Experiments in Fluids

, Volume 53, Issue 3, pp 637–653 | Cite as

The flow over a thin airfoil subjected to elevated levels of freestream turbulence at low Reynolds numbers

  • Sridhar Ravi
  • Simon Watkins
  • Jon Watmuff
  • Kevin Massey
  • Phred Petersen
  • Matthew Marino
  • Anuradha Ravi
Research Article


Micro Air Vehicles (MAVs) can be difficult to control in the outdoor environment as they fly at relatively low speeds and are of low mass, yet exposed to high levels of freestream turbulence present within the Atmospheric Boundary Layer. In order to examine transient flow phenomena, two turbulence conditions of nominally the same longitudinal integral length scale (Lxx/c = 1) but with significantly different intensities (Ti = 7.2 % and 12.3 %) were generated within a wind tunnel; time-varying surface pressure measurements, smoke flow visualization, and wake velocity measurements were made on a thin flat plate airfoil. Rapid changes in oncoming flow pitch angle resulted in the shear layer to separate from the leading edge of the airfoil even at lower geometric angles of attack. At higher geometric angles of attack, massive flow separation occurred at the leading edge followed by enhanced roll up of the shear layer. This lead to the formation of large Leading Edge Vortices (LEVs) that advected at a rate much lower than the mean flow speed while imparting high pressure fluctuations over the airfoil. The rate of LEV formation was dependent on the angle of attack until 10° and it was independent of the turbulence properties tested. The fluctuations in surface pressures and consequently aerodynamic loads were considerably limited on the airfoil bottom surface due to the favorable pressure gradient.


Shear Layer Turbulence Intensity Integral Length Scale Leading Edge Vortex Separate Shear Layer 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.





Lift coefficient


Pitching moment coefficient


Pressure coefficient




Leading edge


Leading edge vortex


Longitudinal integral length scale


Spectral density


Strouhal number (\( St = f.c.{ \sin }(\alpha )/v \))


Trailing edge


Turbulence intensity


Angle of attack


Standard deviation of time-varying surface pressure


Wave number (\( \mu = f \times c/v \))



The authors thank AFOSR, RMIT MAV research group and RMIT technical support staff for their assistance. The authors also thank two anonymous reviewers for their critical, yet valuable, comments.


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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Sridhar Ravi
    • 1
  • Simon Watkins
    • 2
  • Jon Watmuff
    • 2
  • Kevin Massey
    • 2
  • Phred Petersen
    • 2
  • Matthew Marino
    • 2
  • Anuradha Ravi
    • 3
  1. 1.University of TuebingenTuebingenGermany
  2. 2.RMIT UniversityMelbourneAustralia
  3. 3.Vellore Institute of TechnologyVelloreIndia

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