The role of thermal noise in the laminar-turbulent transition of hypersonic boundary layers
The transition of hypersonic boundary layers from laminar to turbulent has important practical implications for the design of hypersonic aircraft. Despite significant progress in recent decades, the phenomenon is still not well understood, particularly for atmospheric flight conditions. Thermal noise, which has origin at the molecular level, has been proposed as a possible explanation for transition in cases where the level of external disturbances is low. In this talk, a method is developed for computing the amplitude of disturbances induced by thermal noise in high-speed compressible boundary layers, beginning from the equations of fluctuating hydrodynamics. The approach relies on a coupling of linear stability theory (LST) with receptivity theory and asymptotic methods. Extensions to the theory in cases for which the stability spectrum is particularly complicated are discussed.