(41f) Multi-Scale Structure of Clustering Particles

In the particle-related engineering equipment such as circulated fluidized bed and pneumatic conveyer, it is well-known that particles form a spontaneous structure. This is the ?particle cluster?. Clustering particles have significant interactions with the surrounding flows and enhance the transport performance of flows drastically. For the innovative designing and advanced controlling of such equipment, it is important to know the characteristics of the particle cluster in detail. However, the behavior of cluster is quite complex because it is a typical phenomenon which has strong non-linearity and high degree of freedom. The physics of particle cluster is still not known well. To promote a better understanding, detailed information on the flow field is needed. In this paper, spatial scale characteristics of clustering particles are investigated by using the flow field data obtained from time-dependent three-dimensional numerical simulations. Eulerian/Lagrangian approach with the two-way coupling is adopted. Individual particle-particle collisions are taken into account by using the hard-sphere model. More than sixteen million particles are tracked in the maximum case. High/low-pass filters are used to investigate relations between the spatial scale component and structure. The three-dimensional structure of clusters is also investigated. The results show that the particle cluster consists of multiple-spatial scale components and the low wave-number, hence the large-scale structure, is dominant. Three-dimensional structure reconstructed from the low-pass filtered data enables us to investigate the essential dynamics of particle clusters in detail. From the domain-size-dependency study, it is found that the structure of particle cluster is sensitive to the spanwise domain size when the periodic boundary condition is used.