Analysis and Control of Vortex Shedding from a Blunt Trailing Edge

Abstract

The work within this thesis is concerned with an unsteady flow phenomenon known as vortex shedding. It is ubiquitous throughout engineering applications and leads to unwanted noise, vibration, and pressure drop in the afflicted systems. Vortex shedding is highly complex, and even with over a century of research on the subject, there are many aspects of the phenomenon that we do not yet understand. This thesis advances the current understanding of how vortex shedding affects the wake of a two-dimensional blunt trailing edge. The investigation begins with an in-depth analysis of the three-dimensional vortex structures that are present in the unsteady wake. It is shown that the blunt trailing edge geometry investigated here results in a wake that contains the same structures as that of cylindrical geometries. Specifically, the mode B secondary instability that was originally observed in the wake of a circular cylinder is found to have a dominant presence. The use of oscillating piezoelectric flaps for controlling the unsteady wake is then investigated. It is found that the actuation configuration designed here is capable of both suppressing and enhancing the vortex shedding pattern in the wake. Moreover, a symmetric shedding mode can be forced for a small range of actuation frequencies, leading to interesting wake behaviour that is not naturally present. Finally, a real-time optimization technique known as adaptive slope-seeking is used to seek an optimal control input for suppressing the wake. The closed-loop controller is capable of reaching and maintaining the optimal input and is robust to slow variations in freestream velocity within the designed operating range.