COMPLIANT COATINGS - THE SIMPLER ALTERNATIVE

Boundary layer manipulation via reactive control strategies is now in vogue,and this topic dominated the meeting in which the present paper was delivered. Reactive flow control requires sensors, actuators and c ontrol algorithms. The payoffs are handsome but the difficulties invol ved are daunting. There are however much simpler alternatives to this kind of sophisticated flow alteration devices and the present article discusses one such alternative: passive compliant walls. The paper rev iews the important developments in the field of compliant coatings tha t took place in the past 10 years. During this period progress in theo retical and computational methods somewhat outpaced that in experiment al efforts. There is no doubt that complaint coatings can be rationall y designed to delay transition and to suppress noise on marine vehicle s as well as other practical hydrodynamic devices. Transition Reynolds numbers that exceed by an order of magnitude those on rigid-surface b oundary layers can be readily achieved. Recent theoretical work indica tes that transition to turbulence could be delayed indefinitely, at le ast in principle, provided that optimized multiple-panel compliant wal ls are used. There is renewed experimental evidence of favorable inter actions of compliant coatings even for air flows and even for turbulen t boundary layers, but more research is needed to confirm these latest results. (C) 1998 Elsevier Science Inc. All rights reserved.