• 대한기계학회논문집
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• 제17권6호
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• pp.1541-1546
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• 1993

본 연구에서는 새로운 유형의 저레이놀즈수 레이놀즈응력모델을 개발하기 위해 Launder등과 Gibson과 Launder에 의해 제시된 레이놀즈응력모델을 벽근처의 저 레이놀즈수 영역까지 확장하였다. 개발된 모델의 성능을 시험하기 위해 두 평판사이 에서 완전히 발달된 2차원 유동을 계산하여 그 결과를 Kimm등에 의해 수행된Navier- Stokes방정식의 직접계산결과와 비교하였으며, 아울러 Launder와 Shima가 제시한 모델로도 계산을 수행하여 그 결과를 비교 검토하였다.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1661-1670
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• 1996

Incompressible flow over a backward-facing step is computed by low Reynolds number turbulence models in order to compare with direct simulation results. In this study, selected low Reynolds number 1st and 2nd (Algebraic Stress Model : ASM) moment closure turbulence models are adopted and compared with each other. Each turbulence model predicts different flow characteristics, different re-attachment point, velocity profiles and Reynolds stress distribution etc. Results by .kappa.-.epsilon. turbulence models indicate that predicted re-attachment lengths are shorter than those by standard model. Turbulent intensity and eddy viscosity by low Reynolds number .kappa.-.epsilon. models are still greater than DNS results. The results by algebraic stress model (ASM) are more reasonable than those by .kappa.-.epsilon. models. The convective scheme is QUICK (Quadratic Upstream Interpolation for Convective Kinematics) and SIMPLE algorithm is adopted. Reynolds number based on step height and inlet free stream velocity is 5100.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회 논문집
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• pp.404-408
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• 2005

The Reynolds strss equation with turbulent energy-length scales was simplified in the nearly homogeneous turbulent equilibrium flow and a modified Reynolds stress model was proposed. Tn the model proposed in the present study, Reynolds stresses can be expressed in the form of algebraic equation, so that the turbulent stresses and related quantities are calculated through relatively simple procedures. The model predicted well the turbulent shear stresses of homogeneous flow in local equilibrium state obtained from experimental results published earlier Constants used In the model was determined universally and its validity was discussed briefly.

• 대한기계학회논문집B
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• 제36권8호
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• pp.829-837
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• 2012

벽면 난류의 항력과 밀접한 관련이 있는 유동구조를 조사하기 위해 $Re_{\tau}$ = 180, 395, 590 의 난류채널유동에 대한 직접수치모사를 수행하였다. 확률밀도함수를 조사하여 레이놀즈 전단응력에 가장 큰 기여를 하는 Q2 이벤트를 파악하였으며 Q2 이벤트의 각도의 변화가 $y^+<50$ 에서는 벽 단위로 스케일링되며, y/h > 0.5 에서는 채널의 높이로 스케일링 됨을 확인하였다. Q2 이벤트를 조건으로 하는 조건부 평균 유동장을 조사하여 레이놀즈 전단응력의 발생과 관련이 있는 유동구조는 주 유동방향의 보텍스 및 헤어핀 형상의 보텍스임을 보였다. 또한, 순간 유동장을 관찰하여 높은 레이놀즈 전단 응력의 분포가 이러한 보텍스 구조와 관련이 있으며 1.5 ~ 3h 의 크기를 갖는 대형유동구조를 구성함을 확인하였다.

• Journal of Mechanical Science and Technology
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• 제15권7호
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• pp.889-894
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• 2001

In this study, the performances of various turbulence closure models are evaluated in the calculation of a transonic flow over axisymmetric bump. k-$\varepsilon$, explicit algebraic stress, and two Reynolds stress models, i.e., GL model proposed by Gibson & Launder and SSG model proposed by Speziale, Sarkar and Gatski, are chosen as turbulence closure models. SSG Reynolds stress model gives best predictions for pressure coefficients and the location of shock. The results with GL model also show quite accurate prediction of pressure coefficients down-stream of shock wave. However, in the predictions of mean velocities and turbulent stresses, the results are not so satisfactory as in the prediction of pressure coefficients.

• 대한기계학회논문집B
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• 제28권8호
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• pp.902-909
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• 2004

A steady-state Reynolds averaged Navier-Stokes simulation was conducted to investigate the distribution of the Reynolds stress tensor inside tip leakage vortex of a linear compressor cascade. Two different inlet flow angles ${\beta}=29.3^{\circ}$(design condition) and $36.5^{\circ}$(off-design condition) at a constant tip clearance size of $1\%$ blade span were considered. Classical methods of solid mechanics, applied to view the Reynolds stress tensor in the principal direction system, clearly showed that the high anisotropic feature of turbulent flow field was dominant at the outer part of tip leakage vortex near the suction side of the blade and endwall flow separation region, whereas a nearly isotropic turbulence was found at the center of tip leakage vortex. There was no significant difference in the anisotropy of the Reynolds normal stresses inside tip leakage vortex between the design and off-design condition.

• 대한기계학회논문집
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• 제15권1호
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• pp.262-273
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• 1991

본 연구에서는 벽면에서의 압력은 압력측정 정치를 제작하여 측정하였으며 평 균유동 및 난류량들은 열선 유속계(hot wire system)을 사용하여 측정하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.560-565
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• 2001

The objective of the present study is to investigate the characteristics for flow and wall shear stress in the aneurysm which is a local dilatation of the blood vessel. The numerical simulation using the commercial software for the laminar and steady flow were carried out over the diameter ratios(ratio of maximum diameter of aneurysm to the diameter of blood vessel) ranging from 1.5 to 2.5 and Reynolds number ranging from 900 to 1800. It was shown that a recirculating vortex occupied the entire bulge with its core located closer to the distal end of the bulge and the strength of vortex increased with increase of the Reynolds number and diameter ratio. Especially, for the Reynolds number of 1800 and diameter ratio of 2.5, the very weak secondary recirculating flow was produced at the left upper of the aneurysm. The position of a maximum wall shear stress was the distal end of the aneurysm(z=18mm) regardless of the Reynolds number and diameter ratios. But the maximum values of the wall shear stress increased in proportion to the increase of Reynolds number and diameter ratio.

• Journal of Advanced Marine Engineering and Technology
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• 제35권7호
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• pp.930-937
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• 2011

The characteristics of mean velocity and turbulence have been analyzed in the circular open channel flow using PIV measurement data for a wide range of water depth. The measured data are fitted to a velocity distribution function over the whole depth of the open channel. Reynolds shear stress and mean velocity in wall unit are compared with the analytic models for fully-developed turbulent boundary layer. Both the mean velocity and Reynolds shear stress have different distributions from the two-dimensional boundary layer flow when the water depth increases over 50% since the influence of the side wall penetrates more deeply into the free surface. The cross-stream Reynolds normal stress also has considerably different distribution in view of its peak value and decreasing rate in the outer region whether the water depth is higher than 50% or not.

• Water Engineering Research
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• 제3권4호
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• pp.247-258
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• 2002

This paper presents a non-isotropic turbulence modeling of flows over bedforms. The Reynolds stress model is used for the turbulence closure. In the model, Launder, Reece, and Rodi's model and Hanjalic and Launder's model are employed f3r the pressure strain correlation term and the diffusion term, respectively. The mean flow and turbulence structures are simulated and compared with profiles measured in the experiments. The numerical solutions from two-equation turbulence models are also provided for comparisons. The Reynolds stress model yields the separation length of eddy similar to the other numerical results. Using the developed model, the resistance coefficients are also estimated for the flows at different Froude numbers. Karim's (1999) relationship is used to determine the bedform geometry. It is found that the values of the form drag and the skin friction are very similar to those obtained by the other turbulence models. meaning higher values of the form drag and lower values of the skin friction compared with the empirical formulas.