Numerical study on the flow and sound characteristics of split three-stream nozzle
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摘要:
采用数值模拟方法研究了引入第三股流后喷管的流动与噪声机理，第三股流涵道比增大对流动与噪声特性的影响。结果表明：引入第三股流使得风扇流速度核心区长度增加，主流核心区末端与自由来流的直接掺混轴向距离缩短，两者间的湍流掺混峰值下降约2.63%，但由于喷流下游剪切层厚度增加，有限的低速第三股流在各方向上的降噪效果有限。第三股流涵道比的增大方便实现，这不仅可以在降低耗油率的同时增加发动机推力，还可以降低排气系统的宽频噪声。第三股流涵道比增大至2.52，不仅使得主流核心区末端的湍流掺混强度减弱，而且使得第三股流与自由来流间强剪切层的掺混强度减弱，主流核心区末端的掺混强度相较于设计工况降低8.57%，各方向上的总声压级均降低，降低峰值约2.37 dB。
Abstract:The influences of the three-stream introduction and the tertiary bypass ratio on the flow and noise characteristics of the three-stream nozzle were studied by the numerical simulation method. The results showed that the three-stream introduction increased the length of the bypass potential core, shortened the axial distance of the direct mixing between the end of the primary potential core and the free stream, and reduced the peak value of the turbulent mixing between them by about 2.63%. However, due to the increase of the shear layer thickness, the low-speed three stream had limited noise reduction effect in all directions. The increase of the tertiary bypass ratio was easy to achieve, at the cost of reducing fuel consumption, and it can increase the engine thrust and reduce the broadband noise of the exhaust system. The increase of tertiary bypass ratio to 2.52 weakened not only the turbulent mixing intensity at the end of the primary potential core, but also the mixing intensity of the strong shear layer between the three stream and the free stream. Compared with the design condition, the mixing intensity at the end of the primary potential core decreased by 8.57%, and the overall sound pressure level decreased in all directions, with a peak value of about 2.37 dB.
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Key words:
- three-stream nozzle /
- bypass ratio /
- mechanism analysis /
- flow characteristic /
- sound characteristic
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图 6 三股流喷管涡量及不同FW-H积分面位置示意
Figure 6. Vorticity and different FW-H integration surfaces of three-stream nozzle
图 7 不同FW-H积分面总声压级对比
Figure 7. Comparison of overall sound pressure level on different FW-H integration surfaces
图 10 双股流与三股流喷管流场时均马赫数分布云图对比
Figure 10. Comparison of time-average Mach number distribution between dual and three-steam nozzle
图 11 双股流与三股流喷管流场
$\sigma_{V'_X} $ 分布云图对比Figure 11. Comparison of
$\sigma_{V'_X} $ distribution between dual and three-steam nozzle
图 12 流场展向涡与静压分布对比
Figure 12. Comparison of spanwise vortex and static pressure distribution
图 13 双股流与三股流喷管总声压级对比
Figure 13. Comparison of overall sound pressure level between dual and three-stream nozzle
图 14 不同观测角噪声频谱对比
Figure 14. Comparison of noise spectra at different observation angles
图 17 不同观测角噪声频谱对比
Figure 17. Comparison of noise spectra at different observation angles
图 21 流场展向涡与静压分布对比
Figure 21. Comparison of spanwise vortex and static pressure distribution
表 1 三股流喷管关键几何参数表
Table 1. Key geometric parameters of three stream nozzle
喷管通道 L7m/Dc8 Lm8/Dc8 Lplug,cowl/Dc8 A7/Ac8 Am/Ac8 θ/（°） 第三股流 1.5 1.0 0.8 2.0 1.65 16 风扇流 2.0 1.15 0.9 2.5 1.50 18 核心流 2.55 0.85 10.0 2.4 1.25 21 
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表 2 三股流喷管进口气动参数表
Table 2. Aerodynamic parameters of three stream nozzle inlet
喷管通道 β π γ V/Vc8 第三股流 1.31 1.2 1.24 0.48 风扇流 2.33 1.6 1.34 0.63 核心流 1.8 3.38
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