This proposal seeks to build on a successful concept demonstration.
In reduced gravity, the resonant acoustic field and streaming flow in a
container drive particles to stable positions along specified surfaces.
The surface shapes can be tailored. In the 1997 Flight Test, four
speakers were used to excite pre-determined resonant modes in a
rectangular chamber containing solid particles. Particle behavior and the
sound spectra were monitored and correlated with the acceleration level
during 52 parabolic flight segments. Randomly-shaped styrofoam particles
and a granular cereal were used to represent particles of various
characteristics. The particles were entrained by the streaming flow in the
chamber, and carried to stable surfaces, where they remained steady without
the rotation which was feared from reading the previous literature. Surface
shapes were correlated with predicted modal pressure contours, and with
those observed in ground tests. The input sound power level required to
form the surfaces is low. Higher sound levels modify the streaming flow,
and are actually less efficient in forming the surfaces. In the proposed
1998 experiments, the effort will be divided between systematic parametric
variations needed to validate and improve prediction technology, and
explorations needed to form complex shapes.
