PROLOGUE

Boundary layer manipulation via reactive control strategies is now in vogue. The payoffs are handsome, but the difficulties involved are daunting. This topic is deferred to the last chapter of the book. There are, however, much simpler alternatives to such sophisticated flow alteration devices, and the present chapter discusses one such alternative: passive compliant walls. We particularly review the important developments in the field of compliant coatings that took place during the past decade or so. During this period, progress in theoretical and computational methods somewhat outpaced that in experimental efforts. There is no doubt that compliant coatings can be rationally designed to delay transition and to suppress noise on marine vehicles as well as other practical hydrodynamic devices. Transition Reynolds numbers that exceed by an order of magnitude those on rigid-surface boundary layers can readily be achieved.