• Journal of Advanced Marine Engineering and Technology
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• 제20권5호
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• pp.39-44
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• 1996

To overcome weak poinks of the standard k-${\varepsilon}$ turbulence model when applied to complex turbulent flows, various modified models were proposed. But their effects are confined to special flow fields. They have still some problems. Recently, an anisotropic k-${\varepsilon}$ turbulence model was also proposed to solve the drawback of the standard k-${\varepsilon}$ turbulence model. This study is concentrated on the evaluation of the anisotropic k-${\varepsilon}$ turbulence model by the analysis of axisymmetric swirling turbulent flow. Results show that the anisotropic k-${\varepsilon}$ turbulence model has scarecely the fundamentally physical mechanism of predicting the swirling structure of flow.

• 대한기계학회논문집B
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• 제21권8호
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• pp.1046-1055
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• 1997

An anisotropic k-.epsilon. turbulence model for predicting the rotating flows is proposed with the simple inclusion of a new parameter dealing with the extra straining effects in the .epsilon.-equation. This model is employed to compute the effects of Coriolis forces on fully-developed flow in a rotating channel. The predicted results indicate that the present model captures fairly well the striking rotational-induced effects on the Reynolds stresses and the mean flow distributions, including the argumentation of turbulent transport on the unstable side (pressure surface) of the channel and its damping on the stable side (suction surface).

• 한국수자원학회논문집
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• 제38권10호
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• pp.871-883
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• 2005

본 논문은 식생된 개수로 흐름에서 난류의 비등방성이 평균유속 및 난류구조에 미치는 영향을 파악하기 위한 수치모의 연구이다. 비등방성 난류모형인 레이놀즈응력모형을 이용하여 식생이 없는 일반 개수로 흐름과 침수 및 정수식생된 개수로 흐름에서의 평균유속 및 난류구조를 수치모의하였다. 수치모의 결과를 기존의 실험결과 및 k-$\epsilon$ 모형과 응력대수식모형에 의한 계산 결과와 비교하였다. 식생이 없는 일반 개수로 흐름과 정수식생된 개수로 흐름에서의 평균유속과 레이놀즈응력을 계산한 결과 등방성 및 비등방성 난류모형에 의한 해석 결과의 차이가 거의 나타나지 않았다. 즉, 난류의 비등방성의 영향이 매우 작은 것으로 나타났다. 그러나 자유수면 및 바닥 근처에서 발생되는 난류의 감쇠효과에 의한 난류의 비등방성은 레이놀즈응력이 가장 잘 예측하는 것으로 나타났다. 침수식생된 개수로 흐름의 경우 식생높이 부근에서 난류의 비등방성이 강하게 발생하는 것으로 나타났다. 계산된 평균유속 및 난류구조는 레이놀즈응력모형이 다른 모형 보다 가장 정확한 예측을 수행하였으며, 등방성 모형인 k-$\epsilon$ 모형은 식생높이 보다 높은 영역에서 평균유속 및 난류강도를 각각 과대 및 과소 예측하는 것으로 나타났다. 또한 계산된 결과를 이용하여 식생된 개수로 흐름에서의 부유사량을 산정한 결과 등방성 난류모형이 부유사량을 과소 산정하는 것으로 나타났다.

• 대한기계학회논문집
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• 제17권8호
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• pp.2069-2078
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• 1993

The buoyancy-driven turbulent thermal convection is predicted using an anisotropic hybrid turbulence model, which is incorporated with a low Reynolds k-.epsilon. turbulence model and an anisotropic buoyant part of algebraic stress model(ASM). The numerical predictions are compared with the Davidson's model,(1) the full ASM and the experimental results of Cheesewright et al.(2) All the models are shown to predict good agreements with the experiments for the averaged turbulence quantities. It is found that the effect of an anisotropic part on the Reynolds stress and the turbulent heat fluxes is substantial. In this study, the present hybrid model gives a fairly reasonable prediction in terms of the computational accuracy, convergence and stability. The contribution of an anisotropic buoyant part to turbulent heat fluxes are also scrutinized over the range of Rayleigh numbers $(4.79{\times}10^{10}{\le}Ra{\le}7.46{\times}10^{10}).$

• 대한기계학회논문집
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• 제14권2호
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• pp.440-452
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• 1990

Comprehensive numberical computations have been made for four turbulent swirling jets with and without recirculation to critically evaluate the accuracy and universality of several exising turbulence models as well as of the modified k-.epsilon. model proposed in the present study. A numerical scheme based on the full Navier-Stoke equations ha been developed and used for this purpose. Inlet conditions are given by experiments, whenever possible, to minimize the error due to incorrect initial conditions. The standard k-.epsilon. model performs well for the strongly swirling jets with recirculation while it underpredicts the influence of swirl for weakly swirling jets. Rodi's swirl correction and algebraic stress model do not exhibit universality for the swirling jets. The present modified k-.epsilon. model derived from algebraic stress model accounts for anisotropy and streamline curvature effect on turbulence. This model performs consistently better than others for all cases. It may be because these flows have a strong dependence of stresses on the local strain of the mean flow. The predictions of truculence intensities indicate that this model successfully reflect the curvature effect in swirling jets, i.e. the stabilizing and destabilizing effects of swirl on turbulence transport.

• Nuclear Engineering and Technology
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• 제36권2호
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• pp.153-164
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• 2004

A computational fluid dynamics (CFD) analysis has been performed to investigate the turbulent flow and heat transfer in a triangular rod bundle with pitch-to-diameter ratios (P/D) of 1.06 and 1.12. Anisotropic turbulence models predicted the turbulence-driven secondary flow in a triangular subchannel and the distributions of the time mean velocity and temperature, showing a significantly improved agreement with the measurements from the linear standard $k-{\epsilon}$ model. The anisotropic turbulence models predicted the turbulence structure for a rod bundle with a large P/D fairly well, but could not predict the very high turbulent intensity of the azimuthal velocity observed in the narrow flow region (gap) for a rod bundle with a small P/D.