e-9: Stability Theory and Boundary-Layer Transition

Successful low-drag design employs methods of boundary-layer control to delay the transition of unstable laminar boundary layers, but a suitable comprehensive theory is needed to guide prediction and control of boundary-layer transition for low-drag hydrodynamics. This report suggests that such a theory must be substantially different from the current nonlinear stability theories. New and less formal nonlinear theories, which combine the growth rates and frequency dependence of the two-dimensional Tollmien-Schlichting waves (which are the basis of the "e-9" method) and the three-dimensional nonlinear processes of modern stability theory, could ultimately lead to improvements in the understanding and manipulation of the transition process in low-drag hydrodynamics, and to the inclusion of disturbance effects. Until such methods are developed, the "e-9" or similar empirically based methods must be relied on for design and analysis.