• Title, Summary, Keyword: 2-equation Turbulence Model equation

Search Result 190, Processing Time 0.033 seconds

A New Wall-Distance Free One-Equation Turbulence Model

  • Nakanishi Tameo
    • 한국전산유체공학회:학술대회논문집
    • /
    • /
    • pp.107-109
    • /
    • 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.

  • PDF

A Comparative Study of 2-Dimensional Turbulence Models for Thermal Discharge (2차원 온배수 난류모형의 비교연구)

  • Choi, Hung-Sik
    • Journal of Korea Water Resources Association
    • /
    • v.32 no.3
    • /
    • pp.225-235
    • /
    • 1999
  • For a comparative evaluation of three turbulence models in the analyses of thermal discharge behavior into a crossflow, a 2-dimemsional near-field numerical model is developed. The selected models are k-$\varepsilon$ and k-ι turbulence models as a 2-equation turbulence model and a 4-equation turbulence model in which the transport equations for mean of the temperature fluctuation squared and its dissipation rate for the consideration of buoyancy production and turbulent heat flux terms are added to a k-$\varepsilon$ turbulence model. The developed models are applied to a steady flow in an open channel with simple geometry and the numerical results agree with the existing experimental data. Numerical results of buoyancy induced gravitational lateral spreading by 4-equation turbulence model agree with the experimental data better than those of 2-quation turbulence models. The flow patterns by 4 and 2-equation turbulence models are similar.

  • PDF

Analysis of Empirical Constant of Eddy Viscosity by Zero- and One-Equation Turbulence Model in Wake Simulation

  • Park, Il Heum;Cho, Young Jun;Kim, Tae Yun;Lee, Moon Ock;Hwang, Sung Su
    • Journal of the Korean Society of Marine Environment & Safety
    • /
    • v.20 no.3
    • /
    • pp.323-333
    • /
    • 2014
  • In this paper, the wakes behind a square cylinder were simulated using two kinds of different turbulence models for the eddy viscosity concept such as the zero- and the one-equation model in which the former is the mixing length model and the latter is the k-equation model. For comparison between numerical and analytical solutions, we employed three skill assessments: the correlation coefficient(r) for the similarity of the wake shape, the error of maximum velocity difference(EMVD) for the accuracy of wake velocity and the ratio of drag coefficient(RDC) for the pressure distribution around the structure. On the basis of the numerical results, the feasibility of each model for wake simulation was discussed and a suitable value for the empirical constant was suggested in these turbulence models. The zero-equation model, known as the simplest turbulence model, overestimated the EMVD and its absolute mean error(AME) for r, EMVD and RDC was ranging from 20.3 % to 56.3 % for all test. But the AME by the one-equation model was ranging from 3.4 % to 19.9 %. The predicted values of the one-equation model substantially agreed with the analytical solutions at the empirical mixing length scale $L=0.6b_{1/2}$ with the AME of 3.4 %. Therefore it was concluded that the one-equation model was suitable for the wake simulation behind a square cylinder when the empirical constant for eddy viscosity would be properly chosen.

Study on the Second Moment Turbulence Model in a Square Sectioned $180^{\circ}$ Bend (정사각단면을 갖는 $180^{\circ}$ 곡관내의 2차 모멘트 난류모형에 관한 연구)

  • 김명호;염성현;최영돈
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.18 no.5
    • /
    • pp.1203-1217
    • /
    • 1994
  • In the present study, in order to analyze a turbulent flow in a square sectiond 180.deg. bend, Kim's low Reynolds number second moment turbulence closure is adopted. In this model, turbulence model constants in the wall region are modified as functions of turbulent Reynolds number by use of near wall turbulent universal properties based on Laufer's experimental results of Reynolds stress distriburions. Algebraic stress model and Reynolds stress equation model are used to verify the low Reynolds number second moment closure. The application of the present low Reynolds number algebraic stress model to the prediction of a square sectioned 180.deg. bend flow gives improved velocities and Reynolds stresses profiles compared with those obtained by using the van Driest mixing length model and present low Reynolds number Reynolds stress equation model.

COMPARISON OF COUPLING METHODS FOR NAVIER-STOKES EQUATIONS AND TURBULENCE MODEL EQUATIONS (Navier-Stokes 방정식과 난류모델 방정식의 연계방법 비교)

  • Lee, Seung-Soo;Ryu, Se-Hyun
    • 한국전산유체공학회:학술대회논문집
    • /
    • /
    • pp.111-116
    • /
    • 2005
  • Two coupling methods for the Navier-Stokes equations and a two-equation turbulence model equations are compared. They are the strongly coupled method and the loosely coupled method. The strongly coupled method solves the Navier-Stokes equations and the two-equation turbulence model equations simultaneously, while the loosely coupled method solves the Navier-Stokes equation with the turbulence viscosity fixed and subsequently solves the turbulence model equations with all the flow quantities fixed. In this paper, performances of two coupling methods are compared for two and three-dimensional problems.

  • PDF

Turbulence Models for the Surface Discharge of Heated Water (표면온배수 난류모형)

  • 최흥식;이길성
    • Water for future
    • /
    • v.23 no.4
    • /
    • pp.445-457
    • /
    • 1990
  • In order to predict the dispersion of a thermal discharge with strong turbulent and buoyant effects, the development of a numerical model using turbulence model and its application are significantly increased. In this study, a 3-dimensional steady-state model for the surface discharge of heated water into quiescent water body is developed. For the model closure of turbulent terms the 4-equation turbulence model is used. For economic numerical simulation, the elliptic governing equations are transformed to the partially parabolic equations. In general, the simulated results by the present model agree well to the experimental results by Pande and Rajaratnam. The model characteristics are presented in comparison with the predicted results of the 2-equation turbulence model by McGuirk and Rodi. Applying the 4-equation turbulence model to the Korea nuclear unit 1 at Kori site, feasibility and efficiency of the present model are validated.

  • PDF

Study on the effect turbulence models for the flow through a subsonic compressor cascade (2차원 아음속 압축기 익렬유동에서의 난류모델 효과에 관한 연구)

  • Nam Gyeong-U;Baek Je-Hyeon
    • 한국전산유체공학회:학술대회논문집
    • /
    • /
    • pp.51-57
    • /
    • 2001
  • The eddy viscosity turbulence models were applied to predict the flows through a cascade, and the prediction performances of turbulence models were assessed by comparing with the experimental results for a controlled diffusion(CD) compressor blade. The original $\kappa-\omega$ turbulence model and $\kappa-\omega$ shear stress transport(SST) turbulence model were used as two-equation turbulence model which were enhanced for a low Reynolds number flow and the Baldwin-Lomax turbulence model was used as algebraic turbulence model. Farve averaged Wavier-Stokes equations in a two-dimensional, curvilinear coordinate system were solved by an implicit, cell-centered finite-volume computer code. The turbulence quantities are obtained by lagging when the men flow equations have been updated. The numerical analysis was made to the flows of CD compressor blade in a cascade at three different incidence angles (40. 43.4. 46 degrees). We found the reversion in the prediction performance of original $\kappa-\omega$ turbulence model and $\kappa-\omega$ SST turbulence model when the incidence angie increased. And the algebraic Baldwin-Lomax turbulence model showed inferiority to two-equation turbulence models.

  • PDF

A Comparative Study of Two-Dimensional Numerical Models for Surface Discharge of Heated Water into Crossflow Field (가로흐름 수역으로 방출되는 2차원 표면온배수 수치모형 비교연구)

  • 이남주;최흥식;이길성
    • Journal of Korean Society of Coastal and Ocean Engineers
    • /
    • v.6 no.1
    • /
    • pp.40-50
    • /
    • 1994
  • For an accurate prediction of the temperature field induced by heated water discharged into a shallow crossflow, a two-dimensional near-field numerical model is developed. It is based on a 4-equation turbulence model in which the transport equations for mean of the temperature fluctuation squared and its dissipation rate are added to those of a 2-equation turbulence model which cannot give the information of the thermal time scale ratio. Vertical diffusion is also considered by including buoyancy production and turbulence heat flux terms. The developed model is applied to a steady flow in an open channel with simple geometry and the results are compared with existing experimental data and those of the already established 2-equation turbulence model. Numerical results of the model agree with the experimental data better than those of the 2-equation model. The present model also simulates quite adequately the physical characteristics of thermal discharge in the jet entrainment and stable regions.

  • PDF

Comparison of Turbulence Models in Homogeneous Channel Flows (등밀도 수로흐름에서 의 난류모형 비교)

  • 이종찬;최병호
    • 한국해양학회지
    • /
    • v.30 no.1
    • /
    • pp.13-26
    • /
    • 1995
  • In this paper three turbulence models including two-equation model by Blumberg and Mellor (1987), one-equation model with mixing length formula of Blackadar's (1962), and zero-equation model of Prandtl's (1925) were compared in homogeneous, unstratified channel flows. Steady flows which a steep-sided trapezoidal trench with uniform discharge, tidal flow and steady wind-driven flow in finite channels are considered in detail. Steady flows in a trench and tidal flows in a finite channel were reproduced fairly accurately and there was virtually no difference among results of three turbulence models. However, In case of steady wind-driven flow only two-equation model reproduced the important features of experimental data. the other two models underestimated the surface velocity. In tidal and wind-driven flows with negligibly small adjective and diffusive effects, the two-equation model gives rise to parabolic profile of eddy viscosity with maximum at the mid0depth, and the one and zero equation model based on Blackadar formula linear profile with maximum at the surface.

  • PDF

Computation of supersonic turbulent base flow using two-equation and Reynolds stress models (2-방정식 및 레이놀즈 응력 모형을 이용한 초음속 난류 기저유동의 수치적 계산)

  • Kim M. H.;Park S. O.
    • Journal of computational fluids engineering
    • /
    • v.2 no.2
    • /
    • pp.9-17
    • /
    • 1997
  • The performance of several turbulence models in computing an axisymmetric supersonic base flow is investigated. A compressible Navier-Stokes code, which incorporates k-ε, k-ω model and Reynolds stress closure with three kinds of pressure-strain correlation model, has been developed using implicit LU-SGS algorithm with second-order upwind TVD scheme. Numerical computations have been carried out for Herrin and Dutton's base flow. It is observed that the two-equation models give large backward axial velocity approaching to the base and somewhat larger variation of base pressure distribution than the Reynolds stress model. It is also found that the Reynolds stress model with third order pressure-strain model in the anisotropy tensor predicts most accurate mean flow field.

  • PDF