Vortex formation of a finite-span synthetic jet: effect of rectangular orifice geometry

Buren, Tyler Van; Whalen, Edward A.; Amitay, Michael

doi:10.1017/jfm.2014.77

Cited by 73 publications

(40 citation statements)

References 31 publications

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“…It should be noted that both figures 7a and 7b show that the direction of the vortex trajectories is determined within roughly r/d = 5, with r (m) being the absolute distance of the vortex from the origin. This is within the near-field range of r/d < AR/2 as determined by Van Buren et al (2014) where the behaviour of the jet can be considered to be two-dimensional (at least in the central plane).…”

Section: Dependency Of Vectoring Behaviour On Strouhal Numbersupporting

confidence: 54%

“…For finite aspect ratio jets, edge effects and three-dimensional jet development play a role. However, results obtained by Van Buren et al (2014) for aspect ratios of AR = 6-18, indicate that edge effects do not reach the central plane up to a distance of approximately y/d < AR/2. In the present research a near-field up to this distance is defined within which three-dimensional effects on the flow in the central plane are assumed negligible.…”

Section: Introductionmentioning

confidence: 92%

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Vectoring of parallel synthetic jets: a parametric study

2016

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The vectoring of a pair of parallel synthetic jets can be described using five dimensionless parameters: the aspect ratio of the slots, the Strouhal number, the Reynolds number, the phase difference between the jets and the spacing between the slots. In the present study, the influence of the latter four on the vectoring behaviour of the jets is examined experimentally, using particle image velocimetry. Time-averaged velocity maps are used to give a qualitative description of the variations in vectoring for a parametric sweep of each of the four parameters independently. A diverse set of vectoring behaviour is observed in which the resulting jet can be merged or bifurcated and either vectored towards the actuator leading in phase or the actuator lagging in phase. Three performance metrics are defined to give a quantitative description of the vectoring behaviour: the included angle between bifurcated branches, the vectoring angle of the total flow and the normalized momentum flux of the flow. Using these metrics, the influence of changes in the Strouhal number, Reynolds number, phase difference and spacing are quantified. Phase-locked maps of the swirling strength are used to track vortex pairs. Vortex trajectories are used to define three Strouhal number regimes for the vectoring behaviour. In the first regime, vectoring behaviour is dominated by the pinch-off time, which is written as function of Strouhal number only. In the second regime, the pinch-off time is invariant and the vectoring behaviour slightly changes with Strouhal number. In the third regime, given by the formation criterion, no synthetic jet is formed. Vortex positions at a single phase, shortly after creation of the lagging vortex pair, are used to propose a vectoring mechanism. This vectoring mechanism explains the observed qualitative and quantitative variations for all four parameters.

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Section: Dependency Of Vectoring Behaviour On Strouhal Numbersupporting

confidence: 54%

Section: Introductionmentioning

confidence: 92%

Vectoring of parallel synthetic jets: a parametric study

2016

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“…Similar flow reversal was reported for a synthetic jet in a cross flow over a flat plate. 41 Furthermore, at α = 15.5 • , the flow has reattached (compared to the baseline flow, see Figure 7) in the vicinity of the jet for both blowing ratios. As previously indicated in Figure 7, the baseline flow is separated in the vicinity of the jet, reattaching farther outboard and downstream.…”

Section: B Time-averaged Actuated Flow Fieldmentioning

confidence: 83%

“…Similarly, Van Buren et al 40,41 performed a fundamental experimental investigation on the effect of different orifice geometries and input parameters on the flow structures associated with a low aspect ratio (AR = 6, 12, and 18) finite-span synthetic jet. Utilizing stereoscopic particle image velocimetry (SPIV), they were able to show the evolution of vortex rings (and the formation of secondary flow structures) issued in quiescent conditions.…”

Section: Introductionmentioning

confidence: 99%

Interaction of a finite-span synthetic jet near the tip of a sweptback wing

Vasile

Amitay

2015

Physics of Fluids

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An experimental investigation was performed to study the three-dimensional flow interaction of a finite-span (aspect ratio of 18) synthetic jet located near the tip of a sweptback wing (cross-sectional profile of NACA 4421, aspect ratio of 4, and sweep angle of 30°) at a Reynolds number of 105 and at three angles of attack of 0°, 9°, and 15.5° (covering the range of attached to separated flow in the vicinity of the synthetic jet). Three blowing ratios were considered as 0.8, 1.2, and 2. Stereoscopic particle image velocimetry data were collected at multiple 2-D planes in the vicinity of the jet’s orifice, which were then used to reconstruct the flow volume, and the effect of the jet’s blowing ratio was analyzed using time-averaged and phase-averaged statistics. The study showed that the flow field in the vicinity of the synthetic jet orifice becomes highly three-dimensional and is governed by the streamwise structures that are associated with the finite span of the orifice (edge vortices). Furthermore, it was demonstrated that the baseline flow field that develops over a swept-back configuration (characterized by spanwise and streamwise vorticity components) is responsible for the immediate breakdown of the coherent structures that are introduced by the synthetic jet orifice and for the formation of the secondary flow structures that were seen in the time-averaged flow field. Moreover, the presence of a tip vortex results in the development of a non-uniform (in the spanwise direction) spanwise boundary layer that becomes more pronounced with increasing angle of attack. Consequently, the development of the flow structures is altered. Finally, the present work suggests that the location of the synthetic jet along the span is not as important (as the angle of attack and the blowing ratio) in the overall formation and evolution of the flow structures issued from the jet. However, the size and strength of these structures are affected by the jet’s spanwise location.

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“…The injection of momentum and vorticity into the flow results in a delay of flow separation . A further description of the mechanisms by which synthetic jets add momentum and vorticity into the flow is detailed in Glezer and Amitay and Van Buren et al . Generally, the strength of an array of synthetic jets is described by the momentum coefficient C μ , which is the ratio of momentum injected during the outsroke of the synthetic jet to the momentum of flow over the airfoil, given by

C_{μ} = \frac{n \overset{I_{j}}{true}}{\frac{1}{2} ρ_{\infty} U_{\infty}^{2} S},

where n is the number of synthetic jets and

\overset{I_{j}}{true}

is the time averaged synthetic jet momentum during outsroke and can be written as

\overset{I_{j}}{true} = \frac{1}{τ} ρ A_{s j} true \int_{0}^{τ} u_{s j}^{2} false(t false) d t .

…”

Section: Introductionmentioning

confidence: 99%

Quantification of the S817 airfoil aerodynamic properties and their control using synthetic jet actuators

2018

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Wind tunnel experiments were conducted at Rensselaer Polytechnic Institute's Center for Flow Physics and Control's subsonic wind tunnel, which experimentally quantified the aerodynamic performance of the S817 airfoil. This study has two main thrusts: Experimentally evaluate common aerodynamic properties of the S817 airfoil, and develop flow control strategies using continuously actuated and pulse‐modulated synthetic jets for future field testing to show the reduction of unsteady loading and increased aerodynamic performance. Quasi‐2D and finite span 3D configurations were utilized, where integrated aerodynamic loading, surface pressure, and stereoscopic particle image velocimetry data were collected to quantify the overall aerodynamic performance and stall characteristics of this airfoil. Experiments showed that synthetic jets, located at x/c=0.35 and angled at 45° with respect to the surface, increased the lift curve slope by 3.8%, the maximum lift coefficient by 10.5%, increased the L/D by as much as 39% at high angles of attack and delayed the stall angle of attack by 3°. Global particle image velocimetry measurements quantified the flowfield and showed flow reattachment could be achieved at various angles of attack using flow control where the flow would otherwise be separated. Near field measurements of the synthetic jet orifice yielded insight as to how synthetic jets interact with the cross‐flow in the time‐ and phase‐averaged sense. For very high angles of attack, a pulsed modulation technique was implemented, demonstrating flow reattachment in scenarios where a sinusoidal synthetic jet actuation scheme was unable to reattach the flow, with the benefit of achieving this with lower energy consumption compared with sinusoidal actuation.

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Vortex formation of a finite-span synthetic jet: effect of rectangular orifice geometry

Cited by 73 publications

References 31 publications

Vectoring of parallel synthetic jets: a parametric study

Vectoring of parallel synthetic jets: a parametric study

Interaction of a finite-span synthetic jet near the tip of a sweptback wing

Quantification of the S817 airfoil aerodynamic properties and their control using synthetic jet actuators

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