• Title, Summary, Keyword: RANS equation

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Analysis of Overflow Characteristics around a Circular-Crested Weir by Using Numerical Model (수치모의를 이용한 원형위어의 월류흐름 특성 해석)

  • Kim, Dae-Geun
    • Journal of Korean Society of Water and Wastewater
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    • v.30 no.2
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    • pp.147-154
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    • 2016
  • The present study used the hydrodynamic numerical model, with the Reynolds-averaged Navier-Stokes equations (RANS) as its governing equations, to analyze overflow characteristics such as the discharge coefficient of circular-crested weir and the flow velocity and pressure distribution of weir crest. The simulation results well reproduced the overflow characteristics of the overfall of circular-crested weir both qualitatively and quantitatively. As for the discharge coefficient, rational results were yielded by the discharge coefficient equation proposed by Hager(1985) in the $H_1/R_b<0.58$ and by the discharge coefficient equation proposed by Samani and Bagheri(2014) in the $H_1/R_b>0.58$, respectively. Because most existing discharge coefficient equations were developed by disregarding the effects of the approach velocity, when they are applied, it is necessary to evaluate the effects of the approach velocity on the overflow head beforehand.

Numerical Flow Analysis of Propeller Type Pump (프로펠러식 펌프의 전산 유동 해석)

  • Yu, Hye-Ran;Park, Warn-Gyu
    • The KSFM Journal of Fluid Machinery
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    • v.9 no.6
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    • pp.29-34
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    • 2006
  • Propeller type pump has been widely used for pumping water in agricultural and manufacturing industry. Since a propeller type pump contains a screw impeller inside a circular casing, the numerical analysis becomes complex. However, the accurate prediction of viscous flow is essential for computing hydrodynamic performances. To analysis the flow and the performance of the propeller type pump, the present work has solved 3D incompressible RANS equations on the multiblocked grid. From the present calculation, small amount of flow separation was shown near hub and the flow was recovered to nearly uniform inflow after one diameter downstream. Torque and thrust coefficient were computed and compared with experiments.

The Variation of Flow Field and Hydrodynamic Coefficients of Submarine by Changes of Angle of Attack and Yaw Angle (유동 방향 변화에 따른 잠수함 주위의 유동 특성과 유체동역학적 계수의 변화)

  • Jang Jin-Ho;Park Warn-Gyu
    • Journal of the Society of Naval Architects of Korea
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    • v.43 no.4
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    • pp.460-466
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    • 2006
  • The three-dimensional RANS equations were applied to analyze the flow field of a submarine. To validate the code, the DARPA SUBOFF bare hull and an eliipsoid at angles of attack of $10^{\circ}\;and\;30^{\circ}$ were simulated and good agreement with experiments was obtained. After the code validation, the flows over the full configuration of DARPA SUBOFF model having a fairwater and four stern appendages were simulated at four angles of attack $(0^{\circ},\;10^{\circ},\;20^{\circ},\;30^{\circ})$ and three yaw angles $(10^{\circ},\;20^{\circ},\;30^{\circ})$ Specifically, the pressure contours and streamlines of fairwater and stern appendage were compared as the angle of attack and yaw angle changed. The variations of hydrodynamic forces were also calculated.

PERFORMANCE ASSESSMENT OF THE RANS TURBULENCE MODELS IN PREDICTION OF AERODYNAMIC NOISE FOR AIR-CONDITIONER INDOOR UNIT (에어컨 실내기의 공력소음 예측을 위한 RANS 난류모델의 성능 평가)

  • Min, Y.H.;Kang, S.;Hur, N.;Lee, C.;Park, J.
    • Journal of computational fluids engineering
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    • v.17 no.4
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    • pp.81-86
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    • 2012
  • The objective of the present study is to investigate the effects of various turbulence models on the aerodynamic noise of an air-conditioner (AC) indoor unit. The results from URANS (unsteady Reynolds-averaged Navier-Stokes) simulations with the standard k-$\varepsilon$, k-$\omega$ shear stress transport (SST) and Spalart-Allmaras (S-A) turbulence models were analyzed and compared with the noise data from the experiments. The frequency spectra of the far-field acoustic pressure were computed using the Farrasat equation derived from the Ffowcs Williams-Hawkings (FW-H) equation based on the acoustic analogy model. Two fixed fan casings and the rotating cross-flow fan were used as the source surfaces of the dipole noise in the Farrasat equation. The result with the standard k-$\epsilon$ model showed a much better agreement with the experimental data compared to the k-w SST and S-A models. The differences in the pressure spectra from the different turbulence models were discussed based on the instantaneous vorticity fields. It was found that the over-estimated power spectra with the k-w SST and S-A models are related to the emphasized small-scale vortices produced with these models.

A New Wall-Distance Free One-Equation Turbulence Model

  • Nakanishi Tameo
    • 한국전산유체공학회:학술대회논문집
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    • pp.107-109
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    • 2003
  • We propose a wall distance free one-equation turbulence model. The model is organized in an extremely simple form. Only a few model constants were introduced into the model. The model is numerically tough and easy-of-use. The model also demonstrated the ability to simulate the laminar to turbulent flow transition. The model has been applied to the channel flow, the plane jet, the backward facing step flow, the flat plate boundary layer, as well as the flow around the 2D airfoil at large angles of attack, which obtained satisfactory results.

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A Study on the Flow Characteristics in Urban Stream Using 3-D Numerical Model (3차원 수치모형을 이용한 도시하천의 흐름특성에 관한 연구)

  • Yoon, Sun-Kwon;Kim, Jong-Suk;Moon, Young-Il;Lee, Il-Ju
    • Proceedings of the Korea Water Resources Association Conference
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    • pp.1287-1292
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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 1D or 2D stream flow that was applied simple momentum equation and fixed energy conservation. Therefore, hydrodynamics flow analysis in rivers has been needed 3D numerical analysis for correct stream flow interpretation. In this study, CFD model on FLOW-3D was applied to stream flow analysis, which solves three dimenson 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 ${\kappa}-{\varepsilon}$, RNG ${\kappa}-{\varepsilon}$ and LES. Those numerical analysis results have been illustrated by the turbulence energy effects, velocity of flow distributions, water level pressure distributions and eddy flows around the piers at Jangwall bridge in urbarn stream.

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Prediction of Resistance and Planing Attitude for Prismatic Planing Hull using OpenFOAM (OpenFOAM을 이용한 주형체 활주선의 저항 및 항주자세 추정)

  • Shi, XiangYu;Zhang, Yang;Yum, Deuk-joon
    • Journal of Ocean Engineering and Technology
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    • v.33 no.4
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    • pp.313-321
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    • 2019
  • The prediction of the hydrodynamic performance of a planing hull vessel is an important and challenging topic for computational fluid dynamic (CFD) applications to naval hydrodynamics. In this paper, the resistance and planing attitude analysis for a Fridsma hull, which is a prismatic planing hull, in still water are numerically studied using OpenFOAM. OpenFOAM is an open source code package based on C++ libraries and the finite volume method (FVM) for the discretization of the RANS equation. The volume of fluid method (VOF) is used to capture the water-air interface and the SST ${\kappa}-{\omega}$ model is used for the turbulence simulation. The overset mesh method is used to capture the large motion of the hull at higher speeds. Before the extensive analysis, uncertainty analyses using various time steps and grid sizes were performed for one ship speed case of Fn = 1.19. The results of the present study are compared with those of a model test, other CFD research, and Savitsky's empirical formula. The results of the present study, following the trend of other CFD results, slightly over predict the resistance and under predict the sinkage and, more significantly, the trim.

Numerical Simulations of Dry and Wet Deposition over Simplified Terrains

  • Michioka, T.;Takimoto, H.;Ono, H.;Sato, A.
    • Asian Journal of Atmospheric Environment
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    • v.11 no.4
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    • pp.270-282
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    • 2017
  • To evaluate the deposition amount on a ground surface, mesoscale numerical models coupled with atmospheric chemistry are widely used for larger horizontal domains ranging from a few to several hundreds of kilometers; however, these models are rarely applied to high-resolution simulations. In this study, the performance of a dry and wet deposition model is investigated to estimate the amount of deposition via computational fluid dynamics (CFD) models with high grid resolution. Reynolds-averaged Navier-Stokes (RANS) simulations are implemented for a cone and a two-dimensional ridge to estimate the dry deposition rate, and a constant deposition velocity is used to obtain the dry deposition flux. The results show that the dry deposition rate of RANS generally corresponds to that observed in wind-tunnel experiments. For the wet deposition model, the transport equation of a new scalar concentration scavenged by rain droplets is developed and used instead of the scalar concentration scavenged by raindrops falling to the ground surface just below the scavenging point, which is normally used in mesoscale numerical models. A sensitivity analysis of the proposed wet deposition procedure is implemented. The result indicates the applicability of RANS for high-resolution grids considering the effect of terrains on the wet deposition.

Computation of Four Quadrant Performance for a Marine Propeller in Open Water (박용 프로펠러의 4상한 단독성능 계산)

  • Hyoung-Tae Kim;Jeong-Jung Kim
    • Journal of the Society of Naval Architects of Korea
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    • v.38 no.4
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    • pp.1-10
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    • 2001
  • A numerical solution method of the incompressible Reynolds-Averaged Navier-Stokes equations is applied for calculating turbulent flows and performances of a marine propeller in open-water, four-quadrant conditions. Computed propeller flows of the model propeller P4381, for which the experimental data of the open-water performances exist, reveal complex viscous-flow characteristics including three-dimensional flow separations in various off-design conditions and also computed propeller thrusts and torques agree quite well with experimental data except some cases for which severe propeller cavitations occurred in the experiment.

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Numerical Analysis of Free Surface Flow around Blunt Bow Ship Model (뭉뚝한 선수 선형 주위 자유수면 유동 수치 해석)

  • Park, Il-Ryong;Suh, Sung-Bu;Kim, Jin
    • Journal of Ocean Engineering and Technology
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    • v.26 no.1
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    • pp.9-16
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    • 2012
  • This paper presents the numerical results of a simulation of the free surface flow around a blunt bow ship model and focuses on the validation of the proposed method with a brief investigation of the relation between the resistance and free surface behavior. A finite volume method based on the Reynolds Averaged Navier-Stokes (RANS) approach is used to solve the governing flow equations, where the free surface, including wave breaking,is captured by using a two-phase Level-Set (LS) method. For turbulence closure, a two equation k-${\varepsilon}$ model with the standard wall function technique is used. Finally, the numerical results are compared with the available experimental data, showing good agreement.