Generating controllable velocity fluctuations using twin oscillating hydrofoils: experimental validation

Harding, Samuel F.; Payne, Grégory S.; Bryden, Ian

doi:10.1017/jfm.2014.257

Cited by 17 publications

(9 citation statements)

References 5 publications

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“…The typical method [23,24] of creating such gusts is to pitch vanes upstream of the test section to yield transverse gusts or to open and close shutters downstream of the test section [25] to create an oscillating freestream. The use of a small number of vanes [26,27] can create distinct vortices, which yield a transverse velocity far from the vortices. Golubev et al [28] numerically modeled two-dimensional sharp-edged and harmonic variations in the oncoming flow interacting with an airfoil at Re c 10;000.…”

Section: Introductionmentioning

confidence: 99%

Vortical Gusts: Experimental Generation and Interaction with Wing

Hufstedler

McKeon

2019

AIAA Journal

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We describe the experimental generation of isolated vortical gusts and the interaction between these gusts and a downstream airfoil at a Reynolds number of 20,000. A standard method of generating a vortical gust has been to rapidly pitch an airfoil. A different approach is presented here: heaving a plate across a tunnel and changing direction rapidly to release a vortex. This method is motivated by the desire to limit a test article's exposure to the wake of the gust generator by moving it to the side of the tunnel. Two suites of experiments were performed to characterize the performance of the gust generators and to measure the forces on and flow around the downstream airfoil. The novel mechanism allowed for measurement of the resumption of vortex shedding from the downstream airfoil, which was impossible with the pitching generator. Nomenclature C L = lift coefficient, lift/(dynamic pressure × wing area) c a = airfoil chord length, m c p = plate chord length, m h = plate heave distance, m Re c = Reynolds number with respect to airfoil's chord length S = heaving speed ratio, V heave ∕U T = heaving time ratio, t heave ∕t cp t = time, s t a = normalized plate acceleration time, t accel ∕t cp t accel = plate acceleration time, s t c = chordwise convective time across airfoil, s t cp = chordwise convective time across plate, s t heave = heaving time, s t p = normalized airfoil pitching time, t pitch ∕t c t pitch = generator pitching time, s U = freestream speed, m∕s u = velocity in x direction, m∕s V heave = plate heaving speed, m∕s v = velocity in y direction, m∕s x = streamwise coordinate, m x 0 = streamwise position computed from unwrapping process, m y = cross-stream coordinate with respect to tunnel midline, m y 0 = initial plate distance from midline, m y peak = cross-stream position of maximum displacement of heaving plate, m y plate = cross-stream position of heaving plate, m y upstream = cross-stream position of pitching gust generator, m z = spanwise coordinate, m α = angle of attack of test article, rad (unless otherwise noted) α 1 = initial angle of pitching gust generator, rad (unless otherwise noted) α 2 = final angle of pitching gust generator, rad (unless otherwise noted) α eff = effective angle of attack of heaving gust generator, rad (unless otherwise noted) α upstream = angle of attack of pitching gust generator, rad (unless otherwise noted) Γ v = circulation of shed vortex, m 2 ∕s Γ v;est;heave = estimated circulation of shed vortex from heaving generator, m 2 ∕s Γ v;est;pitch = estimated circulation of shed vortex from pitching generator, m 2 ∕s Γ 2 = vortex identification criterion Δx = streamwise distance between generator and test article, m τ a = normalized time, t∕t c ω z = vorticity measured in x-y plane, s −1

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Section: Introductionmentioning

confidence: 99%

Vortical Gusts: Experimental Generation and Interaction with Wing

Hufstedler

McKeon

2019

AIAA Journal

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“…unsteady flows (Ham, Bauer & Lawrence 1974;Pierce, Kunz & Malone 1978;Retelle, McMichael & Kennedy 1981;Szumowski & Meier 1996;Harding, Payne & Bryden 2014). Some tunnels combine the independent capabilities of angle of attack and wind speed variation (Favier, Rebont & Maresca 1979;Goodrich & Gorham 2008;Gompertz et al 2011).…”

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confidence: 99%

Airfoil in a high amplitude oscillating stream

et al. 2016

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A combined theoretical and experimental investigation was carried out with the objective of evaluating theoretical predictions relating to a two-dimensional airfoil subjected to high amplitude harmonic oscillation of the free stream at constant angle of attack. Current theoretical approaches were reviewed and extended for the purposes of quantifying the bound, unsteady vortex sheet strength along the airfoil chord. This resulted in a closed form solution that is valid for arbitrary reduced frequencies and amplitudes. In the experiments, the bound, unsteady vortex strength of a symmetric 18 % thick airfoil at low angles of attack was measured in a dedicated unsteady wind tunnel at maximum reduced frequencies of 0.1 and at velocity oscillations less than or equal to 50 %. With the boundary layer tripped near the leading edge and mid-chord, the phase and amplitude variations of the lift coefficient corresponded reasonably well with the theory. Near the maximum lift coefficient overshoot, the data exhibited an additional high-frequency oscillation. Comparisons of the measured and predicted vortex sheet indicated the existence of a recirculation bubble upstream of the trailing edge which sheds into the wake and modifies the Kutta condition. Without boundary layer tripping, a mid-chord bubble is present that strengthens during flow deceleration and its shedding produces a dramatically different effect. Instead of a lift coefficient overshoot, as per the theory, the data exhibit a significant undershoot. This undershoot is also accompanied by high-frequency oscillations that are characterized by the bubble shedding. In summary, the location of bubble and its subsequent shedding play decisive roles in the resulting temporal aerodynamic loads.

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“…(29) do not need to be sinusoidal. In fact, they can be arbitrary functions, as experimentally validated by Harding et al (2014). Thus, the inverse method is more flexible than the analytical; however, the latter is preferred for sinusoidal functions as it is more computationally efficient and avoids the error in least-squares fit in the pseudo-inverse operation.…”

Section: Discrete Inverse Methodsmentioning

confidence: 99%

“…The second approach, which is of interest for this work, is based on deterministic free-stream turbulence in terms of sinusoidal gusts with a single prescribed frequency (Diana et al, , 2013Jancauskas and Melbourne, 1986;Han et al, 2010;Ma et al, 2013). There are number of ways of generating this type of gusts such as: an active turbulence generator (AT-G) (Stapountzis and Graham, 1982;Harding et al, 2014;Argentini et al, 2012), circulation-controlled airfoils (Jancauskas and Melbourne, 1986), multiple fan arrangement (Ma et al, 2013;Cao et al, 2002) , or rotating slotted cylinders (Tang et al, 1996). An ATG represents a set of two or more pitching airfoils, oscillating with a single frequency.…”

Section: Introductionmentioning

confidence: 99%

Determination of complex aerodynamic admittance of bridge decks under deterministic gusts using the Vortex Particle Method

Kavrakov

Argentini

Omarini

et al. 2019

Journal of Wind Engineering and Industrial Aerodynamics

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The accurate description of the aerodynamic forces due to free-stream turbulence acting on a stationary bridge deck represents a challenging task. This paper presents a Computational Fluid Dynamics (CFD) approach based on the two-dimensional (2D) Vortex Particle Method (VPM) for simulation of a six-component complex aerodynamic admittance. Deterministic free-stream turbulence is simulated by modeling the wakes of two fictitious pitching airfoils with vortex particles. For out-of-or in-phase sinusoidal oscillations of the airfoils, a longitudinal or vertical sinusoidal gust is obtained along the centerline, respectively. A closed-form solution, based on an existing mathematical model, is deduced to relate the gust amplitudes and vortex particles' circulation. Positioning a section downstream of the particle release locations yields sinusoidal buffeting forces. The complex aerodynamic admittance is then determined as a transfer function between the buffeting forces and the deterministic free-stream turbulence. A verification of the method is performed for the complex Sears' admittance of a flat plate. Finally, the CFD method is validated against wind tunnel tests for a streamlined bridge deck. The results from both, verification and validation, yielded a good agreement. Applications of the presented method are foreseen in the scope of buffeting analyses of line-like structures under the strip assumption.

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Generating controllable velocity fluctuations using twin oscillating hydrofoils: experimental validation

Cited by 17 publications

References 5 publications

Vortical Gusts: Experimental Generation and Interaction with Wing

Vortical Gusts: Experimental Generation and Interaction with Wing

Airfoil in a high amplitude oscillating stream

Determination of complex aerodynamic admittance of bridge decks under deterministic gusts using the Vortex Particle Method

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