超声波流量计整流器优化设计

气体超声波流量计的测量精度由飞行时间的测量精度和流量计自身的流场适应性决定,流量计的流场适应性又由流量计的声道布置和整流器的性能决定。文章设计了一种内嵌于流量计的整流器,详细阐述了该整流器的结构、各模块的功能。介绍了整流器性能优化的理论依据、过程以及整流器性能优劣的判别准则。该整流器性能优化主要取决于起旋器的优化,文章给出了装有8片起旋器和装有10片起旋器的整流器在直管、单弯管下的性能参数对比,试验结果显示装有10片起旋器的整流器有着更好的流场适应性：重复性满足国标要求,直管示值误差与弯管示值误差的差值<0.3%。文章的创新点在于给出气体超声波流量计整流器设计和优化的理论依据和一整套流程,对于设计气体超声波流量计整流器的科研人员有借鉴意义。     

超声波气体流量计的管道模型仿真和误差分析

为满足不断发展的超声波气体流量计测量精度的需要,改进传感器的设计精度和有效降低安装测试及样机调试成本,针对制约超声波气体流量计测量精度主要误差源之一的管道流场分析问题,结合计算机建模数值仿真技术及实验技术对其流场设计参数以及弯管安装条件等对超声波测量误差产生原因进行定量分析.理论研究和仿真实验结果表明,可以量化分析气体超声波流量计流场误差产生的原因、范围,并通过限定流场修止系数更有效地降低其测量误差,这项研究对该超声波气体流量计的优化设计和工程应用具有一定的指导意义.     

单弯管下游超声流量计的安装和测量性能研究

对大管径多声道超声流量计在单弯管下游流场中的安装和测量性能进行了数值仿真研究,分析了超声流量计在0.1 m、1 m和10 m口径下不同流速、声道数、旋转角以及前直管段长度时测量误差的变化规律。仿真结果表明,交叉声道布置形式对弯管产生的二次流所引入的横向测量误差有很好地抑制作用;对于大口径弯管下游流量测量,采用交叉4声道且将超声流量计安装在弯管下游5D位置可以获得1%的精度,且随着声道数的增多测量误差有减小的趋势;相同雷诺数时的测量误差基本相同。研究结果可为大管径多声道超声流量计的实际安装和使用提供一定的参考。     

压降法测弯管煤粉浓度中整流器性能数值模拟

煤粉浓度是表征输送管道运行状态的重要参数,电站锅炉输粉系统中弯头很常见。为了分析利用压降法测量弯管煤粉浓度时管道流场、整流器对弯管流速分布不均匀的改善效果及整流器的阻力系数,利用流体计算软件Fluent进行数值模拟研究。结果表明,Zanker整流器、非均匀整流器、AMCA整流器对速度不均匀分布的整流效果明显,不同整流器的整流效果不一样,从整流器后管道内速度达到充分发展管流所需直管段长度、整流器压力损失系数和磨损三方面综合考虑选择非均匀整流器。整流器压力损失系数也有差别并不和流通率呈正相关。整流器壁面形成动压高压区,形成的动压高压区压强与整流器流通率成正相关,高速的煤粉颗粒对整流器的冲击使整流器壁面磨损严重。     

超声波气体流量计检测精度影响因素分析

在天然气的管道运输过程中,提高气体流量测量的精度是提高运输效率、避免安全事故发生的关键技术。利用流体力学仿真（CFD）方法建立组合双弯管及变径管道模型,定量计算修正系数,对双声道超声波流量计结构和安装位置对于管道内气体速度场的影响进行研究。通过仿真得出超声波流量计的最优声道位置,并结合实验验证了仿真结果的可信性。模拟结果表明,双弯管和变径管与超声波流量计的安装位置至少为10D才能保证流体充分流动;通过修正系数随雷诺数的变化情况得出双声道超声波流量计的最优声道位置为距管道截面中心0.25D处。研究结论对于不同性质气体的流量检测同样适用,为工业中气体运输检测精度的提高以及超声波流量计的优化提供了依据。     

非线性最小二乘法在多声道超声波流量计测量非理想流动中的应用

针对多声道超声波流量计在流量计算过程中应用的数值积分方法只适用于理想的充分发展流动的问题,提出在测量非理想流动时应用非线性二乘法计算最小的流速误差的平方和,流速误差平方和最小时计算得到的权重系数即为多声道超声波流量计在测量非理想流动时的最优权重系数,提高了流量计在测量非理想流动时的精度。应用计算流体力学仿真软件FLUENT对单弯管和异面双弯管下游5D和10D处的流速测量进行仿真验证,应用优化后的权重系数进行流速计算可以使测量误差减小到±0.5%以内。     

复杂工艺管道巧用弯管流量计实现流量测量

介绍了在走向复杂的工艺管道或各种原因工艺管道直管段不符合流量仪表安装要求的情况下,合理利用弯管流量计测量原理,实现工艺介质流量测量的成功案例,是对弯管流量计在工业生产过程中合理使用的一种探索。     

上游主管结构对水平T形管内冷热流体混合过程热波动的影响

在Fluent平台上对上游主管分别为直管和弯管的两种水平T形管内冷热流体混合过程的热波动进行大涡模拟,获得了管道内部的速度和温度波动情况。并将量纲一时均温度与时均速度,量纲一方均根温度与方均根速度的数值结果和已有文献的试验结果进行对比,两者吻合较好,说明大涡模拟具有一定的可靠性和准确性。在数值模拟的基础上,对两种水平T形管的温度云图与速度矢量图,量纲一时均温度与时均速度和量纲一方均根温度与方均根速度分布进行对比。分析结果表明,受上游弯管产生的二次流的影响,弯管T形管的混合范围,温度与速度的波动幅度较上游为直管的直管T形管要大,说明上游弯管对混合过程及其温度与速度波动具有一定的增强作用。     

超声波流量计的弯管误差分析及修正研究

针对中小口径超声波流量计的弯管二次流误差问题,运用数值仿真技术,分析了弯管二次流垂直误差与水平误差,由二次流流线规律推导出了二次流误差的计算公式。结合实际的流量计测量范围,设定雷诺数的变化范围为3 000~50 000,定量分析了安装在弯管下游5D、10D、20D位置的流量计在不同雷诺数下的误差规律。提出了"用压力差来表现二次流强度,最终结合误差规律通过测量压力差来对弯管二次流误差进行修正"的方法。研究结果表明,在雷诺数29 000之后,10D处的二次流垂直误差超过了5D处的误差,二次流垂直误差和水平误差的最大值分别约为1.2%和0.7%,经过仿真验证结果表明,该修正方法可行。     

压管式水冷板90°弯管内流动及传热特性研究

为优化压管式水冷板中弯管结构，并为微小发热电子器件在水冷板上合理的布局提供指导性意见，通过FLUENT软件，采用RNG k-ε模型，对一款应用于射频功放散热的压管式水冷板“D”形直角弯管处流场及热分布进行三维数值模拟，并通过试验对其结果进行了验证。同时讨论了不同弯曲度和雷诺数对流道内迪恩涡结构、流动阻力及传热特性的影响。结果表明：管道弯曲段压力从外壁到内壁呈梯度减小且总压力损失在弯曲度R/D为1.5～2范围内最小。沿弯管流道方向，“D”形弯管中心线两侧形成迪恩涡，在弯管出口90°截面二次流强度最大。在弯管出口段2D～4D范围内对流换热系数达到极大值，线性拟合得到极大值点位置S₂/D与雷诺数Re之间的关系，S₂/D=0.002 9Re-0.114。研究结果可为微小电子发热器件在水冷板布局提供指导性意见。     

Effects of flow disturbance on an ultrasonic gas flowmeter

A series of tests are carried out to assess the effects of flow disturbance on a small dimension ultrasonic gas flowmeter. Flow disturbances generated by cone couplings, and single and double elbows are investigated. Measurements with a 100 D straight pipe upstream with a smooth connection to the meter body are used as a reference. Our measurements show that the symmetrical disturbance produced by a cone coupling at a 12 D distance from the transducer path does not impair the performance of the flowmeter. An asymmetrical disturbance, such as a single or a double elbow at the same distance, seems generally to give an underestimation of the flow velocity, resulting in reading errors of −1% or worse. Measurements with straight pipes of 10 D, 20 D, 40 D and 80 D between the disturbance and the flowmeter have also been made showing that 10 D can cause an overestimation of flow velocity. Increasing the length of the straight pipe generally decreases the error. More than 80 D straight pipe between the disturbance and the flowmeter is required to give a result within ±1% of reference conditions. The angle between the elbow plane and the transducer plane is changed from 0 to 315° in 45° steps. The meter error is plotted as a function of inlet angle, showing a clear relationship between these values.     

多声道超声流量计在弯管段安装的适应性研究

针对在不具备直管段安装条件时,如何合理地选取多声道超声流量计的声道数量、测量断面及安装角度,本文从数学建模、误差分析、数值计算仿真与试验分析等方面,对DN400多声道超声流量计在弯管中的适应性进行了综合研究.利用高斯-雅克比数值积分法,给出了试验数据处理与数值仿真的数学模型,并分析了模型误差及横流的影响,提出利用双断面测量可减小横流的影响,并在数值仿真和试验中得到了验证.通过对声道数量、测量断面、安装角度进行数值仿真和试验表明,安装角度对低流速测量影响显著,最佳安装角应为0°;高流速测量应选用双断面,可根据测量精度的要求选用8声道或18声道.仿真结果与试验结果得到了很好的吻合,为进一步指导试验奠定了理论基础.     

A method based on a novel flow pattern model for the flow adaptability study of ultrasonic flowmeter

Ultrasonic flowmeters are widely used in industry for accurate measurement. Flow adaptabilities of meters in non-ideal flow fields are usually concerned about by researchers. This paper presents a theoretical analysis method to study the measurement performance of ultrasonic flowmeter. For the specific water flow in single elbow pipe, a novel three-dimensional flow pattern model is invented by the trust region Newton algorithm based on computational fluid dynamics simulation results. In order to verify the correctness of the model, a typical ultrasonic flowmeter with single diametric acoustic path is mainly analyzed. By comparing flow adaptabilities of the meter downstream of the single elbow with both the novel theoretic model analysis approach and simulation method, good agreement is achieved. It is indicated that both the three-dimensional model and its invention method are valid for this study, which is not only helpful to get knowledge of characteristics of disturbed flows, but also provides a practical method to study the flow adaptability of ultrasonic flowmeter in non-ideal flow fields.     

气体涡轮流量计性能优化的模拟与实验研究

以TRZ80气体涡轮流量计为研究对象,采用数值模拟与实验测试相结合的方法,提出了前整流器和后导流体的结构优化方案。通过对结构优化前后流量内部流场特征的分析,揭示了流量计结构与性能优化背后确切的流体力学机制。研究结果表明：前整流器和后导流体区域的压降突变与后导流体尾部的涡旋结构和回流现象是影响流量计计量性能的主要机制。优化的流量计结构可以明显减弱压降突变、涡旋结构与回流现象。优化的流量计结构既可以显著降低流量计的压力损失,又可以明显提高流量计的测量精度与稳定性,其压力损失和线性度误差分别降低了约48.58%和32.43%。研究结果有助于为今后开发与量产计量性能更好的气体涡轮流量计提供理论指导和技术支持。     

Study of acoustic transducer protrusion and recess effects on ultrasonic flowmeter measurement by numerical simulation

In order to improve the measurement performance of dry calibration on ultrasonic flowmeter, the Computational Fluid Dynamic (CFD) modeling approach of the effect on transducer protrusion and recess are mainly discussed in the paper while its effects on ultrasonic flowmeter accuracy are also presented. Through comparing simulation results to experimental data, the CFD modeling is firstly determined. Then, detail analysis on flow field for two typical transducer installations are obtained based on the CFD method. Besides, the mechanism of both flow effects on measurement accuracy are explained and compared respectively, which indicates that negative velocities generated at protrusion and recess locations are the indispensable factors for negative measurement errors. Finally, comparison results show that smaller measurement error can be achieved with protruding transducers, which is a better arrangement type of transducer for ultrasonic flowmeters.     

Correction of flow metering coefficients by using multi-dimensional non-linear curve fitting

Flow disturbances can significantly affect flow metering because the downstream flow of flow disturbances can become unstable and asymmetric, thus resulting in measurement errors in the flow meter. A clamp-on type ultrasonic flow meter is an example of a flow meter that is susceptible to flow disturbances given its diametrical configuration of ultrasonic paths. Several flow rate correction formulas have been suggested to mitigate the effect of flow disturbance for improved flow metering. As a novel method, a multi-dimensional non-linear correction formula is suggested to overcome limitations in flow metering that are attributed to the non-linearity of flow disturbances. The non-linear correction formula comprises n-th order polynomials with multiple variables. To validate the usefulness of the non-linear correction formula, the standard error of estimate (SEE) is introduced. Four types of flow configurations, namely, downstream of a contraction pipe, an expansion pipe, a single elbow joint, and a tee joint, are used to show the effect of the non-linear correction formula. The expanded uncertainty based on the SEE indicates estimated values of 1.29%, 11.14%, 1.07%, and 6.31% for the four upstream flow configurations, respectively. Thus, the effect of the non-linear correction formula is limited according to the upstream flow conditions. In the downstream flow of the contraction pipe and of the single elbow joint, the non-linear correction formula not only harmonizes the distribution of the flow rate deviations but also removes the biases of flow rate deviations with respect to the flow velocity, the installation location, and the diameter ratio.     

New measurement method for very low liquid flow rates using ultrasound

A very small ultrasonic flowmeter for liquids with measuring pipe diameter down to 0.5 mm was developed using disk ultrasonic transducers. The transducer has a hole in the center and the measuring pipe passes through the hole. The vibration mode in the radial direction of the transducer was used, and ultrasound was transmitted and received from outside the pipe wall. The flowmeter can measure a liquid flow rate below 1 ml/min, which corresponds to a Reynolds number of about 40 based on the measuring pipe diameter. The standard deviation of flow rate measurement was 0.01 ml/min (1%) at the flow rate of 1 ml/min.     

孔口流量计正压测试夹具和可膨胀系数的研究

孔口流量计是标准孔板流量计的特殊使用形式,为环境监测领域中常用流量测量元件。孔口流量计在校准时按上游入口压力的不同,其校准方法分为微正压和微负压两种校准工况。两种工况均为国家标准和规范推荐方法,但校准出的流量系数差距达10%。夹具引入的附加差压和仪表流量系数线性度误差是导致两种校准工况流量系数偏差的原因。通过CFD仿真研究,设计对被校准孔口流量计上游压力影响较小的夹具形式和结构参数。在仿真数据的基础上计算得到适用于常用管径和雷诺数范围的孔口流量计的可膨胀修正系数公式。运用上述成果并进行试验验证,正压和负压校准流量系数的差距减小至±0.5%以内。校准流量范围内孔口流量计流量系数线性度也有0.1%左右的提升。