• Title/Summary/Keyword: fluid simulation

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Numerical Modeling of Free Surface Flow over a Broad-Crested Rectangular Weir (사각형 광정위어를 통과하는 자유수면 흐름 수치모의)

  • Paik, Joongcheol;Lee, Nam Joo
    • Journal of Korea Water Resources Association
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    • v.48 no.4
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    • pp.281-290
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    • 2015
  • Numerical simulations of free surface flow over a broad-crested rectangular weir are conducted by using the volume of fraction (VOF) method and three different turbulence models, the k-${\varepsilon}$, RNG k-${\omega}$ and k-${\omega}$ SST models. The governing equations are solved by a second-order accurate finite volume method and the grid sensitivity study of solutions is carried out. The numerical results are evaluated by comparing the solutions with experimental and numerical results of Kirkgoz et al. (2008) and some non-dimensionalized experimental results obtained by Moss (1972) and Zachoval et al. (2012). The results show that the present numerical model can reasonably reproduce the experimental results, while three turbulent models yield different numerical predictions of two distinct zones of flow separation, the first zone is in front of the upstream edge of the weir and the second is created immediately behind the upstream edge of the weir where the flow is separated to form the separation bubble. The standard k-${\varepsilon}$ model appears to significantly underestimate the size of both separation zones and the k-${\omega}$ SST model slightly over-estimates the first separation zone in front of the weir. The RNG k-${\varepsilon}$ model predicts both separation zones in overall good agreement with the experimental measurement, while the k-${\omega}$ SST model yields the best numerical prediction of separation bubble at the upstream edge of the weir.

Effect of Vane Angle of Swirl Type Mixer on Flow Mixing and Pressure Drop in Marine Selective Catalytic Reduction Systems (선박용 SCR 시스템에서 스월형 혼합기의 날개 각도가 유동혼합 및 압력강하에 미치는 영향)

  • Park, Taewha;Sung, Yonmo;Kim, Taekyoung;Choi, Cheolyong;Kim, Duckjool;Choi, Gyungmin
    • Journal of Advanced Marine Engineering and Technology
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    • v.39 no.4
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    • pp.443-448
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    • 2015
  • A swirl type mixer was developed to improve the flow mixing performance of a marine selective catalytic reduction system. In this study, the swirl type mixer and a multi-staged swirl type mixer, in which the angle of the vanes at each stage is controllable were considered to provide the optimal region of angles for the mixers. The effects of the vane angles in both mixers on the uniformity index and pressure drop were investigated using a computational fluid dynamics simulation. In the swirl type mixer, the optimal conditions for the flow mixing performance were observed at vane angles from 30 to 60 degrees when vane angles could be adjusted between 10 to 80 degrees, however, the pressure drop increased continually with increasing vane angle of the mixer. On the other hand, control of the individual staged angles of the multi-staged mixer showed that it is possible to keep enhancing flow mixing performance while reducing the pressure drop.

Basic performance analysis of ocean thermal energy conversion using the refrigerant mixture R32/R152a (R32/R152a 혼합냉매를 적용한 해양온도차발전의 기초성능해석)

  • Cha, Sang Won;Lee, Ho Saeng;Moon, Deok Soo;Kim, Hyeon Ju
    • Journal of Advanced Marine Engineering and Technology
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    • v.38 no.4
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    • pp.502-507
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    • 2014
  • In this paper, performance characteristics of cycles were studied when mixed working fluid was used for ocean thermal energy conversion (OTEC). Among the various mixed refrigerants for industrial heat-pump, R32/R152a used in ocean thermal energy conversion system. For simulations, R32/R152a were used in existing closed cycle and Kalina cycle which is used only ammonia and water as mixed refrigerant. Temperature of the warm heat source was 26 and 29 celsius degree, temperature of the cold heat source was 5 celsius degree. In results of simulation, Gross power of the closed cycle on R32 was 22kW, and efficiency of the cycle was 2.02%. When the mixed refrigerant of R32/R152a, in the ratio of 90 to 10, gross power of the closed cycle was 29.93kW, and efficiency of the cycle was 2.78%. Gross power and cycle efficiency of R32/R152a increased by 36% and 37% than those of existing single refrigerant. Additionally, the same simulations were conducted in Kalina cycle with the same various composition ratio of mixed refrigerant.

Performance Characteristics of Organic Rankine Cycle Using Medium Temperature Waste Heat with Different Working Fluids (중온 배기열을 이용한 유기랭킨사이클 작동유체별 성능특성)

  • Kwon, Dong-Uk;Heo, Ki-Moo;Yoon, Sung-Hoon;Moon, Yoon-Jae;Yoo, Ho-Sun;Lee, Jae-Heon
    • Plant Journal
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    • v.10 no.2
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    • pp.38-47
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    • 2014
  • Renewable Portfolio Standards was introduced into the system in Korea in 2012. Interest in the unutilized and renewable energy sources is increasing. and these being actively investigated. An organic rankine cycle has emerged as an alternative in order to take advantage of bio-gas engine heat of sewage treatment plants whose capacity is 1500 kW. The organic rankine cycle power system was simulated by a simulator which is a commercial program of power plant design and performance analysis. The biogas engine is operated by $460^{\circ}C$ and 2.7 kg/s flow rate in the sewage treatment plant. Working fluids(R-601a, R-123, R-245fa) are selected to use in ORC power system in this temperature range. It was the isopentane that is the best performance among three working fluids. It could be obtained net power of 163.1 kW and efficiency of 13.66% from isopentane in the simulation.

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Characteristic of Mixing and DO Concentration Distribution in Aeration Tank by Microbubble Supply (마이크로버블 공급에 의한 폭기조내 교반과 용존산소 분포 특성)

  • Lim, Ji-young;Kim, Hyun-Sik;Park, Dae-Seok;Cho, Young-Gun;Song, Seung-Jun;Park, Soo-Young;Kim, Jin-Han
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.17 no.5
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    • pp.251-259
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    • 2016
  • This study examined the DO concentration distribution and ORP distribution using microbubbles on pilot-scale aeration tanks. As a result of MLSS mixing and oxygen transfer phenomenon using microbubbles, different DO concentrations were observed depending on the circulation of the liquid with the microbubble supply location on the lateral of an aeration tank. The simulation results of CFD (computational fluid dynamics) program showed that MLSS mixed with a microbubble supply in the middle the reactor is much better than on the left side of the reactor. A single reactor containing an anaerobic, anoxic, and aerobic zone, was evaluated without partition according to the location of the microbubble supply based on the experiments and CFD analysis. MLSS was separated into solid-liquid by the microbubble supply in the aeration tank. Consequently, selecting the appropriate microbubble size is important for MLSS mixing and was maintained at the proper DO concentration for biological treatment.

Technical Consideration for Production Data Analysis with Transient Flow Data on Shale Gas Well (셰일가스정 천이유동 생산자료분석의 기술적 고려사항)

  • Han, Dong-kwon;Kwon, Sun-il
    • Journal of the Korean Institute of Gas
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    • v.20 no.1
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    • pp.13-22
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    • 2016
  • This paper presents development of an appropriate procedure and flow chart to analyze shale gas production data obtained from a multi-fractured horizontal well according to flow characteristics in order to calculate an estimated ultimate recovery. Also, the technical considerations were proposed when a rate transient analysis was performed with field production data occurred to only $1^{st}$ transient flow. If production data show the $1^{st}$ transient flow from log-log and square root time plot analysis, production forecasting must be performed by applying different method as before and after of the end of $1^{st}$ linear flow. It is estimated by an area of stimulated reservoir volume which can be calculated from analysis results of micro-seismic data. If there are no bottomhole pressure data or micro-seismic data, an empirical decline curve method can be used to forecast production performance. If production period is relatively short, an accuracy of production data analysis could be improved by analyzing except the early production data, if it is necessary, after evaluating appropriation with near well data. Also, because over- or under-estimation for stimulated reservoir volume could take place according to analysis method or analyzer's own mind, it is necessary to recalculate it with fracture modeling, reservoir simulation and rate transient analysis, if it is necessary, after adequacy evaluation for fracture stage, injection volume of fracture fluid and productivity of producers.

Impact Analysis of Tributaries and Simulation of Water Pollution Accident Scenarios in the Water Source Section of Han River Using 3-D Hydrodynamic Model (3차원 수리모델을 이용한 한강 상수원구간 지류영향 분석 및 수질오염사고 시나리오 모의)

  • Kim, Eunjung;Park, Changmin;Na, Mijeong;Park, Hyeon;Kim, Bogsoon
    • Journal of Korean Society on Water Environment
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    • v.34 no.4
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    • pp.363-374
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    • 2018
  • The Han River serves as an important water resource for the city of Seoul, Korea and in the neighboring metropolitan areas. From the Paldang dam to the Jamsil submerged weir, the 4 water intake stations that are located for the Seoul metropolitan population were under review in this study. Therefore the water quality management in this section is very important to monitor, analyze and review to rule out any safety concerns. In this study, a 3-D hydrodynamic model, EFDC (Environmental Fluid Dynamics Code), was applied to the downstream of the Paldang Dam in the Han River, which is about 23 km in length, to determine issues related to water resource management. The 3-D grid was composed of 2,168 horizontal grids and three vertical layers. In this case, the hydrodynamic model was calibrated and verified with an observed average daily water surface elevation, water temperature and flow rate data for 3 years (2013~2015). The developed EFDC model proved to reproduce the hydrodynamics of the Han River well. The composition ratios of the noted incoming flows at the monitored intake stations for 3 years and their flow patterns in the river were analyzed using the validated model. It was found that the flow of the Wangsuk Stream depended on the Paldnag dam discharge, and it was noted that the composition ratios of the stream at the intake stations changed accordingly. In a word, the Wangsuk Stream moved mainly along the right bank of the Han River under the condition of a normal dam flow. As can be seen, when the dam discharge rate was low, the incidence of lateral mixing was often seen. The scenario analyses were also conducted to predict the transport of conservative pollutants as in the case of a chemical spill accident. Generally speaking, when scenarios were applied, the arrival time and concentration of pollutants at each intake station was thus predicted.

Geomechanical Stability of Underground Lined Rock Caverns (LRC) for Compressed Air Energy Storage (CAES) using Coupled Thermal-Hydraulic-Mechanical Analysis (열-수리-역학적 연계해석을 이용한 복공식 지하 압축공기에너지 저장공동의 역학적 안정성 평가)

  • Kim, Hyung-Mok;Rutqvist, Jonny;Ryu, Dong-Woo;Synn, Joong-Ho;Song, Won-Kyong
    • Tunnel and Underground Space
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    • v.21 no.5
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    • pp.394-405
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    • 2011
  • In this paper, we applied coupled non-isothermal, multiphase fluid flow and geomechanical numerical modeling using TOUGH-FLAC coupled analysis to study the complex thermodynamic and geomechanical performance of underground lined rock caverns (LRC) for compressed air energy storage (CAES). Mechanical stress in concrete linings as well as pressure and temperature within a storage cavern were examined during initial and long-term operation of the storage cavern for CAES. Our geomechanical analysis showed that effective stresses could decrease due to air penetration pressure, and tangential tensile stress could develop in the linings as a result of the air pressure exerted on the inner surface of the lining, which would result in tensile fracturing. According to the simulation in which the tensile tangential stresses resulted in radial cracks, increment of linings' permeability and air leakage though the linings, tensile fracturing occurred at the top and at the side wall of the cavern, and the permeability could increase to $5.0{\times}10^{-13}m^2$ from initially prescribed $10{\times}10^{-20}m^2$. However, this air leakage was minor (about 0.02% of the daily air injection rate) and did not significantly impact the overall storage pressure that was kept constant thanks to sufficiently air tight surrounding rocks, which supports the validity of the concrete-lined underground caverns for CAES.

Numerical Analysis of Gas Leakage and Diffusion Behavior in Underground Combined Cycle Power Plant (지하 복합발전 플랜트 내에서의 가스 누출 및 확산 거동에 관한 수치해석 연구)

  • Bang, Joo Won;Lee, Seong Hyuk
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.18 no.4
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    • pp.118-124
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    • 2017
  • In this study, a numerical simulation was performed using commercial code Fluent(v.17.1). The underground Combined Cycle Power Plant (CCPP) was simplified to analyze the methane gas leakage with the crack size and position. In addition, extensive numerical simulations were carried out for different crack sizes from 10 mm to 20 mm. The crack position is the gas leakage, which is assumed to be near the pipe elbow and the gas turbine. A total of 4 cases were compared and analyzed. To analyze the gas leakage, the concept of the Lower Flammable Limit (LFL) was applied. The leakage distance was defined in the longitudinal direction, and the transverse direction was estimated and quantitatively analyzed. As a result, the leakage distance in the longitudinal direction varies by 52.3 % depending on the crack size at the same crack position. Moreover, the maximum difference was 34.8 % according to the crack position when the crack sizes are identical. As jet flow impacts on the obstacle and changes its direction, the recirculation flows are formed. These results are expected to provide useful data to optimize the location and number of gas detections in confined spaces, such as underground CCPP.

Estimation of Head Loss Coefficients at Surcharged Square Manhole Using Numerical Model (수치모형을 이용한 과부하 사각형 맨홀에서의 손실계수 산정)

  • Kim, Jung-Soo;Lim, Ga-Hui;Rim, Chang-Soo;Yoon, Sei-Eui
    • Journal of the Korean Society of Hazard Mitigation
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    • v.11 no.3
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    • pp.143-150
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    • 2011
  • Energy loss at manholes, often exceeding friction loss of pipes under surcharged flow, is considered as one of the major causes of inundation in urban area. Therefore, it is important to analyze the head losses at manholes, especially in case of surcharged flow. The stream characteristics were analyzed and head loss coefficients were estimated by using the computational fluid dynamics(CFD) model, FLUENT 6.3, at surcharged square manhole in this study. The CFD model was carefully assessed by comparing simulated results with the experimental ones. The study results indicate that there was good agreement between simulation model and experiment. The CFD model was proved to be capable of estimating the head loss coefficients at surcharged manholes. The head loss coefficients with variation of the ratio of manhole width(B) to inflow pipe diameter(d) and variation of the drop height at surcharged square manhole with a straight-path through were calculated using FLUENT 6.3. As the ratio of B/d increases, head loss coefficient increases. The depth and head loss coefficient at manhole were gradually increased when the drop height was more than 5cm. Therefore, the CFD model(Fluent 6.3) might be used as a tool to simulate the water depth, energy losses, and velocity distribution at surcharged square manhole.