Accuracy Analysis of Ultrasonic Flowmeter for Sewage Based on Fluent DPM Model
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摘要: 针对上游弯管扰乱流场以及污水中颗粒杂质导致超声波衰减问题,基于Fluent Discrete Phase Model(DPM)双向耦合模型进行仿真计算。在污染物浓度为1%情况下,设置4种不同直径的碳酸钙杂质。不同直径杂质的污水中,均出现随着流量点的增大流量系数k值逐渐减小的状况,但在小流量点20 m3/h时,80 μm大颗粒杂质对系数k的影响最大超出了5%,流动速率不足以维持较大的颗粒悬浮在流体中,导致流场中颗粒浓度分布不均,超声波在传播路径上的速度有较大的波动。在压力云图中发现随着颗粒物直径的增加,管道截面上流体速度压力梯度变化较大导致流场波动剧烈,进而影响超声波传播路径上速度的变化,引起流量计产生误差。为了降低大颗粒杂质在下游引起的湍流脉动,在弯角处设置整流器,使用Solidworks建立Laws整流器物理模型。研究发现下游流场更加均匀,速度梯度变化较小,减小了回流涡对超声波在传递路线上的影响。对改善下游流场均匀性,提高超声波流量计在污水中测量精度具有指导意义。Abstract: In order to solve the problem of ultrasonic attenuation caused by the upstream elbow disturbing the flow field and the particle impurities in the sewage, simulation calculations were performed based on the Fluent Discrete Phase Model (DPM) bidirectional coupling model. When the pollutant concentration was 1%, four calcium carbonate impurities of different diameters were set. In the sewage with impurities of different diameters, the flow coefficient k value gradually decreased with the increase of the flow point, but at the small flow point of 20m3/h, the maximum influence of 80 large particle impurities on the coefficient k exceeded 5%, and the flow rate was not enough to keep the larger particles suspended in the fluid, resulting in uneven distribution of particle concentration in the flow field and large fluctuations in the speed of the ultrasonic wave on the propagation path. It was found in the pressure cloud map that with the increase of particle diameter, the fluid velocity pressure gradient on the pipe section changed greatly, resulting in violent fluctuations in the flow field, which in turn affected the change in speed on the ultrasonic wave propagation path and caused errors in the flowmeter. In order to reduce the turbulent pulsation caused by large particle impurities in the downstream, a rectifier was set at the bend, and the Laws rectifier physical model was established using Solidworks. The study found that the downstream flow field was more uniform and the velocity gradient changed less, reducing the influence of the backflow vortex on the ultrasonic wave on the transmission path. It has guiding significance for improving the uniformity of downstream flow field and improving the measurement accuracy of ultrasonic flowmeter in sewage.
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Key words:
- metrology /
- sewage /
- bend pipe /
- ultrasonic flow meter
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表 1 物理参数
Table 1. Physical parameters
Q(m3/h) V(m/s) I(%) Re 20 0.177 4.262 39423 80 0.708 3.584 157692 160 1.415 3.287 315383 400 3.539 2.931 788458 -
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