Inhomogeneous Helicity Effects in Angular-Momentum Transport in Geophysical and Astrophysical Turbulent Flows
Abstract
Helicity (velocity-vorticity correlation) represents some structural information of turbulence. By assuming homogeneous isotropic and non-mirror-symmetric property for the basic fields (the lowest-order fields in a derivative expansion formulation), the Reynolds-stress expression is derived from the fundamental equations. It is shown that inhomogeneous helicity enters the Reynolds-stress expression as the coupling coefficient for the mean absolute vorticity {Ω}* (= 2 ω}{F} + ∇ × {U}) (ω}{F}: angular velocity of system rotation, {U}: mean velocity) [1]. Recently validity of the expression has been confirmed through direct numerical simulations (DNSs) of rotating helical turbulence [2]. Inhomogeneous helicity may play some roles in the formation of large-scale structures in geophysical and astrophysical turbulent flows. A few possible applications, including the generation and sustainment of large-scale vorticity in cyclone and the angular-momentum transport in the stellar convection zone, are discussed. It is shown that the spatial structure of helicity is self-sustained in the central region of a cyclone, and that the angular momentum can be transferred in the outward and equatorward directions by the inhomogeneous helicity effect. [1] Yokoi, N. and Yoshizawa, A. "Statistical analysis of the effects of helicity in inhomogeneous turbulence," Phys. Fluids A 5, 464 (1993). [2] Yokoi, N. and Brandenburg, A. "Large-scale flow generation by inhomogeneous helicity," Phys. Rev. E 93, 033125 (2016).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMNG13A1686Y
- Keywords:
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- 3315 Data assimilation;
- ATMOSPHERIC PROCESSES