WAVE PATTERNS IN A THIN-LAYER OF SAND WITHIN A ROTATING HORIZONTAL CYLINDER

A variety of wave patterns are found to form in a thin layer of sand i nside a cylinder rotated about its horizontal axis of symmetry at cons tant angular velocity. In particular, we observe a spanwise instabilit y characterized by serrated frontal shapes remarkably similar to those seen in Newtonian fluids. Within a certain parameter range, an accomp anying spatial pattern forms on the rising side of the cylinder and tr avels along the cylinder span. The associated phase velocity is relati vely constant, whereas the relevant wavelength increases quadratically with angular rotation speed. Standing waves appear at a critical rota tion rate. Further, in some cases, a propagating cellular pattern form s on the surface of the medium. (C) 1998 American Institute of Physics .