| The gas-liquid separation and transport facilities are replaced by gas-liquid rotodynamic multiphase pump that is not only achieving long distance transportation,large discharge transportation,shortening the platform construction cycle but also reducing the cost.Engineers from all over the world pay great attention to these advantages.But the main drawbacks of gas-liquid rotodynamic multiphase pump are still lack of enough theoretical support and effective design method leading to low efficiency and short service life under the bad operating environment,which led to not be popularized in our country.In order to explore an efficient hydraulic model of gas-liquid multiphase pump,this paper takes the helical axial multiphase pump as the research object and summarizes a set of hydraulic design methods of the pump according to the relevant hydraulic design methods of axial flow pump,inducer and compressor.The flow channel of the original compression units is optimized.Based on the fundamental theory of gas-liquid two-phase flow numerical simulation,the software Fluent is used to simulate the flow field by changing the number of long and short guide blades and the position of the short guide vane in the static vane passage of the multiphase pump.The flow mechanisms and external characteristics of gas-liquid two-phase flow inside the three-stage compression unit are deeply analyzed under different flow and gas content conditions.The main research contents and results are as follows:1)A hydraulic design model for the gas-liquid multiphase pump was established according to the related literatures about optimization design and theory design method of axial flow pump inducer and compressor.Based on the foundation,the study used the optimization formula of inducer blade to optimize the axial length of compressor blade and give a whole set of hydraulic design formulas including axial length calculation formula of impeller vane.In this paper,the most reliable and widely used mathematical model,control equation and discrete scheme for gas-liquid two-phase flow numerical simulation are introduced.2)Using the professional flow field simulation software Fluent,using water and air as the medium,by selecting different lengths and lengt hs of the leaves for the compound stator,Numerical simulation of the whole machine flu id field is carried out under different flow and gas content conditions.Compression unit of gas-liquid multiphase pump pressure field distribution,gas-bearing rate distribution,and velocity distribution diagram are obtained.According to the analysis of two-phase flow mechanism inside flow channel with different blade numbers and the pressurization curve,head curve and efficiency curve of the whole machine under different working conditions were calculated.The results show that the number of composite stator blades has great influence on energy recovery and has severe interferences for inner flow field of the next impeller.There is a certain relationship among the flow passage area,extrusion coefficient and friction loss.When the number of long guide vanes and short guide vanes are 8,respectively,and the hydraulic performance of multiphase pump is optimal.3)Concerning the excessive local pressure for immobile impeller of multiphase pump,a relationship between short guide vanes ' placement and hydraulic performance is obtained by means of CFD analysis to achieve the best placement of short guide vanes.Under design conditions,improving the multiphase pump's hydraulic performance and reducing the local pressure are set as the optimization objective function,while the design parameters of impeller and compound long guide vanes remain unchanged.The results show that placement of short guide vanes have an important influence on hydraulic performance and the internal flow of multiphase pump.There is a best placement of short guide vanes when the position moves from the rear of the flow channel to the front.As the position of short guide vanes move from the rear of the flow channel to the front,there is a flow separation zone starti ng from the rear of the vane chord to the front and becomes smaller and the inlet velocity increases gradually.Under the inevitable condition of gas-liquid separation,when the flow separation zone is located in the middle of the composite guide vane passages,the interference is the weakest for the former stage impeller and the latter stage impeller passage.The relations between the short guide vanes' placement and internal flow field have been revealed and the local high pressure at the top of the tail guide vane is reduced successfully.Some theoretical basis has been established for the optimization of immobile impeller of multiphase pump. |
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