A numerical study of instability and vortex breakdown of swirling flow
A numerical study of instability and vortex breakdown of swirling flow
Direct numerical simulations of both axisymmetric and three-dimensional highly swirling flows are conducted to study the vortex breakdown phenomenon and the onset of helical instabilities.
The enduring debate on the physical reasons underlying the breakdown of slender vortices has widely involved theoretical, experimental and computational studies. In the present investigation, we are motivated by the necessity to evaluate the range of applicability of recent studies which have correlated the global response of this class of flows to their local stability characteristics. In synthesis, the dynamics of the unsteady structures developing in swirling flows are explained according to simplified theories which assume the flow to be locally parallel. These results, which might be considered as the natural extension of concepts well established for two-dimensional jets and wakes, appear to be quite surprising if applied to swirling flows in breakdown configuration. In fact, the presence of one or more large regions of recirculating flow (the vortex bubbles) renders the assumption of near parallelism more strongly violated.
We have carried out a numerical investigation in order to study the evolution of self-sustained oscillations. For this purpose, a finite difference code has been developed and later adapted to perform linear analysis around a given parallel swirling flow. Successively, a comparative study between the global and local analysis methodologies has been conducted. The novelty of the work is represented by the use of simple filtering techniques which can be implicitly activated if the cylindrical coordinates are employed. These have made possible to focus on the nonlinear evolution of higher order modes. We have identified an instability mechanism which cannot be explained by the local theory and whose existence is clearly associated with the presence of recirculating flow.
University of Southampton
Amirante, Dario
52982d32-7317-45e8-ac81-18ab2257e9da
2007
Amirante, Dario
52982d32-7317-45e8-ac81-18ab2257e9da
Amirante, Dario
(2007)
A numerical study of instability and vortex breakdown of swirling flow.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Direct numerical simulations of both axisymmetric and three-dimensional highly swirling flows are conducted to study the vortex breakdown phenomenon and the onset of helical instabilities.
The enduring debate on the physical reasons underlying the breakdown of slender vortices has widely involved theoretical, experimental and computational studies. In the present investigation, we are motivated by the necessity to evaluate the range of applicability of recent studies which have correlated the global response of this class of flows to their local stability characteristics. In synthesis, the dynamics of the unsteady structures developing in swirling flows are explained according to simplified theories which assume the flow to be locally parallel. These results, which might be considered as the natural extension of concepts well established for two-dimensional jets and wakes, appear to be quite surprising if applied to swirling flows in breakdown configuration. In fact, the presence of one or more large regions of recirculating flow (the vortex bubbles) renders the assumption of near parallelism more strongly violated.
We have carried out a numerical investigation in order to study the evolution of self-sustained oscillations. For this purpose, a finite difference code has been developed and later adapted to perform linear analysis around a given parallel swirling flow. Successively, a comparative study between the global and local analysis methodologies has been conducted. The novelty of the work is represented by the use of simple filtering techniques which can be implicitly activated if the cylindrical coordinates are employed. These have made possible to focus on the nonlinear evolution of higher order modes. We have identified an instability mechanism which cannot be explained by the local theory and whose existence is clearly associated with the presence of recirculating flow.
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Published date: 2007
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Local EPrints ID: 466483
URI: http://eprints.soton.ac.uk/id/eprint/466483
PURE UUID: 198aa2d9-32ab-4485-a9f9-53dd14257ff0
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Date deposited: 05 Jul 2022 05:18
Last modified: 16 Mar 2024 20:43
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Author:
Dario Amirante
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