Characterization of nonlinear behavior of an airfoil under stall-induced pitching oscillations

Vasconcellos, Rui; Pereira, Daniel A.; Marques, Flávio D.

doi:10.1016/j.jsv.2016.02.046

Cited by 21 publications

(14 citation statements)

References 26 publications

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“…The nonlinear response of stall-induced oscillations of the tested NACA0012 airfoil restrained by a torsion spring at $34{\rm %}$ of chord was investigated and analyzed by Vasconcellos et al (2016). Sustained LCOs were observed over a broad range of air speeds beyond the onset of the Hopf bifurcation.…”

Section: Resultsmentioning

confidence: 99%

“…If the airfoil is allowed to rotate about its own suspension, as conceived in the present experimental setup, the sudden negative pitching moment will cause the airfoil to reverse its rotation and decrease the AoA. The decrease in the AoA occurs without instantaneous recovery of the lift (Vasconcellos et al, 2016). A delay takes place to reestablish the unsteady loading while the airfoil rotates toward lower angles of incidence.…”

Section: Methodsmentioning

confidence: 97%

“…This is achieved from the relation between the restoring pitching moment and the airfoil’s AoA, which is assessed from measurements of the AoA with respect to the applied static restoring moment as shown in Figure 5. The plot exhibits the characteristics of a hardening nonlinearity that is necessary, through its combination with the aerodynamic nonlinearity, to restrain the airfoil’s motion and achieve the desired amplitudes for the LCOs (Vasconcellos et al, 2016) for the purpose of energy harvesting. Using polynomial fitting, the pitching restoring moment as a function of the AoA, α (rad), is given by M s ( α ) = 2 . 67 α 5 − 0 . 70 α 3 + 0 . 85 α ( N m / rad ) .…”

Section: Methodsmentioning

confidence: 99%

“…This loading induces an airfoil response that is referred to as dynamic stall (Carr, 1988). The loads under dynamic stall are unsteady and carry delay effects that induce airfoil oscillations (Vasconcellos et al, 2016). Sarkar and Bijl (2008) and Furlan et al (2015) observed LCOs of airfoils that are subjected to stall-induced conditions.…”

Section: Introductionmentioning

confidence: 99%

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Power extraction from stall-induced oscillations of an airfoil

Marques

Pereira

Zakaria

et al. 2017

Journal of Intelligent Material Systems and Structures

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Aerodynamic and structural nonlinearities of aeroelastic systems control different aspects of their limit cycle oscillations and bifurcations. One strong nonlinear unsteady aerodynamic effect that results in self-induced oscillations of airfoils is the dynamic stall. So, the concept of power extraction from stall-induced oscillations of a pitching airfoil is investigated. Experiments are performed to explore and enhance the conversion of the oscillations of a NACA0012 airfoil that is restrained elastically in pitching to electrical power. Wind tunnel tests are performed on an airfoil model connected to a DC electric motor to harvest the energy. The effects of varying the position of the axle, which defines the elastic axis, are investigated. Bifurcation diagrams as the air speed is increased and average power estimates for different experimental conditions are used to analyze the power extraction features. The results show an aerodynamic efficiency of about 40% indicating that an airfoil oscillating under the effects of dynamic stall is an adequate platform for energy harvesting.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 97%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Power extraction from stall-induced oscillations of an airfoil

Marques

Pereira

Zakaria

et al. 2017

Journal of Intelligent Material Systems and Structures

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“…It was deduced from the results that, at lower TSR values, dynamic stall was evident causing vortex shedding and in return higher SPL values were generated. This dynamic stall noise occurrence could be improved by operating at optimum TSR value of 1.06 in this case and providing a preset pitch angle [ 41 ]. Another important agreement between the camera and linear array was that both trends followed the 1/r law for increasing distance from the source providing us a way forward for designing wind farm architecture.…”

Section: Discussionmentioning

confidence: 99%

Development of a Linear Acoustic Array for Aero-Acoustic Quantification of Camber-Bladed Vertical Axis Wind Turbine

Butt¹,

Akbar

Aslam³

et al. 2020

Sensors

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Vertical axis wind turbines (VAWT) are a source of renewable energy and are used for both industrial and domestic purposes. The study of noise characteristics of a VAWT is an important performance parameter for the turbine. This study focuses on the development of a linear microphone array and measuring acoustic signals on a cambered five-bladed 45 W VAWT in an anechoic chamber at different tip speed ratios. The sound pressure level spectrum of VAWT shows that tonal noises such as blade passing frequencies dominate at lower frequencies whereas broadband noise corresponds to all audible ranges of frequencies. This study shows that the major portion of noise from the source is dominated by aerodynamic noises generated due to vortex generation and trailing edge serrations. The research also predicts that dynamic stall is evident in the lower Tip speed ratio (TSR) region making smaller TSR values unsuitable for a quiet VAWT. This paper compares the results of linear aeroacoustic array with a 128-MEMS acoustic camera with higher resolution. The study depicts a 3 dB margin between two systems at lower TSR values. The research approves the usage of the 8 mic linear array for small radius rotary machinery considering the results comparison with a NORSONIC camera and its resolution. These observations serve as a basis for noise reduction and blade optimization techniques.

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