Investigation into clustering of synthetic jet actuators for flow separation control applications

Liddle, Stephen; Wood, N. J.

doi:10.1017/s0001924000000518

Cited by 18 publications

(13 citation statements)

References 9 publications

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“…They hypothesized that under this condition these two SJs are combined to form a stronger vortex structure. Liddle et al 14,15 investigated the effect of relative phase difference between the in-line twin SJs in a boundary layer using hot-wire measurements. The power spectral density (PSD) analysis of near-wall velocity in the mid-span plane reveals that the frequency corresponding to the major spectral peak coincides with the SJ operating frequency in most of the investigated cases, but at phase difference ∆φ = 270…”

Section: -2mentioning

confidence: 99%

Vortex dynamics of in-line twin synthetic jets in a laminar boundary layer

2015

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An experimental investigation is conducted on the vortices induced by twin synthetic jets (SJs) in line with a laminar boundary layer flow over a flat plate. The twin SJs operating at four different phase differences, i.e., Δϕ = 0°, 90°, 180°, and 270°, are visualized using a stereoscopic color dye visualization system and measured using a two-dimensional particle image velocimetry (PIV) system. It is found that depending on the phase difference of twin SJs, three types of vortex structures are produced. At Δϕ = 90°, the two hairpin vortices interact in a very constructive way in terms of the vortex size, strength, and celerity, forming one combined vortex. At Δϕ = 270°, the two individual hairpin vortices do not have much interaction, forming two completely separated hairpin vortices that behave like doubling the frequency of the single SJ case. At Δϕ = 0° and 180°, the two hairpin vortices produced by the twin SJ actuators are close enough, with the head of one hairpin vortex coupled with the legs of the other, forming partially interacting vortex structures. Quantitative analysis of the twin SJs is conducted, including the time histories of vortex circulation in the mid-span plane as well as a selected spanwise-wall-normal plane, and the influence of the twin SJs on the boundary layer flow filed. In addition, dynamic mode decomposition analysis of the PIV data is conducted to extract representative coherent structures. Through this study, a better understanding in the vortex dynamics associated with the interaction of in-line twin SJs in laminar boundary layers is achieved, which provides useful information for future SJ-array applications.

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Section: -2mentioning

confidence: 99%

Vortex dynamics of in-line twin synthetic jets in a laminar boundary layer

2015

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“…Zhong et al [14] considered the interaction of a round synthetic jet with a flat-plate laminar boundary layer, and the evolution of the jet vortices (stretching and penetration) for various Reynolds numbers, velocity ratios and formation frequencies. In a related investigation, Liddle & Wood [15] considered streamwise symmetric and asymmetric interactions of clusters of round synthetic jets with the boundary layer. Using flow visualization near the onset of separation on a two-dimensional circular cylinder, Jabbal & Zhong [16] concluded that jet-induced hairpin vortices and stretched vortex rings played a key role in delaying separation.…”

Section: Synthetic-jet Flow Controlmentioning

confidence: 99%

Some aspects of aerodynamic flow control using synthetic-jet actuation

Glezer

2011

Phil. Trans. R. Soc. A.

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Aerodynamic flow control effected by interactions of surface-mounted synthetic (zero net mass flux) jet actuators with a local cross flow is reviewed. These jets are formed by the advection and interactions of trains of discrete vortical structures that are formed entirely from the fluid of the embedding flow system, and thus transfer momentum to the cross flow without net mass injection across the flow boundary. Traditional approaches to active flow control have focused, to a large extent, on control of separation on stalled aerofoils by means of quasi-steady actuation within two distinct regimes that are characterized by the actuation time scales. When the characteristic actuation period is commensurate with the time scale of the inherent instabilities of the base flow, the jets can effect significant quasi-steady global modifications on spatial scales that are one to two orders of magnitude larger than the scale of the jets. However, when the actuation frequency is sufficiently high to be decoupled from global instabilities of the base flow, changes in the aerodynamic forces are attained by leveraging the generation and regulation of 'trapped' vorticity concentrations near the surface to alter its aerodynamic shape. Some examples of the utility of this approach for aerodynamic flow control of separated flows on bluff bodies and fully attached flows on lifting surfaces are also discussed.

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“…Under these assumptions, then, we would expect the calculated orifice flow to be fairly close to fully developed. This implies that the factor λ, appearing in the definition (12) of and introduced in Eq. (6) to correct for the effects of the developing pipe flow in the entry region, will be close to the fully developed value of 1.…”

Section: Resultsmentioning

confidence: 99%

“…A popular generic model of many micro-jet actuators currently being studied for flow-control applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] is depicted in Fig. 1.…”

Section: Introductionmentioning

confidence: 99%

“…This reduces the volume of the cavity, thereby raising the pressure, which then drives a jet through the exit orifice into the boundary layer. If an oscillating electric field is applied to the driver the diaphragm oscillates up and down thereby producing a synthetic jet [1][2][3][4][5][6][7][8][9][10][11][12][13][14]18]. Alternatively if a unidirectional electric field is applied the diaphragm only deflects upwards to produce a kind of pulse jet [15][16][17]; we will follow [16] and call this mode of operation a pressurejump actuator.…”

Section: Introductionmentioning

confidence: 99%

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Is Helmholtz Resonance a Problem for Micro-jet Actuators?

Lockerby

Carpenter

Davies

2007

Flow Turbulence Combust

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A theoretical analysis is described that determines the conditions for Helmholtz resonance for a popular class of self-contained microjet actuator used in both synthetic-and pressure-jump (pulse-jet) mode. It was previously shown that the conditions for Helmholtz resonance are identical to those for optimizing actuator performance for maximum mass flux. The methodology is described for numerical-simulation studies on how Helmholtz resonance affects the interaction of active and nominally inactive micro-jet actuators with a laminar boundary layer. Two sets of numerical simulations were carried out. The first set models the interaction of an active actuator with the boundary layer. These simulations confirm that our criterion for Helmholtz resonance is broadly correct. When it is satisfied we find that the actuator cannot be treated as a predetermined wall boundary condition because the interaction with the boundary layer changes the pressure difference across the exit orifice thereby affecting the outflow from the actuator. We further show that strong inflow cannot be avoided even when the actuator is used in pressurejump mode. In the second set of simulations two-dimensional Tollmien-Schlichting waves, with frequency comparable with, but not particularly close to, the Helmholtz resonant frequency, are incident on a nominally inactive micro-jet actuator. The simulations show that under these circumstances the actuators act as strong sources of 3D Tollmien-Schlichting waves. It is surmised that in the real-life aeronautical applications with turbulent boundary layers broadband disturbances of the pressure field, including acoustic waves, would cause nominally inactive actuators, possibly including pulsed jets, to act as strong disturbance sources. Should this be true it Flow Turbulence Combust (2007) 78:205-222 would probably be disastrous for engineering applications of such massless microjet actuators for flow control.

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Investigation into clustering of synthetic jet actuators for flow separation control applications

Cited by 18 publications

References 9 publications

Vortex dynamics of in-line twin synthetic jets in a laminar boundary layer

Vortex dynamics of in-line twin synthetic jets in a laminar boundary layer

Some aspects of aerodynamic flow control using synthetic-jet actuation

Is Helmholtz Resonance a Problem for Micro-jet Actuators?

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