ON THE STRUCTURE OF 3-DIMENSIONAL SHEAR FLOWS

This paper describes an investigation of structure in moderately dilute three-dimensional shear flows. Structure is defined as a dynamic inhomogeneity or fluctuation in the spatial concentration field. Numerical experiments are performed with large numbers of identical, frictionless, inelastic spheres. The spheres are contained in a fully periodic cubic control volume. A state of shear is maintained in the control volume 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 the concentration, stress, and velocity fields. Visual inspection of the spatial concentration field reveals a strong tendency for spheres with a low coefficient of restitution to form dense elongated clouds. The major axis of the clouds tends to align itself in the direction of the mean velocity and perpendicular to the direction of variation in the mean velocity created by the moving periodic images of the control volume.