Study on velocity oscillating phenomenon of free falling bodies

In order to study the falling velocity oscillating phenomenon,the characteristic of suspending obj ects of five typical rigid bodies inside up-flow were experimentally studied by using a wind tunnel with vertical test section based on the principle of relative motion.The rigid objects include ball,cube,cuboid,cylinder and disc.The mean wind velocities inside the wind tunnel test section were measured by Pitot-Tube and the dynamic status of the obj ects before and after its suspension were recorded by CCD camera and quantitatively analyzed.The experimental re-sults show that the obj ects of symmetrical bodies can maintain a comparatively stable suspension state,while those of asymmetrical bodies continuously oscillate with changing attitude angle due to different drag coefficient and pitch coefficient on the asymmetrical objects.In other words,the symmetrical objects can reach a stable maximum falling speed during free fall,while the asym-metrical bodies are hard to reach expected maximum falling speed.Besides experimental study,a 2-D Computational Fluid Dynamics (CFD)model combined with dynamic mesh technology was also performed,from which the drag coefficient,pitch coefficient and the trajectory of the square inside the flow were obtained.The simulation results can be used to quantitatively explain the falling velocity oscillation of the asymmetrical free falling bodies.