• Journal of Mechanical Science and Technology
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• 제18권10호
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• pp.1782-1798
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• 2004

A numerical study of a natural convection in a rectangular cavity with the low-Reynolds-number differential stress and flux model is presented. The primary emphasis of the study is placed on the investigation of the accuracy and numerical stability of the low-Reynolds-number differential stress and flux model for a natural convection problem. The turbulence model considered in the study is that developed by Peeters and Henkes (1992) and further refined by Dol and Hanjalic (2001), and this model is applied to the prediction of a natural convection in a rectangular cavity together with the two-layer model, the shear stress transport model and the time-scale bound ν$^2$- f model, all with an algebraic heat flux model. The computed results are compared with the experimental data commonly used for the validation of the turbulence models. It is shown that the low-Reynolds-number differential stress and flux model predicts well the mean velocity and temperature, the vertical velocity fluctuation, the Reynolds shear stress, the horizontal turbulent heat flux, the local Nusselt number and the wall shear stress, but slightly under-predicts the vertical turbulent heat flux. The performance of the ν$^2$- f model is comparable to that of the low-Reynolds-number differential stress and flux model except for the over-prediction of the horizontal turbulent heat flux. The two-layer model predicts poorly the mean vertical velocity component and under-predicts the wall shear stress and the local Nusselt number. The shear stress transport model predicts well the mean velocity, but the general performance of the shear stress transport model is nearly the same as that of the two-layer model, under-predicting the local Nusselt number and the turbulent quantities.

• 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.

• 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.

• 설비공학논문집
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• 제15권11호
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• pp.895-901
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• 2003

Direct numerical simulation database of an axial turbulent boundary layer is used to compute frequency and wave number spectra of the wall shear-stress fluctuations in a low-Reynolds number axial turbulent boundary layer. One-dimensional and two-dimensional power spectra of flow variables are calculated and compared. At low wave numbers and frequencies, the power of streamwise shear stress is larger than that of spanwise shear stress, while the powers of both stresses are almost the same at high wave numbers and frequencies. The frequency/streamwise wave number spectra of the wall flow variables show that large-scale fluctuations to the ms value is largest for the streamwise shear stress, while that of small-scale fluctuations to the rms value is largest for pressure. In the two-point auto-correlations, negative correlation occurs in streamwise separations for pressure and spanwise shear stress, and in spanwise correlation for both shear stresses.

• 대한기계학회논문집
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• 제9권4호
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• pp.403-413
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• 1985

본 논문에서는 수직벽 하류에 형성되는 박이 전단층의 발전과 재부착 그리고 재발전 경계층에 대해 평균 속도, 벽면의 압력 분포, 난류 강도, 레이놀즈 전단 압력 및 아직 수직벽에 대해서는 보고된바 없는 난류 떨림 속도 성분들의 3승곱 통계치를 측정하여 난류 구조의 변화를 분석하고 이를 수치적 계산 모델개발의 자 료로 제공하고자 함이 이 연구의 목적이다.

• 동력기계공학회지
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• 제5권1호
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• pp.21-26
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• 2001

This paper represents the turbulent intensity, the turbulent kinetic energy and Reynolds shear stress in the X-Y plane of cone type swirl gas burner measured by using X-probe from the hot-wire anemometer system. The experiment is carried out at flowrate 350 and $450{\ell}/min$ respectively in the test section of subsonic wind tunnel. The turbulent intensity and the turbulent kinetic energy show that the maximum value is formed in the narrow slits distributed radially on the edge of a cone type swirl burner, hence, the combustion reaction is anticipated to occur actively near this region. And the turbulent intensities ${\upsilon}\;and\;{\omega}$ are disappeared faster than the turbulent intensity u due to the inclined flow velocity ejecting from the swirl vanes of a cone type baffle plate of burner. Moreover, the Reynolds shear stress $u{\upsilon}$ is distributed about three times as large as the Reynolds shear stress $u{\omega}$ in the outer region of the cone type gas burner.

• 대한기계학회논문집B
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• 제27권7호
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• pp.920-928
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• 2003

The objective of the present study was to investigate the characteristics of flow and wall shear stress under steady and pulsatile flow in the aneurysm. The numerical simulation using the software were carried out for the diameter ratios ranging from 1.5 to 3.0, Reynolds number ranging from 900 to 1800 and Womersley number, 15.47. For steady flow, 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. The position of a maximum wall shear stress was the distal end of the aneurysm regardless of the Reynolds number and diameter ratios. For the pulsatile flow, a recirculating flow at the bulge was developed and disappeared for one period and the strength of vortex increased with the diameter ratio. The maximum values of the wall shear stress increased in proportion to the diameter ratio. However, the position of a maximum wall shear stress was the distal end of the aneurysm regardless of the diameter ratios.

• 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.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.496-501
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• 2003

Reynolds averaged Wavier-Stokes simulations based on the Reynolds stress model was performed to investigated the effect of inlet flow angle on the distributions 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) were considered. Stress tensor analysis, which transforms the Reynolds stress into the principal direction, was applied to show an anisotropy of the normal stresses. Whereas the anisotropy was highest in the region where the tip leakage vortex collides the suction side of the blade and tip leakage flow enters between blade tip of the pressure side and the endwall, it had the lowest value at the center of tip leakage vortex. It was also found that the magnitude of maximum shear stress at design condition was greater than that of off-design condition.

• 대한기계학회논문집
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• 제9권1호
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• pp.64-70
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• 1985

본 연구에서는 관내분류에 관한 수치 해석을 Reynolds응력 모델 즉 5방정식 모델을 사용하여 흐름의 특성을 구명키로 하였다.