Unsteady Pulsing of Cylinder Wakes

Williams, David R.; Amato, C. W.

doi:10.1007/978-3-642-83831-6_7

Cited by 16 publications

(3 citation statements)

References 25 publications

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“…Using tiny pulsing jets as a control technique with zero net mass addition, Williams & Amato (1989) have demonstrated that the naturally unsteady wake of a circular cylinder could be stabilized by unsteady forcing, appropriately applied in certain combination of amplitude and frequency. The quantity of outflow and inflow in creating the pulsing jets was kept equal in order to satisfy the conservation of mass.…”

Section: Introductionmentioning

confidence: 99%

On wake response to asymmetric blowing in spurts from a blunt trailing edge

Sharma

Pant

2007

Sadhana

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In the present investigation, a technique has experimentally been evolved with the aim to control the unsteady wake dominated by periodic vortexshedding. The technique uses pulsating surface blowing that is applied asymmetrically just before separation from the blunt trailing edge of a thick aerofoil model. Thus, momentum is injected in spurts in only one of the two separated shear layers. The control parameters are the mass flow rate and the forcing frequency of the pulsating blowing. The technique is particularly effective in suppressing the vortex-shedding when the blowing is moderate and the forcing frequency is twice the natural vortex-shedding frequency. As a consequence of injecting momentum in spurts, there is a significant saving in mass flow required to achieve a condition of the momentumless wake. In spite of the initial conditions being strongly asymmetric, the flow pattern in the wake was observed to quickly assume a remarkable symmetry.

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Section: Introductionmentioning

confidence: 99%

On wake response to asymmetric blowing in spurts from a blunt trailing edge

Sharma

Pant

2007

Sadhana

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“…They found that this blowing configuration significantly reduces the flow-induced oscillations. The use of base blowing was also studied by Williams & Amato (1989) who employed pulsating jets through closely spaced, very small holes along the base of the cylinder at Re = 370. Their findings demonstrated that this technique has the capability to suppress vortex shedding and reduce the primary momentum deficit in the wake.…”

Section: Introductionmentioning

confidence: 99%

Flow and aerodynamic noise control of a circular cylinder by local blowing

Maryami,

Arcondoulis,

Liu

2024

J. Fluid Mech.

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In this experimental study, the impact of symmetric local blowing on suppressing the vortex-induced noise of a circular cylinder was investigated. A highly instrumented cylinder with pressure taps and a series of blowing chambers was used to inject air along the span (seven times the cylinder diameter) at circumferential angles $\theta _{b}={\pm }41^{\circ }$ , ${\pm }90^{\circ }$ and ${\pm }131^{\circ }$ corresponding to the boundary layer, shear layers on the cylinder and separated shear layers, respectively. The investigation aimed to understand the noise reduction mechanism of local blowing by conducting near-field pressure and far-field noise measurements in synchronisation with flow field velocity measurements. Near-field pressure was measured around the circumference of the cylinder using a remote-sensing technique and planar particle image velocimetry was implemented to measure the velocity of the wake flow field at a diameter-based Reynolds number of $Re=7\times 10^{4}$ . The results revealed that the interaction of the rolling up separated shear layers, under the influence of high-momentum fluid travelling from the free stream to the wake, induced significant vertical flow movement in the vortex-formation region. This movement led to strong alternating surface pressure fluctuations at the cylinder's shoulders, contributing to the scattering of noise. It was demonstrated that local blowing delayed vortex shedding for all cases, except at $\theta _{b}={\pm }90^{\circ }$ , which elongated the shear layers and pushed the high-momentum transfer area farther downstream. The application of local blowing at $\theta _{b}={\pm }41^{\circ }$ was particularly effective in increasing the vortex formation size due to reduced entrainment of fluid-bearing vorticity.

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“…Continuous or pulsating-based-bleeds could be used to modify the flow in the separated region. For the latter, drag reduction could be achieved with zero net mass addition, with maxi-mum effectiveness at a frequency twice the Kármán shedding frequency 5 . Among the wide variety of active drag reduction techniques that resulted effectively, small jets have shown to be very efficient, enabling separation control with weak actuation 6 .…”

Section: Introductionmentioning

confidence: 99%

Machine-learning flow control with few sensor feedback and measurement noise

et al. 2022

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A comparative assessment of machine-learning (ML) methods for active flow control is performed. The chosen benchmark problem is the drag reduction of a two-dimensional Kármán vortex street past a circular cylinder at a low Reynolds number ( Re = 100). The flow is manipulated with two blowing/suction actuators on the upper and lower side of a cylinder. The feedback employs several velocity sensors. Two probe configurations are evaluated: 5 and 11 velocity probes located at different points around the cylinder and in the wake. The control laws are optimized with Deep Reinforcement Learning (DRL) and Linear Genetic Programming Control (LGPC). By interacting with the unsteady wake, both methods successfully stabilize the vortex alley and effectively reduce drag while using small mass flow rates for the actuation. DRL has shown higher robustness with respect to different initial conditions and to noise contamination of the sensor data; on the other hand, LGPC is able to identify compact and interpretable control laws, which only use a subset of sensors, thus allowing for the reduction of the system complexity with reasonably good results. Our study points at directions of future machine-learning control combining desirable features of different approaches.

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Unsteady Pulsing of Cylinder Wakes

Cited by 16 publications

References 25 publications

On wake response to asymmetric blowing in spurts from a blunt trailing edge

On wake response to asymmetric blowing in spurts from a blunt trailing edge

Flow and aerodynamic noise control of a circular cylinder by local blowing

Machine-learning flow control with few sensor feedback and measurement noise

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