Wake structure and similar behavior of wake profiles downstream of a plunging airfoil

Davari, Ali

doi:10.1016/j.cja.2017.05.007

Cited by 8 publications

(3 citation statements)

References 20 publications

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“…The evolution of the wake is one of the key issues in aerodynamics, because this phenomenon can characterize the various effects that occur when flow passes an airfoil [11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

2021

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Several methods of defining and estimating the width of a turbulent wake are presented and tested on the experimental data obtained in the wake past an asymmetric prismatic airfoil NACA 64(3)-618, which is often used as tip profile of the wind turbines. Instantaneous velocities are measured by using the Particle Image Velocimetry (PIV) technique. All suggested methods of wake width estimation are based on the statistics of a stream-wise velocity component. First, the expansion of boundary layer (BL) thickness is tested, showing that both displacement BL thickness and momentum BL thickness do not represent the width of the wake. The equivalent of 99% BL thickness is used in the literature, but with different threshold value. It is shown that a lower threshold of 50% gives more stable results. The ensemble average velocity profile is fitted by Gauss function and its σ-parameter is used as another definition of wake width. The profiles of stream-wise velocity standard deviation display a two-peak shape; the distance of those peaks serves as wake width for Norberg, while another tested option is to include the widths of such peaks. Skewness (the third statistical moment) of stream-wise velocity displays a pair of sharp peaks in the wake boundary, but their position is heavily affected by the statistical quality of the data. Flatness (the fourth statistical moment) of the stream-wise velocity refers to the occurrence of rare events, and therefore the distance, where turbulent events ejected from the wake become rare and can be considered as another definition of wake width. The repeatability of the mentioned methods and their sensitivity to Reynolds’ number and model quality are discussed as well.

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“…The evolution of the wake is one of the key issues in aerodynamics, because this phenomenon can characterize the various effects that occur when flow passes an airfoil [11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

2021

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“…The previous studies [30][31][32][33] on the same airfoil including surface pressure measurements and wake survey at Reynolds numbers of Re ¼8 � 10 5 and 4.2 � 10 5 revealed that the static stall angle of this airfoil without plasma actuation occurs between 10 to 12 degrees. Beyond the static stall angle of attack, a separation bubble appears, followed by a reverse flow region that gives rise to the static pressure on the upper surface of this airfoil.…”

Section: Resultsmentioning

confidence: 96%

Impact of dielectric barrier discharge plasma on the wake of a wind turbine blade section oscillating in plunge

Maleki

Davari

Soltani

2021

Proceedings of the Institution of Mechanical Engineers, Part A:

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Effects of dielectric barrier discharge plasma have been studied on the wake velocity profiles of a section of a 660 kW wind turbine blade in plunging motion in a wind tunnel. The corresponding unsteady velocity profiles show remarkable improvement when the plasma actuators were operating and the angles of attack of the model were beyond the static stall angles of the airfoil. As a result the drag force was considerably reduced. It is further observed that the plasma-induced flow attenuates the leading edge vortices that are periodically shed into wake and diminishes the large eddies downstream. The favorable effects of the plasma augmentation are shown to occur near the uppermost and lowermost positions of the plunging paths where the wake is primarily dominated by the vortices of the same sign. The wake structure in the presence of the flow induced by the plasma actuators shows that the actual effective angles of attack seen by the plunging airfoil reduces in comparison with that for the case of the plasma augmentation off situation.

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“…When the airfoil is in non-sinusoidal plunging motions (Srikumar et al, 2018), the effects of motions on the thrust performance are investigated under various unsteady parameters. The velocity profiles in the wake of a plunging airfoil were discussed in (Davari, 2017).…”

Section: Introductionmentioning

confidence: 99%

Research on chaotic features of a flow field over a plunging airfoil based on dynamic mode decomposition

Qi¹,

Yang²,

Song³

2021

Journal of Theoretical and Applied Mechanics

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Periodic motion of a plunging airfoil causes continuous changes in the surrounding flow field. The time-dependent thrust coefficient depends entirely on unsteady characteristics of the flow field. On the contrary, the time-dependent thrust coefficient may also reflect the unsteady characteristics of the corresponding flow field. With the fast Fourier transform (FFT) and dynamic mode decomposition (DMD), unsteady aerodynamic forces can be correlated with the flow field characteristics in the frequency domain. In the present paper, DMD is performed to analyze the unsteady characteristics of the flow field around a plunging NACA0012 airfoil at the Reynolds number of 20 000.

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Wake structure and similar behavior of wake profiles downstream of a plunging airfoil

Cited by 8 publications

References 20 publications

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

Impact of dielectric barrier discharge plasma on the wake of a wind turbine blade section oscillating in plunge

Research on chaotic features of a flow field over a plunging airfoil based on dynamic mode decomposition

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