The work described in this thesis is a computational investigation applying linear feedbackudcontrol to reduce form-drag on bluff bodies with a blunt trailing edge. For such bodies, audlarge portion of the aerodynamic drag is associated with an unsteady separated region or wakeuddownstream of the body. The development of tractable feedback strategies to control unsteadyudwakes promises strong benefits, both in terms of industrial applications and for furthering ourudunderstanding of the flow mechanisms at play.udFor this purpose, large-eddy simulations are carried out where a linear feedback controllerudtargets an increase in the mean pressure force on the rear (base) of the body. The flows overudtwo distinct geometries are examined: a backward-facing step and a bluff body with a roundedudleading edge, often referred to as a D-shaped body. The control is effected by zero-net-mass-flux slot jets, responding to sensors located on the body base. Open-loop characterization providesudinformation on the effects of actuation and some physical insight into the relation between theudbase pressure and wake dynamics. System identification is used to obtain a low-order modeludof the flow's response to actuation that can be used for control.udThe control strategy is based on the premise that reducing the fluctuations in the near-wakeudwill cause an increase in the mean base pressure, hence a reduction in form-drag. Theudcontrollers are designed with classical frequency-domain methods, using a sensitivity transferudfunction to attenuate the size of the pressure force fluctuations.udThe influence of parameters such as the Reynolds number and the location and type ofudactuators is studied. For all cases, low-order linear feedback controllers successfully reduceudthe pressure force fluctuations and achieve sensible drag reductions. They do so with higher efficiency than the open-loop forcing considered. Uncertainties in the model and flow conditionsudcan be to some extent mitigated by the robustness of the controller. The results support theudconjecture linking the fluctuating and mean base pressure, although it is observed that furtherudwork is needed before such an approach can be used for optimization.
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