• Journal of the Korean Society of Combustion
• /
• v.7 no.2
• /
• pp.49-61
• /
• 2002

Numerical simulation is performed for stagnating turbulent flows of impinging and countercurrent jets by the Reynolds stress model(RSM). Results are compared with those of the ${\kappa}-{\varepsilon}$ model and available data to assess the flow characteristics and turbulence modes. Three variants of the RSM tested are those of Gibson and Launder(GL), Craft and Launder(GL-CL) and Speziale, Sarkar and Gatski(SSG). As well known, the ${\kappa}-{\varepsilon}$ model overestimates turbulent kinetic energy near the wall significantly. Although the RSM is superior to the ${\kappa}-{\varepsilon}$ model, it shows considerable difference according to how the redistributive pressure-strain term is modeled. Results of the RSM for countercurrent jets are improved with the modified coefficients for the dissipation rate, $C_{{\varepsilon}1}\;and\;C_{{\varepsilon}2}$ suggested by Champion and Libby. The performance of the three variants of the RSM model for stagnating flows are assessed.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.3
• /
• pp.280-293
• /
• 1998

Numerical study on turbulent and mean structures of a turbulent boundary layer with longitudinal and spanwise pressure gradient is carried out by using Reynolds-stress-model (RSM). The existence of pressure gradient in a turbulent boundary layer causes the skewing or divergence of rates of strain, which contributes to production of turbulent kinetic energy. Also, this augmentation of production due to extra rates of strain can increase the turbulent mixing and cause the anisotropy of turbulent intensities in the outer layer. This paper uses the Reynolds Stress Model to capture anisotropy of turbulent structures effectively and is devoted to compare the results computed by using RSM and the standard k-.epsilon. model with experimental data. It is concluded that the RSM can produce the more accurate predictions for capturing the anisotropy of turbulent structure than the standard k-.epsilon. model.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.7
• /
• pp.911-918
• /
• 1997

The turbulent viscous wake flows behind a single airfoil, two-dimensional stationary blade row and three-dimensional rotating blade row were calculated, and the numerical results were compared with experimental ones. The numerical technique was based on the SIMPLE algorithm using three turbulent closure models, standard k-.epsilon. model(WFM), low Reynolds number k-.epsilon. model(LRN) and Reynolds stress model (RSM). In the case of a single airfoil, WFM, LRN and RSM presented fairly good velocity distributions in the wake compared with experimental data. In the case of the stationary blade row, LRN and RSM presented better results than WFM for wake velocity distribution, and especially LRN showed best results among these three turbulent models. In the case of the rotating blade row, WFM and LRN showed fairly good agreement with experimental data of the three-dimensional velocity component distributions in the range from hub to mid span region. LRN was also superior to WFM in accuracy of prediction for the wake velocity distribution as same with the cases of a airfoil and the stationary blade row.

• Proceedings of the KSME Conference
• /
• 2000.04b
• /
• pp.485-490
• /
• 2000

The effect of curvature, rotation, variable cross-section can make very complex flow pattern in turbo-machinery such as Pumps, compressors, turbines, In this study of turbulent flow characteristics rotating $90^{\circ}$ curved duct under a Plane rate of strain condition is computationally analyzed. The objective of this study is to understand the complex turbulent flow phenomena in turbo-machinery passage by analyzing the modeled rotating $90^{\circ}$ curved duct flow. RSM(Reynolds Stress Model) was employed for the turbulence modeling of Reynolds stress in momentum equations proposed by Shin(1995). The three dimensional computational code which adopts RSM for trubulence modeling was newly developed for the generalized curvilinear coordinate.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.13 no.7
• /
• pp.588-594
• /
• 2001

The purpose of this study is to investigate the thermal and hydrodynamic characteristics of the channel in corrugated plate type heat exchangers numerically. Numerical work has been conducted using the Reynolds Stress Model(RSM) by utilizing the commercial finite-volume code, FLUENT. Based on this model, the dependence of heat transfer and friction factor on geometrical parameters have been investigated. It is found that larger corrugation angle give higher values of heat transfer coefficients and friction factors. As the reynolds number increases, the heat transfer coefficient also increases. It is also observed that the heat transfer coefficient reaches maximum while the friction factor stays relatively low at same corrugation angle. Through the analysis, it is found that the optimum corrugation angle for the heat exchanger performance exists. It is noted that the flow repulsions at the contact point of the two fluid streams make the low mixing more active for larger corrugation angle and high reynolds number.

• Journal of the Korean Society of Safety
• /
• v.11 no.3
• /
• pp.66-74
• /
• 1996

Numerical simulations were carried out using standard Reynolds stress turbulence model(LRR model) and modified RSM(Janicka model ) to validate these models in combustion flow fields. Two flames were selected for use as a benchmark data for model testing. One is a conventional jet diffusion flame that has the effect of suppression of turbulence by combustion. The other is a triple jet diffusion flame that designed to give high turbulence to the periphery of the flame and to remove the low Reynolds-number flow fields. As a result, it was found that the modification of standard RSM model is indispensable in the modelling of flames with low turbulence region. And it is also necessary to improve the existing modified models for the universal use.

• 한국전산유체공학회:학술대회논문집
• /
• 2001.10a
• /
• pp.44-50
• /
• 2001

A numerical study was made to choose the better turbulence model for the flow in the discharge flow path from a diffuser to a wall. In this study standard $\kappa-\epsilon$ model(SKE), RNG $\kappa-\epsilon$ model(RNG), and Reynolds stress model(RSM) were applied. In case of the flow with relatively high Reynolds number at a diffuser inlet, the pressure loss coefficients by RNG have a tendency to be near to those by SKE at small ratio(below about 0.35) of $h/D_o$, but to those by RSM at large ratio(above about 0.35). At large ratio RNG begins to enlarge the effects of rapid strain and streamline curvature. RNG & RSM are recommended as the appropriate turbulence models for this case. But it is noticeable that the velocity gradient pattern in RNG is same as in SKE, and also that the total pressure distribution in RNG is same as in RSM only at swirling flow area, same as in SKE only at main flow area.

• Proceedings of the KSME Conference
• /
• 2000.11b
• /
• pp.473-478
• /
• 2000

In this study, the characteristics of the three-dimensional turbulent flow in a rotating square sectioned $90^{\circ}$ bend were investigated by numerical simulation and experiment. In the experimental study, the characteristics of a developing turbulent flow are measured using hot-wire anemometer to seize the rotational effects on the flow characteristics and to compare the results of computational simulation with Reynolds stress model. Each refinement is shown to lead to an appreciable improvement in the agreement between measurement and computation.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2019.05a
• /
• pp.93-93
• /
• 2019

식생이 있는 개수로 흐름의 분석이 중요한 이유는 식생이 흐름 특성과 유사이송 및 하상변동에 영향을 주어 복잡한 흐름 현상을 만들어 내기 때문이다. 식생 밀도, 식생 길이, 식생이 식재된 형태에 따라 흐름의 현상이 달라지며, 흐름 특성의 변화로 인해 하상 및 주변 하천구조물에 영향을 줄 수 있다. 하천의 식생은 대부분 폭과 길이가 제한된 모습으로 존재하는 경우가 많으며, 식생이 존재하는 영역에서는 식생항력에 의해 유속이 감소하고 식생이 없는 영역에서 유속이 증가한다. 식생항력에 의해 변화된 흐름 특성은 일정 거리를 지나면 평형상태에 도달하게 되며, 식생의 경계면에서는 전단층이 발달하여 모멘텀의 교환이 활발하게 발생하는 현상을 보인다. 식생 흐름의 특성을 분석하기 위해 수치모형으로는 식생 흐름의 강한 비등방성을 모의할 수 있는 비등방성 수치모형이 적합하다. 본 연구에서는 부분 식생이 식재된 개수로에서 RSM (Reynolds stress model)을 이용하여 식생과 식생 주변의 흐름 특성 및 난류량을 분석하였다. 흐름의 변화에 따라 크게 3 구간으로 나누어 흐름 특성을 파악할 수 있으며, 식생의 밀도와 식생 영역의 폭의 길이에 따라 각 구간의 길이가 달라지는 것을 확인하였다.

• International Journal of Aeronautical and Space Sciences
• /
• v.17 no.1
• /
• pp.8-19
• /
• 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.