| It is difficult to reduce the noise of two-phase flow in the pipeline system and it has a great impact on the surrounding environment.Therefore,the vibration and noise of the pipeline caused by the pressure fluctuation of two-phase flow field can not be ignored.The gas-liquid two-phase flow makes the internal medium of water muffler no longer single liquid phase,and the influence of flow and medium changes its acoustic performance.In this paper,firstly,the theory of sound propagation in the pipe is introduced,which extends from the one-dimensional plane wave equation to the three-dimensional sound wave equation in the moving medium of the circular cross-section pipe.At the same time,the sound velocity of the gas-liquid two-phase mixed fluid is deduced,and the sound velocity in the gas-liquid two-phase pipe is indirectly simulated by using COMSOL.It is known that the existence of the gas phase has a great influence on the sound velocity of the mixed fluid.Based on the comparative study of two-phase flow model,according to the flow form of gas-liquid mixing pipeline,using the turbulence and two-phase flow module in COMSOL software,the two-phase flow field characteristics of gas-liquid mixing section and muffler section are calculated according to different gas-liquid flow rate and working pressure,and the influence of gas-liquid inlet velocity ratio and working pressure on gas holdup is obtained.At the same time,the phase distribution,pressure distribution and velocity distribution of the internal flow field of the muffler with different flow time,such as the tube muffler,the perforated tube muffler,the air bag muffler and the sound-absorbing material muffler are calculated,which is good for the analysis of the acoustic characteristics of the muffler in two-phase medium.Then,the hydrodynamic sound source and the acoustic analogy model are discussed.It is determined that the two-phase flow noise is the dipole noise caused by the pressure fluctuation.The noise characteristics of the gas-liquid mixing section are calculated by using the acoustic analogy module of FLUENT software,and the frequency-domain characteristics of the two-phase flow noise in different conditions are obtained.Using COMSOL acoustic module,the transmission loss of the muffler under single-phase background flow and two-phase background flow is calculated.The results show that the background flow in the frequency range of 0-4000 hz has little effect on the transmission loss.Then the transmission loss of four kinds of mufflers in two-phase medium is calculated.The results show that the peak value of transmission loss moves to the low-frequency direction in gas-liquid two-phase medium,the acoustic performance in low-frequency section is greatly improved,and the high-frequency section is decreased.Finally,a simulation experiment platform of gas-liquid mixing pipeline is built to measure the insertion loss of muffler under different working conditions.The results show that the muffler with single liquid phase has good performance in low frequency,and the performance of muffler in low frequency is reduced in gas-liquid two-phase flow. |
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