Hydrodynamics of an oscillating cylinder inline with steady current

TL;DR

This study numerically investigates the wake and force behaviors of an oscillating cylinder in steady currents across various amplitudes and wavelengths, revealing complex wake interactions, synchronized modes, and limitations of the Morison equation at higher wavelengths.

Contribution

It provides new insights into wake interactions and force characteristics of oscillating cylinders in steady flows, highlighting the limitations of existing predictive models.

Findings

Identification of wake interaction regimes at different wavelengths.

Discovery of synchronized and desynchronized wake modes.

Assessment of Morison equation accuracy for force prediction.

Abstract

Wake and force characteristics of an oscillating cylinder in inline steady currents are investigated numerically over a wide parameter space of dimensionless oscillation amplitude ($A^* = 0.01 - 0.50$) and wavelength ($\lambda^* = 0.4 - 25$) at a fixed Reynolds number $Re = 500$. Fundamental issues addressed in this study are the interactions of wakes induced by steady approaching flow and cylinder oscillations and the influences of the governing parameters of $A^$ and $\lambda^$ on such interactions. Whilst the collinear flow is dominated by wakes induced by cylinder oscillation at $\lambda^* \leq 1.5$ and steady current at $\lambda^* \geq 10$, it exhibits characteristics of nonlinear interactions of wakes induced by the cylinder oscillation and steady current at $\lambda^* = 1.5 - 10$, such as the formation of multiple synchronized modes interleaved with desynchronized modes. The synchronized mode varies with both $\lambda^$ and $A^$, forming an inclined Arnold's tongue across $\lambda^-A^$ space. There is a wide variability of the vortex shedding pattern in each synchronized mode. Variations of different hydrodynamic force coefficients with $\lambda^$ and $A^$ are investigated with physical interpretations based on the wake characteristics. The applicability of the Morison equation in predicting inline force fluctuations is examined. We found that the Morison equation shows reasonable accuracy only for a small range of $\lambda^* \leq 1.5$. Beyond this range, its performance deteriorates due to the influence of steady current on wake characteristics.