The scales of the leading-edge separation bubble

Smith, James; Pisetta, Gabriele; Viola, Ignazio Maria

doi:10.1063/5.0045204

Cited by 11 publications

(10 citation statements)

References 38 publications

(57 reference statements)

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“…For example, on plane D at , the streamwise velocity of the LEVs is, on average, . This is in agreement with the findings of Siala and Liburdy (2019), Ōtomo, Henne, Mulleners, Ramesh, and Viola (2020) and Smith et al. (2021), who found that the LEV convects downstream at approximately the mean shear layer velocity.…”

Section: Resultssupporting

confidence: 89%

“…For example, on plane D at 𝜂 = 0 • , the streamwise velocity of the LEVs is, on average, 0.53U ∞ . This is in agreement with the findings of Siala and Liburdy (2019), Ōtomo, Henne, Mulleners, Ramesh, and Viola (2020) and Smith et al (2021), who found that the LEV convects downstream at approximately the mean shear layer velocity. In fact, assuming that the external shear layer velocity is approximately U ∞ , and the internal flow is approximately stagnant, the mean shear layer velocity is U ∞ /2.…”

Section: E8-11supporting

confidence: 93%

“…At the conditions tested in this study, the flow is fully separated at the sharp leading edge, and thus the effect of a lower is expected to be moderate. The separation point is fixed, and laminar to turbulent transition occurs almost immediately downstream of the separation point (Crompton & Barrett, 2000; Smith, Pisetta, & Viola, 2021). The vortex sheet roll-up is -dependent and the range of turbulent scales increases with (Ho & Huerre, 1984).…”

Section: Introductionmentioning

confidence: 99%

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Vortex flow of downwind sails

Arredondo-Galeana

Babinsky²,

Viola³

2023

Flow

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This paper sets out to investigate the vortex flow of spinnaker yacht sails, which are low-aspect-ratio highly cambered wings used to sail downwind. We tested three model-scale sails with the same sections but different twists over a range of angles of attack in a water tunnel at a Reynolds number of 21 000. We measured the forces with a balance and the velocity field with particle image velocimetry. The sails experience massively separated three-dimensional flow and leading-edge vortices convect at half of the free-stream velocity in a turbulent shear layer. Despite the massive flow separation, the twist of the sail does not change the lift curve slope, in agreement with strip theory. As the angle of attack and the twist vary, flow reattachment might occur in the time-average sense, but this does not necessarily result in a higher lift to drag ratio as the vorticity field is marginally affected. Finally, we investigated the effect of secondary vorticity, vortex stretching and diffusion on the vorticity fluxes. Overall, these results provide new insights into the vortex flow and associated force generation mechanism of wings with massively separated flow.

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Section: Resultssupporting

confidence: 89%

Section: E8-11supporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

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Vortex flow of downwind sails

Arredondo-Galeana

Babinsky²,

Viola³

2023

Flow

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“…For small α, Kutta-Joukowski theory for thin airfoils predicts that the centre of lift is a constant independent of α and is located at a point one quarter of the chord length ahead of the CoV (Anderson 2010). We thus include a constant term as well as one that quadratically decreases with α, the latter yielding a better fit to our experimental measurements and which may reflect the pressure redistribution due to flow reattachment on the upper surface of the plate at low α (Smith, Pisetta & Viola 2021). At larger α for which fully separated flow can be expected, free streamline theory predicts that the centre of pressure moves towards the middle of the plate as α → π/2 and does so approximately linearly (Wu 1955;Lamb 1993;Sefat & Fernandes 2011).…”

Section: Aerodynamic Coefficients and Parameters In The Modelmentioning

confidence: 99%

Centre of mass location, flight modes, stability and dynamic modelling of gliders

Goodwill

Wang

et al. 2022

J. Fluid Mech.

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Falling paper flutters and tumbles through air, whereas a paper airplane glides smoothly if its leading edge is appropriately weighted. We investigate this transformation from ‘plain paper’ to ‘paper plane’ through experiments, aerodynamic modelling and free flight simulations of thin plates with differing centre of mass (CoM) locations. Periodic modes such as fluttering, tumbling and bounding give way to steady gliding and then downward diving as the CoM is increasingly displaced towards one edge. To explain these observations, we formulate a quasi-steady aerodynamic model whose force and torque coefficients are informed by experimental measurements. The dependencies on angle of attack reflect the transition from attached to separated flow and a dynamic centre of pressure, effects that prove critical to reproducing the observed motions of paper planes in air and plates in water. Because the model successfully accounts for unsteady and steady flight modes, it may be usefully applied to further problems involving actuated motions, feedback control and interactions with ambient flows.

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“…Flow separation on lifting surfaces such as wings, fins, and blades, is often an undesirable phenomena that occurs when the boundary layer of a fluid flowing over a solid surface loses momentum due to an adverse pressure gradient and hence, the streamlines no longer follow the solid contour [1]. When laminar to turbulent transition occurs, at moderate Reynolds numbers, the flow reattaches after separation, forming a short laminar separation bubble (LSB) on the suction side of the foil [2][3][4][5]. Contrarily, if the adverse pressure gradient is too high such as at a high angle of attack, the flow remains separated [6,7].…”

Section: Introductionmentioning

confidence: 99%

A Low Cost Oscillating Membrane for Underwater Applications at Low Reynolds Numbers

Arredondo-Galeana

Kiprakis

Viola

2022

JMSE

Self Cite

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Active surface morphing is a nonintrusive flow control technique that can delay separation in laminar and turbulent boundary layers. Most of the experimental studies of such control strategy have been carried out in wind tunnels at low Reynolds numbers with costly actuators. In contrast, the implementation of such a control strategy at low cost for an underwater environment remains vastly unexplored. This paper explores active surface morphing at low cost and at low Reynolds for underwater applications. We do this with a 3D printed foil submerged in a water tunnel. The suction surface of the foil is covered with a magnetoelastic membrane. The membrane is actuated via two electromagnets that are positioned inside of the foil. Three actuation frequencies (slow, intermediate, fast) are tested and the deformation of the membrane is measured with an optosensor. We show that lift increases by 1%, whilst drag decreases by 6% at a Strouhal number of 0.3, i.e., at the fast actuation case. We demonstrate that surface actuation is applicable to the marine environment through an off the shelf approach, and that this method is more economical than existing active surface morphing technologies. Since the actuation mechanism is not energy intensive, it is envisioned that it could be applied to marine energy devices, boat appendages, and autonomous underwater vehicles.

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The scales of the leading-edge separation bubble

Abstract: The scales of the leading-edge separation bubble

Cited by 11 publications

References 38 publications

Vortex flow of downwind sails

Vortex flow of downwind sails

Centre of mass location, flight modes, stability and dynamic modelling of gliders

A Low Cost Oscillating Membrane for Underwater Applications at Low Reynolds Numbers

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