Flexural Wave Modulation And Mitigation In Airfoils Using Acoustic Black Holes

This study introduces a framework for the design and implementation of acoustic black holes (ABHs) in airfoils. A generalized multiparameter damped-ABH generation function is mapped onto airfoils based on the National Advisory Committee for Aeronautics series. Representative geometries and a uniformly distributed baseline, all with the same mass of structure and damping are fabricated using multimaterial PolyJet three-dimensional 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, substantial spatial and temporal modulation of flexural waves by ABH 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.