Nonlinear Instability Characterization of Hypersonic Laminar Boundary Layer

Abstract

This study presents the experimental characterization of instability waves upon a hypersonic laminar boundary layer of a flared-cone model using a nonintrusive optical diagnostic [that is, a focused laser differential interferometer (FLDI)], with special emphasis on the nonlinear behavior of instability waves. To begin with, the application of FLDI technique on hypersonic instability waves was validated with a surface-mounted fast response pressure sensor. Subsequently, the development of instability waves along both streamwise and wall-normal directions was comprehensively investigated by traversing the focus of the FLDI through the hypersonic laminar boundary layer. Power spectral density analysis shows the coexistence of various instability waves up to 1.4 MHz, and the corresponding variation of each instability wave was described. Bicoherence analysis of FLDI measurement identifies different types of nonlinear interaction through a phase-locked mechanism, and the nonlinear evolution along the streamwise and wall-normal directions was elaborated on.