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Outline
To investigate the flow noise characteristics in reducer pipes，unsteady numerical simulations of the flow field were performed using large eddy simulation （LES） coupled with the Smagorinsky subgrid‑scale model.Fluctuating pressure analysis was employed to study the distribution of acoustic source intensity inside the pipes.Acoustic sources were extracted using the Lighthill acoustic analogy method，and the acoustic field in the reducer pipe was calculated via the acoustic finite element method.Experimental comparisons validated the reliability of the numerical approach.With overall sound pressure level （OSPL） as the optimization criterion，a hyperbolic structure was adopted to optimize the reducer pipe.Results show that this computational method effectively predicts flow‑induced noise in reducer pipes，with a relative error below 3% compared to experimental results.Peak pressure fluctuation intensity occurs at the inlet and outlet transition sections，with maximum fluctuating pressure root mean square （Cp，RMS） values of 0.086 3 and 0.083 1，respectively.OSPL values at the transition section，outlet，and inlet are 138.07 dB，135.48 dB，134.35 dB，respectively.The hyperbolic structure significantly reduces pressure fluctuations at the transition section and internal flow noise，decreasing OSPL at the inlet，transition section，and outlet by 7.37%，8.85%，and 8.23%.This study provides theoretical references for structural optimization of reducer pipes.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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