Fluid-Structure Simulations of Vortex Shedding Induced Vibrations on Two In-Line Cylinders in Water Cross-Flow

Abstract

Abstract Experimental tests accessing both fluid and structure behaviors are mandatory for a consistent assessment of fluid-structure interaction (FSI) numerical simulations. In this paper, published results of an experimental configuration of two in-line cantilever cylinders subjected to water cross-flow were considered: instantaneous fluid velocities and pressure are available on several positions inside the test section, together with the cylinder vibrations. FSI simulations were performed by coupling Ansys Fluent (for the fluid domain) with Ansys Mechanical (for the solid domain). URANS simulations and Scale-Adaptive Simulations (SAS) were employed as CFD simulation approach. The structure displacements were taken into account through an Arbitrary Lagrangian-Eulerian approach. The fluid-structure coupling was 2-way explicit. Simulations were performed for two different water mass flow rates. For the highest one, vortex-induced resonance is observed experimentally. The numerical results show consistent agreement in terms of shedding frequency and velocity spectra behind the cylinders. The calculated vibration response is overall consistent for the cylinders not featuring vortex-induced resonance; nevertheless, the experimentally observed vortex-induced resonance could not be reproduced by the numerical simulations. The inability to calculate the resonance is explained by the fact that it is found to be caused by the 4th shedding harmonic being in resonance with the cylinder natural frequency: this high harmonic peak could not be numerically reproduced, even by SAS.