• Title, Summary, Keyword: vortex shedding

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Effect of viscoelasticity on two-dimensional laminar vortex shedding in flow past a rotating cylinder

  • Kim, Ju-Min;Ahn, Kyung-Hyun;Lee, Seung-Jong
    • Korea-Australia Rheology Journal
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    • v.21 no.1
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    • pp.27-37
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    • 2009
  • In this work, we numerically investigate the effect of viscoelasticity on 2D laminar vortex dynamics in flows past a single rotating cylinder for rotational rates $0{\leq}{\alpha}{\leq}5$ (the rotational rate ex is defined by the ratio of the circumferential rotating velocity to free stream velocity) at Re=100, in which the vortex shedding has been predicted to occur in literature for Newtonian fluids. The objective of the present research is to develop a promising technique to fully suppress the vortex shedding past a bluff body by rotating a cylinder and controlling fluid elasticity. The predicted vortex dynamics with the present method is consistent with the previous works for Newtonian flows past a rotating cylinder. We also verified our method by comparing our data with the literature in the case of viscoelastic flow past a non-rotating cylinder. For $0{\leq}{\alpha}{\leq}1.8$, the frequency of vortex shedding slightly decreases but the fluctuation of drag and lift coefficient significantly decreases with increasing fluid elasticity. We observe that the vortex shedding of viscoelastic flow disappears at lower ${\alpha}$ than the Newtonian case. At ${\alpha}$=5, the relationship between the frequency of vortex shedding and Weissenberg number (Wi) is predicted to be non-monotonic and have a minimum around Wi=0.25. The vortex shedding finally disappears over critical Wi number. The present results suggest that the vortex shedding in the flow around a rotating cylinder can be more effectively suppressed for viscoelastic fluids than Newtonian fluids.

NUMERICAL ANALYSIS OF THE FLOW AROUND A ROTARY OSCILLATING CIRCULAR CYLINDER USING UNSTEADY TWO DIMENSIONAL NAVIER-STOKES EQUATION (Navier-Stokes 식을 이용한 회전 진동하는 2차원 원형 실린더 주위 유동 해석)

  • Lee, M.K.;Kim, J.S.
    • Journal of computational fluids engineering
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    • v.16 no.3
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    • pp.8-14
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    • 2011
  • Although the geometry of circular cylinder is simple, the flow is complicate because of the flow separation and vortex shedding. In spite of many numerical and experimental researches, the flow around a circular cylinder has not been clarified even now. It has been known that the unsteady vortex shedding from a circular cylinder can vibrate and damage a structure. Lock-on phenomenon is very important in the flow around an oscillating circular cylinder. The lock-on phenomenon is that when the oscillation frequency of the circular cylinder is at or near the frequency of vortex shedding from a stationary cylinder, the vortex shedding synchronizes with the cylinder motion. This phenomenon can be recognized by the spectral analysis of the lift coefficient history. At the lock-on region the vortex is shedding by the modulated frequency to the body frequency. However, the vortex is shedding by the mixed frequencies of natural shedding and forced body frequency in the region of non-lock-on. In this paper, it was analyzed the relation between the frequency of rotary oscillating circular cylinder and the vortex shedding frequency.

A numerical study of vortex shedding and lock-on behind a square cylinder in a laminar flow (층류유동에서 사각실린더 주위의 와류쉐딩과 공진현상에 관한 수치해석적 연구)

  • Jeong, Yeong-Jong;Jo, Sang-Hyeon;Choe, Hae-Cheon;Gang, Sin-Hyeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.5
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    • pp.573-583
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    • 1998
  • Effects of the oscillating incoming flow on vortex shedding and lock-on behind a square cylinder are investigated using numerical simulations at a Reynolds number of 100. Vortex shedding occurred at low forcing frequencies of the incoming flow similar to the natural vortex shedding. As the forcing frequency further increases, the shedding frequency decreases to the half of the forcing freqnency. For a sufficiently large frequency, vortex shedding returns to the natural vortex shedding irrespective of the forcing amplitude. Also, the lock-on region becomes wider with higher forcing amplitudes. The phase diagram between the drag and lift shows a simple periodic behavior in the lock-on region, while a complicated periodic phase relation is observed when there is no lock-on.

Aerodynamic measurements of across-wind loads and responses of tapered super high-rise buildings

  • Deng, Ting;Yu, Xianfeng;Xie, Zhuangning
    • Wind and Structures
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    • v.21 no.3
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    • pp.331-352
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    • 2015
  • A series of wind tunnel tests were conducted on tapered super high-rise buildings with a square cross section by applying synchronous pressure measurement technology. The effects of global strategy of chamfered modification on aerodynamic loads and wind-induced responses were investigated. Moreover, local aerodynamic strategies of opening a ventilation slot in the corner of equipment and refuge floors were carried out. Results show that the global strategy of tapered elevation increased the vortex shedding frequency, but reduced vortex shedding energy, leading to reduction of across-wind aerodynamic loads and responses. Chamfered modification suppressed the across-wind vortex shedding effect on tapered buildings. Opening the ventilation slot further suppressed the strength of vortex shedding and reduced the residual energy related to vortex shedding in aerodynamic loads of chamfered buildings. Finally, the optimized locations of local aerodynamic strategies were suggested.

Flow Interaction of Shedding Vortex with Injected Normal Blowing

  • Mon, Khin-Oo;Lee, Chang-Jin;Koo, Hee-Seok
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.239-243
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    • 2012
  • This paper is concerned with turbulent flow computations using Large Eddy Simulation (LES) and the flow interaction of vortex shedding in a cylindrical duct flow driven by mass blowing through the wall. The purpose is to analyze non-linear combustion characteristics in the presence of vortex shedding generated in a hybrid rocket motor. Experimental studies have shown sudden changes in pressure (referred as a DC-shift), which depend on the strength of vortex strength of incoming flow. The combustion instability because of a sudden change in pressure fluctuations is mainly related with the interaction between vortex shedding. Therefore LES computation on a duct with injected normal blowing was performed to simulate the turbulent flow interactions with the behaviors of vortices and vortex structures along the injected wall.

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Tower Flange Design Considering Vortex Shedding (Vortex Shedding을 고려한 Tower Flange 설계)

  • Lee Hyunjoo;Choi Wonho;Lee Seung-Kuh
    • 한국신재생에너지학회:학술대회논문집
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    • pp.68-71
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    • 2005
  • In the case of wind turbine design, Optimization of tower structure is very important because tower generally takes about $20\%$ of overall turbine cost. In this paper, we calculated wind loads considering vortex shedding, and optimized tower flange using the calculation results. For optimization, we used FEM to analyze structural strength of the flange and blade momentum theory to calculate wind loads.

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Vortex Shedding Frequency for a 2D Hydrofoil with a Truncated Trailing Edge (뒷날이 잘린 2차원 수중익의 와도 흘림 주파수)

  • Lee, Seung-Jae;Lee, Jun-Hyeok;Suh, Jung-Chun
    • Journal of the Society of Naval Architects of Korea
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    • v.51 no.6
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    • pp.480-488
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    • 2014
  • Vortex shedding which is the dominant feature of body wakes and of direct relevance to practical engineering problems, has been intensively studied for flows past a circular cylinder. In contrast, vortex shedding from a hydrofoil trailing edge has been studied to much less extent despite numerous practical applications. The physics of the problem is still poorly understood. The present study deals with $K{\acute{a}}rm{\acute{a}}n$ vortex shedding from a truncated trailing-edge hydrofoil in relatively high Reynolds number flows. The objectives of this paper are twofold. First, we aim to simulate unsteady turbulent flows past a two dimensional hydrofoil through a hybrid particle-mesh method and penalization method. The vortex-in-cell (VIC) method offers a highly efficient particle-mesh algorithm that combines Lagrangian and Eulerian schemes, and the penalization method enables to enforce body boundary conditions by adding a penalty term to the momentum equation. The second purpose is to investigate shedding frequencies of vortices behind a NACA 0009 hydrofoil operating at a zero angle of attack.

The Interaction of Vortex Shedding Behavior in Hybrid Rocket Combustion (와류간섭에 의한 하이브리드로켓 연소 특성)

  • Park, Kyung-Soo;Lee, Chang-Jin;Shin, Kyung-Hoon
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.244-248
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    • 2012
  • A series of hybrid rocket combustion experiments were carried out with PMMA/GOx changing diameter and length of the disk installed at pre-chamber. The disk can generate vortex shedding flow and change flow conditions prior to entering the fuel grain which could also alter the combustion characteristics and pressure oscillations. The interaction of vortex shedding in the pre-chamber and small-scale vortices adjacent to burning surfaces by using combustion test.

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Experimental studies on possible vortex shedding in a suspension bridge - Part I - Structural dynamic characteristics and analysis model

  • Law, S.S.;Yang, Q.S.;Fang, Y.L.
    • Wind and Structures
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    • v.10 no.6
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    • pp.543-554
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    • 2007
  • The suspension bridge is situated in an area of complex topography with both open sea and overland turbulence characteristics, and it is subject to frequent typhoon occurrences. This paper investigates experimentally the possible vortex shedding events of the structure under high wind and typhoon conditions. A single-degree-of-freedom model for the vibration of a unit bridge deck section is adopted to determine the amplitude of vibration and to estimate the parameters related to the lifting force in a vortex shedding event. The results of the studies are presented in a companion paper (Law, et al. 2007). In this paper, statistical analysis on the measured responses of the bridge deck shows that the vibration response at the first torsional mode of the structure has a significant increase at and beyond the critical wind speed for vortex shedding as noted in the wind tunnel tests on a section model of the structure.

Experimental study on possible vortex shedding in a suspension bridge - Part II - Results when under typhoon Babs and York

  • Law, S.S.;Yang, Q.S.;Fang, Y.L.
    • Wind and Structures
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    • v.10 no.6
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    • pp.555-576
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    • 2007
  • Statistical analysis on the measured responses of a suspension bridge deck (Law, et al. 2007) show that vibration response at the first torsional mode of the structure has a significant increase at and beyond the critical wind speed for vortex shedding as noted in the wind tunnel tests on a sectional model. This paper further analyzes the measured responses of the structure when under typhoon conditions for any possible vortex shedding events. Parameters related to the lifting force in such a possible event and the vibration amplitudes are estimated with a single-degree-of-freedom model of the system. The spatial correlation of vortex shedding along the bridge span is also investigated. Possible vortex shedding events are found at both the first torsional and second vertical modes with the root-mean-square amplitudes comparable to those predicted from wind tunnel tests. Small negative stiffness due to wind effects is observed in isolated events that last for a short duration, but the aerodynamic damping exhibits either positive or negative values when the vertical angle of wind incidence is beyond ${\pm}10^{\circ}$. Vibration of the bridge deck is highly correlated in the events at least in the middle one-third of the main span.