입방체 주위의 기류 해석에 의한 표준 k-ε 모델과 Low-Reynolds Number형 k-ε 모델의 성능 비교

장현재(Chang Hyun-Jae) 대한건축학회 2009 대한건축학회논문집 Vol.25 No.10

Standard k-ε model was made for fully developed turbulence and has been utilized with wall function for the flow around wall. However when standard k-ε model, high Reynolds number model, is applied to CFD simulation specially in the air flow region of separation, reattachment and transition, the accuracy of analysis cannot be assured. For improving the weakness like these of standard k-ε model, many types of Low-Reynolds number k-ε model have been suggested. In this study, the analysis accuracy was compared between standard k-ε model, Abe-Nagano-Kondo model which is Low-Reynolds number k-ε model, and improved Abe-Nagano-Kondo model for the air flow around cube. As a result, improved Abe-Nagano-Kondo model showed the highest analysis accuracy on separation, reattachment and recirculation among them.

벽면에 부착된 사각 실린더 주변 유동에 대한 난류모델 비교연구

Jun-Young Bae,Gi-Su Song 해양환경안전학회 2020 해양환경안전학회지 Vol.26 No.4

본 논문에서는 건물, 교량 및 해양구조물에 많이 적용되는 기본적인 형상인 벽면에 부착되어 있는 사각실린더 주변의 유동에 대해, 3개의 난류모델(v2-f 모델, k-ω 모델, k-ε 모델)을 적용하여 URANS 수치해석을 각각 수행하고, 그 결과를 비교하였다. 이 유동 은 물체의 모서리에서 발생하는 칼만와(karman vortex) 때문에 본질적으로 강한 비정상성을 가지고 있으며, 물체의 후류 영역에서도 매우 복잡한 유동구조를 가지고 있다고 알려져 있다. 3개의 난류모델이 적용된 수치해석으로부터 예측되는 평균 유동장과 지배적인 유동 의 주파수를 Wang et al.(2004; 2006)의 실험결과와 비교하였다. 비교 결과, v2-f 모델이 적용된 URANS 결과가 실험결과와 가장 유사한 결과를 보여주었고, k-ω 모델도 우수한 결과를 보인 반면, k-ε 모델은 본 대상 유동에 적용하기에 부족함을 확인하였다. 따라서 강한 박리가 존재하는 유동의 해석 시에는 v2-f 모델은 좋은 선택이다. 그리고 유동의 박리 제어를 위한 연구에 활용될 것으로 기대된다. The flow past a wall mounted square cylinder, a typical and basic shape of building, bridge or offshore structure, was simulated using URANS computation through adoption of three turbulence models, namely, the k-ε model, k-ω model, and the v2-f model. It is well known that this flow is naturally unstable due to the Karman vortex shedding and exhibits a complex flow structure in the wake region. The mean flow field including velocity profiles and the dominant frequency of flow oscillation that was from the simulations discussed earlier were compared with the experimental data observed by Wang et al. (2004; 2006). Based on these comparisons it was found that the v2-f model is most accurate for the URANS simulation; moreover, the k-ω model is also acceptable. However, the k-ε model was found to be unsuitable in this case. Therefore, v2-f model is proved to be an excellent choice for the analysis of flow with massive separation. Therefore, it is expected to be used in future by studies aiming to control the flow separation.

Analysis of Empirical Constant of Eddy Viscosity by k-ε and RNG k-ε Turbulence Model in Wake Simulation

Il Heum Park,Young Jun Cho,Jong Sup Lee 해양환경안전학회 2019 海洋環境安全學會誌 Vol.25 No.3

The wakes behind a square cylinder were simulated using two-equation turbulence models, k-ε and RNG k-ε models. For comparisons between the model predictions and analytical solutions, we employed three skill assessments:, the correlation coefficient for the similarity of the wake shape, the error of maximum velocity difference (EMVD) of the accuracy of wake velocity, and the ratio of drag coefficient (RDC) for the flow patterns as in the authors’ previous study. On the basis of the calculated results, we discussed the feasibility of each model for wake simulation and suggested a suitable value for an eddy viscosity related constant in each turbulence model. The k-ε model underestimated the drag coefficient by over 40 %, and its performance was worse than that in the previous study with one-equation and mixing length models, resulting from the empirical constants in the ε-equation. In the RNG k-ε model experiments, when an eddy viscosity related constant was six times higher than the suggested value, the model results were yielded good predictions compared with the analytical solutions. Then, the values of EMVD and RDC were 3.8 % and 3.2 %, respectively. The results of the turbulence model simulations indicated that the RNG k-ε model results successfully represented wakes behind the square cylinder, and the mean error for all skill assessments was less than 4 %.

Numerical simulation of dense interflow using the k-ε turbulence model

Choi, Seongwook,Choi, Sung-Uk 한국수자원학회 2017 한국수자원학회논문집 Vol.50 No.9

본 연구에서는 중층 밀도류를 모의할 수 있는 k-ε 난류모형의 지배방정식을 제시하고 수치모의를 수행하였다. 깊은 수체에 모형을 적용하여 중층 밀도류를 모의하고 게산된 유속과 초과밀도 분포를 분석하였다. 밀도류의 주 흐름방향을 따라 물 연행으로 인해 유속이 감소되는 것과 Richardson 수의 증가로 인해 유속 변화율이 감소되는 것을 관찰하였다. 유속과 초과밀도의 유사성을 확인하였으나, 난류운동에너지와 소산율의 유사성에서는 보이지 않았다. k-ε 모형의 모의 결과를 이용하여 중층 밀도류의 층적분 모형에서 사용될 수 있는 형상계수를 계산하였다. 또한, 층적분 모형을 이용하여 k-ε 모형에서 사용되는 부력관련 모형상수 (c₃ɛ)와 부피팽창계수 (β0)를 계산하였다. This study presents a numerical model for simulating dense interflows. The governing equations are provided and the finite difference method is used with the k-ε turbulence model. The model is used to simulate a dense interflow established in a deep ambient water, resulting velocity and excess density profiles. It is observed that velocity decreases in the longitudinal direction due to water entrainment in the vicinity of the outlet and rarely changes for increased Richardson number. Similarity collapses of velocity and excess density are obtained, but those of turbulent kinetic energy and dissipation rate are not. A shape factor for the dense interflow is obtained from the simulated profiles. The value of this shape factor can be used in the layer-averaged modeling of dense interflows. In addition, a buoyancy-related parameter (c₃ɛ) for the k-ε model and the volume expansion coefficient (β0) are obtained from the simulated results.

Analysis of Empirical Constant of Eddy Viscosity by k-ε and RNG k-ε Turbulence Model in Wake Simulation

박일흠,조영준,이종섭 해양환경안전학회 2019 海洋環境安全學會誌 Vol.25 No.3

The wakes behind a square cylinder were simulated using two-equation turbulence models, k-ε and RNG k-ε models. For comparisons between the model predictions and analytical solutions, we employed three skill assessments:, the correlation coefficient for the similarity of the wake shape, the error of maximum velocity difference (EMVD) of the accuracy of wake velocity, and the ratio of drag coefficient (RDC) for the flow patterns as in the authors’ previous study. On the basis of the calculated results, we discussed the feasibility of each model for wake simulation and suggested a suitable value for an eddy viscosity related constant in each turbulence model. The k-ε model underestimated the drag coefficient by over 40%, and its performance was worse than that in the previous study with one-equation and mixing length models, resulting from the empirical constants in the ε-equation. In the RNG k-ε model experiments, when an eddy viscosity related constant was six times higher than the suggested value, the model results were yielded good predictions compared with the analytical solutions. Then, the values of EMVD and RDC were 3.8% and 3.2%, respectively. The results of the turbulence model simulations indicated that the RNG k-ε model results successfully represented wakes behind the square cylinder, and the mean error for all skill assessments was less than 4%.

The Comparison of Various Turbulence Models of the Flow around a Wall Mounted Square Cylinder

배준영,송지수 해양환경안전학회 2020 해양환경안전학회지 Vol.26 No.4

The flow past a wall mounted square cylinder, a typical and basic shape of building, bridge or offshore structure, was simulated using URANS computation through adoption of three turbulence models, namely, the k-ε model, k-ω model, and the v2-f model. It is well known that this flow is naturally unstable due to the Karman vortex shedding and exhibits a complex flow structure in the wake region. The mean flow field including velocity profiles and the dominant frequency of flow oscillation that was from the simulations discussed earlier were compared with the experimental data observed by Wang et al. (2004; 2006). Based on these comparisons it was found that the v2-f model is most accurate for the URANS simulation; moreover, the k-ω model is also acceptable. However, the k-ε model was found to be unsuitable in this case. Therefore, v2-f model is proved to be an excellent choice for the analysis of flow with massive separation. Therefore, it is expected to be used in future by studies aiming to control the flow separation.

K-ε 난류모델이 배터리냉각 시스템 성능해석에 미치는 영향

정석훈,서현규 한국기계기술학회 2017 한국기계기술학회 학술대회논문집 Vol.2017 No.04

This paper aims to reveal the effects of the K-ε turbulence model on the performance analysis of battery cooling system for electric vehicle. The maximum temperature, the difference of temperature, and temperature distributions on the battery module were compared with and without K- ε turbulence model under the different flow rate. It was found that there was no need to apply K-ε turbulence model when the flow rate is over 500m3/h because the difference of maximum temperature is under the 6℃.

K-ε 난류모델이 배터리냉각 시스템 성능해석에 미치는 영향

정석훈,서현규 한국기계기술학회 2017 한국기계기술학회지 Vol.19 No.4

This paper aims to reveal the effects of the K-ε turbulence model on the performance analysis of battery cooling system for electric vehicle. The maximum temperature, the difference of temperature, and temperature distributions on the battery module were compared with and without K-ε turbulence model under the different flow rate. It can be expected that the maximum temperature of K-ε turbulence model is corrected by using the average error rate without the result of K-ε turbulence model.

난류모형을 적용한 장애물이 있는 파이프내의 유동장 수치시뮬레이션

곽승현(Seung-Hyun Kwag) 한국항해항만학회 2005 한국항해항만학회지 Vol.29 No.6

장애물이 있는 배관속의 점성유동을 다양한 난류모형을 적용하여 해석하였다. 적용한 난류모형은 k-ε, k-ω, Spalart-Allmaras, Reynolds stress 이고, 배관내의 격자는 구조격자(structured grid) 이다. 속도벡터, 압력분포, 반복계산(iteration)에 의한 잔류치(residual), 양정(dynamic head) 등을 모사하였다. 4개의 난류모형을 배관유동에 적용하였고 상용 프로그램을 사용하여 해석을 수행하였다. The flow analysis is made to simulate the turbulent flow in the pipe with an obstacle. The models used are k-ε, k-ω, Spalart-Allmaras and Reynolds. The structured grid is used for the simulation. The velocity vector, the pressure contour, the change of residual along the iteration number and the dynamic head are simulated for the comparison of four example cases. For the analysis, the commercial code is used.

Finite element analysis of 2D turbulent flows using the logarithmic form of the k-ε model

Hiroshi Hasebe,Takashi Nomura 한국풍공학회 2009 Wind and Structures, An International Journal (WAS Vol.12 No.1

The logarithmic form for turbulent flow analysis guarantees the positivity of the turbulence variables as k and ε of the k-ε model by using the natural logarithm of these variables. In the present study, the logarithmic form is incorporated into the finite element solution procedure for the unsteady turbulent flow analysis. A backward facing step flow using the standard k-ε model and a flow around a 2D square cylinder using the modified k-ε model (the Kato-Launder model) are simulated. These results show that the logarithmic form effectively keeps adequate balance of turbulence variables and makes the analysis stable during transient or unsteady processes.