On experimental sensitivity analysis of the turbulent wake from an axisymmetric blunt trailing edge

The sensitivity to steady local disturbances of the turbulent wake over a 3D blunt body with an axisymmetric trailing edge is investigated at Re = 2.1 × 104. The flow presents a favored m = 2 azimuthal periodicity due to the mounting of the body. It is proved that two asymmetric flows cohabit and generate a statistically symmetric natural flow. Topology shifts are random but are visible after a large number of global mode periods. The statistical symmetry is highly sensitive to any steady antisymmetric disturbance. As a consequence, depending on its position, a small control cylinder (considered as a disturbance with m = 1 azimuthal periodicity) in the close wake fixes the flow to one asymmetric topology affecting shedding activity as well as drag. On the contrary, a thin control ring (i.e., m = 0 disturbance) preserves the mean flow symmetry and has a greater impact on global mode frequency and drag. Whatever the disturbance, the sensitivity of the wake to control devices is concentrated into the mixing layers; the observed effects seem to depend more upon their local turbulent characteristics than on the global inviscid dynamics of vorticity.