[CCoE Notice] MS Thesis Presentation

[Abercrombie, Irene F]

MS Thesis Defense

INSTABILITY OF A VORTEX COLUMN DUE TO TURBULENCE GENERATED AXIAL FLOW

Eric Stout

Date: Wednesday, August 14th,  2013

Location: Mechanical Engineering (large) Conference Room
Time: 2:30 PM

Committee Chair:
Dr. Fazle Hussain

Committee Members:
Dr. Ralph Metcalfe
Dr. Gemunu Gunaratne



Axial flow generated by turbulence on an initially two-dimensional vortex column, the Lamb-Oseen vortex, is studied theoretically and by direct numerical simulation of the Navier-Stokes equations. Azimuthally wrapped filaments of opposite circulations, discussed for the case of two oppositely oriented filaments, advect radially in opposite directions, leading to radial separation of the filaments and net axial flow on the vortex axis. Axial velocity is found to grow as t5/2 from the simulation results, closely matching the analytically determined growth rate. Derivation of the axial flow magnitude predicts the onset of instability due to axial flow via the q(≡peak azimuthal velocity/peak axial velocity) criterion. Simulation results show (limited) renewed growth when q decreases below the unstable limit, likely dominating the  previously discussed parent-offspring hairpin vortex mechanism for regenerative growth and suggesting possible breakup of the initially normal mode stable vortex at higher Re due to ambient turbulence.

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