Suppression of dynamic-stall vortices over pitching airfoils by leading-edge suction

Karim, Md. Ahsanul; Acharya, Mukund

doi:10.2514/3.12155

Cited by 65 publications

(23 citation statements)

References 6 publications

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“…Unlike the previous cases, here the dynamic stall delay is believed to be caused by reverse flow accumulation inside the cavity and therefore an approximately similar delay is observed regardless of the pitch rate. However, for larger reduced frequencies, the accumulation rate of the reverse flow increases [22] leading to a larger lift peak at the higher pitch rate. On the other hand, the loss of lift after the vortex convection is approximately similar to the clean airfoil.…”

Section: Cavitymentioning

confidence: 95%

“…It is necessary for the control technique to be implemented prior to the formation of the dynamic stall vortex in order to influence the vortex lift and the severe stall conditions that follow the vortex departure [21,22,27,30,36]. The control strategy needs to be implemented near the airfoil LE [22,37,38].…”

Section: Introductionmentioning

confidence: 99%

“…Gardner et al [21] studied the influence of fluid injection into the flow through different jet configurations and noted a considerable reduction in the vortex lift. Karim and Acharya [22] used flow removal as a means to reduce the vortex strength. Similarly, periodic excitation has been shown to reduce the hysteresis in the lift considerably [23,24].…”

Section: Introductionmentioning

confidence: 99%

“…The control strategy needs to be implemented near the airfoil LE [22,37,38]. Trailing edge (TE) devices have been observed to have a minimalistic effect on the dynamic stall process unless the control area is very large [39e41].…”

Section: Introductionmentioning

confidence: 99%

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Methods to control dynamic stall for wind turbine applications

2016

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a b s t r a c tDynamic stall (DS) on a wind turbine is encountered when the sectional angles of attack of the blade rapidly exceeds the steady-state stall angle of attack due to in-flow turbulence, gusts and yawmisalignment. The process is considered as a primary source of unsteady loads on wind turbine blades and negatively influences the performance and fatigue life of a turbine. In the present article, the control requirements for DS have been outlined for wind turbines based on an in-depth analysis of the process. Three passive control methodologies have been investigated for dynamic stall control: (1) streamwise vortices generated using vortex generators (VGs), (2) spanwise vortices generated using a novel concept of an elevated wire (EW), and (3) a cavity to act as a reservoir for the reverse flow accumulation. The methods were observed to delay the onset of DS by several degrees as well as reduce the increased lift and drag forces that are associated with the DSV. However, only the VG and the EW were observed to improve the post-stall characteristics of the airfoil.

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Section: Cavitymentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Methods to control dynamic stall for wind turbine applications

2016

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“…The effect of this suction on the flow development and the associated surface-pressure distribution varies with the angle of attack, as one would expect from the results of Karim and Acharya. 5 35 deg, respectively. The pressure data also showed that in each of these cases suction at rates higher than the values specified resulted only in increasing the leading-edge suction peak, whereas suction at levels lower than those specified allowed the vortex to form to varying extents, depending on the magnitude of the parameters.…”

Section: Effect Of Suction On the Surface-pressure Distributionsmentioning

confidence: 98%

Controlled leading-edge suction for management of unsteady separation over pitching airfoils

Alrefai

Acharya

1996

AIAA Journal

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The effect on the unsteady surface pressures of controlled suction from a span wise slot, located at 2% chord in the suction surface of a two-dimensional NACA 0012 airfoil model, was examined in detail for a wide range of pitch rates with a constant velocity ramp motion. The experiments were conducted in the Andrew Fejer Wind 1\mnel at the Illinois Institute of Technology's Fluid Dynamics Research Center. The optimum suction required to meet three different control objectives, suppression of the dynamic-stall vortex, delaying detachment of the vortex from the airfoil surface, and maximizing the unsteady lift, was determined for different pitch rates and angles of attack. The pressure data were used to develop specifications for the flow state over the airfoil surface that would meet these objectives. Such specifications are necessary for the development of on-line flow management systems. A procedure was also developed to account for variations in suction and motion history.= dimensionless suction flow rate, QsKU^c 1 ) <2 opt = optimum suction rate for a given objective Q s = volumetric suction flow rate Re c = chord Reynolds number, U^c/v S = surface vorticity flux, (l/p)(dp/Qs) S + = dimensionless surface vorticity flux, 2cS/ Uŝ = coordinate along airfoil surface t p = time period for pitch-up motion through an angle Aa UQQ = freestream velocity a = angle of attack a + = dimensionless pitch rate, (Aac)/(^(7 00 ) Aa = change in angle of attack during pitch up p = fluid density v = fluid kinematic viscosity Introduction and Background

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Feedforward Control of Lift Hysteresis during Periodic and Random Pitching Maneuvers

Grimaud

Williams

2015

Notes on Numerical Fluid Mechanics and Multidisciplinary Design

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Suppression of dynamic-stall vortices over pitching airfoils by leading-edge suction

Cited by 65 publications

References 6 publications

Methods to control dynamic stall for wind turbine applications

Methods to control dynamic stall for wind turbine applications

Controlled leading-edge suction for management of unsteady separation over pitching airfoils

Feedforward Control of Lift Hysteresis during Periodic and Random Pitching Maneuvers

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