The influence of free-stream turbulence on the fluctuating loads experienced by a cylinder exposed to a turbulent cross-flow

The impact of several ‘flavours’ of free-stream turbulence (FST) on the structural response of a cantilever cylinder, subjected to a turbulent cross-flow is investigated. At high enough Reynolds numbers, the cylinder generates a spectrally rich turbulent wake that contributes significantly to the experienced loads. The presence of FST introduces additional complexity through two primary mechanisms: directly, by imposing a fluctuating velocity field on the cylinder’s surface, and indirectly, by altering the vortex shedding dynamics, modifying the experienced loads. We employ concurrent temporally resolved particle image velocimetry and distributed strain measurements using Rayleigh backscattering fibre optic sensors to instrument the surrounding velocity field and the structural strain respectively. By using various turbulence-generating grids, and manipulating their distance to the cylinder, we assess a broad FST parameter space allowing us to explore individually the influence of the transverse integral length scale ( $\mathcal{L}_{13}/D$ ) and turbulence intensity of the FST on the developing load dynamics. The FST enhances the magnitude of the loads acting on the cylinder. This results from a decreased vortex formation length, increased coherence of regular vortex shedding, and energy associated with this flow structure in the near wake. The cylinder’s structural response is driven mainly by the vortex shedding dynamics, and its modification induced by the presence of FST, i.e. the indirect effect outweighs the direct effect. From the explored FST parameter space, turbulence intensity was seen to be the main driver of enhanced loading conditions, presenting a positive correlation with the fluctuating loads magnitude at the root.