Visualization of an incompressible wake with base bleed

The wake behind a two-dimensional bluff body has been photographed in water in order to investigate the modifying effect of base bleed. With this technique it has been possible to measure velocities at chosen points and from these make simultaneous estimates of the base pressure and of the strength of individual vortices in the wake. The results suggest that the observed decay in the vortex structure of the wake is related to variations in the conditions of mixing between the base fluid and the external stream.