Direct numerical simulation of pattern formation in subaqueous sediment

TL;DR

This paper uses direct numerical simulation to study pattern formation in subaqueous sediment, revealing how flow regimes influence dune types and validating results with experimental data.

Contribution

It introduces a simulation approach combining immersed boundary and soft-sphere models to analyze sediment pattern formation under different flow conditions.

Findings

Pattern types depend on flow regime: small dunes in laminar, vortex dunes in turbulent.

Simulated pattern characteristics match experimental measurements.

Particle transport rates align with empirical models across regimes.

Abstract

We present results of direct numerical simulation of incompressible fluid flow over a thick bed of mobile, spherically-shaped particles. The algorithm is based upon the immersed boundary technique for fluid-solid coupling and uses a soft-sphere model for the solid-solid contact. Two parameter points in the laminar flow regime are chosen, leading to the emergence of sediment patterns classified as `small dunes', while one case under turbulent flow conditions leads to `vortex dunes' with significant flow separation on the lee side. Wavelength, amplitude and propagation speed of the patterns extracted from the spanwise-averaged fluid-bed interface are found to be consistent with available experimental data. The particle transport rates are well represented by available empirical models for flow over a plane sediment bed in both the laminar and the turbulent regimes.