题目：Experiments in Fluids - Master Lecture Series (III) Quantitative Hydrodynamics from Trajectory Imaging
时间：2024年4月22日 10:30-11:30
地点：机械与动力工程学院 振华会议室
腾讯会议：730488085
邀请人：彭迪 教授（叶轮机械研究所）
Biography
Cameron Tropea graduated from the University of Toronto in Engineering Sciences, followed by a Masters degree in Mechanical Engineering (1977). He completed his Dr.-Ing. in Civil Engineering at the Technical University of Karlsruhe (1982) and his Habilitation in Fluid Mechanics at the University of Erlangen-Nürnberg (1991) where he was appointed as Professor of Fluid Mechanics until 1997. This was followed by an appointment as head of the Institute of Fluid Mechanics and Aerodynamics at the Technische Universität Darmstadt.
Abstract
The behavior of a free-falling rigid sphere impacting normally onto, and penetrating into a quiescent liquid pool is examined. Parameters, which are varied include the impact velocity, the density, and the diameter of the sphere. Observations of the sphere trajectory in time are made using two orthogonally placed high-speed cameras, yielding the velocity and acceleration vector through repeated differentiation of the time resolved trajectories.
Upon penetration, the sphere goes through three very distinct phases of penetration, denoted as the submersion, deceleration and settling phase, each clearly identifiable through either features seen in trajectory direction or in changes of velocity. These phases exist for all impact Reynolds numbers and density ratios investigated, and their respective duration remains astoundingly constant in terms of dimensionless time. The motion of the sphere is analyzed using a scalar force balance for each of instantaneous drag and lift, yielding quantitative estimates of the drag and lift coefficients throughout the trajectory. The variation of these forces can be phenomenologically explained by unsteady wake behavior arising from strong deceleration and through transient asymmetry, leading to variations in trajectory curvature. Despite the large trajectory randomness observed in repetitive experiments, there exist strong commonalities in motion behavior.
