• Title, Summary, Keyword: RANS equation

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Analysis of the flood Characteristics in the Woo-Ee Stream Using FLOW-3D (FLOW-3D를 이용한 우이천의 홍수특성 분석)

  • Yoon, Sun-Kwon;Moon, Young-Il;Kim, Jong-Suk;Oh, Keun-Taek;Lee, Su-Gon
    • 한국방재학회:학술대회논문집
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    • pp.603-607
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    • 2007
  • Recently, the frequency of unexpecting heavy rains has been increased due to abnormal climate and extreme rainfall. There was a limit to analyze one dimension or two dimension stream flow of domestic rivers that was applied simple momentum equation and fixed energy conservation. Therefore, hydrodynamics flow analysis in rivers has been needed three dimensional numerical analysis for correct stream flow interpolation. In this study, CFD model on FLOW-3D was applied to stream flow analysis, which solves three dimension RANS(Reynolds Averaged Navier-Stokes Equation) control equation to find out physical behavior and the effect of hydraulic structures. Numerical simulation accomplished those results was compared by using turbulence models such as $k-{\backepsilon}$, RNG $k-{\backepsilon}$ and LES. Those numerical analysis results have been illustrated to bends and junctions by the turbulence energy effects, velocity of flow distributions, water level pressure distributions and eddy flows.

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Numerical Analysis of Flow Distribution in the Scaled-down APR+ Using Two-Equation Turbulence Models (2방정식 난류모델을 이용한 축소 APR+ 내부 유동분포 수치해석)

  • Lee, Gong Hee;Bang, Young Seok;Cheong, Ae Ju
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.27 no.4
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    • pp.220-227
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    • 2015
  • Complex thermal hydraulic characteristics exist inside the reactor because the reactor internals consist of fuel assembly, internal structures and so on. In this study, to examine the effect of Reynolds-Averaged Navier-Stokes (RANS)-based two-equation turbulence models in the analysis of flow distribution inside a 1/5 scaled-down APR+, simulation was performed using the commercial computational fluid dynamics software, ANSYS CFX R.13 and the predicted results were compared with the measured data. It was concluded that reactor internal flow pattern was locally different depending on the turbulence models. In addition, the prediction accuracy of k-${\varepsilon}$ model was superior to that of other two-equation turbulence models and this model predicted the relatively uniform distribution of core inlet flow rate.

Analysis of Hydraulic effects on Piers and Transverse Overflow Type Structures in Urban Stream (도시하천의 교각 및 횡단 월류형 구조물에 의한 수리영향 분석)

  • Yoon, Sun-Kwon;Chun, Si-Young;Kim, Jong-Suk;Moon, Young-Il
    • Journal of Korea Water Resources Association
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    • v.41 no.2
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    • pp.197-212
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    • 2008
  • Recently, stream flow analysis has been accomplished by one or two dimensional equations and was applied by simple momentum equations and fixed energy conservations which contain many condition limits. In this study, FLOW-3D using CFD (Computational Fluid Dynamics) was applied to stream flow analysis which can solve three dimensional RANS (Reynolds Averaged Navier-Stokes Equation) control equation to find out physical behaviors and the effect of hydraulic structures. Numerical simulation accomplished those results was compared by using turbulence models such as ${\kappa}-{\varepsilon}$, RNG (Renormalized Group) ${\kappa}-{\varepsilon}$ and LES (Large Eddy Simulation). Numerical analysis results have been illustrated by the turbulence energy effects, velocity of flow, water level pressure and eddy flows around the piers and transverse overflow type structures. These results will be able to used by basis data that catch hold of effects on long-term bed elevation changes, sediment accumulations, scours and water aggravations by removal of obsolete transverse over flow type structures in urban stream.

Numerical Analysis of Synchronous Edge Wave Known as the Driving Mechanism of Beach Cusp (Beach Cusp 생성기작으로 기능하는 Synchronous Edge Wave 수치해석)

  • Lee, Hyung Jae;Cho, Yong Jun
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.31 no.6
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    • pp.409-422
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    • 2019
  • In this study, we carried out the 3D numerical simulation to investigate the hydraulic characteristics of Synchronous Edge wave known as the driving mechanism of beach cusp using the Tool Box called the ihFoam that has its roots on the OpenFoam. As a wave driver, RANS (Reynolds Averaged Navier-Stokes equation) and mass conservation equation are used. In doing so, we materialized short-crested waves known as the prerequisite for the formation of Synchronous Edge waves by generating two obliquely colliding Cnoidal waves. Numerical results show that as can be expected, flow velocity along the cross section where waves are focused are simulated to be much faster than the one along the cross section where waves are diverged. It is also shown that along the cross section where waves are focused, up-rush is moving much faster than its associated back-wash, but a duration period of up-rush is shortened, which complies the typical characteristics of nonlinear waves. On the other hand, due to the water-merging effect triggered by the redirected flow toward wave-diverging area at the pinacle of run-up, along the cross section where waves are diverged, offshore-ward velocity is larger than shore-ward velocity at the vicinity of shore-line, while at the very middle of shoaling process, the asymmetry of flow velocity leaned toward the shore is noticeably weakened. Considering that these flow characteristics can be found without exception in Synchronous Edge waves, the numerical simulation can be regarded to be successfully implemented. In doing so, new insight about how the boundary layer streaming occur are also developed.

Performance Evaluation of Two-Equation Turbulence Models for 3D Wing-Body Configuration

  • Kwak, Ein-Keun;Lee, Nam-Hun;Lee, Seung-Soo;Park, Sang-Il
    • International Journal of Aeronautical and Space Sciences
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    • v.13 no.3
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    • pp.307-316
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    • 2012
  • Numerical simulations of 3D aircraft configurations are performed in order to understand the effects of turbulence models on the prediction of aircraft's aerodynamic characteristics. An in-house CFD code that solves 3D RANS equations and two-equation turbulence model equations are used. The code applies Roe's approximated Riemann solver and an AF-ADI scheme. Van Leer's MUSCL extrapolation with van Albada's limiter is also adopted. Various versions of Menter's $k-{\omega}$ SST turbulence models as well as Coakley's $q-{\omega}$ model are incorporated into the CFD code. Menter's $k-{\omega}$ SST models include the standard model, the 2003 model, the model incorporating the vorticity source term, and the model containing controlled decay. Turbulent flows over a wing are simulated in order to validate the turbulence models contained in the CFD code. The results from these simulations are then compared with computational results from the $3^{rd}$ AIAA CFD Drag Prediction Workshop. Numerical simulations of the DLR-F6 wing-body and wing-body-nacelle-pylon configurations are conducted and compared with computational results of the $2^{nd}$ AIAA CFD Drag Prediction Workshop. Aerodynamic characteristics as well as flow features are scrutinized with respect to the turbulence models. The results obtained from each simulation incorporating Menter's $k-{\omega}$ SST turbulence model variations are compared with one another.

A study on the identification of underwater propeller singing phenomenon (수중 프로펠러 명음 현상의 규명에 관한 연구)

  • Kim, Taehyung;Lee, Hyoungsuk
    • The Journal of the Acoustical Society of Korea
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    • v.37 no.2
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    • pp.92-98
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    • 2018
  • This paper is a study on the generation mechanism of propeller singing based on the cavitation tunnel test, underwater impact test, finite element analysis and computational flow analysis for the model propeller. A wire screen mesh, a propeller and a rudder were installed to simulate ship stern flow, and occurrence and disappearance of propeller singing phenomenon were measured by hydrophone and accelerometer. The natural frequencies of propeller blades were predicted through finite element analysis and verified by contact and non-contact impact tests. The flow velocity and effective angle of attack for each section of the propeller blades were calculated using RANS (Reynolds Averaged Navier-Stokes) equation-based computational fluid analysis. Using the high resolution analysis based on detached eddy simulation, the vortex shedding frequency calculation was performed. The numerical predicted vortex shedding frequency was confirmed to be consistent with the singing frequency and blade natural frequency measured by the model test.

A Numerical Study on a Circulation Control Foil using Coanda Effect (코앤다 효과를 이용한 순환 제어 날개의 수치적 연구)

  • J.J. Park;S.H. Lee
    • Journal of the Society of Naval Architects of Korea
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    • v.37 no.2
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    • pp.70-76
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    • 2000
  • A numerical study on the viscous flow around a 2-dimensional circulation control foil is carried out for application on the field of naval architecture and ocean engineering. The governing equations are the RANS and the continuity equations. The equations are discretized by finite difference method and MAC method and the pressure poisson equation is calculate by a SOR method and an O-type non-staggered boundary fitted coordinate system which is overlapped near the slot is used to improve the numerical accuracy. Turbulence is approximated by a modified Baldwin-Lomax turbulence model. In the present paper, the Coanda effect on a 2-dimensional foil of a 20% thickness ellipse with modified rounded trailing edge has been numerically studied. The change in drag and lift of the foil with various jet momentums are calculated and compared to the experimental results to show good agreements.

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Application of CFD in The Analysis of Aerodynamic Characteristics for Aircraft Propellers (전산유체역학을 이용한 항공기 프로펠러 공력특성 연구)

  • Cho, Kyuchul;Kim, Hyojin;Park, Il-Ju;Jang, Sungbok
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.40 no.11
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    • pp.917-926
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    • 2012
  • The analysis of aerodynamic characteristics for aircraft propellers is studied to develop high efficiency composite propellers. It is to verify the accuracy and reliability of predicting the efficiency characteristics of aircraft propellers by applying nonlinear numerical analysis. The numerical simulation method incorporated the CFD code, which is based on RANS (Reynolds Averaged Navier-Stocks) equation. The study includes a comparative analysis between the numerical simulation results and the wind tunnel test results of the full-scale aircraft propeller. The comparison shows that thrust and power coefficients of the propeller calculated by nonlinear numerical analysis are higher than those based on the results generated from the wind tunnel test. The efficiency of the propeller calculated by numerical analysis matches closely to the efficiency based on the wind tunnel test results. The verification results are analyzed, then, will be used in optimizing the design and manufacture of the subject aircraft propeller studied.

3D RANS Simulation and the Prediction by CRN Regarding NOx in a Lean Premixed Combustion in a Gas Turbine Combustor (희박 예혼합 가스터빈 연소기 3 차원 전산 해석 및 화학반응기 네트워크에 의한 NOx 예측)

  • Yi, Jae-Bok;Jeong, Dae-Ro;Huh, Kang-Yul;Jin, Jae-Min;Park, Jung-Kyu;Lee, Min-Chul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.12
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    • pp.1257-1264
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    • 2011
  • This paper presents 3D simulation by STAR-CCM+ for lean premixed combustion in a stationary gas turbine combustor with separate pilot and main nozzles. The constant for the source term in the flame area density transport equation was modified to account for a low global equivalence ratio and validated against measurement data. A Partially-premixed Coherent Flame Model(PCFM) involves propagation of a laminar premixed flame with the predicted flame surface density and equilibrium assumption in the burned gas with spatial inhomogeneity. The conditions for cooling by radiation and convection are considered for accurate determination of the heat flux on the wall. A parametric study is of the pilot-fuel-to-total-fuel-ratio is carried out. A chemical reactor network (CRN) was constructed on the basis of the 3D simulation results and compared against measurements of NOx.

Simulation of Turbulent Flow and Surface Wave Fields around Series 60 $C_B$=0.6 Ship Model

  • Kim, Hyoung-Tae;Kim, Jung-Joong
    • Journal of Ship and Ocean Technology
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    • v.5 no.1
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    • pp.38-54
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    • 2001
  • A finite difference method for calculating turbulent flow and surface wave fields around a ship model is evaluated through the comparison with the experimental data of a Series 60 $C_B$=0.6 ship model. The method solves the Reynolds-averaged Navior-Stokes Equations using the non-staggered grid system, the four-stage Runge-Kutta scheme for the temporal integration of governing equations and the Bladwin-Lomax model for the turbulence closure. The free surface waves are captured by solving the equation of the kinematic free-surface condition using the Lax-Wendroff scheme and free-surface conforming grids are generated at each time step so that one of the grid surfaces coincides always with the free surface. The computational results show an overall close agreement with the experimental data and verify that the present method can simulate well the turbulent boundary layers and wakes as well as the free-surface waves.

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