Investigation of mechanisms of high lift for a flat-plate airfoil undergoing small-amplitude plunging oscillations

Research output: Contribution to journalArticle

25 Citations (Scopus)
70 Downloads (Pure)

Abstract

Two high-lift mechanisms, namely, convected leading-edge vortices and stable deflected jets, have previously been identified for an airfoil undergoing small-amplitude plunging oscillations. In this paper the effect of geometry is investigated through direct comparison of the forces and flowfields associated with small-amplitude plunging oscillations of a NACA 0012 airfoil and a flat plate for 0 deg and a poststall angle of attack of 15 deg with a Reynolds number of 10,000. For 0 deg at high Strouhal numbers, the NACA airfoil experiences stable deflected jets responsible for very large lift coefficients, whereas the flat plate experiences deflected jets that are prone to periodic oscillation in direction, resulting in oscillation of the lift coefficient with a period on the order of 100 cycles. It is postulated that this jet switching is driven by the leading-edge vortex (LEV). At 15 deg angle of attack, the flat plate is shown to produce a comparable increase in lift up to a Strouhal number of unity, but after this, the lift performance deteriorates. This is due to the leading-edge vortices convecting further from the upper surface. At higher plunge velocities, a new mode of LEV behavior is observed. The upper-surface LEV pairs with the lower-surface LEV to form a dipole that convects against the freestream and is rapidly dissipated. This results in a highly separated time-averaged flow, and thus in low lift and high drag.
Original languageEnglish
Pages (from-to)968-980
Number of pages13
JournalAIAA Journal
Volume51
Issue number4
DOIs
Publication statusPublished - Apr 2013

Fingerprint

Airfoils
Vortex flow
Strouhal number
Angle of attack
Drag
Reynolds number
Geometry

Cite this

@article{38bbdd4323944f069d67b15555ead165,
title = "Investigation of mechanisms of high lift for a flat-plate airfoil undergoing small-amplitude plunging oscillations",
abstract = "Two high-lift mechanisms, namely, convected leading-edge vortices and stable deflected jets, have previously been identified for an airfoil undergoing small-amplitude plunging oscillations. In this paper the effect of geometry is investigated through direct comparison of the forces and flowfields associated with small-amplitude plunging oscillations of a NACA 0012 airfoil and a flat plate for 0 deg and a poststall angle of attack of 15 deg with a Reynolds number of 10,000. For 0 deg at high Strouhal numbers, the NACA airfoil experiences stable deflected jets responsible for very large lift coefficients, whereas the flat plate experiences deflected jets that are prone to periodic oscillation in direction, resulting in oscillation of the lift coefficient with a period on the order of 100 cycles. It is postulated that this jet switching is driven by the leading-edge vortex (LEV). At 15 deg angle of attack, the flat plate is shown to produce a comparable increase in lift up to a Strouhal number of unity, but after this, the lift performance deteriorates. This is due to the leading-edge vortices convecting further from the upper surface. At higher plunge velocities, a new mode of LEV behavior is observed. The upper-surface LEV pairs with the lower-surface LEV to form a dipole that convects against the freestream and is rapidly dissipated. This results in a highly separated time-averaged flow, and thus in low lift and high drag.",
author = "David Cleaver and Zhijin Wang and Ismet Gursul",
year = "2013",
month = "4",
doi = "10.2514/1.J052213",
language = "English",
volume = "51",
pages = "968--980",
journal = "AIAA Journal",
issn = "0001-1452",
publisher = "American Institute of Aeronautics and Astronautics Inc.",
number = "4",

}

TY - JOUR

T1 - Investigation of mechanisms of high lift for a flat-plate airfoil undergoing small-amplitude plunging oscillations

AU - Cleaver, David

AU - Wang, Zhijin

AU - Gursul, Ismet

PY - 2013/4

Y1 - 2013/4

N2 - Two high-lift mechanisms, namely, convected leading-edge vortices and stable deflected jets, have previously been identified for an airfoil undergoing small-amplitude plunging oscillations. In this paper the effect of geometry is investigated through direct comparison of the forces and flowfields associated with small-amplitude plunging oscillations of a NACA 0012 airfoil and a flat plate for 0 deg and a poststall angle of attack of 15 deg with a Reynolds number of 10,000. For 0 deg at high Strouhal numbers, the NACA airfoil experiences stable deflected jets responsible for very large lift coefficients, whereas the flat plate experiences deflected jets that are prone to periodic oscillation in direction, resulting in oscillation of the lift coefficient with a period on the order of 100 cycles. It is postulated that this jet switching is driven by the leading-edge vortex (LEV). At 15 deg angle of attack, the flat plate is shown to produce a comparable increase in lift up to a Strouhal number of unity, but after this, the lift performance deteriorates. This is due to the leading-edge vortices convecting further from the upper surface. At higher plunge velocities, a new mode of LEV behavior is observed. The upper-surface LEV pairs with the lower-surface LEV to form a dipole that convects against the freestream and is rapidly dissipated. This results in a highly separated time-averaged flow, and thus in low lift and high drag.

AB - Two high-lift mechanisms, namely, convected leading-edge vortices and stable deflected jets, have previously been identified for an airfoil undergoing small-amplitude plunging oscillations. In this paper the effect of geometry is investigated through direct comparison of the forces and flowfields associated with small-amplitude plunging oscillations of a NACA 0012 airfoil and a flat plate for 0 deg and a poststall angle of attack of 15 deg with a Reynolds number of 10,000. For 0 deg at high Strouhal numbers, the NACA airfoil experiences stable deflected jets responsible for very large lift coefficients, whereas the flat plate experiences deflected jets that are prone to periodic oscillation in direction, resulting in oscillation of the lift coefficient with a period on the order of 100 cycles. It is postulated that this jet switching is driven by the leading-edge vortex (LEV). At 15 deg angle of attack, the flat plate is shown to produce a comparable increase in lift up to a Strouhal number of unity, but after this, the lift performance deteriorates. This is due to the leading-edge vortices convecting further from the upper surface. At higher plunge velocities, a new mode of LEV behavior is observed. The upper-surface LEV pairs with the lower-surface LEV to form a dipole that convects against the freestream and is rapidly dissipated. This results in a highly separated time-averaged flow, and thus in low lift and high drag.

UR - http://www.scopus.com/inward/record.url?scp=84876523887&partnerID=8YFLogxK

UR - http://dx.doi.org/10.2514/1.J052213

U2 - 10.2514/1.J052213

DO - 10.2514/1.J052213

M3 - Article

VL - 51

SP - 968

EP - 980

JO - AIAA Journal

JF - AIAA Journal

SN - 0001-1452

IS - 4

ER -