Exploration of Phononic Subsurfaces for Hypersonic Boundary Layer Disturbance Reduction

The phenomenon of boundary layer transition at high Mach numbers carries with it a variety of unfavorable effects, such as increased skin friction drag, increased viscous wall heating, and an overall decrease in performance efficiency for the vehicle. A new type of passive laminar flow control (LFC) technology for hypersonic flight is introduced in the form of a phononic subsurface (PSub), a purposefully engineered subsurface architected material offering a highly tailorable frequency-dependent amplitude and phase response characteristics at the surface interfacing with the flow. Here, we apply PSubs to the wall boundary of a Mach 5.35 hypersonic flat plate with second mode dominant instability content and analyze their effects using linear stability theory (LST) and direct numerical simulation (DNS). We show that the presence of a specifically tuned PSub acts to strongly reduce the growth rate of Mack’s second mode by approximately threefold.