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Title: Simulation and feedback control of simplified vehicle flows
Author: Evstafyeva, Olga
ISNI:       0000 0004 7427 7600
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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The present doctoral work investigates wake flow behind a square-back Ahmed body at laminar and turbulent Reynolds numbers. At low Reynolds numbers the Ahmed body wake undergoes a series of bifurcations towards symmetry breaking state. Using Large Eddy Simulations, which resolve the boundary layer down to the wall, the sequence of symmetry breaking bifurcations is captured numerically for the first time. Large Eddy Simulations are then used to investigate the reflectional symmetry breaking behaviour in the turbulent regime, where it manifests as slow and random bi-modal switching between the asymmetric states. The bi-modal switch from one state to the other is captured for the first time numerically, allowing to study the effects of wake displacement on the instantaneous wake structures. A linear feedback control strategy, designed to attenuate base pressure force fluctuations is tested on the Ahmed body flow. At low Reynolds numbers the strategy is successful; a moderate base pressure recovery and a concomitant drag reduction are achieved and the wake is re-symmetrised. A similar control approach is also benchmarked at higher Reynolds numbers, where the flow exhibits turbulent separation. The preliminary results suggest that the controller is unlikely to reduce drag and other actuation/sensing arrangements need to be investigated. This work motivates future attempts to develop a linear feedback controller based on the strategy described herein, but with better selected actuation and sensing. Further work is also required to better understand the physical mechanism behind bi-modal switching in the wake.
Supervisor: Morgans, Aimee Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral