Mechanical and Civil Engineering Seminar

Ph.D. Thesis Defense

Abstract: Accurate prediction of hypersonic boundary-layer transition is critical for controlling aerothermodynamic loading on vehicles. Current tools, such as direct numerical simulations (DNS) and global methods, albeit accurate, are computationally expensive, whereas linear stability theory and parabolized stability equations are cheaper but may be unreliable for more complex flows. We thus introduce a novel technique, the One-Way Navier-Stokes (OWNS) Equations, which is capable of accurately tracking modal, non-modal, and multi-modal instabilities in complex 2D or 3D flows at considerably less computational expense compared to DNS. This technique can also be used in an input-output framework to efficiently compute worst-case disturbances leading to the fastest transition to turbulence, which can serve as a powerful design tool. We have also developed a methodology to restrict input-output analyses to physically realizable disturbances, i.e. disturbances from the free-stream, to study natural boundary-layer receptivity.  All of the aforementioned tools are part of a new package called the Caltech Stability and Transition Analysis Toolkit (CSTAT), a comprehensive stability code designed to perform a variety of analyses from subsonic to hypersonic regimes for boundary and free-shear layers in generalized, non-orthogonal curvilinear coordinates.