Study On Optimizing Structure To Improve Flow Field Adaptability Of Gas Ultrasonic Flowmeter

In recent years,the market share and output value of ultrasonic flowmeters have been greatly improved,and the sales share of gas ultrasonic flowmeters is more than 70%.Compared with other flowmeters,ultrasonic flowmeters have many advantages,such as high measuring accuracy,small pressure loss,large range ratio,easy installation and maintenance.Because of the acceleration of industrialization,low carbon economy gets more attention.As the basic tool of natural gas metering,the problem of how to improve the measurement accuracy of gas ultrasonic flowmeter needs to be solved urgently.The measurement error caused by the installation effect in the flow field adaptability problem is the main factor affecting the measurement accuracy of ultrasonic flowmeter.For the small and medium caliber ultrasonic flowmeter,it is difficult to carry out multi-channel arrangement because of the limited space of measuring section.In this paper,DN40 monophonic gas ultrasonic flowmeter is taken as the research object.In order to improve the adaptability of the flow field,the structure of the measuring section of the flowmeter is optimized.Through the combination of numerical simulation and experiment,the following studies are made:1.In view of the situation that the upstream of the flowmeter has elbow turbulence,the structure of the measuring section is improved,and five different sizes of reduced diameter and variable rectangular section structure schemes are designed.Different inlet flows are set by CFD technology,and the flow field in each structure size is simulated and analyzed,and the velocity distribution of the flow field in the measured section is obtained.According to the velocity distribution of the measured section,it is shown that both the reduced diameter and the variable rectangular section structure can improve the velocity distribution of the flow field.By further studying the K coefficient of the straight elbow pipe in the same measuring section,it is concluded that the structure with variable rectangular section is superior to the structure with reduced diameter.In the case of considering the pressure loss,the length-width ratio of the rectangular section is 1.6,which meets the requirements.The measurement performance of the primary base table structure and the rectangular section structure with the aspect ratio of 1.6 was studied experimentally.Through the combination of simulation and experiment,it was proved that the measurement section with the variable rectangular section structure and the aspect ratio of 1.6 was the optimal structure to reduce the elbow turbulence and improve the measurement accuracy of the flowmeter.2.The influence of flow field pulsation factors on the instantaneous linear velocity of ultrasonic flowmeter is studied.Firstly,the instantaneous linear velocity fluctuation of the base table structure,the reduced diameter structure and the variable rectangular section structure under different Reynolds numbers were studied by numerical simulation,and it was found that the instantaneous linear velocity of the variable rectangular section structure was easily affected by the flow field fluctuation.Based on the rectangular structure of the measuring section,the guide vane was added,and three different guide vane layout schemes were designed.Through numerical simulation,the instantaneous linear velocity fluctuation graphs of each scheme under different Reynolds numbers were obtained.It was found that the fluctuation of instantaneous linear velocity with the guide vane was slowed down compared with that without the guide vane.Through quantitative analysis of the numerical simulation results,the variance of instantaneous linear velocity is obtained.By comparing the variance of instantaneous linear velocity,the effect of scheme Ⅲ is proved to be better than that of scheme Ⅰ and scheme Ⅱ.By indirectly comparing the instantaneous flow fluctuation between scheme Ⅰ and scheme Ⅲ,it is obtained that scheme Ⅲ is an optimal structure to restrain the flow pulsation.3.Through the comprehensive analysis of the joint effects of elbow turbulence and flow field pulsation,the flow field of the rectangular guide vane structure is analyzed,and the results show that the velocity distribution of the rectangular guide vane structure is still relatively uniform.The K-coefficient of the straight elbow with the same measuring section structure is further compared with that without the guide vane,the measurement accuracy is slightly improved and the influence of flow field pulsation is inhibited.Rectangular guide vane structure(rectangular length-width ratio of the measuring section is 1.6,two guide vane are added)is an optimization structure to reduce the error caused by installation effect and improve the measurement accuracy of ultrasonic flow meter.In this paper,the analysis results of the flow field adaptability of the ultrasonic flowmeter through the structural improvement provide some reference for the relevant follow-up research.