Second Mode Disturbance Sensitivity and Reductionin Hypersonic Boundary Layers by Tuned Phononic Materials

The field of phononic materials has blossomed in the previous three decades. These tunable metamaterials allow for large stop gaps and pass gaps for a large frequency bands, making them highly relevant to a variety of engineering applications. In our current research we apply these materials as a passive flow mechanism to the problem of second-mode instabilities in a Mach 5.35 hypersonic boundary layer. These instabilities behave as trapped acoustic waves propagating in the region between the wall boundary and the sonic line. In our current research, we utilize two in-house computational approaches: a direct numerical simulation of the linear disturbance equations (LDE) with two-way coupling between the phononic material and the flow, and an in-house linear stability (LST) solver. In both simulations, the phononic material is placed at the wall boundary as a phononic subsurface (termed 'PSub'). We demonstrate successful reduction of second mode growth rates while exploring the parameter space of these PSubs and their effect on disturbance growth.