Experimental study of the sweep-back angle on the aerodynamic performance of a flapping flexible wing

Authors

Department of Aerospace Engineering, Amirkabir University of Technology

10.22044/jsfm.2026.15355.3918

Abstract

The present study experimentally investigates the effect of flexible wing sweep-back angle on the aerodynamic characteristics and the thrust and lift coefficients. The experiments were conducted at Reynolds numbers of 42,000 to 170,000, which is the flight range for natural birds with dimensions close to pigeons. The model consists of two parts of rigid (at root) and flexible (at tip) and the oscillation is provided by an electro-mechanical system. The results show that increasing the speed at dimensionless frequencies less than 0.2 has caused a decrease in the wing lift. The thrust coefficient versus speed graph at angles of attack of zero to 6 degrees is completely different from angles of attack greater than 6 degrees; So that at an angle of attack of 3 degrees, the changes in speed were less than 10 percent; But at an angle of attack of 18 degrees, the thrust coefficient decreased by 50 percent as the speed increased from 5 to 20 meters per second. Also, the flexibility of the wing has caused the dynamic pressure difference of the flow to change the shape of the wing and ultimately reduce the lift coefficient of the wing. Likewise, the flow structure from an angle of attack of 9 degrees onwards is such that it is not capable of producing propulsive force.

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Journal of Solid and Fluid Mechanics
Volume 15, Issue 6
January and February 2026
Pages 535-544

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