Three-dimensional wake dynamics of a twisted cylinder

Abstract

The flows past a twisted cylinder are studied at low Reynolds numbers using three-dimensional (3D) direct numerical simulations. For comparison, the flows over uniform circular and elliptic cylinders are also investigated. The similar transformations from the two-dimensional (2D) laminar regime to the 3D wake transition regime in the wake of a uniform cylinder are not observed for a twisted cylinder. The wakes of a twisted cylinder inherently display 3D wake patterns owing to the effects of geometrical perturbations. The 3D wakes of the twisted cylinder are still in the stable laminar regime at low Reynolds numbers, leading to continuous variations of various flow quantities with increasing Reynolds numbers. The transformations of the shedding patterns result in discontinuous changes in these flow quantities, such as aerodynamic forces, shedding frequencies, and vortex formation lengths. In addition, some novel characteristics appear in the 3D vortex structures of a twisted cylinder. The spanwise vortex wavelength presents a lock state with the structural wavelength. The shedding vortices are oblique to the cylinder axis in the near wake, and the dislocation occurs among different segments of vortices along the spanwise direction. Moreover, the effects of these vortex features on other flowing quantities are investigated.