• Title/Summary/Keyword: Reynolds-Averaged Navier-Stokes equation

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Hydrodynamic characteristics of X-Twisted rudder for large container carriers

  • Ahn, Kyoung-Soo;Choi, Gil-Hwan;Son, Dong-Igk;Rhee, Key-Pyo
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.4 no.3
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    • pp.322-334
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    • 2012
  • This paper shows the numerical and experimental results about the hydrodynamic characteristics of X-Twisted rudders having continuous twist of the leading edge along the span. All the results were compared with those of the semi-balanced rudder. Calculation through the Reynolds-Averaged Navier-Stokes Equation (RANSE) code with propeller sliding meshes shows large inflow angle and fast inflow velocity in the vicinity of ${\pm}0.7$ R from the shaft center, so it may cause cavitation. Also, X-Twisted rudder has relatively small inflow angles along the rudder span compared with semi-balanced rudder. For the performance validation, rudders for two large container carriers were designed and tested. Cavitation tests at the medium sized cavitation tunnel with respect to the rudder types and twisted angles showed the effectiveness of twist on cavitation and the tendency according to the twist. And the resistance, self-propulsion and manoeuvring tests were also carried out at the towing tank. As a result, in the case of X-Twisted rudder, ship speed was improved with good manoeuvring performance. Especially, it was found out that manoeuvring performance between port and starboard was well balanced compared with semi-balanced rudders.

DESIGN OPTIMIZATION OF UPPER PLENUM OF PBMR USING RESPONSE SURFACE APPROXIMATION (반응면기법을 이용한 PBMR 기체냉각형 고온가스로 상층부의 최적설계)

  • Lee, S.M.;Kim, K.Y.
    • 한국전산유체공학회:학술대회논문집
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    • pp.187-194
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    • 2010
  • Shape optimization of an upper plenum of PBMR type gas cooled nuclear reactor has been performed by using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) analysis and surrogate modeling technique. The objective function is defined as a linear combination of uniformity of flow distribution in the core and pressure drop in the upper plenum and the core. The ratio of thickness of slot to diameter of rising channels, ratio of height of upper plenum to diameter of rising channels, and ratio of eight of the slot at inlet to outlet, are used as design variables for optimization. Design points are selected through Latin-hypercube sampling. The optimal point is determined through surrogate-based optimization method which uses 3-D RANS analyses at design points. The results show that the optimum shape represent remarkably improved performance in flow uniformity and friction loss than the reference shape.

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ANALYSIS OF HEAT TRANSFER OF INCLINED IMPINGING JETS ON A CONCAVE SURFACE (엇갈리게 기울어진 충돌제트들에 의한 오목면 상의 열전달 성능해석)

  • Heo, M.W.;Lee, K.D.;Kim, K.Y.
    • Journal of computational fluids engineering
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    • v.16 no.2
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    • pp.11-16
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    • 2011
  • Numerical analyses have been carried out to analyze the three-dimensional turbulent heat transfer by impingement jet on a concave surface with variation of geometric configurations. Three-dimensional Reynolds averaged Navier-stokes equations have been calculated using the shear stress transport turbulent model. The numerical results for heat transfer rate were validated in comparison with the experimental data. The distance between jet nozzles and angle of inclined jet nozzle were selected as the geometric variables. Area-averaged Nusselt numbers on concave surface are evaluated to find the characteristics of heat transfer with the two geometric variables. The heat transfer increases as the distance between jet nozzles increases, and the inclined impinging jets show much better heat transfer performance than the vertical impinging jet.

HEAT-TRANSFER ANALYSIS OF A COOLING CHANNEL WITH INCLINED ELLIPTICAL DIMPLES (기울어진 타원형 딤플이 부착된 냉각 유로에 대한 열전달 성능해석)

  • Kim, H.M.;Moon, M.A.;Kim, K.Y.
    • Journal of computational fluids engineering
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    • v.17 no.1
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    • pp.1-7
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    • 2012
  • This paper deals with a parametric study on inclined elliptical dimples to enhance heat transfer in a channel. Three-dimensional Reynolds-averaged Naiver-Stokes equations are solved to estimate flow and heat transfer in dimpled channel. As turbulence closure, the low-Re shear stress transport model is employed. Two non-dimensional geometric variables, dimple ellipse diameter ratio and angle of main diameter to flow direction are selected for the parametric study. The inclined elliptical dimples show higher heat-transfer performance but with higher pressure drop compared to the circular dimples. And there is an optimum inclination angle that gives the maximum heat transfer.

DESIGN OPTIMIZATION OF UPPER PLENUM OF PBMR USING RESPONSE SURFACE APPROXIMATION (반응면기법을 이용한 PBMR 기체냉각형 고온가스로 상층부의 최적설계)

  • Lee, S.M.;Kim, K.Y.
    • Journal of computational fluids engineering
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    • v.15 no.3
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    • pp.16-23
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    • 2010
  • Shape optimization of an upper plenum of a PBMR type gas cooled nuclear reactor has been performed by using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) analysis and surrogate modeling technique. The objective function is defined as a linear combination of uniformity of flow distribution in the core and pressure drop in the upper plenum and the core. The ratio of thickness of slot to diameter of rising channels, ratio of height of upper plenum to diameter of rising channels, and ratio of height of the slot at inlet to outlet, are used as design variables for optimization. Design points are selected through Latin-hypercube sampling. The optimal point is determined through surrogate-based optimization method which uses 3-D RANS analyses at design points. The results show that the optimum shape represent remarkably improved performance in flow uniformity and friction loss than the reference shape.

CFD Application for Prediction of Ship Added Resistance in Waves

  • Kim, Byung-Soo;Kim, Yonghwan
    • Journal of Advanced Research in Ocean Engineering
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    • v.4 no.3
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    • pp.135-145
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    • 2018
  • This paper deals with the added resistance of a ship in waves using computational fluid dynamics (CFD). The ship added resistance is one of the key considerations in the design of energy-efficient ship. In this study, the added resistance of a LNG carrier in head waves is computed using a CFD code to consider the nonlinearity and the viscous effects. The unsteady Reynolds Averaged Navier-Stokes equation (RANS) is numerically solved and the volume of fluid (VOF) approach is used to simulate the free surface flows. The length of incident wave varies from half the ship length to twice the ship length. To investigate the nonlinearity effect, both the linear wave condition and the nonlinear wave condition are considered. The heave and pitch motions are calculated along with the added resistance, and the wave contours are obtained. Grid convergence test is conducted thoroughly to achieve the converged motion and resistance values. The calculated results are compared and validated with experimental data.

Design Optimization of a Printed Circuit Heat Exchanger Using Surrogate Models (대리모델들을 이용한 인쇄형 열교환기의 최적설계)

  • Lee, Sang-Moon;Kim, Kwang-Yong
    • The KSFM Journal of Fluid Machinery
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    • v.14 no.5
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    • pp.55-62
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    • 2011
  • Shape optimization of a Printed circuit heat exchanger (PCHE) has been performed by using three-dimensional Reynolds-Averaged Navier-Stokes (3-D RANS) analysis and surrogate modeling techniques. The objective function is defined as a linear combination of effectiveness of the PCHE term and pressure drop in the cold channels of the PCHE. The cold channel angle and the ellipse aspect ratio of the cold channel are used as design variables for the optimization. Design points are selected through Latin-hypercube sampling. The optimal point is determined through surrogate-based optimization method which uses 3-D RANS analyses at design points. The results of three types of surrogate model are compared each other. The results of the optimizations indicate improved performance in friction loss but low performance in effectiveness than the reference shape.

Numerical Analysis on the Flow Field and Heat Transfer Characteristics of Longitudinal Vortices in Turbulent Boundary Layer - On the Common Flow Up - (3차원 난류경계층 내에 존재하는 종방향 와동의 유동장 및 열전달 특성에 관한 수치해석(II) - Common Flow Up에 관하여 -)

  • Yang Jang-Sik
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.9
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    • pp.799-807
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    • 2005
  • The flow characteristics and the heat transfer rate on a surface by the interaction of a pair of vortices are studied numerically. To analyze the common flow up produced by vortex generators in a rectangular channel flow, the pseudo-compressibility viscous method is introduced into the Reynolds-averaged Navier-Stokes equation for 3-dimensional unsteady, incompressible viscous flows. To predict turbulence characteristics, a two-layer $k-\varepsilon$ turbulence model is used on the flat plate 3-dimensional turbulence boundary The computational results predict accurately Reynolds stress, turbulent kinetic energy and flow field generated by the vortex generators. The numerical results, such as thermal boundary layers, skin friction characteristics and heat transfers, are also reasonably close to the experimental data.

Numerical Simulation on Interactions of Longitudinal Vortices in a Turbulent Boundary Layer (종방향 와동과 난류경계층의 상호작용에 관한 수치해석)

  • Yang Jang-Sik
    • Journal of Advanced Marine Engineering and Technology
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    • v.29 no.6
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    • pp.637-644
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    • 2005
  • This paper describes the numerical simulation of the interaction between longitudinal vortices ("common flow up") and a 3-D turbulent boundary layer over a flat plate To analyze the common flow up Produced from vortex generators. the flow field behind the vortex generators Is modeled by the information that is available from studies on a half-delta winglet. Also. the Reynolds-averaged Navier-Stokes equation for three-dimensional turbulent flows. together with a two-layer turbulence model to resolve the near-wall flow, is solved by the method of AF-ADI. The computational results predict that the boundary layer is thinned in the regions where the secondary flow is directed toward the wall and thickened where it is directed away from the wall Also. the numerical results. such as Reynolds stresses. turbulent kinetic energy and skin friction characteristics generated from the vortex generators . are reasonably close to the experimental data.

Numerical Study on Inertial Oscillations in the Spin-up of Fluid in a Circular Cylinder (원통 내 스핀업 유동에서의 관성진동에 관한 수치해석적 연구)

  • 서용권
    • Journal of Ocean Engineering and Technology
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    • v.15 no.3
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    • pp.9-19
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    • 2001
  • In this paper we present the aspect of inertial oscillation typically observed in the spin-up of fluids at low Rossby numbers in a circular cylinder. Numerical computations for the quasi three-dimensional equation as well as one-dimensional equation are performed to estimate the predictability of the one-dimensional equation with Ekman pumping/suction models. It is assumed that the discrepancy between the two results may be attributed to the inertial oscillation The detailed analysis to the numerical results reveals that the axial plane is dominated by a comparatively strong oscillatory flows caused by the inertial oscillation. In view of the fact that the time-averaged flow field however agrees to the Taylor-Proudman theorem, it is recommended that further analysis is needed to obtain an improved one-dimensional model like the Reynolds-averaged Navier-Stokes equation for turbulent flows.

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