래디얼 수문 개도에 따른 유동유발 진동의 전산해석

최창용 한국기계기술학회 2022 한국기계기술학회지 Vol.24 No.1

Among the various causes of the vibration problem of the radial sluice gate used in Saemangeum, the effect of flow-induced vibration was studied by the method of computational fluid analysis. In this study, the effect on the flow-induced vibration of the Saemangeum radial sluice gate was evaluated by 2D unsteady flow numerical analysis using ANSYS Fluent. Gate opening cases of 0.2m, 0.3m, 0.4m, 0.5m, and 1.0m were analyzed. As a result, the flow-induced vibration characteristics due to the instability of turbulent flow were observed through FFT analysis. As the gate opening increases, the frequency of the maximum amplitude moves gradually to a lower frequency region with the reduction of the magnitude. Therefore the flow-induced vibration effects can be considered as small with the gate opening increase.

철도역에서 양 방향 군중 유동의 전산 해석

남성원(Seong Won Nam) 대한기계학회 2020 大韓機械學會論文集B Vol.44 No.8

철도역에서의 양 방향 군중 유동에 대한 전산 해석을 하였다. 군중 유동 해석의 개념은 입자 유동과 유사하다. 전산유체 해석법과 마찬가지로, 계산 영역을 격자로 나누고, 입출구 경계 조건으로부터 각 격자에 대한 포텐셜 값을 부여하여 경로선을 구한다. 이 경로선이 기본 이동 경로이지만, 공간 이용상황에 따라 언제든지 변경될 수 있다. 예를 들면, 이동하려는 방향에 느린 선행 보행자가 있거나, 마주치는 보행자가 있는 경우이다. 특정한 규칙 기반 시스템에 따라, 이 빠른 보행자는 원래의 경로를 변경할 새로운 경로를 찾는다. 여기서 고려된 주요 인자는 보행 속도, 시야각도, 직진성, 우측통행 여부 등이다. 지하철 환승역의 다양한 개찰구 모델과 미로 모델을 이용하여 해석 프로그램의 성능을 확인하였다. 해석 결과, 보행자들은 최단 거리로만 이동하지 않으며, 수시로 경로를 변경함을 보여준다. In this study, bidirectional crowd flow in railway stations has been computationally analyzed. The concept of computational crowd flow is very similar to that of particle-laden flow. Similar to general computational fluid dynamics, the computational domain is divided into meshes and potential values are calculated for each cell by providing boundary conditions for inlets and outlets. Path line, which is the basic moving path, is then calculated according to the potential value. However, the path line varies based on the space used by the crowd. Consider, for example, a slow pedestrian walking in the direction that another pedestrian is moving toward, or that a slow pedestrian encounters a pedestrian walking in the opposite direction. According to a specific rule-based system, the relatively fast pedestrian searches for new paths, changing their original route. The main factors such as walking speed, viewing angle, straightness, and walking side (right) were considered. Various ticket gate models of a metro station and maze models were used to verify the performance of the program. The analysis results demonstrate that pedestrians do not move along the shortest path, but vary their paths periodically.

탈질 설비 내 안내 깃의 기하학적 형상에 따른 공력 성능에 대한 전산 해석적 연구

이창식,김민규,안병희,정희택 한국청정기술학회 2022 청정기술 Vol.28 No.4

The flow pattern at the inlet of the catalyst layer in a selective catalytic reduction (SCR) system is one of the key parameters influencing the performance of the denitrification process. In the curved diffusing parts between the ammonia injection grids and the catalyst layers, guide vanes are installed to improve flow uniformity. In the present study, a numerical simulation has been performed to investigate the effect of the geometrical configuration of the guide vanes on the aerodynamic characteristics of a denitrification facility. This application has been made to the existing SCR process in a large-scaled coal-fired power plant. The flow domain to be solved covers the whole region of the flow passages from the exit of the ammonia injection gun to the exit of the catalyst layers. ANSYS-Fluent was used to calculate the three-dimensional steady viscous flow fields with the proper turbulence model fitted to the flow characteristics. The root mean square of velocity and the pressure drop inside the flow passages were chosen as the key performance parameters. Four types of guides vanes were proposed to improve the flow quality compared to the current configuration. The numerical results showed that the type 4 configuration was the most effective at improving the aerodynamic performance in terms of flow uniformity and pressure loss. 선택적 촉매환원 시스템 내 촉매 층 입구의 흐름 패턴은 탈질 설비의 성능에 영향을 미치는 주요한 특성 중 하나이다. 암모니아 주입 그리드와 촉매 층 사이의 곡확산부에는 유동 균일성을 개선하기 위해 안내 깃이 설치된다. 본 연구에서는 대형 석탄화력 발전소의 선택적 촉매환원 시스템을 적용 대상으로 하여 안내 깃의 기하학적 구성이 탈질 설비의 공기역학적 특성에 미치는 영향을 조사하기 위해 수치 해석을 수행하였다. 해석할 유동장은 암모니아 주입구의 출구부터 촉매 층 출구까지의 유동이 흐르는 전 영역을 포함한다. 3차원 정상상태, 점성 유동장을 해석하기 위해 상용 소프트웨어인 ANSYS-Fluent을 사용하여유동 특성에 맞는 적절한 난류 모델을 적용하였다. 유동장 내부의 속도 및 압력 강하의 루트 평균 제곱을 주요 성능 매개변수로 선택했다. 현재 운용 중인 설비와 비교하여 흐름 품질을 개선하기 위해 4가지 유형의 안내 깃이 제안되었다. 해석 결과, 4번째 형상이 유동 균일성과 압력 등 관점에서 가장 좋은 공력 성능을 나타내었다.

액화 수소용 니들 밸브의 유량계수 및 고유유량 특성 분석

황나규미(Na-Gyu-Mi Hwang),강정호(Jung-Ho Kang),한승호(Seung-Ho Han),오진식(Jin-Sik Oh),곽주환(Kwak Joo-hwan) 한국기계가공학회 2024 한국기계가공학회지 Vol.23 No.2

Liquefied hydrogen equipment is utilized in extremely low-temperature environments. Therefore, various core technologies are required for the commercialization of related equipment in the fields of storage, transportation, and utilization. In particular, the use of needle valves is expanding to facilitate the rapid supply of liquefied hydrogen, even at open flow rates. Therefore, a need exists to estimate the flow coefficient considering the shape design factors of needle valves and evaluate the inherent flow characteristics with respect to opening rates. In this study, a computational fluid dynamics analysis was performed to estimate the flow coefficient and evaluate the inherent flow characteristics based on the opening rates. The estimation of flow coefficient was achieved by varying the entrance angle as a shape design factor of the needle valve. It was observed that the flow coefficient tended to decrease as the entrance angle increased, and the inherent flow characteristics exhibited a quick opening behavior. The flow coefficients obtained from the experimental test and computational fluid dynamics analysis agreed well, within an error range of 4%.

수직축 조류 터빈 발전효율 평가를 위한 유동-터빈 연동 CFD 해석 (II)

이진학(Jin-Hak Yi),오상호(Sang-Ho Oh),박진순(Jin-Soon Park),이광수(Kwang-Soo Lee),이상열(Sang-Yeol Lee) 한국해양공학회 2013 韓國海洋工學會誌 Vol.27 No.3

CFD (computational fluid dynamics) analyses that considered the dynamic interaction effects between the flow and a turbine were performed to evaluate the power output characteristics of two representative vertical?axis tidal?current turbines: an H?type Darrieus turbine and Gorlov helical turbine (GHT). For this purpose, a commercial CFD code, Star?CCM+, was utilized, and the power output characteristic were investigated in relation to the scale ratio using the relation between the Reynolds number and the lift?to?drag ratio. It was found that the power coefficients were significantly reduced when the scaled model turbine was used, especially when the Reynolds number was lower than 105. The power output characteristics of GHT in relation to the twisting angle were also investigated using a three?dimensional CFD analysis, and it was found that the power coefficient was maximized for the case of a Darrieus turbine, i.e., a twisting angle of 0°, and the torque pulsation ratio was minimized when the blade covered 360° for the case of a turbine with a twisting angle of 120°.

냉동유닛을 적용한 탑차 내부의 온도 및 유동 균일성에 대한 연구

최연성,왕 쩐 후안,권영철 한국기계기술학회 2019 한국기계기술학회지 Vol.21 No.4

In this study, the distribution of internal temperature and flow by forced blowing of the refrigeration unit installed in a truck were investigated. The temperature stability inside the box was measured from the experiment using the standard calorimeter and the constant temperature and humidity chamber. Using the computerized analysis method, the uniformity of temperature and flow inside the box was verified in the longitudinal direction(central section) and unidirectional direction(lateral sections of ⅓ and ⅔ points) of the box. The set temperature inside the box was -20℃, and the air flow rate of the refrigeration unit were 70, 80 and 90㎥/min. In the temperature stability experiment, the temperature deviation inside the box was within ±1℃ of the set value. The faster the air flow rate of the refrigeration unit, the lower the temperature and flow uniformity. The temperature and flow uniformity inside the box were most effective at 70㎥/min. Because the temperature and flow deviation were the smallest in the longitudinal direction and the upper and lower section.

전산유체역학(CFD)을 활용한 치악산 자연휴양림의 산불 및 연기전파 모델 분석

김재경(Jaekyoung Kim),강준석(Junsuk Kang) 한국방재학회 2022 한국방재학회논문집 Vol.22 No.5

본 연구는 치악산 자연휴양림에서 산불의 확산 경로, 도달시간과 확산 양상을 분석하였다. 산지 지형으로 발생하는 유동장분석과 연소모델 생성을 위해, 전산유체역학(Computational Fluid Dynamics, CFD) 프로그램인 Simcenter STAR-CCM+를 활용하였다. 도메인의 크기는 16 km2로 생성하고, 제 1 캠핑장에서 발화가 시작되는 것을 가정하였다. 모델 격자는 약 600만 개가 생성되었으며, 시뮬레이션이 시작된 후 1시간 동안 온도와 연기의 전파를 분석했다. 시간에 따른 확산 경로 분석을 위해 Implicit Unsteady 해석과, 유동장 분석을 위해서 Molecular Diffusivity 기능을 사용하였다. 본 연구를 통해 도출되는 결과는 다음의 세 가지다. 1) 산불 확산은 풍향 및 산지 지형으로 인한 연돌효과의 영향을 받는다. 2) 캠핑장에서 서쪽 500 m 떨어진 지점까지 산불이확산되는데 소요 시간은 22분 가량이며, 평균 1,200 ℃ 이상의 높은 온도를 보였다. 3) 산불의 인화점(Ignition Point)과 발화점(Flash Point)의 차이에서 발생하는 산불과 연기의 확산 속도는 시간의 변화에 따라 더 빨라졌다. This study analyzed the arrival time and diffusion pattern of a wildfire at Chiak Mountain, Wonju, Korea. Simcenter STAR-CCM+, which is a computational fluid dynamics program, was used to analyze flow fields generated by mountain topography and to create a combustion model. The size of the area under study was 16 km², and ignition was conducted at the first campsite. Approximately six million mesh were generated. The temperature and propagation of soot were analyzed for 1 h after the simulation was started. Implicit unsteady analysis was used for time-dependent diffusion, and molecular diffusivity was used for flow field analysis. The results were as follows. 1) The spread of the wildfire was affected by the stack effect derived from the wind direction and mountain topography. 2) Approximately 22 min were required for the wildfire to spread from the campground to a western point 500 m away, and the average temperature was 1,200 ℃ or higher. 3) The spread of the wildfire and soot caused by the difference between the ignition and flash points of the wildfire became faster over time.

바이크 세차기 노즐의 물 공급 압력과 각도에 따른 세척 효율 분석

장용재,임동균 한국기계기술학회 2020 한국기계기술학회지 Vol.22 No.2

In this paper, internal and external flow analysis of nozzle for a automatic bike washing machine was performed using Ansys Fluent, by varying nozzle injection pressure and angle. The pressure and velocity distributions generated at the nozzle outlet from internal flow analysis were applied for inlet condition of the external flow analysis of the nozzle. As a criterion for the cleaning efficiency, the shear stress condition provided by EHEDG[5] was used and an area of shear stress of 3 Pa or more according to the spray angle and pressure was compared. It is expected that the results of this paper will be applied to the development of automatic contactless bike washing nozzle.

45° 원형층돌분류의 혼합유동구조에 대한 난류모델 평가

김장권(J. K. Kim),오석형(S. H. Oh) 한국동력기계공학회 2009 한국동력기계공학회 학술대회 논문집 Vol.2009 No.6

In this paper, the CFD analysis using various turbulent models has been performed to evaluate which type of turbulent models can predict well the mixing flow structure of 45° impinging round jet. This CFD analysis has been carried out through the commercial Fluent software. As a result, any of turbulent models cannot predict the experimental results definitely all over the flow range. However, as compared with the experimental results, the turbulent model of realizable(RLZ) k-ε only predicts well in the limited range between X/X₀= 1.1 and X/X₀=2.0.

실링 챔버내 유로형상이 탄소섬유의 탄화공정에 미치는 영향에 대한 연구

고동국,압드엘모타립 하마다,이교우,임익태 한국기계기술학회 2021 한국기계기술학회지 Vol.23 No.6

This paper studies the flow characteristics inside the low-temperature carbonization(LTF) including sealing chamber with labyrinth. The flow behavior inside the furnace was analyzed according to different labyrinth shapes. The effects of labyrinth baffle number, and clearance between upper and lower baffles in the sealing chamber were investigated. The large vortex and stagnation region are generated in the chamber when the gap between the baffle and baffle is small. As a result, the gas discharge flow rate can be increased by 29.4% when the flow space of labyrinth is made 75% of the baffle length.