Eventos Anais de eventos
ENCIT 2022
19th Brazilian Congress of Thermal Sciences and Engineering
Particle displacements over interacting barchans
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.ENCIT2022.CIT22-0024
Abstract
Barchans are dunes of crescentic shape formed in areas of unidirectional fluid flow and limited amount of grains. They can be found in several environments, such as deserts, rivers, oceans, and even on the surface of Mars. Due to the large timescales of desert (years) and Martian (decades) dunes, physicists and geophysicists perform experiments with subaqueous barchans to understand the dynamics of barchan fields in a few minutes. In some recent works, we investigated the short-range interactions of two subaqueous barchans, and showed five different patterns arising from the interaction. It has been proposed that the appearance of different patterns depends on the Shields number and the ratio of the number of particles in each dune. Also, we investigated the binary field of barchans composed of grains of different sizes and proposed a timescale for the collision of the dunes. The present study aims to understand and quantify the displacements of particles over barchans, for both monodisperse and bidisperse mixture of grains, during different barchan-barchan interactions. The experimental setup consisted of a 5-m-long closed-conduit channel with a rectangular cross-section (width = 160 mm and height = 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 deformed into barchan dunes. A conventional camera, placed on the top of the channel, was used to acquire images of the interactions. Matlab codes were developed to identify and follow particles over time. As preliminary results, we computed mean velocities, mean displacements, and the stopping/moving ratio of particles. Also, for monodisperse dunes, we calculated the movement density and sediment flux. The results of this study may explain why downstream dunes accelerate in some cases, and reveal details of the granular dynamics under different conditions.
Keywords
Dunes, Barchan-barchan interactions, Particle Displacements
