Flexural wave modulation and mitigation in airfoils using acoustic black holes

TL;DR

This paper presents a new design framework for acoustic black holes in airfoils, demonstrating significant vibration reduction and wave modulation through experimental and finite element analysis, with applications in noise reduction and flow control.

Contribution

Introduces a generalized multi-parameter design method for ABHs in airfoils, validated by experiments and FEA, enabling effective flexural wave modulation.

Findings

Up to 10 dB reduction in trailing edge vibrations

Broadband 5 dB vibration reduction across the chord

Substantial spatial and temporal wave modulation achieved

Abstract

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.