• 한국해양공학회지
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• 제23권5호
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• pp.1-8
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• 2009

This paper is a continuation of the recent development on Hermite-based divergence free element method and deals with a non-isothermal fluid flow thru the buoyancy driven flow in a square enclosure with temperature difference across the two sides. The basis functions for the velocity field consist of the Hermite function and its curl while the basis functions for the temperature field consists of the Hermite function and its gradients. Hence, the number of degrees of freedom at a node becomes 6, which are the stream function, two velocities, the temperature and its x and y derivatives. This paper presents numerical results for Ra = 105, and compares with those from a stabilized finite element method developed by Illinca et al. (2000). The comparison has been done on 32 by 32 uniform elements and the degree of approximation of elements used for the stabilized finite element are linear (Deg. 1) and quadratic (Deg. 2). The numerical results from both methods show well agreements with those of De vahl Davi (1983).

• 한국전산유체공학회지
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• 제18권1호
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• pp.77-82
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• 2013

The error in measuring temperature profiles by thermocouple inside boundary layer mostly comes from the conduction heat transfer of the thermocouple. The error is not negligible when the conductivity of the thermocouple is very high. In this study, the effect of conduction heat transfer of the thermocouple on the temperature profile inside boundary layer was examined by considering both free-stream velocity and a thermocouple position. The conduction error of an E-type thermocouple was investigated by numerical analysis of three-dimensional conjugate heat transfer for various velocity profiles of boundary layer and thermocouple positions.

• 대한기계학회논문집B
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• 제22권9호
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• pp.1195-1207
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• 1998

Periodic pulsations in the static pressure near turbine surfaces as blade rows move relative to each other is one of the important sources of turbine unsteadiness. The present experiment aims to investigate the effect of the static pressure pulsations on the interaction of film coolant flows from two rows of staggered holes with mainstream and its effect on film cooling heat transfer. Potential flow pulsations are generated by the rotating shutter mechanism installed downstream of the test section, The free-stream Strouhal number based on the boundary layer thickness is in the range of 0.033 - 0.33, and the amplitude of about 10-20%. Measured are time-averaged and phase-averaged velocity variations, pressure variations and temperature distributions of the flow field. Experimental conditions are identified by boundary layer measurements. Injectant behavior is characterized by the measurements of unsteady pressure in the plenum chamber and free-stream static pressure. The film cooling effectiveness is evaluated from the insulated wall temperature measurement. It has been found that bulk flow pulsation provides very large diffusion of the injectants and the effectiveness is significantly reduced by the flow pulsations.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.220-225
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• 2007

This paper is a continuation of the recent development on the hermite-based divergence free basis function and deals with a non-isothermal fluid flow thru the buoyancy driven flow in a square cavity with temperature difference across the two sides. The basis functions for the velocities consist of the hermite function and its curl. However, the basis for the temperature are the hermite function and its gradienst. Hence, the number of degrees of freedom at a node becomes 6, which are the stream function, two velocities, the temperature and its x- and y-derivatives. Numerical results for the streamlines, the temperatures, the x-velocities and the y-velocities show good agreements with those of De vahl Davis[7].

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제11권1호
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• pp.57-70
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• 2007

The effects of variable viscosity, blowing or suction on mixed convection flow of a viscous incompressible fluid past a semi-infinite horizontal flat plate aligned parallel to a uniform free stream in the presence of the wall temperature distribution inversely proportional to the square root of the distance from the leading edge have been investigated. The equations governing the flow are transformed into a system of coupled non-linear ordinary differential equations by using similarity variables. The similarity equations have been solved numerically. The effect of the viscosity temperature parameter, the buoyancy parameter and the blowing or suction parameter on the velocity and temperature profiles as well as on the skin-friction coefficient and the Nusselt number are discussed.

• 대한기계학회논문집
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• 제14권3호
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• pp.725-733
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• 1990

본 연구에서는 Raju등의 연구의 확장으로 일정한 온도로 유지되는 경사진 평 판에 대하여 혼합대류 전 영역에 유효한 부력계수(.xi.)로서 (1+Gr$^{2}$$_{x}$cos.gamma./ Re$^{4}$$_{x}$)$_{-1}$를 적용하여 비상사 경계층 방정식을 유도하였다. 또한 적분 형 경계조건을 가진 편미분 경계층방정식을 유한차분법으로 Keller와 Cebeci의 Box scheme을 6차로 적용하여 수치해석하였다. 부력계수가 큰 영역에서 Mucoglu등의 해 석적 연구결과는 일정한 온도와 45˚의 경사를 유지하는 평판에 대한 Ramachandran의 실험적 연구결과와 약 10%정도 벗어난다. 이에 Ramachandran의 실험적 연구를 해석 적으로 재고찰하였다.하였다.

• Journal of Mechanical Science and Technology
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• 제16권5호
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• pp.720-731
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• 2002

Flow with moving free surfaces is analyzed with an the Eulerian coordinate system. This study proposes a semi-implicit filling algorithm using VOF in which the PLIC (Piecewise Linear Interface Calculation) -type interface reconstruction method and the donor-acceptor-type front advancing scheme are adopted. Also, a new scheme using extrapolation of the stream function is proposed to find the velocity of the node that newly enters the computational domain. The effect of wall boundary conditions on the flow field and temperature field is examined by numerically solving a two-dimensional casting process.

• Journal of Mechanical Science and Technology
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• 제16권10호
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• pp.1346-1354
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• 2002

The purpose of this work is to study the effects of specularly reflecting wall under the combined radiative and laminar free convective heat transfer in an infinite square duct. An absorbing and emitting gray medium is enclosed by the opaque and diffusely emitting walls. The walls may reflect diffusely or specularly. Boussinesq approximation is used for the buoyancy term. The radiative heat transfer is evaluated using the direct discrete ordinates method. The parameters under considerations are Rayleigh number, conduction to radiation parameter, optical thickness, wall emissivity and reflection mode. The differences caused by the reflection mode on the stream line, and temperature distribution and wall heat fluxes are studied. Some differences are observed for the categories mentioned above if the order of the conduction to radiation parameter is less than order of 10$\^$-3/ fer the range of Rayleigh number studied. The differences at the side wall heat flux distributions are observed as long as the medium is optically thin. As the top wall emissivity decreases, the differences between these two modes are increased. As the optical thickness decreases at the fixed wall emissivity, the differences also increase. The difference of the streamlines or the temperature contours is not as distinct as the side wall heat flux distributions. The specular reflection may alter the fluid motion.

• 대한기계학회논문집
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• 제10권5호
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• pp.635-644
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• 1986

A Compuressible turbulent boundary layer effect of the high temperature, accelerating gas flow through the De-Laval nozzle on combustion chamber pressure is numerically investigated. For this purpose, the coupled momentum integral equation and energy integral equation are solved by the Bartz method, and 1/7 power law for both the turbulent boundary layer velocity distribution and temperature distribution is assumed. As far as the boundary layer thicknesses are concerned, we can obtain reasonable solutions even if relatively simple approximations to the skin friction coefficient and stanton number have been used. The effects of nozzle wall cooling and/or mass flow rate on the boundary layer thicknesses and the combustion chamber pressure are studied. Specifically, negative displacement thickness is appeared as the ratio of the nozzle wall temperature to the stagnation temperature of the free stream decreases, and, consequently, it makes the combustion chamber pressure low.

• 대한기계학회논문집
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• 제12권4호
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• pp.847-864
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• 1988

본 연구에서는 연료분출에 박리가 있는 경우와 없는 경우 각각에 대하여 화염 대 근처의 국부가속 현상이 박리에 의하여 어떻게 영향을 받는가를 실험적으로 규명하 고, 나아가서 종래에 행해져 왔던 관련 연구 결과를 재검토할려고 한다.