超声波在循环水流量测量中的应用研究

发布时间：2018-01-03 03:38

本文关键词：超声波在循环水流量测量中的应用研究　出处：《东南大学》2015年硕士论文　论文类型：学位论文

【摘要】：大口径循环水流量测量一直是热工测量中的一个难点,准确测量循环水流量对于火电机组的节能具有重要意义。超声波时差法通过测量超声波沿声道逆顺流传播时间,求得管道内流体流量,是实现循环水流量测量的方法之一。但由于实际管路中含有弯头、阀门等局部阻力件,且阻力件下游直管段长度不足以保证被测截面处流体流动处于充分发展的流速分布状态,现有超声波测量方法难以获得满意的测量精度,因此针对如何解决超声波流量计在大口径循环水流量测量中精度偏低这一问题,论文从以下3个方面展开了研究：结合工业现场的测量条件,论文设计了不同湍流模型及网格密度的仿真方案,利用英国国家工程实验室在小口径管道上得到的实验数据,对不同仿真方案的结果进行了对比,验证了仿真方法的可行性,获得了结果相对较好的仿真方案,以某火电机组循环水系统为研究对象,采用CFD仿真方法建立了与循环水管路条件相一致的三维仿真模型,并运用Tecplot软件分析了循环水管道内流体的流动状况。对具备多声道测量条件时,论文设计了不同超声波测量方案,利用建立的循环水仿真模型,研究了不同雷诺数条件下声道数、数值积分算法、传感器安装位置、声道安装角度、通道旋转角度与测量数据的关系,并采用相对平均误差对不同测量方案的结果进行评价,结果表明声道数、数值积分算法、传感器安装位置以及通道旋转角度均影响超声波测量精度,在各测量位置处至少可以得到2种在现有测量条件下可获得1%以内正确度的测量方法；而当仅具备单声道测量条件时,虽然改变传感器安装位置及通道旋转角度能够在一定程度上提高测量正确度,但仍然无法获得1%以内的测量精度。针对单声道超声波流量计在循环水流量测量中测量精度偏低这一问题,论文创新性的提出采用广义回归神经网络(GRNN),建立了以雷诺数、传感器安装位置为网络输入的流量传感器系数修正模型,研究了训练样本数、光滑因子与网络输出结果的关系,结果表明基于该模型所得到的修正后测量结果可使现有数据的准确度得到较大的提高。通过VB与MATLAB混合编程的方法编写了相关软件,能够对超声波测量结果进行自适应修正。
[Abstract]:Large diameter circulating water flow measurement is always a difficult problem in thermal measurement, accurate measurement of the circulating water flow has important significance for energy conservation of thermal power units. The ultrasonic time difference method by measuring the ultrasonic channel along the inverse downstream propagation time, obtain the flow of fluid in pipeline, is one of the methods to realize the circulating water flow measurement. But due to the actual pipeline with elbows, valves and other local resistance, and the resistance of a downstream straight pipe length is not enough to guarantee that the measured section of the fluid flow velocity distribution in full development, the existing ultrasonic measurement method is difficult to obtain satisfactory measurement accuracy, so in order to solve the ultrasonic flowmeter in large diameter circulating water flow measurement accuracy in the low the problem, research papers from the following 3 aspects: the measuring condition of industrial field, this paper designed different turbulence model and grid The simulation scheme of density, the experimental data by the National Engineering Laboratory in small caliber pipeline, the comparison of the different simulation results verify the feasibility of the simulation methods, the simulation results of a better plan, with circulating water system of a thermal power unit as the research object, established a three-dimensional simulation model is consistent with the circulating water pipeline conditions using CFD simulation method, and the analysis of the fluid flow in a circulating water pipeline by using Tecplot software. The multichannel measurement conditions, this paper designed different ultrasonic measurement scheme, using the circulating water simulation model is established, the number of channels is investigated under different Reynolds number conditions, numerical integral algorithm the sensor installation position, track installation angle, rotation angle and the relationship between the channel measurement data, and the use of different measurement results of mean relative error Evaluation results show that the number of channels, the numerical integration algorithm, the sensor position and channel rotation were affecting the accuracy of ultrasonic measurement in each measuring position at least can get 2 kinds can be obtained within 1% accuracy in the existing measurement conditions and measurement methods; and when only with single channel measurement conditions, although the change of sensor installation the position and the channel rotation angle can improve the measuring accuracy to a certain extent, but still unable to obtain the measurement accuracy of less than 1%. For the single channel ultrasonic flowmeter in the circulating water flow measurement accuracy is low the problem, put forward the innovation of this paper uses the generalized regression neural network (GRNN), established by Reynolds number correction model of flow sensor coefficient of the sensor installation position as the network input, the number of training samples, the relationship between smooth factor and the output of the network. The results show that The revised measurement results based on this model can greatly improve the accuracy of the existing data. Through the mixed programming method of VB and MATLAB, the related software has been compiled, which can make adaptive correction to the ultrasonic measurement results.

【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM621

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