Investigation of the pressure response of different Pitot tubes

Pitot tubes are commonly used to measure gas flow in ducts. The integration of the velocity profile which allows the calculation of the gas flow is described in several international standards such as ISO 3966 or ISO 10780.The common working principle of Pitot tubes is based on the measurement of the differential pressure between the two different pressure taps. The gas velocity is related to this differential pressure through a flow coefficient depending on the Pitot tube type.In case of stable flow, in a pressurized duct, fluctuations of the in-line pressure, even low, can occur. If the response times of the two pressure lines (static and total) between the Pitot tube head and the differential pressure sensor are not equal, these fluctuations can be seen as fluctuations of the measured differential pressure and then of the calculated velocity.This phenomenon is investigated for different design of Pitot tubes and the difference in behaviour of the two pressure lines is highlighted.     

Air velocity and flow measurement using a Pitot tube

The accurate measurement of both air velocity and volumetric airflow can be accomplished using a Pitot tube, a differential pressure transducer, and a computer system which includes the necessary hardware and software to convert the raw transducer signals into the proper engineering units. The incorporation of sensors to measure the air temperature, barometric pressure, and relative humidity can further increase the accuracy of the velocity and flow measurements. The Pitot tube measures air velocity directly by means of a pressure transducer which generates an electrical signal which is proportional to the difference between the pressure generated by the total pressure and the still air (static pressure). The volumetric flow is then calculated by measuring the average velocity of an air stream passing through a passage of a known diameter. When measuring volumetric flow, the ‘passage of a known diameter’ must be designed to reduce air turbulence as the air mass flows over the Pitot tube. Also, the placement of the pitot tube in the passage will influence how accurately the measured flow tracks the actual flow through the passage. Calibrating the measurement system in a wind tunnel can further increase the accuracy of the velocity and the flow measurements. This objective of this paper is to provide the field engineer with single, concise source of information on flow measurement using a Pitot tube.     

Calculation of the Pitot tube correction factor for Newtonian and non-Newtonian fluids

This paper presents the numerical investigation performed to calculate the correction factor for Pitot tubes. The purely viscous non-Newtonian fluids with the power-law model constitutive equation were considered. It was shown that the power-law index, the Reynolds number, and the distance between the impact and static tubes have a major influence on the Pitot tube correction factor. The problem was solved for a wide range of these parameters. It was shown that employing Bernoulli's equation could lead to large errors, which depend on the magnitude of the kinetic energy and energy friction loss terms. A neural network model was used to correlate the correction factor of a Pitot tube as a function of these three parameters. This correlation is valid for most Newtonian, pseudoplastic, and dilatant fluids at low Reynolds number.     

The effect of turbulence on a multi-hole Pitot calibration

Accurate calibrations of multi-hole Pitot tubes require thousands of measurements spanning ranges of the fluid's velocity, and the pitch and yaw angles. When calibrating a commercially-manufactured multi-hole Pitot tube in NIST's low-turbulence wind tunnel, we found hysteresis in certain ranges of airspeed, pitch angle, and yaw angle. In the worst case, the hysteresis caused a calibration error of 30%. We demonstrate that the hysteresis was caused by a flow instability associated with flow separation. A turbulence intensity of only 1% removes the hysteresis; however, the calibration depends on the turbulence intensity over the entire range of our measurements (0.25–2%). Therefore, multi-hole Pitot tubes should be calibrated and used at the same turbulence levels.     

Experimental and numerical investigations of the factors affecting the S-type Pitot tube coefficients

In greenhouse gas emission monitoring from industrial stacks, the most common device used to measure stack gas velocity is the S-type Pitot tube. Various factors such as the Reynolds number and misalignment of the installation angle can be additional error sources for the S-type Pitot tube coefficients due to harsh environments. Manufacturing quality of the S-type Pitot tube is also a factor affecting on the measurement uncertainty of stack gas velocity. In the present study, wind tunnel experiments were conducted in Korea Research Institute of Standards and Science (KRISS) standard air speed system to examine the effects of various factors on the S-type Pitot tube coefficients. Numerical simulations were also used to understand flow phenomena around the S-type Pitot tube in the presence of misalignment and distortion of the geometry. The results indicate that misalignment of the pitch and yaw angle change within ±10° changes the S-type Pitot tube coefficients by approximately 2% compared with normal values. The manufacturing quality resulted in unstable values of the coefficients within 2%. However, variations of the Reynolds number (Re_D=3.0×10³–2.2×10⁴) had no significant effect on the S-type Pitot tube coefficients.     

The impact of geometric parameters of a S-type Pitot tube on the flow velocity measurements for greenhouse gas emission monitoring

In the monitoring of greenhouse gas emission from industrial smoke-stacks, the most common device used to measure the stack gas velocity is the S-type Pitot tube in South Korea, which is used to estimate the volumetric flow rate by what is termed the Continuous Emission Monitoring System (CEMS). The S-type Pitot tube installed in the stack is inevitably affected during velocity measurements by velocity changes, yaw and pitch angle misalignments due to the harsh environments. Various geometries of the S-type Pitot tube can affect the characteristics of the S-type Pitot tube coefficients, including the degree of sensitivity to velocity changes and yaw and pitch yaw angle misalignments. Nevertheless, there are no detailed guidelines pertaining to the S-type Pitot tube geometry considering accurate and reliable measurements in the ISO, EPA and ASTM international standards. In the present study, S-type Pitot tubes with various geometric parameters, in this case the distance between the impact and wake orifices and the bending angle of the orifices, were manufactured by a 3D printer. Wind tunnel experiments were conducted in the Korea Research Institute of Standards and Science (KRISS) air speed standard system to determine the optimal geometry of an S-type Pitot tube for the accuracy velocity measurements in actual smokestacks which undergo velocity changes and yaw and pitch angle misalignments. Particle image velocimetry was also used to understand the flow phenomena around an S-type Pitot tube under various geometric and misalignment conditions by means of qualitative visualization. The results indicate that S-type Pitot tubes with a long effective length have more constant distributions of the S-type Pitot tube coefficients when the velocity changes from 2 m/s to 15 m/s. The error indexes for yaw angle misalignments show that S-type Pitot tube models with large effective lengths are less affected by yaw angle misalignments. The S-type Pitot tube coefficients were mostly insensitive to the both positive and negative pitch angle misalignments regardless of the velocity and geometry of the various models tested.     

皮托管在气流测量中一些问题的探讨

皮托管在气流速度测量中受多种因素影响。怎样使测量的数据准确可靠，除了仪器设备外，还要找出影响测量结果的其他原因并对其修正，就显得十分重要。本文的主要目的就是探讨在气流测量中风速的有关修正问题（如水的密度、压力损失、压缩性影响）。以国家气象计量站的设备和测量数据为例，经过水的密度、压力损失、压缩性影响的修正，60m／s时，其修正量为-0．5m／s。这就是为什么在高速时，标准风速偏高的原因。这一结果对于国内国际比对，使气流速度的量值与世界统一具有重要意义。     

A Pitot tube system for obtaining water velocity profiles with millimeter resolution in devices with limited optical access

An automated, miniature, S-type Pitot tube system was created to obtain fluid velocity profiles at low flows in equipment having limited optical access, which prevents the use of standard imaging techniques. Calibration of this non-standard Pitot tube at small differential pressures with a custom, low-pressure system is also described. Application of this system to a vertical, high-pressure, water tunnel facility (HWTF) is presented. The HWTF uses static flow conditioning elements to stabilize individual gaseous, liquid, or solid particles with water for optical viewing. Stabilization of these particles in the viewing section of the HWTF requires a specific flow field, created by a combination of a radially expanding test section and a special flow conditioner located upstream of the test section. Analysis of the conditioned flow field in the viewing section of the HWTF required measurements across its diameter at three locations at 1 mm spatial resolution. The custom S-type Pitot tube system resolved pressure differences of <100 Pa created by water flowing at 5–30 cm/s while providing a relatively low response time of ~300 s despite the small diameter (<1 mm) and long length (340 mm) of the Pitot tube needed to fit the HWTF geometry. Particle imaging velocimetry measurements in the central, viewable part of the HWTF confirmed the Pitot tube measurements in this region.     

Flow measurement of CO2 in a binary gaseous mixture using an averaging Pitot Tube and Coriolis mass flowmeters

To combat the growing emissions of CO₂ from industrial processes, Carbon Capture and Storage (CCS) and Carbon Capture and Utilization technologies (CCU) have been accepted worldwide to address these pressing concerns. So as to efficiently manage material and financial losses across the entire stream, accurate accounting and monitoring through fiscal metering of CO₂ in CCS transportation pipelines are core and required features for the CCS technologies. Moreover, these technical requirements are part of the legal compliance schemes and guidelines from various regulatory bodies. The CO₂ transportation pipelines will likely have multiple inputs from different capture plants, each with varying composition of CO₂ and thus introducing impurities into the CO₂ stream. The presence of other ordinary or hydrocarbon gases in the CO₂ gas stream could affect the functionality of metering instruments by introducing additional errors, particularly in the case of volumetric flowmeters. In this study, volumetric and direct mass measurement methods for the flow measurement of CO₂ mixtures using two totally different metering principles are experimentally evaluated. An Averaging Pitot Tube with Flow Conditioning Wing (APT-FCW) and Coriolis mass flowmeters (CMF) are used to assess the flow metering of CO₂ in a binary gaseous mixture. Different gases (nitrogen, air, oxygen, argon and propane) are diluted as contaminants into the pure CO₂ gas flow for various mass fractions to produce an adulterated mixture of the CO₂ gas. Comparative analysis of the measurement results under these flow conditions relative to that of pure CO₂ gas show that the measurement error of the APT-FCW sensor increases with the mass fraction of the diluent component, and gases with density closer to that of CO₂ have a much lesser effect on the performance of the APT-FCW flow sensor for smaller mass fractions. The CMF proved to be very reliable in the gas combination processes and as a reference meter for the APT-FCW sensor. Further analytical observations are discussed in detail.     

涡街流量计在电厂瓦斯计量中的应用

乌石化公司热电厂在瓦斯计量上选用了德国科隆公司生产的涡街流量计VFM5090,介绍仪表选型、测量原理、安装、故障处理等方面内容。     

New air speed calibration system at NMIJ for air speeds up to 90 m/s

National Metrology Institute of Japan (NMIJ) has established a high air speed standard facility and has been providing a calibration service since 2015. The facility has an air speed range of 40 m/s to 90 m/s with a relative expanded uncertainty (k = 2) of 0.63%. The purpose of this primary standard is mainly to contribute to the improvement of meteorological observation research and to the evaluation of flow field inside a turbo machine and around a high speed vehicle. The reference air speed is derived from the national primary gas flowrate standard of Japan. A conversion device from flowrate to air speed is installed in the test line of the closed-loop calibration facility. The reference air speed at the nozzle exit of the conversion device is obtained by comparing the integral of the air speed profiles and the reference volume flowrate. The total pressure tube used as a transfer standard is then calibrated against the reference air speed at the center of the nozzle exit. The Eiffel-type wind tunnel, which is a working standard for the daily calibration service, is calibrated using this total pressure tube. The present paper describes the calibration system, the traceability chain, and an uncertainty analysis using a validation method.     

Parametric study and numerical analysis of empty and foam-filled thin-walled tubes under static and dynamic loadings

In this paper the crushing behavior of thin-walled tubes under static and dynamic loading is investigated. First, a finite element (FE) model for empty thin-walled tube was constructed and validated by available experimental and numerical data. The comparison between the FE results and the existing numerical solutions as well as the available experimental results showed good agreements. Next, a model for the foam was adopted and implemented in an in-house FE code. The implemented isotropic foam model was then used to simulate the behavior of foam-filled tubes under both static and dynamic loadings. Good agreement was observed between the results from the model with those obtained by analytical relations and experimental test data. The validated FE model was then used to conduct a series of parametric studies on foam-filled tapered tubes under static and dynamic loadings. The parametric studies were carried out to determine the effect of different parameters such as the number of oblique sides, foam density and boundary conditions on crushing behavior of rectangular tubes. The characteristic included deformed shapes, load–displacement, fold length and specific energy absorptions.     

An anomalous method of using a camera in determining the velocity distribution within a boundary layer

The current study proposes a cost-effective technique wherein a camera can be used anomalously in tandem with the working of a pitot tube in determining the velocity distribution within a boundary layer. The technique involves the traversal of a pitot tube at a uniform velocity inside the width of boundary layer and simultaneously imaging the change in meniscus location of liquid column in the corresponding manometer, inside a wind tunnel set-up. The study aims in establishing a relation between the traversal velocity and the free stream velocity. The proposed approach holds the advantage of providing velocity values at equally spaced locations within the boundary layer, with the number of values depending on the velocity of retraction (traversal away from the surface) as well as the frame rate of recording. Experiments were performed at different combinations of retraction velocity ($V_r$) and Fan Speed for establishing the method. An optimum velocity at which the pitot tube should be retracted was determined based on convergence of trend of the variation in instantaneous meniscus locations to a standard reference trend. Results show that dimensionless optimum velocity (${\overline{V}}_o$) defined as the optimum ratio between tunnel velocity ($U_t$) and $V_r$ is related to the Fan Speed (FS) by ${\overline{V}}_o\propto$ FS${}^{0.6}$. Additionally, with regard to the manual traversing performed, the probability density function plots show that traversing manually at $\overline{V}\gg {\overline{V}}_o$ introduces higher non-uniformity in the results, thereby preferable to perform the traversal closer to values of ${\overline{V}}_o$. Using the results obtained from the developed imaging technique, the velocity variation within the boundary layer was studied. The technique was successful in precisely locating the prominent points inside a boundary layer for a particular flow condition. Finally as a case study, the imaging approach was also utilized in determining the effect of roughness change across the seam of a cricket ball on its aerodynamics. This case study also shows that the technique is successful in obtaining the flow characteristics of a general boundary layer as well as a flow separation case.     

On the impact of anemometer size on the velocity field in a closed wind tunnel

In the present paper, experimental and numerical investigations of the flow around different types and sizes of anemometers are presented and discussed.The measurements of the flow field at different distances upstream of the anemometer are performed with a laser Doppler Anemometer. The computational results are in good agreement with the experimental ones since the observed deviations are of the same order of magnitude. These results show that anemometers may induce a strong distortion of the velocity field, even far upstream of the anemometer. This distortion has to be taken into account in the anemometer calibration field to yield reliable and consistent measurements.     

An experimental test system for the generation,control and analysis of sinusoidal pulsatile pipe flows (An application case for time dependent flow measurements)

The hardware and software of an experimental test system which has been designed, constructed and operated for the analysis of transitional characteristics of a laminar time-dependent flow field into turbulence with comprehensive uncertainty analysis are the major contents of the paper. Therefore presentation herein aims to offer an application case in terms of time-dependent measurement and data acquisition technology using an electronic digital mass flow control (MFC) unit at laboratory site instead of previously used pressure driven mechanisms. The flow field is a sinusoidal pulsatile one in order to simulate the real practice and to utilize the simplicity in production, control and analysis of oscillation. The previous background and the updated portrait on the transitional pulsatile flow [1], [2] are outlined to determine the relevant flow parameters and their critical ranges, the details of the measurement and data acquisition systems and the proposed methodologies. The production of the controlled pulsatile flow and the generated flow characteristics, the methodology for the analysis, accuracy and sensitivity of the measurement and data acquisition chains are given for the purpose. The overall uncertainties of the velocity and pressure measurement chains are found to be ±3.2% and ±1.3%, respectively. The range of the experimental research devised to investigate the interactive influences of oscillation frequency, f and velocity amplitude ratio, A₁ in the intermediate and the inertia dominant regions of pulsatile flow field with an emphasis on transition to turbulence is presented via sample measurements of mean velocity and pressure waveforms as solid outputs without going into details on physical aspects of flow dynamics.     

静止补偿有源滤波器实现方法

分析了基于电流检测的并联APF动态监控原理,提出了由微机控制的APF动态监控系统.对其进行了理论分析,介绍了系统结构和控制方案.实验表明该系统有效地解决了有源电力滤波器容量与开关频率的矛盾,不仅能同时完成无功补偿、谐波抑制和三相电流平衡的三大功能,而且对系统参数的变化适应性更强,补偿效果好.     

离心压气机相似转速数值研究

以某型地面燃机的离心式低压压气机为对象进行了全三维数值模拟,分别计算了折合转速相同但进口总温、总压及物理转速不同的7种状态的压气机工作特性曲线,其中物理转速分别为90%、100%及105%。结果表明:折合转速相同时流场的相似程度较高但性能差别较大,随着进口总温升高、总压减小雷诺数降低,压气机增压比、效率降低。     

An investigation into the preforming of tubes

A major disadvantage of traditional cold forging is represented by the inability to forge slender geometries such as tubes, because these tend to collapse under axial forces. Recent research has revealed that, for the forming of hollow flanged components from tubes, a controlled material flow can be achieved by injection forging. However if the height of the flange is high compared to the wall thickness of the tube, instability problems arise causing the tube to buckle. According to previous work by the authors this may be prevented by increasing the wall thickness of the tube locally through the preforming of a simple inner flange on the tube. These preliminary investigations have been restricted to a reduced number of component geometries in terms of the major process parameters; being the inner- to outer-tube diameter proportion and the flange-towall-thickness ratio. In continuation of this work the present paper focuses on a systematic mapping of the optimal preform design in order to allow an establishment of actual preform design rules for the injection forging of tubular components for a whole range of parameter combinations. The analysis builds on a comprehensive finite element analysis in conjunction with experimental tests in aluminium performed for strategically important parameter combinations in order to support the theoretically established formability limit diagrams.     

注水井井下流量、压力同步测量的研究

论述了井下流量、压力同步检测器及其在油田注水井分层测量中的应用,详细阐述井下流量、压力检测器的测量原理及计算方法。该项研究成果在国内首次实现了井下流量、压力同步测量。