Noise Analysis And Noise Reduction Methods Of Gas Transmission Station Venting System

When natural gas was being vented in gathering station,the instantaneous velocity of the vent pipe exports was large,natural gas mixed with static atmosphere sharply and made a lot of jet noise.For the venting system noise problem,by using ANSYS FLUENT software,based on the LES and FW-H Acoustic analogy theory,the simulation of vent pipe jet flow field and acoustic field was proceeded.Design the expand-chamber type silencer combining with the results of simulation,improve its structure parameters and put forward an effective scheme to reduce the noise.Details were as follows:(1)In order to study the sound production mechanism of the vent pipe,simulate and analyze the jet flow field firstly.Establish a two-dimensional axisymmetric model using ICEM software and proceed the steady simulation of flow field.Obtain the jet structure according to the simulation results,and confirm the length of potential flow core segment was 6.8D,the velocity remained same with the exit velocity in this area,which was the main noise area.The velocity of jet flow reduced rapidly in transition segment and reduced to zero gradually in the main segment.(2)Proceed the unsteady simulation of the jet flow field using LES,capture the whole process of squirt from the pipe exit and cut out the vorticity graph of different times.Observe the vortex's generation,matching and the process of spread to downstream consequently.Finally confirm that the forming process of coherent structure produced the vent noise.(3)Combining with the results of unsteady simulation,using LES model and FW-H Acoustic analogy theory,the simulation of radiation sound field was proceeded.By observing sound pressure level frequency spectrum graph in different monitorings we could get:The sound pressure level of vent noise was bigger in low frequency segment,which belonged to low-frequency noise.The maximum sound pressure level in ground was 109dB.And with the increasing of velocity,the sound pressure level in the same monitoring increased.On the jet axis,the sound pressure level reduced with the increasing distance,which had the obvious directivity in radial direction.In the axial distance of 5m,10m,15m,20m,the average sound pressure level reached the maximum in radial distance of 5m,10m,10m,20m respectively,the max pressure level reached the maximum in 5m,10m,10m,15m respectively.When evaluated the vent noise subjectively using A?B?C three kinds of weight method,get the max sound pressure level were 103dB(A)?112?5dB(B)?117dB(C)respectively.(4)According to the radiation noise frequency spectrum graph establish the expand-chamber type silencer model,calculate the expansion ratio and length of silencer.To get the wider silencing frequency design two expansion chambers,and insert spiles on both sides of the chamber and between the buffles.The simulation results showed that:The expand-chamber type silencer had a good silencing effect,the amount of noise elimination of each monitoring was among 0-40dB,the max sound pressure level was controled under 90dB,the average value was controled about 60dB;The pressure loss rate of silencer was 22.6%,which could satisfy the aerodynamic performance of the vent pipe.