| One-dimensional steady-state and transient gas-liquid two-phase pipe flow are widely found in petroleum engineering,chemistry,nuclear power and other fields.In petroleum engineering,the design of gas-liquid two-phase processing equipment and the selection of pipe size require in-depth study of two-phase flow characteristics,including flow pattern,liquid holdup,pressure gradient and propagation property of pressure wave and liquid holdup wave.This thesis will discuss theses isses in order to improve the prediction accuracy of two-phase flow.In this paper,the following aspects of gas-liquid two-phase pipe flow were studied:(1)A total of 355 air-water two-phase steady-state experimental tests are carried out on a large scale two-phase flow test rig with eight inclination angles.The test section is a transparent plexiglass pipe with a length of 8m and an inner diameter of40 mm.Superficial liquid and gas velocity varied from 0.02m/s to 3.76m/s and from0.33m/s to 36m/s,respectively.High-speed camera is adopted to capture dynamic images of gas-liquid two-phase flow in the pipe.The pressure and differential pressure sensors are used to measure the pressure fluctuation and the average pressure gradient under different flow conditions.The average liquid holdup is obtained by using manual measurement.The two-phase flow pattern under different inclination angles is determined by a combination of high-speed camera and pressure fluctuation.Typical flow patterns in two-phase pipe flow have been observed:stratified flow(stratified smooth flow and stratified wavy flow),slug flow,bubble flow,and annular flow.(2)Unified flow pattern prediction model of Barnea are validated by using observed flow patterns.The Barnea model preforms well for predicting flow patterns under different inclination angles in the entire flow region,except for the region near stratified-annular flow or the slug-annualr transition boundary.Four two-phase flow steady-state prediction model(Beggs-Brill,Mukherjee,Gomez and Kaya)are selected and validated by using the average liquid holdup and pressure gradient data obtained by experiments.All four models overestimated the average liquid holdup,while the prediction values of average pressure gradient are affected by the inclination angle.When inclination angle is less than 20 degree,Gomez model gave a higher value and there were discrete data points.When inclination angle is greater than20 degree,all four models underestimated the average pressure gradient.(3)The 3D transient two-phase flow simulation of horizontal,inclined and vertical pipe is carried out by using VOF method.The flow pattern,liquid holdup pulsation and pressure pulsation at several cross setions is obtatined by simulation.By comparing images captured by high-speed camera and air fraction contours of pipe cross-section,it was found that the VOF method can effectively discriminate the flow pattern while providing more flow details.The effecs of inclination angle,gas velocity,liquid viscosity on flow pattern,pressure and liquid holdup pulsation,and probability density curve of liquid holdup were analyzed and discussed.(4)Mathmatical properties of the 1D drift flux model are discussed and the model is discretized by using a hybrid shock capture scheme,namely AUSM family scheme.The discretized 1D drift flux model is applied to simulate gas-liquid two-phase pipe flow with variying inlet velocity and constant outlet pressure.The results calculated by the AUSM family scheme(AUSMD,AUSMV,AUSMDV)are basically the same.The influence of drift velocity correlation on slow transient flow was studied,three models are selected,namely Bendksen,Joseph and Morrias drift velocity relations.It can be found that the drift velocity relation only affects the amplitude of the liquid holdup and pressure,while the shape of the liquid holdup and pressure curve remains unchanged and is parallel to each other.Based on MUSCL method and Runge-Kutta method,the class of AUSM schemes with first order accuracy in time and space are extended to second order accuracy.Compared with the results obtained by the AUSM schemes with first order accuracy,it can be concluded that schemes with high order accuracy caputure pressure waves significantly better than low order precision schemes,while there is no obvious advantages for capturing void fraction waves.When the spatial accuracy is second-order,improving the time accuracy does not bring significant performance improvement.(5)The mathematical analysis of the 1D seven-equation two fluid model is carried out.Unlike the mathematical properties of the drift flux model,the two fluid model maintains hyperbolic characteristics in all flow ranges.The model is discretized by using Godunov scheme with shock-capturing capability.The model was validated by two experiments,one is the flow with varying inlet velocity and constant outlet pressure,the other is the flow with constant inlet pressure and rapid valve close at outlet.It is found that the 1D 7-equation two-fluid model successfully captured the wave propagation characteristics of the two test cases. |
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