Flow control of a sharp-edged airfoil

Miranda, Sérgio; Telionis, Demetri P.; Zeiger, Matthew

doi:10.2514/6.2001-119

Cited by 8 publications

(4 citation statements)

References 5 publications

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“…An extensive survey of the literature in this area reveals that only Wu et al (1998) have considered both f SL and f wake in their studies. In contrast, other studies of post-stall separation control account for f wake but do not consider f SL ( 2001; Miranda, Telionis & Zeiger 2001;Chen & Beeler 2002). Finally, a majority of studies that have examined massively separated flow past airfoils with deflected flaps (e.g.…”

Section: Constituents Of a Separated Airfoil Flowmentioning

confidence: 89%

“…The scaling for Kármán vortex shedding due to Roshko (1954) is f wake ∼ U ∞ /W wake , where W wake is the characteristic width of the wake, and this scaling is fundamentally different from that of f sep . In many studies (Wu et al 1998;Miranda et al 2001), W wake is assumed to be equal to c sin(α) where c is the airfoil chord length and α is the angle of attack. In cases where the separation extends over a significant portion of the airfoil (or a flap), it has been customary to assume L sep = c (Bar-Sever 1989; Seifert et al 1993;Ravindran 1999;Wygnanski 2000;Darabi & Wygnanski 2002;Funk et al 2002;Postl et al 2004), but this might significantly overestimate the correct length scale in cases where the wake vortex shedding dominates the dynamics.…”

Section: Scaling Of Characteristic Frequenciesmentioning

confidence: 99%

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Nonlinear dynamics and synthetic-jet-based control of a canonical separated flow

et al. 2010

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A novel flow configuration devised for investigation of active control of separated airfoil flows using synthetic jets is presented. The configuration consists of a flat plate, with an elliptic leading edge and a blunt trailing edge, at zero incidence in a free stream. Flow separation is induced on the upper surface of the airfoil at the aft-chord location by applying suction and blowing on the top boundary of the computational domain. Typical separated airfoil flows are generally characterized by at least three distinct frequency scales corresponding to the shear layer instability, the unsteadiness of the separated region and the vortex shedding in the wake, and all these features are present in the current flow. Two-dimensional Navier-Stokes simulations of this flow at a chord Reynolds number of 6 104 have been carried out to examine the nonlinear dynamics in this flow and its implications for synthetic-jet-based separation control. The results show that there is a strong nonlinear coupling between the various features of the flow, and that the uncontrolled as well as the forced flow is characterized by a variety of lock-on states that result from this nonlinear coupling. The most effective separation control is found to occur at the highest forcing frequency for which both the shear layer and the separated region lock on to the forcing frequency. The effects of the Reynolds number on the scaling of the characteristic frequencies of the separated flow and its subsequent control are studied by repeating some of the simulations at a higher Reynolds number of 1 105. © 2010 Cambridge University Press

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Section: Constituents Of a Separated Airfoil Flowmentioning

confidence: 89%

Section: Scaling Of Characteristic Frequenciesmentioning

confidence: 99%

Nonlinear dynamics and synthetic-jet-based control of a canonical separated flow

et al. 2010

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“…where f is the vortex-shedding frequency and L′ is a characteristic length, defined as the projection of the model perpendicular to the freestream (Miranda, 2005) (Fig. 8A).…”

Section: Aerodynamic Force Measurementsmentioning

confidence: 99%

Aerodynamics of the flying snake Chrysopelea paradisi: how a bluff body cross-sectional shape contributes to gliding performance

Holden

Socha

Cardwell

et al. 2014

Journal of Experimental Biology

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A prominent feature of gliding flight in snakes of the genus Chrysopelea is the unique cross-sectional shape of the body, which acts as the lifting surface in the absence of wings. When gliding, the flying snake Chrysopelea paradisi morphs its circular cross-section into a triangular shape by splaying its ribs and flattening its body in the dorsoventral axis, forming a geometry with fore-aft symmetry and a thick profile. Here, we aimed to understand the aerodynamic properties of the snake's cross-sectional shape to determine its contribution to gliding at low Reynolds numbers. We used a straight physical model in a water tunnel to isolate the effects of 2D shape, analogously to studying the profile of an airfoil of a more typical flyer. Force measurements and time-resolved (TR) digital particle image velocimetry (DPIV) were used to determine lift and drag coefficients, wake dynamics and vortexshedding characteristics of the shape across a behaviorally relevant range of Reynolds numbers and angles of attack. The snake's crosssectional shape produced a maximum lift coefficient of 1.9 and maximum lift-to-drag ratio of 2.7, maintained increases in lift up to 35 deg, and exhibited two distinctly different vortex-shedding modes. Within the measured Reynolds number regime (Re=3000-15,000), this geometry generated significantly larger maximum lift coefficients than many other shapes including bluff bodies, thick airfoils, symmetric airfoils and circular arc airfoils. In addition, the snake's shape exhibited a gentle stall region that maintained relatively high lift production even up to the highest angle of attack tested (60 deg). Overall, the crosssectional geometry of the flying snake demonstrated robust aerodynamic behavior by maintaining significant lift production and near-maximum lift-to-drag ratios over a wide range of parameters. These aerodynamic characteristics help to explain how the snake can glide at steep angles and over a wide range of angles of attack, but more complex models that account for 3D effects and the dynamic movements of aerial undulation are required to fully understand the gliding performance of flying snakes.

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“…Since the change in structural resonance from benchtop measurements is larger than the change in shedding frequency as given in Table 2, this suggests that the membrane's first resonance mode may not be excited by the fluid. It has been speculated by other work that the shedding frequency will lock on to the natural resonant frequency of the membrane (Miranda et al, 2005;Rojratsirikul et al, 2010;Scott et al, 2012;Timpe et al, 2013). This is due to the larger density of the structure relative to the surrounding fluid behaving as a moving wall.…”

Section: Vortex Sheddingmentioning

confidence: 96%

Fluid–structural dynamic characterization of an electroactive membrane wing

Hays

Hart

Guettler

et al. 2015

Journal of Intelligent Material Systems and Structures

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The interactions between low-Reynolds-number fluid flow and an electroactive membrane wing is characterized to illustrate changes in harmonic and transient behavior from electric field excitation of the membrane wing. The wing is constructed of a dielectric elastomer material that changes its tension as a function of the applied field. The field excitation leads to changes in the shape of the wing under aerodynamic loads and subsequently, increased lift and delay of stall. Prior work in time-averaged lift and drag characterization is extended to better understand dynamic characteristics. Benchtop membrane structural dynamics are compared with visual image correlation, hotwire measurements, and particle image velocimetry within a low-Reynolds-number wind tunnel. An applied electric field leads to a 13.7% reduction in structural resonance of the membrane under ambient conditions while wind tunnel measurements illustrate a 5.1% reduction in resonance under the same applied field. Despite these differences, the structural and fluid dynamic harmonics are closely correlated for low-Reynolds-number flow at 10 m/s.

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Flow control of a sharp-edged airfoil

Cited by 8 publications

References 5 publications

Nonlinear dynamics and synthetic-jet-based control of a canonical separated flow

Nonlinear dynamics and synthetic-jet-based control of a canonical separated flow

Aerodynamics of the flying snake Chrysopelea paradisi: how a bluff body cross-sectional shape contributes to gliding performance

Fluid–structural dynamic characterization of an electroactive membrane wing

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