Gyrational motion of disks during free‐fall
作者:
Ronald E. Stewart,
Roland List,
期刊:
Physics of Fluids(00319171)
(AIP Available online 1983)
卷期:
Volume 26,
issue 4
页码: 920-927
ISSN:0031-9171
年代: 1983
DOI:10.1063/1.864241
出版商: AIP
数据来源: AIP
摘要:
Experiments with disks having diameters from 2.0 to 3.1 cm falling freely in air at speeds of 1.7–3.3 m sec−1were conducted with a vertically driven, also falling, high‐speed camera in order to show that the gyroscopic‐like motion, gyration, is the most general type of rotational motion. From analysis of the films, position and orientation were measured throughout the fall and translatory and angular motions were determined, together with the forces and torques which caused the motion. The existence of gyrational motions was confirmed together with straight oscillatory and rotational fall behavior. Typical nutation/precession frequencies were in the range of 6–11 Hz while typical angular frequencies about the minor axis were 1.8–3.0 Hz. The likelihood of gyration increased with particle density. The observed gyration characteristics of disks were similar to predictions for oblate spheroids. Further, it is postulated that air influences can cause rotation about a horizontal diameter to become unstable and to consequently evolve into gyration. This gyrational motion may represent a very general mode of free fall for other shapes in a similar range of Reynolds numbers from 2000–5000.
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