摘要

Three-dimensional direct numerical simulations of vortex shedding behind cylinders have been performed when the body diameter and the incoming flow involved spanwise linear nonuniformity. Four configurations were considered: the shear flow, the tapered cylinder and their combination which gave rise to the so called adverse and aiding cases. In contrast with the observations of other investigators, these computations highlighted distinct vortical features between the shear case and the tapered case. In addition, it was observed that the shear case and the adverse case (respec. tapered case and aiding case), yielded similar flow topology. This phenomenon was explained by the spanwise variations of U/D which seemed to govern/characterize these flows. For the cases involving a shear flow a secondary flow was observed, whereas for the tapered cylinder in an uniform flow an singular spanwise velocity component with low magnitude was exhibited. Cellular shedding mode was identified for the four configurations. The taper induced vortex-adhesion points at the location between cells. The lower frequencies of the cells, compared to two-dimensional cylinder in uniform flow, were found to be connected with the oblique vortex shedding.