气液两相流流型压差波动的PDF特征

气液两相流的流型对其流动和传热特性有很大影响,所以如何识别流型一直是两相流研究中的重要课题.本文运用数字信号处理技术,对水平管空气-水两相流动不同流型的压差波动信号进行了分析.通过提取压差波动信号的概率密度函数(PDF)分布特征,找到了各种流型的特征,可以作为流型识别的一种方法.     

基于 CEEMDAN 和概率神经网络的 起伏振动气液两相流型识别

起伏振动气液两相流型准确识别对漂浮核动力平台安全稳定运行有重要意义。通过对比静止和起伏振动管道的压差信号以及对应的频谱图发现,起伏振动管道内的压差信号波动幅度更大且包含更多的频率分量,两种流型均含有主频率,该频率为起伏振动频率。针对起伏振动状态气液两相流压差信号的复杂性,分别采用自适应白噪声的完备总体经验模态分解(CEEMDAN)和集合经验模态分解(EEMD)对小波降噪后的压差信号进行模式分解,发现CEEMDAN能够在减少模式分量的同时获得更多有效的分量。通过计算spearman相关系数选择具有表征意义的IMF分量进行Hilbert变换计算能量作为特征值,采用概率神经网络对流型进行识别。结果表明,采用CEEMDAN进行模式分解结合概率神经网络的识别方法准确率达到95.83%,能够用于起伏振动下气液两相流型识别。     

气液两相流压差信号的Lipschitz指数分析

利用小波分析理论来分析气液两相流压差波动信号的奇异性,提出一种利用小波分析的Lipschizs指数与信号的能量特征相结合的识别方法,可以识别出水平管内气液两相流的四种流型.     

基于EEMD-Hilbert谱的气液两相流钝体绕流流型识别

为了有效识别气液两相流的流型,以水和空气为实验介质,以涡街流量计为元件诱发钝体绕流,通过管壁差压法获取气液两相流钝体绕流的尾迹波动信号,采用集总经验模态分解对信号进行分解,通过Hilbert变换得到Hilbert边际谱,利用最大互相关系数法对固有模态函数进行筛选,选取特征固有模态函数能量比分别与体积含气率、两相雷诺数构建流型图。结果表明,构建的两类新流型图对单相水、泡状流、塞状流、弹状流等典型流型的识别率分别可达91.67%和88.89%,能较好地满足工程实际应用的需求。     

气液两相流系统的小波软测量技术

提出了一种基于小波分析技术的气液两相流流型判别软测量模型.气液两相流中简单、易测而且可靠的差压波动信号作为软测量模型中的辅助变量,气液两相流的流型作为模型中的主导变量,利用小波分析技术建立了主导变量和辅助变量之间的数学关系,进而通过测量差压波动信号可以对气液两相流的流型进行判别.实验证明所建立的软测量模型是有效的.     

油气润滑系统流型识别方法研究

提出了一种基于油气润滑系统油气两相流压差波动信号来识别流型的方法。首先借助Fluent提取了油气润滑系统水平管道中常见的四种流型的压差波动信号作为训练和识别的样本;然后采用EMD(经验模态分解)方法提取油气流流型压差波动信号的特征;最后采用PSO-PNN算法对油气两相流流型进行了识别。结果表明:油气两相流流型与压差波动信号之间存在对应关系,通过对压差波动信号的分析可以获取流型信息;油气两相流的压差波动信号具有非平稳特性,采用EMD方法可以较好地提取流型信息;优化后PNN模型可较好地识别油气润滑水平管道内油气两相流流型。     

基于遗传算法/神经网络组合技术的气液两相流型辨识

通过采用遗传算法训练BP神经网络、优化网络权值的技术,对气液两相流的流型进行了辨识研究,在此基础上建立了基于遗传算法/神经网络组合技术的气液两相流流型的预测模型,从而为发动机轴承腔内润滑油气液两相流流型识别提供了技术支持,也为考虑轴承腔气液两相流的相关设计和实验工作提供了技术条件。     

汽车液压制动系统气液两相流流型的识别

建立了汽车液压制动系统中气液两相流流型检测装置,根据压差波动信号,利用Hilbert-Huang变换(HHT)对制动液两相流流型进行识别,并利用高速摄像机采集不同工况下制动液的气液两相流流型图像。结果表明,制动时车轮转速越高,压差信号幅值越大,幅值主要集中在0～50Hz区域;识别制动时的制动液流型为一种泡状流。高速摄影的结果验证了液压制动管路中制动液为泡状流;制动转速越高,气泡越小。结论揭示了制动时汽车制动液的气液两相流流型,说明利用测量制动液的压差波动信号进行HHT就可以识别其流型。     

一种基于经验模式分解的气液两相流流型识别方法

提出了一种基于经验模式分解的气液两相流流型识别方法.该方法首先对压差波动信号进行经验模式分解,将其分解为多个平稳的固有模式函数之和,再选取若干个包含主要流型信息的IMF分量,并从中提取时域特征指标-峭度系数作为LVQ神经网络的输入参数,从而实现流型的智能识别.对水平管内空气-水两相流流型的识别结果表明:以EMD为预处理器提取峭度系数的LVQ网络识别方法具有更高的识别率,可以准确、有效地识别流型.     

气液两相流型在线识别系统的开发和应用

在统计理论和小波理论的基础上,把神经网络应用到流型识别中,采用VB语言编程完成了软件的开发.按照信号测量、信号特征提取和流型识别3个实现流型客观自动识别的步骤,建立了一套气液两相流流型在线识别系统,在气液两相流实验系统上采集了180组仿真样本进行仿真实验.结果显示:流型正确识别率为91.7%,此系统应用于流型识别,不仅具有较高的识别率,而且很好地实现了识别结果的实时显示,运行速度快,达到了流型在线识别的目的.     

非均匀来流对涡轮流场的影响

涡轮机械的非均匀进口来流会使得涡轮的流场不均匀,从而影响涡轮的工作性能。本文根据涡轮的工作机理,建立了存在叶尖间隙的涡轮流动模型,考虑来流的周向非均匀性,研究了涡轮流场的变化规律,讨论了不同来流参数对涡轮流场参数的影响。     

T型管流场混合多相流与欧拉多相流模型的数值研究

以计算流体动力学(CFD)的多相流数值计算理论及方法为基础,对处于复杂工况的T型管连接装置腔内流场进行了数值模拟分析,采用标准湍流模型和标准壁面函数对T型管接头内部流场进行了数值模拟;同时以混合模型求得的解作为用欧拉多相流模型的初始条件,采用欧拉多相湍流模型进行了对T型管接头内部流场数值计算.最后对两种模型计算得到的T型管接头内部流场的压力场、速度场及气相的体积分数(VOF)分布进行了对比分析.计算结果将指导的结构优化设计及失效分析.     

基于层流流量计的航发燃油流量动态测量技术研究

为解决航空发动机过渡态燃油测量问题,研究了基于层流流量计(LFM)的航空燃油流量动态测量技术.设计了一款量程为0～3 000 mL/min的液体LFM,在小型涡轮喷气式发动机试车台上对其进行了试验,并与科里奥利流量计(CMF)进行了比对,试验结果显示LFM具有优秀的动态特性.当发动机处于稳态时,LFM测量结果与CMF吻...     

Effect of high beta values on mass flow through critical flow nozzles

In a previous work (Stewart et al., Flow Measurement and Instrumentation 10(1) (1999) 27–34) the authors presented improved calculations for the mass flow of a gas through a critical flow nozzle. The work in Stewart et al. is applicable only when the nozzle throat to pipe diameter ratio, β, is low (<0.15). Whilst it is preferable to use a critical flow nozzle with a low β, practical considerations may dictate otherwise. This work extends the calculations to include high β values, explaining the problems encountered in these situations and the procedure for calculating the mass flow accordingly. The same four gases are covered, dry CO₂-free air, nitrogen, argon, and methane. A new empirical correction factor for use with high β critical flow nozzles is presented which, when combined with the work in Stewart et al., provides an accurate yet simple method for calculating the mass flow of these gases through critical flow nozzles with a wide range of β values.     

PEMFC 全功率变流量喷射器流场特性研究

针对质子交换膜燃料电池全功率氢循环对喷射器变流量的需求,提出并设计了不同嵌套方式的四喷嘴喷射器,以实现不同工况下变流量性能。为研究不同嵌套方式喷射器的流场特性及其循环性能,采用计算流体力学方法对喷射器进行建模和分析。结果表明,部分嵌套喷射器的内部流场比全嵌套喷射器的内部流场稳定;当二次流压力和背压不变时,一次流压力从6 bar(1 bar=100 kPa)增加到10 bar,部分嵌套喷射器引射比先上升后下降,在压力为7 bar时存在最大值;而全嵌套喷射器引射比是下降的趋势,通过与实验数据的比较,部分嵌套喷射器具有更优的性能;最后通过多喷嘴PWM逻辑控制,实现了170 kW燃料电池全功率变流量拟线性调控性能,满足燃料电池在变功率运行下的氢循环需求。     

Influence of flow disturbances on the performance of industry-standard LNG flow meters

In the last decade significant progress has been achieved in the development of measurement traceability for LNG inline metering technologies such as Coriolis and ultrasonic flow meters. In 2019, the world's first LNG research and calibration facility has been realised thus enabling calibration and performance testing of small and mid-scale LNG flow meters under realistic cryogenic conditions at a maximum flow rate of 200 m³/h and provisional mass flow measurement uncertainty of 0.30% (k = 2) using liquid nitrogen as the calibration fluid. This facility enabled, for the first time, an extensive test programme of LNG flow meters under cryogenic conditions to be carried out to achieve three main objectives; the first is to reduce the onsite flow measurement uncertainty for small and mid-scale LNG applications to meet a target measurement uncertainty of 0.50% (k = 2), the second is to systematically assess the impact of upstream flow disturbances and meter insulation on meter performance and the third is to assess transferability of meter calibrations with water at ambient conditions to cryogenic conditions. SI-traceable flow calibration results from testing six LNG flow meters (four Coriolis and two ultrasonic, see acknowledgment section) with water in a water calibration facility and liquid nitrogen (LIN) in the LNG research and calibration facility under various test conditions are fully described in this paper. Water and LIN calibration data were compared and it was observed that the influence of removing the meter insulation on mass flow rate measurement accuracy can be more significant (meter error > ±0.50%) than the influence of many typical upstream disturbances when the meter is preceded by a straight piping length equal to twenty pipe diameters (20D) with no additional flow conditioning devices, in particular for ultrasonic meters. The results indicate that the correction models used to transfer the water calibration to cryogenic conditions (using LIN) can potentially result in mass flow rate measurement errors below ±0.5%, however, the correction models are specific to the meter type and manufacturer. This work shows that the target measurement uncertainty of 0.50% can be achieved if the expanded standard error of the mean value measured by the meter is smaller than 0.40% (k = 2). It is planned to repeat these tests with LNG in order to compare the results with the LIN tests presented in this paper. This may reveal that testing with an explosion safe and environmentally friendly fluid such as LIN produces representative results for testing LNG flow meters.     

基于流场仿真的多路阀流道结构优化

采用流体仿真软件对多路换向阀的桥路进行流场仿真,并通过速度场和压力场的对比,指出了多路阀桥路流道结构的优化方向和优化结果.仿真结果表明,在桥路结构转折处采用圆弧过渡,能够大大减少压力损失、平缓流场,为液压元件流道结构设计提供了一种工程设计的新途径,具有广阔的应用前景.     

The humidity effect on air flow rates in a critical flow venturi nozzle

A Critical Flow Venturi Nozzle (CFVN) is usually calibrated using dry air. Yet CFVNs in industrial and calibration service centers are often used to measure flow rates of humid air. Therefore, ISO 9300 provides the calculation method for the humidity effect on discharge coefficients of CFVN. However, since this method is only due to a theoretical analysis, it is important to confirm and check the ISO calculation method for the humidity effect on CFVN with its isentropic analysis by means of an experimental method.In this experiment, three CFVNs with diameters of 0.4, 0.8 and 1.6 mm were calibrated with dry air (with the dew point −40 °C), in a primary air flow standard system with a mercury sealed piston prover, installed at the Korea Research Institute of Standards and Science (KRISS). Another piston prover, a portable dry piston prover, was used as a reference meter and was also calibrated in the primary standard system using dry air. The repeatability of this dry piston prover was confirmed with the deviation being less than 0.05%. The CFVNs were tested with this dry piston prover, using humid air. For air types with high humidity, the humidity effect on flow rates through the CFVNs showed quite significant difference between the experimental results and those from the ISO method with isentropic analysis. But for air types with low humidity, its effect was relatively insignificant.