  The long time dynamics of large particles trapped in two inhomogeneous
turbulent shear flows is studied experimentally. Both flows present a common
feature, a shear region that separates two colliding circulations, but with
different spatial symmetries and temporal behaviors. Because large particles
are less and less sensitive to flow fluctuations as their size increases, we
observe the emergence of a slow dynamics corresponding to back-and-forth
motions between two attractors, and a super-slow regime synchronized with flow
reversals when they exist. Such dynamics is substantially reproduced by a one
dimensional stochastic model of an over-damped particle trapped in a two-well
potential, forced by a colored noise. An extended model is also proposed that
reproduces observed dynamics and trapping without potential barrier: the key
ingredient is the ratio between the time scales of the noise correlation and
the particle dynamics. A total agreement with experiments requires the
introduction of spatially inhomogeneous fluctuations and a suited confinement
strength.
