| A detailed understanding of the physical processes that lead to instability and transition in the external viscous boundary layers of airfoils has been the goal of researchers for decades. This study seeks to enhance our understanding of Gortler and Tollmien-Schlichting instabilities{09}through{09}a critical review of prior theoretical methodology and fundamental experiments, the development of dimensionally consistent disturbance equations, and novel interpretation of the resulting flow physics revealed by their solutions to explain the process of transition.; Gortler vortices arise in boundary layers along concave surfaces due to centrifugal effects and these vortices in combination with other instabilities play an important role in triggering early transition. Of the two distinct theoretical approaches to Gortler instability, the marching technique initiated by Hall led to multiple neutral curves that depended on the initial condition and its location, and the classical normal-node approach where each study predicted a unique but different neutral curve. This study critically examines the two approaches, provides explanations for the differences, and shows that the two can produce compatible results for constant concave curvature.; The first ever study of Gortler instability on variable curvature surfaces is presented. A hitherto unknown phenomenon of the Gortler vortices lifting off in the convex region is observed. |
