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Aiming at the problem of flow noise reduction in sudden expansion pipe, this paper investigates the flow noise characteristics of viscoelastic fluid in a sudden expansion pipe and reveals the noise reduction mechanism. The flow noise in the sudden expansion pipe could be controlled by viscoelastic fluid which is obtained by mixing the surfactant with water. Based on the finite extensible nonlinear elastic model with Peterlin approximation (FENE-P), the flow noise is calculated by using Fluent UDF, combined with Large Eddy Simulation and the Ffowcs Williams-Hawkings method. The Reynolds number is 8000, the maximum polymer tensile length is 10, and the Weissenberg number (We) ranges from 0.1 to 12. The results show that when We reaches a certain value, the flow field is stabilised and the generation of vortices is delayed. Thus, the formation of large vortex that generates low-frequency noise is inhibited. The fluctuating pressure and fluctuating velocity inside the pipeline and at the pipe wall are reduced significantly, so that flow noise will be suppressed from the perspective of sound source. With the increase of We, the effect of noise reduction is enhanced and the frequency range of noise reduction is extended, but when We exceeds a certain value, the noise reduction effect reaches the threshold.
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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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