• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.107-109
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• 2003

We propose a wall distance free one-equation turbulence model. The model is organized in an extremely simple form. Only a few model constants were introduced into the model. The model is numerically tough and easy-of-use. The model also demonstrated the ability to simulate the laminar to turbulent flow transition. The model has been applied to the channel flow, the plane jet, the backward facing step flow, the flat plate boundary layer, as well as the flow around the 2D airfoil at large angles of attack, which obtained satisfactory results.

• 해양환경안전학회지
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• 제20권3호
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• pp.323-333
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• 2014

In this paper, the wakes behind a square cylinder were simulated using two kinds of different turbulence models for the eddy viscosity concept such as the zero- and the one-equation model in which the former is the mixing length model and the latter is the k-equation model. For comparison between numerical and analytical solutions, we employed three skill assessments: the correlation coefficient(r) for the similarity of the wake shape, the error of maximum velocity difference(EMVD) for the accuracy of wake velocity and the ratio of drag coefficient(RDC) for the pressure distribution around the structure. On the basis of the numerical results, the feasibility of each model for wake simulation was discussed and a suitable value for the empirical constant was suggested in these turbulence models. The zero-equation model, known as the simplest turbulence model, overestimated the EMVD and its absolute mean error(AME) for r, EMVD and RDC was ranging from 20.3 % to 56.3 % for all test. But the AME by the one-equation model was ranging from 3.4 % to 19.9 %. The predicted values of the one-equation model substantially agreed with the analytical solutions at the empirical mixing length scale $L=0.6b_{1/2}$ with the AME of 3.4 %. Therefore it was concluded that the one-equation model was suitable for the wake simulation behind a square cylinder when the empirical constant for eddy viscosity would be properly chosen.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.23-26
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• 2002

An evaluation of one algebraic and two one-equation eddy viscosity-transport turbulence closure models as implemented to the CFDS(Characteristic Flux Difference Splitting) scheme is presented for the efficient computation of the turbulent flow. Comparisons of Baldwin-Lomax model as algebraic turbulence model and Baldwin-Barth and Spalart-Allmaras model as one-equation turbulence model are presented for three test cases for 3-dimensional flow. The numerical result of the CFDS schem is examined through comparison with the experimental data.

• 대한기계학회논문집
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• 제18권4호
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• pp.967-976
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• 1994

A tensor invariant model equation for the turbulent energy dissipation rate is proposed in the present study, which is able to simulate secondary straining effects such as curvature effects without the introduction of additional empirical input. The source term in this model has a combined form of the generation term due to the mean vorticity with the conventional one due to the mean strain rate. An extended low-Reynolds-number $k-\epsilon$ turbulence model involving this new model equation is tested for a turbulent Coutte flow between coaxial cylinders with inner cylinder rotated, which is a well defined example of curved flows. The predicted results indicate that the present model works much better for this flow, compared with previous models.

• 해양환경안전학회지
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• 제25권3호
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• pp.344-353
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• 2019

The wakes behind a square cylinder were simulated using two-equation turbulence models, $k-{\varepsilon}$ and RNG $k-{\varepsilon}$ models. For comparisons between the model predictions and analytical solutions, we employed three skill assessments:, the correlation coefficient for the similarity of the wake shape, the error of maximum velocity difference (EMVD) of the accuracy of wake velocity, and the ratio of drag coefficient (RDC) for the flow patterns as in the authors' previous study. On the basis of the calculated results, we discussed the feasibility of each model for wake simulation and suggested a suitable value for an eddy viscosity related constant in each turbulence model. The $k-{\varepsilon}$ model underestimated the drag coefficient by over 40 %, and its performance was worse than that in the previous study with one-equation and mixing length models, resulting from the empirical constants in the ${\varepsilon}-equation$. In the RNG $k-{\varepsilon}$ model experiments, when an eddy viscosity related constant was six times higher than the suggested value, the model results were yielded good predictions compared with the analytical solutions. Then, the values of EMVD and RDC were 3.8 % and 3.2 %, respectively. The results of the turbulence model simulations indicated that the RNG $k-{\varepsilon}$ model results successfully represented wakes behind the square cylinder, and the mean error for all skill assessments was less than 4 %.

• 한국해양학회지
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• 제30권1호
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• pp.13-26
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• 1995

Blumberg와 Mellor(1987)의 2 방정식 난류모형, Bleackadar(1962)의 1 산정식을 이용한 1 방정식 난류모양 및 Prandtl(1925)의 혼합거리식을 이용한 0 방정식 난류모 양을 일련의 등밀도 문제에 적용 비교하였다. 구체적으로 일정유량이 주어진 수심이 급변하는 수로의 흐름, 유한수로에서 의 조류의 연직구조 및 일정수심 수로에서 의 정 상상태 취송류 문제에 대하여 비교되었다. 불규칙한 수심에 일정유량이 주어진 수로 흐름 및 점모양을 이용한 조류의 수치실험에서는 적용된 난류모양 모두 거의 비슷한 결과를 보였으며, 비교적 관측된 유속구조와 부합하는 좋은 결과를 보였다. 그러나 정 상상태의 취송류 경우에는 2 방정식만이 관측된 유속과 부합하는 유속구조를 재현하 였으며, Blackadar의 l 산정식을 이용한 1, 0 방정식 난류모형은 수면근처의 유속을 관측치보다 작게 계산하였다. 이류항 및 수평확산항의 영향이 작은 조류 및 취송류의 경우, 2 방정식 난류모형에 의한 연직와점성계수 이류항 및 수평확산항의 영향이 작은 조류 및 취송류의 경우, 2 방정식 난류모양에 의한 연직와점성계수 및 특성길이의 연 직분포는 중간수심에서 최대값을 갖는 포물형이었으며, Blackadar의 l 산정식을 사용 한 1, 0 방정식 난류모형에 의한 연직와점성계수 및 혼합특성길이의 연직분포는 수면 에서 최대인 선형에 가까웠다.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2007년도 정기총회 및 학술발표대회
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• pp.603-607
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• 2007

Recently, the frequency of unexpecting heavy rains has been increased due to abnormal climate and extreme rainfall. There was a limit to analyze one dimension or two dimension stream flow of domestic rivers that was applied simple momentum equation and fixed energy conservation. Therefore, hydrodynamics flow analysis in rivers has been needed three dimensional numerical analysis for correct stream flow interpolation. In this study, CFD model on FLOW-3D was applied to stream flow analysis, which solves three dimension RANS(Reynolds Averaged Navier-Stokes Equation) control equation to find out physical behavior and the effect of hydraulic structures. Numerical simulation accomplished those results was compared by using turbulence models such as $k-{\backepsilon}$, RNG $k-{\backepsilon}$ and LES. Those numerical analysis results have been illustrated to bends and junctions by the turbulence energy effects, velocity of flow distributions, water level pressure distributions and eddy flows.

• International Journal of Aeronautical and Space Sciences
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• 제13권3호
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• pp.307-316
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• 2012

Numerical simulations of 3D aircraft configurations are performed in order to understand the effects of turbulence models on the prediction of aircraft's aerodynamic characteristics. An in-house CFD code that solves 3D RANS equations and two-equation turbulence model equations are used. The code applies Roe's approximated Riemann solver and an AF-ADI scheme. Van Leer's MUSCL extrapolation with van Albada's limiter is also adopted. Various versions of Menter's $k-{\omega}$ SST turbulence models as well as Coakley's $q-{\omega}$ model are incorporated into the CFD code. Menter's $k-{\omega}$ SST models include the standard model, the 2003 model, the model incorporating the vorticity source term, and the model containing controlled decay. Turbulent flows over a wing are simulated in order to validate the turbulence models contained in the CFD code. The results from these simulations are then compared with computational results from the $3^{rd}$ AIAA CFD Drag Prediction Workshop. Numerical simulations of the DLR-F6 wing-body and wing-body-nacelle-pylon configurations are conducted and compared with computational results of the $2^{nd}$ AIAA CFD Drag Prediction Workshop. Aerodynamic characteristics as well as flow features are scrutinized with respect to the turbulence models. The results obtained from each simulation incorporating Menter's $k-{\omega}$ SST turbulence model variations are compared with one another.

• 대한기계학회논문집B
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• 제40권2호
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• pp.75-83
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• 2016

터보기계 내부 유동장은 역압력구배, 고속 유동으로 인해 매우 복잡하며, 이를 해석하기 위해 보다 정교한 난류 모델이 요구된다. 유동 해석을 위해 대수모델, 2-방정식 와점도 모델 등이 널리 사용되고 있으나, 매우 복잡한 유동을 모사하는데 어려움이 있다. 본 연구에서는 복잡한 유동에서의 예측성능이 우수하다고 알려진 Durbin의 V2-F난류 모델을 자체 개발 코드인 T-Flow에 적용하였으며, 채널 및 압축기 캐스캐이드 유동 해석 결과를 이용하여 난류 모델을 검증하였다. 또한 저속 압축기 동익 해석을 통해 터보기계 내부 유동에서의 적용 가능성을 판단하였다. 그 결과, V2-F난류 모델은 1-방정식, 2방정식 난류 모델보다 우수한 블레이드 표면 압력 분포 예측성능을 보였다.

• 한국해안해양공학회지
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• 제6권3호
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• pp.205-215
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• 1994

난류모형을 도입하여 풍성류에 대한 3차원 수치모형을 수립하고, 풍성류 계산에 있어서 연직 와점성계수 산정방법들에 대한 비교평가를 수행하였다. 검토된 방법은 함수형(0-방정식), 1-방정식, 2개의 2-방정식 난류모형($ extsc{k}$-$\varepsilon$과 $textsc{k}$-ι)이며, 난류모형은 난류확산 특성길이의 연직분포에 대한 비교를 통하여 각 방법의 특징이 검토되었다. 양단이 막힌 수로와 순환수로에서 유속의 연직분포 계산결과를 수리실험자료와 비교검증하였다. 분석결과에 의하면 1-방정식 난류모형에 적합한 난류확산 특성길이 산정식은 포물선형이었으며, 2-방정식 난류모형($textsc{k}$-ι 모형과 $textsc{k}$-$\varepsilon$모형)은 대체로 실험치와 일치하는 경향을 보였다. 바람에 의한 영향이 전수심에 미치지 않는 경우에 가정된 연직 와점성계수의 분포는 바람이 영향을 미치는 수심까지만 적용되며, 영향이 없는 수심에서는 연직확산이 거의 일어나지 않아 적정성계수의 크기가 0에 가까웠다.