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Lateral instability of dense granular flows on a rough incline

Börzsönyi, T; Ecke, RE; McElwaine, JN (Research Ins for Solid State / Cambridge)
Thursday 08 January 2009, 12:15-12:30

Seminar Room 1, Newton Institute


Dense granular flows are often observed to become unstable and form inhomogeneous structures in nature or industry. The nature of such instabilities is often not understood in details, and in certain cases even the existence of the instability and the structure of the developing pattern is not yet explored. We present experimental and numerical (MD) results about a longitudinal stripe state that arises from instabilities of the uniform flowing state of granular media on a rough inclined plane. It is know that longitudinal vortices can be formed in dilute flows where the mean density is less than 50% of the random close packed density. We show that a robust longitudinal stripe state is formed already in dense flows staarting at mean densitites of about 0.95. We measure the mean density of the flow, the lateral profiles of the velocity, the flow height, the transmitted light intensity and the surface fluidisation. The form of the stripes depends critically on the mean density of the flow. At high density faster flowing regions correspond to height maxima of the modulated height profile. At higher inclination where the average density becomes significantly lower we find the previously reported state, where faster flow occurs in the lower regions of the flow. Molecular dynamics simulations reveal details of the internal flow structure and confirm a transition between the dense and dilute regimes.


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