| Among the numerous flowmeters,Ultrasonic Gas Flowmeter(USFM)stands out with its unique advantages and has gradually developed into an internationally recognized natural gas trading settlement tool.The measurement accuracy of ultrasonic gas flowmeter mainly depends on the transducer configuration of measuring pipe,ultrasonic signal detection and processing and flow velocity profile.Among them,the flow field is the most direct and key factor that affects the measurement accuracy of USFM.However,there are few studies on improving the flow profile at home and abroad.Therefore,this thesis is devoted to improving the measuring accuracy of ultrasonic gas flowmeter by optimizing the flow field.This thesis mainly improve the flow profile and change the flow field type through the research and design of a novel flow conditioner,and finally enhance the ultrasonic gas flowmeter measurement accuracy.This thesis analyzes and studies the flow field related problems in the acoustic measurement area of the ultrasonic gas flowmeter,mainly including: by studying the flow field types and flow velocity profiles in different flow channels,the optimal flow channel structure is determined;by designing a novel flow conditioner and simulating flow field and acoustic field,the steady flow effect of the flow conditioner is verified;by doing quantitative experiment,the significant improvement of measurement accuracy of ultrasonic gas flowmeter is proved.The research content of this thesis is as follows:1.Study on the influence of flow channel structure on velocity distribution.In this thesis,numerical analysis and simulation research are carried out on the traditional circular pipe structure,and it is found that turbulence and non-uniform velocity profile will cause the distortion of ultrasonic propagation trajectory,and then affect the measurement accuracy of the whole ultrasonic gas flowmeter.According to the Reynolds Number(Re)and the calculation method of the characteristic length of rectangular flow channel,the Computational Fluid Dynamics method(CFD)of COMSOL software is used.The CFD module carries out numerical analysis and simulation on two different rectangular flow channels,and designs a rectangular flow channel that ensures the laminar flow state inside.The rectangular channel structure is suitable for the small ultrasonic gas flowmeter studied in this thesis.2.Design and simulation of a new flow conditioner.First of all,combined with computer aided drawing tool Solid Works designed for small ultrasonic gas flowmeter flow conditioner.Secondly,the flow conditioner is compared with a single rectangular pipe to analyze the fluid rectification effect of ultrasonic gas flowmeter.Finally,through fluid-acoustic coupling simulation,the propagation trajectory of ultrasonic wave in the flow conditioner is simulated.3.Experimental verification of the effect of flow conditioner on improving the measuring accuracy of ultrasonic gas flowmeter.Under the same experimental conditions,two identical experimental prototypes were used to install the flow conditioner and a single rectangular pipe in the flow meter,respectively.The 10 standard flow rates were verified 3 times by standard measurement experiments,and the indication error and repeatability data of the two groups of experiments were obtained to verify the performance of the flow conditioner. |
