This paper is concerned with the motion of small gas bubbles, equivalent
diameter about 1.0 mm, in isotropic turbulent flows. Data on the mean velocity
of
rise and the dispersion of the bubbles have been obtained numerically by
simulating
the turbulence as a sum of Fourier modes with random phases and amplitudes
determined by the Kraichnan and the von Kármán–Pao
energy-spectrum
functions, and by calculating
the bubble trajectories from a reasonably well-established equation of
motion. The
data cover the range β[les ]1, where β is the ratio between the
turbulence intensity and
the velocity of rise of the bubbles in still fluid. An approximate analysis
based
on the assumption that β is small yields results that compare favourably
with
the numerical data, and clarifies the important role played by the lift
forces
exerted by the fluid.