Rotation-induced wake reorganization in wavy cylinders

This study investigates the interplay between rotation and spanwise geometric modulation in governing the wake dynamics of circular cylinders at a subcritical Reynolds number, Re=3000 using large eddy simulations. Rotation rates (0≤α≤5) are applied to smooth and sinusoidally modulated cylinders with wavelengths λ/Dm=1.894,3.79, and 6.06. The primary wake phenomena, including Kármán vortex shedding, circumvolving layer (CVL) formation, and Taylor–Görtler (TG) vortex development, are systematically mapped in a rotation–waviness plane. The results identify three distinct wake regimes: the organized wake (OW), the transitional wake (TW), and the reorganized stable wake (RSW). At low rotation rates (OW), all configurations sustain a coherent Kármán vortex street modulated by surface waviness. Increasing α triggers a transition to the TW regime, characterized by the breakdown of spanwise coherence and the emergence of centrifugal instabilities (CVL and TG vortices). While the onset of TG vortices is similar across geometries, their spatial development is highly wavelength-dependent. Short wavelengths confine TG activity near the surface, leading to localized unsteadiness. In contrast, longer wavelengths facilitate a distributed interaction between TG vortices and CVL, promoting a coherent reorganization into the RSW state. The aerodynamic response reflects these transitions, with the TW regime exhibiting a peak in lift fluctuations due to the breakdown of primary vortex shedding. Notably, the long-wavelength configuration facilitates global wake stabilization, achieving maximum mean lift while suppressing unsteady loads, thereby providing a physical basis for manipulating wake topologies.