CURRENT STATUS OF THE USE OF WALL COMPLIANCE FOR LAMINAR-FLOW CONTROL

This paper presents a brief review of some recent work on the the use of wall compliance for laminar-flow control. Four main topics are cove red. Firstly comparisons between theory and experiment for instability and transition in flat-plate boundary layers over compliant walls are considered. Good agreement is found for the Gaster experiments in wat er. But the theory does not corroborate the more recent experimental s tudy of Lee et al. (T. Lee, M. Fisher, W.H. Schwarz, Journal of Fluid Mechanics 288 (1995) 37) in air. Secondly, the results of recent numer ical simulations of the divergence instability are discussed. In agree ment with experimental evidence it is found that the divergence onset speed for laminar flow is much higher than for turbulent flow. This im plies that previous estimates of the onset speed based on potential fl ow are very conservative. Thirdly, the use of multiple-panel compliant walls for laminar-flow control is reviewed. Theory and numerical simu lation strongly suggest that transition can be postponed to indefinite ly high Reynolds numbers by the use of such walls. Lastly, recent work is reviewed on the effects of wall compliance on other instability me chanisms, such as inflexion-point instabilities and cross-flow vortice s and absolute instabilities for the three-dimensional, rotating-disc boundary layer. (C) 1998 Elsevier Science Inc, All rights reserved.