Fig. 3. DPIV measurements of flow created by a mechanical wake generator. Images correspond to a meridian symmetry plane of the wake vortex ring. Streamlines of the velocity field (i.e. lines tangent to each vector in the velocity field) are plotted in yellow. Exit plane of the vortex generator is located at the upper margin of the frame. Flow is directed vertically downward. Flow field is 20 cm in height. (A) View of vortex ring propagating downstream from the mechanical wake generator in the laboratory reference frame. (B) Same vortex ring as in A, viewed in a reference frame that moves at the speed of the propagating vortex ring. The full extent of the vortex is clearly visible from this perspective. White arrows indicate location of vortex ring in A and B.