Dissipated power within a turbulent flow forced homogeneously by magnetic particles

E. Falcon, J.-C. Bacri, and C. Laroche
Université Paris Diderot, Sorbonne Paris Cité, MSC, UMR 7057 CNRS, F-75 013 Paris, France

Reference: Physical Review Fluids 2, 102601(R) (2017) - Rapid Communication

URL: https://link.aps.org/doi/10.1103/PhysRevFluids.2.102601
DOI: 10.1103/PhysRevFluids.2.102601   

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''.

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Video: Random motions of magnetic particles within a container in response to an alternating magnetic field (Slow down 12.5 times – Real time: 2.4s)

See also press items from:
cnrsCNRS Research News "Des particules magnétiques pour étudier la turbulence", 13 Nov. 2017 ;   
Tweeter_@INSIS_CNRS 13 Nov. 2017
cnrs in Lettre "En direct des labos" 14 Nov. 2017
 P7 Web site Université Paris Diderot, 14 nov. 2017; Web site of MSC laboratory, 14 nov. 2017

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