A jet noise reduction technique by using the external chevron nozzle with lobed mixer in the double-mixing exhaust system is investigated under cold conditions.The computations of jet field and the experiments of nois...A jet noise reduction technique by using the external chevron nozzle with lobed mixer in the double-mixing exhaust system is investigated under cold conditions.The computations of jet field and the experiments of noise field are conducted with scaled model of high-bypass-ratio turbofan engine mixing exhaust system composed of external chevron nozzle with lobed mixer.The computational results indicate that comparing with the baseline nozzle with lobed mixer,the external chevron nozzle with lobed mixer increases mixing of jet and ambient air near the nozzle exit.The experimental results show that the external chevron nozzle with lobed mixer has better jet noise reduction at low frequencies,and this reduction rises with the increase of chevron bend angle.The experimental results also show that the external chevron nozzle with lobed mixer has sound pressure level(SPL)increase which is not obvious at high frequencies.With chevron bend angle increasing,SPL has relatively marked increase at 60°(directivity angle measured from upstream jet axis)and little fluctuations at 90°and 150°.The external chevron nozzle with lobed mixer has overall sound pressure level(OASPL)reduction in varying degrees at 60°and 150°,but it has little OASPL increase at 90°.展开更多
针对高速列车气动噪声越来越大的问题,本文以高速列车某车型为参考建立1∶1受电弓区域局部模型,基于宽频带噪声源模型、LES大涡模拟及FW-H声学模型,运用弓头仿生降噪和底部空腔主动射流降噪的整体降噪措施,采用数值模拟法研究高速列车...针对高速列车气动噪声越来越大的问题,本文以高速列车某车型为参考建立1∶1受电弓区域局部模型,基于宽频带噪声源模型、LES大涡模拟及FW-H声学模型,运用弓头仿生降噪和底部空腔主动射流降噪的整体降噪措施,采用数值模拟法研究高速列车受电弓区域的降噪效果。结果表明:受电弓弓头和底部空腔是气动噪声的主要来源;降噪后,主要噪声源的声功率级都有了较大降幅,其中弓头和空腔部位分别降低了15.28 d B和16.92 d B;中高楼层住宅处的降噪效果更佳,最大声压级降低位置在距地面18 m高处(距受电弓25 m远处),降低了4.94 d BA;远场声压级在低频区域降噪效果更为显著,特别是在800 Hz位置声压级降幅最大,降低了8.21 d BA。展开更多
针对高速列车气动噪声越来越大的问题,本文以高速列车某车型为参考建立1:1受电弓区域局部模型,基于宽频带噪声源模型、LES大涡模拟及FW-H声学模型,运用弓头仿生降噪和底部空腔主动射流降噪的整体降噪措施,采用数值模拟法研究高速列车受...针对高速列车气动噪声越来越大的问题,本文以高速列车某车型为参考建立1:1受电弓区域局部模型,基于宽频带噪声源模型、LES大涡模拟及FW-H声学模型,运用弓头仿生降噪和底部空腔主动射流降噪的整体降噪措施,采用数值模拟法研究高速列车受电弓区域的降噪效果。结果表明:受电弓弓头和底部空腔是气动噪声的主要来源;降噪后,主要噪声源的声功率级都有了较大降幅,其中弓头和空腔部位分别降低了15.28 d B和16.92 d B;中高楼层住宅处的降噪效果更佳,最大声压级降低位置在距地面18 m高处(距受电弓25 m远处),降低了4.94 d BA;远场声压级在低频区域降噪效果更为显著,特别是在800 Hz位置声压级降幅最大,降低了8.21 d BA。展开更多
文摘A jet noise reduction technique by using the external chevron nozzle with lobed mixer in the double-mixing exhaust system is investigated under cold conditions.The computations of jet field and the experiments of noise field are conducted with scaled model of high-bypass-ratio turbofan engine mixing exhaust system composed of external chevron nozzle with lobed mixer.The computational results indicate that comparing with the baseline nozzle with lobed mixer,the external chevron nozzle with lobed mixer increases mixing of jet and ambient air near the nozzle exit.The experimental results show that the external chevron nozzle with lobed mixer has better jet noise reduction at low frequencies,and this reduction rises with the increase of chevron bend angle.The experimental results also show that the external chevron nozzle with lobed mixer has sound pressure level(SPL)increase which is not obvious at high frequencies.With chevron bend angle increasing,SPL has relatively marked increase at 60°(directivity angle measured from upstream jet axis)and little fluctuations at 90°and 150°.The external chevron nozzle with lobed mixer has overall sound pressure level(OASPL)reduction in varying degrees at 60°and 150°,but it has little OASPL increase at 90°.
文摘针对高速列车气动噪声越来越大的问题,本文以高速列车某车型为参考建立1∶1受电弓区域局部模型,基于宽频带噪声源模型、LES大涡模拟及FW-H声学模型,运用弓头仿生降噪和底部空腔主动射流降噪的整体降噪措施,采用数值模拟法研究高速列车受电弓区域的降噪效果。结果表明:受电弓弓头和底部空腔是气动噪声的主要来源;降噪后,主要噪声源的声功率级都有了较大降幅,其中弓头和空腔部位分别降低了15.28 d B和16.92 d B;中高楼层住宅处的降噪效果更佳,最大声压级降低位置在距地面18 m高处(距受电弓25 m远处),降低了4.94 d BA;远场声压级在低频区域降噪效果更为显著,特别是在800 Hz位置声压级降幅最大,降低了8.21 d BA。
文摘针对高速列车气动噪声越来越大的问题,本文以高速列车某车型为参考建立1:1受电弓区域局部模型,基于宽频带噪声源模型、LES大涡模拟及FW-H声学模型,运用弓头仿生降噪和底部空腔主动射流降噪的整体降噪措施,采用数值模拟法研究高速列车受电弓区域的降噪效果。结果表明:受电弓弓头和底部空腔是气动噪声的主要来源;降噪后,主要噪声源的声功率级都有了较大降幅,其中弓头和空腔部位分别降低了15.28 d B和16.92 d B;中高楼层住宅处的降噪效果更佳,最大声压级降低位置在距地面18 m高处(距受电弓25 m远处),降低了4.94 d BA;远场声压级在低频区域降噪效果更为显著,特别是在800 Hz位置声压级降幅最大,降低了8.21 d BA。
