Effect of spanwise confinement on flag flutter: Experimental measurements

Doaré, Olivier; Mano, David; Ludena, Juan Carlos Bilbao

doi:10.1063/1.3662127

Cited by 17 publications

(25 citation statements)

References 18 publications

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“…They found a significant 3D effect on the vortical structures for smaller span, and its stabilizing influence through a reduction of the pressure difference across the flag. Doare, Mano & Ludena (2011) show that a 2D model always underestimates the critical velocity relative to 3D experimental data. By bounding the flexible plate between two spanwise walls, they are able to quantify the difference due to 3D spanwise effects.…”

Section: Introductionmentioning

confidence: 91%

Three-dimensional effects on flag flapping dynamics

2015

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We examine three-dimensional (3D) effects on the flapping dynamics of a flag, modelled as a thin membrane, in uniform fluid inflow. We consider periodic spanwise variations of length S (ignoring edge effects), so that the 3D effects are characterized by the dimensionless spanwise wavelength γ = S/L, where L is the chord length. We perform linear stability analysis (LSA) to show increase in stability with γ , with the purely 2D mode being the most unstable. To confirm the LSA and to study nonlinear responses of 3D flapping, we obtain direct numerical simulations, up to Reynolds number 1000 based on L, coupling solvers for the Navier-Stokes equations and that for a thin membrane structure undergoing arbitrarily large displacement. For nonlinear flapping evolution, we identify and characterize the effect of γ on the distinct flag motions and wake vortex structures, corresponding to spanwise standing wave (SW) and travelling wave (TW) modes, in the absence and presence of cross-flow respectively. For both SW and TW, the response is characterized by an initial instability growth phase (I), followed by a nonlinear development phase (II) consisting of multiple unstable 3D modes, and tending, in long time, towards a quasi-steady limit-cycle response (III) dominated by a single (most unstable) mode. Phase I follows closely the predictions of LSA for initial instability and growth rates, with the latter increased for TW due to suppression of restoring forces by the cross-flow. Phase II is characterized by multiple competing flapping modes with energy cascading towards the more unstable mode(s). The wake is characterized by interwoven (SW) and oblique continuous (TW) shed vortices. For phase III, the persistent single dominant mode for SW is the (most unstable) 2D flag displacement with a continuous parallel wake structure; and for TW, the fundamental oblique travelling-wave flag displacement corresponding to the given γ with continuous oblique shedding. The transition to phase III occurs slower for greater γ . For the total forces, drag decreases for both SW and TW with decreasing γ , while lift is negligible in phase I and II and comparable in magnitude to drag in phase III for any γ .

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Section: Introductionmentioning

confidence: 91%

Three-dimensional effects on flag flapping dynamics

2015

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“…The objective of covering only one third of the width of the plate with piezoelectric film is to reduce the impact of the sectioning process on the global rigidity of the plate. For each experiment and a given electrode length and position, the experimental procedure is as follows : the piezoelectric plate is placed in a wind tunnel of rectangular transversal section 10 cm wide and 5 cm high with transparent walls that allow visual access from the outside [40]. The negative electrodes of the piezoelectric films are shunted while a resistance R is connected between the positive electrodes (see figure 3-d).…”

Section: Optimization Of the Electrodes' Positionmentioning

confidence: 99%

Influence and optimization of the electrodes position in a piezoelectric energy harvesting flag

Piñeirúa

Doaré

Michelin

2015

Journal of Sound and Vibration

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International audienceFluttering piezoelectric plates may harvest energy from a fluid flow by converting the plate's mechanical deformation into electric energy in an output circuit. This work focuses on the influence of the arrangement of the piezoelectric electrodes along the plate's surface on the energy harvesting efficiency of the system, using a combination of experiments and numerical simulations. A weakly non-linear model of a plate in axial flow, equipped with a discrete number of piezoelectric patches is derived and confronted to experimental results. Numerical simulations are then used to optimize the position and dimensions of the piezoelectric electrodes. These optimal configurations can be understood physically in the limit of small and large electromechanical coupling

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“…These studies report a strong correlation between the distance of the plate to the channel walls and the dynamics of the plate. The three-dimensional effects of confinement in the spanwise direction have been studied experimentally (Doaré, Mano & Ludena 2011a) and also analytically (Doaré, Sauzade & Eloy 2011b) and it has been concluded that the reduction in the gap between the plate and the walls in the spanwise direction has a destabilizing effect on the dynamics of the system, especially for plates with larger inertia. Finally, Auregan & Depollier (1995) used a quasi-static frictionless fluid model to study a similar problem of aeroelastic instability of the human soft palate and provided an explanation for the occurrence of snoring.…”

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confidence: 98%

Flutter instability of a thin flexible plate in a channel

Shoele

Mittal

2015

J. Fluid Mech.

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The stability of a thin flexible plate confined inside an inviscid two-dimensional channel is examined using a nonlinear eigenvalue analysis method. A new Green's function for the vortex wake of the flexible plate inside the channel, as well as its rapidly convergent series approximation, is proposed. Comparison with a fully coupled Navier-Stokes fluid-structure interaction model indicates that the current inviscid model successfully predicts the flutter boundary for a confined flexible plate. The analysis also shows that confinement has a destabilizing effect on heavy plates. Furthermore, as the confinement is increased, the oscillating frequency of the plate increases and new peaks appear in its stability curve. Asymmetric placement of the plate within the channel, especially when the plate is very close to one wall, also modifies the stability curve of the system by shifting the mode transition points toward smaller fluid-to-plate inertia ratios. Our study suggests that the degree of confinement and asymmetric placement of the plate in the channel could be used to alter the flutter instability of the plate, and to adjust the frequency of flutter.

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Effect of spanwise confinement on flag flutter: Experimental measurements

Cited by 17 publications

References 18 publications

Three-dimensional effects on flag flapping dynamics

Three-dimensional effects on flag flapping dynamics

Influence and optimization of the electrodes position in a piezoelectric energy harvesting flag

Flutter instability of a thin flexible plate in a channel

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