Research On Acoustic Characteristic Of High Pressure-drop Multistage Steam Trap

This paper is completed with the support of the national natural science fund(number: 51569012).Due to the multiplex internal structure of high pressure-drop trap,the valve is prone to cavitation,flow-induced vibration and even water hammer when running under the condition of opening and closing in high parameters.The phenomena above not only cause noise and many other issues,but also lead to different damage to the equipment,equipment safety and human health.The structure of multistage decompression is generally used to suppress the high-level noise of the high pressure drop trap in the world.However,the problem,how the multistage structure is designed to multistage eliminate noise and reduce vibration at specific high pressure-drop conditions,needs to be solved urgently.In this paper,following researches are carried out for the problems above.(1)The phenomena,hazards and generation mechanism of noise of high pressure-drop steam trap were introduced.According to research status and methods for the flow-induced noise and the problem of acoustic attenuation performance of valve at home and abroad,the necessity of changing the parameters of valve internals was put forward for improving its muffler performance.(2)Working principle of anti-cavitation and designing process of trim to throttle was presented.CFD(Computational Fluid Dynamics)software was used to simulate the steady-state flow field of high pressure-drop multistage trap and piping with different parameters of valve internals to analyze its internal flow.Simulation of transient flow field was executed by setting steady-state simulation results as initial values,and the data of the flow-induced noise was extracted after the simulation was converged,which prepares for the numerical simulation of flow induced noise of high pressure steam trap.(3)The basic theory of numerical simulation of the flow-induced noise was introduced,and the type of sound source was analyzed and determined.Based on FFT(Fast Fourier Transform)and AML(Automatic Matched Layer),the information of the sound field was obtained by numerical simulation using LMS Virtual.Lab with the source information calculated by the transient flow field as exciting source.The influences of different sleeve diameters,sleeve wall thicknesses and sleeve clearance distances on the sound pressure and frequency of trap and pipe flow noise were compared and analyzed,which could provide a reference for the study of noise induced by high pressure-drop steam trap.(4)Acoustic finite element method and the theory of transmission loss of muffler element were introduced.Sound pressure distribution law,monitoring point sound pressure response curves and transmission loss curves were figured through the study on numerical simulation of muffler performance of high pressure-drop multistage trap with different parameters of internals applying LMS Virtual.Lab.The effects of different sleeve diameters,sleeve wall thicknesses and sleeve clearance distances on the amount of transmission loss and frequency of noise were compared and analyzed,which could provide a reference for the study of muffler performance of high pressure-drop steam trap.The researches above provide references for researches for relationship between different parameters of valve internals and the flow-induced noise,and a basis for optimizing valve internals to induce noise;new ideas and methods of prediction for research on muffler performance of trap were pointed out.