• Title/Summary/Keyword: Reynolds number

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Characteristics of Sparkover Discharge in Flowing Air with Reynolds Number's Variable (Reynolds Number를 변수로한 유동공기의 방전특성에 관한 연구)

  • 김영훈;이동인;이광식;김상구
    • Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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    • 1990.10a
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    • pp.41-46
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    • 1990
  • This paper shows the characteristics of sparkover discharge in flowing air ranging from O(Reynolds number, Re to 10.52$\times$104(Re). Also, we investigated changes of dis-charge pattern for constant input power by adjustment of the Re. The important results obtained from this paper are as followers. The maxinum sparkover voltage of flowing air are about 6.3[kV] higher than those of static air. The discharge pattern can be controlled by adjustment of the Re.

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Effects of Dimple Depth and Reynolds Number on the Flow and Heat Transfer in a Dimpled Channel (딤플이 설치된 채널에서 레이놀즈 수 및 딤플 깊이에 따른 유동 및 열전달 특성)

  • Ahn, Joon;Lee, Young-Ok;Lee, Joon-Sik
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.3253-3258
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    • 2007
  • A large eddy simulation (LES) has been conducted for the flow and heat transfer in a dimpled channel. Two dimple depths of 0.2 and 0.3 times of the dimple print diameter (= D) have been compared at the bulk Reynolds number of 20,000. Three Reynolds numbers of 5,000, 10,000 and 20,000 have been studied, while the dimple depth is kept as 0.2 D. With the deeper dimple, the flow reattachment occurs father downstream inside the dimple, so that the heat transfer is not as effectively enhanced as the case with shallow ones. At the low Reynolds number of 5,000, the Nusselt number ratio is as high as those for the higher Reynolds number, although the value of heat transfer coefficient decreases because of the weak shear layer vortices.

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Development of Low-Reynolds-Number Ssecond Moment Turbulence Closure by DNS Data (DNS 자료에 의한 저레이놀즈수 2차 모멘트 난류모형의 개발)

  • Sin, Jong-Geun;Choe, Yeong-Don
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.8
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    • pp.2572-2592
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    • 1996
  • A low-Reynolds-number second moment turbulence closure was developed with the aid of DNS data. Model coefficients of nonlinear return to isotropy term were derived by use of Cayley-Hamilton theorem and two component turbulence limit condition as the functions of invariances of anisotropy and turbulent Reynolds number. Launder and Tselepidakis' cubic mean pressure strain model was modified to fit the predicted pressure-strain components to the DNS data. Two component turbulence limit condition was the precondition to be satisfied in developing the second moment turbulence closure for the realizable Reynolds stress prediction. But the satisfactions of Reynolds stress level and pressure-strain level of each component were compromised because the satisfaction of both levels was impossible.

A COMPARATIVE STUDY OF TWO AND THREE DIMENSIONAL LOW REYNOLDS NUMBER FLOW (2차원 및 3차원 저레이놀즈수 유동 해석 비교 연구)

  • Lee, Jae-Hun;Jung, Kyoung-Jin;Lee, Kil-Tae;Kang, In-Mo
    • 한국전산유체공학회:학술대회논문집
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    • 2009.11a
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    • pp.3-7
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    • 2009
  • In this study, two and three dimensional low Reynolds number flows are compared. For the two dimensional flow, an airfoil was considered and for the three dimensional low wing and full-body aircraft were considered. Because a flight condition of the aircraft is in a low Reynolds number flow, itl requires reflecting flow transition. In the two dimensional analysis, transition is predicted using en method. In the three dimensional flow, the effect of transition is included using k-w SST turbulence models.

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A Study on the Inlet Pressure Build-Up at Bearing Entrance (베어링 입구에서 발생하는 선단압력에 관한 연구)

  • 김종수;김경웅
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.8
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    • pp.1921-1930
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    • 1993
  • In order to evaluate the inlet pressure correctly, the full Navier-Stokes equations are solved numerically for the computational domain which covers the cavity region between pads as well as the bearing film. A nonuiform grid system is adopted to reduce the number of grid points, and the numerical solutions are obtained for a wide range of Reynolds number in laminar regime with various values of the distance between pads. The numerical results show that the inlet pressure is significantly affected by Reynolds number and the distance between pads. An expression for the loss coefficient in terms of Reynolds number and non-dimensional distance between pads is obtained on the basis of the numerical results. It is found that the inlet pressure over the whole range of numerical solutions can be fairly accurately estimated by applying the formula for the loss coefficient to the extended Bernoulli equation.

Numerical Study on the Wind Flow Over Hilly Terrain (언덕지형을 지나는 유동의 수치해석적 연구)

  • 김현구;이정묵;경남호
    • Journal of Korean Society for Atmospheric Environment
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    • v.13 no.1
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    • pp.65-77
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    • 1997
  • A theoretical and numerical investigation on the boundary-layer flow over a two- or three-dimensional hill is presented. The numerical model is based on the finite volume method with boundary-fitted coordinates. The k-$\varepsilon$ turbulence model with modified wall function and the low-Reynolds-number model are employed. The hypothesis of Reynolds number independency for the atmospheric boundary-layer flow over aerodynamically rough terrain is confirmed by the numerical simulation. Comparisons of the mean velocity profiles and surface pressure distributions between the numerical predictions and the wind-tunnel experiments on the flow over a hill show good agreement. The linear theory provides generally good prediction of speed-up characteristics for the gentle-sloped hills. The flow separation occurs in the hill slope of 0.5 and the measured reattachment points are compared with the numerical prediction. It is found that the k- $\varepsilon$ turbulence model is reasonably accurate in predicting the attached flow, while the low- Reynolds-number model is more suitable to simulate the separated flows.ows.

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Experimental Study on the Unsteady Behavior of a Confined Impinging jet (국한 충돌 제트의 비정상 거동에 대한 실험적 연구)

  • Kim, Kyung-Chun;Oh, Sung-Jin;Lee, In-Won
    • 한국가시화정보학회:학술대회논문집
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    • 2005.12a
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    • pp.23-27
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    • 2005
  • The flow characteristics in a confined slot jet impinging on a flat plate were Investigated by using cinematic Particle Image Velocimetry technique. The jet Reynolds number was varied from 250 to 1000 for a fixed jet-to-plate spacing of H/W=5. We found that the vortical structures in the shear layer are developed with increase of Reynolds number and that the jet becomes unsteady by the interaction of vortex pairs between 500 and 750 of Reynolds number. Vortical structures and their temporal evolution are verified by using cinematic Particle Image Velocimetry technique.

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NUMERICAL ANALYSIS OF ERGUN'S EQUATION FOR INTERIOR BALLISTIC ANALYSIS (강내탄도 해석에 사용되는 Ergun식에 관한 수치적 연구)

  • Bae, S.W.;Sung, H.G.;Roh, T.S.
    • 한국전산유체공학회:학술대회논문집
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    • 2010.05a
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    • pp.473-478
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    • 2010
  • In this study, the Ergun's equation has been verified in order to calculate pressure drop of the two phase flow. The equation had been used in the high Reynolds number region for interior ballistic analysis in spite of being verified in the low Reynolds number region. Therefore additional verification seems to be inevitable. Thus, the validity of the equation has been verified using CFD in the high Reynolds number cases of the diameter-particle ratio 10, 13 and 16.

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A FLOW CHARACTERISTICS FOR Y-CONNECTION IN HIGH-REYNOLDS-NUMBER FLOW SYSTEM (고레이놀즈수 유동 장치에서 Y형 이음의 유동 특성)

  • Park, Jung Gun;Park, Jong Ho;Park, Young Chul
    • Journal of computational fluids engineering
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    • v.18 no.2
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    • pp.1-8
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    • 2013
  • In nuclear power plant, the reactor cooling system has maintained high-Reynolds-number flow above 1E+07 to cool a heat generated by the reactor. To minimize uncertainty for flow calibration, it is necessary to simulate the high Reynolds' number flow. Y-connection is selected to connect four (4) parallel high flow circulation pumps for maintaining the high flow rate. This paper describes the characteristics for Y-connection by computer flow simulation. It was confirmed through the results that the pressure loss of the Y-connection was lower than that of T-connection. Also as the connection angle of Y-connection was small, as the pressure loss was low.

A Nonlinear Low-Reynolds-Number k -$\varepsilon$ Model for Turbulent Separated and Reattaching Flows (난류박리 및 재부착 유동의 해석을 위한 비선형 저레이놀즈수 k -$\varepsilon$ 난류모형의 개발)

  • 박태선;성형진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.8
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    • pp.2051-2063
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    • 1995
  • An improved version of nonlinear low-Reynolds-number k-.epsilon. model is developed. In this model, the limiting near-wall behavior and nonlinear Reynolds stress representations are incorporated. Emphasis is placed on the adoption of Ry(.iden. $k^{1}$2/y/.nu.) instead of $y^{[-10]}$ (.iden. $u_{{\tau}/y/{\nu}}$) in the low-Reynolds-number model for predicting turbulent separated and reattaching flows. The non-equilibrium effect is examined to describe recirculating flows away from the wall. The present model is validated by doing the benchmark problem of turbulent flow behind a backward-facing step. The predictions of the present model are cross-checked with the existing measurements and DNS data. The model performance is shown to be generally satisfactory.