| Pipeline system has been widely used in water supply, heating, oil, and other fields under the rapid progress in science and technology as well as modernization. These pipeline system ensured the normal life of the people, and promoted the rapid development of the country’s economy, science and technology, etc. In addition, the charging line of the shipbuilding industry has been widely used in many field, such as hydraumatic and oil and so on. There were many bends in pipeline system. The flow of fluid in pipe has been one of the focus of field of fluid mechanics. Bend was widely used in agriculture and industry, aviation, ships and so on because of its advantages of saving space, fluid transport, heat exchange, etc. With the enhance of production efficiency of the modernization, it was easy to see that the bend pipe system was widely used in petroleum, chemical industry, hydropower and other areas. The rationality of the design of pipeline system played a decisive role in the management and operation. So it promoted the development of fluid mechanics and the application of the bend in engineering by understanding of the flow mechanism of fluid in pipe bending.In recent years, the rapid development of computer software, numerical simulation technology got the favour of many researchers by high efficiency, low cost, strong adaptability, wide application. In this paper, bend the flow field and acoustic field was numerically studied by the computational fluid dynamics Fluent software of the finite volume method. First the turbulent flow of fluid was finite element simulated by using large eddy simulation model. Then the individual monitoring-station of acoustic pressure signal was obtained by solving the FW-H equation. The calculation of SIMPLE algorithm was implemented by using the Fluent14.5. Finally the calculated sound pressure signals were analyzed and studied.The following three aspects were mainly studied in this paper.1.Firstly the nature and equation of turbulence was introduced. Secondly the large eddy simulation principle and control equation and the vortex sound theory, acoustic analogy method were given. Then the equations of fluid dynamics and flow field numerical simulation method were derived. The modeling and meshing was completed basing on the above theory. The flow field and acoustic field of the 90° bend was implemented numerical studies by using fluent software. The simulation results show that:(1)When t= 7.0×10-2 (s), with increasing angle of θ, the vortex in bend are more and more obvious, and the vortex from the bend of the outer wall move to inner wall. All the bending section presents the phenomenon that outside wall pressure bigger, the speed lesser, but pressure smaller, the speed bigger in inner wall due to the effect of secondary flow; (2) On the section of 9=90°, with the changing of time, the vortex of velocity field in same cross-section has experienced a series of changes, the velocity is stable finally; (3)The vortex appeared in the flow field with the action of secondary flow, there was a sound pressure because of the fusion or fission between the vortex and vortex, the small fluctuation of sound pressure came out in first the whole process. Then there was a bigger sound pressure because of the fusion or fission between the vortex and vortex. Finally the flow field and acoustic field went to plateau at the same time. On the cross section of θ=0°-90°, the peak of sound pressure showed the increasing trend, reached maximum when θ=90°.On this cross section got the maximum sound pressure values.2.The 90° circular cross section bend was implemented numerical studies by using fluent software. The vortex was easy appear because of existing rotated flow turbulence structure of the bend. Interactions between the vortex and the vortex will cause certain influence to the sound field of the bend. The simulation results indicate:(1)The turbulence appeared after the liquid water into the pipe. There was a sound pressure because of the strong interaction between the vortex and vortex.The sound pressure in the tube changed over time. The sound pressure amplitude fluctuate before 0.1s. The sound pressure in the tube became no longer change after 0.1s. With the increase of inlet pressure in the pipe, the pressure variation law with time has not changed. (2) During the process that the bend radius didn’t change, the peak sound value of sound pressure presented the increasing trend. The sound pressure stable value increased with the increase of inlet pressure. (3) When the inlet pressure was constant, with the increase of bend radius, the peak pressure showed a decreasing trend, but stable value of sound pressure also was declining tendency.3.The Fluent software was used for implementing the numerical simulation of the sound field in the export with different bending degree of circular cross section bend. It was investigated that the change rule between the bend pipe bending degree and the outlet pressure. The outside conditions unchanged, the study was from two aspects including a fixed radius of curvature constant and a fixed constant bending part length. The influence of the bending 0 to the sound field of the bend exports was monitored during the whole process of the change of the bend from 30°to 180°. The simulation results show:(1)If curvature radius keeping constant, the peak value of sound pressure demonstrated increasing tendency during the process that the bent pipe bending degree 0 changed from 30°～180°. The sound pressure stable value showed a increasing trend in the overall trend with the increase of bending degree 0. (2) When the length of the bend unchanged, with the increase of bend pipe bending 0, the sound pressure peak presented increasing trend in overall process, meanwhile the sound pressure stable value has also been increasing.
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