  A shear flow of liquid metal (Galinstan) is driven in an annular channel by
counter-rotating traveling magnetic fields imposed at the endcaps. When the
traveling velocities are large, the flow is turbulent and its azimuthal
component displays random reversals. Power spectra of the velocity field
exhibit a $1/f^\alpha$ power law on several decades and are related to
power-law probability distributions $P(\tau)\sim\tau^{-\beta}$ of the waiting
times between successive reversals. This $1/f$ type spectrum is observed only
when the Reynolds number is large enough. In addition, the exponents $\alpha$
and $\beta$ are controlled by the symmetry of the system : a continuous
transition between two different types of Flicker noise is observed as the
equatorial symmetry of the flow is broken, in agreement with theoretical
predictions.
