• Wind and Structures
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• 제8권6호
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• pp.455-467
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• 2005

The effects of upstream velocity profiles on the flow around a low-rise rectangular prism submerged in a turbulent boundary layer have been investigated. Three different boundary layer profiles are generated, which are characterized by boundary layer height, displacement thickness, and momentum thickness. Flow characteristics variations caused by the different layers such as those in turbulent kinetic energy distribution and locations of re-circulating cavities and reattachment points have been precisely measured by using a PIV (Particle Image Velocimetry) technique. Observations were made in a boundary layer wind tunnel at $Re_H$=7900, based on a model height of 40 mm and a free stream velocity of 3 m/s with 15 - 20% turbulence intensity.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.131-135
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• 2001

The atomization characteristics of an annular liquid (water) sheet of small radius with a core gas (air) flow were studied. Different sizes of annular gaps (0.2, 0.4 and 0.8 mm) were tested to find the effect of liquid sheet thickness on SMD. The inner diameter of the gas port for the core gas flow was 4 mm. Cross-section averaged SMD was measured for various liquid and gas velocities. Regions of the SMD decrease with the increase of the liquid velocity always existed regardless of the liquid sheet thickness. This attributes to the transition of the flow patterns of spray and also to the aerodynamic interaction between the atomizing gas and the ripples on the liquid sheet surface.

• Tribology and Lubricants
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• 제20권5호
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• pp.284-291
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• 2004

We present a three-dimensional average flow model considering elastic deformation of pad asperities for chemical mechanical planarization. To consider the contact deformation of pad asperities in the calculation of the flow factor, three-dimensional contact analysis of a semi-infinite solid based on the use of influence functions is conducted from computer generated three dimensional roughness data. The average Reynolds equation and the boundary condition of both force and momentum balance are used to investigate the effect of pad roughness and external pressure conditions on film thickness and wafer position angle.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 1999년도 제1회 학술대회논문집(KIASC 1st conference 99)
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• pp.157-160
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• 1999

Enthalpy transport in a pulse tube was investigated by two-dimensional analysis of mass, momentum and energy equations of the gas as well as energy conservation of the tube wall. The mean temperature of the gas and the tube wall was obtained directly by assuming that the outer surface of a pulse tube is adiabatic. Effects of operating frequency, tube wall thickness, velocity ratio and velocity phase angle between both ends of a pulse tube on net enthalpy flow were shown.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.9-13
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• 2001

In the present study, the friction coefficients (Fanning and Moody coefficients) and the Nusselt number is reviewed from an educational point of view. It is discussed that these dimensionless numbers can be treated with two lengh scales. Also, the similarity between the momentum and heat transfer is discussed based on the length scales.

• Journal of Advanced Marine Engineering and Technology
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• 제10권4호
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• pp.50-56
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• 1986

This report deals with a study on the boundary layer characteristics of TP620 hydrofoil in the steady state by using two dimensional boundary layer theory. On the basis of complex velocity and laminar and turbulent boundary layer theory, the author attempts to know some tendency by evaluating the performance characteristic values of TP620 hydrofoil working in a uniform flow. In deriving characteristic values, he calculates numerically velocity, momentum thickness, skin friction coefficient, shape factor, and displacement thickness on the TP620 hydrofoil working at each attack angle in a uniform flow. Applying this present numerical calculation using Thwaites' and Head's method, the results of boundary layer on the hydrofoil are shown to be influenced by surface velocity and attack angle.

• 대한기계학회논문집
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• 제11권6호
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• pp.1026-1035
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• 1987

본 연구에서는 두께방향에 따른 유동을 해석하는데 "fountain effect" 및 열 전달 현상을 동시에 고려하면서 진전하는 자유표면의 형상을 정확히 구하기 위한 유한 요소법을 이용한 수치해석법을 제안하고 그 방법을 적용하여 금형벽의 온도를 변화시 켜가면서 구체적인 유동특성을 해석하였다.특성을 해석하였다.

• 한국전산유체공학회지
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• 제10권1호
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• pp.99-106
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• 2005

Performance of first, second and third order accurate methods for calculation of in viscid fluxes in fluid flow governing equations are investigated here. For the purpose, an upwind method based on Roe's scheme is used to solve 2-dimensional Euler equations. To increase the accuracy of the method two different schemes are applied. The first one is a second and third order upwind-based algorithm with the MUSCL extrapolation Van Leer (1979), based on primitive variables. The other one is an upwind-based algorithm with the Chakravarthy extrapolation to the fluxes of mass, momentum and energy. The results show that the thickness of shock layer in the third order accuracy is less than its value in second order. Moreover, applying limiter eliminates the oscillations near the shock while increases the thickness of shock layer especially in MUSCL method using Van Albada limiter.

• 설비공학논문집
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• 제6권4호
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• pp.453-462
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• 1994

An unsteady quasi one-dimensional model of momentum, heat and mass transfer in a falling film of a vertical plate absorber which is cooled by air was developed using the integral method. Energy conservation of the absorber wall is considered in the model. The model can predict absorption rate, film thickness and mean velocity as well as concentration and temperature profiles. Predictions of steady state temperature and concentration profiles for LiBr/water system for constant wall temperature condition are in good agreement with the two-dimensional finite difference method solutions. Effects of operating conditions, such as convective heat transfer coefficient between the cooling air and the absorber wall, cooling air temperature and film thickness at inlet, on absorption rate of water vapor into LiBr/water solution were shown.

• 대한조선학회지
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• 제23권1호
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• pp.13-22
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• 1986

Axisymmetric turbulent thick boundary layers on a rotating body of revolution are calculated numerically in the paper. Richardson number is introduced to the mixing length to take account of swirl effects on Reynolds stresses. Interactions of the boundary layer and the external potential flow are included by adding the displacement thickness of boundary layers on the original body. Pressure distributions on the body surface are estimated by integrating normal momentum equation across the boundary layer. A model is designed and tested in the wind tunnel. Mean velocities are measured. Through the present study, swirl effects on the thick axisymmetric boundary layer development are considerable in comparison with those of non-totating cases. Rotational motion generally increase boundary layer thickness, axial skin friction coefficients, and form drags. Circumferential flow can be reversed to induce negative skin friction when the section area is reduced.