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.