Influence Of Bends On Measurement Accuracy Of Ultrasonic Flowmeter In Heating System

At present,the research on the measurement accuracy of large diameter ultrasonic flowmeter which is used for obtaining the data of managing heat-supply network and trading measurement between heat source plants and heating enterprises is still lacking.In the actual heating system,the measurement accuracy of ultrasonic flowmeter is easy to be affected by the upstream baffles.The downstream flow field of bends with different combinations of heating systems were analyzed by CFD numerical simulation and then got the simulation measurement error.By comparing the simulation measurement error with the experiment measurement error,the measurement error of the ultrasonic flowmeter in heating system with different combinations of bends are analyzed.The main work and conclusions are listed as follows:(1)Select the equal-diameter and the variable-diameter ultrasonic flowmeter and install them on the DN150 and DN80 ideal pipe.After that the velocity contour of the downstream flow field is analyzed.The results show that when the fluid reaches the measuring section,the fluid is close to the fully developed flow under the condition of the ideal pipe.The measurement error of ultrasonic flowmeter satisfy the accuracy requirements.The results of CFD numerical simulation and experiment can verify each other,which can prove the correctness of the numerical simulation model.(2)By the simulation of inside and downstream flow field of single bend(bend diameter ratio is 1.5),the distribution of the secondary flow can be clearly captured,and the change of velocity gradient in the flow direction is observed.Based on that,the downstream flow field of the double bends is analyzed.The simulation results show that there are obvious eddy currents in the downstream flow field of the double bends.By comparing the ratio of the radial velocity to the main flow velocity,the effect of the double bends on the accuracy of the ultrasonic flowmeter is more intense than the single bend,and the influence decreases with the increase of the distance between the measuring section and bends.(3)Select the equal-diameter and the variable-diameter ultrasonic flowmeter for the plane double bends downstream flow field simulation analysis.The simulation results showthat the secondary flow of the bends can't be fully developed when the fluid flows through plurality of tight connection bends.The centrifugal force acting on the different bends is reversed and partly canceled,then obtain the relatively evenly velocity distribution.