Generation of periodic gusts with a pitching and plunging airfoil

Wei, Nathaniel; Kissing, Johannes; Tropea, Cameron

doi:10.1007/s00348-019-2815-1

Cited by 16 publications

(8 citation statements)

References 34 publications

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“…Wakes and vortices of oscillating airfoils are often used in wind tunnel experiments as gust generators to simulate downstream wings in gusts. Examples of this type of experimental facilities include the use of oscillating airfoils or a cascade of airfoils (Gilman & Bennett 1966;Booth & Yu 1986;Wilder & Telionis 1998;Brion et al 2015;Wei, Kissing & Tropea 2019a;Wei et al 2019b;Wu et al 2020), and fixed airfoils with oscillating flaps (Bicknell & Parker 1972;Jones & Moore 1972). The two-dimensionality of the experimentally generated gusts, wakes and vortices has not been considered so far as a function of the generating parameters, such as the frequency and the amplitude of the airfoil motion.…”

Section: Oscillating Wakes As Gust Generatorsmentioning

confidence: 99%

Coherence of unsteady wake of periodically plunging airfoil

2022

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We present an experimental investigation of the flow structure in the near wake of a NACA0012 airfoil plunging sinusoidally at a chord Reynolds number of Re = 20 000 and for a wide range of reduced frequency k and Strouhal number based on peak-to-peak amplitude St. Estimated mean thrust coefficients using the mean and fluctuating velocity fields confirm the St2 dependence as well as a significant effect of the reduced frequency for k ≤ 1. Generally, time-averaged flow quantities are better correlated with St than k in the range tested (k ≤ 3.14 and St ≤ 0.24). Analysis of the streamwise flow and cross-flow in the near wake using two-point cross-correlations and proper orthogonal decomposition reveals that the unsteady characteristics are even better correlated with St than the mean flow quantities. The percentage energy of the fundamental wake modes of the streamwise flow and the flapping mode of the cross-flow increases with increasing St, but at different rates in the drag-producing and thrust-producing wakes. There are similarities to the wake synchronisation behind oscillating bodies. The spanwise-averaged cross-correlation coefficient in the measurement domain grows linearly for small St (in drag-producing wakes), and is nearly constant at a high value for larger St (in thrust-producing wakes). Results show that the Strouhal number is the most important parameter that determines the degree of two-dimensionality of the wake, and suggest that spanwise vortices are quasi-two-dimensional for St ≥ 0.05 and x/c ≤ 4. The implications for experimental gust generators using oscillating airfoils are discussed.

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Section: Oscillating Wakes As Gust Generatorsmentioning

confidence: 99%

Coherence of unsteady wake of periodically plunging airfoil

2022

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“…Vortex-airfoil interactions were also simulated by oscillating an upstream airfoil, hence generating a vortex which subsequently interacted with the downstream wing (Wilder and Telionis 1998;Gregory 2015, 2017). There are many experimental studies that produced periodic travelling gusts by oscillating airfoils or cascade of airfoils (Gilman and Bennett 1966;Booth and Yu 1986;Brion et al 2015;Wei et al 2019aWei et al , 2019bWu et al 2020), and by oscillating flaps (Jones and Moore 1972;Bicknell and Parker 1972).…”

Section: Introductionmentioning

confidence: 99%

Interaction of quasi-two-dimensional vortical gusts with airfoils, unswept and swept wings

2022

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A nearly two-dimensional vortex of small core size has been produced by the transient plunging motion of an upstream airfoil and it interacted with the downstream wings. Depending on the offset distance of the vortex and wing angle of attack, the incident vortex filament deforms, diffuses, and loses coherence, while inducing leading-edge vortex formation and shedding from the wing. No significant spanwise flow develops in the incident vortices during the interaction. The interaction with the swept wing at each spanwise plane appears to be unaffected by the other spanwise planes. The counter-clockwise vortex induces a positive lift peak as it approaches the wing, which can be predicted by the potential flow assumption. The peak lift force is proportional to the circulation of the incident vortex and has its maximum near the zero-offset distance. The minimum lift coefficient is reached after the vortex has just passed and caused flow separation on the lower surface. The maximum lift coefficients for the finite unswept and swept wings can be estimated by making a correction for the aspect ratio and using the independence principle. The only exception is observed for the swept wing at a post-stall angle of attack for which the leading-edge vortex shedding becomes parallel to the leading-edge and increases the peak lift force. Graphical abstract

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“…In the present study further possible applications of this 2D active grid will be presented. While in [15] two guiding vanes and in [16] a pitching and plunging airfoil was used to vary the AoI, this study will show further possibilities by varying the number and geometry of the used shafts. The presented 2D active grid can be equipped with up to nine individual moving shafts, resulting in a high flexibility in inflow generation.…”

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confidence: 95%

How to design a 2D active grid for dynamic inflow modulation

Wester¹,

Krauss²,

Neuhaus³

et al. 2020

Preprint

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Wind turbines operate under very dynamic conditions in the atmospheric boundary layer. Rapid changes of the angle of the incoming flow are caused by so called extreme conditions, either directly by changes of the wind direction or indirectly by gust induced changes of the angle for a rotating blade of the wind turbine. This dynamic changes lead frequently to the aerodynamic phenomenon of dynamic stall, which is known to generate a massive lift overshoot and therefore an increase of loads acting on the wind turbine. In this study an experimental approach to modulate the inflow in a wind tunnel in a two-dimensional manner will be presented. For a complete characterization of the possibilities of the so-called 2D active grid, it is investigated with different modifications of the used shafts. In addition to the hardware alterations, the influence of the dynamic motion of the grid is also extensively investigated. The benefit of a 2D active grid upstream of the airfoil is the possibility to induce dynamic phenomena without the need to dynamically pitch the airfoil itself. This allows for simultaneous measurements of the flow field around airfoils with temporally high resolving particle image velocimetry (PIV) and load cells. Disturbing effects, such as those caused by the inertia of a moving airfoil, can be avoided. In addition to this dynamic changes in the angle of attack, it will be shown that the 2D active grid design enables to generate fast velocity fluctuations to mimic longitudinal inflow variations. These two features can be combined, resulting in angle of attack and velocity changes on small time scales with any phase shift between them to imitate different inflow situations such as yaw effects.

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Generation of periodic gusts with a pitching and plunging airfoil

Cited by 16 publications

References 34 publications

Coherence of unsteady wake of periodically plunging airfoil

Coherence of unsteady wake of periodically plunging airfoil

Interaction of quasi-two-dimensional vortical gusts with airfoils, unswept and swept wings

How to design a 2D active grid for dynamic inflow modulation

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