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Large Scale Dynamics and 1/f Fluctuations in Turbulence
In a turbulent flow, many length scales contain energy. It is known for a long time that how the energy depends on the length scale is independent of details of the flow forcing or dissipation. Less in known about the temporal evolution of the turbulent field, in particular for the largest scales. I present a variety of experiments (Rayleigh Benard convection, swirling flows, dynamo effect and 2d periodic flows) in which the largest scales of the flow display interesting dynamical features. For some parameter regimes the largest scale appears through a bifurcation over a turbulent background. Turbulent fluctuations induce long time fluctuations, including random reversals and 1/f fluctuations. The origin of these long time fluctuations will be discussed.