Integrated Transition Prediction: A Case Study in Supersonic Laminar Flow Control

Laminar flow control (LFC) is one of the key enabling technologies for quiet and efficient supersonic aircraft. Recent work at Arizona State University has led to the development of a novel concept for passive LFC on crossflow dominated flow configurations. It employs distributed leading-edge roughness to limit the growth of naturally dominant instabilities that would otherwise lead to an earlier onset of transition. LFC technology development under DARPA's Quiet Supersonic Platform (QSP) and NASA's Supersonic Vehicle Technology (SVT) programs includes both wind-tunnel and flight experiments aimed at further development of roughness based LFC at close to full-scale Reynolds numbers, and design studies for integrating this new concept into the overall vehicle design. Companion theoretical studies at NASA Langley Research Center have the objective of providing both an enhanced physical understanding to facilitate the optimization of roughness based LFC, and a physics based transition prediction capability for this and other LFC configurations. This paper outlines the findings based on a preliminary exploration of the parameter space, in terms of receptivity plus linear and nonlinear development of stationary crossflow instabilities on an infinite-span swept airfoil at a free-stream Mach number of 2.4 and chord Reynolds number of 16.3 million. The findings are used to advocate a holistic approach for transition prediction, which accounts for all major stages within transition (namely, receptivity, linear growth, nonlinear interactions and secondary instability) in an integrated manner.