Biomimetic bluff body drag reduction by self-adaptive porous flaps

Mazellier, Nicolas; Feuvrier, Audrey; Kourta, Azeddine

doi:10.1016/j.crme.2011.11.006

Cited by 17 publications

(7 citation statements)

References 28 publications

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“…In the optimal regime, they observed a travelling wave through the array with a frequency that matched the vortex shedding frequency. Several other studies have also observed this travelling wave, and many report a lock-in at optimal conditions between the travelling wave frequency and the shedding frequency (Kunze & Brücker 2012;Venkataraman & Bottaro 2012;Mazellier et al 2012).…”

Section: Velocity Profile Vorticesmentioning

confidence: 76%

Dynamic interactions of multiple wall-mounted flexible flaps

O’Connor¹,

Revell²

2019

J. Fluid Mech.

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Coherent waving interactions between vegetation and fluid flows are known to emerge under conditions associated with the mixing layer instability. A similar waving motion has also been observed in flow control applications, where passive slender structures are used to augment bluff body wakes. While their existence is well reported, the mechanisms which govern this behaviour, and their dependence on structural properties, are not yet fully understood. This work investigates the coupled interactions of a large array of slender structures in an open-channel flow, via numerical simulation. A direct modelling approach, whereby the individual structures are fully resolved, is realised via a lattice Boltzmann-immersed boundary-finite element model. For steady flow conditions at low–moderate Reynolds number, the response of the array is measured over a range of mass ratio and bending rigidity, spanning two orders of magnitude, and the ensuing response is characterised. The results show a range of behaviours which are classified into distinct states: static, regular waving, irregular waving and flapping. The regular waving regime is found to occur when the natural frequency of the array approaches the estimated frequency of the mixing layer instability. Furthermore, after normalising with respect to the natural frequency of the array, the frequency response across the examined parameter space collapses onto a single curve. These findings indicate that the coherent waving mode is in fact a coupled instability, as opposed to a purely fluid-driven response, and that this specific regime is triggered by a lock-in between the fluid and structural natural frequencies.

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Section: Velocity Profile Vorticesmentioning

confidence: 76%

Dynamic interactions of multiple wall-mounted flexible flaps

O’Connor¹,

Revell²

2019

J. Fluid Mech.

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“…Taylor et al [17] and Allen and Smits [1] examined the potential use of a flexible splitter plate, which is made of a piezoelectric membrane, attached to a bluff body for generation of electricity from vortex-sheddinginduced vibration of the plate. Flexible membranes have been considered recently by Mazellier et al [11] to control the wake generated behind a square cylinder. In particular, their device consisting of a couple of flaps made from the combination of a rigid plastic skeleton coated with a porous fabric mimicking the shaft and the vane of the birds feathers, led to a net drag reduction of about 22 %.…”

Section: Introductionmentioning

confidence: 99%

The PELskin project: part IV—control of bluff body wakes using hairy filaments

et al. 2016

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The passive control of bluff body wakes using a sparse layer of elastic hairy filaments has been investigated via a series of numerical simulations and compared to selected experiments under well-controlled boundary conditions. It has been found that a distribution of filaments spaced half of the dominant three dimensional instability and resonating with the main shedding frequency can drastically delay the three dimensional transition of the wake behind a circular cylinder. It will also be shown that when using a pair of rows of filaments symmetrically spaced by an azimuthal angle, the wake topology can be deeply affected as well as the value of the integral force coefficients of the cylinder. In the most favourable case, a coupled three dimensional transition delay and strongly reduced values of the drag and of the lift fluctuation can be simultaneously achieved. These results hold also for higher Reynolds-number flows as shown in experiments on a cylinder with hairy flaps attached to the aft part. The lock-in effect of structural vibration of the flaps with the vortex shedding is assumed to be the reason for a sudden change in the shedding cycle as soon as the motion amplitude is high enough to modify the wake. In line with this hypothesis, it has been demonstrated that a long elastic filament pinned on the centerline of a forced spatially developing mixing layer can interact with the vortex dynamics delaying the pairing process-leading to a reduced thickness of the layer. These findings show that a properly designed fluid structure interaction can indeed lead to technological benefits in terms of wake control: drag reduction, vibration control and possibly palliation of aeroacoustic emissions.

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“…A large number of studies have been devoted to the aerodynamics over a bluff body such as cylinders, and rigid or flexible splitter plate in the wake of bluff bodies are known to control the vortex shedding (e.g., Akili et al, 2005;Shulka et al, 2013). Mazellier et al (2012) showed that the mean drag force applied on a square cylinder was reduced by feather-inspired porous plates fitted on the sides of the square cylinder. As shown in this study, the interaction between the fluid and flexible flaps may also reduce the fluctuations of aerodynamic forces applied to the bluff bodies.…”

Section: Discussion the Effect Of Flexible Flaps On Aerodynamic Performancementioning

confidence: 99%

Flexible Flaps Inspired by Avian Feathers Can Enhance Aerodynamic Robustness in low Reynolds Number Airfoils

Murayama

Nakata

2021

Front. Bioeng. Biotechnol.

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Unlike rigid rotors of drones, bird wings are composed of flexible feathers that can passively deform while achieving remarkable aerodynamic robustness in response to wind gusts. In this study, we conduct an experimental study on the effects of the flexible flaps inspired by the covert of bird wings on aerodynamic characteristics of fixed-wings in disturbances. Through force measurements and flow visualization in a low-speed wind tunnel, it is found that the flexible flaps can suppress the large-scale vortex shedding and hence reduce the fluctuations of aerodynamic forces in a disturbed flow behind an oscillating plate. Our results demonstrate that the stiffness of the flaps strongly affects the aerodynamic performance, and the force fluctuations are observed to be reduced when the deformation synchronizes with the strong vortex generation. The results point out that the simple attachment of the flexible flaps on the upper surface of the wing is an effective method, providing a novel biomimetic design to improve the aerodynamic robustness of small-scale drones with fixed-wings operating in unpredictable aerial environments.

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Biomimetic bluff body drag reduction by self-adaptive porous flaps

Cited by 17 publications

References 28 publications

Dynamic interactions of multiple wall-mounted flexible flaps

Dynamic interactions of multiple wall-mounted flexible flaps

The PELskin project: part IV—control of bluff body wakes using hairy filaments

Flexible Flaps Inspired by Avian Feathers Can Enhance Aerodynamic Robustness in low Reynolds Number Airfoils

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