Abstract:

We report measurements of global dissipated power within a turbulent flow homogeneously forced at small scale by a new forcing technique. The forcing is random in both time and space within the fluid by using magnetic particles in an alternating magnetic field. By measuring the growth rate of the fluid temperature, we show how the dissipated power is governed by the external control parameters (magnetic field, and number N of particles). We experimentally found that the mean dissipated power scales linearly with these parameters, as expected from the magnetic injected power scalings. These experimental results are well described by simple scaling arguments showing that the main origins of the energy dissipation are due to viscous turbulent friction of particles within the fluid and to the inelasticity of collisions. Finally, by measuring the particle collision statistics, we also show that the particle velocity is independent of N, and is only fixed by the magnetic ``thermostat''.

CNRS Research News "Des particules magnétiques pour étudier la turbulence", 13 Nov. 2017 ;   

in Lettre "En direct des labos" 14 Nov. 2017
  Web site Université de Paris, 14 nov. 2017; Web site of MSC laboratory, 14 nov. 2017