Intermittency measurement in two-dimensional bacterial turbulence
Abstract
In this paper, an experimental velocity database of a bacterial collective motion, e.g., Bacillus subtilis, in turbulent phase with volume filling fraction 84 % provided by Professor Goldstein at Cambridge University (UK), was analyzed to emphasize the scaling behavior of this active turbulence system. This was accomplished by performing a Hilbert-based methodology analysis to retrieve the scaling property without the β -limitation. A dual-power-law behavior separated by the viscosity scale ℓν was observed for the q th -order Hilbert moment Lq(k ) . This dual-power-law belongs to an inverse-cascade since the scaling range is above the injection scale R , e.g., the bacterial body length. The measured scaling exponents ζ (q ) of both the small-scale (k >kν ) and large-scale (k <kν ) motions are convex, showing the multifractality. A log-normal formula was put forward to characterize the multifractal intensity. The measured intermittency parameters are μS=0.26 and μL=0.17 , respectively, for the small- and large-scale motions. It implies that the former cascade is more intermittent than the latter one, which is also confirmed by the corresponding singularity spectrum f (α ) versus α . Comparison with the conventional two-dimensional Ekman-Navier-Stokes equation, a continuum model indicates that the origin of the multifractality could be a result of some additional nonlinear interaction terms, which deservers a more careful investigation.
- Publication:
-
Physical Review E
- Pub Date:
- June 2016
- DOI:
- 10.1103/PhysRevE.93.062226
- arXiv:
- arXiv:1607.07940
- Bibcode:
- 2016PhRvE..93f2226Q
- Keywords:
-
- Physics - Fluid Dynamics;
- Physics - Biological Physics
- E-Print:
- 23 pages, 7 figures. This paper is published on Physical Review E, 93, 062226, 2016