Role of Transverse Displacements in the Formation of Subaqueous Barchan Dunes

Autor(es)

Alvarez, Carlos A. ^[1] ; Franklin, Erick M. ^[1]

Afiliação do(s) autor(es)

^[1] UNICAMP Univ Campinas, Sch Mech Engn, Rua Mendeleyev 200, Campinas, SP - Brazil

• Tipo de documento: Artigo Científico
• Fonte: Physical Review Letters; v. 121, n. 16 OCT 19 2018.
• Citações Web of Science: 4

Resumo

Crescentic shape dunes, known as barchan dunes, are formed by the action of a fluid flow on a granular bed. These bedforms are common in many environments, existing under water or in air, and being formed from grains organized in different initial arrangements. Although they are frequently found in nature and industry, details about their development are still to be understood. In a recent paper {[}C. A. Alvarez and E. M. Franklin, Phys. Rev. E 96, 062906 (2017)], we proposed a timescale for the development and equilibrium of single barchans based on the growth of their horns. In the present Letter, we report measurements of the growth of horns at the grain scale. In our experiments, conical heaps were placed in a closed conduit and individual grains were tracked as each heap, under the action of a water flow, evolved into a barchan dune. We identified the trajectories of the grains that migrated to the growing horns, and found that most of them came from upstream regions on the periphery of the initial heap, with an average displacement of the order of the heap size. In addition, we show that individual grains had transverse displacements by rolling and sliding that arc not negligible, with many of them going around the heap. The mechanism of horns formation revealed by our experiments contrasts with the general picture that barchan horns form from the advance of the lateral dune flanks due to the scaling of migration velocity with the inverse of dune size. Our results change the way in which the growth of subaqueous barchan dunes is explained. (AU)

• Processo FAPESP: 16/13474-9 - Instabilidades em escoamentos granulares densos
• Beneficiário: Erick de Moraes Franklin
• Modalidade de apoio: Auxílio à Pesquisa - Regular