  This study introduces a framework for the design and implementation of
acoustic black holes (ABHs) in airfoils. A generalized multi-parameter
damped-ABH generation function is mapped onto NACA series airfoils.
Representative geometries and a uniformly distributed baseline, all with the
same mass of structure and damping are fabricated using multi-material PolyJet
3D printing. Laser Doppler vibrometer measurements along the airfoil chord in
response to a broadband 0.1 - 12 kHz excitation show a decrease in trailing
edge vibrations by as much as 10 dB, a broadband 5 dB reduction across the
entire chord as well as substantial spatial and temporal modulation of flexural
waves by ABH-embedded foils. Finite element analysis (FEA) models are developed
and validated based on the measured data. Furthermore, a parametric FEA study
is performed on a set of comparable designs to elucidate the scope of
modulation achievable. These findings are applicable to trailing-edge noise
reduction, flow control, structural enhancement and energy harvesting for
airfoils.
