• Title, Summary, Keyword: Turbulent-laminar transition

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Drag Prediction of Elliptic Airfoil (타원형 에어포일의 항력 예측)

  • Kim C. W.;Park Y. M.;Kwon K. J.;Lee J. Y.
    • 한국전산유체공학회:학술대회논문집
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    • pp.23-26
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    • 2004
  • Drag prediction is sought for the aifoil having laminar and turbulent flow characteristics with CFD code being unable to predict transition to turbulent flow. Laminar flow simulation presents some insight to the transition position. Separate simulations with laminar and turbulent flow and their combination estimate the drag of the airfoil containing laminar and turbulent flow characteristics.

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Friction Factor for Circular Pipe with Uniform Roughness (균일조도 원형관 마찰계수)

  • Yoo, Dong Hoon
    • Journal of The Korean Society of Civil Engineers
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    • v.13 no.5
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    • pp.165-172
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    • 1993
  • On the basis of Nikuradse laboratory experiments conducted in circular pipe with uniform roughness, five flow regimes are defined with respect to the characteristics of boundary layer such as laminar, transition laminar, smooth turbulent, transition turbulent and rough turbulent flows. Two cases are found for the transition laminar flow: one for the transition between laminar flow and smooth turbulent flow and the other for the one between laminar flow and rough turbulent flow. They all can be clearly determined by the relative roughness or the ratio of pipe diameter to the roughness. Explicit functions are developed for the estimation of pipe friction factor for the various flow conditions including turbulent flow regimes, which have excellent agreement with the Nikuradse laboratory data.

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A Study on Degradation Characteristic and Flow Behavior in De-NOx Catalyst (탈질촉매 내 열화특성과 유동상태에 관한 연구)

  • Hwang, Seung-Min
    • Journal of Environmental Science International
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    • v.19 no.9
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    • pp.1093-1101
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    • 2010
  • In this study, the indirect correlation of degradation characteristic and flow behavior in the de-NOx catalyst is investigated experimentally. The inner flow behavior in the de-NOx catalyst is varied from turbulent flow to laminar flow and the degradation of the de-NOx catalyst is remarkably affected by the inner flow. The degradation of the catalyst is increased in the upstream region near the inlet because injected turbulent flow enhances the adhesion of ash particle on the catalyst surface. The degradation of the catalyst near the inlet also governs the overall efficiency of the catalyst. The amount of adhered ash particles on the catalyst surface decreases as they progress downstream. This is due to the inner flow transition from turbulent flow to laminar flow.

ANALYSIS OF LAMINAR AND TURBULENT MIXED FLOW AROUND AN AIRFOIL (익형 주위의 층류와 난류가 혼합된 유동해석)

  • Kim, C.W.;Lee, Y.G.
    • 한국전산유체공학회:학술대회논문집
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    • pp.87-89
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    • 2009
  • In the present paper, transition turbulence model is applied to the NACA64(3)618 and detailed flow features are studied. The turbulence model is sensitive to the boundary layer grid quality and y+ of the grid was limited to 1. The prediction of the transition region is dependent on the local flow condition. The pressure coefficient distribution of the transition turbulence model is compared with that of the fully turbulent mode and the drag distribution of the transition turbulence model was compared with that of the wind tunnel test.

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Visualization of Turbulent Flow around a Sphere (구 주위 난류유동에 관한 가시화 연구)

  • Jang, Young-Il;Lee, Sang-Joon
    • 유체기계공업학회:학술대회논문집
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    • pp.401-402
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    • 2006
  • The turbulent flow around a sphere was investigated using two experimental techniques: smoke-wire flow visualization in wind tunnel at Re=5300, 11000 and PIV measurements in a circulating water channel. The smoke-wire visualization shows flow separation points near an azimuthal angle of $90^{\circ}$, recirculating flow, transition from laminar to turbulent shear layer, evolving vortex roll-up and fully turbulent eddies in the sphere wake. The mean velocity field measured using a PIV technique in x-y center plane demonstrates the detailed near-wake structure such as nearly symmetric recirculation region, two toroidal vortices, laminar separation, transition and turbulent eddies. The PIV measurements of turbulent wake in y-z planes show that a recirculating vortex pair dominates the near-wake region.

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Design and Wind Tunnel Tests of a Natural Laminar Flow Airfoil (자연층류 익형 설계 및 시험)

  • Lee, Yung-Gyo;Kim, Cheol-Wan;Shim, Jae-Yeul;Kim, Eung-Tae;Lee, Dae-Sung
    • 한국전산유체공학회:학술대회논문집
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    • pp.354-357
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    • 2008
  • Drag reduction is one of main concerns for commercial aircraft companies than ever because fuel price has been tripled in ten years. In this research, Natural Laminar Flow airfoil is designed and tested to reduce drag at cruise condition, $c_l$=0.3, Re=3.4${\times}$10$^6$ and M=0.6. NLF airfoil is characterized by delayed transition from laminar to turbulent flow, which comes from maintaining favorable pressure gradient to downstream. Transition is predicted by solving Boundary Layer equations in viscous boundary layer and by solving Euler Equation outside the boundary layer. Once boundary layer thickness and momentum thickness are obtained, $e^N$-method is used for transition point prediction. As results, KARI's NLF airfoil is designed and shows better characteristics than NLF-0115. The characteristics are tested and verified at low Reynolds numbers, but at high Reynolds numbers, laminar flow characteristics are not obtainable because of fully turbulent flow over airfoil surfaces. Precious experiences, however, relating NLF airfoil design, subsonic and transonic tests are acquired.

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Numerical Calculation of Turbulent Boundary Layer on Rotating Helical Blades (회전(回轉)하는 나선(螺旋)날개 위에서의 경계층(境界層) 해석(解析))

  • Keon-Je,Oh;Shin-Hyoung,Kang
    • Bulletin of the Society of Naval Architects of Korea
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    • v.21 no.2
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    • pp.9-17
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    • 1984
  • Laminar and turbulent boundary layers on a rotating sector and a helical blade are calculated by differential method. The estimation of three dimensional viscous flows provide quite useful informations for the design of propellers and turbo-machinery. A general method of calculation is presented in this paper. Calculated laminar boundary layer on a sector shows smooth development of flows from Blasius' solution at the leading edge to von Karman's solution of a rotating disk at the down-stream. Eddy viscosity model is adopted for the calculation of turbulent flows. Turbulent flows on a rotating blade show similar characters as laminar flows. But cross-flow angle of turbulent flows are reduced in comparison with laminar boundary layers. Effects of rotation make flow structures significantly different from two-dimensional flows. In the range of Reynolds number of model scale propellers, large portion of the blade are still in the transition region from laminar to turbulent flows. Therefore viscous flow pattern might be quite different on the blade of model propeller. The present method of calculation is to be useful for the research of scale effects, cavitation, and roughness effects of propeller blades.

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Pipe Friction in Transition Flow (천이류에서의 관마찰)

  • Yoo, Dong Hoon
    • Journal of The Korean Society of Civil Engineers
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    • v.13 no.4
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    • pp.101-109
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    • 1993
  • On the basis of Nikuradse laboratory experiments. two transition flow regimes are defined with respect to the characteristics of boundary layer. One is the transitional turbulent flow which has a transitional characteristics between smooth turbulent flow and rough turbulent flow, and the other may be called as transitional laminar flow which has transitional features between laminar flow and turbulent flow. The laboratory results of Nikuradse are carefully re-examined, and the flow regions are clearly defined. The velocity profile of the transitional turbulent flow is described by newly formulated equation, and the Darcy-Weisbach friction coefficient for the transitional turbulent flow is determined based on the theoretical form of profile equation, which is far better accurate than Colebrook-White equation. Difficulties still arise for the description of velocity profile when the flow undergoes from laminar to turbulent. In this case a linear interpolation procedure is proposed for the estimation of friction coefficient.

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Wall Pressure Fluctuations of the Boundary Layer Flow at the Nose of and Axisymmetric Body (축대칭 물체 선단에서 발생하는 경계층 내 벽면 변동 압력에 관한 연구)

  • 신구균;홍진숙;김상윤;김상렬;박규철
    • Journal of KSNVE
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    • v.10 no.4
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    • pp.602-609
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    • 2000
  • When an axisymmetric body moves through air the boundary layer near the stagnation region remains laminar and subsequently it goes through transition to turbulent. The experimental investigation described in this paper concerns the characteristics of wall pressure fluctuations at the initial stage of boundary layer flow including transition. Flush-mounted microphones are used to measure the wall pressure fluctuations at the transition and turbulent boundary layer region of a blunt axisymmetric body in the low noise wind tunnel. It if found from this study that the wall pressure fluctuations in the transition region is higher than that in the turbulent region.

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PREDICTION OF AIRFOIL CHARACTERISTICS WITH VARIOUS TURBULENCE MODELING (다양한 난류 모텔에 따른 익형 특성 예측)

  • Kim, C.W.;Lee, Y.G.;Lee, J.Y.
    • 한국전산유체공학회:학술대회논문집
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    • pp.50-52
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    • 2007
  • In the present paper, some difficulties encountered in predicting airfoil characteristics are described and solutions for those problems are discussed Since drag is determined by the amounts of pressure and, especially, shear stress, accurate estimation of shear stress is very crucial. However shear stress computation is dependent on the grid density and turbulence model, it should be consistent in preparing grid and turbulence model. When the transition from laminar to turbulent happen at the middle of airfoil, CFD solver should divide the region into laminar and turbulent region based on the transition location.

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