Optimal control of vortex shedding using low-order models. Part II?model-based control

In Part I, an approach to deriving low-order models suitable for use in the development of active control strategies for separated flows was presented. The methodology proposed was applied to a numerical simulation of the incompressible, unsteady wake flow behind a circular cylinder at Re=100, with control action achieved via cylinder rotation. The resulting low-order models were found to predict the flows in four open-loop test cases with sufficient fidelity to justify their application in model-based control of the vortex-shedding flow. In Part II, optimal control theory is used to implement the model-based control, and data from numerical simulations of the controlled flow are presented. It is found that the level of wake unsteadiness can be reduced, even when the low-order model is reset on the basis of limited flow field information. The degree of reduction is dependent on the accuracy of the low-order model, and ways of refining it in the light of control simulations are considered. However, results from two straightforward approaches to this problem suggest that it is easy to ‘over-tune’ the model, resulting in less successful control.