摘要:
气液两相流在流动过程中表现出非平稳的特性,简单的频域分析或时域分析方法不能很好地分析信号的波动特性,所以引入了时频联合分析方法。时频分析能看到气液两相流差压信号的能量强度和密度的分布,通过多次实验发现泡状流时能量主要分布在10~35Hz 的高频段内,能量强度小;弹状流时能量主要集中分布在0~5Hz 低频段和10~35Hz 高频带内,能量明显增大;塞状流时能量主要集中分布在0~5Hz 低频段内,能量强度是3种流型中最大的。为了研究气液两相流的动态特性,通过多孔孔板流量计在水平管气液两相流中采集得到不同流型的差压信号,采用自适应线性调频小波时频分析方法分析动态差压信号。具体步骤:首先分析信号的分解次数,残余的信号能量低于总信号能量的10%,即可认为被完全分解,对分解后的结果进行分析,得到不同流型的时频分布特征,具有很高的时频分辨率,时频谱图中显示出不同流型分量信号的时频分布特征;然后从时频谱图中提取3个特征值建立三维散点图,图中显示了信号特征值和流型之间的关系,并通过散点图分析不同特征值对气液两相流中信号的流型的影响,达到流型识别的目的。Chirplet 变换具有较高的时频分辨率,能消除噪声的干扰,信号的瞬时频率信息可以清楚地显示出来。
Abstract:
The gas-liquid two-phase flow shows non-stationary characteristics which cannot be well analyzed by traditional frequency or time domain analysis.In this study,the dynamic differ-ential pressure signal of two-phase flow is sampled for flow characteristics analysis and flow pat-tern identification.A time-frequency analysis technique with adaptive Chirplet transformation is introduced,which could profile the energy intensity and density distribution of non-stationary signal.The multi-hole orifices plate flowmeter is used to generate the dynamic differential pres-sure signal in a horizontal gas-liquid two-phase pipe.The dynamic differential pressure signals sampled in the pipe are of non-stationary characteristics which are determined by the flow patterns.The adaptive Chirplet transformation is adopted to process the dynamic differential pressure signals.The stages of the method are:Firstly,the differential signals are decomposed and reconstructed by optimized parameters and the ratio of the residual energy of the signal to the total energy is kept lower than 10% to ensure the useful components of the signal are completely decomposed.Secondly,the time-frequency distribution characteristics of different flow patterns are analyzed by transforming the reconstructed signals.The time-frequency spectra of the trans-formation contain signal components’time-frequency information which reflects the flow proper-ties of different flow patterns.The time-frequency spectra show that the energy of bubbly flow is mainly concentrated in a relatively high-frequency band (15-35)Hz with a low energy intensity. The energy of slug flow is distributed in the low-frequency band (0-5)Hz and the high-frequency band (10-35)Hz,and the signal energy is increased.The energy of plug flow is of low frequency characteristic ranging (0-5)Hz,and the energy intensity is the largest among the three flow pat-terns.Thirdly,three eigenvalues from the spectra are extracted and a 3D scatter plot chart is established,aiming to connect the signal features with flow pattern characteristics.It is found that there is a connection between the flow variances and the alteration of eigenvalues,which could identify the gas-liquid two-phase flow patterns.This method,having higher time-frequency resolution,could provide good noise reduction performance.The instantaneous frequency infor-mation of the signal components could be clearly demonstrated.
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