Spatiotemporal Characteristics of Turbulent Flows Around Partially Submerged Circular Cylinders

Abstract

This paper presents a time-resolved particle image velocimetry investigation of the spatiotemporal characteristics of the wake flow around a partially submerged horizontal circular cylinder with and without upstream ice cover. This study is applicable to offshore structures such as ice booms. In the experiments, the cylinder was submerged with 50% of its surface below the free surface and the Reynolds number was 10,000. A reference experiment was performed with the cylinder fully immersed in the uniform flow for comparison. Due to the absence of an upper shear layer, the recirculation length of the submerged cylinder is longer, but the turbulence levels are lower compared to the uniform case, and an upstream ice cover reduces the recirculation length and turbulence levels around the submerged cylinder compared to the open water case. The wake of the cylinders is highly anisotropic, regardless of boundary condition, with vertical fluctuating velocities being dominant over streamwise fluctuating velocities in the uniform case and vice versa in the submerged cases. In the uniform case, the turbulence production is maximum on the wake centerline, but in the submerged cases, the maximum turbulence production occurs within the shear layer. The frequency spectra of fluctuating velocities also showed that the wake of a submerged cylinder is characterized by multiple low, distinct frequencies indicative of a wide range of vortical structures, regardless of the upstream flow condition.