V2-F 난류 모델의 터보기계 유동 해석 적용

박재현(Jae Hyeon Park),손동경(Dong Kyung Sohn),김창현(Chang Hyun Kim),백제현(Je Hyun Baek) 대한기계학회 2016 大韓機械學會論文集B Vol.40 No.2

터보기계 내부 유동장은 역압력구배, 고속 유동으로 인해 매우 복잡하며, 이를 해석하기 위해 보다 정교한 난류 모델이 요구된다. 유동 해석을 위해 대수모델, 2-방정식 와점도 모델 등이 널리 사용되고 있으나, 매우 복잡한 유동을 모사하는데 어려움이 있다. 본 연구에서는 복잡한 유동에서의 예측성능이 우수하다고 알려진 Durbin의 V2-F 난류 모델을 자체 개발 코드인 T-Flow에 적용하였으며, 채널 및 압축기 캐스캐이드 유동 해석 결과를 이용하여 난류 모델을 검증하였다. 또한 저속 압축기 동익 해석을 통해 터보기계 내부 유동에서의 적용 가능성을 판단하였다. 그 결과, V2-F난류 모델은 1-방정식, 2방정식 난류 모델보다 우수한 블레이드 표면 압력 분포 예측성능을 보였다. Since a turbomachine has complex flow characteristics, which are caused by adverse pressure gradient and high speed motion, an elaborate turbulence model is needed to accurately predict the flow. Some turbulence models such as an algebraic or a two-equation eddy viscosity model have been used for in-house RANS-code, but it is difficult to obtain good result for several complex flows. In this study, Durbin‘s V2-F turbulence model, which has been known for better prediction for severe flow separation, is applied to T-Flow. It was validated for simple cases such as channel and compressor cascade, and its applicability to turbomachinery was shown by analyzing internal flow of a single rotor. As a result, the V2-F turbulence model shows better blade surface pressure distribution than the one-and-two equation turbulence model.

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.

강한 박리 유동을 동반한 초음속 수축-확장 사각 노즐유동에 적합한 난류 모델과 압축성 보정 모델의 평가

이주용,신준수,성홍계 항공우주시스템공학회 2018 항공우주시스템공학회지 Vol.12 No.5

초음속 수축-확대 사각 노즐 내 강한 유동 박리를 동반한 초음속 유동에 적합한 난류 모델과 압축성 보정 모델을 평가하였다. 난류 모델로는 Yang과 Shih의 Low-Re k-ε 모델, Menter의 k-ω SST 모델, Wilcox의 k-ω 모델을 평가하였다. 압축성 효과를 보다 정확하게 예측하기 위하여 각각의 난류 모델에 Sarkar와 Wilcox의 압축성 보정 모델을 적용하였다. 각 난류 모델과 압축성 보정 모델의 결과는 실험 데이터와 비교하여 분석을 하였다. 난류 모델에 따라 충격파의 위치와 압력 회복률이 다르게 나타났으나 압축성 보정을 통해 더욱 개선된 결과를 얻었다. The objective of this study is to investigate the turbulence models with compressibility correction for large separation-flow in a supersonic convergent-divergent rectangular nozzle. As turbulence models, Yang and Shih’s Low-Re k-ε model, Mener’s k-ω SST model and Wilcox’s k-ω model were evaluated. In order to get a significant compressible effects, Sarkar and Wilcox compressibility correction models were applied to the turbulence models respectively. Also, the simulation results were compared with experimental data. The turbulence model with compressibility correction model improves both of shock position and pressure recovery, but deteriorates the length of Mach disk.

균열 전자기장이 인가된 관내 유동장에서 난류모델의 개량연구

손영욱(Young-uk Sohn),이정묵(Choung Mook Lee) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.9

The flows under electromagnetic field have quite different characteristics from that of usual fluids. The turbulence is one of them. The characteristics of turbulence in MHD flow is related to the change of energy balance in local fluctuations affected by electromagnetic field. To show the turbulent characteristics in MHD flow, the turbulence model is modified relating to the turbulence with electromagnetic field. The induced electromagnetic field due to flow is neglected in modified turbulence model under assumption of small magnetic Reynolds number. The computed results in a rectangular duct show that turbulence intensity is increased under a positive Lorentz force in the flow direction. But, when magnetic field alone is applied to flow, the calculated results show the damping of turbulence.

재순환유동 예측을 위한 k-ɛ 난류모델 개선에 대한 연구

이영모(Y.M. Lee),김철완(C.W. Kim) 한국전산유체공학회 2016 한국전산유체공학회지 Vol.21 No.2

The standard k-ɛ and realizable k-ɛ models are adopted to improve the prediction performance on the recirculating flow. In this paper, the backward facing step flows are used to assess the prediction performance of the recirculation zone. The model constants of turbulence model are obtained by the experimental results and they have a different value according to the flow. In the case of an isotropic flow situation, decaying of turbulent kinetic energy should follow a power law behavior. In accordance with the power law, the coefficients for the dissipation rate of turbulent kinetic energy are not universal. Also, the other coefficients as well as the dissipation coefficient are not constant. As a result, a suitable coefficients can be varied according to each of the flow. The changes of flow over the backward facing step in accordance with model constants of the k-ɛ models show that the reattachment length is dependent on the growth rate(λ) and the k-ɛ models can be improved the prediction performance by changing the model constants about the recirculating flow. In addition, it was investigated for the curvature correction effect of the k-ɛ models in the recirculating flow. Overall, the curvature corrected k-ɛ models showed an excellent prediction performance.

타원혼합 이차모멘트 모델을 사용한 난류 자연대류 해석

최석기(S.K. Choi),한지웅(J.W. Han),김성오(S.O. Kim),이태호(T.H. Lee) 한국전산유체공학회 2016 한국전산유체공학회지 Vol.21 No.4

In this paper a computation of turbulent natural convection in enclosures with the elliptic-blending based differential and algebraic flux models is presented. The primary emphasis of the study is placed on an investigation of accuracy of the treatment of turbulent heat fluxes with the elliptic-blending second-moment closure for the turbulent natural convection flows. The turbulent heat fluxes in this study are treated by the elliptic-blending based algebraic and differential flux models. The previous turbulence model constants are adjusted to produce accurate solutions. The proposed models are applied to the prediction of turbulent natural convections in a 1:5 rectangular cavity and in a square cavity with conducting top and bottom walls, which are commonly used for validation of the turbulence models. The relative performance between the algebraic and differential flux model is examined through comparing with experimental data. It is shown that both the elliptic-blending based models predict well the mean velocity and temperature, thereby the wall shear stress and Nusselt number. It is also shown that the elliptic-blending based algebraic flux model produces solutions which are as accurate as those by the differential flux model.

난류모델에 따른 SMART BLADE 공력 특성 연구

박성철,하광태,정재호 한국유체기계학회 2023 한국유체기계학회 논문집 Vol.26 No.5

This study presents an analysis of the aerodynamic performance characteristics of 20 m rotor blades for the NREL CART3 wind turbine within the SMART BLADES and SMART BLADES-2 projects. Three-dimensional Computational Fluid Dynamics (CFD) analysis was conducted to investigate the aerodynamic behavior. The Reynolds Averaged Navier-Stokes (RANS)-based turbulence model was utilized for numerical simulations, and the results were compared with Fraunhofer’s Blade Elementary Momentum Theory (BEMT) results. The aerodynamic performance characteristics of the rotor blades were evaluated using three turbulence models: Spalart Allmaras (S-A), standard k-ω, and Shear Stress Transform (SST) k-ω. The turbulence models demonstrated good agreement with the BEMT results at wind speeds below the rated power. However, under rated power wind speed conditions, the S-A and standard k-ω turbulence models exhibited an underprediction of aerodynamic performance. This discrepancy was attributed to an overestimation of the flow delamination point and recirculation region near the blade hub. Therefore, i t is r ecommended t o employ t he S S T k-ω turbulence model, which accurately captures turbulence phenomena both inside and outside the boundary layer, for rated power speed conditions.

난류흐름의 화학적 동역학 모델 (TKM) 개발: 대류경계층 내의 NO_x-O₃ 단순 광화학 기작에 대한 난류혼합의 영향 연구

김미숙 ( Mi-sug Kim ) 한국환경기술학회 2017 한국환경기술학회지 Vol.18 No.2

많은 환경모델에서는 물질의 이송 또는 확산현상에서의 난류의 영향을 잘 묘사하면서도 보통 2 개의 반응물질에 대한 화학반응속도에서는 난류의 영향이 무시된 평균값만을 표기한다. 본 연구에서는 난류의 영향이 고려된 비선형의 2차 화학반응속도로 표현된 1차원 수직 난류흐름의 화학적 동역학 모델(1-D TKM)을 개발하였으며 그 첫 번째 적용사례를 제시하였다. 연구목적은 한 낮에 형성되는 대기의 대류혼합층(CBL) 내에서 상호작용하는 두 물질(지표에서 배출되는 물질 A와 대류혼합층의 상부로부터 유입되는 물질 B)간의 불완전 혼합과정을 정량적으로 설명하는 것으로 비균질의 CBL내에서 두 물질간의 하향식-상향식 확산에 대한 시뮬레이션을 수행하고 기존의 다른 모델형식과 비교하였다. 완전혼합을 가정하는 CBL에서 난류의 영향은 거의 무시될 수 있었으나 하층부와 상층부에서는 분리의 영향과 유입농도는 화학적 특성에 매우 민감하였으며 물리적 특성과 수치해석에는 덜 민감하였다. 반응속도 상수에 가장 민감한 인자로는 분리영향이며 상부의 유입농도의 영향은 매우 작았고 지표의 배출인자의 민감도는 그 특성에 따라 다양하게 나타났다. Numerous environmental models well describe turbulent effects on transport and dispersion phenomena. However, a chemical reaction rate between two species uses an only mean value ignored the turbulent effect. This study aims at developing a simple one-dimensional model to quantitatively account for turbulence-induced incomplete mixing of two interacting chemical species. Top-down and bottom-up(TDBU) diffusion of two reactive species in an inhomogeneous convective boundary layer(CBL) are simulated by means of 1-D vertical turbulent chemical kinetics model(TKM). The model incorporates an asymmetric convective model(ACM) scheme and a concentration field splitting method(CSM) using a phenomenal extent of reaction. The derived governing equations are integrated using forward finite differences. The TKM is applied to both irreversible and reversible reactions between ozone and nitric oxide in the summer daytime convective atmospheric boundary layer. Results, in the form of vertical profiles of reactants concentrations and intensities of segregation in the convective boundary layer show that for both the irreversible and reversible reactions, segregation is significant near the boundaries where the reactants sources are located. Segregation for the irreversible reaction is everywhere larger than for the reversible reaction because the photolysis of NO₂ tends to increase the NO concentrations while the covariances of the reacting species remain relatively constant. Comparison of the reactant concentrations from the TKM to a conventional kinetic model(CKM) that ignores effects of segregation reveals consistency in that everywhere in the CBL the TKM results lie between a no-reaction case and the CKM results.

난류모델 변화에 따른 수평축 풍력터빈 유동해석 및 출력성능 예측

김범석(Bum-suk Kim),음학진(Hark-jin Eum),원종범(Jong-bum Won),김만응(Mann-eung Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

Despite of the laminar-turbulent transition region co-exist with fully turbulence region around the leading edge of an airfoil, still lots of researchers apply to fully turbulence models to predict aerodynamic characteristics. It is well known that fully turbulent model such as standard k-model couldn't predict the complex stall and the separation behavior on an airfoil accurately, it usually leads to over prediction of the aerodynamic characteristics such as lift and drag forces. So, we apply correlation based transition model to predict aerodynamic performance of the NREL (National Renewable Energy Laboratory) Phase Ⅳ wind turbine. And also, compare the computed results from transition model with experimental measurement and fully turbulence results. Results are presented for a range of wind speed, for a NREL Phase Ⅳ wind turbine rotor. Low speed shaft torque, power, root bending moment, aerodynamic coefficients of 2D airfoil and several flow field figures results included in this study. As a result, the low speed shaft torque predicted by transitional turbulence model is very good agree with the experimental measurement in whole operating conditions but fully turbulent model(k-ε) over predict the shaft torque after 7m/s. Root bending moment is also good agreement between the prediction and experiments for most of the operating conditions, especially with the transition model.

수평축 풍력터빈의 공력 하중 비교 (Ⅰ)

김진(Jin Kim),강승희(Seung-Hee Kang),유기완(Ki-Wahn Ryu) 한국항공우주학회 2016 韓國航空宇宙學會誌 Vol.44 No.5

본 연구에서는 난류 유입조건을 갖는 수평축 풍력터빈 블레이드의 공력 하중에 대해 초점을 맞추어 연구하였다. 난류모델은 풍속과 방향에 대한 변동을 포함하며, 그 특성은 난류강도와 표준편차로 표현된다. IEC61400-1에서는 정상 난류 모델과 정상 풍속 측면도에 대해서 피로해석을 수행하도록 규정하고 있다. 이를 위해 공력 최적설계 절차를 통해 얻어낸 ㎿급 수평축 풍력터빈 블레이드 허브와 저속 회전축에 대한 공력하중 해석을 수행한다. 공력하중 성분은 수치적인 절차를 통해 얻어내며 이를 블레이드 회전 특성을 고려하여 해석적으로 검토하였다. 난류 조건을 고려했을 때의 최대 추력과 토크의 변동치는 난류 조건을 고려하지 않았을 때의 값들에 비해 5~8 배 더 큰 값을 보였다. 따라서 난류 조건을 반영한 하중 해석은 풍력터빈 블레이드의 구조설계에 있어서 필수적임을 확인하였다. This study focused on the aerodynamic loads of the horizontal axis wind turbine blade due to the normal turbulence inflow condition. Normal turbulence model (NTM) includes the variations of wind speed and direction, and it is characterized by turbulence intensity and standard deviation of flow fluctuation. IEC61400-1 recommends the fatigue analysis for the NTM and the normal wind profile (NWP) conditions. The aerodynamic loads are obtained at the blade hub and the low speed drive shaft for MW class horizontal axis wind turbine which is designed by using aerodynamically optimized procedure. The 6-components of aerodynamic loads are investigated between numerical results and load components analysis. From the calculated results the maximum amplitudes of oscillated thrust and torque for LSS with turbulent inflow condition are about 5~8 times larger than those with no turbulent inflow condition. It turns out that the aerodynamic load analysis with normal turbulence model is essential for structural design of the wind turbine blade.