Velocity fidelity of flow tracer particles

Recent developments concerning the unsteady dynamic forces on a spherical particle at finite Reynolds number are reviewed for solid particles and clean micro-bubble. A particle frequency response function and an energy transfer function are derived for a solid particle or a contaminated micro-bubble in gas or liquid flow. A simple, unified method for estimating the cut-off frequency, or cut-off size, of a solid particle or a contaminated bubble is developed. Particle motion in isotropic turbulence is examined. Responses of the tracer particle to integral length scale structure, to turbulence energy, and to Taylor micro-scale structure are discussed in terms of the particle turbulence diffusivity, the particle turbulence intensity, and the ensemble average of the second invariant of fluid turbulence deformation tensor evaluated on the particle trajectory.