• 대한기계학회논문집B
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• 제32권2호
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• pp.83-91
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• 2008

A three-dimensional computation was conducted to understand effects of the low Reynolds number on the performance in a low-speed axial compressor at the design condition. The low Reynolds number can originates from the change of the air density because it decreases along the altitude in the troposphere. The performance of the axial compressor such as the static pressure rise was diminished by the separation on the suction surface with full span and the boundary layer on the hub, which were caused by the low Reynolds number. The total pressure loss at the low Reynolds number was found to be greater than that at the reference Reynolds number at the region from the hub to 85% span. Total pressure loss was scrutinized through three major loss categories in a subsonic axial compressor such as the profile loss, the tip leakage loss and the endwall loss using Denton#s loss model, and the effects of the low Reynolds number on the performance were analyzed in detail.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 춘계 학술대회논문집
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• pp.138-141
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• 2007

A three-dimensional computation was conducted to understand effects of the low Reynolds number on the performance in a low-speed axial compressor at the design condition. The low Reynolds number can originates from the change of the air density became it decreases along the altitude in the troposphere. The performance of the axial compressor such as the static pressure rise wag diminished by the separation on the suction surface and the boundary layer on the hub, which were caused by the low Reynolds number. The total pressure loss at the low Reynolds number was found to be greater than that at the reference Reynolds number at the region from the hub to 90% span. Total pressure loss was scrutinized through three major loss categories in a subsonic axial compressor such as profile loss, tip leakage loss and endwall loss using Denton's loss model, and effects of the low Reynolds number on the performance were analyzed in detail.

• 대한기계학회논문집
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• 제19권3호
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• pp.741-750
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• 1995

The turbulent buoyancy-driven flow in 2-dimensional enclosed cavities heated from the vertical side is numerically calculated for both cases of a Rayleigh number of 5*10$^{10}$ for air and 2.5*10$^{10}$ for water. Three different turbulence models are considered : standard k-.epsilon. model of Ozoe and low-Reynolds-number model of Lam and Bremhorst, and another low-Reynolds-number model of Davidson. The results indicate that the use of low-Reynolds number models is recommended for the indoor airflow computation, and the results from Davidson model are reasonably close to the reported experimental data. A sensitivity study shows that the amounts of wall-heat transfer and the velocity profiles with the Lam and Bremhorst model largely depend on the choice of the wall function for .epsilon..

• 에너지공학
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• 제2권3호
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• pp.251-257
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• 1993

유한체적법(Finite Volume Method)을 이용하여 블럭이 부착된 수평 유로의 강제 대류 열전달 현상을 해석하였다. 블럭의 갯수, Reynolds 수 그리고 블럭 간의 간격을 변화시키면서 해석하였고 블럭이 부착된 수평판은 전도벽면 (conducting plate)으로 해석하였다. 블럭내에서는 1/2 체적과 전체적에서 열원이 있다고 가정하였으며, 유동은 2차원 정상상태 비압축성 유동이라고 하였다. 전체적에서 열원이 있는 경우보다 1/2 체적에서 열원이 있는 경우가 전체 온도값이 높게 나타났으며, Reynolds 수와 블럭 사이의 간격이 커질수록 온도값이 낮아진다. 수평판이 단열되어 있는 경우보다 전도벽면으로 해석한 경우가 온도값이 낮게 나타나며 수평판이 단옅되어 있다고 가정한 경우에는 최고온도 값의 위치가 단열면 근처이나 전도벽면의 경우에는 블럭내의 중심에서 우측으로 치우쳐 있다. 그리고, 블럭의 1/2 체적에서 열원이 있는 경우의 최고 온도 위치는 블럭의 전체적에서 열원이 있는 경우의 위치보다 더 상단에 치우침을 알 수 있다. Nusselt 수는 블럭 윗면의 좌측 부분에서 다른 부분보다 높은 수치를 나타내고 있으며 Reynolds 수가 커질수록 Nusselt 수의 값이 증가한다. 그리고, 블럭내의 최고 온도값은 이러한 무차원 변수들과의 상관 함수를 이용하여 예측하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제34권2호
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• pp.235-242
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• 2010

본 연구는 열교환기의 가열된 표면위에 부착된 지열수 스케일의 조도 영향을 검증하기 위한 강제 대류 열전달에 관한 실험적 연구이다. 실험은 원형 원관 위에 5종류의 실리카 스케일 입자를 균일하게 부착하여 행하였다. Reynolds수는 13,000에서 50,000의 범위에서 행하였다. 국소와 평균 열전달 특성은 스케일 입자 크기와 레이놀즈수의 함수로서 측정하였으며 평균오염저항을 이들의 결과로부터 평가하고 그들의 특성들을 분석 하였다. 원관의 열전달 특성은 지열수 스케일의 오염에 의해, 특히 입자 크기에 의해 크게 변화하였다. 또한 국소와 평균 Nusselt수는 원관 간격과 Reynolds 수에 의해 크게 의존 되었다.

• 대한토목학회논문집
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• 제33권1호
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• pp.93-100
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• 2013

본 연구에서는 트윈박스 단면인 이순신대교의 레이놀즈수 변화에 따른 공기력의 영향을 살펴보는데 그 목적이 있다. 이를 위하여 1/30 대축척 모형을 제작하여 공군사관학교 아음속 중형 풍동에서 최대 풍속 70m/s까지 풍속을 증가시켜가면서 공기력을 측정하여, 전북대학교 소형풍동에서 수행한 저레이놀즈수 풍동실험 결과와 비교하였다. 본 연구 대상 교량 단면은 레이놀즈수의 영향을 받는 것으로 나타났으며, 고레이놀즈수 실험 결과 기존 저레이놀즈수 실험보다 항력계수는 약 23%정도 낮은 수준인걸로 나타났다. 또한 경계층 촉진장치를 효과적으로 이용하면 기존의 저레이놀즈수 풍동실험 조건에서 고레이놀즈수 모사 실험이 가능한 것으로 판단된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2297-2302
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• 2007

Numerical simulations are conducted to analyze conjugate heat transfer characteristics in a ribbed channel. In this simulation, the effects of Reynolds number and heat capacity of the solid channel wall on convective heat transfer are observed in the turbulent flow regime. In the case of the conducting wall against isothermal wall, the relative ratio of the thermal resistance between the solid wall and the flow field varies with Reynolds number. Thus the characteristics of the conjugate heat transfer are changed with the Reynolds number. Heat capacity ratio affects the temperature fluctuation inside solid wall. The temperature fluctuation inside the solid wall decreases with increasing the heat capacity of the solid wall so that the convective heat transfer increases. When the thermal conductivity ratio is smaller than 10, the effects of flow characteristics on heat transfer are changed.

• 한국해양공학회지
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• 제11권4호
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• pp.122-129
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• 1997

Flow characteristics of two-dimensional closed square cavities near unsteady critical Reynolds numbers were studied numerically at five Reynolds numbers : 8${\times}10^3$, 8.5${\times}10^3$, 9${\times}10^3$, 9.5${\times}10^3$ and $10^4$ were investigated. A convection conservative difference scheme based upon SOLA to maintain the nearly 2nd-order spatial accuracy was adopted on irregular grid formation. Irregular grid number is 80${\times}$80 and its minimum size is about 1/400 of the cavity height(H) and its maximum is about 1/53 H. The result shows that the critical Reynolds number indicating the emergence of flow unsteadiness exists near Re=8.5${\times}10^3$ and their flow patterns reveal periodic fluctuation during transient and fully-developed stages.

• Journal of Advanced Marine Engineering and Technology
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• 제20권5호
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• pp.22-29
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• 1996

Flow characteristics of two-dimensional closed square cavities near unsteady critical Reynolds numbers were studied numerically at four Reynolds numbers : $8{\times}10^3,\;8.5{\times}10^3,\;9{\times}10^3\;and\;9.5{\times}10^3.$ A convection conservative difference scheme based upon SOLA to maintain the nearly 2nd-order spatial accuracy is adopted on irregular grid formation. Irregular grid number is $80{\times}80$ and its minimum size is about 1/400 of the cavity height(H) and its maximum is about 1/53 H. The result shows that the critical Reynolds number indicating the emergence of flow wnsteadiness is ranging from Re=$8{\times}10^3\;to\;8.5{\times}10^3$ and their flow patterns reveal periodic fluctuation during transient and fully developed stages. But macroscopic flow behavior in terms of instantaneous and time-mean characteristics represent remarkable difference.

• 대한기계학회논문집B
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• 제27권6호
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• pp.821-827
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• 2003

Fully developed turbulent flow in a square duct is numerically predicted with two nonlinear low-Reynolds-number ${\kappa}-{\varepsilon}$ models. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in detail with each other. It is found that the nonlinear low-Reynolds-number ${\kappa}-{\varepsilon}$ model adopted in a commercial code is unable to predict accurately duct flows involving turbulence-driven secondary motion with the prediction level of secondary flows one order less than that of the experiment.