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SUMMARY:Tollmien-Schlichting Route to Elastoinertial Turbulence - Michael 
 Graham (University of Wisconsin-Madison)
DTSTART:20220331T140000Z
DTEND:20220331T143000Z
UID:TALK171218@talks.cam.ac.uk
DESCRIPTION:Recent studies of channel and pipe flows of dilute polymer sol
 utions at Reynolds numbers Re~1000-10000 have revealed a viscoelasticity-d
 riven chaotic flow state denoted elastoinertial turbulence (EIT). &nbsp\;C
 omputations indicate that EIT displays tilted sheetike layers of polymer s
 tretch with weak spanwise-oriented flow structures &ndash\; a sharp contra
 st to the 3D quasistreamwise vortex structures that make up inertia-driven
  Newtonian turbulence. Direct simulations of two-dimensional channel flow 
 of a FENE-P fluid have revealed the existence of a family of flows that is
  nonlinearly self-sustained by viscoelasticity with structure closely rela
 ted to the classical Tollmien-Schlichting (TS) wave. &nbsp\;At Reynolds nu
 mber Re=3000\, there is a solution branch with TS-wave structure but which
  is not connected to the Newtonian solution branch. &nbsp\;At fixed Weisse
 nberg number\, Wi\, and increasing Reynolds number from 3000-10000\, this 
 attractor goes from displaying a sheet of weak polymer stretch to an exten
 ded sheet of very large polymer stretch. This evolution arises from the co
 il-stretch transition when the local Weissenberg number at the hyperbolic 
 stagnation point of the Kelvin cat's eye structure of the TS wave exceeds 
 1/2. At Re=10000\, the Newtonian TS wave evolves continuously into the EIT
  state as Wi is increased from zero to about 13. The multilayer structure 
 emerges through a ``sheet-shedding" process by which the individual sheets
  &nbsp\;break up to form the layered multisheet structure characteristic o
 f EIT. &nbsp\;\nFinally\, having established the connection between the TS
  wave solution and EIT\, we consider the question of how low in Reynolds n
 umber this solution family persists. At Wi=30\, we find that the viscoelas
 tic TS wave (EIT) solution family persists down to Re between &nbsp\;below
  200. &nbsp\;These results may be related to observations of non-laminar f
 low in polymer solutions at Reynolds numbers below the Newtonian transitio
 n threshold.
LOCATION:Seminar Room 1\, Newton Institute
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