• Title/Summary/Keyword: turbulent velocity intensity

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Fall Velocity Measurement in the Turbulent Flow Using Image Analysis Method (영상해석 기법을 이용한 난류 흐름 중 침강속도의 측정)

  • Yun, Sang-Hun;Yu, Gwon-Gyu;Yun, Byeong-Man
    • Journal of Korea Water Resources Association
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    • v.34 no.6
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    • pp.745-751
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    • 2001
  • Fall velocities of sand particles in the turbulent flow are analyzed through measurements using PTV. PTV is believed to be the only instrument to measure the fall velocity in the turbulent flow, since it can trace the individual particle. The method is verified by comparison with existing formula for still-water case. The experimental results show that the fall velocity in the turbulent flow decreases compared with that in still water, and decreases by 40% as the turbulent intensity normalized by the friction velocity increases upto 1.

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Development of k-$\epsilon$ model for prediction of transition in flat plate under free stream with high intensity (고난류강도 자유유동에서 평판 경계층 천이의 예측을 위한 난류 모형 개발)

  • Baek, Seong Gu;Lim, Hyo Jae;Chung, Myung Kyoon
    • 유체기계공업학회:학술대회논문집
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    • 2000.12a
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    • pp.337-344
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    • 2000
  • A modified k-$\epsilon$ model is proposed for calculation of transitional boundary layer flows. In order to develop the eddy viscosity model for the problem, the flow is divided into three regions; namely, pre-transition region, transition region and fully turbulent region. The pre-transition eddy-viscosity is formulated by extending the mixing Length concept. In the transition region, the eddy-viscosity model employs two length scales, i.e., pre-transition length scale and turbulent length scale pertaining to the regions upstream and the downstream, respectively, and a university model of stream-wise intermittency variation is used as a function bridging the pre-transition region and the fully turbulent region. The proposed model is applied to calculate three benchmark cases of the transitional boundary layer flows with different free-stream turbulent intensity ( $1\%{\~}6\%$ ) under zero-pressure gradient. It was found that the profiles of mom velocity and turbulent intensity, local maximum of velocity fluctuations, their locations as well as the stream-wise variation of integral properties such as skin friction, shape factor and maximum velocity fluctuations are very satisfactorily Predicted throughout the flow regions.

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Turbulent Flow Characteristics using Plane Jet on Impingement Surface (평면제트를 이용한 충돌면에서의 난류유동 특성)

  • 윤순현
    • Journal of Advanced Marine Engineering and Technology
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    • v.22 no.4
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    • pp.429-435
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    • 1998
  • Experiments were conducted to investigate the turbulent flow characteristics from on oblique impingement surface to an plane jet at the jet Reynolds number(Re based on the nozzle width) $3{\times}10^4$ The jet mean velocity and turbulent intensity profiles have been measured along the impingement surface by hot-wire anemometer. The nozzle-to-plate distance(H/B) ranged from 2 to 10 and the oblique angle (a) from 45 to 90 degree. Also the secondary peak of the turbulent intensity was observed at H/B=4 S/B 5 and a=90 degree. It has been found that the stagnation point shifted toward the minor flow region as the oblique angle decreased and the position of the stagnation point nearly coincided with that of the maximum turbulent intensity.

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Turbulent Couette Flow between Coaxial Cylinders with Inner Cylinder Rotating (내측원관이 회전하는 동심이중원관 사이의 난류 쿠에트 유동에 관한 연구)

  • 김광용;김진욱;조용철
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.3
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    • pp.540-546
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    • 1992
  • Turbulent Couette flow between coaxial cylinders with inner one rotating has been investigated experimentally and numerically. The radius ratio of the coaxial cylinders is 0.43. Mean velocity and turbulent stresses have been measured by hot-wire anemometer in the range of Reynolds number based on the velocity at rotating wall and the radial distance between walls, 60,900-187,000. For the numerical computation, the Reynolds stress model has been used as a turbulence closure model. Measurements of mean velocity show that the velocity profile of wall layer largely deviates from universal logarithmic law due to the effect of streamline curvature, especially in the region near the stationary outer cylinder. The results computed with the Reynolds stress model agree well with the experimental data in the prediction of circumferential intensity of turbulent fluctuations. However, the computed level of radial intensity is much higher than the measurement. Curvature-corrected versions of the Reynolds stress model improves the prediction of turbulent intensities, but the results are not fully satisfactory.

Reduced Frequency Effects on the Near-Wake of an Oscillating Elliptic Airfoil

  • Chang, Jo-Won;Eun, Hee-Bong
    • Journal of Mechanical Science and Technology
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    • v.17 no.8
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    • pp.1234-1245
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    • 2003
  • An experimental study was carried out to investigate the reduced frequency effect on the near-wake of an elliptic airfoil oscillating in pitch. The airfoil was sinusoidally pitched around the center of the chord between -5$^{\circ}$and +25$^{\circ}$angles of attack at an airspeed of 3.4 m/s. The chord Reynolds number and reduced frequencies were 3.3 ${\times}$10$^4$, and 0.1, 0.7, respectively Phase-averaged axial velocity and turbulent intensity profiles are presented to show the reduced frequency effects on the near-wake behind the airfoil oscillating In pitch. Axial velocity defects in the near-wake region have a tendency to increase in response to a reduced frequency during pitch up motion, whereas it tends to decrease during pitch down motion at a positive angle of attack. Turbulent intensity at positive angles of attack during the pitch up motion decreased in response to a reduced frequency, whereas turbulent intensity during the pitch down motion varies considerably with downstream stations. Although the true instantaneous angle of attack compensated for a phase-lag is large, the wake thickness of an oscillating airfoil is not always large because of laminar or turbulent separation.

Turbulent Mixing Flow Characteristics of Solid-Cone Type Diesel Spray

  • Lee, Jeekuen;Shinjae Kang;Park, Byoungjoon
    • Journal of Mechanical Science and Technology
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    • v.16 no.8
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    • pp.1135-1143
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    • 2002
  • The intermittent spray characteristics of the single-hole diesel nozzle (d$\sub$n/=0.32 mm) used in the fuel injection system of heavy-duty diesel engines were experimentally investigated. The mean velocity and turbulent characteristics of the diesel spray injected intermittently into the still ambient were measured by using a 2-D PDPA (phase Doppler particle analyzer) . The gradient of spray half-width linearly increased with time from the start of injection, and it approximated to 0.04 at the end of the injection. The axial mean velocity of the fuel spray measured along the radial direction was similar to that of the free air jet within R/b= 1.0-1.5 regardless of elapsing time, and its non-dimensional distribution corresponds to the theoretical velocity distributions suggested by Hinze in the downstream of the spray flow fields. The turbulent intensity of the axial velocity components measured along the radial direction represented the 20-30% of the U$\sub$cι/ and tended to decrease in the outer region. The turbulent intensity in the trailing edge was higher than that in the leading edge.

The Influence of Turbulent Intensity and Ignition Energy Affected on Early Combustion Process (초기연소과정에 미치는 난류강도 및 점화에너지의 영향)

  • Kim, M.H.;Kim, Y.H.;Lee, J.T.
    • Transactions of the Korean Society of Automotive Engineers
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    • v.3 no.6
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    • pp.274-284
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    • 1995
  • The effect of turbulence and ignition energy on flame kernel growth in mathanol-air mixtures has been studied in a constant volume vessel. Experiments were made under different turbulent intensity conditions, ignition energy and over a range of equivalence ratio. Characteristics of turbulent flow were grasped by measurments of gas pressure and visualization of flame propagation. Flow velocity was measured by use of hot wire anemometer. A comparison of the effect of turbulence on ignition probability and flame kernel volume variation ratio is also presented.

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Investigation of the Three-dimensional Turbulent Flow Fields in Cone Type Gas Burner for Furnace - On the Turbulent Characteristics - (난방기용 콘형 가스버너에서 3차원 난류 유동장 고찰 - 난류특성치에 대하여 -)

  • Kim, J.K.;Jeong, K.J.;Kim, S.W.;Kim, I.K.
    • Journal of Power System Engineering
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    • v.5 no.1
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    • pp.21-26
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    • 2001
  • This paper represents the turbulent intensity, the turbulent kinetic energy and Reynolds shear stress in the X-Y plane of cone type swirl gas burner measured by using X-probe from the hot-wire anemometer system. The experiment is carried out at flowrate 350 and $450{\ell}/min$ respectively in the test section of subsonic wind tunnel. The turbulent intensity and the turbulent kinetic energy show that the maximum value is formed in the narrow slits distributed radially on the edge of a cone type swirl burner, hence, the combustion reaction is anticipated to occur actively near this region. And the turbulent intensities ${\upsilon}\;and\;{\omega}$ are disappeared faster than the turbulent intensity u due to the inclined flow velocity ejecting from the swirl vanes of a cone type baffle plate of burner. Moreover, the Reynolds shear stress $u{\upsilon}$ is distributed about three times as large as the Reynolds shear stress $u{\omega}$ in the outer region of the cone type gas burner.

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The Flow Characteristics with Variation of Nozzle-to-nozzle Angles on Unventilated Dual Jests (이중제트에서 노즐과 노즐사이의 각도 변화에 따른 유동 특성)

  • Kim, Dong-Keon;Kim, Moon-Kyoung;Yoon, Soon-Hyun
    • Journal of Advanced Marine Engineering and Technology
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    • v.32 no.8
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    • pp.1231-1239
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    • 2008
  • The characteristics of flow on unventilated dual jets was experimentally investigated. The two nozzles each with an aspect ratio of 20 were separated by 6 nozzle widths. Reynolds number based on nozzle width was set to 5,000 by nozzle exit velocity. All measurements were made over a range of nozzle-to-nozzle angles from $0^{\circ}$ to $25^{\circ}$. The particle image velocimetry and pressure transducer were employed to measure turbulent velocity components and mean static pressure, respectively. It was shown that a recirculation zone with sub-atmospheric static pressure was bounded by the inner shear layers of the individual jets and the nozzles plated. As nozzle-to-nozzle inclined angles were decreased, it was found that the spanwise turbulent intensity is greater than the streamwise turbulent intensity in the merging region. In the combined region, the velocity of dual jets agree well with that of single jet, but the turbulence intensity of dual jets not agree with that of single jet.

The characteristics of static pressure recovery in a conical diffuser with a swirling flow (선회류 유입에 대한 원추디퓨저의 정압회복 특성)

  • Jeong, Hyo-Min;Jeong, Han-Sik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.7
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    • pp.937-945
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    • 1998
  • The purpose of this paper is to investigate the relationship between pressure recovery and turbulent characteristic value of velocity and pressure, in the case where a swirling flow streams into a conical diffuser. The results of both measurements of the wall pressure fluctuation and velocity fluctuation revealed them to role the large part of the total pressure loss of the flow. The cause of the fluctuation of flow was showed to be the flow separation at the inlet of diffuser at low intensity of swirl, but the flow of diffuser center was instable at high intensity of swirl. The static pressure recovery depends strongly on the magnitude of the turbulent energy in the diffuser, and that this magnitude of the turbulent energy varies as the intensity of swirl at the diffuser inlet.