Direct numerical simulation of flapping flags in grid-induced turbulence

TL;DR

This study employs a GPU-accelerated DNS approach to investigate how grid-induced turbulence affects the flapping motion of flexible flags, revealing turbulence's influence on oscillation characteristics and spectral features.

Contribution

It introduces a novel DNS framework with grid-generated turbulence to analyze flexible flag dynamics, enhancing understanding of fluid-structure interactions in turbulent flows.

Findings

Turbulence alters flag oscillation amplitude and frequency.

Spectral analysis detects turbulence's fingerprint on flag motion.

Flow characteristics are validated against known turbulence results.

Abstract

A fully-resolved direct-numerical-simulation (DNS) approach for investigating flexible bodies forced by a turbulent incoming flow is designed to study the flapping motion of a flexible flag at moderate Reynolds number. The incoming turbulent flow is generated by placing a passive grid at the inlet of the numerical domain and the turbulence level of the flow impacting the flag can be controlled by changing its downstream distance from the grid. The computational framework is based on the immersed boundary method for dealing with arbitrary geometries and implemented using a graphics-processing-unit (GPU) accelerated parallelisation to increase the computational efficiency. The grid-induced turbulent flow is first characterised by means of the comparison with well-known results for decaying turbulence and a scale-by-scale analysis. Then, the flag-in-the-wind problem is revisited by exploring the effect of the turbulence intensity on self-sustained flapping. Whilst the latter is still manifesting under strong fluctuations, the main features of the oscillation (including its amplitude and frequency) are altered by turbulence, whose fingerprint can also be qualitatively detected by spectral analysis. Besides their relevance for advancing the fundamental understanding of fluid-structure interaction in turbulence, these findings have potential impact for related applications, e.g., aeroelastic energy harvesting or flow control techniques.