• Title/Summary/Keyword: $ {\kappa}-{\varepsilon}$ Model

Search Result 172, Processing Time 0.03 seconds

A NUMERICAL SIMULATION OF THE PRESSURE COEFFICIENT AROUND A CUBIC BUILDING MODEL (수치풍동 기법을 이용한 정사각형 건물 주위의 풍압계수에 관한 연구)

  • Yeo, Jae-Hyun;Hur, Nahm-Keon;Won, Chan-Shik;Kim, Sa-Ryang;Choi, Chang-Koon
    • 한국전산유체공학회:학술대회논문집
    • /
    • 2007.10a
    • /
    • pp.162-166
    • /
    • 2007
  • In the present study, the pressure coefficient of a cubic building model is numerically simulated. Three turbulence models of standard ${\kappa}-{\varepsilon}$, RNG ${\kappa}-{\varepsilon}$ and LES are adopted and the results are compared with the available experimental data. From the results, it has been found that RNG ${\kappa}-{\varepsilon}$ turbulence model and LES turbulence model were shown to predict fairly well the experimental pressure coefficient. In contrast, the results of the standard ${\kappa}-{\varepsilon}$ turbulence model showed large discrepancies in pressure coefficient on the side and top surfaces of the cubic building, which limits the applicability of the standard ${\kappa}-{\varepsilon}$ turbulence model on wind engineering.

  • PDF

Finite element analysis of 2D turbulent flows using the logarithmic form of the κ-ε model

  • Hasebe, Hiroshi;Nomura, Takashi
    • Wind and Structures
    • /
    • v.12 no.1
    • /
    • pp.21-47
    • /
    • 2009
  • The logarithmic form for turbulent flow analysis guarantees the positivity of the turbulence variables as ${\kappa}$ and ${\varepsilon}$ of the ${\kappa}-{\varepsilon}$ model by using the natural logarithm of these variables. In the present study, the logarithmic form is incorporated into the finite element solution procedure for the unsteady turbulent flow analysis. A backward facing step flow using the standard ${\kappa}-{\varepsilon}$ model and a flow around a 2D square cylinder using the modified ${\kappa}-{\varepsilon}$ model (the Kato-Launder model) are simulated. These results show that the logarithmic form effectively keeps adequate balance of turbulence variables and makes the analysis stable during transient or unsteady processes.

Assessment of Turbulence Models for Engine Intake and Compression Flow Analysis (엔진 흡입.압축과정의 유동해석을 위한 난류모델의 평가)

  • Park, Kweon-Ha;Kim, Jae-Gon
    • Journal of Advanced Marine Engineering and Technology
    • /
    • v.32 no.8
    • /
    • pp.1129-1140
    • /
    • 2008
  • Many turbulence models have been developed in order to analyze the flow characteristics in an engine cylinder. Watkins introduced k-${\varepsilon}$ turbulence model for in-cylinder flow, and Reynolds modified turbulence dissipation rate by applying rapid transformation theory, Wu suggested k-${\varepsilon}-{\tau}$ turbulence model in which length scale and time scale are separated to introduce turbulence time scale, and Orszag proposed k-${\varepsilon}$ RNG model. This study applied the models to in-cylinder flow induced by intake valve and piston moving. All models showed similar flow fields during early stage of intake stroke. At the end of compression stroke, ${\kappa}-{\varepsilon}$ Watkins, ${\kappa}-{\varepsilon}$ Reynolds and ${\kappa}-{\varepsilon}$ RNG predicted well second and third vortex, especially ${\kappa}-{\varepsilon}$ RNG produced new forth vortex near central axis at the lower part of cylinder which was not predicted by the other models.

Development of Multiple Production $\varepsilon$ Equation Model in Low Reynolds Number $\kappa$-$\varepsilon$ Model with the Aid of DNS Data (저 레이놀즈수 $\kappa$-$\varepsilon$psilon.모형에서 DNS 자료에 의한 $\varepsilon$방정식의 다중 생성률 모형 개발)

  • Sin, Jong-Geun;Choe, Yeong-Don
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.20 no.1
    • /
    • pp.304-320
    • /
    • 1996
  • A multiple production .epsilon. equation model was developed in the low Reynolds number $\kappa$-$\varepsilon$ model with the aids of DNS data. We derived the model theoretically and avoided the use of empirical correlations as much as possible in order for the model to have generality in the prediction of complex turbulent flow. Unavoidable model constants were, however, optimized with the aids of DNS data. All the production and dissipation models in the $\varepsilon$ equation were modified with damping functions to satisfy the wall limiting behavior. A new $f_{\mu}$ function, turbulent diffusion and pressure diffusion model for the k and .epsilon. equations were also proposed to satisfy the wall limiting behavior. By, computational investigation on the plane channel flows, we found that the multiple production model for .epsilon. equation could improve the near wall turbulence behavior compared with the standard production model without the complicated empirical modification. Satisfication of the wall limiting conditions for each turbulence model term was found to be most important for the accurate prediction of near wall turbulence behaviors.

A Prediction of the Flow Characteristics around Buildings with the Turbulent Models (난류모델에 따른 건물주위의 유동 예측)

  • Lee, Seung-Ho;Yeo, Jae-Hyun;Hur, Nahm-Keon;Choi, Chang-Koon
    • 한국전산유체공학회:학술대회논문집
    • /
    • 2008.03b
    • /
    • pp.168-171
    • /
    • 2008
  • In the present study, turbulent flows around cubic and L-shape buildings were simulated numerically. Standard ${\kappa}$-$\varepsilon$, RNG ${\kappa}$-$\varepsilon$, LES turbulence models were adopted for the present simulation. The wind pressure coefficients from these results were compared with the available experimental data. The result of RNG ${\kappa}$-$\varepsilon$ and LES turbulent models gave better prediction than that of standard ${\kappa}$-$\varepsilon$ turbulent model which is widely used in the turbulent flow simulation.

  • PDF

3-D Numerical Study on a Oblique Jet Impingement for Fluid flows and Heat Transfer Characteristics Using ${\kappa}-{\varepsilon}-\bar {{\upsilon}'^ 2}$ Model (${\kappa}-{\varepsilon}-\bar {{\upsilon}'^ 2}$ 모델을 이용한 경사진 충돌제트의 유동장 및 열전달 특성에 대한 3차원 수치해석적 연구)

  • Choi, Bong-Jun;Lee, Jung-Hee;Choi, Young-Ki
    • Proceedings of the KSME Conference
    • /
    • 2000.04b
    • /
    • pp.789-794
    • /
    • 2000
  • The Paper studies the flow and heat transfer characteristics to a jet impinging at different oblique angles, to a plane surface by numerical methods. The flowfield and heat transfer rate associated with the oblique Impingement of an axisymmetric jet are of interest as a result of its presence in numerous technological Problems. For the computation of heat transfer rate, the standard ${\kappa}-{\varepsilon}$ and ${\kappa}-{\varepsilon}-\bar {{\upsilon}'^ 2}$ turbulent model were adapted. The accuracy of the numerical calculations was compared with various experimental data reported in the literature. ${\kappa}-{\varepsilon}-\bar {{\upsilon}'^ 2}$ model showed better agreement with experimental data than standard ${\kappa}-{\varepsilon}$ model in prediction of the turbulent intensity and the heat transfer rate. In the case of computation of flowfield, the study carries on the ${\alpha}=45$ deg, h/D=4.95. The jet Reynolds number based on the nozzle diameter(D), was 48,000. For the computation of heat transfer rate, the Re=20,000, the jet orifice-to-plate spacings(L/D) are 4, 6 and 10, and the angle between the axis of the jet orifice and the plate surface is set at 30, 45, 60, or 90 deg. For the smaller spacings, the near-peak Nusselt numbers are not significantly effected by the initial decreases in the Jet angle. The overall shape of the local Nusselt number x-axis profile is influenced by both the jet orifice-to-plate spacing and the jet angle.

  • PDF

Assessment of Reynolds Stress Model for the Analysis of Floating Flames in Stagnating Flows (정체유동에서의 난류 부상 화염 해석을 위한 Reynolds 응력 모델의 검증)

  • Im, Yong-Hoon;Huh, Kang-Yul
    • Journal of the Korean Society of Combustion
    • /
    • v.7 no.2
    • /
    • pp.49-61
    • /
    • 2002
  • Numerical simulation is performed for stagnating turbulent flows of impinging and countercurrent jets by the Reynolds stress model(RSM). Results are compared with those of the ${\kappa}-{\varepsilon}$ model and available data to assess the flow characteristics and turbulence modes. Three variants of the RSM tested are those of Gibson and Launder(GL), Craft and Launder(GL-CL) and Speziale, Sarkar and Gatski(SSG). As well known, the ${\kappa}-{\varepsilon}$ model overestimates turbulent kinetic energy near the wall significantly. Although the RSM is superior to the ${\kappa}-{\varepsilon}$ model, it shows considerable difference according to how the redistributive pressure-strain term is modeled. Results of the RSM for countercurrent jets are improved with the modified coefficients for the dissipation rate, $C_{{\varepsilon}1}\;and\;C_{{\varepsilon}2}$ suggested by Champion and Libby. The performance of the three variants of the RSM model for stagnating flows are assessed.

  • PDF

Numerical Simulation of Flow Field and Organism Concentration in a UV Disinfection Channel

  • Li, Chan;Deng, Baoqing;Kim, Chang-Nyung
    • Proceedings of the KSME Conference
    • /
    • 2008.11b
    • /
    • pp.2816-2821
    • /
    • 2008
  • This paper investigates the flow field and organism concentration in a UV disinfection channel in which vertical ultraviolet lamps are arranged in a staggered configuration. Turbulence is described by low Reynolds number ${\kappa}-{\varepsilon}$ turbulence model and standard ${\kappa}-{\varepsilon}$ turbulence model, respectively. P-1 method has been employed to solve the radiative transfer equation. The obtained incident radiation is used to compute the inactivation term in the species equation. The CFD results are in good agreement with the existing experimental data for the UV channel. For the flow field, the low-Reynolds number ${\kappa}-{\varepsilon}$ model is superior to the standard ${\kappa}-{\varepsilon}$ model. The approach velocity has a significant effect on the disinfection efficiency. The organism concentration at the outlet decreases fast to a low inlet velocity.

  • PDF

Three-Dimensional Thermohydrodynamic Analysis of Journal Bearings Operating in Turbulent Region Using $kappa-varepsilon$ Model (난류상태로 운전되는 저어널베어링에서의 $kappa-varepsilon$ 모델을 이용한 3-차원 THD해석)

  • 이득우;김경웅
    • Tribology and Lubricants
    • /
    • v.3 no.1
    • /
    • pp.39-46
    • /
    • 1987
  • Frictional loss in turbulent regime is abnormally increased compared with in laminar regime. Thus the consideration of temperature rise across fluid film is significant in analysis and conventional isothermal theory loses its usefulness for performance prediction. This paper proposes to the three-dimensional thermohydrodynamic analysis of finite journal bearings operating under turbulent condition using two-equation model($\kappa-\varepsilon$ model) proposed by Hassid & Poreh. The equations are solved numerically by finite difference method. We make the analysis applicable even at large eccentricity when back flow of the lubricants occurs and axial flow is no longer ignored compared to circumferential flow.

Prediction of Fully Developed Turbulent Flow in a Square Duct with Nonlinear Low-Reynolds-Number κ-ε Models (비선형 저레이놀즈수 κ-ε 난류모델에 따른 정사각형 덕트내 완전 발달된 난류유동 예측)

  • Myong, Hyon-Kook,
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.27 no.6
    • /
    • pp.821-827
    • /
    • 2003
  • Fully developed turbulent flow in a square duct is numerically predicted with two nonlinear low-Reynolds-number ${\kappa}-{\varepsilon}$ models. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in detail with each other. It is found that the nonlinear low-Reynolds-number ${\kappa}-{\varepsilon}$ model adopted in a commercial code is unable to predict accurately duct flows involving turbulence-driven secondary motion with the prediction level of secondary flows one order less than that of the experiment.