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TURBULENCE SIMULATION FOR BEDLOAD SEDIMENT TRANSPORT

H. V. Truong
Department of Civil and Environmental Engineering, Ritsumeikan University Noji Higashi 1-1-1, Kusatsu, Shiga 525-8577, Japan

John Craig Wells
Department of Civil Engineering Ritsumeikan University 1-1-lNojihigashi, Kusatsu, Shiga, 525-8577 Japan

Gretar Tryggvason
Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN, USA

要約

In "bedload transport", sediment particles are driven in a thin layer near the sediment bed by a (normally) turbulent flow, thereby shaping rivers and the seacoast. Herein, we present a fictitious-domain method for numerical simulation of the dense-phase motion of solid particles in turbulent liquid, possibly including a free liquid-gas surface, and apply it to bedload sediment transport in rotating drum flows and in minimal channel flow with a stress-free lid.
To accelerate progress in understanding and modelling of bedload transport, we aim to perform "quasidirect" numerical simulation that resolves all stress-supporting eddies, i.e. at least down to the scale of particle diameter. For computatational tractability, we employ the "fictitious domain" technique wherein a standard incompressible Navier-Stokes solver is applied on a fixed uniform Cartesian grid. In the present implementations, the grid density allows at least four points per particle diameter. A variable-density solver is modified to recover rigid body motion inside particles by adding body forces to the governing equation. The resolution should capture, though roughly, the eddies mentioned above, but is not sufficient to resolve boundary layers around particles.
We compare computational results with experimental data from rotating drums, including a new "open-perimeter" drum that permits a free-surface flow over the particle bed. Overall agreement between experimental and simulated values of bed and free-surface angles is satisfactory. We then present data from simulations of bedload transport in a doubly-periodic "minimal channel" with a nominal friction Reynolds number of 250, and 40 grid points in the vertical and span directions. Though under-resolved, we believe these are the first reported simulations of bedload transport that are "quasi-DNS" in the sense that they resolve the particle-scale turbulence.