ON THE STRUCTURE OF 3-DIMENSIONAL SHEAR FLOWS

This paper describes an investigation of structure in moderately dilut e three-dimensional shear flows. Structure is defined as a dynamic inh omogeneity or fluctuation in the spatial concentration field. Numerica l experiments are performed with large numbers of identical, frictionl ess, inelastic spheres. The spheres are contained in a fully periodic cubic control volume. A state of shear is maintained in the control vo lume by moving the upper periodic image in one direction and the lower image in the opposite direction. As the coefficient of restitution of the spheres is lowered, conditions in the control volume deviate from a state of simple shear, exhibiting strong wavelike fluctuations in t he concentration, stress, and velocity fields. Visual inspection of th e spatial concentration field reveals a strong tendency for spheres wi th a low coefficient of restitution to form dense elongated clouds. Th e major axis of the clouds tends to align itself in the direction of t he mean velocity and perpendicular to the direction of variation in th e mean velocity created by the moving periodic images of the control v olume.