| Multiphase flow is a common flow phenomenon encountered in nature and industrial production process,which usually shows a complex and changeable flow state with the characteristic of highly randomness,and has many parameters to be measured.Phase superficial velocity,as the important flow process parameter,is closely related to the flow rate,holdup and actual flow velocity of each individual phase in a multiphase flow.Therefore,its accurate measurement has great significance for the establishment of flow mechanism model,the monitoring of production process,and the assurance of stable and safe operation.Aiming at the measurement of phase superficial velocity and overall superficial velocity of oil-gas-water multiphase flow with complicated flow field,this thesis proposes a new measurement method based on the continuous wave ultrasonic Doppler technique.By taking the propagation mechanism of ultrasound and the flow characteristics of different flow regimes into consideration,ultrasonic/electrical multimodality non-invasive sensor structure is designed.Through comprehensive analysis of the amplitude and frequency characteristics of the Doppler shift signal generated by multiple scatterers in the measurement space,decoupling frameworks of the ultrasonic Doppler shift signal are constructed based on different signal processing algorithms to extract actual velocities of different dispersed phases or different flow structures.According to the principle of fluid mechanics,multimodal measurement information is fused to establish novel theoretical models to acquire the phase superficial velocity and overall superficial velocity.The main works accomplished are as follows.(1)According to the flow characteristics of different flow regimes and the complementarity of different sensing techniques,ultrasonic/electrical multimodality non-invasive sensor structure and their combination configuration are designed.The continuous wave ultrasonic Doppler sensor is used to acquire the Doppler shift signal that reflects the velocity information of multiple scatterers in the measurement space,and the pulse wave ultrasonic sensor and the ring-shaped conductance sensor are respectively used to acquire the gas holdup and water holdup fluctuations.Further,the multimodal measurement system is developed by modular method,and the signal-to-noise ratio is above 60 d B.Test boards of different modes could communicate with each other through the industrial high-speed bus to ensure their cooperative work.Dynamic experiments of gas-water two-phase flow and oil-gas-water three-phase flow are conducted on a horizontal multiphase flow test loop,and the flowing information of typical flow regimes are acquired by the multimodal measurement system,which provides a reliable data basis for subsequent modeling researches.(2)For the gas-water slug flow,the continuous wave ultrasonic Doppler sensor and ring-shaped conductance sensor are combined to synchronously acquire the Doppler shift signal and water holdup fluctuations in the flow process.Based on the analysis of slug flow characteristics,according to the frequency response of the ultrasound to different flow structures,the empirical mode decomposition method is adopted to decompose the Doppler shift signal into a set of fluctuated components with different scales.Strong inner correlations between the main fluctuated components and the flow structures in a slug unit are found,and the estimation model of the structural velocities of gas-water slug flow is further established.Compared with theoretical reference values,Root Mean Square Errors(RMSEs)of the estimated structural velocities are smaller than 0.17 m/s.A double-threshold method is proposed to process the water holdup time series to obtain the average water holdup within different regions in a slug unit.Based on the structural velocities and the regional water holdup,a slug closure model is established to calculate the gas and water superficial velocities and the overall superficial velocity.Dynamic experimental results show that the RMSE is smaller than 0.14 m/s compared with inlet reference values.(3)For oil-gas-water three-phase dispersed flow,the combined sensor of continuous wave ultrasonic Doppler and ring-shaped conductance are used to synchronously acquire the Doppler shift signal and water holdup fluctuations in the flow process,and a superficial velocity acquisition scheme based on the time-frequency decomposition and joint analysis of multimodal measurement signals is proposed.Firstly,the water holdup fluctuations are decomposed by the continuous wavelet transform to get the local wavelet energy coefficients map on the time-frequency diagram to characterize the local flow structures of typical flow regimes.Then,the Doppler shift signal is decomposed into a set of components by the ensemble empirical mode decomposition method.By correlating these components with different local flow structures,the actual flow velocities of oil droplets and gas bubbles are extracted.Finally,ignoring the slippage between oil and water,a semi-homogeneous model is established to calculate the gas and liquid superficial velocities and the overall superficial velocity on the premise of phase holdup estimations.Dynamic experimental results show that the RMSE is smaller than 0.07 m/s compared with inlet reference values.(4)For oil-gas-water three-phase stratified flow,the continuous wave ultrasonic Doppler sensor,the ring-shaped conductance sensor and a pulse wave ultrasonic sensor with three transducers are combined to synchronously acquire the Doppler shift signal,the water holdup fluctuations and the height of gas-liquid interface in the flow process.Considering the amplitude and frequency responses of ultrasound to different flow structures,phase holdup estimation model is established,and a Doppler shift signal decoupling framework is constructed based on the signal amplitude segmentation and the multivariable joint time-frequency decomposition methods to extract the gas-liquid interface velocity and oil droplets velocity.By analyzing the force and momentum balance between different phases,a novel three-fluid model of water-based dispersed wavy flow is established to calculate the oil,gas and water superficial velocities and the overall superficial velocity on the basis of making full use of multimodal measurement information.Dynamic experimental results show that the RMSE is smaller than 0.09 m/s compared with inlet reference values. |
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