Granular Gases of Anisotropic Particles

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Similar to continua, one can define different states of aggregation for granular materials. Granular gases are loose ensembles of solid particles like the Saturn rings or sand storms. In contrast to atomic or molecular gases, collisions are dissipative and energy has to be supplied continuously in order to keep the state of motion. This energy is distributed by collisions into the diffferent rotational and translational degrees of freedom. Granular gases are prepared most easily under microgravity conditions. Although they are uniquely suited for studies of statistical dynamics of multiparticle systems, there are only few experimental studies. This is primarily due to the difficulties in the preparation of microgravity experiments and the implementation of a suitable excitation. We investigate granular gases of shape-anisotropic particles and focus on the following questions:- How does the kinetic energy distribute among the degrees of freedom?- How do such gases cool, when no energy is supplied?- What is the relation between excitation parameters and granular temperature?- What is the spatial distribution of the particles and the dynamic quantities in the cooling gas?First experiments were performed already by students within the REXUS program, about 100 sec of video sequences of a weakly excited gas in zero gravity were recorded. These experiments are, regarding the quality of the data obtained, on international top level. The available data have been evaluated only to a very small part. Further experiments will be performed tentatively by the principal investigator of this proposal in 2012 on a suborbital flight with a STIG-B rocket (Armadillo Aerospace). In addition, we will perform drop tower experiments to study influences of excitation parameters and particle geometries. The evaluation of the data available so far and those expected within the next months, as well as interpretation and modeling, are a comprehensive and ambitious program that shall be accomplished within this project. This will lead to qualitatively new insights in the understanding of granular gases and the verification of existing models.