• 제목/요약/키워드: Turbulent Flows

검색결과 739건 처리시간 0.031초

파형 벽면이 외층의 난류량에 미치는 영향에 대한 고찰 (Influence of Wavy Surface on the Turbulence in the Outer Layer)

  • Na, Yang
    • 대한기계학회논문집B
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    • 제25권8호
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    • pp.1053-1059
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    • 2001
  • Results from direct numerical simulation and LDV measurements are analyzed to investigate the influence of structured surface on turbulence in the outer layer. To provide a well-defined surface roughness, sinusoidal wavy surface was used. Even though flows over smooth and wavy surface show very different process for maintaining turbulence in the vicinity of the wall, there are some evidences that the turbulence in the outer layer has a universal characteristics and it may be possible to give a speculative interpretation that similarity of turbulent structures arises because Reynolds stress producing motion is similar regardless of different turbulence generation mechanisms embedded in both cases.

고속열차의 차간 공간에 의해 발생하는 실내소음 특성 분석 (Noise generated from the inter-coach spacing of a high-speed train)

  • 최성훈;박준홍;박찬경
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2006년도 춘계학술대회논문집
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    • pp.1449-1452
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    • 2006
  • When fluid at high speed flows over an open cavity, large acoustic pressure fields inside the cavity are produced by fluid/structure interactions at the downstream end of the cavity. The inter-coach spacing is one of the most important sources of the aero-acoustic noise of a high-speed train. This noise can usually be heard as low frequency structure-borne noise inside the train. In this study experiments were performed in order to investigate the effects of mud-flap length on the aeroacoustic noise generation inside high-speed trains. Results of the measurement confirmed that the characteristics of the noise generated from the inter-coach spacing are strongly dependent on the size of the gap. Also investigated are the characteristics of the turbulent flow after the inter-coach spacing and consequent generation of the aeroacoustic noise inside the cabin.

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저 레이놀즈 수 개수로 난류흐름의 직접수치모의: 난류의 비등방성 해석 (Direct Numerical Simulation of Low-Reynolds-Number Turbulent Flows in an Open-Channel: An Analysis of Turbulence Anisotropy)

  • 정영훈;최성욱;최정일
    • 한국수자원학회:학술대회논문집
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    • 한국수자원학회 2004년도 학술발표회
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    • pp.376-380
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    • 2004
  • 측벽이 존재하는 개수로 난류흐름에 대한 DNS 자료를 이용하여 난류의 비등방성을 해석하였다. 측벽의 2등분선(sidewall bisector)에서 난류강도의 분포를 통해 바닥과 자유수면에서의 비등방성을 분석하고, AIM을 도입하여 흐름장 전반에 걸쳐 세부적인 비등방성 해석을 수행하였다. 측벽의 2등분선에서의 난류강도의 분포를 통해 바닥과 자유수면 근처에서 난류강도가 강한 비등방성을 갖는 것을 볼 수 있었다. 또한 3개의 다른 영역에서 AIM의 도입을 통해 측벽이나 바닥근처에서는 난류의 비등방성이 구형 관수로 흐름과 유사한 것으로 나타났으나, 개수로 난류흐름의 주된 특성이 velocity-dip phenomena가 존재하는 영역에서는 구형 관수로 흐름과는 달리 천이영역이 존재한다는 것을 알 수 있었다.

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영상해석기법을 이용한 침강속도 측정 (Fall-Velocity Measurement Using Image Analysis Technique)

  • 윤병만;유권규;노영신
    • 한국수자원학회논문집
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    • 제34권4호
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    • pp.327-333
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    • 2001
  • PTV는 비디오 카메라로 기록된 영상의 분석을 통하여 흐름속도를 측정한다. 이러한 PTV 방법을 이용하여 유사의 침강속도를 측정하였다. 실험을 통해 측정된 정지 유체내 유사의 침강속도를 기존문헌에 제시된 값과 비교 분석한 결과, 침강속도 측정에 PTV를 이용할 수 있음이 입증되었다. 따라서 PTV를 이용하면난류흐름 중의 침강속도 측정이 가능해져 난류흐름 중의 침강속도 특성 규명에 기여할 수 있을 것이다.

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모델 가스터빈 연소기에서 등온 선회유동의 대 와동 모사 (Large Eddy Simulation of an Isothermal Swirling Flow in a Model Gas Turbine Combustor)

  • 황철홍;이창언
    • 유체기계공업학회:학술대회논문집
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    • 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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    • pp.462-468
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    • 2004
  • Large eddy simulation(LES) methodology used to model isothermal non-swirling and swirling flows in a model gas turbine combustor. The LES solver was implemented on parallel computer consisting 16 processors. To verify the capability of LES code and characterize swirling flow, the results was compared with that of Reynolds Averaged Navier-Stokes(RANS) using k -$\epsilon$ model as well as experimental data. The results showed that the LES and RANS well predicted the mean velocity field of a non-swirling flow. Specially, the LES showed a very excellent prediction performance for the corner recirculation zone. In swirling flow, comparing with the results obtained by RANS, LES showed a better performance in predicting the mean axial and azimuthal velocities, and the central recirculation zone. Finally, unsteady phenomena of turbulent flow was examined with LES methodology.

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축 대칭 물체 주위의 점성유동 계산 (A Computation of Viscous Flows on an Axisymmetric Body)

  • 류재문
    • 대한조선학회논문집
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    • 제28권1호
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    • pp.19-26
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    • 1991
  • 난류유동 지배 방정식인 타원형 레이놀즈 방정식을 수치계산에 의해 계산하였다. 계산 대상으로는 실험결과가 많이 알려진 축 대칭 물체를 택하였다. 수치적으로 얻어지는 물체접합 좌표계를 사용하였고, 난류모형으로는 $\kappa-\varepsilon$모형으로써 경계면 근처의 복잡한 유동특성을 추정할 수 있도록 영역을 2개로 나누어 계산하는 2층모형(two-layer model)을 사용하였다. 입구면의 경계조건을 사용하여 물체의 중앙부 이후부터 계산을 수행하였다. 입구면에서의 속도와 난류량 등은 경계층 방정식을 풀어 얻어진 결과와 평판의 경계층 자료로부터 얻어진 결과를 사용하였으며, 이로부터 입구면 조건이 점성유동 해석 결과에 미치는 영향을 조사하였다.

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안쪽 축이 회전하는 환형관내 천이유동에 관한 연구 (A Study on the Transitional Flows in a Concentric Annulus with Rotating Inner Cylinder)

  • 김영주;황영규;우남섭
    • 설비공학논문집
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    • 제14권10호
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    • pp.833-843
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    • 2002
  • The present experimental and numerical investigations are performed for the characteristics of transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin- friction coefficients have been measured for the fully developed flow of water and glycerine-water solution (44%) with the inner cylinder rotating at speed of 0∼600 nm, respectively. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime.

A Study on Prediction of the Base Pressures for an Axi-Symmetric Body

  • Baik, Doo-Sung;Han, Young-Chool
    • Journal of Mechanical Science and Technology
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    • 제15권10호
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    • pp.1423-1433
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    • 2001
  • A flow modeling method has been developed to analyze the flow in the annular base (rear- facing surface) of a circular engine nacelle flying at subsonic speed but with a supersonic exhaust jet. Real values of exhaust gas properties and temperature at an altitude of 30, 000 feet are employed. Potential flows of the air and gas streams are computed for the flow past a separated wake. Then a viscous jet mixing is superimposed on this inviscid solution. Conserva- tion of mass, momentum and energy for the wake flow field is achieved by multiple iterations with modest computer requirements.

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1단 전기집진기에서 난류확산과 2차유동이 입자의 농도분포에 미치는 영향 (Effects of Turbulence Diffusion and Secondary Flows on the Particle Concentration Distribution in Single Stage ESP)

  • 정상현;김상수;김용진
    • 대한기계학회논문집
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    • 제19권9호
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    • pp.2271-2282
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    • 1995
  • Numerical simulations for the effects of secondary flow and turbulence diffusion on the particle concentration distributions have been carried out for the single stage electrostatic precipitator. The electrohydrodynamic secondary flow, particle concentration distribution and collection efficiency have been evaluated as a function of dimensionless parameters such as Re, $N_{end}$, $P_{e}$ x. The results of simulations show that for increasing secondary flow intensity the concentration distribution is drastically deformed and collection efficiency is decreased which is more than due to turbulent diffusion.n.n.

원봉주위의 난류유동에 대한 수치해석 (Numerical Prediction of Turbulent Flow over a Circular Cylinder)

  • 박태선
    • 한국전산유체공학회지
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    • 제7권1호
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    • pp.20-27
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    • 2002
  • Flow over a circular cylinder is studied numerically using a turbulence model. Based on the κ-ε-f/sub μ/ model of Park and Sung[6], a new damping function is used. The efficiency of the strain dependent damping function is addressed for vortex-shedding flows past a circular cylinder. The mean velocity and Reynolds stresses are compared with available experimental data at Re/sub D/= 3900. Also, the computational results for the Strouhal number are evaluated at several Reynolds number. The predictions by κ-ε-f/sub μ/ model are in good agreement with the experiments.