| 90°bend pipe of circular-section with fore-end valve which can completefluid conveying, heat and quality exchanging is able to save the layout spaceeffectively, realize fluid conveying and heat, quality exchange, so it iswidely used in industrial, agricultural and shipbuilding industry, especially inthe main drain system piping, seawater cooling lines and oil pipelines andpipeline system ships and submarines with the limited space. Flow in90°bend pipe of circular-section with fore-end valve is influenced by manyfactors, such as valve body structure and the degree of opening, bend degree,flow Mach number and so on. The flow field is very complicated, it can formseparation zone, secondary flow near the wall, these phenomena cause fluidtotal pressure and energy loss, oscillation or pulsating, which generate theflow and structure noise, so flow and noise research in90°bend pipe ofcircular-section with fore-end valve has practical application value.Based on90°, Rc/D=0.75bend pipe of circular-section with fore-endvalve as the research object, three-dimensional geometry model was built andhigh quality grid was gained based on grid generation software Hypermeshand Tgrid. The3-D turbulent flow in90°, Rc/D=0.75bend pipe ofcircular-section with fore-end valve is simulated by large eddy simulation method in different inlet velocity and different valve opening, and the internalunsteady flow field characteristics and the characteristics of pressurefluctuations on wall turbulent boundary layer are obtained. We make use ofthe boundary element method to calculate the direct radiation noise generated,and fluctuating pressure incentive structure vibration producing radiationnoise is calculated based on the modal superposition method based on theunsteady flow analysis.Conclusions are drawn out:(1)LES method is applicable to internal fluidflow characteristics of90°, Rc/D=0.75bend pipe of circular-section withfore-end valve by comparing the butterfly valve fully open, the inlet velocity3.5m/s conditions with the PIV experimental results.(2)flow characteristics of90°, Rc/D=0.75bend pipe of circular-section with fore-end valve is mainlyaffected by the impact of the valve structure and elbow curvature, there areobvious zone of high-speed and low-speed，while vortex structure, thebackflow, vortex and secondary flow were revealed.(3) The fluctuatingpressure in the turbulent boundary layer caused by vortex structure in thecontinuous formation and shedding process in the flow field，on the one hand,randomly fluctuating pressure produces directly radiation noise, soundpressure level is higher in the low frequency and the sound pressure level arewithin the range of200dB. On the other hand, fluctuating pressure incentive structure vibration also produce radiation noise, which is lower than directradiation noise pressure level, the maximum sound pressure level after200Hzis related with the coupled modal frequency. |
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