Flexible flapping airfoil propulsion at low Reynolds numbers


Heathcote, S. and Gursul, I., 2005. Flexible flapping airfoil propulsion at low Reynolds numbers. In: 43rd AIAA Aerospace Sciences Meeting and Exhibit, 2005-01-01.

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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.


Item Type Conference or Workshop Items (Paper)
CreatorsHeathcote, S.and Gursul, I.
Uncontrolled Keywordsairfoils,reynolds number,propulsion,tunnels
DepartmentsFaculty of Engineering & Design > Mechanical Engineering
ID Code2085


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