Analysis On Wind-induced Vibration Of Real And Artificial Poplar Leaves

The deformation and vibration of real and artificial poplar leaves in windwas studied by wind tunnel experiment. The results of video recording show that thereal poplar leaves went through a series of states with the increasing wind speed,including static deformation, large amplitude and low frequency vibration, highfrequency vibration, curling and reconfiguration to steady shape, and so on. Then thecritical wind speed were found out. The man-made poplar leaves which are made ofPVC film of0.175mm thickness with the same shape go through a similar process aswind speed rises. Meanwhile, a single vortex, a pair of vortexes or non-vortex couldbe found in the cross section of the fluid field by PIV, which corresponding to thestates of static deformation, curling and reconfiguration to steady shape and vibration.It was showed with How-wire that a single peak which induced by vortex sheddingbehind the leaves was observed with fluctuating velocity spectrum of the wake.When it became vibration, multi-peak were found, corresponding to the vibrationfrequency and harmonic frequency.The measurements on the man-made poplar leaves different in size of blade andpetiole conclude that the critical state of changing from static deformation to largeamplitude and low frequency vibration and changing from high frequency vibrationto reconfiguration to steady shape are influenced by two dimensionless parameters.One is the length to width ratio of the petiole and the other is Reynolds number basedon blade length. When the state of large amplitude and low frequency vibration arises,the Reynolds number of blade is stable as the characteristic length of petiole rises,which interprets the state only determined by the Reynolds number; While theReynolds number goes up, when the state of reconfiguration to steady shape occurs,which interprets that the length of the petiole has an effect on tree stability.