• 한국전산유체공학회지
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• 제4권3호
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• pp.44-51
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• 1999

A modified version of SST turbulence model is suggested to simulate unsteady separated flows over oscillating airfoils. The original SST model, which shows good performance in predicting various steady flows, often results in oscillatory behavior of aerodynamic loads in large separated flow regions. It is shown that this oscillatory behavior is due to the adoption of the absolute value of vorticity in generalizing the original model. As a remedy, a modification is made such that the vorticity in the original SST model is replaced by strain rate. The present model is verified for a mild separated airfoil flow at fixed angle of incidence and for unsteady flowfields about oscillating airfoils. The results are compared with BSL model and original SST model. It is illustrated that the present model gives a better agreement with the experimental results than other two models.

• 한국항공우주학회지
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• 제31권8호
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• pp.1-7
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• 2003

본 연구에서는 새로운 $\varepsilon$-SST 난류 모델을 이용하여 벽면 근처에 위치한 정사각주 주위의 유동장에 대한 수치해석을 수행하였다. SST 난류 모델을 수정하여 새롭게 제안된 $\varepsilon$-SST 모델은 뭉툭한 물체 주위의 박리 영역에서 기존의 2-방정식 난류 모델보다 향상된 해석 결과를 보임을 확인하였다. $\varepsilon$-SST 모델을 이용하여 박리가 수반되는 유동영역에 대한 효율적인 해석이 가능할 것이다. 또한, 본 연구에서는 임계 간극 이하에서는 주기적인 와류배출이 억제됨을 입증하였으며, 스트로할수는 간극의 높이와 벽면 경계층의 두께의 영향을 받는 다는 것을 확인할 수 있었다.

• 한국추진공학회지
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• 제17권1호
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• pp.18-25
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• 2013

초음속 축소-확대 노즐 유동을 정확하게 해석하기 위하여, 실험치와 해석값 사이의 비교를 통해 난류모델 성능평가를 수행한다. Boussinesq 가정을 적용한 RANS 방정식으로 2차원 노즐 유동을 해석하되, Spalart-Allmaras, RNG k-${\varepsilon}$, 그리고 k-${\omega}$ SST 난류모델을 평가에 사용한다. 각 모델들로 계산된 노즐 벽면의 압력구배 및 충격파 구조는 실험 데이터와 유사한 결과를 보였는데, 그 중에서도 SST 난류모델이 실험값에 가장 근접한 해석결과를 나타내었다.

• 대한토목학회논문집
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• 제44권3호
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• pp.329-336
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• 2024

우리나라에 설치된 다기능보의 경우 가동보 구간은 수문의 부분 개방 시 수문 개방 높이와 하류의 관리수위에 의해 자유도수 또는 수중도수 형태의 흐름이 발생한다. 본 연구에서는 수문 아래를 지나 흐르며 발생하는 수중도수를 수치모의하고 평균흐름, 난류량, 그리고 상대수심 등에 대하여 분석하였다. 수치모의를 위하여 unsteady Reynolds-averaged Navier-Stokes 방정식과 volume of fluid 기법, 그리고 k-ω SST 난류모형을 이용하였다. 기존에 수행된 다른 연구자들의 실험 결과를 이용하여 수치모형을 검증하여 수치모형이 도수에서 발생하는 이상흐름을 적절히 모의하는 것을 검토하였다. 또한 내부 평균흐름 및 난류량의 분포에 대하여 모의하여 분포 형태에 대해 분석하고, 자유수면과 재순환영역의 길이 등을 분석하였다.

• 한국전산유체공학회지
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• 제10권4호통권31호
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• pp.1-11
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• 2005

A numerical study of the evaluation of turbulence models for thermal striping phenomenon is performed. The turbulence models chosen in the present study are the two-layer model, the shear stress transport (SST) model and the V2-f model. These three models are applied to the analysis of the triple-jet flow with the same velocity but different temperatures. The unsteady Reynolds-averaged Navier-Stokes (URANS) equation method is used together with the SIMPLEC algorithm. The results of the present study show that the temporal oscillation of temperature is predicted by the SST and V2-f models, and the accuracy of the mean velocity, the turbulent shear stress and the mean temperature is a little dependent on the turbulence model used. In addition, it is shown that both the two-layer and SST models have nearly the same capability predicting the thermal striping, and the amplitude of the temperature fluctuation is predicted best by the V2-f model.

• 한국공간구조학회논문집
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• 제15권1호
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• pp.75-84
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• 2015

This paper presents the dimensionless wall distance, y+ effect on SST turbulent model for wind turbine blade. The National Renewable Energy Laboratory (NREL) Phase VI wind turbine was used for the study, which the wind tunnel and structural test data has publicly available. The near wall treatment and turbulent characteristics have important role for proper CFD simulation. Most of the CFD development in this area is focused on advanced turbulence model closures including second moment closure models, and so called Low-Reynolds (low-Re) number and two-layer turbulence models. However, in many cases CFD aerodynamic predictions based on these standard models still show a large degree of uncertainty, which can be attributed to the use of the $\epsilon$-equation as the turbulence scale equation and the associated limitations of the near wall treatment. The present paper demonstrates the y+ definition effect on SST (Shear Stress Transport) turbulent model with advanced automatic near wall treatment model and Gamma theta transitional model for transition from lamina to turbulent flow using commercial ANSYS-CFX. In all cases the SST model shows to be superior, as it gives more accurate predictions and is less sensitive to grid variations.

• Wind and Structures
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• 제17권1호
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• pp.87-105
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• 2013

Modeling an equilibrium atmospheric boundary layer (ABL) in an empty computational domain has routinely been performed with the k-${\varepsilon}$ turbulence model. However, the research objects of structural wind engineering are bluff bodies, and the SST k-${\omega}$ turbulence model is more widely used in the numerical simulation of flow around bluff bodies than the k-${\varepsilon}$ turbulence model. Therefore, to simulate an equilibrium ABL based on the SST k-${\omega}$ turbulence model, the inlet profiles of the mean wind speed U, turbulence kinetic energy k, and specific dissipation rate ${\omega}$ are proposed, and the source terms for the U, k and ${\omega}$ are derived by satisfying their corresponding transport equations. Based on the proposed inlet profiles, numerical comparative studies with and without considering the source terms are carried out in an empty computational domain, and an actual numerical simulation with a trapezoidal hill is further conducted. It shows that when the source terms are considered, the profiles of U, k and ${\omega}$ are all maintained well along the empty computational domain and the accuracy of the actual numerical simulation is greatly improved. The present study could provide a new methodology for modeling the equilibrium ABL problem and for further CFD simulations with practical value.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2001년도 추계 학술대회논문집
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• pp.51-57
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• 2001

The eddy viscosity turbulence models were applied to predict the flows through a cascade, and the prediction performances of turbulence models were assessed by comparing with the experimental results for a controlled diffusion(CD) compressor blade. The original $\kappa-\omega$ turbulence model and $\kappa-\omega$ shear stress transport(SST) turbulence model were used as two-equation turbulence model which were enhanced for a low Reynolds number flow and the Baldwin-Lomax turbulence model was used as algebraic turbulence model. Farve averaged Wavier-Stokes equations in a two-dimensional, curvilinear coordinate system were solved by an implicit, cell-centered finite-volume computer code. The turbulence quantities are obtained by lagging when the men flow equations have been updated. The numerical analysis was made to the flows of CD compressor blade in a cascade at three different incidence angles (40. 43.4. 46 degrees). We found the reversion in the prediction performance of original $\kappa-\omega$ turbulence model and $\kappa-\omega$ SST turbulence model when the incidence angie increased. And the algebraic Baldwin-Lomax turbulence model showed inferiority to two-equation turbulence models.

• International Journal of Aeronautical and Space Sciences
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• 제17권1호
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• pp.8-19
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• 2016

This paper investigates the effects of inlet turbulence conditions and near-wall treatment methods on the heat transfer prediction of gas turbine vanes within the range of engine relevant turbulence conditions. The two near-wall treatment methods, the wall-function and low-Reynolds number method, were combined with the SST and ${\omega}RSM$ turbulence model. Additionally, the RNG $k-{\varepsilon}$, SSG RSM, and $SST_+{\gamma}-Re_{\theta}$ transition model were adopted for the purpose of comparison. All computations were conducted using a commercial CFD code, CFX, considering a three-dimensional, steady, compressible flow. The conjugate heat transfer method was applied to all simulation cases with internally cooled NASA turbine vanes. The CFD results at mid-span were compared with the measured data under different inlet turbulence conditions. In the SST solutions, on the pressure side, both the wall-function and low-Reynolds number method exhibited a reasonable agreement with the measured data. On the suction side, however, both wall-function and low-Reynolds number method failed to predict the variations of heat transfer coefficient and temperature caused by boundary layer flow transition. In the ${\omega}RSM$ results, the wall-function showed reasonable predictions for both the heat transfer coefficient and temperature variations including flow transition onset on suction side, but, low-Reynolds methods did not properly capture the variation of the heat transfer coefficient. The $SST_+{\gamma}-Re_{\theta}$ transition model showed variation of the heat transfer coefficient on the transition regions, but did not capture the proper transition onset location, and was found to be much more sensitive to the inlet turbulence length scale. Overall, the Reynolds stress model and wall function configuration showed the reasonable predictions in presented cases.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.627-630
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• 2003

This work presents a numerical procedure to optimize the shape of three-dimensional channel with angled ribs mounted on one of the walls to enhance turbulent heat transfer. The response surface method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of flow and heat transfer. SST turbulence model is used as a turbulence closure. The width-to-height ratio of the rib, rib height-to-channel height ratio, pitch-to-rib height ratio and attack angle of the rib are chosen as design variables. The objective function is defined as a linear combination of heat-transfer and friction-loss related terms with weighting factor. D-optimal experimental design method is used to determine the data points. Optimum shapes of the channel have been obtained for the weighting factors in the range from 0.0 to 1.0.