The effects of yaw and finite length upon the vortex wakes of stationary and vibrating circular cylinders

Ramberg, S. E.

doi:10.1017/s0022112083000397

Cited by 194 publications

(133 citation statements)

References 19 publications

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“…In the absence of vibration, the spanwise vortex rows forming downstream of the cylinder are not parallel to its axis. Such oblique vortex shedding, also observed for fixed rigid cylinders (Ramberg 1983;Thakur et al 2004;Willden & Guerbi 2010), is not captured by the IP. It can be noted that the obliquely shed vortices are not perpendicular to the oncoming flow and the shedding angle remains lower than the inclination angle, as also reported in previous works (e.g.…”

Section: Introductionmentioning

confidence: 88%

“…The influence of body inclination on the system behavior was quantified in the above mentioned studies, especially by assessing the validity of the independence principle (IP). The IP, which was also thoroughly analyzed in the case of inclined rigid cylinders, either fixed or forced to oscillate (Van Atta 1968;Ramberg 1983;Thakur et al 2004;Zhao et al 2009;Willden & Guerbi 2010), assumes that the flow dynamics is determined by the component of the oncoming flow perpendicular to the cylinder and that the component aligned with the cylinder axis, the axial component, has a negligble impact. As a result, the IP states that the system behaviors in the inclined and normal configurations should match once the physical quantities (e.g.…”

Section: Introductionmentioning

confidence: 99%

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The onset of vortex-induced vibrations of a flexible cylinder at large inclination angle

Bourguet

Triantafyllou

2016

J. Fluid Mech.

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The onset of the vortex-induced vibration (VIV) regime of a flexible cylinder inclined at 80 • within a uniform current is studied by means of direct numerical simulations, at Reynolds number 500, based on the body diameter and inflow velocity magnitude. A range of values of the reduced velocity, defined as the inverse of the fundamental natural frequency, is examined in order to capture the emergence of the body responses and explore the concomitant reorganization of the flow and fluid forcing. Additional simulations at normal incidence confirm that the independence principle, which states that the system behavior is determined by the normal inflow component, does not apply at such large inclination angle. Contrary to the normal incidence case, the free vibrations of the inclined cylinder arise far from the Strouhal frequency, i.e. the vortex shedding frequency downstream of a fixed rigid cylinder. The trace of the stationary body wake is found to persist beyond the vibration onset: the flow may still exhibit an oblique component that relates to the slanted vortex shedding pattern observed in the absence of vibration. This flow component which occurs close to the Strouhal frequency, at a high and incommensurable frequency compared to the vibration frequency, is referred to as Strouhal component; it induces a high-frequency component in fluid forcing. The vibration onset is accompanied by the appearance of novel, low-frequency components of the flow and fluid forcing, which are synchronized with body motion. This second dominant flow component, referred to as lock-in component, is characterized by a parallel spatial pattern. The Strouhal and lock-in components of the flow coexist over a range of reduced velocities, with variable contributions, which results in a variety of mixed wake patterns. The transition from oblique to parallel vortex shedding, that occurs during the amplification of the structural responses, is driven by the opposite trends of these two component contributions: the decrease of the Strouhal component magnitude, associated with the progressive disappearance of the high-frequency force component, and simultaneously, the increase of the lock-in component magnitude, which dominates once the fully-developed VIV regime is reached and the flow dynamics is entirely governed by wake-body synchronization.

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Section: Introductionmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

The onset of vortex-induced vibrations of a flexible cylinder at large inclination angle

Bourguet

Triantafyllou

2016

J. Fluid Mech.

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“…Applying the 'cosine law' (Ramberg 1983;Hayashi & Kawamura 1995) or the independence principle to calculate the drag yields…”

Section: Formation Of Water Rivuletsmentioning

confidence: 99%

Turbulent wake of an inclined cylinder with water running

Alam

Zhou

2007

J. Fluid Mech.

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This paper presents the results of an experimental study of fluid dynamics around an inclined circular cylinder with and without water running over its surface, covering water rivulet formation, fluid forces on the cylinder, near wake and their interrelationships. The cylinder inclination angle (α) with respect to incident flow was between 55 • and 80 • . It has been found that water running over the cylinder surface may behave quite differently, depending on the Reynolds number (Re), and subsequently impact greatly upon the fluid dynamics around the cylinder. As such, five flow categories are classified. Category A: one water rivulet was observed, irrespective of α, at the leading stagnation point at a small Re. Category B: the rivulet splits into two, symmetrically arranged about the leading stagnation line, once Re exceeds a critical value that depends on α. The two rivulets may further switch back to one, and vice versa. Category C: two symmetrical straight rivulets occur. Category D: the two rivulets shift towards the flow separation line with increasing Re and oscillate circumferentially. The oscillation reaches significant amplitude when the rivulets occur at about 70 • from the leading stagnation point. This increased amplitude is coupled with a rapid climb in the mean and fluctuating drag and lift, by a factor of near 5 for the fluctuating lift at α = 80 • . Meanwhile, the flow structure exhibits a marked variation. For example, Strouhal number and vortex formation length decrease, along with an increase in spanwise vorticity concentration, velocity deficit, and coherence between vortex shedding and fluctuating lift. All these observations point to the occurrence of a 'lock-in' phenomenon, i.e. the rivulet oscillation synchronizing with flow separation. A rivulet-vortex-induced instability is proposed to be responsible for the well reported rain-wind-induced vibration associated with the stay cables of cablestayed bridges. Category E: the two rivulets shift further downstream just beyond the separation line; the shear layers behind the rivulets become highly turbulent, resulting in weakened vortex shedding, flow fluctuating velocities and fluctuating fluid forces. Based on the equilibrium of water rivulet weight, aerodynamic pressure and friction force between fluid and surface, an analysis is developed to predict the rivulet position on the cylinder, which agrees well with measurements.

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“…Ramberg (1983), por sua vez, no estudo de cilindros rígidos levantou questões importantíssimas sobre a validade do PI, sendo que notou a grande sensibilidade que o sistema possui de acordo com as condições de contorno nas extremidades. Este fato deve-se à tridimensionalidade intrínseca aos escoamentos ao redor de cilindros inclinados como, por exemplo, o escoamento apresentado na Figura 2.17.…”

Section: A Questão Da Inclinação Em Relação Ao Perfil De Correnteza: unclassified

“…Extraído de Ramberg (1983). (b) Esquematização da esteira obtida por Ramberg para cilindros inclinados de comprimento finito.…”

Section: A Questão Da Inclinação Em Relação Ao Perfil De Correnteza: unclassified

Estudo experimental das vibrações induzidas pela emissão de vórtices em cilindros flexíveis inclinados em relação à correnteza.

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The effects of yaw and finite length upon the vortex wakes of stationary and vibrating circular cylinders

Cited by 194 publications

References 19 publications

The onset of vortex-induced vibrations of a flexible cylinder at large inclination angle

The onset of vortex-induced vibrations of a flexible cylinder at large inclination angle

Turbulent wake of an inclined cylinder with water running

Estudo experimental das vibrações induzidas pela emissão de vórtices em cilindros flexíveis inclinados em relação à correnteza.

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