| At the time of regulating metering and sub-transmission at natural gas gathering station, along with the changing of the medium flow state in pipes, the formation of a vortex disturbance appeared, as a result of the friction between pipe walls, and ultimately produces a fluid dynamic noise, which also named as flow noise. The flow noise at natural gas gathering station comes mainly from steel elbows, tees and other components and manifolds, pressure regulators, filter separators and other equipment.For the issue of exceeding the standard of flow noise at natural gas gathering station, in order to carry out the analysis of the formation mechanism and influence of different factors for the flow noise in elbow pipes and manifolds, a combination theory method of a large eddy simulation and FW-H analogy sound theoretical has been proposed. Meanwhile, with the introduction of small hole muffler technology, an appropriate analytical model is established, and combining with the flow noise value, to analyze the effectiveness and adaptability of holes muffler, and make rational and effective natural gas gathering station flow noise control measures, and the research contents are as follows:(1) The study of flow noise at natural gas gathering station is based on the combination theory of large eddy simulation and FW-H acoustic analogies. Through the simulation of flow noise propagated from station elbows and manifolds and the discussion of their influencing factors, the effectiveness of this combination theory in the field of flow noise in natural gas gathering station research has been proved.(2) Aiming at the problems of flow noise at gas gathering station, elbows and manifolds calculation models have been established, and using ANSYS Fluent software to take the flow noise calculation, in order to analyze the distribution of sound pressure level (SPL). Calculation results show that:The maximum noise level at station elbows reaches100dB, and that at manifolds reaches110dB, both are beyond the standard of the environment noise level (70dB); The frequency distribution of elbows and manifolds flow noise corresponding to the pressure level range is wide, and each frequency corresponding to some certain acoustic energy, of course, the flow noise belongs to a kind of broadband noise.(3) According to the level distribution of elbow flow noise, different elbow models have been built, and with the help of acoustic analysis software, the changing of SPL under different conditions been studied, as well. Studies have shown that:The vocal mechanism of elbow flow noise is primarily the role of the secondary flow and vortex flow, which increases with decreasing elbow angle or increasing elbow radius, at the same time, the weakening impact of transient flow can effectively control the level of flow noise at the elbow; And with the pressure upgrade every0.1MPa, the SPL near elbow pipe walls increases1～3dB.(4) Meeting different types of the attachment of the inlet and outlet pipes at manifolds, the distribution of flow noise SPL has been calculated, and with the influence of different transmission styles analyzed. The results show that:When the inlet and outlet pipes are staggered, the SPL and the acoustic energy at the end of the inlet pipe increases with the inlet pipe diameter decreases, and the rate of increasing is growing; However, when the inlet and outlet pipes are alignment, the jet flow damage on the manifold walls are reduced and the jet flow SPL is much lower.(5) On the basis of reasonably determining exceeding standard problems of natural gas gathering station flow noise, with the introduction of small hole muffler technology and the establishment of models of manifolds with small hole muffles, and then the design parameters are as follows:The holes aperture of3mm, the number of holes for480, muffler pipe diameter and length of60mm and650mm respectively. Installing a small hole muffler in the inlet pipe of manifolds, and then analysis holes muffler noise level reduction. The results show that:The small holes muffler can effectively reduce the noise level, for low frequency sound pressure level, noise reduction up to37.4dB, average noise reduction to20.9dB. |
