Aerodynamic Characteristics Investigation Of Ginkgo Leaf

This paper is about the deformation,vibration,state changes,and aerodynamic forces of ginkgo leaves at step by step increasing wind speeds.The geometrical parameters involved are the sector angle and crack depth of the lamina,and the length to width ratio of the petiole.The physical parameters studied are lamina Reynolds number,and the elastic modulus of the petiole and the bending strength of lamina.?1?As the increase of wind speed from 0 to 20m/s,the state of a typical leaf changes from stationary to low frequency sway,first steady,medium frequency vibration,second steady,high frequency vibration,and third steady.The cross-sectional shapes of a reconfigured leaf at steady state include U-shape,S-shape,?-shape,?-shape,long-cylinder-shape and horn-shapes.The leaves of larger sector angle has more opportunity to be at steady state than the leaves of smaller sector angle at the same wind speed.The leaves of deeper crevasse are more steady than the ones of shallow crevasse.?2?The drag coefficient C_D decreases as the increase of Reynolds number,but it tends to a constant if Re is larger than 4×10⁴.The petiole curves downstream and the petiole angle and lamina angle increases as the wind speed increases,which helps to decrease the frontal area of the deformed lamina.The drag coefficient decreases with the increase of petiole angle,lamina angle.The measured Vogel component?=-1.4^-0.7 in the range of wind speed 2⁹m/s,and?=-0.4⁰.7 in the range of wind speed 10¹6m/s.?3?There are three vibration modes of ginkgo leaves.Vibration mode is the main factor affecting the vibration frequency.The vibration frequency decreases with the increase of the sector angle and increases with the increase of wind speed,When the mode of vibration is simultaneous.Frequency lock vibration phenomenon will appear,when the vibration frequency of the leaf is consistent with the natural frequency of the petiole.?4?The elastic modulus of petiole and the bending strength of lamina were measured by cantilever beam model.The elastic modulus of the petiole is mainly distributed between?1.6×10⁸⁴.1×10⁸?N/m²,and the bending strength of the lamina is mainly in the range of 4×10^-78×10^-7N/m².