Influence Of Incoming Flow On The Measurement Characteristics Of Swirlmeter

Swirlmeter is fluid oscillation flow meter,with the advantages of large measurement range,strong output signal and insensitive to temperature,pressure,viscosity and other physical properties,it has gain more and more acceptance and been widely used in natural gas industry.Due to the existing of rotary machines,valves and the change of natural gas physical property,swirling flow,turbulent flow and gas-liquid two phase flow are produced in pipe line.The measurement of swirlmeter is affected,measurement error is enlarged and even disabled under some extreme conditions,while the research on swirlmeter is few.Therefore,in this paper,based on the CFD simulation,the flow characteristic in swirlmeter during measuring steady flow,turbulent flow and two phase flow is studied.The structure of flow filed and influence of various incoming conditions on swirlmeter is analyzed.The conclusions are as follows:1.Study of the flow character inside swirlmeter.Through analyzing the fluid flow in swirlmeter,especially in convergent section and throat region,it is found that the fluid is accelerated and vortex flow is then generated at the outlet of swirler,and the scale of the vortex core becomes smaller as the passage constricts.The rapid expansion of flow passage at divergent section results in reflux and then direct impact on the vortex.The vortex core was displaced from the centerline of the flow passage due to the reflux,the displacement starts at the inlet of throat and reaches the maximum at the end of throat.As the location of this reflux varies,resulting in a displacement not along any particular direction but with high regularity.Based on the simulation results,the shift of the vortex core is a secondary spiral rotation,which rotates around the centerline of the tube giving the whole swirling flow in the throat the appearance of a precessing vortex.The vortex precession dominates the flow distribution in swirlmeter.2.The influence study of tube structure on swirlmeter performance.The numerical simulation results show that the throat diameter and convergent angle dominate the flow distribution in swirlmeter.A larger convergent angle increases the velocity at convergent region and throat section.The smaller throat diameter comes with stronger pressure fluctuation and larger vortex precession frequency,while increases the diameter could reduce the measuring pressure.Through changing the convergent angle from 11°to 8°and meanwhile increasing the diameter from 32mm to 37mm,the pressure loss performance is improved.After experimental verification,the swirlmeter pressure loss is reduced with 22%and 17.7%under flow rates of70m~3/h and 100m~3/h,respectively,and maintains a high measuring accuracy.3.Study of unsteady incoming flow on swirlmeter metrological performance.The valves,shrinkage pipe,rotary machine and other devices which installed at upstream may produce disturbed flow,the flow field is non-uniform and has influence on the internal flow of swirlmeter.It is found that a small opening of valve upstream leading to the increasing of flow velocity,the measurement error occurs.For an opening of 7%,the error is as high as 30%,which is unacceptable during flow measurement.For the larger openings or with a longer straight pipe in from of swirlmeter,the influence is much smaller.When the straight pipe length is 5D,the swirlmeter is no longer under the influence of non-uniform flow which produced by upstream devices.For swirling incoming flows,rotation directions result in different influences.When the direction is the same with that in swirlmeter,the EPR is reduced and the pressure loss is also reduced,while it increases the pressure loss when direction is opposite.Measurement error is found under the influence of swirling flow and it's different under different swirling conditions.4.The study of swirlmeter under gas-liquid two phase flow.The existing of liquid phase leading to the decrease of flow velocity in swirlmeter,the flow field is different especially under high liquid volume fraction condition.It is unable to produce a strong and stable vortex flow due to the decreasing of gas velocity,the vortex precession starts to disappear and the intensity of pressure fluctuation is then reduced.When the liquid volume fraction is 1%,the pressure difference in the cross-section at the end of throat is 15%of that under gas single phase flow.Based on the experiment results,it is found that the influence of liquid phase on flow measure is acceptable when the liquid volume fraction is less than 0.2%.However,when the liquid volume fraction is over 1.1%,the swirlmeter is unable to measure the fluid flow.