Spatio-temporal spectral analysis of a forced cylinder wake

TL;DR

This study investigates the spatio-temporal spectral characteristics of a cylinder wake under rotary oscillations at Re=100, revealing energy cascades and stability boundaries through innovative spectral analysis and drag calculations.

Contribution

It introduces a novel spectral analysis method to characterize forced wake dynamics and stability, linking flow energy distribution to wake behavior and forces.

Findings

Identification of energy cascade mechanisms at high forcing amplitudes

Detailed mapping of stability boundaries between global and convective instability

Quantitative relationship between wake properties and drag force

Abstract

The wake of a circular cylinder performing rotary oscillations is studied using hydrodynamic tunnel experiments at $Re=100$. Two-dimensional particle image velocimetry on the mid-plane perpendicular to the axis of cylinder is used to characterize the spatial development of the flow and its stability properties. The lock-in phenomenon that determines the boundaries between regions of the forcing parameter space were the wake is globally unstable or convectively unstable is scrutinized using the experimental data. A novel method based on the analysis of power density spectra of the flow allows us to give a detailed description of the forced wake, shedding light on the energy distribution in the different frequency components and in particular on a cascade-like mechanism evidenced for a high amplitude of the forcing oscillation. In addition, a calculation of the drag from the velocity field is performed, allowing us to relate the resulting force on the body to the wake properties.