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Incorporating acoustic black holes in hydrofoils

Fluid-loaded structures such as turbine blades, ship hulls, and aircraft wings are required to withstand turbulent flow-induced structural vibrations and yet be lightweight. In this study, the feasibility of applying the concept of acoustic black holes (ABHs) into hydrofoils as a means to mitigate flow-induced structural vibrations is evaluated. ABHs are geometrical tapers that “trap” flexural vibrations near an ideal edge. Practical implementations of this approach involve the use of damping material near the truncated edge. Optimization of the ABH thickness profile, number of ABH elements, and the damping layer for mitigating surface vibrations is performed using finite element simulations. Select designs are then fabricated leveraging multi-material polyjet 3-D printing technology. Surface vibrations of the test samples subject to leading-edge excitations are characterized using laser Doppler vibrometry. Test results are compared with simulation data and a design framework/tool for ABH implementation in hydrofoils is formulated. [Work sponsored by the Office of Naval Research.]