• Title, Summary, Keyword: RANS equation

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ROTATING FLOW ANALYSIS AROUND A HAWT ROTOR BLADE USING RANS EQUATIONS (RANS 방정식을 이용한 HAWT 로터 블레이드의 회전 유동장 해석)

  • Kim, T.S.;Lee, C.;Son, C.H.;Joh, C.Y.
    • Journal of computational fluids engineering
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    • v.13 no.2
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    • pp.55-61
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    • 2008
  • The Reynolds-Averaged Navier-Stokes(RANS) analysis of the 3-D steady flow around the NREL Phase VI horizontal axis wind turbine(HAWT) rotor was performed. The CFD analysis results were compared with experimental data at several different wind speeds. The present CFD model shows good agreements with the experiments both at low wind speed which formed well-attache flow mostly on the upper surface of the blade, and at high wind speed which blade surface flow completely separated. However, some discrepancy occurs at the relatively high wind speeds where mixed attached and separated flow formed on the suction surface of the blade. It seems that the discrepancy is related to the onset of stall phenomena and consequently separation prediction capability of the current turbulence model. It is also found that strong span-wise flow occurs in stalled area due to the centrifugal force generated by rotation of the turbine rotor and it prevents abrupt reduction of normal force for higher wind speed than the designed value.

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 Viscous Flows around a Ship with a Drift Angle and the Effects of Stern Hull Form on the Hydrodynamic Forces (사항중인 선체 주위의 점성유동 계산 및 조종유체력에 선미형상이 미치는 영향)

  • Sun-Young Kim;Yeon-Gyu Kim
    • Journal of the Society of Naval Architects of Korea
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    • v.38 no.3
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    • pp.1-13
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    • 2001
  • RANS solver has been developed to solve the flows past a ship with a drift angle. The solver employs a finite volume method for the spatial discretization and Euler implicit method for the time integration. Turbulent flows are simulated by Spalart-Allmaras one-equation model. Developed solver is applied to analyze the hydrodynamic forces and flows of two tankers with a same forebody but different afterbodies. The computed flows and hydrodynamic forces are compared with the measured flows and captive model test data. The computed results show good agreements with experimental data and show clearly the effects of stern hull form on the hydrodynamic forces and the flows.

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Hydraulic Characteristics in the Movable Venturi Flume with Circular Cone (원뿔형 벤츄리수로의 수리특성)

  • Kim, Dae Geun
    • Journal of Korean Society of Water and Wastewater
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    • v.27 no.2
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    • pp.177-184
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    • 2013
  • This study analyzed the hydraulic characteristics of a venturi flume with a circular cone using a 3-D numerical model which uses RANS(Reynolds-Averaged Navier-Stokes Equation) as the governing equation. The venturi flume with the circular cone efficiently measures the discharge in the low-flow to high-flow range and offers the advantage of accurate discharge measurements in the case of a low flow. With no influence of the tail-water depth, the stage-discharge relationship and the flow behaviors were analyzed to verify the numerical simulation results. Additionally, this study reviewed the effect of the tail-water depth on the flow. The stage-discharge relationship resulting from a numerical simulation in the absence of an effect by the tail-water depth showed a maximum margin of error of 4 % in comparison to the result of a hydraulic experiment. The simulation results reproduced the overall flow behaviors observed in the hydraulic experiment well. The flow starts to become influenced by the tail-water depth when the ratio of the tail-water depth to the total head exceeds approximately 0.7. As the ratio increases, the effect on the flow tends to grow dramatically. As shown in this study, a numerical simulation is effective for identifying the stage-discharge relationship of a venturi flume with various types of venturi bodies, including a venturi flume with a circular cone.

Numerical Viscous Flow Analysis of Ducted Marine Propeller (Ducted Marine Propeller의 점성 유동 수치 해석)

  • Yu Hye-Ran;Jung Young-Rae;Park Warn-Gyu
    • 한국전산유체공학회:학술대회논문집
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    • pp.188-193
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    • 2003
  • The present work solved 3D incompressible RANS equation on a rotating, non-orthogonal multi-blocked grid system to efficiently analyze ducted marine propulsor with rotor-stator interaction. To handle the interface boundary between a rotor and a stator maintaining the conservative property, the sliding multiblock technique using the cubic spline interpolation and the bilinear interpolation technique were applied. To validate present code, a turbine flow having rotor- stator interaction was simulated. Time averaged pressure coefficients were compared with experiments and good agreement was obtained. After the code validation, the flowfield around a single-stage ducted marine propulsor was simulated.

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Numerical Simulation of 2-D Wing-In-Ground Effect (2차원 해면효과의 수치계산)

  • Yang Chen-Jun;Shin Myung-Soo
    • 한국전산유체공학회:학술대회논문집
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    • pp.90-98
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    • 1998
  • 본 논문은 2차원 해면효과의 수치계산 결과를 정리하였다. 지면으로부터의 높이변화에 따른 점성유동장을 계산하기 위하여 지배방정식으로는 비압축성 RANS방정식을, 시간에 대하여 서는 음해법으로 프로그램을 구성하였다. 압력항은 가상압축성을 도입 4차 수치확산항을 추가하는 것에 의해 계산하였으며, 높은 레이놀즈수에서의 효과적인 계산을 위해 Baldwin-Lomax 난류 모델을 도입하였다. 해면효과가 없는 무한유중에서의 NACA-0012단면 계산결과를 실험데이터와 비교하는 것에 의해 프로그램의 타당성을 확인하였다. NACA-6409와 두께비 $4.6\%$의 날개에 대하여 해면효과를 고려한 계산을 수행하였다. 높이의 변화에 따라 계산된 무차원계수, 압력 및 속도분포는 해면효과의 특성을 잘 보여주고 있다.

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Numerical Simulation of 2-D Wing-In-Ground Effect (2차원 해면효과의 수치계산)

  • Yang Chen-Jun;Shin Myung-Soo
    • Journal of computational fluids engineering
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    • v.3 no.1
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    • pp.54-62
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    • 1998
  • 본 논문은 2차원 해면효과의 수치계산 결과를 정리하였다. 지면으로부터의 높이변화에 따른 점성유동장을 계산하기 위하여 지배방정식으로는 비압축성 RANS 방정식을, 시간에 대하여서는 음해법으로 프로그램을 구성하였다. 압력항은 가상압축성과 4차 수치확산항을 추가하는 것에 의해 계산하였으며, 높은 레이놀즈 수에서의 효과적인 계산을 위해 Baldwin- Lomax 난류모델을 도입하였다. 해면효과가 없는 무한유중에서의 NACA-0012 단면 계산결과를 실험 데이터와 비교하는 것에 의해 프로그램의 타당성을 확인하였다. NACA-6409와 두께 비 4.6%의 날개에 대하여 해면효과를 고려한 계산을 수행하였다. 계산결과, 높이의 변화에 따라 계산된 무차원계수, 압력 및 속도분포는 해면효과의 특성을 잘 보여주고 있다.

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Numerical Analysis of Wind Turbine of Drag Force Type with change of Blade Number and Pitch Angle (수직항력식 터빈을 이용한 풍력발전 시스템의 형상 변화 및 피치각 변화에 관한 유동해석)

  • Park C.;Park G. S.;Park W. G.;Yoon S. H.
    • 한국전산유체공학회:학술대회논문집
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    • pp.61-64
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    • 2004
  • To analyze the performance of Wind turbine of the drag force type, 3-D RANS equations were solved by the iterative time marching method on sliding multiblock grid system. The numerical flow simulations by changing blade number and pitch angle were carried out : blade number = 15, 20 circumferentially; pitch angle = $30^{\circ},\; 50^{\circ}$ radially. The torque coefficient was also calculated.

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Numerical investigation of Turbulent Flow in $270^{\circ}$ Bend using DES approaches (DES 모형을 이용한 270도 곡관 내 난류유동에 관한 수치해석)

  • Seo, Jeong-Sik;Shin, Jong-Keun;Hong, Seong-Ho;Choi, Young-Don
    • Proceedings of the SAREK Conference
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    • pp.558-563
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    • 2007
  • Detached Eddy Simulation(DES) is performed for turbulent flow of the $270^{\circ}$ bend at a Reynolds number of 56,690. A Fine grid generation is used near a wall in order to satisfy the wall boundary condition of y+<1. Turbulence models adopted for DES and Reynolds Average Navier Stokes(RANS) simulation are SST(Shear Stress Transfort) model. Solutions for both streamwise and circumferential velocity components are compared with the experimental data by Lee for $270^{\circ}$ bend and by Chang for $180^{\circ}$ bend.

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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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