Research On The Mechanism Of Aerodynamic Noise Generation Of Natural Gas Manifold And Its Noise Reduction Method

In the gas pipeline stations design, in order to make a more stable flow of fluid, manifolds are needed to be set before and after separation, measurement or pressure regulating device. Manifolds'usage in gas transmission system is great, yet there is a serious noise pollution problem. Currently research on manifolds noise is rare at domestic and abroad. To meet the provisions of the National Environmental Noise Pollution Prevention Act, and reduce the harm to human body and mind in this paper, manifolds are regarded as research objects, establishing gathering pipes aerodynamic noise prediction model based on acoustic analogy FW-H equation. In order to verify the feasibility of the pneumatic noise prediction model, the model experiment is carried out based on the similarity principle. By comparing the numerical value and the simulation value, the correctness of the numerical simulation is verified. On the basis of this, this paper studies the influencing factors and the noise characteristics of the pipe noise, and explores the generation mechanism of the pneumatic noise, and puts forward the methods and suggestions to provide reference for future engineering application.(1) In this paper, based on the similarity principle, the model test is carried out, and the noise of manifold under different working parameters is studied by the combination of model test and numerical simulation. And the numerical simulation results are compared with the experimental results, which verifies the correctness of the numerical simulation. In the numerical simulation, only the dipole sound source is considered. That means only the pulsating pressure is calculated as an incentive, which can be get by the accuracy of test results. Finally, it can be verified that the dipole sound source is the main sound source.(2) Using the coupling method of CFD and acoustic software, the prediction model of the pneumatic noise of manifold pipe is established. Noise energy distribution manifolds and distribution of noise source are shown as follow:the noise energy is mainly in the range of 0-400HZ. According to the analysis of the flow field analysis manifolds, as well as the measuring point SPL, it can be received that maximum noise position is central location of manifold pipe in near the center of the rear wall. Sound pressure level variation direction along the tube axis, substantially parabolic variation. The change rule of the sound pressure level along the axial direction of manifold pipe presents a parabola.(3) The numerical simulation is carried out by establishing the prediction model of the pneumatic noise of the manifold pipe. When changing the flow state of manifolds, manifolds noise variation is:1) As the pressure increases, the SPL increases, and the noise also increases, but the increase was not obvious. That proved that the pressure is not the main factor.2) As the velocity increases, the SPL increases, and the noise also increases, but the rate of increase for each interval is different. With the increases of velocity of flow, the rate of increase grows before it is reduced. In order to achieve the purpose of reducing the manifolds noise, there is a need to reduce the flow rate, and as far as possible to keep it under 10 m/s.(4) Coupling method of CFD and acoustic software,when changing the structure of manifolds, manifolds noise variation is as follows:1) With the ratio of the inlet pipe and manifolds diameter increased, namely with the inlet pipe diameter reduced, sound pressure level and the noise increased, the growth of the overall sound pressure level increase first and then decrease along with that of the inlet pipe diameter and manifolds. When the ratio of the inlet pipe and manifolds diameter reached 1:1.5 to 1:2, the growth rate of the overall sound pressure level runs up to the maximum, then gradually decreases. It is recommended that manifolds diameter and the inlet pipe diameter of ratio is less than 1.5 as much as possible.2) With the increase of the outlet pipe diameter, sound pressure level increases, the noise reduces, and the growth of the overall sound pressure level increase first and then decrease along with that of the outlet pipe diameter and manifolds. When the ratio of the outlet pipe and manifolds diameter reached 1:1.5 to 1:2, the growth rate of the overall sound pressure level achieves the maximum, and then decreases little by little. It is recommended that manifolds diameter and the outlet pipe diameter of ratio is less than 1.5 as much as possible.3) With the spacing of the outlet pipe increasing, the sound pressure level reduces, and the noise decreases.(5) According to the research of the manifolds noise generation mechanism, combined with the principle of noise reduction, the noise reduction method can be summed up. Meanwhile, for a project case, active noise reduction can be in progress by optimizing the operation parameters and the structure form. Then a numerical model is established to simulate the noise reduction effect. It can be concluded that the manifold gets obvious noise reduction effect by optimized, and change the operating parameters is the most simple and effective method to reduce the noise.(6) In the view of a practical project case, passive noise reduction can be carried out for the sound-absorbing material on the portal package.1) By studying the sound absorption effect of different materials of sound absorption material, it can be drawn that with the increase of the sound-absorbing material flow resistance rate, and noise reduction effect is better. Sound-absorbing material flow resistivity at 0?10000 Pa·s/m2 range, after linea fitting, flow resistivity and total sound pressure level of the relationship is y=-0.0026x+86.185.2) Through the study of the sound absorption and noise reduction effect of different thickness of the sound absorption material, it can be obtained that with the increase of the thickness of the sound-absorbing material, and noise reduction effect is better. Sound-absorbing material at a thickness range of 0?100mm, thickness and overall sound pressure level of the relationship is y=-0.2317x+85.787.