Coherence of Velocity Fluctuations in Turbulent Flows

We investigate the spatiotemporal quantity of coherence for turbulent velocity fluctuations at spatial distances of the order or larger than the integral length scale l0. Using controlled laboratory experiments, an exponential decay as a function of distance is observed with a decay rate that depends on the flow properties. The same law is observed in two different flows, indicating that it can be a generic property of turbulent flows.