Abstract
This work proposes a subwavelength porous meta-liner with broadband sound absorption from 900 to 1,200 Hz. The meta-liner consists of four subunits, which are made up of porous material and hollow coiling slit embedded in it. Each subunit is designed by adjusting the length of its coiling slit to achieve resonance in the target frequency and examined by the finite element method (FEM). These subunits are arranged in an axial direction uniformly and radial direction periodically to propose a meta-liner duct. Then, the noise reduction of the propeller system with the meta-liner duct is measured by the microphone array. The result shows that the propeller with the meta-liner duct can reduce the noise level of the ducted propeller between 3.6 and 5.5 dB in the design frequency range, which also effectively reduces the noise level in the broadband frequency range. Therefore, the meta-liner shows a good application prospect in the noise reduction of the propeller.
Highlights
The noise reduction problem of small-scale unmanned aerial vehicles (UAVs) is widely researched for the improvement of the competitiveness in the civil market and the increase of the concealment in the military application (Mueller, 2001; Christian and Cabell, 2017)
Except for reducing the noise level of the propeller, the ducted propeller can improve the aerodynamic efficiency of the UAVs and protect the propeller blade from damage
We present the numerical and experimental investigations on sound absorption of subwavelength porous meta-liner
Summary
The noise reduction problem of small-scale unmanned aerial vehicles (UAVs) is widely researched for the improvement of the competitiveness in the civil market and the increase of the concealment in the military application (Mueller, 2001; Christian and Cabell, 2017). Melamine foam is chosen as the base porous material of the subunit in the design, because of its good sound absorption performance in the high-frequency range. To obtain the broadband sound absorption at target frequencies, it is significant to design the parameters of the subunit and construct a meta-liner. If the boundary condition belongs to a soft type of the porous material, the density and bulk modulus should be FIGURE 4 | Structure of the meta-liner duct. By the finite element method, the absorption performances of these subunits are calculated and plotted in FIGURE 8 | Averaged spectrum levels over the microphones in the array for the propeller with a rigid duct, a lined duct, and the background.
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