Flow About Cylinders With Surface Perturbations

Nigim, Hani H.; Batill, Stephen M.

doi:10.1006/jfls.1997.0116

Cited by 19 publications

(5 citation statements)

References 10 publications

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“…For the former, acoustics excitations (Blevins, 1985), heating the cylinder (Lecordier et al, 1991), oscillating the cylinder at an appropriate frequency or frequency-modulation (Berger, 1967;Nakano and Rockwell, 1991;Tokumaru and Dimotakis, 1991;Suryanarayana et al, 1993), blowing and suction (Bearman, 1965), and recently electromagnetic force control (Kim and Lee, 2001) are typical examples. For the latter, typical examples are surface protrusions (Nigim and Batill, 1997) to change the flow separation location, shrouds to affect the fluid entrainment (Zdravkovich, 1997), the rear-wake stabilizer to minimize the mutual interactions of separated shear layers (Bearman, 1965;Eisenlohr and Eckelmann, 1989), and recently use of a very small control cylinder to efficiently suppress the wake behind the main cylinder (Strykowski and Sreenivasan, 1990).…”

Section: Introductionmentioning

confidence: 99%

Wake flow pattern modified by small control cylinders at low Reynolds number

Kuo

Chiou

Chen

2007

Journal of Fluids and Structures

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Section: Introductionmentioning

confidence: 99%

Wake flow pattern modified by small control cylinders at low Reynolds number

Kuo

Chiou

Chen

2007

Journal of Fluids and Structures

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“…More complicated two-dimensional configurations involving equally-spaced multiple spanwise wires protruding from the surface of a cylinder have been studied first preliminarily by Nebres (1992) and later by Nigim and Batill (1997). In these studies, the shedding frequency and the drag coefficient were shown to vary with the location of tripping for a given wire size and Reynolds number.…”

Section: Introductionmentioning

confidence: 99%

Correlation between single-wire and multi-wire tripping of the flow past a circular cylinder

Joshi¹,

Ekmekci²

2019

Fluid Dyn. Res.

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An experimental study is carried out to explore if the collective influence of multiple tripwires applied spanwise on a circular cylinder can be correlated to the well-known effects of single-wire tripping from previous studies. Constant Temperature Anemometry and Particle Image Velocimetry tests were conducted on single-wire-and two-wire-fitted cylinders in subcritical flow. Noting that a single tripwire can only influence the shedding frequency when it is within a certain range of locations on the cylinder surface, two scenarios for twowire-fitted cylinders are noteworthy: (1) One of the two wires can fall within this range of locations. This is the case where flow features for the two-wirefitted cylinder are identical to the single-wire-fitted one. In this category, the Karman vortex shedding loses its coherence and a bistable separation behavior sets in when the influential wire is at the first critical location (+/−θ c1 ) of the single-wire application. (2) Both tripwires can be in the range of locations where the single tripwire application influences the shedding frequency. This is the scenario where flow is controlled by both tripwires. The most dominant influence comes from the tripwire that is closer to the θ c location (another critical location identified by previous studies for single-wire applications). Furthermore, in this category, the drastic attenuation of the Karman instability and the onset of the bistable shear-layer separation occur when one of the wires is at a new θ c1 location that is about 5°-7°larger than the θ c1 reported for single-wire tripping by previous studies. This change in θ c1 comes together with a large degree of near-wake contraction to satisfy the simultaneous entrainment demand needed for the early transition of both shear layers in the two-wire-fitted case. A shortage of fluid in satisfying such an increased entrainment demand is speculated to be the cause of the observed shift in θ c1 .

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“…Nigim et al [7] investigated the influence of small circular surface perturbations (diameter d, spacing S) on the drag force and the vortex shedding of a circular cylinder. Their results show that when S/d < 3, for d-type arrays [8] the mean value of drag is almost constant and less than that for a smooth-surface cylinder.…”

Section: Introductionmentioning

confidence: 99%

Control of vortex shedding on a circular cylinder using self-adaptive hairy-flaps

Kunze

Brücker

2011

Comptes Rendus. Mécanique

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Experiments on separation control using flexible self-adaptive hairy-flaps are presented herein. The wake-flow behind a circular cylinder is investigated without and with flexible hairy-flaps at the aft-part of the cylinder. Flow dynamics and hair motion were measured by particle image velocimetry and image processing in a range of Reynolds number 5000 < Re < 31 000. The experiments and POD analysis show, that the hairy-flaps alter the natural vortex separation cycle in such a way that the vortices do not shed in a zigzag like arrangement as in the classical von Kármán vortex street but in line in a row with the cylinder wake axis. Thus, the wake-deficit is largely reduced. Furthermore, flow fluctuations are considerably reduced about 42% in streamwise and 35% in transversal direction compared to the reference case without hairy-flaps, too. The condition for this mode change is the lock-in of the vortex shedding with a traveling wave running through the flexible hair bundles in transversal direction at the aft-part of the cylinder. As a consequence, the vortex shedding frequency is increased, the length of the separation bubble is decreased and drag force is decreased, too. The lock-in appears as a jump-like change of the shedding frequency and a jump in the Strouhal-Reynolds number diagram. However, when the characteristic length for the normalized frequency is chosen as the length of the separation bubble instead of the cylinder diameter, the Str-Re dependence is regular again. This hints on the relevance of the resonator model as proposed by Sigurdson and Roshko (1988) [16] on vortex shedding mechanism when boundary conditions are changed such as in our case, where the hairy-flap bundle imposes a flexible wall with visco-elastic coupling in transversal direction.

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Flow About Cylinders With Surface Perturbations

Cited by 19 publications

References 10 publications

Wake flow pattern modified by small control cylinders at low Reynolds number

Wake flow pattern modified by small control cylinders at low Reynolds number

Correlation between single-wire and multi-wire tripping of the flow past a circular cylinder

Control of vortex shedding on a circular cylinder using self-adaptive hairy-flaps

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