Crossflow Instabilities - Theory & Technology
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Over the years, the crossflow instability has been the primary challenge for Laminar Flow Control (LFC). Favorable pressure gradients used to stabilize streamwise instabilities destabilize crossflow. For years, it seemed as though the only solution to crossflow control was surface suction. The perceived complications with moving parts and additional maintenance were always discouraging factors toward laminarizing swept wings. This final hurdle may have been overcome with Arizona State University's (ASU's) technique of passive nonlinear biasing of stationary crossflow wave growth. The past decade or so has seen significant advances in experimental methods and computational tools and in the identification of important factors such as: environmental conditions on the appearance of stationary and traveling waves; secondary instability causing local transition in stationary-crossflowdominated flows; extreme sensitivity of the stationary disturbance to leading-edge, very small, surface roughness; nonlinear effects and modal interaction; and extreme sensitivity of stationary wave growth to very weak convex curvature. By carefully studying the basic physics, these advances have lead to a new and promising opportunity for transition delay. Termed "Swept Wing Laminar Flow Control (SWLFC)", this can be accomplished by distributed roughness, holes, or glow discharge applied at the leading edge. This promising technique is currently also being evaluated for supersonic flight (Saric and Reed 2002a,b). 2003 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
