An experimental modal testing method for subcritical flow around a cylinder

TL;DR

This paper introduces a novel experimental modal testing method using Dynamic Mode Decomposition to extract flow modes around a cylinder at subcritical Reynolds numbers, enhancing understanding of flow physics and fluid-solid interactions.

Contribution

It is the first to experimentally extract dominant flow modes in subcritical flow around a cylinder using DMD, aligning well with numerical results and revealing flow-structure interactions.

Findings

First-order von Kármán mode observed at Re as low as 19.3

Extracted modes agree with numerical literature

Reveals correlation between flow modes and fluid-solid instability

Abstract

Modal analysis of fluid flows is essential to understand flow physics and fluid-solid interaction mechanisms, and to implement flow control. Unlike unstable flow, the intrinsic attenuation of subcritical flow has led to failures to experimentally extract the subcritical flow modes clearly. To this end, this paper proposes a modal testing method for subcritical flows. Using Dynamic Mode Decomposition (DMD), dominate modes of flow around a cylinder at subcritical Reynolds numbers are extracted experimentally for the first time. The extracted structures and parameters of the modes are in good agreement with the numerical results in the literature. It is found that the first-order von K\'arm\'an mode can be observed at a Reynolds number as low as 19.3, which is very close to the lower boundary of subcritical vortex induced vibrations (VIV). This experimental observation elucidates the correlation between von K\'arm\'an mode and fluid-solid interaction instability in subcritical flows.