In this paper we consider the control of disturbances in a channel where surface sensing and actuation (blowing/suction) are used. Unlike in many other studies, the flow is not assumed to be periodic. As a result disturbances are allowed over the full range of unstable wave numbers/frequencies, and spatially growing disturbances can be studied explicitly. However, a major drawback is that, even for two-dimensional flow, the order of the numerical model is extremely large. Model order reduction based on a non-linear least squares fit is used to generate a model plus an uncertainty bound that are suitable for control design purposes. These are used to produce a robustly stable H controller. The behaviour of this controller is compared with those designed assuming periodic flow. It is shown that a non-periodic controller can perform satisfactorily in cases where a periodic one will not.

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