• Title/Summary/Keyword: turbulence and fluid dynamics

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Numerical Study on the Observational Error of Sea-Surface Winds at leodo Ocean Research Station (수치해석을 이용한 이어도 종합해양과학기지의 해상풍 관측 오차 연구)

  • Yim Jin-Woo;Lee Kyung-Rok;Shim Jae-Seol;Kim Chong-Am
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.18 no.3
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    • pp.189-197
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    • 2006
  • The influence of leodo Ocean Research Station structure to surrounding atmospheric flow is carefully investigated using CFD techniques. Moreover, the validation works of computational results are performed by the comparison with the observed data of leodo Ocean Research station. In this paper, we performed 3-dimensional CAD modelling of the station, generated the grid system for numerical analysis and carried out flow analyses using Navier-Stokes equations coupled with two-equation turbulence model. For suitable free stream conditions of wind speed and direction, the interference of the research station structure on the flow field is predicted. Beside, the computational results are benchmarked by observed data to confirm the accuracy of measured date and reliable data range of each measuring position according to the wind direction. Through the results of this research, now the quantitative evaluation of the error range of interfered gauge data is possible, which is expected to be applied to provide base data of accurate sea surface wind around research stations.

Study on Computational Fluid Dynamics(CFD) Simulation for De-NOx in the incinerator at Taebaek city (태백시 소각로 내 NOx 제거를 위한 전산유체역학(CFD) simulation 연구)

  • Kim, Ji-Hyun;Park, Young-Koo
    • Journal of the Korean Applied Science and Technology
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    • v.30 no.2
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    • pp.320-332
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    • 2013
  • The feed air to MSW incinerator influences on the residence time of combustion gas, removal of unburnt ash and exiting gas temperature. Thus the secondary air volume could present sufficient residence time which can maintain the exiting temperature over $850^{\circ}C$. The secondary air also relates directly with the turbulence in the inside of combustion chamber, which finally provide the stable combustion condition. The present study designed a modern incinerator for a field scale, and evaluation of the potential amount of primary air based on the daily combustible quantity. From the evaluated primary air volume, the secondary air flow rate could be estimated, and its dynamic behavior was verified. In addition, the obtained air volume enables to find an optimum operation condition of the combustion. As a result of the CFD simulation, the air ratio 75 : 25 between primary and secondary air amount was optimum ratio than design criteria 72 : 28. And the flow velocity ratio of front-back of secondary air jet nozzle was found excellent at 1 : 3. In addition, the result of applied to the plant, the removal efficiency of NOx and CO generation would concentration of CO.

Temperature Prediction Method for Superheater and Reheater Tubes of Fossil Power Plant Boiler During Operation (화력발전 보일러 과열기 및 재열기 운전 중 튜브 온도예측기법)

  • Kim, Bum-Shin;Song, Gee-Wook;Yoo, Seong-Yeon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.5
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    • pp.563-569
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    • 2012
  • The superheater and reheater tubes of a heavy-load fossil power plant boiler can be damaged by overheating, and therefore, the degree of overheating is assessed by measuring the oxide scale thickness inside the tube during outages. The tube temperature prediction from the oxide scale thickness measurement is necessarily accompanied by destructive tube sampling, and the result of tube temperature prediction cannot be expected to be accurate unless the selection of the overheated point is precise and the initial-operation tube temperature has been obtained. In contrast, if the tube temperature is to be predicted analytically, considerable effort (to carry out the analysis of combustion, radiation, convection heat transfer, and turbulence fluid dynamics of the gas outside the tube) is required. In addition, in the case of analytical tube temperature prediction, load changes, variations in the fuel composition, and operation mode changes are hardly considered, thus impeding the continuous monitoring of the tube temperature. This paper proposes a method for the short-term prediction of tube temperature; the method involves the use of boiler operation information and flow-network-analysis-based tube heat flux. This method can help in high-temperaturedamage monitoring when it is integrated with a practical tube-damage-assessment method such as the Larson-Miller Parameter.

Efficiency of Different Roof Vent Designs on Natural Ventilation of Single-Span Plastic Greenhouse (플라스틱 단동온실의 천창 종류에 따른 자연환기 효과)

  • Rasheed, Adnan;Lee, Jong Won;Kim, Hyeon Tae;Lee, Hyun Woo
    • Journal of Bio-Environment Control
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    • v.28 no.3
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    • pp.225-233
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    • 2019
  • In the summer season, natural ventilation is commonly used to reduce the inside air temperature of greenhouse when it rises above the optimal level. The greenhouse shape, vent design, and position play a critical role in the effectiveness of natural ventilation. In this study, computational fluid dynamics (CFD) was employed to investigate the effect of different roof vent designs along with side vents on the buoyancy-driven natural ventilation. The boussinesq hypothesis was used to simulate the buoyancy effect to the whole computational domain. RNG K-epsilon turbulence model was utilized, and a discrete originates (DO) radiation model was used with solar ray tracing to simulate the effect of solar radiation. The CFD model was validated using the experimentally obtained greenhouse internal temperature, and the experimental and computed results agreed well. Furthermore, this model was adopted to compare the internal greenhouse air temperature and ventilation rate for seven different roof vent designs. The results revealed that the inside-to-outside air temperature differences of the greenhouse varied from 3.2 to $9.6^{\circ}C$ depending on the different studied roof vent types. Moreover, the ventilation rate was within the range from 0.33 to $0.49min^{-1}$. Our findings show that the conical type roof ventilation has minimum inside-to-outside air temperature difference of $3.2^{\circ}C$ and a maximum ventilation rate of $0.49min^{-1}$.

Parametric Numerical Study on the Performance of Helical Tidal Stream Turbines (헬리컬 터빈의 설계인자에 따른 성능 연구)

  • Han, Jun-Sun;Choi, Da-Hye;Hyun, Beom-Soo;Kim, Moon-Chan;Rhee, Shin-Hyung;Song, Mu-Seok
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.14 no.2
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    • pp.114-120
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    • 2011
  • The characteristics of a helical turbine to be used for tidal stream energy conversion have been numerically studied with varying a few design parameters. The helical turbines were proposed aiming at mitgating the well known poor cut-in characteristics and the structural vibration caused by the fluctuating torque, and the basic concept is introducing some twisting angle of the vertical blade along the rotation axis of the turbine. Among many potential controling parameters, we focused, in this paper, on the twisting angle and the height to diameter ratio of the turbine, and, based on the numerical experiment, We tried to propose a configuration of such turbine for which better performance can be expected. The three-dimensional unsteady RANS equations were solved by using the commercial CFD software, FLUENT with k-${\omega}$ SST turbulence model, and the grid was generated by GAMBIT. It is shown that there are a range of the twisting angle producing better efficiency with less vibration and the minimum height to diameter ratio above which the efficiency does not improve considerably.

Numerical Simulation of Spatiotemporal Distribution of Chaff Clouds for Warship Defense using CFD-DEM Coupling (CFD-DEM 연동을 통한 함정용 채프운의 시공간 분포 해석)

  • Uk Jin Jung;Moonhong Kim;Dongwoo Sohn
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.36 no.2
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    • pp.93-103
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    • 2023
  • Warships widely spread numerous chaffs using a blast, which form chaff clouds that create false radar cross-sections to deceive enemy radars. In this study, we established a numerical framework based on a one-way coupling of computational fluid dynamics and discrete element method to simulate the spatiotemporal distribution of chaff clouds for warships in the air. Using the framework, we investigated the effects of wind, initial chaff cartridge angle, and blast pressure on the distribution of chaff clouds. We observed three phases for the chaff cloud diffusion: radial diffusion by the explosion, omnidirectional diffusion by turbulence and collision, and gravity-induced diffusion by the difference in the fall speed. The wind moved the average position of the chaff clouds, and the diffusion due to drag force did not occur. The direction of radial diffusion by the explosion depended on the initial angle of the cartridge, and a more vertical angle led to a wider distribution of the chaffs. As the blast pressure increased, the chaff clouds spread out more widely, but the distribution difference in the direction of gravity was not significant.

A Numerical Calculation for the Optimum Operation of Cyclone-based Combustion System (선회류 방식 연소시스템의 최적 조업을 위한 수치해석)

  • Kim, Min-Choul;Lee, Jae-Jeong;Lee, Gang-Woo;Kim, Ji-Won;Shon, Byung-Hyun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.12 no.2
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    • pp.1005-1012
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    • 2011
  • This research carried out a 3-dimensional simulation using computerized fluid dynamics (CFD) for the flow characteristics, temperature distribution, velocity distribution and residence time, etc. in a reactor in order to derive the optimal combustion conditions of an innovative combustion system. The area-weighted average temperature of the outlet of a furnace during combustion at a condition of fuel input rate 1.5 ton/hr, residence time 1.25 sec and air/fuel ratio 2.1 was $1,077^{\circ}C$, which is a suitable temperature for energy recovery and treatment of air pollutants. Exhaust gas is discharged through a duct at a 40~50 m/s maximum speed along strong vortexes at the center of a combustion chamber, so strong turbulence is created at the center of a combustion chamber to enhance the combustion speed and combustion efficiency. In this system, the optimum operation conditions to prevent incomplete combustion and suppress the formation of thermal NOx were air/fuel ratio 1.9~2.1 and fuel input rate 1.25~1.5 ton/hr.