Characteristics of the near wake of a cylinder at low Reynolds numbers

An experimental study has been made of the near wake of two two-dimensional bluff bodies, a circular cylinder and a flat ribbon in the regimes corresponding to the 2-D steady and 2-D periodic wake. Velocity measurements from both hot-wire and laser Doppler anemometry are compared. Detailed measurements of the velocity field in air in the near wake, in isothermal conditions, are presented. The evolutions of the mean longitudinal velocity and the rms transverse velocity fluctuation on the center line can be plotted in a universal form whatever the value of the Reynolds number. These measurements show also that the onset of the instability is related to a critical value of an interaction term characteristic of the strength of the shear layers and the shear layer spacing at the end of the recirculation zone.