Wake dynamics of the flow around an anguilliform cylinder at low Reynolds numbers

An anguilliform cylinder (AC) is designed with consideration of 3D geometric perturbations inspired by anguilliform swimmers. The flow characteristics around the AC are numerically investigated via three-dimensional (3D) direct numerical simulations at low Reynolds numbers (Re) ranging from 100 to 600. This analysis is compared with analogous investigations concerning flow phenomena around a uniform circular cylinder (CC) and an elliptical cylinder (EC). The effects of the Re on the Strouhal number (St) and the force coefficients reveal the 3D wake transition process of different cylinder types, as well as the flow-controlling effects of the anguilliform geometry disturbances. In comparison to the uniform CC and EC, the anguilliform cylinder demonstrates notable achievements in mitigating both the fluctuating lift force and mean drag force. Furthermore, the AC exhibits more elongated separated shear layers when compared with the CC and EC, leading to substantial suppression of coherent vortex shedding across broad spanwise regions. These 3D vortical characteristics directly contribute to the reduction of aerodynamic forces. The values of flowing quantities are influenced by the presence of anguilliform surfaces. Notably, the anguilliform shape of the AC results in higher values of the base pressure coefficient and induces 3D undulatory separations along the cylinder surface. This configuration facilitates prolonged vortex formation lengths and diminishes turbulent kinetic energy in the near wake. These distinct flowing features of AC are linked to its efficacy in suppressing vortex shedding and reducing aerodynamic forces.