• Title/Summary/Keyword: Standard $\kappa-\varepsilon$ model

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Numerical Analysis on Recirculation Generated by Obstacles around a Cooling Tower (냉각탑 주위의 장애물에 의한 재순환 현상에 관한 수치해석)

  • Lee Jung-Hee;Choi Young-Ki
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.7
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    • pp.578-586
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    • 2006
  • The present study has been conducted to examine the effect of obstacles around a cooling tower and an air-guide to prevent recirculation. In order to analyze the interaction between external flow and cooling tower exit flow, the external region as well as the cooling, tower are included in computational domain. Two dimensional analysis is performed using the finite volume method with non-orthogonal and unstructured grid system. The standard ${\kappa}-{\varepsilon}$ turbulence model is used. To investigate the recirculation phenomena, flow and temperature fields are calculated with three approaches such as, the distance between cooling tower and obstacle, the allocated geometrical type, and the effect of height of obstacle. In addition, the air-guide is considered in the current computation. The mean recirculation rate increases with the height of obstacle. The effect of air-guide to reduce the mean recirculation rate is obviously observed.

Computational fluid dynamics simulation for tuned liquid column dampers in horizontal motion

  • Chang, Cheng-Hsin
    • Wind and Structures
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    • v.14 no.5
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    • pp.435-447
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    • 2011
  • A Computational Fluid Dynamics model is presented in this study for the simulation of the complex fluid flows with free surfaces inside the Tuned Liquid Column Dampers in horizontal motion. The characteristics of the fluid model of the TLCD in horizontal motion include the free surface of the multiphase flow and the horizontal moving frame. In this study, the time depend unsteady Standard ${\kappa}-{\varepsilon}$ turbulent model based on Navier-Stokes equations is chosen. The volume of fluid (VOF) method and sliding mesh technique are adopted to track the free surface of water inside the vertical columns of TLCD and treat the moving boundary of the walls of TLCD in horizontal motion. Several model solution parameters comprising different time steps, mesh sizes, convergence criteria and discretization schemes are examined to establish model parametric independency results. The simulation results are compared with the experimental data in the dimensionless amplitude of the water column in four different configured groups of TLCDs with four different orifice areas. The predicted natural frequencies and the head loss coefficient of TLCDs from CFD model are also compared with the experimental data. The predicted numerical results agree well with the available experimental data.

A Study on Ventilation Characteristics of LNG Carrier Hood room by PIV and CFD (PIV와 CFD에 의한 LNG선박의 Hood room 환기특성에 관한 연구)

  • Cho, D.H.;Kim, D.C.;Kim, M.E.;Lee, Y.H.
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.673-679
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    • 2000
  • LNG Carriers are currently known as sole commercial means of shipping natural gas on the sea. They are designed to proven dangerous explosion for shipping a lot of gas over long distance. In this study. In this study, a scaled model chamber was made to investigate ventilation characteristics of the hood room in LNG carrier. Experimental study was performed in model using visualization equipments with laser apparatus and image intensifier CCD camera gated by an AOM controller Twelve different kinds of measuring area were selected as experimental condition. Instant simultaneous velocity vectors at whole field were measured by using 2-D PIV system which software adopts two-frame grey-level cross correlation algorithm. To look into stagnation area of hood room for LNG carrier, a three-dimensional numerical simulation with standard ${\kappa}-{\varepsilon}$ model was carried out by using PHOENICS for three kinds of Reynolds number, $6.5{\times}10^3$, $9.7{\times}10^3\;and\;1.29{\times}10^4$, based on the cavity inlet velocity and cavity height. The flow pattern showed the large scale counter-clockwise forced-vortex rotated at center area, small eddies at each corner and stagnation area located at left-back upper side of model.

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A Study on Oxy-Fuel Combustion System with Multi-Jet Burner-Numerical Simulation with PDF Combustion Model (다공 동축 버너를 이용한 순산소 연소 시스템에 관한 연구-PDF 연소 모델을 이용한 수치해석)

  • Kim, Hyeon-Jun;Choi, Won-Young;Bae, Soo-Ho;Hong, Jung-Goo;Shin, Hyun-Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.32 no.7
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    • pp.504-512
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    • 2008
  • The characteristics of nonpremixed oxy-fuel flame in a multi-jet burner were experimentally and numerically investigated. The overall flow rate of fuel and oxygen was fixed, and the oxygen feeding ratio (OFR) was varied by 0.25, 0.5, and 0.75. The results of numerical simulation were compared with the measured results which are temperature profile and direct flame observation. The probability density function (PDF) model was applied accounting to the description between turbulence and chemistry, and standard ${\kappa}-{\varepsilon}$ model was used for turbulent flow field. Equilibrium assumption is very reasonable due to fast chemistry of the oxy-fuel combustion. Thus, the equilibrium calculation based on Gibbs free energy minimization was guaranteed to generate the solution of the oxy-fuel combustion. The result was obtained by numerical simulation. The predicted radial temperature profiles were in good agreement with the measured results. The flame length was shorten and was intensified with the decrease of OFR because the mixture of fuel and oxidizer are fast mixed and burnt. The maximum temperature became lower as the OFR increased, as a consequence of large flame surface area.

A Study On Heat Transfer and Flow Characteristics for Boring in Sewer by Rotating Cutter Tool (회전노즐장비 작동시 하수관내의 열전달 및 유동현상에 관한 연구)

  • Park Young-Ki;Lee Jang-Choon;Lee Dong-Joo
    • Journal of Environmental Science International
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    • v.15 no.1
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    • pp.95-100
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    • 2006
  • Heat transfer and flow characteristics in a pipe in which the rotating cutting tool for boring a underground pipe without digging were considered in this study. The amount of heat generation due to the friction between the rotating cutter and pipe wall, mixing (low of air and water injected to cool down are the two important factors to design the boring machine Computational fluid dynamics analysis using the Eulerian mixture model and the standard $\kappa-\varepsilon$ turbulence model was used to analyze the complex phenomena in a pipe during the process. Results show that pipe wall temperature decreased with increasing the cooling water inlet velocity. it is also shown that pipe wail temperature was lowered when the cutter rotation speed was increased until 600 rpm. There was no further cooling effect over 600 rpm.

Analysis of Performance of Cross-Flow Fan with Various Rear Guiders (리어가이더 형상변화에 따른 횡류홴 성능해석)

  • Kim, Dong-Won;Lee, Jun-Hwan;Park, Seong-Gwan;Kim, Yun-Je
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.2076-2082
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    • 2003
  • A cross-flow fan is widely used on many industrial fields: mining industry, automobile and home appliances, etc. The design point of the cross-flow fan is generally based on the region within low static pressure and high flow rate. It relatively makes high dynamic pressure at low speed because a working fluid passes through an impeller blade twice. However, it has low static pressure efficiency between 30% and 40% because of relative high impact loss. Recently, in the air-conditioning systems, the operating behaviors at the off-design points are highly regarded to broaden the application area for various air-cooling loads. Especially, at the lower flow rate, there exists a rapid pressure head reduction, a noise increase and an irregular flow field against a rearguider as a scroll of centrifugal fan. Numerical analyses are carried out for investigating the flow characteristics in a cross-flow fan including the impeller, the rearguider and the stabilizer. Especially, various types of rearguiders are estimated by numerical and experimental methods to insure the stable operation in the region of lower flow rate. Numerical domains are discretized by hexahedral cells. Three-dimensional, unsteady governing equations are solved using FVM, PISO algorithm, sliding grid system and standard ${\kappa}-{\varepsilon}$ turbulence model. ASHRAE standard fan tester is also used to estimate the performance of the modeled crossflow fan.

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Investigation of the essential parameters governing starting characteristic in the second throat exhaust diffuser for high altitude simulation (고도모사용 2 차목 초음속 디퓨져 시동특성에 영향을 미치는 파라미터에 관한 연구)

  • Park, Sung-Hyun;Park, Byung-Hoon;Lim, Ji-Hwan;Yoon, Woong-Sup
    • Proceedings of the KSME Conference
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    • 2008.11b
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    • pp.2642-2647
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    • 2008
  • Starting characteristics of the axi-symmetric supersonic exhaust diffuser(SED) with a second throat are numerically investigated. Main purpose of this study is to predict theoretical starting pressure of STED using 1-D normal shock theory and to present the range of optimum starting pressure through parametric study with essential design parameters of STED influencing on starting performance. Renolds-Average Navier-Stokes equations with a standard ${\kappa}-{\varepsilon}$ turbulence model incorporated with standard wall function are solved to simulate the diffusing evolutions of the nozzle plume. Minimum(optimum) starting pressure difference of $20{\sim}25%$ between 1-D theory and experimental evidences validated from previous results[5] is also applied to predict those in this system. The analysis results indicate that dominant parameters for diffuser starting in this system is diffuser expansion ratio($A_d/A_t$), which has optimum value 120 and second throat area ratio($A_d/A_{st}$), which has optimum range $3.3{\sim}3.5$.

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Numerical Simulation of Air Flow and Gas Dispersion around Obstacles

  • Nguyen The-Due;Park Warn-Gyu;Duong Ngoe-Hai
    • 한국전산유체공학회:학술대회논문집
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    • 2003.10a
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    • pp.253-254
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    • 2003
  • Computations of the mean and turbulence flows over three-dimensional hill of conical shape have implemented. Beside the standard ${\kappa}-{\varepsilon}$ , two other modifications proposed by Detering & Etling and Duynkerke for atmospheric applications were also considered. These predictions were compared with the data of a wind tunnel experiment. From the comparison, it was concluded that all three models predict the mean flow velocities equally well while only the Duynkerke's model accurately predicts the turbulence data statistics. It also concluded that there are large discrepancies between model predictions and the measurements near the ground surface. The flow field, which was obtained by using the Duynkerke's modification, was used to simulate gas dispersion from an upwind source. The calculation results are verified based on the measurement data. Modifications of the turbulent Schmidt number were carried out in order to match the measured results. The code was used to investigate the influence of the recirculation zone behind a building of cubical shape on the transport and dispersion of pollutant. For a stack behind and near the obstacle, some conclusions about the effect of the stack height and stack location were derived.

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DEVELOPMENT OF GENERAL PURPOSE THERMO/FLUID FLOW ANALYSIS PROGRAM NUFLEX (범용 열/유체 유동해석 프로그램 NUFLEX의 개발)

  • Hur, Nahm-Keon;Won, Chan-Shik;Ryou, Hong-Sun;Son, Gi-Hun;Kim, Sa-Ryang
    • 한국전산유체공학회:학술대회논문집
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    • 2007.04a
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    • pp.87-90
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    • 2007
  • A general purpose program NUFLEX for the analysis 3-D thermo/fluid flow and pre/post processor in complex geometry has been developed, which consists of a flow solver based on FVM and GUI based pre/post processor. The solver employs a general non-orthogonal grid system with structured grid and solves laminar and turbulent flows with standard/RNG ${\kappa}-{\varepsilon}\;SST$ turbulence model. In addition, NUFLEX is incorporated with various physical models, such as interfacial tracking, cavitation, MHD, melting/solidification and spray model. For the purpose of verification of the program and testing the applicability, many actual problems are solved and compared with the available data. Comparison of the results with that by STAR-CD or FLUENT program has been also made for the same flow configuration and grid structure to test the validity of NUFLEX.

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Analysis of Edge Overcoating in Continuous Hot-Dip Galvanizing (연속식 용용아연도금 공정에서의 단부 과도금 현상에 대한 수치 해석)

  • Ahn, Gi-Jang;Kim, Sang-Joon;Cho, Choong-Won;Chung, Myung-Kyoon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.7
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    • pp.763-770
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    • 2004
  • The problem of edge overcoating developed near the edge of the steel strip is studied quantitatively in the gas wiping process of continuous hot-dip galvanizing. It has been assumed that the edge overcoating occurs due to the reduced impact pressure of wiping gas on the strip edge and it is one of detrimental problems to the quality of coating products. In order to analyse the edge overcoating problem numerically, three-dimensional unsteady flows due to the gas wiping are calculated by using a commercial code, STAR-CD. Standard $\kappa$-$\varepsilon$ model is used as a turbulence model. The 1D code for calculation of coating thickness is constructed by using continuity and Navier-Stokes equations. The calculation results have shown good agreement with measurements of edge overcoating thickness, taken from galvanizing line trials. Therefore it is conformed that the major cause of edge overcoating is the reduced impact pressure of wiping gas on the strip surface.