Large Low-Frequency Oscillations Initiated by Flow Control on a Poststall Airfoil

Bernardini, Chiara; Benton, Stuart I.; Hipp, Kyle D.; Bons, Jeffrey P.

doi:10.2514/1.j054321

Cited by 12 publications

(9 citation statements)

References 28 publications

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“…This, as previous studies have suggested, implied that the observed oscillations are possibly related to global oscillations in the flow circulation. In their study on lowfrequency oscillations Bernardini et al 21 highlight, as it has been documented experimentally and numerically in the literature, that large amplitude low-frequency oscillations in the lift force are generally detected for airfoils experiencing leading edge type stall at post-stall angles of attack. This behavior, in combination with the classification of the airfoil performance at the studied Reynolds number as a combined leading-edge and trailing-edge type, matches the observed oscillations in the spectral content.…”

Section: Airfoil Unsteady Lift Coefficientmentioning

confidence: 91%

“…[8][9][10][11][12][13][14] The unsteady flow about airfoils has generally been linked to vortex shedding processes from separation bubbles, 15 bluff-body shedding, 16 8,23 Until recently it was thought that such low-frequency oscillations were only present prior to stall at high angles of attack. However, a recent study by Bernardini et al 21 showed that low-frequency oscillations can also be excited and exist in the post-stall flow field.…”

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confidence: 99%

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Poststall Hysteresis and Flowfield Unsteadiness on a NACA 0012 Airfoil

Hristov

Ansell

2018

AIAA Journal

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The current study was conducted to understand flow field unsteadiness associated with static stall hysteresis on an NACA 0012 airfoil at Rec = 1.0 × 10 6 . Unsteady pressure measurements were acquired to evaluate the performance of the airfoil, and a hysteresis loop was identified in the vicinity of the airfoil Cl,max. Two fundamentally different flow regimes were observed at poststall angles of attack for the airfoil during the upstroke and downstroke branches of the hysteresis loop. A Fourier analysis of the surface pressure distributions was used to attribute the flow field unsteadiness to a low-frequency, high-amplitude oscillation across the leading-edge region during the upstroke, along with a regular bluff-body shedding frequency across the separated region of the airfoil. The low-frequency oscillations were observed to be more dominant for the upstroke branch, while the bluff-body shedding process was more dominant in the downstroke branch. The flow field unsteadiness was observed to become more energetic at lower post-stall angles of attack.In addition, time-resolve particle image velocimetry data were acquired across the leading-edge region of the airfoil to qualitatively and quantitatively describe the unsteadiness in the flow. These data were used to link the low-frequency oscillations across the leading edge of the airfoil during the upstroke to a quasi-periodic surging of the flow, which was also associated with an advancing and retreating of the separation location across the surface.

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Section: Airfoil Unsteady Lift Coefficientmentioning

confidence: 91%

mentioning

confidence: 99%

Poststall Hysteresis and Flowfield Unsteadiness on a NACA 0012 Airfoil

Hristov

Ansell

2018

AIAA Journal

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Section: Airfoil Unsteady Lift Coefficientmentioning

confidence: 99%

“…1.3, after Zaman et al 8,23 Until recently it was thought that such low-frequency oscillations were only present prior to stall at high angles of attack. However, a recent study by Bernardini et al 21 showed that low-frequency oscillations can also be excited and exist in the post-stall flow field.…”

Section: Introductionmentioning

confidence: 99%

Post-Stall Hysteresis and Flow Field Unsteadiness on an NACA 0012 Airfoil

Hristov

Ansell

2017

55th AIAA Aerospace Sciences Meeting

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“…Also, Hipp et al [27] performed a numerical simulation in order to investigate the control of the flow in leading-edge of an aerofoil. Finally, Bernardini et al [28] performed a numerical research in order to obtain the oscillation of flow characteristics due to flow control over an aerofoil. However, all of the presented methods have not provided sufficient information regarding the tip vortices and the behaviour of the regime during the flow injection.…”

Section: Introductionmentioning

confidence: 99%

Effects of Boundary Layer Control Method on Hydrodynamic Characteristics and Tip Vortex Creation of a Hydrofoil

Ghadimi

Tanha

Kourabbasloo

et al. 2017

Polish Maritime Research

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There is currently a significant focus on using boundary layer control (BLC) approach for controlling the flow around bodies, especially the foil sections. In marine engineering this is done with the hope of increasing the lift -to -drag ratio and efficiency of the hydrofoils. In this paper, effects of the method on hydrodynamic characteristics and tip vortex formation of a hydrofoil are studied. Steady water injection at the tip of the hydrofoil is simulated in different conditions by using ANSYS-CFX commercial software. Validity of the proposed simulations is verified by comparing the obtained results against available experimental data. Effects of the injection on the lift, drag, and lift -to -dragratio are studied and the ranges within which the injection has the most positive or negative effects, are determined. Furthermore, flow pattern and pressure variation are studied upon the water injection to determine the most positive and negative case and to ascertain the main reasons triggering these phenomena.

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Large Low-Frequency Oscillations Initiated by Flow Control on a Poststall Airfoil

Cited by 12 publications

References 28 publications

Poststall Hysteresis and Flowfield Unsteadiness on a NACA 0012 Airfoil

Poststall Hysteresis and Flowfield Unsteadiness on a NACA 0012 Airfoil

Post-Stall Hysteresis and Flow Field Unsteadiness on an NACA 0012 Airfoil

Effects of Boundary Layer Control Method on Hydrodynamic Characteristics and Tip Vortex Creation of a Hydrofoil

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