• 제목/요약/키워드: anemometer height

검색결과 32건 처리시간 0.024초

톱니형 휜이 부착된 원주의 근접후류특성 연구 (III) - 속도회복 메카니즘에 관하여 - (Characteristics of Near Wake Behind a Circular Cylinder with Serrated Fins (III) - Mechanism of Velocity Recovery -)

  • 류병남;김경천;부정숙
    • 대한기계학회논문집B
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    • 제27권3호
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    • pp.347-356
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    • 2003
  • The characteristics of near wakes of circular cylinders with serrated fins are investigated experimentally using a hot-wire anemometer for various freestream velocities. Near wake structures of the fin tubes are observed using a phase average technique. With increasing fin height and decreasing fin pitch. oscillation of streamwise velocity increases. It file oscillation of lateral velocity decreases. The time averaged V-component velocity distribution of the finned tube is contrary to that of the circular cylinder due to the different strength of entrainment flow. This strength is affected by the distance of (equation omitted) = 1.0 contour lines. (equation omitted) = 1.0 contour line approaches to the wake center line when the fin density is increased. When the distance between (equation omitted) = 1.0 contour lines comes close the shear force should be increased and the flow toward the wake center line can be more strengthened because of the shear force. Factors related to the velocity recovery in the near wake of the finned tube are attributed to tile turbulent intensity, the boundary layer thickness. the position and strength of entrainment process.

4각 덕트의 입구영역에서 천이 정상유동의 입구길이에 관한 연구 (A Study on Entrance Length of Developing Transitional Steady Flows in a Square Duct)

  • 박길문;유영태;고영하
    • 설비공학논문집
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    • 제2권1호
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    • pp.1-10
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    • 1990
  • In the present study, the entrance length, velocity profiles and waveforms of developing transitional steady flows in a square duct are investigated analytically and experimentally. The systems of conservation equations for transitional steady duct flows are solved analytically by linearizing non-linear convective terms and adoption of modified eddy viscosity from empirical correlations. Analytical solutions of velocity profiles for developing transitional steady flow were obtained in the form of infinite series. The experimental study for transitional steady flow in a square duct with $40mm{\times}40mm{\times}4000mm$($width{\times}height{\times}length$) was carried out to measure velocity profiles and other parameters by using a hot-wire anemometer with data acquisition and processing system. The entrance length of developing transitional steady flows in a square duct was $L_e{\fallingdotseq}0.02{\cdot}Re,st{\cdot}D_h$, and the overshoot was occured at about 30 times of hydraulic diameter because of the effect of external velocity of boundary layer and instantaneous acceleration.

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인공 도로협곡 관측 자료를 활용한 전산유체역학모델 검증 (Verification of Computational Fluid Dynamics Model Using Observation Data in Artificial Street Canyon)

  • 김도형;홍선옥;이대근;이영곤;김백조
    • 대기
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    • 제26권3호
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    • pp.423-433
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    • 2016
  • In this study, performance of a computational fluid dynamics (CFD) model is assessed from analysis on air flow pattern which is observed in the artificial street canyon. Field observations focusing on flows were conducted at an artificial street canyon in Magok region. For the observation of three-dimensional airflow structures, twelve three-dimensional wind anemometers (hereafter, CSAT3) were installed inside the street canyon. The street canyon was composed of two rectangular buildings with 35-m length, 4-m width, and 7-m height. The street width (distance between the buildings) is 7 m, making the street aspect ratio (defined by the ratio of building height to street width) of 1. For the observation of above-building wind, a CSAT3 was installed above the northwest-side building. Southwesterly, westerly and northwesterly were dominant in the street canyon during the observations. Because wind direction is parallel to the street canyon in the southwesterly case, westerly and northwesterly were selected as inflow directions in numerical simulations using a computational fluid dynamics model developed through the collaborative research project between National Institute of Meteorological Sciences and Seoul National University (CFD_NIMR_SNU). The observations showed that a well-structured vortex flow (skimming flow) and an evidence of a small eddy at the corner of the downwind building and ground appeared. The CFD_NIMR_SNU reproduced both the observed flow patterns reasonably well, although wind speeds inside the street canyon were underestimated.

한반도 지상 풍속의 장기 추세 추정: 관측 자료의 물리적 및 통계적 보정 (Long-Term Trend of Surface Wind Speed in Korea: Physical and Statistical Homogenizations)

  • 최영주;박창현;손석우;김혜진
    • 대기
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    • 제31권5호
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    • pp.553-562
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    • 2021
  • The long-term trend of surface wind speed in Korea is estimated by correcting wind measurements at 29 KMA weather stations from 1985 to 2019 with physical and statistical homogenization. The anemometer height changes at each station are first adjusted by applying physical homogenization using the power-law wind profile. The statistical homogenization is then applied to the adjusted data. A standard normal homogeneity test (SNHT) is particularly utilized. Approximately 40% of inhomogeneities detected by the SNHT match with the sea-level-height change of each station, indicating that an SNHT is an effective technique for reconciling data inhomogeneity. The long-term trends are compared with homogenized data. Statistically significant negative trends are observed along the coast, while insignificant trends are dominant inland. The mean trend, averaged over all stations, is -0.03 ± 0.07 m s-1 decade-1. This insignificant trend is due to a trend change across 2001. A decreasing trend of -0.10 m s-1 decade-1 reverses to an increasing trend of 0.03 m s-1 decade-1 from 2001. This trend change is consistent with mid-latitude wind change in the Northern hemisphere, indicating that the long-term trend of surface wind speed in Korea is partly determined by large-scale atmospheric circulation.

평면 난류 오프셋 제트에 관한 연구 (A Study on the Plane Turbulent Offset Jet)

  • 유정열;강신형;채승기;좌성훈
    • 대한기계학회논문집
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    • 제10권3호
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    • pp.357-366
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    • 1986
  • 본 연구에서는 3공피토우관 및 열선유속계를 사용하여 벽에 평행한 2차원 난류제트의 난류량들을 측정하였고, 스캐니 밸브를 이용하여 벽면아력분포를 측정함 으로써 재순환 영역을 포함한 전체유동장에서의 유동특성을 고찰하였다. 또한 잘 알려진 표준 k-.epsilon. 난류모형 및 유선곡률을 고려한 수정된 k-.epsilon. 난류모형을 이용하여 측정 수치해석을 수행하였다.

수직으로 놓인 후향계단위를 흐르는 유체유동에 미치는 부력의 영향에 관한 연구 (Buoyancy-Affected Separated Laminar Flow over a Vertically Located, Two-Dimensional Backward-Facing Step)

  • 백병준;박복춘;김진택
    • 대한기계학회논문집
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    • 제17권5호
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    • pp.1253-1261
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    • 1993
  • 본 연구에서는 수직 평판에 위치한 후향계단면 위를 흐르는 유체유동의 특성, 즉 재부착점, 박리 및 재순환 영역에 미치는 부력의 영향을 수치해석 및 실험으로 조사한다. 유동의 가시화를 통해 재부착점의 위치를 측정하며 레이저도플러 유속계 (5W,Ar-Ion,DANTEC)에 의한 속도분포 및 CTA(constant temperature anemoneter,55M01 과 55M20, DANTEC)를 사용한 온도분포를 동시에 측정 함으로써 유동 특성 및 열전달에 미치는 부력의 영향을 검토한다.

2次元 亂流 Stepped Wall Jet 의 流動特性 (Flow Characteristics of Two-Dimensional Turbulent Stepped Wall Jet)

  • 부정숙;김경천;박진호;강창수
    • 대한기계학회논문집
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    • 제9권6호
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    • pp.732-742
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    • 1985
  • 본 논문에서는 이 2차원 재부착분류(본문에서는 stepped wall jet라 명명함) 유동장을 재부착상류 부분, 재부착점 근방, 재부착 이후의 재발전 벽면분류 지역의 세 영역으로 구분하여 재부착 길이, 평균속도, 벽면정압을 측정하고 on-line에 의한 디지 틀 데이터 처리기법을 이용하여 난류강도, 레이놀즈 전단응력, 속도의 3승적(triple velocity product), integral length scale, Taylor's microscale 등을 실험적으로 구 하여 재부착 상류 부분에서는 자유분류와 비교하고, 재부착 이후에서는 2차원 벽면분 류와 비교하기로 한다.그리하여 초기 교란을 받는 분류가 벽면에 재부착하여 2차원 벽면분류로 재발전되어 가는 과정에 있어서의 평균 유동장과 급격한 변화를 갖는 난류 특성을 상세히 조사하여, 보다 일반적으로 적용될 수 있는 난류모델을 개발함에 있어 서 실험적인 자료를 제공하고자 한다. Fig. 1은 본 실험의 유동장에 대한 개약도를 보여주고 있다.

UHF 센서 탑재 UAV를 이용한 지표층 열 플럭스 산출 (Estimation of Surface Layer Heat Flux Using the UHF Sensor Installed on UAV)

  • 김민성;권병혁;윤홍주
    • 한국전자통신학회논문지
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    • 제13권1호
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    • pp.265-276
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    • 2018
  • 지상에 고정된 기기로 감시하기 어려운 대기 하층의 관측 사각 지역에서 유용한 관측 및 자료 분석 기술을 개발하였다. 상층 기상 관측에 사용되는 UHF 라디오존데를 UAV에 탑재하여 기온과 상대습도의 연직 자료를 원격 수집하여 10 m 기상 타워에서 측정한 자료와 비교하였다. 검증된 연직 분포로부터 외삽된 지표 기온과 총체 전달 방법을 이용하여 대기 안정도 변화에 따른 현열 플럭스를 추정하였다. 지상에서 3차원 초음파 풍속계로 측정한 현열 플럭스와 비교한 결과는 원격탐사로 산출되는 현열 플럭스에 허용되는 오차 범위 30%보다 작은 23% 이내의 오차를 보였다. UAV 관측 현열 플럭스로부터 추정한 대기경계층 고도는 대기 오염 확산 모델에 유용한 자료를 실시간, 경제적으로 제공할 수 있다.

평균 방법이 도시 난류 플럭스에 미치는 영향 (Effects of Different Averaging Operators on the Urban Turbulent Fluxes)

  • 권태헌;박문수;이채연;최영진
    • 대기
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    • 제24권2호
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    • pp.197-206
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    • 2014
  • The effects of different averaging operators and atmospheric stability on the turbulent fluxes are investigated using the vertical velocity, air temperature, carbon dioxide concentration, and absolute humidity data measured at 10 Hz by a 3-dimensional sonic anemometer and an open-path $CO_2/H_2O$ infrared gas analyzer installed at a height of 18.5 m on the rooftop of the Jungnang KT building located at a typical residential area in Seoul, Korea. For this purpose, 7 different averaging operators including block average, linear regression, and moving averages during 100 s, 300 s, 600 s, 900 s, and 1800 s are considered and the data quality control procedure such as physical limit check and spike removal is also applied. It is found that as the averaging interval becomes shorter, turbulent fluxes computed by the moving average become smaller and the ratios of turbulent fluxes computed by the 100 s moving average to the fluxes by the 1800 s moving average under unstable stability are smaller than those under neutral stability. The turbulent fluxes computed by the linear regression are 85~92% of those computed by the 1800 s moving average and nearly the same as those computed by 900 s moving average, implying that the adequate selection of an averaging operator and its interval will be very important to estimate more accurate turbulent fluxes at urban area.