• Title, Summary, Keyword: RANS equation

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Internal Wave-Maker using Momentum Source Term of RANS Equation Model (RANS 방정식의 운동량 원천항을 이용한 내부조파)

  • Choi, Jun-Woo;Ko, Kwang-Oh;Yoon, Sung-Bum
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.21 no.2
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    • pp.182-190
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    • 2009
  • For RANS equation model using VOF scheme Lin and Liu (1999) developed internal wave-maker method to generate target wave trains by using designed mass source functions of the continuity equation. By using this method studies on various numerical wave experiments has been achieved without the problem caused by wave reflection due to an external wave-maker. In this study, the wave-maker method to generate target wave trains by using a momentum source function was proposed. The computational results obtained by applying the mass and momentum source functions into FLUENT were compared with each other. To see its applicability, the hydraulic experiment of Luth et al. (1994) were numerically simulated and their measurements are compared with the computations, and the vertical variations of computed results were shown and investigated.

Hybrid RANS/LES Method for Turbulent Channel Flow (채널난류유동에 대한 하이브리드 RANS/LES 방법)

  • Myeong, Hyeon-Guk
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.8
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    • pp.1088-1094
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    • 2002
  • A channel flow with a high Reynolds number but coarse grids is numerically studied to investigate the prediction possibility of its turbulence which is three-dimensional and time-dependent. In the present paper, a Reynolds-Averaged Navier-Stokes (RANS) model, a Large Eddy Simulation (LES) and a Navier-Stokes equation with no model are tested with a new approach of hybrid RANS/LES, which reduces to RANS model in the boundary layers and at separation, and to Smagorinsky-like LES downstream of separation, and then compared with each other. It is found that the simulations of hybrid RANS/LES method sustain turbulence like those of LES and with no model, and the results are stable and fairly accurate. This indicates strongly that gradual improvements could lead to a simple, stable, and accurate approach to predict turbulence phenomena of wall-bounded flow.

NUMERICAL SIMULATIONS OF SUPERSONIC FLOWS USING POROUS AND ROUGH WALL BOUNDARY CONDITIONS (다공성 벽면(porous-wall)과 거칠기가 있는 벽면(rough-wall)에 관한 경계조건을 이용한 초음속 흐름의 수치모사)

  • Kwak, E.K.;Yoo, I.Y.;Lee, D.H.;Lee, S.
    • Journal of computational fluids engineering
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    • v.14 no.4
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    • pp.23-30
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    • 2009
  • The existing code which solves two-dimensional RANS(Reynolds Averaged Navier-Stokes) equations and 2-equation turbulence model equations was modified to enable numerical simulation of various supersonic flows. For this, various boundary conditions have been implemented to the code. Bleed boundary condition was incorporated into the code for calculating wall mean flow quantities. Furthermore, boundary conditions for the turbulence quantities along rough surfaces as well as porous walls were applied to the code. The code was verified and validated by comparing the computational results against the experimental data for the supersonic flows over bleed region on a flat plate. Furthermore, numerical simulations for supersonic shock boundary layer interaction with a bleed region were performed and their results were compared with the existing computational results.

NUMERICAL SIMULATION OF SUPERSONIC FLOW USING POROUS AND ROUGH WALL BOUNDARY CONDITIONS (다공성 벽면(porous-wall)과 거칠기가 있는 벽면(rough-wall)에 과한 경계조건을 이용한 초음속 흐름의 수치모사)

  • Kwak, E.K.;Yoo, I.Y.;Lee, S.
    • 한국전산유체공학회:학술대회논문집
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    • pp.104-111
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    • 2009
  • The existing code which solves two-dimensional RANS(Reynolds Averaged Navier-Stokes) equations and 2-equation turbulence model equations was modified to enable numerical simulation of various supersonic flows. For this, various boundary conditions have been implemented to the code. Bleed boundary condition was incorporated into the code for calculating wall mean flow quantities. Furthermore, the boundary conditions for the turbulence quantities along rough surfaces as well as porous walls were applied to the code. The code was verified and validated by comparing the computational results against the experimental data for the supersonic flows over bleed region on a flat plate. Using the newly modified code, numerical simulations were performed and compared with other computational results as well as the experimental data for the supersonic flows over an oblique shock with a bleed region.

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Visous resistance analysis of a ship using numerical solutions (수치해를 이용한 선박의 점성저항 해석)

  • 곽영기
    • Journal of Ocean Engineering and Technology
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    • v.11 no.2
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    • pp.100-106
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    • 1997
  • Viscous flow around an actual ship is calculated by an use of RANS(Reynolds-averaged Navier-Stokes) solver. Reynolds stress is modelled by using k-$\varepsilon$ turbulence model and the law of wall is applied near the body. Body fitted coordinates are introduced for the treatment of the complex boundary of the ship hull form. The transformed equations in the computational domain are numerically solved by an employment of FVM(Finite Volume Method). SIMPLE(Semi-Implcit Pressure Linked Equation) method is adopted in the calculation of pressure and the solution of the disssssssscretized equation is obtained by the line-by-line method with the use of TDMA(Tri-Diagonal Matrix Algorithme). The subject ship model of actual calculation is 4,410 TEU class container carrier. For 4 geosim models the calculated viscous resistancce values are compared with the model test results and analyzed on their componentss. The resistance performance of an actual ship is predicted very resonably, so this mothod may be utilized as a design tool of hull form.

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Numerical Calculation of Viscous Flows for Two HSVA Tankers (HSVA 두 탱커 선형에 대한 점성유동 계산)

  • Kwak, Young-Ki
    • Journal of Ocean Engineering and Technology
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    • v.13 no.2
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    • pp.138-146
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    • 1999
  • The viscous flow around a ship hull is calculated by the use of RANS(Reynolds-averaged Navier-Stokes) solver. Reynolds stresses are midelled by using the k-${epsilon}$ turbulence model and the law is applied near the body. Body fitted corrdinates are introduced for the treatment of the complex boundary of the ship hull form and the governing equations in the physical domain transformed into ones in the computational domain. The transformed equations are numerically solved by an employment of FVM(Finite Volume Method). SIMPLE(Semi-Implicit Pressure Linked Equation) method is adopted in the calculation of pressure and the solution of the sidcretized equation is obtained by the line-by-line method with the use of TDMA(Tri-Diagonal Matrix Algorithme). To assure the proprietty of this computing method, HSVA tanker and Dyne hull are calculated ar both model and ship scale Reynolds number. Their reaults of pressure distributions on fore and aft body, axial velocity contours and transverse velocity velocity vectors and viscous resistance coefficients are compared with other's experiments and calculations.

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Hybrid RANS/LES Simulation of Subsonic Cavity Flow (Hybrid RANS/LES 방법을 이용한 이음속 공동 유동의 수치적 모사)

  • Chang K. S.;Park S. O.;Choi S. K.
    • Journal of computational fluids engineering
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    • v.9 no.2
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    • pp.23-29
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    • 2004
  • A numerical simulation of an incompressible cavity flow is conducted using the hybrid turbulence model. The model adopted is a modified type of DES using k- ε two-equation model. Cavity geometry and flow condition are based on Cattafesta's experiment. Computational results are compared with the results of Cattafesta's experiment. The simulation successfully predicts the oscillatory features and the Strouhal number of the oscillation compares very favorably with that of the dominant mode of experimental data. Vorticity contours obtained from the simulation data are consistent with the smoke visualization of the Cattafesta's experiment. The coherent structures of cavity flow are also investigated using Q criterion.

Numerical Simulation of Supersonic Inlet Flow (초음속 흡입구 유동의 수치모사)

  • Kwak, Ein-Keun;Yoo, Il-Yong;Lee, Seung-Soo;Jung, Suk-Young
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.133-137
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    • 2009
  • Numerical simulations of flows in an axisymmetric supersonic inlet with bleed regions were performed. For the simulations, the existing code which solves the RANS(Reynolds Averaged Navier-Stokes) equations and 2-equation turbulence model equations was transformed to axisymmetric form and bleed boundary condition was applied to the code. In this paper, the modified code was validated by comparing the results against an experimental data and other computational results for flow on a bump and over an oblique shock with bleed region. Using the code, numerical simulations were performed for the flow in the inlet with multiple bleed regions.

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Detached Eddy Simulation of a Developing Turbulent Flow in a 270° Curved Duct (DES 기법을 이용한 270°곡덕트에서 발달하는 난류 유동의 수치해석)

  • Seo, Jeong-Sik;Shin, Jong-Keun;Choi, Young-Don;Lee, Joo-Cheol
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.32 no.6
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    • pp.471-478
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    • 2008
  • Detached Eddy Simulation (DES) is performed for developing turbulent flow of the $270^{\circ}$ curved duct at a Reynolds number of 56,690. The curvature ratio on the basis of a centric radius $R_c$ and a duct height H is 3.357. Turbulence models adopted are k-$\omega$ model for Reynolds Average Navier-Stokes (RANS) equation Simulation and Shear Stress Transport (SST) model for DES. DES is used as the hybrid computation technique combined with RANS-SST and Large Eddy Simulation (LES). Predicted results are compared with measured results including the distributions of Reynolds stresses and the flow characteristics on the symmetric plane of curved duct are presented. Judging from the comparison between the predicted and the measured results, the DES approach is applicable to calculate the developing turbulent flow in a $270^{\circ}$ curved duct.