Flow control: new challenges for a new Renaissance

As traditional scientific disciplines individually grow towards their maturity, many new opportunities for significant advances lie at their intersection. For example, remarkable developments in control theory in the last few decades have considerably expanded the selection of available tools which may be applied to regulate physical and electrical systems. These techniques hold great promise for several applications in fluid mechanics, including the delay of transition and the regulation of turbulence. Such applications of control theory require a very balanced perspective, in which one considers the relevant flow physics when designing the control algorithms and, conversely, takes into account the requirements and limitations of control algorithms when designing both reduced-order flow models and the fluid-mechanical systems to be controlled themselves. Such a balanced perspective is elusive, however, as both the research establishment in general and universities in particular are accustomed only to the dissemination and teaching of component technologies in isolated fields. To advance, we must not toss substantial new interdisciplinary questions over the fence for fear of them being "outside our area"; rather, we must break down these very fences that limit us, and attack these challenging new questions with a Renaissance approach. In this spirit, this paper surveys a few recent attempts at bridging the gaps between the several scientific disciplines comprising the field of how control, in an attempt to clarify the author's perspective on how recent advances in these constituent disciplines fit together in a manner that opens up significant new research opportunities. Published by Elsevier Science Ltd.