Transient growth of perturbations on scales beyond the accretion disc thicknessстатья

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Дата последнего поиска статьи во внешних источниках: 14 августа 2017 г.

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[1] Razdoburdin D. N., Zhuravlev V. V. Transient growth of perturbations on scales beyond the accretion disc thickness // Monthly Notices of the Royal Astronomical Society. — 2017. — Vol. 467, no. 1. — P. 849–872. A turbulent state of spectrally stable shear flows can be developed and sustained according to the bypass scenario of transition. If it works in non-magnetized boundless and homogeneous quasi-Keplerian flow, then transiently growing shearing vortices should supply turbulence with energy. Employing the large shearing box approximation, as well as a set of global disc models, we study the optimal growth of the shearing vortices in such a flow in the whole range of azimuthal length-scales, λy, compared to the flow scaleheight, H. It is shown that with the account of the viscosity the highest possible amplification of shearing vortices, Gmax , attains maximum at λy ≲ H and declines towards both the large scales λy ≫ H and the small scales λy ≪ H in good agreement with analytical estimations based on balanced solutions. Our main attention is directed to the large-scale vortices λy ≫ H, which produce Gmax  ∝ (Ω/κ)4, where Ω and κ denote local rotational and epicyclic frequencies, respectively. It is demonstrated that the large-scale vortices acquire high-density perturbation as they approach the instant of swing. At the same time, their growth is not affected by bulk viscosity. We check that Gmax  obtained globally is comparable to its local counterpart, and the shape and localization of global optimal vortices can be explained in terms of the local approach. The obtained results allow us to suggest that the critical Reynolds number of subcritical transition to turbulence in quasi-Keplerian flow, as well as the corresponding turbulent effective azimuthal stress should substantially depend on shear rate. [ DOI ]

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