| In emergency working conditions,the pressure relief valve is needed to release the pressure of natural gas pipeline system quickly.High-speed fluid and unsteady flow induce strong sound pressure,which produces wide-band fluid-induced noise inside the valve and affects the normal operation of the pipeline system.Therefore,based on computational fluid dynamics(CFD)method and acoustic analogy method,unsteady large Eddy simulation(LES)and Ffowcs Williams-Hawkings acoustic analogy model were used to study the flow characteristics,flow-induced noise characteristics and noise reduction methods of pressure safety valves.The main research contents and conclusions are as follows:(1)The numerical simulation method of flow characteristics,fluid-induced noise and related theories used in this work are studied,and the reliability of the numerical simulation method is verified by combining with the full-size experimental data conducted by southwest Research Institute in the United States.(2)For a pilot pressure safety valve,the flow field,noise location and frequency spectrum characteristics of the valve were studied at a fixed opening,and the flow characteristics and fluid-induced noise characteristics of the pressure safety valve were revealed.The results show that there are two main types of internal noise in safety valve,one is dipole source caused by pressure disturbance caused by fluid high-speed impacting wall,the other is quadrupole source caused by turbulence,and the dipole source is dominant.The frequency of noise is mainly concentrated in 500-2000 Hz,and the SPL is the highest in the direction of 120° Angle with the outlet axis,and the total SPL decays the fastest in the direction of 0-0.5m along the outlet axis.(3)The pressure safety valve models with different opening degrees were established,and the influence of opening height,inlet pressure and other factors on the location,spectrum and directivity of noise sources was studied.The results show that with the increase of opening height,the maximum sound pressure increases gradually,and the position of the dipole source changes obviously,while that of the quadrupole source remains unchanged.The inlet pressure has no effect on the noise spectrum,directivity and source position,and the SPL of each frequency band increases with the increase of inlet pressure.(4)Based on the characteristics of fluid-induced noise,the noise reduction principle and performance of single-stage porous plate and multi-stage porous plate are compared and analyzed.The results show that the single-stage porous plate is effective for noise reduction in the 500-1750 hz range,and the loudest power level is reduced by 14 d B.Based on the single-stage porous plate,a multi-stage porous plate noise reduction scheme is proposed.The Mach number in most areas of the flow field is less than 1,and the flow tends to be stable.It is effective to reduce the noise in the range of 1000-4500 Hz,and the loudest power level is reduced by 22 d B,which meets the requirements of EI guide.The noise reduction performance of multi-stage porous plate is better than that of single-stage porous plate,which provides a new idea and scheme for solving the flow induced noise problem of safety valve. |
