Unsteady pulsing of cylinder wakes

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

doi:10.2514/6.1988-3532

Cited by 12 publications

(8 citation statements)

References 2 publications

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“…The pulsating jet adds net momentum to the flow by the second-order streaming effect, without adding any mass to the flow. Williams and Amato [45] demonstrated the suppression of the vortex shedding (at Re = 370) by producing unsteady pulsing at the trailing edge or base of the cylinder through a small slit, spanning the length of the cylinder. They found that the region of re-circulating flow decreased behind the cylinder as the forcing was increased.…”

Section: Flow Around Circular Cylindermentioning

confidence: 99%

Plasma Actuators for Bluff Body Flow Control

Козлов

2006

3rd AIAA Flow Control Conference

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The aerodynamic plasma actuators have shown to be efficient flow control devices in various applications. In this study the results of flow control experiments utilizing single dielectric barrier discharge plasma actuators to control flow separation and unsteady vortex shedding from a circular cylinder in cross-flow are reported. This work is motivated by the need to reduce landing gear noise for commercial transport aircraft via an effective streamlining created by the actuators. The experiments are performed at Re D = 30,000. Using either steady or unsteady actuation, Karman shedding is totally eliminated, turbulence levels in the wake decrease significantly and near-field sound pressure levels are reduced by 13.3 dB. Unsteady actuation at an excitation frequency of St D = 1 is found to be most effective. The unsteady actuation also has the advantage that total suppression of shedding is achieved for a duty cycle of only 25%. However, since unsteady actuation is associated with an unsteady body force and produces a tone at the actuation frequency, steady actuation is more suitable for noise control applications. In addition, plasma actuator optimization study is performed to improve the flow control efficiency and to reach higher Reynolds number. This part of the research is intended to maximize the body force produced by plasma discharge (steady and unsteady) which is a function of various parameters such as dielectric material, size of electrodes, their overlap, frequency, voltage, etc. Detailed experiments are performed in a controlled environment with no-external-flow condition with several different dielectric materials of various thicknesses. Plasma induced velocity (using glass Pitot probe), body force (using high precision weighing scale), and power dissipation are measured at various voltages and frequencies. Optimal voltage waveform and frequency has been found which resulted in time averaged maximum induced velocity and body force. This has resulted in an order of magnitude improvement of the actuator effect.

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Section: Flow Around Circular Cylindermentioning

confidence: 99%

Plasma Actuators for Bluff Body Flow Control

Козлов

2006

3rd AIAA Flow Control Conference

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“…Free-shear flows originate from some kind of surface upstream be it a nozzle, a moving body or a splitter plate, and flow control devices can therefore be placed on the corresponding walls albeit far from the fully-developed regions. Examples of such control include changing of the geometry of a jet exit from circular to elliptic (Gutmark and Ho, 1986), using periodic suction/injection in the lee side of a blunt body to affect its wake (Williams and Amato, 1989), and vibrating the splitter plate of a mixing layer (Fiedler et al, 1988). These and other techniques are extensively reviewed by Fiedler and Fernholz (1990), who offer a comprehensive list of appropriate references, and more recently by Gutmark et al (1995) and Viswanath (1995).…”

Section: Wall-bounded and Free-shear Flowsmentioning

confidence: 99%

Modern Developments in Flow Control

Gad‐el‐Hak

1996

Applied Mechanics Reviews

266

114

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This brief article reviews the important advances in the field of flow control that took place during the past few years. This broad area of research remains of great interest for its numerous potential benefits for both the military and civilian sectors. Spurred by the recent developments in chaos control, microfabrication and neural networks, reactive control of turbulent flows is now in the realm of the possible for future practical devices. Other less complex control schemes, passive as well as active, are more market ready and are also witnessing resurgence of interest.

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“…He was also able to use the microphone as the sensor for the feedback; this enabled the sound field to be even further reduced, although the vortex street as detected by the hot wire was less attenuated than before. (Williams & Amato 1989 used similar actuation a t a Reynolds number of 370 to reduce the wake momentum deficit and also observed that the vortex street was suppressed ; their control was open loop in that they did not use feedback.) This paper describes experiments performed both in air and water.…”

Section: Introductionmentioning

confidence: 99%

Feedback control of vortex shedding at low Reynolds numbers

1993

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This paper describes experiments undertaken to study in detail the control of vortex shedding from circular cylinders at low Reynolds numbers by using feedback to stabilize the wake instability. Experiments have been performed both in a wind tunnel and in an open water channel with flow visualization. It has been found that feedback control is able to delay the onset of the wake instability, rendering the wake stable at Reynolds numbers about 20% higher than otherwise. At higher flow rates, however, it was not possible to use single-channel feedback to stabilize the wake - although, deceptively, it was possible to reduce the unsteadiness recorded by a near-wake sensor. When control is applied to a long span only the region near the control sensor is controlled. The results presented in this paper generally support the analytical results of other researchers.

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Unsteady pulsing of cylinder wakes

Cited by 12 publications

References 2 publications

Plasma Actuators for Bluff Body Flow Control

Plasma Actuators for Bluff Body Flow Control

Modern Developments in Flow Control

Feedback control of vortex shedding at low Reynolds numbers

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