Span effect on the turbulence nature of flow past a circular cylinder

TL;DR

This study explores how the span of a domain influences the turbulence characteristics of flow past a circular cylinder at high Reynolds number, revealing conditions under which 2D and 3D turbulence features coexist due to geometric effects.

Contribution

It demonstrates the impact of span length on turbulence dynamics, showing that small spans induce two-dimensionalization of flow structures even in highly anisotropic geometries.

Findings

Small span induces rapid two-dimensionalization of vortex structures.

3D small-scale structures detach from walls regardless of anisotropy.

Coexistence of 2D and 3D turbulence occurs depending on domain geometry.

Abstract

Turbulent flow evolution and energy cascades are significantly different in two-dimensional (2D) and three-dimensional (3D) flows. Studies have investigated these differences in obstacle-free turbulent flows, but solid boundaries have an important impact on the cross-over between 3D to 2D turbulence dynamics. In this work, we investigate the span effect on the turbulence nature of flow past a circular cylinder at Re=10000. It is found that even for highly anisotropic geometries, 3D small-scale structures detach from the walls. Additionally, the natural large-scale rotation of the K\'arm\'an vortices rapidly two-dimensionalises those structures if the span is 50% of the diameter or less. We show this is linked to the span being shorter than the Mode B instability wavelength. The conflicting 3D small-scale structures and 2D K\'arm\'an vortices result in 2D and 3D turbulence dynamics which can coexist at certain locations of the wake depending on the domain geometric anisotropy.