Numerical Investigation of Second-Mode Attenuation over Carbon/Carbon Porous Surfaces

Abstract

Axisymmetric direct numerical simulations of a spatially developing hypersonic boundary layer over a sharp 7 deg half-angle cone at at Reynolds numbers , , and have been carried out. The streamwise extent of the simulated domain is 0.9 m. The boundary layer is excited with the one-time application of a broadband pulse that is advected downstream over an impermeable wall and a complex impedance boundary condition (IBC) modeling the acoustic response of carbon/carbon (C/C) ultrasonically absorptive porous surfaces. The complex IBCs are derived as an output of a pore-scale aeroacoustic analysis: the inverse Helmholtz solver (IHS) and algebraic low-order models. The IHS estimate of the C/C impedance is compared to other methods for porous acoustic absorbers, revealing uncertainties in the applicability of analytical models for porous absorbers. The introduction of the IBCs in all cases leads to a significant attenuation of the instability waves, up to one order of magnitude reduction in pressure perturbation amplitude for the case.