圆柱形声腔内衬三聚氰胺泡沫降噪方法

针对运载火箭整流罩内高强度的噪声问题，采用圆柱声腔内衬理论、有限元仿真和声学试验研究了三聚氰胺泡沫材料的中低频（100~400Hz）降噪特性。将三聚氰胺泡沫内衬等效为阻抗边界，给出了圆柱声腔简正频率的修正公式。测试了20mm、30mm、40mm厚三聚氰胺泡沫的流阻和吸声系数，通过虚拟阻抗管仿真校验了三聚氰胺泡沫的声学参数、给出了表面声阻抗率。对比了内衬理论、阻抗边界仿真、实体仿真的简正频率。建立了运载火箭整流罩圆柱段缩比模型的噪声试验平台，对空桶和敷设三种厚度三聚氰胺泡沫等四种工况进行了仿真分析和噪声试验，对比了不同厚度三聚氰胺泡沫的降噪效果。结果表明圆柱声腔内衬三聚氰胺泡沫后简正频率减小，且减小量与三聚氰胺泡沫衬里的厚度成正比；三聚氰胺泡沫衬里在中低频段仍能达到约4~8dB的降噪效果。

A Method for Noise Attenuation in Cylindrical Cavity with Melamine Foam Lining

The low-medium(100~400Hz) frequency noise attenuation in cylindrical cavity with melamine foam lining is investigated theoretically, numerically, and experimentally. With the melamine foam being equivalent to the impedance boundary, the formulas of the natural frequency of the cylindrical cavity are deduced. The flow resistance and sound absorption coefficient of the melamine foam with different thickness are tested, and the other acoustic parameters of the melamine foam are validated by simulation. Then the surface impedance data is given by simulation, and the data is used to calculate the theoretical and numerical natural frequencies of the cylindrical cavity with impedance boundary, and these results are compared with the results of the simulation in which melamine foam is 3D solid element. A scale model of the cylindrical section of the payload fairing is fabricated, and the acoustic responses inside the cylinder under noise excitation are tested and simulated. The results show that the melamine foam lining leads to decreasing of the natural frequencies, and these reductions are proportional to the thickness of the melamine foam. The noise attenuation of the melamine foam lining on low-medium frequency can reach to nearly 4~8dB.