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COBEM 2021
26th International Congress of Mechanical Engineering
Barchan-barchan interactions with bidisperse grains
Submission Author:
Willian Righi Assis , SP
Co-Authors:
Willian Righi Assis, Fernando David Cúñez, Erick de Moraes Franklin
Presenter: Willian Righi Assis
doi://10.26678/ABCM.COBEM2021.COB2021-1346
Abstract
Barchans are dunes of crescentic shape with horns pointing downstream which are formed in areas of unidirectional fluid flow and a limited amount of granular material. Fields of barchans are found in deserts, rivers, the bottom of oceans, and even in extraplanetary environments, and the regulation of their size involves the interaction between different barchans within a field. In a recent work (Assis and Franklin (2020)), we investigated experimentally the short-range binary interactions of subaqueous barchans, including collisions, in both aligned and off-centered configurations of dunes with monodisperse grains. As a result, we identified five interaction patterns for both aligned and off-centered configurations and proposed two maps that provide a comprehensive classification for barchan-barchan interactions based on the ratio between the number of grains of each dune, Shields number, and alignment of barchans. The aim of the present study is to investigate the motion and interaction between two barchans with different particle sizes. The experimental setup consisted of a 5 m long closed-conduit channel with a rectangular cross-section (width γ = 160 mm and height β = 50 mm). A water reservoir, two centrifugal pumps, a flow straightener, a settling tank, and a return line are part of the equipment as well. With the channel filled with water, two separated quantities of grains were poured in the test section before imposing a water flow, forming two conical piles that were afterward deformed into barchan dunes. The particles were glass spheres divided into two different populations of different diameters, but with the same density, and they formed initially two bidisperse piles. The upstream pile was always smaller or equal than the downstream one, since the dune velocity varies inversely with its size, so that dunes interacted actively during the experiments. As preliminary results, we could observe that the proportion of grains of different diameters within the dune can affect the type of interaction pattern. Furthermore, we propose a characteristic collision time, which relates the distances between the dunes, the imposed flow velocity, the initial sizes of the dunes and the proportion of particles.
Keywords
Dunes, Barchan-barchan interactions, Bidisperse grains
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