Coherent Structures and Extreme Events in Rotating Multiphase Turbulent Flows

Abstract

International audienceBy using direct numerical simulations at unprecedented resolution we study turbulence under rotation in presence of simultaneous direct andinverse cascades. The accumulation of energy at large scale leads to the formation of vertical coherent regions with high vorticity oriented along the rotation axis. By seeding the flow with millions of inertial particles we quantify -for the first time- the effects of those coherent vertical structures on the preferential concentration of light and heavy particles. Furthermore, we quantitatively show that extreme fluctuations, leading to deviations from anormal-distributed statistics, result from the entangled interaction of the vertical structures with the turbulent background. Finally, we present the first --ever-- measurement of the relative importance between Stokes drag, Coriolis and centripetal forces along the trajectories of inertial particles. We discovered that vortical coherent structures lead to unexpected diffusion properties for heavy and light particles in the directions parallel and perpendicular to the rotation axis

Kinetic Turbulence in Astrophysical Plasmas: Waves and/or Structures?

“…6(a)-6(b) and 6(g)-6(h)], which are very close to unity for k ⊥ 1/ρ i , regardless of the order m or of the threshold ξ. This is most likely a consequence of the pressure balance (6), which we studied in the preceding paragraphs. It is interesting to note that the ratios tend to converge towards the KAW predictions below the ion gyroradius rather then below the ion inertial scale.…”

“…Finally, we mention that the general approach employed here is not exclusively limited to kinetic range turbulence in astrophysical plasmas and we hope it might find exciting applications in a broad range of turbulent systems where waves and structures have been observed [5][6][7]20]. An immediate extension of the method lends itself in the context of inertial range plasma turbulence, where it could be used to study the interplay between structures and waves based on a generalized Alfvén ratio [19,96].…”

“…This appears to be a reasonable choice given that the kinetic scale structures carry both significant magnetic field and density fluctuations as shown in what follows. For Cluster measurements, δb is used as a proxy for δn e to obtain the LIM under the assumption of pressure balance (6). The conditional averages may eventually become energetically insignificant, since the averaging volume shrinks with the threshold ξ.…”

“…To this end, we introduce a set of novel diagnostic measures, appropriate for the study of waves and structures in a kinetic plasma, such as the weakly collisional solar wind [19]. The general approach outlined in this paper and the conclusions drawn from it are, however, not exclusively limited to kinetic scale plasma turbulence and could be applicable to a wide range of turbulent regimes and environments where waves and structures can be identified [5][6][7]20]. Different theoretical concepts have been considered to explain the properties of weakly collisional plasma turbulence at kinetic scales below the ion thermal gyroradius.…”

Statistical features of rapidly rotating decaying turbulence: Enstrophy and energy spectra and coherent structures

“…Yang and Domaradzki 42 , Müller and Thiele 43 , Mininni et al 44 , and Biferale et al 45 showed that the energy spectrum of rotating turbulence is approximately k −2 or k −2 ⊥ . However, Smith and Lee 46 and Sen et al 47 argued that the energy spectrum is proportional to k −3 ⊥ .…”