A 90° elbow model was built and the velocity distribution inside the pipeline was obtained by means of computational fluid dynamics (CFD).The calculation of transit-time of acoustic waves was operated by adding up transit-time in each grid one by one along the acoustic paths,in order to imitate the principle of ultrasonic flowmeters.Experiment system was established in the laboratory,and experiments were carried out to verify the simulation results.The results show that in downstream of the 90° elbow,the flow measuring deviations decrease while the distance between the flowmeter and the elbow increases.Taking a 6 path ultrasonic flowmeter installed 10D downstream of a 90° elbow for instance,the precision of measurement varies according to the angle of the acoustic planes.Compared with the flow measuring relative errors when acoustic plane is installed parallel or perpendicular to the elbow plane,the flow measuring relative errors are smaller when acoustic planes are installed inclined with the elbow plane,and the inclining installation makes acoustic paths evading the lower velocity distribution.In practice,the installation angles of acoustic planes influence the precision of multi-path ultrasonic flowmeter,when the flow distribution is non-ideal.Once multi-path ultrasonic flowmeters are installed in the downstream of the flow blocking parts,the angel of acoustic planes must be chosen according to the flow distribution,with the purpose of reducing the measuring errors led by asymmetric velocity distributions.%采用计算流体力学(CFD)方法,建立90°单弯管道内气体流动的仿真模型,获得管道内流场分布情况,通过对声路上每个网格内声波传播时间逐个累计的方式模拟超声波流量计原理计算渡越时间.搭建超声波气体流量计量实验系统,通过实验验证仿真结果.研究结果表明:在90°单弯管道下游,随直管段距离增加,多声道超声波气体流量计的计量偏差逐渐减小.以90°单弯管下游10D位置安装的六声道超声波流量计为例,声平面角度变化使计量相对误差发生变化.相对于与弯管平面平行或者垂直安装的方式,与弯管平面倾斜安装能有效避开流速分布的低速区,降低计量误差.在实际应用中,当管道内流场分布非对称时,多声道流量计声平面安装角度的变化会影响流量计量效果.在阻流件下游安装多声道超声波流量计,需根据流场分布特点选择适当的声平面安装角度,降低非对称流速分布对精度带来的影响.
展开▼
