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Droplet dynamics and the decay of turbulence

Fluid turbulence is fascinating in part because it seems naturally resistant to organization. With modern instrumentation, we have great control over the properties of turbulence generated in the laboratory and great resolution in the measurement of the properties.

I describe experiments motivated by two issues: the rate of kinetic energy consumed by turbulence and the rate of sedimentation of droplets in a multiphase turbulent flow. In a wind-tunnel experiment that reached higher Reynolds numbers than ever before and covered more than two orders of magnitude in the Reynolds number, we measured the decay rate of turbulence with unprecedented precision.

Surprisingly we do not generally know how quickly turbulence decays, though the process underlies general turbulence phenomena and modeling. What we found in this experiment is that the Reynolds number played no role in setting the decay rate when it was high enough. A separate experiment mimics an atmospheric cloud and combines techniques for precisely.