Physical insights into the wake structure and vortex dynamics of a circular cylinder modified by helical strakes

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Abstract
The influence of helical strakes on the near-bed junction flow and wake dynamics of a wall-mounted circular cylinder is investigated using improved delayed detached eddy simulation. At a Reynolds number of 7500, the characteristics of flow past a helical straked cylinder with a strake height of 0.2d and a pitch of 10d are examined using a plain cylinder as the reference configuration, where d is the cylinder diameter. The cylinder is vertically positioned at the domain's base, with one of the strakes aligned at 0° to the incoming flow. Results show that the strakes suppress the development of the horseshoe vortex by modifying the near-wall junction flow and promoting asymmetric, three-dimensional vortex structures. The wake becomes increasingly incoherent due to the interaction of the vortical structures from multiple strake-induced separating shear layers. Surface pressure distribution indicates localized flow separation along the edges of the strakes, while wall shear stress is redistributed into localized regions of high and low intensity due to the guided motion of the flow by the strakes. Spectral analysis shows that the strakes shift the spectral energy to a broader range of frequencies. Finally, spectral proper orthogonal decomposition reveals a redistribution of modal energy from the low-order to the higher-order modes, highlighting the role of strakes in disrupting and fragmenting the large-scale coherent wake structures.
Funding Information
  • Natural Sciences and Engineering Research Council of Canada (RGPIN-2024-04295)

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