• 대한기계학회논문집
• /
• 제18권5호
• /
• pp.1203-1217
• /
• 1994

In the present study, in order to analyze a turbulent flow in a square sectiond 180.deg. bend, Kim's low Reynolds number second moment turbulence closure is adopted. In this model, turbulence model constants in the wall region are modified as functions of turbulent Reynolds number by use of near wall turbulent universal properties based on Laufer's experimental results of Reynolds stress distriburions. Algebraic stress model and Reynolds stress equation model are used to verify the low Reynolds number second moment closure. The application of the present low Reynolds number algebraic stress model to the prediction of a square sectioned 180.deg. bend flow gives improved velocities and Reynolds stresses profiles compared with those obtained by using the van Driest mixing length model and present low Reynolds number Reynolds stress equation model.

• 한국전산유체공학회지
• /
• 제6권4호
• /
• pp.35-42
• /
• 2001

In this study, numerical calculations are carried out in order to evaluate the performance of low-Re Reynolds stress model based on SSG model for a swirling turbulent flow in a pipe. The results are compared with those of k-ε model, GL model and the experimental data. The results show that low-Re Reynolds stress model and GL model give better results than k-ε model. In the region near the wall, low-Re Reynolds stress model improves the predictions. However, there is no large difference between the predictions with two Reynolds stress models.

• 대한기계학회논문집
• /
• 제17권6호
• /
• pp.1596-1608
• /
• 1993

본 연구에서는 좀더 정량적인 이론에 바탕하여 제레이놀즈수 2차모멘트 난류모형을 유도하려 한다.

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

• 대한기계학회논문집B
• /
• 제24권1호
• /
• pp.1-8
• /
• 2000

A modified low-Reynolds-number Reynolds stress model is developed for the calculation of drag-reducing turbulent flows induced by polymer injection. The results without polymer injection are compared with the results of direct numerical simulation to ensure the validity of the basic model. In case of drag reduction, profiles of mean velocity and Reynolds stress components, in two-dimensional channel flow, obtained with a proper value of viscosity ratio are presented and discussed. Computed mean velocity profile is in very good agreement with experimental data. And, the qualitative behavior of Reynolds stress components with the viscosity ratio is also reasonable.

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

• 대한토목학회논문집
• /
• 제26권5B호
• /
• pp.529-537
• /
• 2006

본 논문에서는 식생된 개수로 흐름의 수치모의에 필요한 항력가중계수의 영향을 분석하였다. 이를 위해 시간 및 공간 평균기법을 이용하여 식생된 개수로 흐름에서 레이놀즈응력의 수송방정식을 유도하였다. 그 결과 총 레이놀즈응력은 시간의 변동 성분에 의한 레이놀즈응력과 공간상의 변동 성분에 의한 레이놀즈응력의 합이며, 총 레이놀즈응력의 수송방정식을 수치모의하기 위한 항력가중계수의 값은 $C_{fk}$ = 1.0인 것으로 나타났다. 그러나 시간의 변동 성분에 의한 레이놀즈응력을 수치모의하기 위해서는 거의 영에 가까운 항력가중계수를 갖는 것으로 나타났다. 이는 과거의 수치모의 연구에서 항력가중계수의 값이 거의 영에 가까울 때 실험결과와 잘 일치했는지에 대한 중요한 이유이다. 즉, 공간상의 변동성분에 의한 레이놀즈응력의 값은 실험을 통해 측정하기 매우 어렵기 때문에 식생된 개수로 흐름에서 측정된 레이놀즈응력은 대부분 시간상의 변동성분에 의한 레이놀즈응력이기 때문이다. 또한 레이놀즈응력모형을 이용하여 항력가중계수에 따른 식생된 개수로 흐름을 수치모의하고 기존의 실험 결과와 비교하였다. 그 결과 평균유속과 레이놀즈응력의 경우 항력가중계수의 영향은 작은 것으로 나타났으나, 난류강도 분포에서는 항력가중계수의 영향이 매우 크게 발생하였다. 또한 총 레이놀즈응력과 시간의 변동성분에 의한 레이놀즈응력의 수송방정식에서 각 항의 수지분석을 통하여 항력가중계수가 난류강도에 미치는 영향을 분석하였다.

• 한국전산유체공학회지
• /
• 제2권2호
• /
• pp.9-17
• /
• 1997

The performance of several turbulence models in computing an axisymmetric supersonic base flow is investigated. A compressible Navier-Stokes code, which incorporates k-ε, k-ω model and Reynolds stress closure with three kinds of pressure-strain correlation model, has been developed using implicit LU-SGS algorithm with second-order upwind TVD scheme. Numerical computations have been carried out for Herrin and Dutton's base flow. It is observed that the two-equation models give large backward axial velocity approaching to the base and somewhat larger variation of base pressure distribution than the Reynolds stress model. It is also found that the Reynolds stress model with third order pressure-strain model in the anisotropy tensor predicts most accurate mean flow field.

• 대한기계학회논문집B
• /
• 제20권8호
• /
• pp.2572-2592
• /
• 1996

A low-Reynolds-number second moment turbulence closure was developed with the aid of DNS data. Model coefficients of nonlinear return to isotropy term were derived by use of Cayley-Hamilton theorem and two component turbulence limit condition as the functions of invariances of anisotropy and turbulent Reynolds number. Launder and Tselepidakis' cubic mean pressure strain model was modified to fit the predicted pressure-strain components to the DNS data. Two component turbulence limit condition was the precondition to be satisfied in developing the second moment turbulence closure for the realizable Reynolds stress prediction. But the satisfactions of Reynolds stress level and pressure-strain level of each component were compromised because the satisfaction of both levels was impossible.

• 대한기계학회논문집
• /
• 제17권2호
• /
• pp.416-425
• /
• 1993

To investigate the characteristics of the merged jet arising from the interaction of two opposing curved wall jets over a circular cylinder in still air, mean velocity, Reynolds stresses, triple moments and integral length scale were measured using hot-wire anenometry. The turbulent kinetic energy and shear stress budget were evaluated using the measured data. The variations of the Reynolds stresses, the triple moment and integral length scale are severe in the interaction region. The pressure diffusion terms are found to be very large when compared the other terms in the interaction region. The distributions of the Reynolds stress and the triple moment in the similar region are found to be similar to those of conventional plane jets.