• 한국전산유체공학회지
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• 제21권4호
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• pp.102-111
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• 2016

In this paper a computation of turbulent natural convection in enclosures with the elliptic-blending based differential and algebraic flux models is presented. The primary emphasis of the study is placed on an investigation of accuracy of the treatment of turbulent heat fluxes with the elliptic-blending second-moment closure for the turbulent natural convection flows. The turbulent heat fluxes in this study are treated by the elliptic-blending based algebraic and differential flux models. The previous turbulence model constants are adjusted to produce accurate solutions. The proposed models are applied to the prediction of turbulent natural convections in a 1:5 rectangular cavity and in a square cavity with conducting top and bottom walls, which are commonly used for validation of the turbulence models. The relative performance between the algebraic and differential flux model is examined through comparing with experimental data. It is shown that both the elliptic-blending based models predict well the mean velocity and temperature, thereby the wall shear stress and Nusselt number. It is also shown that the elliptic-blending based algebraic flux model produces solutions which are as accurate as those by the differential flux model.

• 대한기계학회논문집
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• 제12권3호
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• pp.607-621
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• 1988

본 연구에서는 미세격자구역에서 속도에 관한 모든 운송방정식(transport equation)과 압력방정식을 푸는 완전미세격자법을 채택하였고 거친 격자구역에서는 K, $\varepsilon$ 방정식모델과 Boussinesq의 난류모델로 과점성계수를 구하는 방법 대신 레이놀 즈응력을 대수식으로 직접 구하는 대수응력모델(algebraic stress model, ASM)을 사용하여 해석하였다.

• International Journal of Aeronautical and Space Sciences
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• 제2권2호
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• pp.28-38
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• 2001

A numerical method for the assessment and correction of tunnel wall interference effects on forced-oscillation testing is presented. The method is based on the wall pressure signature method using computed wall pressure distributions. The wall pressure field is computed using unsteady three-dimensional full Navier-Stokes solver for a 70-degree pitching delta wing in a wind tunnel. Approximately-factorized alternate direction implicit (AF-ADI) scheme is advanced in time by solving block tri-diagonal matrices. The algebraic Baldwin-Lomax turbulence, model is included to simulate the turbulent flow effect. Also, dual time sub-iteration with, local, time stepping is implemented to improve the convergence. The computed wall pressure field is then imposed as boundary conditions for Euler re-simulation to obtain the interference flow field. The static computation shows good agreement with experiments. The dynamic computation demonstrates reasonable physical phenomena with a good convergence history. The effects of the tunnel wall in upwash and blockage are analyzed using the computed interference flow field for several reduced frequencies and amplitudes. The corrected results by pressure signature method agree well with the results of free air conditions.

• 대한기계학회논문집
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• 제16권11호
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• pp.2111-2118
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• 1992

본 연구에서는 원관 내 및 평판 위의 흐름에 있어서 잘 확립된 벽면의 법칙을 적용하여 봉다발의 열전달계수를 예측하여 보고자 한다.

• 대한기계학회논문집
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• 제19권10호
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• pp.2630-2636
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• 1995

A theoretically based prediction for the determination of the subchannel friction factor at low pitch to the rod diameter ratio (P/D < 1.2) in the bare rod bundle flow has been developed. The present model assumes the validity of the Law of Wall over the entire flow area. The algebraic form of the Law of the Wall is integrated over the entire flow area and the local friction velocity variation along the rod periphery is considered in this study. The present method is applied to the rod bundles with P/D < 1.2, and the prediction results show good agreement with the available experimental data.

• Nuclear Engineering and Technology
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• 제23권4호
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• pp.401-409
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• 1991

본 연구에서는 길이 방향의 핀이 달린 봉 다발의 난류 마찰계수를 예측할 수 있는 해석적 모델이 개발되었다. 현재 KMRR의 연료봉으로 핀이 달린 봉다발이 고려되고 있다. 본 모델에서는“Law of the Wall”이 전체 수로에 적용 가능하다고 가정하였다. 전체 수로를 작은 요소 수로와 핀 간 수로로 나누고 각 요소 수로마다“Law of the Wall”속도 분포 곡선을 적분하여 난류 마찰계수를 예측할 수 있는 해석적 방정식을 얻는다. 이 방법을 KMRR 연료봉에 적용한 결과 6핀 실험결과는 잘 예측하고 8핀 실험 결과는 15％ 정도 높게 예측하였다.

• 대한기계학회논문집B
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• 제24권2호
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• pp.316-323
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• 2000

A nonlinear low-Reynolds-number heat transfer model is developed to predict turbulent flow and heat transfer in separated and reattaching flows. The $k-{\varepsilon}-f_{\mu}$ model of Park and Sung (1997) is extended to a nonlinear formulation, based on the nonlinear model of Gatski and Speziale (1993). The limiting near-wall behavior is resolved by solving the $f_{\mu}$ elliptic relaxation equation. An improved explicit algebraic heat transfer model is proposed, which is achieved by applying a matrix inversion. The scalar heat fluxes are not aligned with the mean temperature gradients in separated and reattaching flows; a full diffusivity tensor model is required. The near-wall asymptotic behavior is incorporated into the $f_{\lambda}$ function in conjunction with the $f_{\mu}$ elliptic relaxation equation. Predictions of the present model are cross-checked with existing measurements and DNS data. The model preformance is shown to be satisfactory.

• 대한기계학회논문집
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• 제10권3호
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• pp.357-366
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• 1986

본 연구에서는 3공피토우관 및 열선유속계를 사용하여 벽에 평행한 2차원 난류제트의 난류량들을 측정하였고, 스캐니 밸브를 이용하여 벽면아력분포를 측정함 으로써 재순환 영역을 포함한 전체유동장에서의 유동특성을 고찰하였다. 또한 잘 알려진 표준 k-.epsilon. 난류모형 및 유선곡률을 고려한 수정된 k-.epsilon. 난류모형을 이용하여 측정 수치해석을 수행하였다.

• 대한기계학회논문집B
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• 제23권8호
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• pp.1063-1071
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• 1999

Fine grid calculations are reported for the developing turbulent flow in a curved duct of square cross-section with a radius of curvature to hydraulic diameter ratio ${\delta}=Rc/D_H=3.357 $ and a bend angle of 720 deg. A sequence of modeling refinements is introduced; the replacement of wall function by a fine mesh across the sublayer and a low Reynolds number algebraic second moment closure up to the near wall sublayer in which the non-linear return to isotropy model and the cubic-quasi-isotropy model for the pressure strain are adopted; and the introduction of a multiple source model for the exact dissipation rate equation. Each refinement is shown to lead to an appreciable improvement in the agreement between measurement and computation.

• 한국추진공학회지
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• 제9권3호
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• pp.49-59
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• 2005

파형벽면이 존재하는 채널유동에 대한 난류열전달이 난류모델에 의해서 조사되었다. Park et at.[1]의 비선형 k- f - f$_{모델이 수정되었고, 외재적인 비선형 열유속모델이 사용되었다 선택된 레이놀즈수는 Re$_{b}$ =6760이고 형상변화 (0 $\leq$ $\alpha$/$\lambda$$\leq$0.15 and 0.25 $\leq$A/H$\leq$4.0.)에 따른 열전달을 조사하였다. 모델의 성능을 검증하기 위하여 큰에디모사법이 선택된 경우에 수행되었다. 큰에디모사법의 결과와 비교할 때 모델성능은 일반적인 경향을 잘 예측하였다. 비선형 k- $\varepsilon$ - f$_{모델을 이용하여 파형벽면에 의한 열전달의 증가 특징과 형상의 영향이 조사되었다.