涡轮流量传感器在旋转来流中的特性研究

本文对涡轮流量传感器在旋转来流中的特性进行了理论和实验研究。利用涡轮流量传感器的数学模型,给出了涡轮转速、仪表常数与来流旋转角之间的理论关系式。计算了来流旋转强度及上游直管段长度变化时,仪表常数的变化情况。设计了能获得不同来流旋转强度的旋转发生器,并获得了大量的实验数据。实验结果与理论计算值在较大的流量范围内甚为吻合。     

Study on the design and performance of a bi-directional cone flowmeter

The present study explores a novel design of cone flowmeter for bi-directional flow metering application. Two identical cone shapes are machined with their base circle surfaces joined together with a small step in between them and differential pressure measurement is done across the apex of the cones. The bi-directional cone flowmeter is tested under fully developed flow conditions and its performance under double 90° bend (out-of-plane) is also evaluated. The bi-directional cone flowmeter is tested in a circular pipe (inside diameter of 101 mm) with water as the working medium for the flow Reynolds number ranging from 1.18×10⁵ to 5.48×10⁵. Influence of the half cone angle (α) and the location of static pressure taps on the coefficient of discharge (C_d) of a cone flowmeter are studied. Two cones with half cone angles α=30° and α=45° with a constant constriction ratio (β) of 0.75 are studied. Static pressure taps are located on both sides of the bi-directional cone. Two sets of locations of static pressure taps are studied. First set includes two static pressure taps on the pipe wall in the planes of apexes of the bi-directional cone—called apex taps. Second set includes pressure taps on the pipe wall in the planes at a distance D/4 away from the apexes of the bi-directional cone—called D/4 taps. Double 90° bend (out-of-plane) is placed at 1.5D, 5.5D, 9.5D and 13.5D upstream to the bi-directional cone flowmeter. It is observed that the apex static pressure taps located in the plane of apexes of the bi-directional cone result in statistically consistent coefficient of discharge for all Reynolds numbers covered in this study. The results suggest that the bi-directional cone flowmeter is insensitive to the swirl created by double 90° bend (out-of-plane) placed at the upstream of cone flowmeter, if placed at a distance of 9.5D or more.     

Performance evaluation of piezoelectric and differential pressure sensor for vortex flowmeters

Piezoelectric and transient differential pressure sensors are two among the most widely employed sensors for vortex flowmeter application. The present study evaluates the performance of these two techniques under fully developed and disturbed flow conditions. Firstly, the location of the transient differential pressure sensor is optimized to obtain high amplitude signals and good linearity in Strouhal number. Empirical mode decomposition method in combination with autocorrelation decay is successfully employed at high Reynolds numbers to identify the vortex shedding frequency in presence of hydrodynamic noise. The performance of the differential pressure sensor deteriorates significantly under disturbed flow conditions at low Reynolds number due to the presence of low frequency components. This deterioration in the signal quality limits the lower operating range of the flowmeter with differential pressure sensor. The output signals of the piezoelectric sensor and differential pressure sensor under no flow condition are compared to obtain the background noise due to piping vibrations and electrical interferences. These results will help a designer to suggest robust signal processing algorithms for vortex frequency detection.     

Response of a dual triangulate bluff body vortex flowmeter to oscillatory flow

In this paper, on an experimental facility, the measurement characteristics of a diameter 50 mm dual triangulate bluff body vortex flowmeter in steady flow and oscillatory flow were investigated. Then, the Hilbert Huang Transformation (HHT) method was used to assess the anti-interference performances and the vortex street stability in oscillatory flow for the dual triangulate bluff body vortex flowmeter and a single bluff body vortex flowmeter. Offline simulation was carried out on the anti-interference performances of the dual triangulate bluff body vortex flowmeter signal noise in oscillatory flow by the method of the EMD-scales filter. The major findings are: (a) in most case, the EMD-scales filter may be as good at de-noising effect for the dual bluff body vortex flowmeter in oscillatory flow than that for the single bluff body vortex flowmeter in oscillatory flow. The vortex street stability in oscillatory flow for the dual bluff body is similar to that for the single bluff body. (b) In some special case, the EMD-scales filter is unable to play a better de-nosing role for the dual bluff body vortex flowmeter in oscillatory flow. The invalid condition of the EMD-scales filter for the dual bluff body vortex flowmeter in oscillatory flow is different to that of the single bluff body vortex flowmeter and it was advanced in this paper. (C) The vortex street stability for the dual bluff body vortex flowmeter is better than that for the single bluff body vortex flowmeter.     

Influence of blockage and shape of a bluff body on the performance of vortex flowmeter with wall pressure measurement

Experimental and numerical investigations are carried out with various bluff body shapes to identify an appropriate shape which can be used for vortex flowmeter application. In both the cases vortex shedding frequency is inferred from the fluctuation of wall pressure. The numerical simulations are carried out with cylindrical and triangular bluff bodies to understand the vortex shedding phenomenon and to identify an appropriate turbulence model for this class of flows with wall pressure measurement. The simulations reveal that the k-ε RNG model predicts the Strouhal number closer to the experimental results than other models. The experimental investigations are carried out with several bluff body shapes, such as triangular, trapezoidal, conical, cylindrical and ring shapes, with water as the working medium. In this context, the effects of sampling rate, tap location and blockage effects are explored. The results suggest that the axisymmetric tapping is better than differential pressure tapping in terms of signal amplitude. The non-dimensional location of the static pressure tap is found to be 0.714 times diameter of pipe times blockage. The trapezoidal bluff body is found to be the best among all the bluff bodies investigated in terms of signal amplitude and constancy of Strouhal number. The vortex flowmeter performance is also measured under disturbed flow conditions created by using gate valve and bends. These results are significant because they provide an optimum bluff body shape and blockage, and also present the performance of vortex flow meter under disturbed flow conditions which is rather seldom reported in the literature.     

Study on the effect of vertex angle and upstream swirl on the performance characteristics of cone flowmeter using CFD

Computational Fluid Dynamics (CFD) has emerged as a revolutionary tool for optimizing the design of any flowmeter for given conditions. The flow features obtained with CFD are more extensive compared to experiments. In the present study, CFD code ‘FLUENT” after validation has been used to investigate the effect of cone vertex angle and upstream swirl on the performance of cone flowmeter. The values of discharge coefficient ($C_d$) evaluated for different vertex angles shows that the value of discharge coefficient is independent of Reynolds number and its value decreases with increase in vertex angle. In the presence of upstream disturbance in the form of swirl, the value of discharge coefficient is also independent of Reynolds number and its value is only marginally affected by the magnitude of swirl. The flow in a longitudinal plane shows the presence of a pair of contra-rotating vortices in the recirculation region just downstream of the cone. The velocity profile downstream becomes stable after a distance of about 5D.     

Influence of swirl on the discharge coefficients of sonic nozzles

Flow characteristics of a swirl generator are studied using an open circuit flow loop, and influence of upstream swirl on the discharge coefficients of sonic nozzles is investigated using a high pressure gas flow standard measurement system. The open circuit flow loop consists of swirl generator, testsection, sonic nozzle, suction fan and LDV system. The gas flow measurement system comprises two compressors, storage tank, temperature control loop, sonic nozzle testsection, weighing tank, gyroscopic scale and data acquisition system. Experiments are performed at various nozzle throat diameters, inlet pressures and angles of swirl generator. As the angle of swirl generator becomes larger, axial velocities decrease near the wall and rapidly increase in the pipe core, and swirl velocities increase to form swirl flow. Influence of upstream swirl on discharge coefficients becomes greater as the intensity of swirl increases and as the nozzle throat diameter is enlarged. Variation trend with Reynolds number, however, is very similar each other regardless of swirl intensity.     

一种新式差压流量计的设计与应用

该文分析了影响蒸汽流量准确计量的主要因素,介绍了传统的蒸汽流量计如孔板流量计和涡街流量计的使用局限性,详细介绍了一种基于皮托管原理的新式差压式流量计的设计原理、结构特点及其标定方法,通过实例给出了典型蒸汽工况下选择流量计的考虑因素,以及应用这种新式差压式流量计的选型和计算过程。     

Note: anti-strong-disturbance signal processing method of vortex flowmeter with two sensors

Some digital signal processing methods have been used to deal with the output signal of vortex flowmeter for extracting the flow rate frequency from the noisy output of vortex flow rate sensor and achieving the measurement of small flow rate. In applications, however, the power of noise is larger than that of flow rate sometimes. These strong disturbances are caused by pipe vibration mostly. Under this condition the previous digital signal processing methods will be unavailable. Therefore, an anti-strong-disturbance solution is studied for the vortex flowmeter with two sensors in this Note. In this solution, two piezoelectric sensors are installed in the vortex probe. One is called the flow rate sensor for measuring both the flow rate and vibration noise, and the other is called the vibration sensor for detecting the vibration noise and sensing the flow rate signal weakly at the same time. An anti-strong-disturbance signal processing method combining the frequency-domain substation algorithm with the frequency-variance calculation algorithm is proposed to identify the flow rate frequency. When the peak number of amplitude spectrum of the flow rate sensor is different from that of the vibration sensor, the frequency-domain subtraction algorithm will be adopted; when the peak number of amplitude spectrum of the flow rate sensor is the same as that of the vibration sensor, the frequency-variance calculation algorithm will be employed. The whole algorithm is implemented in real time by an ultralow power micro control unit (MCU) to meet requirements of process instrumentation. The experimental results show that this method can obtain the flow rate frequency correctly even if the power of the pipe vibration noise is larger than that of the vortex flow rate signal.     

Flow development behind a swirl generator in a hot-water standard measuring facility for large volume rates

The flow development behind a swirl generator according to EN 14154 of a gravimetric cold- and hot-water standard measuring facility is shown at different positions by measurements carried out using Stereoscopic Particle Image Velocimetry (SPIV). Hereby, the effects of the swirl generator downstream are shown, and the prevailing flow condition is evaluated by means of characteristic values.SPIV is suited as a fast and accurate measurement procedure for the high-resolution determination – temporally and spatially – of 3C velocity profiles in piping.     

Analysis of signals from vortex flowmeters

The vortex flowmeter is used to measure the flow of fluids especially where the requirements include wide rangeability and the use of flowmeters with no moving part. It is common knowledge that process conditions affect the operation of a vortex flowmeter, and a customary approach is to introduce flow conditioners so that the measurement output from a vortex flowmeter conforms to specified standards. Some recent studies have shown how to apply signal analysis to the signal from vortex flowmeters to enhance performance, but the signal which has been typically analysed is the pulse train. In this paper,we advocate a new approach which involves detailed analysis of the unconditioned signal from the sensor prior to conventional signal conditioning. The results obtained from this approach open opportunities for the development of alternative signal conditioners and transmitters which not only enhance the quality of the measurement output from a vortex flowmeter but also make it possible to use the flowmeter for monitoring the condition of the plant.     

Dynamic characteristics of an unsteady flow through a vortex tube

Dynamic flow characteristics of a counter-flow vortex tube is investigated using hot-wire and piezoelectric transducer (PZT) measurements. The experimental study is conducted over a range of cold air outlet ratios (Y=0.3, 0.5, 0.7, and 1.0) and inlet pressure 0.15 MPa. Temperatures are measured at the cold air outlet and along the vortex tube wall. Hot-wire is located at cold outlet and PZT is installed at inner vortex tube by mounting at throttle valve. The cold outlet temperature results show that the swirl flow of vortex tube is not axisymmetric. The hot-wire and PZT results show that there exist two distinct kinds of frequency, low frequency periodic fluctuations and high frequency periodic fluctuations. It is found that the low frequency fluctuation is consistent with the Helmholtz frequency and the high frequency fluctuation is strongly related with precession oscillation.     

Pressure measurement technique and installation effects on the performance of wafer cone design

The present study explores novel pressure averaging technique for wafer cone flowmeter design and its robustness in the presence of double 90° bend (out-of-plane) and gate valve as a source of upstream flow disturbance. The wafer cone flowmeter is tested in a circular pipe (inside diameter of 101 mm) with water as the working medium for the flow Reynolds number ranging from 1.19×10⁵ to 5.82×10⁵. Influence of the half cone angle (α) on the coefficient of discharge (C_d) of wafer cone flowmeter is studied with this new pressure averaging technique. Half cone angles considered in this study are 30° and 45° with a constant constriction ratio (β) of 0.75. The upstream static pressure tap is located at 1D upstream of the wafer cone. The downstream pressure averaging technique comprises eight circumferential holes of diameter 2 mm on the maximum diameter step of the wafer cone. The pressure taps are communicated through the support strut which serves as a downstream static pressure tap. The disturbance causing elements are individually placed at 1.5D, 5.5D, 9.5D and 13.5D upstream to the wafer cone flowmeter. The wafer cone flowmeter is also tested with gate valve opening of 25%, 50% and 75% for all the arrangements considered. The 30° cone is found to be better than 45° cone for the range of Reynolds number covered in the present study. The results show that the 30° wafer cone flowmeter with novel downstream pressure averaging technique is insensitive to the swirl flow created by a double 90° bend (out-of-plane) and requires an upstream length of 9.5D with a gate valve as a source of flow disturbance.     

Experimental verification and numerical simulation of a vortex flowmeter at low Reynolds numbers

This study presents experimental verification and numerical simulations of a vortex flow meter in the Reynolds number range between 8300 and 50,000. A custom-designed bluff body with a wedge back shape was used in the flowmeter. A shedding frequency of the flowmeter was measured in an air duct using a hot-film probe. To evaluate the accuracy of the flowmeter, a measurement uncertainty analysis was performed. Numerical simulations of the vortex flowmeter were performed with the open source code OpenFOAM. Transient simulations of periodic vortex shedding behind the bluff body were performed using different simulation methods depending on the pipe Reynolds number, such as Direct Numerical Simulation (DNS), Large Eddy Simulation (LES) and Unsteady Reynolds Averaged Navier Stokes (URANS) method. The simulated vortex shedding frequencies matched the experimental data very well. Experiments and simulations demonstrated a clear linear dependence of the shedding frequency on the volumetric flow rate over the entire range of Reynolds numbers. In addition, numerical simulations were used to study the main mechanisms of vortex formation and shedding behind the considered bluff body.     

An investigation into the effects of installation on the performance of insertion flowmeters

An electromagnetic and a turbine insertion flowmeter were tested in three different flow conditions inside a 0.590-m bore pipe inserted in the National Engineering Laboratory (NEL) large water flow measurement facility. The results were compared with velocity measurements obtained from a laser Doppler velocimeter (LDV). The advantage of using such a reference measurement is that LDV is non-intrusive and does not affect the velocity profile itself.Of the meters tested, one was supplied with a whole meter calibration factor and the other was supplied with a calibration factor for the D/2 position.For both meters, application of the respective manufacturer's blockage correction improved the velocity measurements, reducing the differences between the LDV and corrected insertion meter measurements and the difference between the integrated insertion meter measurements and the gravimetric measurements.Swirling and skew flow profiles were generated by the installation of the NEL designed swirl generator and flow disturber, respectively. Neither of these disturbed profiles affected the performance of either of the meters in terms of accuracy of measurement compared with the LDV readings. The profiles themselves, however, changed the velocities at the D/8 and 7D/8 points, making single point estimates of the mean velocity inappropriate. A complete 13-point traverse, integrated using the method of cubics as described in BS 1042 [1] (Section 2.3: Measurement of fluid flow in closed conduits, 1992), gave acceptable estimates of mean velocity in both swirling and skew flow for both probes.     

组合涡发生器在螺旋板式换热器上的强化传热研究

在螺旋板式换热器螺旋通道内设置三角翼和椭圆柱组合涡发生器,利用流体计算软件Fluent进行三维数值模拟。研究了Re为4000～7000内组合涡发生器对通道平均Nu和平均阻力系数f的影响,并应用场协同原理进行了分析。与只加装椭圆柱涡发生器的螺旋板式换热器进行对比,结果表明,纵向涡发生器产生的二次流能改善螺旋通道内的速度场与温度场的协同性,起到强化换热作用。在正三角形排列方式下,组合涡发生器通道的平均Nu比椭圆柱涡发生器的平均Nu增大8.7%,阻力因子f减小23.7%,强化换热的效果较好。     

NUMERICAL STUDY OF FLOW IN CONICAL DIFFUSER WITH VORTEX GENERATOR JETS

To develop vortex generator jet (VGJ) method for flow control, the turbulence flow in a 144°conical diffuser with and without vortex generator jets are simulated by solving Navier-Stokes equations with κ -ε turbulence model. The diffuser performance, based on different velocity ratio (ratio of the jet speed to the mainstream velocity), is investigated and compared with the experimental study. On the basis of the flow characteristics using computation fluid dynamics (CFD) method observed in the conical diffuser and the downstream development of the longitudinal vortices, attempt is made to correlate the pressure recovery coefficient with the behavior of vortices produced by vortex generator jets.     

涡流发生器在流体机械流动控制中应用研究进展

从实验测量和数值计算两个方面对涡流发生器流动控制的基础研究和应用研究进行评述,介绍了涡流发生器在流体机械流动控制中的应用及其取得的主要研究成果,最后指出了涡流发生器发展存在的问题和发展方向.     

旋流驱动微粒转动的性能与实验

分析了旋流产生的机制及其驱动微粒运动的机理,建立了颗粒在旋流中的力学模型。以微米级的颗粒(几微米到几百微米)为例,分析了两支微管对向喷射所产生的旋流场的特点和颗粒在旋流场中的受力情况以及运动特点和运动规律。讨论了颗粒的尺寸、形状、位置变化对其旋转性能的影响,并通过实验验证了提出方法的可行性。分析和实验表明:两支平行微管相对喷射可以产生旋流,旋流可以驱动颗粒在其流场内稳定旋转。颗粒在旋流场内的运动性能与流场参数和微粒的形状、尺寸、偏心有关,减小颗粒的初始位置的偏心,减少公转成分,有利于颗粒姿态的捕捉和调整。即使颗粒参数变化,合理匹配流场参数,提出的方法仍然可以可以稳定地驱动颗粒转动。     

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。