Lift Enhancement at Low Reynolds Numbers Using Self-Activated Movable Flaps

Schlüter, Jörg

doi:10.2514/1.46425

Cited by 51 publications

(45 citation statements)

References 7 publications

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“…Thus, this feature of automatic activation, as opposed to active control techniques which require an energy input to come into action, provides industry with yet another reason to study ways to mimic this mechanism. Much experimental [11][12][13][14][15] as well as computational work [16][17][18] has been done simulating this behaviour and the results obtained indeed prove the effectiveness of a poro-elastic coating over a surface. For instance, a substantial drop in the mean drag, lift, and drag fluctuations, as well as a noteworthy increase in mean lift, has been observed.…”

Section: Introductionmentioning

confidence: 50%

Numerical modeling of flow control on a symmetric aerofoil via a porous, compliant coating

Venkataraman

Bottaro

2012

Physics of Fluids

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A passive actuation technique, that entails covering the suction side of an aerofoil with a poro-elastic carpet, is presented. Numerical modeling of the coupled fluid-structure interaction problem is performed for a low Reynolds number regime, characteristic of micro aerial vehicles. The immersed boundary technique is employed, which offers the advantage of using Cartesian grids for complex geometries. By suitably selecting the characteristics of the carpet, to synchronise characteristic time scales of the fluid and the structural systems, significant drag reduction and/or lift enhancement can be achieved, associated with modifications of the length scales of the shed vortices and a mild intensification of their intensity. A parametric analysis shows that such a coating is able to affect the topology of the flow in the proximity of the rear of the aerofoil, by adapting spontaneously to the separated flow.

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Section: Introductionmentioning

confidence: 50%

Numerical modeling of flow control on a symmetric aerofoil via a porous, compliant coating

Venkataraman

Bottaro

2012

Physics of Fluids

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“…With the aim of reproducing this effect, Schatz et al [21] have shown that a self-activated spanwise flap near the trailing edge of an aerofoil can enhance lift by more than at a Reynolds number of . In a similar experiment, Schluter [22] has also demonstrated that lift-breakdown is less severe when the flap is used. Wang and Schluter [24] have extended the analysis to a three dimensional wing basically confirming the aforementioned effects.…”

Section: Introductionmentioning

confidence: 99%

The PELskin project-part V: towards the control of the flow around aerofoils at high angle of attack using a self-activated deployable flap

et al. 2016

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During the flight of birds, it is often possible to notice that some of the primaries and covert feathers on the upper side of the wing pop-up under critical flight conditions, such as the landing approach or when stalking their prey (see Fig. 1) . It is often conjectured that the feathers pop up plays an aerodynamic role by limiting the spread of flow separation . A combined experimental and numerical study was conducted to shed some light on the physical mechanism determining the feathers self actuation and their effective role in controlling the flow field in nominally stalled conditions. In particular, we have considered a NACA0020 aerofoil, equipped with a flexible flap at low chord Reynolds numbers. A parametric study has been conducted on the effects of the length, natural frequency, and position of the flap. A configuration with a single flap hinged on the suction side at 70 % of the chord size c (from the leading edge), with a length of matching the shedding frequency of vortices at stall condition has been found to be optimum in delivering maximum aerodynamic efficiency and lift gains. Flow evolution both during a ramp-up motion (incidence angle from to with a reduced frequency of , being the free stream velocity magnitude), and at a static stalled condition () were analysed with and without the flap. A significant increase of the mean lift after a ramp-up manoeuvre is observed in presence of the flap. Stall dynamics (i.e., lift overshoot and oscillations) are altered and the simulations reveal a periodic re-generation cycle composed of a leading edge vortex that lift the flap during his passage, and an ejection generated by the relaxing of the flap in its equilibrium position. The flap movement in turns avoid the interaction between leading and trailing edge vortices when lift up and push the trailing edge vortex downstream when relaxing back. This cyclic behaviour is clearly shown by the periodic variation of the lift about the average value, and also from the periodic motion of the flap. A comparison with the experiments shows a similar but somewhat higher non-dimensional frequency of the flap oscillation. By assuming that the cycle frequency scales inversely with the boundary layer thickness, one can explain the higher frequencies observed in the experiments which were run at a Reynolds number about one order of magnitude higher than in the simulations. In addition, in experiments the periodic re-generation cycle decays after 3–4 periods ultimately leading to the full stall of the aerofoil. In contrast, the 2D simulations show that the cycle can become self-sustained without any decay when the flap parameters are accurately tuned.

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“…This phenomenon has been the subject of many research studies. Schlüter (2010) could show that by attaching rigid flaps, via a hinge, on the upper surface of the wing, the C L max is increased for a series of tested aerofoils (NACA 0012, NACA 4412, SD 8020). Schlüter also showed that the flaps bring the additional benefit of gradual stall rather than a more severe lift crisis.…”

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Upstream shear-layer stabilisation via self-oscillating trailing edge flaplets

Talboys

Brücker

2018

Exp Fluids

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This is the published version of the paper.This version of the publication may differ from the final published version. Permanent repository link AbstractThe flow around a symmetric aerofoil (NACA 0012) with an array of flexible flaplets attached to the trailing edge has been investigated at Reynolds numbers of 100,000-150,000 using high-speed time-resolved particle image velocimetry (HS TR-PIV) and motion tracking of the flaplets' tips. Particular attention has been made on the upstream effect on the boundary layer evolution along the suction side of the wing, at angles of attack of 0 • and 10• . For the plain aerofoil, without flaplets, the boundary layer on the second half of the aerofoil shows the formation of rollers as the shear-layer rolls-up in the fundamental instability mode (linear state). Proper orthogonal decomposition analysis shows that non-linear modes are also present, the most dominant being the pairing of successive rollers. When the flaplets are attached, it is shown that the flow-induced oscillations of the flaplets are able to create a lock-in effect that stabilises the linear state of the shear layer, whilst delaying or damping the growth of non-linear modes. It is hypothesised that the modified trailing edge is beneficial for reducing drag and can reduce aeroacoustic noise production in the lower frequency band, as indicated by an initial acoustic investigation. List of symbols

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Lift Enhancement at Low Reynolds Numbers Using Self-Activated Movable Flaps

Cited by 51 publications

References 7 publications

Numerical modeling of flow control on a symmetric aerofoil via a porous, compliant coating

Numerical modeling of flow control on a symmetric aerofoil via a porous, compliant coating

The PELskin project-part V: towards the control of the flow around aerofoils at high angle of attack using a self-activated deployable flap

Upstream shear-layer stabilisation via self-oscillating trailing edge flaplets

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