Space-Filling Square Fractal 격자에서 발달된 난류 유동 내 자유 전파하는 저선회 화염의 특성에 관한 연구

강연세(Yeonse Kang),이기만(Keeman Lee) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11

The turbulent flow generated by applying the space-filling square fractal grid to the shape of the central turbulence generating plate, which plays a key role in forming the lifted flame of the low swirl injector, was observed in the nonreacting and reacting flow fields. Through the study of the non-reacting flow field, the turbulent mean velocity profile before and after the nozzle was investigated, and it was observed that the characteristic of divergent flow without an inner recirculation region was observed. Furthermore, the development and dissipation region of turbulent energy induced by the fractal grids were classified through the turbulent intensity, which is expected to generate various interactions between the turbulent flow and the turbulent flame front in the lifted flame configuration.

선회 형태 혼합날개가 장착된 연료집합체 내부유동 분포 수치해석

이공희(Gonghee Lee),신안동(Andong Shin),정애주(Aeju Cheong) 대한설비공학회 2016 설비공학 논문집 Vol.28 No.5

As a turbulence-enhancing device, a mixing vane installed at a spacer grid of the fuel assembly plays a role in improving the convective heat transfer by generating either swirl flow in the subchannels or cross flow between fuel rod gaps. Therefore, both configuration and arrangement pattern of a mixing vane are important factors that determine the performance of a mixing vane. In this study, in order to examine the flow distribution features inside 5×5 fuel assembly with swirl-type mixing vanes used in benchmark calculation of OECD/NEA, simulations were conducted with commercial CFD software ANSYS CFX R.14. Predicted results were compared to data measured from MATiS-H (Measurement and Analysis of Turbulent Mixing in Subchannels-Horizontal) test facility. In addition, the effect of swirl-type mixing vanes on flow pattern inside the fuel assembly was described.

연료분무 및 연소 2 : 난류선회 유동장에서 고체입자의 dispersion 특성 해석

황명하 ( Myungha Hwang ),김용모 ( Yongmo Kim ) 한국액체미립화학회 2015 한국액체미립화학회 학술강연회 논문집 Vol.2015 No.-

The Eulerian-Lagrangian approach has been applied to numerically analyze the characteristics of the turbulent particle-laden, swirling flow in a coaxial-jet combustor. Turbulence is represented by the k-ε model and the particle dispersion by turbulence is modeled by the stochastic tracking approach. A mixture of air and lightly loaded, spherical, glass-particles with a prescribed sizedistribution enters the primary jet, while a swirling stream of air flows through the annulus. Special emphasis is given on the particle dispersion characteristics such as the particle trajectories, residence times, and size distribution. Numerical results are compared with experimental data in terms of mean and turbulent quantities for carrier and discrete phases. Numerical results indicate that the present approach yields the reasonably good conformity with experimental data.

수소 난류 확산화염에서의 선회류에 의한 배기배출물 특성

오정석(Jeongseog Oh),윤영빈(Youngbin Yoon) 대한기계학회 2010 大韓機械學會論文集B Vol.34 No.3

동축공기 수소 난류 확산화염에서 선회류가 NOx에 미치는 영향을 연구하였다. 공기와의 혼합을 증가시키기 위해 동축공기관에 스월러의 각도를 30, 45, 60, 90°로 바꾸어가며 화염길이와 질소산화물 배출수준을 측정하였다. 연료 속도를 85.7~160.2 ㎧, 동축공기 속도는 7.4~14.4 ㎧로 조절하였다. 실험을 통해 동축 공기 속도 증가에 따라 화염길이와 질소산화물 배출수준은 증가하였고, 회전류 증가에 따라 감소함을 관찰하였다. EINOx에 미치는 동축공기와 회전류 영향을 상사하기 위하여 far-field 개념의 유효직경 (dF,eff)을 도입하여 동축공기와 선회류에 의한 혼합효과를 표현하였다. 질소산화물 배기배출지표는 화염체류시간(~τR<SUP>1/2.8</SUP>)과 전체 신장률(~SG<SUP>1/2.8</SUP>)영향을 받았다. The effect of swirl flow on NOx in a nonpremixed turbulent hydrogen jet with coaxial air was studied. The swirl vane angle was varied from 30° to 90°. The fuel jet air velocity and coaxial air velocity were varied in an attached flame region as uF=85~160㎧ and uA=7~14㎧. The objective of the current study was to analyze the characteristics of nitrous oxide emission in a swirl flow and to propose a new parameter for EINOx scaling. The experimental results show that EINOx decreases with the swirl vane angle and increased with flame length. Further, EINOx scaling factors can be determined by considering the effective diameter (dF,eff) in a far field concept. The EINOx increased in proportion to the flame residence time (~τR<SUP>1/2.8</SUP>) and the global strain rate (~SG<SUP>1/2.8</SUP>).

안내덕트 내부 난류유동구조에 따른 열전달 특성변화 수치해석

유근종(Geun Jong Yoo),최훈기(Hoon Ki Choi),최기림(Kee Lim Choi) 대한기계학회 2011 大韓機械學會論文集B Vol.35 No.9

본 연구에서는 복합화력발전소 가스터빈 출구가스 안내덕트 내부의 가스유동장이 배열회수보일러 전열기구에 미치는 영향을 CFD기법을 이용하여 분석하였다. 안내덕트 내부 난류흐름의 경우, 유속의 편차가 크고 선회 효과 및 상승류 현상이 심한 특징을 가지고 있음으로 이와 같은 유동의 수치해석을 위해 2개 방정식 난류점성 모델 중 RNG k-? 모델을 사용하였으며 유동장의 영향을 가장 많이 받는 배열 회수보일러 최종과열기관의 열전달특성변화를 파악하기위하여 NTU 방식을 이용한 수치해석결과와, 산업계에서 적용하는 설계기법에 의한 결과를 비교하였다. Because of the instability of a flow pattern in the inlet transition square duct (hereinafter referred to as “transition duct”) of a heat recovery steam generator (hereinafter referred to as “HRSG”) in a combined cycle power plant, the Reynolds number in the first row of a tube bank is differs sharply from that in the sectional area of the transition duct. This causes differences in the heat flux in each tube in the tube bank. The computational fluid dynamics (CFD) predictions provide three-dimensional results for velocity, temperature, and other flow parameters over the entire domain of the duct and HRSG. A renormalization group theory (RNG) based k-? turbulent model is used for obtaining the results cited in this study. A porous media option is used for modeling the tube banks and the number of transfer units method is used for determining the heat transfer characteristics. This study describes a comparison between the numerical simulation results and actual design output.

혼합날개 형상이 연료집합체 내부유동 형태에 미치는 영향에 관한 연구

이공희(Gong Hee Lee),정애주(Ae Ju Cheong) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

The ability to accurately predict the flow and temperature distributions in the fuel assemblies is important to the thermal-hydraulic performance and the safe operation of Pressurized Water Reactor(PWR). In general, the flow and temperature distributions inside PWR fuel assembly depends on the configuration and the arrangement pattern of the mixing vane. In addition, this flow consists of the swirl flow in a subchannel and the cross flow between the rod gaps. In this study, in order to examine the effect of the mixing vane arrangement patterns on the flow distributions inside the fuel assembly, simulations were conducted with the commercial CFD software, ANSYS CFX R.14. The predicted results were compared with the measured data from the MATiS-H (Measurement and Analysis of Turbulent Mixing in Subchannels-Horizontal) test facility. Although there were locally differences between the prediction and the measurement, ANSYS CFX R.14 predicted the time averaged velocity field in the reliable level. The predicted horizontal and vertical velocity components were more in agreement with the measured data than the axial velocity component. While the effect of both the swirl flow and the cross flow was dominant for the split-type mixing vane arrangement, the effect of the cross flow was not significant for the swirl-type one.

전산유체역학 소프트웨어 적용성에 관한 규제 지침 개발을 위한 연료집합체 내부유동 분포 수치해석

이공희(Gong Hee Lee),정애주(Ae Ju Cheong) 대한기계학회 2018 大韓機械學會論文集B Vol.42 No.6

가압경수로에서 연료봉 다발 표면의 적절한 열제거는 노심 열적여유도 및 안전성 확보를 위해 중요하다. 많은 전산유체역학 소프트웨어들이 혼합날개가 장착된 연료집합체 내부의 복잡한 유동을 예측하기 위해 사용되어 왔으나, 전산유체역학 소프트웨어의 종합적인 평가를 위한 국내 규제지침이 마련되어 있지 않다. 따라서, 규제 관점에서 국내 원자력 안전 분야에 대한 전산유체역학 소프트웨어의 적용성에 관한 체계적인 평가 및 지침 마련이 필요하다. 본 연구에서는 국내 원자력 안전 분야에 대한 전산유체역학 소프트웨어의 적용성에 관한 체계적인 평가 및 지침 마련을 위해 원자력 안전 문제 계산에서 불확도를 제공하는 주요 인자들인 대류항 차분법 정확도 및 난류 모델이 선회 형태의 혼합날개가 장착된 연료집합체 내부의 난류 유동분포 예측 성능에 미치는 영향에 대한 민감도 분석 결과를 설명하였다. In a pressurized water reactor (PWR), appropriate heat removal from the surface of a fuel rod bundle is crucial to ensure thermal margins and safety. Although many computational fluid dynamics (CFD) software have been used to predict complex flows inside fuel assemblies with mixing vanes, no domestic regulatory guidelines exist for comprehensively evaluating CFD software. Therefore, from a nuclear regulatory perspective, performing a systematic assessment and preparing domestic regulatory guidelines are necessary to determine whether valid CFD software is used for nuclear safety problems. In this study, we provide a systematic evaluation and guidance on the applicability of CFD software to the area of domestic nuclear safety. The results of a sensitivity analysis for the effect of the discretization scheme accuracy for the convection terms and turbulence models (which are main factors that contribute to uncertainty in calculations of nuclear safety problems) on the prediction performance for the turbulent flow distribution inside the fuel assembly with swirl-type mixing vanes were explained.

선회 형태 혼합날개가 장착된 연료집합체 내부 난류유동 분포 수치해석

이공희(Gong-hee Lee),정애주(Ae-ju Cheong) 한국유체기계학회 2014 한국유체기계학회 학술대회 논문집 Vol.2014 No.11

축대칭 선회난류의 수치해석에 의한 비등방 k-ε 난류모델의 評價

이연원(Yeon-Won LEE) 한국마린엔지니어링학회 1996 한국마린엔지니어링학회지 Vol.20 No.5

모형 가스터빈 연소기의 입구 형상변화에 따른 연소 불안정성에 관한 LES 연구

황철홍(Cheol-hong Hwang),이창언(Chang-eon Lee) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.5

The effects of combustion instability on flow structure and flame dynamics with the inlet configurations in a model gas turbine combustor were investigated using large eddy simulation (LES). A G-equation flamelet model was employed to simulate the unsteady flame behaviors. As a result of mean flow field, the change of divergent half angle(α ) at combustor inlet results in variations in the size and shape of the central toroidal recirculation (CTRZ) as well as the flame length by changing corner recirculation zone (CRZ). The case of α = 45° show smaller size and upstream location of CTRZ than those of 90° and 30° by the development of higher swirl velocity. The flame length in the case of α = 45° is shorter than other cases, while the case of α = 30° yields the longest flame length due to the decrease of effective reactive area with the absence of CRZ. Through the analysis of pressure fluctuation, it was identified that the case of α = 45° shows the largest damping effect of pressure oscillation in all configurations and brings in the noise reduction of 2.97㏈, compared to that of α = 30° having the largest pressure oscillation. These reasons were discussed in detail through the analysis of unsteady phenomena related to recirculation zone and flame surface. Finally the effects of flame-acoustic interaction were evaluated using local Rayleigh parameter.