Periodic Phenomena Observed with Spherical Particles in Horizontal Pipes.
A thin layer of spherical particles resting on the bottom of a round pipe was observed to form into essentially equally spaced clumps or islands at fluid velocities only slightly greater than those required to initiate particle movement. This phenomenon appeared to be similar to dune formation in open channels since the ratio of the square of the stream velocity, U, and the product of the gravitational constant, g(L), and the island wavelength, lambda, was correlated by the same function of island height and velocity, particle diameter, and fluid depth regardless of whether the flow was through a closed conduit or an open channel.
Thomas
D G
DG