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Title: Vortex stability and breakdown : direct numerical simulation and stability analysis using BiGlobal and parabolised formulations
Author: Broadhurst, Michael Stuart
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2007
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This thesis concerns the application and implementation of recently developed stability techniques to the understanding of vortex stability and breakdown. The instability analysis of vortical flows was originally motivated by a need to understand the breakdown of aircraft wake vortices and the physics of the vortex breakdown phenomenon. A more recent application is the stability analysis of the vortex wake developed from a Formula 1 front wing. Typically, the model problem when considering vortex dominated flows is the Batchelor trailing vortex. The results of a BiGlobal linear stability analysis of a Batchelor vortex show that there are many unstable helical perturbation modes covering a wide range of axial wavenumbers. Direct numerical simulation of a corresponding unstable helical disturbance developing on an axially periodic vortex demonstrates a non-linear energy transfer mechanism responsible for a loss of energy in the mean flow. Relaxing the assumption of periodicity allows axial gradients to develop, and leads to an abrupt drop in axial velocity indicative of vortex breakdown. Direct numerical simulation of a vortex in an external pressure gradient also suggests that axial pressure gradients significantly influence the onset of vortex breakdown. With a BiGlobal stability analysis assuming axial homogeneity and neglecting streamwise gradients, this motivates the need for an analysis technique that can account for both velocity and pressure gradients. One such technique is the parabolised stability equations, and the current research has successfully implemented this technique and demonstrated its validity by comparing the results with direct numerical simulation.
Supervisor: Sherwin, Spencer ; Theofilis, Vassilis ; Blackburn, Hugh ; Mughal, Shahid Sponsor: McLaren Racing
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available