Velocity fidelity of flow tracer particles（速度流示踪粒子的忠诚）.pdf

)riginah Experiments in Fluids 22 (1996) 1-13 ~ Springer-Verlag 1996 Velocity fidelity of flow tracer particles R. Mei Abstract Recent developments concerning the unsteady dy- the following fundamental questions are sources of frequent namic forces on a spherical particle at finite Reynolds num- concern in applying those optical techniques: ber are reviewed for solid particles and clean micro-bubble. 1) how well does the velocity of a tracer (or seed) particle of A particle frequency response function and an energy trans- given size represent the unsteady fluid velocity? fer function are derived for a solid particle or a contaminated 2) how does one determine the largest possible size of the seed micro-bubble in gas or liquid flow. A simple, unified method particles for a flow field of given time scales without for estimating the cut-off frequency, or cut-off size, of a solid affecting the velocity fidelity? particle or a contaminated bubble is developed. Particle Since experimental conditions vary widely, it is not possible to motion in isotropic turbulence is examined. Responses of the give simple answers to those questions. The fluid may be liquid tracer particle to integral length scale structure, to turbulence or gas and the seed particles may be solid, liquid droplets, or energy, and to Taylor micro-scale structure are discussed gas bubbles. The fluid velocity may range from micron per in terms of the particle turbulence diffusivity, t