Skip to main content
    • Aa
    • Aa

Airfoil in a high amplitude oscillating stream

  • C. Strangfeld (a1) (a2), H. Müller-Vahl (a2) (a3), C. N. Nayeri (a2), C. O. Paschereit (a2) and D. Greenblatt (a3)...

A combined theoretical and experimental investigation was carried out with the objective of evaluating theoretical predictions relating to a two-dimensional airfoil subjected to high amplitude harmonic oscillation of the free stream at constant angle of attack. Current theoretical approaches were reviewed and extended for the purposes of quantifying the bound, unsteady vortex sheet strength along the airfoil chord. This resulted in a closed form solution that is valid for arbitrary reduced frequencies and amplitudes. In the experiments, the bound, unsteady vortex strength of a symmetric 18 % thick airfoil at low angles of attack was measured in a dedicated unsteady wind tunnel at maximum reduced frequencies of 0.1 and at velocity oscillations less than or equal to 50 %. With the boundary layer tripped near the leading edge and mid-chord, the phase and amplitude variations of the lift coefficient corresponded reasonably well with the theory. Near the maximum lift coefficient overshoot, the data exhibited an additional high-frequency oscillation. Comparisons of the measured and predicted vortex sheet indicated the existence of a recirculation bubble upstream of the trailing edge which sheds into the wake and modifies the Kutta condition. Without boundary layer tripping, a mid-chord bubble is present that strengthens during flow deceleration and its shedding produces a dramatically different effect. Instead of a lift coefficient overshoot, as per the theory, the data exhibit a significant undershoot. This undershoot is also accompanied by high-frequency oscillations that are characterized by the bubble shedding. In summary, the location of bubble and its subsequent shedding play decisive roles in the resulting temporal aerodynamic loads.

Corresponding author
Email address for correspondence:
Linked references
Hide All

This list contains references from the content that can be linked to their source. For a full set of references and notes please see the PDF or HTML where available.

R. K. Amiet 1990 Gust response for flat-plate airfoils and the kutta condition. AIAA J. 28 (10), 17181727.

T. K. Barlas  & G. Van Kuik 2010 Review of state of the art in smart rotor control research for wind turbines. Prog. Aerosp. Sci. 46 (1), 127.

W. Birnbaum 1923 Die tragende Wirbelfläche als Hilfsmittel zur Behandlung des ebenen Problems der Tragflügeltheorie. Z. Angew. Math. Mech. 3 (4), 290297.

M. S. H. Boutilier  & S. Yarusevych 2012 Parametric study of separation and transition characteristics over an airfoil at low reynolds numbers. Exp. Fluids 52 (6), 14911506.

D. Favier , A. Agnes , C. Barbi  & C. Maresca 1988 Combined translation/pitch motion-a new airfoil dynamic stall simulation. J. Aircraft 25 (9), 805814.

K. Gompertz , C. Jensen , P. Kumar , D. Peng , J. W. Gregory  & J. P. Bons 2011 Modification of transonic blowdown wind tunnel to produce oscillating freestream Mach number. AIAA J. 49 (11), 25552563.

K. Granlund , B. Monnier , M. Ol  & D. Williams 2014 Airfoil longitudinal gust response in separated vs. attached flows. Phys. Fluids 26 (2), 114.

D. Greenblatt 2015 Unsteady low-speed wind tunnel design. In 31st AIAA Aerodynamic Measurement Technonoly & Ground Testing Conference, Dallas, TX.

D. Greenblatt 2016 Unsteady low-speed wind tunnels. AIAA J. doi:10.2514/1.J054590.

R. Isaacs 1945 Airfoil theory for flows of variable velocity. J. Aeronaut. Sci. 12 (1), 113117.

J. G. Leishman  & A. Bagai 1998 Challenges in understanding the vortex dynamics of helicopter rotor wakes. AIAA J. 36 (7), 11301140.

H. Müller-Vahl , C. Strangfeld , C. N. Nayeri , C. O. Paschereit  & D. Greenblatt 2015 Control of thick airfoil, deep dynamic stall using steady blowing. AIAA J. 53 (2), 277295.

M. V. Ol 2007 Vortical structures in high frequency pitch and plunge at low Reynolds number. In 37th AIAA Fluid Dynamics Conference and Exhibit, Miami, FL.

G. A. Pierce , D. L. Kunz  & J. B. Malone 1978 The effect of varying freestream velocity on airfoil dynamic stall characteristics. J. Am. Helicopter Soc. 23 (2), 2733.

J. P. Retelle , J. M. McMichael  & D. A. Kennedy 1981 Harmonic optimization of a periodic flow wind tunnel. J. Aircraft 18 (8), 618623.

C. Strangfeld , H. Müller-Vahl , C. N. Nayeri , C. O. Paschereit  & D. Greenblatt 2014 Airfoil subjected to high-amplitude free-stream oscillations: theory and experiments. In 7th AIAA Theoretical Fluid Mechanics Conference, AIAA Aviation, Atlanta, GA.

C. Strangfeld , C. L. Rumsey , H. Müller-Vahl , D. Greenblatt , C. N. Nayeri  & C. O. Paschereit 2015 Unsteady thick airfoil aerodynamics: experiments, computation, and theory. In 45th AIAA Fluid Dynamics Conference, Dallas, TX.

A. P. Szumowski  & G. Meier 1996 Forced oscillations of airfoil flows. Exp. Fluids 21 (6), 457464.

W. A. Timmer 2008 Two-dimensional low-reynolds number wind tunnel results for airfoil naca 0018. Wind Engng 32 (6), 525537.

S. Wagner , R. Bareiss  & G. Guidati 1996 Wind Turbine Noise. Springer.

B. G. van der Wall  & J. G. Leishman 1994 On the influence of time-varying flow velocity on unsteady aerodynamics. J. Am. Helicopter Soc. 39 (4), 2536.

Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Journal of Fluid Mechanics
  • ISSN: 0022-1120
  • EISSN: 1469-7645
  • URL: /core/journals/journal-of-fluid-mechanics
Please enter your name
Please enter a valid email address
Who would you like to send this to? *



Full text views

Total number of HTML views: 4
Total number of PDF views: 103 *
Loading metrics...

Abstract views

Total abstract views: 214 *
Loading metrics...

* Views captured on Cambridge Core between September 2016 - 27th June 2017. This data will be updated every 24 hours.