Session M20: Instability in Shear Layers
8:00 AM–10:10 AM, Tuesday, November 22, 2011
Room: 323
Chair: Luca Brandt, KTH Royal Institute of Technology
Abstract ID: BAPS.2011.DFD.M20.4
Abstract: M20.00004 : Optimal disturbances in shearing and swirling flows
8:39 AM–8:52 AM
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Abstract 
Author:
Conor Daly
(University of Cambridge)
Over the past twenty years transient energy density growth of
linearly stable disturbances has shown to be the likely
instigator for transition to turbulence in parallel shear flows.
In this vein, optimal linear perturbations are calculated for two
flows which have a mixture of forces acting on the fluid body.
These are; rotating plane Couette flow (RPCF), which combines
pressure-driven shear and swirl, and cylindrical
Couette-Poiseuille flow (CCPF), which combines pressure-driven
and Couette shear. Contours are presented of the maximum
achievable linear transient growth, $G$, over the full
range of wavenumbers within the linearly stable parameter
regimes. Reference is made to experimental works on each flow and
we examine the role that optimal disturbances have in the
different transition phenomena that are observed. It is found
that the contours of $G$ fall qualitatively alongside
the points of transition in the two flows, in support of the
notion that large linear transient growth can act a precursor to
transition. Despite the combination of effects acting on each
fluid, transition in both flows falls in the range
$10^2
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.DFD.M20.4