Study On Leakage Acoustic Generation Mechanism And Source Characteristics Of Gas-liquid Two-phase Flow Pipelines

With the application of oil and gas mixed transportation pipelines is becoming more and more popular,so it is of great significance to ensure the safety of oil and gas mixed transportation pipeline system.For pipeline leakage detection,acoustic detection technology has been paid more and more attention because of its advantages.It has achieved good results in the application of single-phase pipeline in production engineering.However,acoustic leakage detection technology for oil and gas mixed pipeline is almost blank,and many technical problems have not been effectively solved.In this paper,the coupling acoustic leakage detection and two-phase flow theory are combined organically to discuss the acoustic generation mechanism and acoustic characteristics of two-phase flow pipeline leakage,providing technical support for the safe operation of mixed transportation pipeline.Gas-liquid two-phase flow is the most important flow form in the process of oil-gas pipeline transportation.According to the basic principle of acoustic method,the characteristics of acoustic generation and the acoustic characteristics of gas-liquid two-phase pipeline leakage directly affect the accuracy of leakage judgment,which is the basis of acoustic leakage detection technology.In this paper,the leakage process of gas-liquid two-phase flow pipeline is studied.The leakage sound field of gas-liquid two-phase flow through the leakage orifice on the pipe wall under three common flow patterns,namely,stratified smooth flow,stratified wave flow and slug flow,is theoretically analyzed,numerically simulated and experimentally studied.The main research work and achievements of this paper are as follows:(1)The leakage flow characteristics and acoustic characteristics of gas-liquid two-phase flow pipeline are studied.The flow characteristics and phase separation characteristics of gas-liquid two-phase flow in pipelines with different flow patterns and leaking directions are analyzed theoretically.The mechanism of leakage sound source in gas-liquid two-phase flow pipeline is analyzed,that is,the sound of fluid in pipeline and the sound of pipeline vibration.Based on literature review,the acoustic wave generation model of single-phase flow in gas-liquid pipeline is summarized,and the acoustic wave generation model of two-phase flow in pipeline is established,which lays a theoretical foundation for the acoustic field of gasliquid two-phase flow leakage.(2)An experimental device for leak detection of gas-liquid two-phase flow pipeline is built.The acoustic characteristics of gas-liquid two-phase flow pipeline leakage are studied experimentally.The diameter of horizontal experimental pipeline for leak detection of air-water two-phase flow is 37 mm.The apertures of leakage simulator is 4 mm,5 mm,6 mm,7 mm and 8 mm.The leakage orifices are located at the upper,middle and lower parts of the pipe wall respectively.A variety of signal processing methods are proposed for leakage acoustic signals of two-phase flow.The relationship between dynamic pressure fluctuation amplitude and gas-liquid flow rate in the steady flow process of stratified smooth flow,stratified wave flow and slug flow in gas-liquid two-phase flow pipeline is established.It is used to determine the fluctuation of background noise amplitude of steady flow under each flow pattern.(3)The dynamic pressure signals collected by different flow patterns are processed.The dynamic pressure wave characteristics of stratified smooth flow,stratified wave flow and slug flow are obtained when the leakage orientation and leakage aperture changed.The effects of leakage orientation,gas-liquid flow rate and aperture on the amplitude of acoustic leakage signal of gas-liquid two-phase flow are studied.It is concluded that the leakage signals under each flow pattern are affected by the gas-liquid flow rate,the orientation of the leakage hole and the aperture in turn from large to small.By comparing and analyzing the amplitude and frequency methods of different leakage acoustic signals,it is concluded that the mean method and EMD decomposition method have high accuracy for leakage detection of each flow pattern.The frequency range of leakage acoustic energy for each flow pattern is obtained.The generation model of twophase flow pipeline leakage sound source is established,and the instantaneous leakage sound wave amplitude of two-phase flow is obtained by using the empirical formula of phase separation pressure drop,which provides a basis for setting the threshold of leakage amplitude change of stratified smooth flow and slug flow.(4)Flow field simulation of gas-liquid two-phase pipeline leakage opening process is realized by UDF programming which based on Fluent dynamic grid technology.Based on the theory of the leakage flow characteristics of stratified flow and slug flow,the mechanism of acoustic leakage is analyzed based on flow field.Through the analysis of the characteristics of the upper and lower leakage flow field,the characteristics of the leakage sound source are analyzed.In order to improve the accuracy of leak judgment,this paper proposed that analyze leak instantaneous acoustic wave and leak continuous acoustic wave simultaneously.In this paper,the characteristics of leakage acoustic wave are clarified through the study of the generation mechanism of leakage acoustic wave in gas-liquid two-phase flow.The influence of various factors on the change of leaking sound source and the characteristics of leaking sound wave are obtained,which will prepare for the further study of gas-liquid two-phase pipeline leak detection and localization.This research is the basis of acoustic leakage detection and the key of acoustic leakage detection technology for gas-liquid two-phase flow.