• Title/Summary/Keyword: Single Wake

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A study on the three dimensional turbulent flow analysis of wake flow behind rotating blade row between hub and midspan (허브와 중앙스팬 사이의 회전익 후류 3차원 난류유동해석에 관한 연구)

  • No, Su-Hyeok;Jo, Gang-Rae
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.7
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    • pp.911-918
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    • 1997
  • The turbulent viscous wake flows behind a single airfoil, two-dimensional stationary blade row and three-dimensional rotating blade row were calculated, and the numerical results were compared with experimental ones. The numerical technique was based on the SIMPLE algorithm using three turbulent closure models, standard k-.epsilon. model(WFM), low Reynolds number k-.epsilon. model(LRN) and Reynolds stress model (RSM). In the case of a single airfoil, WFM, LRN and RSM presented fairly good velocity distributions in the wake compared with experimental data. In the case of the stationary blade row, LRN and RSM presented better results than WFM for wake velocity distribution, and especially LRN showed best results among these three turbulent models. In the case of the rotating blade row, WFM and LRN showed fairly good agreement with experimental data of the three-dimensional velocity component distributions in the range from hub to mid span region. LRN was also superior to WFM in accuracy of prediction for the wake velocity distribution as same with the cases of a airfoil and the stationary blade row.

WAKE CHARACTERISTICS BEHIND TWO SPHERES IN A SIDE-BY-SIDE ARRANGEMENT (병렬로 배열된 두 개의 구에서 발생하는 후류의 특성 연구)

  • Kim, Dong-Joo
    • Journal of computational fluids engineering
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    • v.12 no.4
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    • pp.61-67
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    • 2007
  • Numerical simulation of laminar flow over two spheres in a side-by-side arrangement is carried out to investigate the effect of the inter-sphere spacing on the flow characteristics. The Reynolds numbers considered are 100, 250, and 300, covering the steady axisymmetric, steady planar-symmetric, and unsteady planar-symmetric flows in the case of a single sphere. Results show that the drag and lift coefficients and wake structures are significantly modified depending on both the Reynolds number and the spacing between the spheres. At Re=100, the flow is steady planar-symmetric irrespective of the spacing, but it shows some variation according to the spacing at Re=250 and 300. That is, the flow maintains planar symmetry of the single-sphere wake at large spacings, while it loses the symmetry at small spacings due to the generation of new asymmetric vortical structures. It is also shown that the drag and lift coefficients generally increase with decreasing inter-sphere spacing because the high pressure region is formed near the gap between the spheres.

The near wake of three circular cylinders in an equilateral triangular arrangement at a low Reynolds number Re=100

  • Bai, Honglei;Lin, Yufeng;Alam, Md. Mahbub
    • Wind and Structures
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    • v.30 no.5
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    • pp.451-463
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    • 2020
  • Two-dimensional numerical simulations are conducted at a low Reynolds number Re = 100 to investigate the near wake of three identical circular cylinders that are arranged in an equilateral triangular configuration. The incident angle of the three-cylinder configuration with respect to incoming flow is varied from θ = 0° to 60°, while the spacing between adjacent cylinders (L) covers a wide range of L/D = 1.25-7.0, where D is diameter of the cylinder. Typical flow structures in the near wake of the three-cylinder configuration are identified, including a single Karman vortex street, bistable flip-flopping near wake, anti-phase and/or in-phase vortex shedding, shear layer reattachment, and vortex impingement, depending on the configuration (L/D, θ). The behavior of Strouhal number (St) is discussed in detail, echoing the distinct structures of near wake. Furthermore, fluid forces on the individual cylinders are examined, which, though highly depending on (L/D, θ), exhibit a close correlation to the near wake behavior.

Change of Vortex Dynamics in the Cylinder Wake by the Lock-on to Oscillatory Incident Flow (진동 유동장에서 유동공진에 의한 실린더 후류의 와류 특성 변화)

  • Kim, Won-Tae;Sung, Jae-Yong;Yoo, Jung-Yul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.11
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    • pp.1645-1654
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    • 2003
  • When vortex shedding is locked-on to a single frequency oscillatory flow, the variations of vortex dynamics are investigated using a time-resolved PIV system. Wake regions of recirculation and vortex formation, dynamic behavior of the shed vortices and the Reynolds stress fields are measured in the wake-transition regime at the Reynolds number 360. In the lock-on state, reduction of the wake region occurs and flow energy distributed downstream moves upstream being concentrated near the cylinder base. To observe the dynamic behavior of the shed vortices, the trajectory of the vortex center extended to the inside of the wake bubble is considered, which describes well the formation and evolution processes. The Reynolds stresses and their contributions to overall force balance on the wake bubble manifest the increase of the drag force by the lock-on.

Effects of Wake-Passing Orientation and Frequency on Unsteady Boundary Layer Transition on an Airfoil (주기적 통과 후류의 방향과 주파수가 익형 위 비정상 천이경계층에 미치는 영향)

  • Gang, Sin-Hyeong;Park, Tae-Chun;Jeon, U-Pyeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.5
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    • pp.685-694
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    • 2002
  • Effects of wake-passing orientation and frequency on the wake-induced boundary layer transition on a NACA0012 airfoil are investigated. The wakes are generated by rotating cylinders clockwise (CW) and counterclockwise (CCW) around the airfoil. Time- and phase-averaged streamwise mean velocities and turbulent fluctuations are measured with a single hot-wire probe. Wall skin frictions are estimated by the Computational Preston Tube Method (CPM). The pressure distribution on the airfoil is different according to the wake-passing orientation and frequency. Turbulent patches are generated in the laminar boundary layer due to the passing wake and the boundary layer becomes temporarily transitional. The transition process is significantly affected by the pressure gradient and the turbulent patches. For the receding wake, the turbulent patches propagate more rapidly than those for the approaching wake because adverse pressure gradient becomes larger. As the frequency increases, onset location of transition moles upstream and the boundary layer near the trailing edge becomes more transitional.

Robust Search Method for Ship Wake Using Two Wake Sensors (두 개의 항적 센서를 이용한 수상 항적 탐색 방법)

  • Lee, Young-Hyun;Ku, Bon-Hwa;Chung, Suk-Moon;Hong, Woo-Young;Ko, Han-Seok
    • The Journal of the Acoustical Society of Korea
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    • v.29 no.3
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    • pp.155-164
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    • 2010
  • This paper proposes a robust detection method for ship wake search using two wake sensors. A long trailing wake in the rear of a surface ship is generated along the track of surface ships. In this paper, we assume that the nearer the surface ship, the stronger wake strength is and a two-sensor based wake homing torpedo can sense for the wake strength. On this assumption we propose a simple wake detection and search method using information of wake strength. Experimental results using monte-carlo simulation demonstrate that the proposed method yields better performance in search time than previous method, which uses a single sensor. Our method is shown faster by about 45 seconds than previous method to achieve the same performance. Also, it can improve the detection performance of torpedo in the case of short wake length.

Experimental Study on the Effects of Upstream Periodic Wakes on Cascade with Tip Clearance (주기적 후류가 누설유동이 존재하는 익렬 유동에 미치는 영향에 대한 실험적 연구)

  • Im, Ji-Hyun;Kim, Dong-Hyun;Joo, Won-Goo
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.1986-1991
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    • 2003
  • To research on change of blade row flow field with tip clearance caused by upstream periodic wake, an apparatus that generate periodic wake through traversing cylinders were installed. Then how movement of upstream wake affect cascade flow and tip leakage flow were measured. Cylinder was installed in front of 50% of chord length, and traversing velocity was calculated at approximately 11.7m/s regarding inlet velocity and chord length. To measure three-dimensional velocity of flow inside blade row, single slanted hot-wire was used. From the results, when the periodic wake is inserted, the flow inside of cascade is dominantly affected by vortex that is generated from cylinder. This periodic wake affects passage vortex and tip leakage vortex.

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Experimental Study on Flows within an Unshrouded Centrifugal Impeller Passage(I)-At the Shockless Condition- (개방형 원심회전차의 내부유동장에 관한 실험적 연구(1)-무충돌 유입조건에서-)

  • 김성원;조강래
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.9
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    • pp.2261-2270
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    • 1995
  • Flow patterns were measured in an unshrouded centrifugal impeller. The flow rate in measurements was fixed at the value corresponding to a nearly zero incidence at the blade inlet. By using a single slanted hot-wire probe and a Kiel probe mounted on the impeller hub disk, the 3-D relative velocities and the rotary stagnation pressures were measured in seven circumferential planes from the inlet to the outlet of the impeller rotating at 700rpm, which diameter is 0.39 meter, and the static pressures and the slip factor at the impeller outlet were calculated from the measured values. From the measured data, the primary/secondary flows, the leakage flows, the wake-jet flows, static pressure distribution on blade surfaces and the wake production mechanism in the impeller passage were investigated.

Characteristics of Wakes in a Viscous Liquid Medium of a Simulated GTL Process (모사된 GTL공정의 점성액체 매체에서 wake의 특성)

  • Lim, Dae Ho;Jang, Ji Hwa;Kang, Yong;Jun, Ki Won
    • Korean Chemical Engineering Research
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    • v.49 no.5
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    • pp.571-576
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    • 2011
  • Characteristics of bubble driven wakes were investigated in a simulated GTL process(0.102 m ${\times}$ 1.5 m in height) with viscous liquid medium. Effects of gas velocity(0.04 ~ 0.12 m/s) and liquid viscosity(0.001 ~ 0.050 $Pa{\cdot}s$) on the wake characteristics such as rising velocity, frequency, size and holdup were determined by employing a resistivity probe method. The wake phase formed behind the rising multi-bubbles as well as single bubbles were detected effectively from the conductivity fluctuations measured by the probe. Compressed, filtered and regulated air and aqueous solutions of Carboxy Methyl Cellulose(CMC) were used as a dispersed gas phase and a continuous liquid medium, respectively. It was found that the rising velocity and size of wake phase increased with an increase in gas velocity or liquid viscosity. The holdup and frequency of wake phase increased with increasing gas velocity due to the increase of gas input into the process with increasing gas velocity. However, the values of holdup and frequency of wake phase decreased with increasing liquid viscosity, since the size of bubbles and thus that of wakes increased with increasing liquid viscosity. The ratio of wake holdup to that of gas phase, which was in the range of 0.25 ~ 0.48, increased with an increase in liquid viscosity but decreased with gas velocity. The wake characteristics were well correlated in terms of operating variables within this experimental conditions.

Turbulent Wake Flow around Tubes in Single Row Tube Banks (일렬관군에서의 난류 후류특성에 관한 연구)

  • 조석호;부정숙
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.5
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    • pp.1023-1031
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    • 1989
  • An experimental study is conducted to investigate the turbulent wake flow around tubes in vertical single row tube banks. All measurements are performed at Reynolds number(Re$_{max}$) 4.2*10$_{3}$ - 2.5*10$_{4}$ with varying tube spacings from the wide pitch ratio(H/D=3.07) to the very narrow one(H/D=1.23). Flow patterns are visualized using the smoke-wire method. Mean static pressures, velocity components, and various statistical quantities of turbulence are obtained by the computer on-line technique. In the case of wide tube spacings, the near wakes of tube show similar trends to those of a single tube, and their flow indicats an anisotropic turbulence. However, as the pitch ratio decreases, wide and narrow wakes appear alternately behind adjacent tubes due to the deflected flow. Also, in the case of H/D .leq. 1.54, Karman vortex is not formed at the side of relatively wide wake.e.