• Title/Summary/Keyword: 원주후류

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Characteristics of Two-Dimensional Turbulent Wake Flow behind a Circular Cylinder (圓柱 뒤의 2 次元 後流 流動 特性)

  • 부정숙;윤순현;이종춘;강창수
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.9 no.5
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    • pp.555-563
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    • 1985
  • Two-dimensional turbulent wake flow behind a circular cylinder is investigated experimentally by suing linearized constant temperature hot wire anemometer. Turbulent fluctuations and mean velocity defects are measured in the rage of 5 dia.- 500 dia. downstream from the cylinder and for the Reynolds numbers of 2000-4000. Results with statistical treatment and digital data processing techniques are as follows: (1) The transition region from near wake to far wake is 30 dia. - 50 dia. downstream from the cylinder. (2) In the near wake, it is found that strong periodic ( f=845Hz) coherent structure exists. (3) It shows that the inertial subrange is 180Hz-2000Hz in self preservation region.

Numerical Solutions for the Flow past a Cylinder (원주주위를 지나는 흐름에 관한 수치해석)

  • 조용식;윤태훈
    • Water for future
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    • v.21 no.3
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    • pp.291-291
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    • 1988
  • The two dimensional time dependent flow past a circular cylinder is analyzed numerically. In the analysis, equations of conservation of mass and momentum are transformed to equations of stream function-vorticity and vorticity transport, and nondimensionalized by nondimensional parameters representing flow characteristics, The resulting stream function-vorticity equstion and vorticity transport equation are solved by successive over relaxation scheme and alternating direct implicit scheme. Numerical experments are performed for the flow in the range of Reynolds number 125 to 275. The time dependent streamlines, vorticities, pressure on cylinder surface, separation angle, and drag and lift coefficients are calculated, and the method for estimation of pressure on cylinder surface and the outer boundary limit are developed.

- Numerical Solutions for the Flow past a Cylinder- (원주주위를 지나는 흐름에 관한 수치해석)

  • 조용식;윤태훈
    • Water for future
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    • v.31 no.4
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    • pp.291-297
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    • 1998
  • The two dimensional time dependent flow past a circular cylinder is analyzed numerically. In the analysis, equations of conservation of mass and momentum are transformed to equations of stream function-vorticity and vorticity transport, and nondimensionalized by nondimensional parameters representing flow characteristics, The resulting stream function-vorticity equation and vorticity transport equation are solved by successive over relaxation scheme and alternating direct implicit scheme. Numerical experiments are performed for the flow in the range of Reynolds number 125 to 275. The time dependent streamlines, vorticities, pressure on cylinder surface, separation angle, and drag and lift coefficients are calculated, and the method for estimation of pressure on cylinder surface and the outer boundary limit are developed.

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The Effect of Free Stream Turbulence on the Coherent Structures in the near Wake of a Circular Cylinder (원주 후류의 응집구조에 대한 자유흐름 난류강도의 영향)

  • 정양범;양종필
    • Journal of Advanced Marine Engineering and Technology
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    • v.18 no.1
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    • pp.60-72
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    • 1994
  • The effect of free stream tubulence on the coherent structure in the near wake of a circular cylinder was investigated by a conditional sampling technique. The measurements were made from C.T.A. with hot wire I-probe and a Split-film sensor. Contours of phase-averaged velocity and vorticities were presented and discussed. It was found that the value of the vortex strength increased with increasing free stream turbulence which can enhance the roll-up of the shear layer.

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Turbulent Wake Structure Behind a Spinning Circular Cylinder (회전하는 원주후류의 2차원 난류구조)

  • 부정숙;김경천;류병남
    • Journal of Advanced Marine Engineering and Technology
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    • v.16 no.4
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    • pp.39-49
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    • 1992
  • The coherent wake structures behind a spinning cylinder placed in a uniform flow were experimentally investigated by means of phase averaging technique. With a fixed cylinder Reynolds number (Re=6,600), the conditionally sampled velocity vectors were obtained at a section of 3.0 and 10 diameters behind the cylinder for the range of spin parameter S(the ratio of the peripheral velocity to that of the uniform flow) 0 to 2. Spectral analysis and vorticity contours of the velocity data show that up to S=1.2, a Karman vortex street exists within the wake, however, the coherent structures become obscure and their vorticity strength decreases as S increase. Beyond S=1.2, a distinct vortex shedding frequency no longer exists, furthermore coherent structures disappear when S is over 1.6.

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Measurements of the Cylinder Wake with a Volume PTV (High-Density 3D-PTV) (고밀도 3D-PTV (Volume PTV)에 의한 원주후류 측정 해석)

  • Hwang, T.G.;Cho, K.R.;Pyeon, Y.B.;Cho, Y.B.;Moon, K.R.;Jo, H.J.;Doh, D.H.
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.88-91
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    • 2008
  • A Hybrid-Genetic-Algorithm based 3D-PTV has been constructed by introducing the conventional GA-3D-PTV. The measurement system consists of two-high-definition-cameras(1k ${\times}$ 1k), a Nd-Yag laser and a host computer. The system has been used to measure the wake of a cylinder. The Reynolds number is 1120. The structures of the wake have been quantified in detail than the results obtained ever before.

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A Study on Wake Flow behind a pair of Circular Cylinders with gap (간격을 갖는 원주열의 후류특성에 관한 연구)

  • 김준호;최민선;조대환;이경우
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • 2001.05a
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    • pp.135-139
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    • 2001
  • This experimental study investigates the wake flow behind a pair of cylinders displaced normal to a free stream. In this experiment, the principal aim is to investigate the transition mechanism of the large vortex generating process in the wake having unique vortex shedding pattern. associated with the gap difference between the cylinders. The detailed visualization is carried out using the PIV measurement. The transition mechanism of the large generating vortex is clarified by showing the streak lines. the vorticity and the statistical fluctuating velocity distributions.

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The Characteristic Calculation of the Wake through Cylinders by Vortex Method (와법을 이용한 원주군을 지나는 후류의 특성 계산)

  • Ro, Ki-Deok;Oh, Se-Kyung;Byun, Yong-Sue
    • Journal of Advanced Marine Engineering and Technology
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    • v.34 no.1
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    • pp.76-83
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    • 2010
  • The Characteristics of the flow field through cylinders with in-line and staggered arrangements were calculated by vortex method. Vortex distributions and velocity profiles around the cylinders with in-line and staggered arrangements were simulated at the pitch ratio of Pt/D=1.25~2.0 and Reynolds number of Re=$4.0{\times}10^1{\sim}4.0{\times}10^4$. As the results the vortices of clockwise at the upper separation point cylinder and the vortices of anticlockwise at the lower separation point of each cylinder were generated at both in-line and staggered arrangements. The generation of the reverse flow in the rear region of the cylinders was caused by the pitch ratio and Reynolds number, the boundary region was at the pitch ratio of Pt/D=1.5 and Reynolds number of Re=$4.0{\times}10^2{\sim}4.0{\times}10^3$ in case of in-line arrangement and was at the pitch ratio of Pt/D=1.4 and Reynolds number of Re=$4.0{\times}10^1{\sim}4.0{\times}10^2$ in case of staggered arrangement.

Characteristics of Near Wake Behind a Circular Cylinder with Serrated Fins (II) - Comparison of Time Mean Flow Fields- - (톱니형 휜이 부착된 원주의 근접후류특성 연구 (II) - 시간평균 유동장 비교 -)

  • Ryu, Byeong-Nam;Kim, Gyeong-Cheon;Bu, Jeong-Suk
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.8
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    • pp.1191-1200
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    • 2002
  • The measurements of velocity vectors are made in the near wake(X/d=5.0) of a circular cylinder with serrated fins. Velocity of fluid which flow through fins decreases as increasing fin height and freestream velocity and decreasing fin pitch. Therefore the velocity distribution at X/d=0.0 has lower gradient with increasing freestream velocity and fin height and decreasing fin pitch. The discontinuity of the streamwise velocity gradient is observed near the fin edge and causes significant changes in V-component velocity distribution in the near wake. This change attributes to the differences in Strouhal number and entraintment flow behavior. Increased turbulent intensity around a circular cylinder due to the serrated fins and entrainment flow are important factors for the recovery of velocity defect. The widths of velocity and turbulent intensity distribution of fin tubes are wider than those of a circular cylinder. The normalized velocity and turbulent intensity distributions with a hydraulic diameter which is proposed in this paper are in closer agreement with those of a circular cylinder.

Effect of External Acoustic Excitation on Wake behind a Circular Cylinder (외부 음향여기가 원주 후류 유동에 미치는 효과에 관한 연구)

  • Choi, Jae-Ho;Lee, Sang-Joon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.5
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    • pp.603-609
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    • 1999
  • The effect of an external acoustic excitation on the wake structure behind a circular cylinder was experimentally investigated. The sound wave was excited in the frequency range of the shear layer instability and two sound pressure levels of 114 and 120dB were used in this study. As a result, the acoustic excitation modified the wake structure by increasing the velocity fluctuation energy without changing the vortex shedding frequency. The acoustic excitation enhanced the vortex shedding process and promoted the shear layer instability. Consequently, the acoustic excitation reduced the length of the vortex formation region and decreased the base pressure. In addition, the vortex strength of vortices was increased and the width of the wake was spread out due to the acoustic excitation. When the excitation frequency was identical to the shear layer instability frequency, the effect of the external flow control on the cylinder wake was maximized. In addition, with increasing the sound pressure level, the effect of the external acoustic excitation on the wake structure increased.