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The cooling system can be carried out by the flow pressure difference through the outside protrusion of an underwater vehicle. This system can prevent the low line frequency pipe noise from the pump’s excitation. However, the protrusion is external, generating the hydrodynamic noise and destroying the acoustic stealth of underwater vehicles. Two protrusion models with a rectangular inlet and a circular inlet were created. The flow field and sound field were numerically calculated. The generation property of the hydrodynamic noise from the two protrusions on the condition of different flow velocities was analyzed. It is indicated that the total radiated sound power of the protrusion with the rectangular inlet is slightly lower than that with the circular inlet. To further reduce the hydrodynamic noise, the protrusion with the rectangular inlet was carried out by the flow control through the serrations. The noise reduction effect of the protrusion with the rectangular inlet by the leading-edge serrations is better than that by the tail-edge serrations. The optimized parameters of the serrations were summarized. To validate the numerical calculation results, four protrusion models were designed and fabricated, and the experimental tests were done in the gravity low-noise water tunnel. The results show that the protrusion with the rectangular inlet by the serrations optimization has a better noise reduction effect in the frequency range from 10 Hz to 2000 Hz. The results in this paper can provide some references for the low-noise design of protrusions of underwater vehicles.
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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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