Flexible flapping airfoil propulsion at low Reynolds numbers

By S. Heathcote, I. Gursul. 2005

398 citations recorded by the source corpus.

Water tunnel experiments on a flexible airfoil plunging with constant amplitude have been carried out for Reynolds numbers of 0 to 27000. Peaks in thrust coefficient at intermediate values of airfoil stiffness were observed at both zero and non-zero Reynolds numbers, indicating that a degree of flexibility is beneficial at low Reynolds numbers. Time-averaged velocity fields and momentum flux data revealed a broader, higher-velocity jet in cases of optimum airfoil stiffness. Stronger vortices, separated by a larger lateral distance, characterised the corresponding instantaneous velocity fields. The flexibility causes the airfoil to pitch passively; the phase angle of the pitch was found to lead the plunge. Pitch amplitude and trailing-edge amplitude were found to be single-valued functions of pitch phase angle. The shape characteristics of the airfoil could therefore be described by the pitch phase angle only. Thrust coefficient was found to be a function of only two parameters: Strouhal number and pitch phase angle. For each Strouhal number, a peak in thrust coefficient was observed at a particular value of the pitch phase angle. The optimum pitch phase angle was found to tend to a limit of 105±5 degrees at very large Strouhal numbers. A significant thrust benefit was observed over very stiff airfoils when the optimum flexibility is utilized.

Subfields: Aerospace Engineering, Computational Mechanics

View Paper: https://www.semanticscholar.org/paper/5117b48ce002f490706048efb146744f8419406e

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In Aerospace Engineering

In Computational Mechanics

Citations in the corpus

Recent progress in flapping wing aerodynamics and aeroelasticity (2010, methodology): “[32]]; (C) wing cross-sections used in the experiment for spanwise flexible wing studies [extracted from Ref.”
Direct measurement of thrust and efficiency of an airfoil undergoing pure pitching (2015, background): “An experimental study by Heathcote & Gursul (2007) for pure heaving at Reynolds numbers of 10 000, 20 000 and 30 000 showed propulsive efficiencies under 28 %.”
Flapping Wing Aerodynamics: Progress and Challenges (2008, background): “To answer this question Heathcote and Gursul [36] performedwater tunnel experiments on a harmonically plunging flexible airfoil with chordwise flexibility at Reynolds numbers between 9000 and 27,000.”
Effects of flexibility on the aerodynamic performance of flapping wings (2011, methodology): “(i) Thrust generation of a purely plunging chordwise flexible aerofoil in water in forward flight at Re = 9 × 103, studied experimentally by Heathcote & Gursul (2007) and numerically for one particular motion frequency by Shyy et al. (2010).”