynolds number range Re = 15, 000 - 85, 000. Measurements were carried out for the pressure drop, the positions of zero shear stress and maximum velocity, and the velocity distributions in annuli of radius ratios, ${\alpha}$=0.26, 0.4 and 0.56, respectively. The experimental results showed that the positions of zero shear stress and maximum velocity were only weakly dependent on the Reynolds number.

• 대한기계학회논문집
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• 제18권9호
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• pp.2443-2453
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• 1994

The structure of turbulence of fully developed flow through four concentric annuli with the rough outer wall was investigated experimentally for a Reynolds number range Re=15, 000-93, 000. Turbulence intensities were measured in three(u, v, w) directions, and turbulence shear stresses in annuli of radius=0.13, 0.26, 0.4 and 0.56, respectively. Due to the square roughness element attached periodically along the axial direction, the radial velocity fluctuations show similar distribution regardless of the different .alpha.cases. However, the axial and circumferential velocity fluctuation profiles demonstrate the longitudinal turbulence structures are strongly influenced by the .alpha. values. The turbulent eddy viscosity deduced form mean velocity distributions and the measured Reynolds shear stresses are also presented and discussed.

• 설비공학논문집
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• 제7권1호
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• pp.81-88
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• 1995

Fully developed turbulent flow through three concentric annuli with both the rough inner and outer walls was experimentally investigated for a Reynolds number range Re=15,000-85,000. Measurements were made of the pressure drop, the positions of zero shear stress and maximum velocity, and the velocity distributions in annuli of radius ratios, ${\alpha}=0.26$, 0.4 and 0.56, respectively. The experimental results showed that the positions of zero shear streess and maximum velocity were only weakly dependent on the Reynolds number. It was also found that the position of zero shear stress was not coincident with that of maximum velocity. Furthmore, the former was influenced more sensitively than the latter on the square-ribbed roughness along the axial direction.

• 대한기계학회논문집
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• 제19권7호
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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.

• Journal of Advanced Marine Engineering and Technology
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• 제23권1호
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• pp.54-61
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• 1999

The fully developed turbulent momentum and heat transfer induced by the roughness elements on the outer wall surfaces in concentric annuli are analytically studied on the basis of a modified turbu-lence model. The resulting momentum and heat transfer are discussed in terms of various parame-ters such as the radius ratio the roughness density Reynolds number and Prandtl number accord-ing to the heating condition. The study shows that certain artificial roughness elements may be used to enhance heat transfer rates with advantage from the overall efficiency point of view.

• 설비공학논문집
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• 제11권1호
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• pp.1-9
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• 1999

For roughened annular pipes with diameter ratios of 0.26, 0.39, and 0.56 and with Reynolds numbers ranging 13,000 to 67,000, friction factor, autocorrelation coefficients, power spectral density functions, and integral length scales for each flow condition using X-type hot wire anemometry system are experimentally investigated. Distributions of these quantities show that the times which the streamwise autocorrelation coefficients become zero first increase with decreasing the radius ratios of concentric annuli and Reynolds numbers, however the power spectra density functions increase with increasing the radius ratios and Reynolds number.

• 대한기계학회논문집B
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• 제21권7호
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• pp.891-899
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• 1997

This paper presents the results of a detailed experimental examination of fully developed asymmetric flows between annular tubes with square-ribbed surface roughness. The main emphasis of the research has been on establishing the turbulence structure, particularly in the central region of the channel where the two dissimilar wall flows interact. Measurements have included profiles of time mean velocities, turbulence intensities, turbulent shear stresses, triple velocity correlations, skewness, and flatness. The region of greatest interaction is characterized by strong diffusional transport of turbulent shear stress and kinetic energy from rough toward the smooth wall region, giving rise to an appreciable separation between the planes of zero shear stresses depending on positions of roughness on the walls.

• Journal of Advanced Marine Engineering and Technology
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• 제21권2호
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• pp.136-143
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• 1997

직경 비가 0.56인 이중동심관에 내외측모두 매끈한 벽면, 벽면 거칠기를 안측, 외측, 그리고 양측 모두의 4경우에 대한 난류 유동과 열전달특성을 실험과 이론으로 연구하였다. 시간평균속도분포, 마찰계수, 그리고 최대 속도 지점과 전단응력이 0인 지점들을 피토튜브와 X형 열선 풍속계로 측정하였다. 이중동심관내에서 4가지 경우에 따른 사각돌출형 거칠기효과가 난류 유동과 열전달에 미치는 영향을 수정난류모델을 기초로 하여 연구하였다. 직경비, 거칠기 위치, 레이놀즈수, 그리고 프란틀수 등의 여러 변수에 의해서 난류 유동과 열전달을 고찰하였다. 본 연구는 전체적 효율 측면에서 유리하게 열전달율을 향상시킬수 있는 거칠기 구조를 밝혔다.

• 대한기계학회논문집
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• 제11권1호
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• pp.88-96
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• 1987

본 논문에서는 Maubach의 방법에 내재된 불합리한점을 보완하고자 Fig.1(b)와 같이 .iota.=0인 곳에서 속도구배를 ㄹ변환하여 마찰계수와 조도함수를 계산하였다. 이 방법에 의해 얻어진 속도분포에서는 .iota.=0인 곳에서 속도구배에 불연적성이 일어나지 않는다.

• 대한기계학회논문집B
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• 제23권5호
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• pp.587-592
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• 1999

The combined effects of radius ratio and roughness pitch ratio on the turbulent fluid flow characteristics of the fully developed flow in the annullar tubes with rib-roughened core walls were determined for Reynolds number ranging from 12,000 to 66,000. To understand the underlying physical phenomena responsible for friction factor enhancement, measurements of velocity profiles and zero shear stress and maximum velocity positions were combined to propose the friction factor correlation. Friction factors were found to be a function of the roughness pitch ratio and radius ratio.