• Title/Summary/Keyword: 혼성난류모델

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A Hybrid Turbulence Model for Prediction of Buoyancy-Driven Turbulent Thermal Convection Flow (부력에 의한 난류 열대류의 혼성 난류모델)

  • 김태규;성형진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.8
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    • pp.2069-2078
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    • 1993
  • The buoyancy-driven turbulent thermal convection is predicted using an anisotropic hybrid turbulence model, which is incorporated with a low Reynolds k-.epsilon. turbulence model and an anisotropic buoyant part of algebraic stress model(ASM). The numerical predictions are compared with the Davidson's model,(1) the full ASM and the experimental results of Cheesewright et al.(2) All the models are shown to predict good agreements with the experiments for the averaged turbulence quantities. It is found that the effect of an anisotropic part on the Reynolds stress and the turbulent heat fluxes is substantial. In this study, the present hybrid model gives a fairly reasonable prediction in terms of the computational accuracy, convergence and stability. The contribution of an anisotropic buoyant part to turbulent heat fluxes are also scrutinized over the range of Rayleigh numbers $(4.79{\times}10^{10}{\le}Ra{\le}7.46{\times}10^{10}).$

Numerical Simulation of Interaction between Composite Breakwater and Seabed under Regular Wave Action by olaFlow Model (olaFlow 모델에 의한 규칙파작용 하 혼성방파제-해저지반의 상호작용에 관한 수치시뮬레이션)

  • Bae, Ju-Hyun;Lee, Kwang-Ho;Jung, Uk Jin;Kim, Do-Sam
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.30 no.6
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    • pp.270-285
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    • 2018
  • The behavior of wave-induced pore water pressure inside the rubble mound and seabed, and the resultant structure failure are investigated, which are used in design of the composite breakwater representing the coastal and harbor structures. Numerical simulation techniques have been widely used to assess these behaviors through linear and nonlinear methods in many researches. While the combination of strongly nonlinear analytical method and turbulence model have not been applied yet, which can simulate these characteristics more accurately. In this study, olaFlow model considering the wave-breaking and turbulent phenomena is applied through VOF and LES methods, which gives more exact solution by using the multiphase flow analytical method. The verification of olaFlow model is demonstrated by comparing the experimental and numerical results for the interactions of regular waves-seabed and regular waves-composite breakwater-seabed. The characteristics of the spatial distributions of horizontal wave pressure, excess-pore-water pressure, mean flow velocity and mean vorticity on the upright caisson, and inside the rubble mound and seabed are discussed, as well as the relation between the mean distribution of vorticity size and mean turbulent kinetic energy. And the stability of composite breakwater are also discussed.

Development of the intermittency turbulence model for a plane jet flow (자유 평면 제트유동 해석을 위한 간혈도 난류모델의 개발)

  • 조지룡;정명균
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.3
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    • pp.528-536
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    • 1987
  • In a turbulent free shear flow, the large scale motion is characterized by the intermittent flow which arises from the interaction between the turbulent fluid and the irrotational fluid of the environment through the mean velocity gradient. This large scale motion causes a bulk convection whose effect is similar to the spatial diffusion process. In this paper, the total diffusion process is proposed to be approximated by weighted sum of the bulk convection due to the large scale motion and the usual gradient diffusion due to small scale motion. The diffusion term in conventional .kappa.-.epsilon. model requires on more equation of the intermittency transport equation. A production term of this equation means mass entrainment from the irrotational fluid to the turbulent one. In order to test the validity of the proposed model, a plane jet is predicted by this method. Numerical results of this model is found to yield better agreement with experiment than the standard .kappa.-.epsilon. model and Byggstoyl & Kollmann's model(1986). Present hybrid diffusion model requires further tests for the check of universality of model and for the model constant fix.

On the Large Eddy Simulation of Temperature Field Using Dynamic Mixed Model in a Turbulent Channel (동적혼성 모델을 이용한 난류채널의 온도장 해석)

  • Lee Gunho;Na Yang
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.10
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    • pp.1255-1263
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    • 2004
  • An a priori test has been conducted for the dynamic mixed model which was generalized for the prediction of passive scalar field in a turbulent channel flow The results from a priori tests indicated that dynamic mixed model is capable of predicting both subgrid-scale heat flux and dissipation rather accurately. The success is attributed to the explicitly calculated resolved term incorporated into the model. The actual test of the model in a LES a posteriori showed that dynamic mixed model is superior to the widely used dynamic Smagorinsky model in the prediction of temperature statistics.

Numerical Simulation of Wave Pressure Acting on Caisson and Wave Characteristics near Tip of Composite Breakwater (for One Directional Irregular Waves) (혼성방파제 케이슨에 작용하는 파압과 선단 주변에서 파랑특성에 관한 수치모의(일방향불규칙파에 대해))

  • Jun, Jae-Hyoung;Choi, Goon-Ho;Lee, Kwang-Ho;Kim, Do-Sam
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.32 no.6
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    • pp.531-552
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    • 2020
  • In the previous study, both the wave characteristics at the tip of composite breakwater and on caisson were investigated by applying olaFlow numerical model of three-dimensional regular waves. In this paper, the same numerical model and layout/shape of composite breakwater as applied the previous study under the action of one directional irregular waves were used to analyze two and three-dimensional spatial change of wave force including the impulsive breaking wave pressure applied to trunk of breakwater, the effect of rear region, and the occurrence of diffracted waves at the tip of caisson located on the high crested rubble mound. In addition, the frequency spectrum, mean significant wave height, mean horizontal velocity, and mean turbulent kinetic energy through the numerical analysis were studied. In conclusion, the larger wave pressure occurs at the front wall of caisson around the still water level than the original design conditions when it generates the shock-crushing wave pressure in three-dimensional analysis condition. Which was not occurred by two-dimensional analysis. Furthermore, it was confirmed that the wave pressure distribution at the caisson changes along the length of breakwater when the same significant incident wave was applied to the caisson. Although there is difference in magnitude, but its variation shows the similar tendency with the case of previous study.

Numerical Simulation of Nonlinear Interaction between Composite Breakwater and Seabed under Irregular Wave Action by olaFlow Model (olaFlow 모델에 의한 불규칙파 작용하 혼성방파제-해저지반의 비선형상호작용에 관한 수치시뮬레이션)

  • Lee, Kwang-Ho;Bae, Ju-Hyun;Jung, Uk Jin;Choi, Goon-Ho;Kim, Do-Sam
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.31 no.3
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    • pp.129-145
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    • 2019
  • For the design of composite breakwater as representative one of the coastal and harbor structures, it has been widely discussed by the researchers about the relation between the behavior of excess-pore-water pressure inside the rubble mound and seabed caused by the wave load and its structural failure. Recently, the researchers have tried to verify its relation through the numerical simulation technique. The above researches through numerical simulation have been mostly applied by the linear and nonlinear analytic methods, but there have been no researches through the numerical simulation by the strongly nonlinear mutiphase flow analytical method considering wave-breaking phenomena by VOF method and turbulence model by LES method yet. In the preceding research of this study, olaFlow model based on the mutiphase flow analytical method was applied to the nonlinear interaction analysis of regular wave-composite breakwater-seabed. Also, the same numerical techniques as preceding research are utilized for the analysis of irregular wave-composite breakwater-seabed in this study. Through this paper, it is investigated about the horizontal wave pressures, the time variations of excess-pore-water pressure and their frequency spectra, mean flow velocities, mean vorticities, mean turbulent kinetic energies and etc. around the caisson, rubble mound of the composite breakwater and seabed according to the changes of significant wave height and period. From these results, it was found that maximum nondimensional excess-pore water pressure, mean turbulent kinetic energy and mean vorticity come to be large equally on the horizontal plane in front of rubble mound, circulation of inflow around still water level and outflow around seabed is formed in front of rubble caisson.

3D-Numerical Simulation of Wave Pressure Acting on Caisson and Wave Characteristics near Tip of Composite Breakwater (혼성방파제의 케이슨에 작용하는 파압과 선단 주변에서 파랑특성에 관한 3차원수치시뮬레이션)

  • Choi, Goon-Ho;Jun, Jae-Hyoung;Lee, Kwang-Ho;Kim, Do-Sam
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.32 no.3
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    • pp.180-201
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    • 2020
  • It has been widely known that the effect of diffracted waves at the tip of composite breakwater with finite length causes the change of standing wave height along the length of breakwater, the spatial change of wave pressure on caisson, and the occurrence of meandering damage on the different sliding distance in sequence. It is hard to deal with the spatial change of wave force on trunk of breakwater through the two-dimensional experiment and/or numerical analysis. In this study, two and three-dimensional numerical techniques with olaFlow model are used to approach the spatial change of wave force including the impulsive breaking wave pressure applied to trunk of breakwater, the effect of rear region, and the occurrence of diffracted waves at the tip of caisson located on the high crested rubble mound. In addition, it is thoroughly studied the mean wave height, mean horizontal velocity, and mean turbulent kinetic energy through the numerical analysis. In conclusion, it is confirmed that the larger wave pressure occurs at the front wall of caisson around the still water level than the original design conditions when it generates the shock-crushing wave pressure checked by not two-dimensional analysis, but three-dimensional analysis through the change of wave pressure applied to the caisson along the length of breakwater.

Large Eddy Simulation of Turbulent Passive Scalar in a Channel with Strong Wall Injection (대와류모사 기법을 이용한 강한 벽분사가 있는 채널 내에서의 난류 유동장 및 온도장 해석)

  • Kim, Hak-Jong;Na, Yang
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.6
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    • pp.628-637
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    • 2004
  • The present study investigates the performance of dynamic mixed model (DMM; Zang et ai.) in a channel with strong wall injection through a Large eddy simulation (LES) technique. The DMM results are compared with those of DNS and the results obtained with popular dynamic Smagorinsky model (DSM). Better agreement is achieved when using the DMM with box filter than DSM and coarse DNS in predicting the first and second order statistics as well as large-scale structures of velocity and temperature fields. Such favorable features of DMM are attributed to the fact that it explicitly calculates the modified Leonard stress term and only models the remaining cross and the SGS Reynolds stress terms and, thus, it reduces the excessive burden put on the model coefficient of DSM. Also it is demonstrated that the DMM can be successfully extended to the prediction of temperature (passive scalar) field where strong streamwise inhomogeneity exists.