Comparison of vortex formation by linearly or angularly accelerated objects in a quiescent flow

The formation of vortices in a quiescent flow is studied for different types of vortex generators. Three types of vortex generators are considered: a classical piston-cylinder configuration, a sharp edge object translated along a straight trajectory from rest, and a two dimensional rectangular flat plate that is rotated 180° about its span-wise axis. The velocity field induced by the motion of these objects is measured by means of time-resolved particle image velocimetry and Lagrangian methods are used to track the evolution of the shear layer, the generation of coherent vortical structures, and the characteristics of these vortices. Special attention is directed toward identifying non-dimensional values describing the vortex formation time and vortex circulation and energy. The geometry of the translated objects and the linear or angular acceleration profiles for the different vortex generators are varied to explore their influence on the vortex formation process and the characteristics of the shed vortices.