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Sutirtha Sengupta (University of California Santa Cruz, USA)
Date & Time
Tue, 09 July 2019, 15:30 to 16:30
Emmy Noether Seminar Room, ICTS Campus, Bangalore

We propose a mechanism for generation of vorticity in a rotating  cylindrical shear flow and predict the effect of background  rotation through three-dimensional linear sta- bility analysis and  direct numerical simulations (DNSs). Our linear theory predicts  a positive feedback of angular momentum for moderate rotation  rates that agree well with early time evolution of DNSs with  weak rotation. These runs show the growth of low az- imuthal  wavenumber (m ' 1) modes of instabilty (see left panel of 1) at early times with subsequent onset of centrifugal instabilities that arrests the initial spin-up of the core of the cylinder.

For stronger background rotation, we observe the emergence of  helical (m ? 2) modes of instability from very early times (see left panel of 1) which drain angular momentum out of the core of the cylinder, and is consistent the linear theory predictions at high rotation rates. We discuss possible implications of this study for understanding the emer-gence and growth of large-scale vortices as commonly observed in DNSs of turbulent convection  as well as natural flows in astrophysical and geophysical  contexts.