Three-dimensional numerical investigations on lift and drag characteristics of bird wing performing flapping motion

Abstract

Present work carries out numerical investigations for 3-D model of flapping bird wing (owl) by use of commercial software ANSYS Fluent 15.0. In past, mostly standard air foil has been used to study flow characteristics of flapping motion. In the present study, geometry selection of owl wing has been done based on similar research reported in literature. Computations are carried out to simulate lift and drag characteristics of owl wing for different parameters, such as Reynolds number, angle of attack, frequency and amplitude. In the computational domain, dynamic meshing has been used to impart motion to the wing with the help of User Defined Function. Spring based smoothing function is selected for smoothing during dynamic motion of the wing. Literature reports that propulsive power can be generated by the flapping motion of wing beyond certain value of flapping frequency. Flapping motion in 3-D can be considered as a combination of both rotational and translational motions. For simplicity, the rotational motions are assumed to be present only about two axes, namely about stream-wise and span-wise directions. Effect of phase difference between the two rotational motions has been investigated and presented in the form of force coefficient ratio (R), which is the ratio of mean lift coefficient to mean drag coefficient. Critical value of Reynolds number has been computed at which the value of ratio R becomes equal to unity. Results show that an increase in flapping frequency is associated with a decrease in the value of mean drag coefficient.