• 제목/요약/키워드: Mean Flow Field

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ADCP 자료의 공간평균을 이용한 평균유속장 산정에 대한 검증 (Validation of Assessment for Mean Flow Field Using Spatial Averaging of Instantaneous ADCP Velocity Measurements)

  • 김동수;강부식
    • 한국환경과학회지
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    • 제20권1호
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    • pp.107-118
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    • 2011
  • While the assessment of mean flow field is very important to characterize the hydrodynamic aspect of the flow regime in river, the conventional methodologies have required very time-consuming efforts and cost to obtain the mean flow field. The paper provides an efficient technique to quickly assess mean flow field by developing and applying spatial averaging method utilizing repeatedly surveyed acoustic Doppler current profiler(ADCP)'s cross-sectional measurements. ADCP has been widely used in measuring the detailed velocity and discharge in the last two decades. In order to validate the proposed spatial averaging method, the averaged velocity filed using the spatial averaging was compared with the bench-mark data computed by the time-averaging of the consistent fix-point ADCP measurement, which has been known as a valid but a bit inefficient way to obtain mean velocity field. The comparison showed a good agreement between two methods, which indicates that the spatial averaging method is able to be used as a surrogate way to assess the mean flow field. Bed shear stress distribution, which is a derived hydrodynamic quantity from the mean velocity field, was additionally computed by using both spatial and time-averaging methods, and they were compared each other so as to validate the spatial averaging method. This comparison also gave a good agreement. Therefore, such comparisons proved the validity of the spatial averaging to quickly assess mean flow field. The mean velocity field and its derived riverine quantities can be actively used for characterizing the flow dynamics as well as potentially applicable for validating numerical simulations.

대칭 및 비대칭 유동장에서 다회선 초음파 유량계의 유속분포 적분 방법 평가 (Performance Evaluation of the Velocity Profile Integration for the Multi-Path Ultrasonic Flowmeter in Symmetric & Asymmetric Flow Field)

  • 김주영;김경진;박성하
    • 유체기계공업학회:학술대회논문집
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    • 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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    • pp.370-377
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    • 2002
  • Generally, the system of calculation for the multi-path ultrasonic flow meters can be divided into two methods by how to get the mean velocity, namely, weighting and direct method. Weighting-method derive the mean velocity through modeling in theoretical velocity profile. Direct-method derive the mean velocity though actual flow distribution. The system of calculation varies with maker's transducer configuration and integration method. Each system has merits and demerits. This paper describes the system of integration that calculates line velocity over cross-section of the circular pipe. Flow rate mr discussed in this paper is a difference between theoretical flow rate and integrated flow rate according to values of Reynolds number in symmetric flow field or theoretical flow rate and integrated flow rate according to rotated model in asymmetric flow field.

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음장 재구성에 의한 관내 평균유속 측정 (Mean Flow Velocity Measurement Using the Sound Field Reconstruction)

  • 김건순;정완섭;권휴상;박경암;백종승;유성연
    • 대한기계학회논문집B
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    • 제24권7호
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    • pp.924-929
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    • 2000
  • This paper addresses a new technique of measuring the mean flow velocity over the cross sectional area of the pipe using sound field reconstruction. When fluid flows in the pipe and two plane waves propagate oppositely through the medium, the flow velocity causes the change of wave number of the plane waves. The wave number of the positive going plane wave decreases and that of negative going one increases in comparison to static medium in the pipe. Theoretical backgrounds of this method are introduced in detail and the measurement of mean flow velocity using the sound field reconstruction is not affected by velocity profile upstream of microphones.

PIV 계측에 의한 고주파수 초음파 유동장 해석에 관한 연구 (A Study on the Flow Field Analysis with a High-frequency Ultrasonic by PIV Measurement)

  • 이상범;송민근;손승우;정광수;주은선
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 춘계학술대회논문집E
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    • pp.727-732
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    • 2001
  • The purpose of this study is to compare the time mean velocity distribution, the time mean kinetic energy, and the time mean turbulence intensity between vertical and horizontal flow fields in a coaxial circular pipe by PIV measurement. Experiments are performed at a Reynolds number 2,000, measuring regions divided as the section regions A, B, C, D in flow fields. The angle of the high-frequency ultrasonic is selected in the direction of $45^{\circ}$ to the flow axes and it is reflected several times. In results, it is clarified that the effect of gravity is given in the vertical flow field compared with the horizontal flow field and the ultrasonic affects the turbulence enhancement. And kinetic energy and turbulence intensity with ultrasonic are shown slightly bigger than those in flow field without it.

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난류 파이프 유동에서의 레이놀즈 수 영향: Part I. 평균 유동장 및 저차 난류통계치 (REYNOLDS NUMBER EFFECTS ON TURBULENT PIPE FLOW PART I. MEAN FLOW FIELD AND LOW-ORDER STATISTICS)

  • 강창우;양경수
    • 한국전산유체공학회지
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    • 제16권4호
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    • pp.28-38
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    • 2011
  • Large eddy simulation(LES) of fully developed turbulent pipe flow has been performed to investigate the effect of Reynolds number on the flow field at $Re_{\tau}$=180, 395, 590 based on friction velocity and pipe radius. A dynamic subgrid-scale model for the turbulent subgrid-scale stresses was employed to close the governing equations. The mean flow properties, mean velocity profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. The Reynolds number effects were observed in the mean velocity profile, root-mean-square of velocity fluctuations, Reynolds shear stress and turbulent viscosity.

덕트의 유무에 따른 Gun식 가스버너의 난류유동장 특성 고찰 (Investigation on the Turbulent Flow Field Characteristics of a Gun-Type Gas Burner with and without a Duct)

  • 김장권;정규조
    • 동력기계공학회지
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    • 제10권4호
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    • pp.17-24
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    • 2006
  • The turbulent flow field characteristics of a gun-type gas burner with and without a duct were investigated under the isothermal condition of non-combustion. Vectors and mean velocities were measured by hot-wire anemometer system with an X-type hot-wire probe in this paper. The turbulent flow field with a duct seems to cause a counter-clockwise recirculation flow from downstream to upstream due to the unbalance of static pressure between a main jet flow and a duct wall. Moreover, the recirculation flow seems to expand the main jet flow to the radial and to shorten it to the axial. Therefore, the turbulent flow field with a duct increases a radial momentum but decreases a axial momentum. As a result, an axial mean velocity component with a duct above the downstream range of about X/R=1.5 forms a smaller magnitude than that without a duct in the inner part of a burner, but it shows the opposite trend in the outer part.

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偏心된 二重圓管의 環狀部를 지니는 層流流動에서의 連度場 및 溫度場의 確立에 대한 硏究 (A study on the development of the velocity and temperature fields in a laminar flow through an eccentric annular ducts)

  • 이택식;이상산
    • 대한기계학회논문집
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    • 제10권6호
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    • pp.861-869
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    • 1986
  • 본 연구에서는 동시확립문제의 속도장해석에 있어서 단면내의 속도분포에 대 한 일체의 가정을 하지 않고 운동량방정식을 직접 해석하여 단면내의 속도분포를 구하 였다. 또한 Prandtl수, 반경비 및 편심도가 열전달특성에 미치는 영향에 대한 해석 도 수행하였다.

비대칭 잠제 주변의 파고 및 흐름의 3차원적인 수리특성에 관한 수치모의 (A Numerical Simulation on Three-Dimensional Hydrodynamic Characteristics of Wave Height and Flow around Asymmetric Submerged Breakwaters)

  • 이우동;허동수;서성부
    • 한국해양공학회지
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    • 제25권3호
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    • pp.19-27
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    • 2011
  • In case of constructing submerged breakwaters for the purpose of preventing coastal erosion, the number of submerged breakwaters, as well as their asymmetry is dependent on the field conditions. The aim of the present study was to examine the 3-D hydrodynamic characteristics (3-D wave field, wave height, mean water level, and mean flow) around the asymmetric submerged breakwaters using a 3-D numerical model, LES-WASS-3D, which was validated through a comparison with existing experimental data and showed fairly nice agreement. From the numerical results, the wave height, mean water level, and mean flow are discussed in relation with the variation in the breakwater length ratio.

Correlation analysis of the wind of a cable-stayed bridge based on field monitoring

  • Li, Hui;Laima, Shujin;Li, Na;Ou, Jinping;Duan, Zhondong
    • Wind and Structures
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    • 제13권6호
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    • pp.529-556
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    • 2010
  • This paper investigates the correlation of wind characteristics monitored on a cable-stayed bridge. Total five anemoscopes are implemented into the bridge. Two out of 5 anemoscopes in inflow and two out of 5 anemoscopes in wake-flow along the longitudinal direction of the bridge are installed. Four anemoscopes are respectively distributed at two cross-sections. Another anemoscope is installed at the top of the tower. The correlation of mean wind speed and direction, power spectral density, the turbulent intensity and integral length of wind in flow at two cross-sections are investigated. In addition, considering the non-stationary characteristics of wind, the spatial correlation in time-frequency is analyzed using wavelet transform and different phenomenon from those obtained through FFT is observed. The time-frequency analysis further indicates that intermittence, coherence structures and self-similar structures are distinctly observed from fluctuant wind. The flow characteristics around the bridge deck at two positions are also investigated using the field measurement. The results indicate that the mean wind speed decrease when the flow passing through the deck, but the turbulence intensity become much larger and the turbulence integral lengths become much smaller compared with those of inflow. The relationship of RMS (root mean square) of wake-flow and the mean wind speed of inflow is approximately linear. The special structures of wake-flow in time-frequency domain are also analyzed using wavelet transform, which aids to reveal the forming process of wake-flow.

음장이 등온원통으로부터의 강제대류 열전달에 미치는 영향 (Effect of Sound Field on the Forced Convection Heat Transfer from an Isothermal Cylinder)

  • 권영필
    • 대한기계학회논문집
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    • 제12권2호
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    • pp.373-380
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    • 1988
  • 본 연구의 목적은 음장의 입자속도가 기류의 평균속도와 비슷한 크기인 경우에 원통으로부터 열전달의 동특성과 한 사이클의 평균값인 평균열전달이 음장에 의하여 어떠한 영향을 받는가를 구하기 위한 것이다.