Head geometry effects on pneumatic three-hole pressure probes for wide angular range

Recent investigations Argüelles et al. (2008) [5] have demonstrated that it is possible to increase the operative angular range of pneumatic three-hole pressure probes (THP) using a two-zoned method in the data reduction procedure. In this study, the influence of the head geometry on the performance of this type of probes is addressed, especially in the extended regions of the angular range, previously unconsidered in the literature. Three different geometries have been built to carry out the analysis, corresponding to cylindrical, trapezoidal and cobra type probes, with a separation angle of 60° between the holes. Additionally, cylindrical and cobra type probes have been manufactured with angular distances of 30° and 45° between the holes, in order to advance the effect of the construction angle on the probes performance. The uncertainty transmitted from the measurements to the resultant flow variables has been also addressed. Moreover, the sensitivity of the different head designs to variations in the Reynolds number or deviations of the flow with respect to the measurement plane of the probe (pitch misalignments) has been addressed. Major conclusions indicate that cobra type probes provide the largest operative angular range, while cylindrical designs minimize the errors in the determination of both pressure and velocity flow variables when the Reynolds number or the pitch angle differ from the baseline calibration.     

Reynolds number effects on the non-nulling calibration of a cone-type five-hole probe for turbomachinery applications

The effects of Reynolds number on the non-nulling calibration of a typical cone-type fivehole probe have been investigated for the representative Reynolds numbers in turbomachinery. The pitch and yaw angles are changed from −35 degrees to 35 degrees with an angle interval of 5 degrees at six probe Reynolds numbers in range between 6.60 × 10³ and 3.17× 10⁴. The result shows that not only each calibration coefficient itself but also its Reynolds number dependency is affected significantly by the pitch and yaw angles. The Reynolds-number effects on the pitchand yaw-angle coefficients are noticeable when the absolute values of the pitch and yaw angles are smaller than 20 degrees. The static-pressure coefficient is sensitive to the Reynolds number nearly all over the pitch- and yaw-angle range. The Reynolds-number effect on the totalpressure coefficient is found remarkable when the absolute values of the pitch and yaw angles are larger than 20 degrees. Through a typical non-nulling reduction procedure, actual reduced values of the pitch and yaw angles, static and total pressures, and velocity magnitude at each Reynolds number are obtained by employing the calibration coefficients at the highest Reynolds number (Re=3.17×10⁴) as input reference calibration data. As a result, it is found that each reduced value has its own unique trend depending on the pitch and yaw angles. Its general tendency is related closely to the variation of the corresponding calibration coefficient with the Reynolds number. Among the reduced values, the reduced total pressure suffers the most considerable deviation from the measured one and its dependency upon the pitch and yaw angles is most noticeable. In this study, the root-mean-square data as well as the upper and lower bounds of the reduced values are reported as a function of the Reynolds number. These data would be very useful in the estimation of the Reynolds-number effects on the non-nulling calibration.     

A new calibration facility for water flowrate at high Reynolds number

A new test facility has been constructed for the National Metrology Institute of Japan (NMIJ) and the National Institute of Advanced Industrial Science and Technology (AIST) for calibration of feedwater flowmeters used in nuclear power stations at Reynolds numbers of up to 18 million. This very large Reynolds number is achieved in a 600 mm pipe at a flowrate of 3.33  m³/s (12,000  m³/h) and a water temperature of 70  ^°C. This calibration facility consists of a circulation loop with four pumps and four reference flowmeter sets, a prover system, a heating and cooling unit, and other components. The expanded uncertainty of this facility is 0.077%. The present paper describes, in detail, the new facility, the calibration method of the reference flowmeter, experiments for flow field, uncertainty estimation, and the results of an example calibration.     

Real time in situ ellipsometric and gravimetric monitoring for electrochemistry experiments

This work describes a new system using real time spectroscopic ellipsometer with simultaneous electrochemical and electrochemical quartz crystal microbalance (EQCM) measurements. This method is particularly adapted to characterize electrolyte/electrode interfaces during electrochemical and chemical processes in liquid medium. The ellipsometer, based on a rotating compensator Horiba Jobin-Yvon ellipsometer, has been adapted to acquire Psi-Delta spectra every 25 ms on a spectral range fixed from 400 to 800 nm. Measurements with short sampling times are only achievable with a fixed analyzer position (A=45 degrees ). Therefore the ellipsometer calibration is extremely important for high precision measurements and we propose a spectroscopic calibration (i.e., determination of the azimuth of elements according to the wavelength) on the whole spectral range. A homemade EQCM was developed to detect mass variations attached to the electrode. This additional instrument provides further information useful for ellipsometric data modeling of complex electrochemical systems. The EQCM measures frequency variations of piezoelectric quartz crystal oscillator working at 5 MHz. These frequency variations are linked to mass variations of electrode surface with a precision of 20 ng cm(-2) every 160 ms. Data acquisition has been developed in order to simultaneously record spectroscopic ellipsometry, EQCM, and electrochemical measurements by a single computer. Finally the electrodeposition of bismuth telluride film was monitored by this new in situ experimental setup and the density of electroplated layers was extracted from the optical thickness and EQCM mass.     

A novel adaptive sliding mode control with application to MEMS gyroscope

This paper presents a new adaptive sliding mode controller for MEMS gyroscope; an adaptive tracking controller with a proportional and integral sliding surface is proposed. The adaptive sliding mode control algorithm can estimate the angular velocity and the damping and stiffness coefficients in real time. A proportional and integral sliding surface, instead of a conventional sliding surface is adopted. An adaptive sliding mode controller that incorporates both matched and unmatched uncertainties and disturbances is derived and the stability of the closed-loop system is established. The numerical simulation is presented to verify the effectiveness of the proposed control scheme. It is shown that the proposed adaptive sliding mode control scheme offers several advantages such as the consistent estimation of gyroscope parameters including angular velocity and large robustness to parameter variations and external disturbances.     

Liquid low-flow calibration rig using syringe pump and weighing tank system

A calibration rig consisting of a syringe pump and a weighing tank system that can operate in the flow rate range of 0.02–60 L/h was developed in this study. This paper discusses the design considerations of the calibration methods, the development of the rig, the calibration results, and the uncertainty analysis conducted on the rig. A weighing tank system that minimizes the effects of outlet tube contact and evaporation was developed. The syringe pump system was designed using a servomotor, a precise ball screw, and a linear encoder, and it was calibrated using the developed weighing tank system via the standing start and stop method over the target range of flow rates with light oil and industrial gasoline. Several flowmeters were calibrated using the syringe pump via the flying start and finish method. During the flowmeter calibration stage, the effect of the evaporation error was eliminated because the calibration rig can form a closed pipeline system. The influence of dissolved gas and the position dependence of the syringe pulse factor on the calibration accuracy were investigated experimentally. As a result, all obtained syringe pulse factors were found to be within ±0.02% of each other. The preliminary expanded uncertainties (k=2) of the calibration rig were estimated to be 0.066% and 0.070% for mass and volumetric flows, respectively.     

Double S-type Pitot Tube for velocity field study of fire whirls

In this paper we present a pressure measurement instrument based on the S-type Pitot tube modified to measure the two velocity components of a high temperature flow assuming that the flow is locally two-dimensional. The development of this new device, which we designate as the Double S-type Pitot Tube, is related to the difficulty and the lack of precision of measurements with a standard S-type Pitot tube in flows with unknown directions like the case of fire whirls in laboratory experiments. The design construction and calibration method of the device are described. The pitch angle of the flow and the velocity coefficients of the probe are analysed experimentally in a wind tunnel calibration as well as the associated errors. The use of this sensor in a fire whirl laboratory test is shown and the results are compared with those of simple S-type Pitot tubes in the same test. The obtained results show the applicability and better performance of the novel device.     

Acoustic velocity measurements in resonators of thermoacoustic systems using hot-wire anemometry

Acoustic velocity measurements in resonators of thermoacoustic systems using hot-wire anemometry technique flow are presented. The hot-wire calibration is based on the determination of the acoustic velocity reference value through an acoustic pressure measurement and their relationship using a linear acoustic model. In this model, an analytical approach involving the coupling between the sound source and the resonant cavity effects and the viscous and the thermal effects in the boundary layers is used. The amplitude and phase calibrations are reported for the first time, simultaneously, either by varying the sound source input voltage for a fixed frequency, or by varying the frequency for a given source input voltage. The amplitude calibration is detailed by using a filtering technique to eliminate either the acoustic streaming effects or the anemometer basic electric voltage variations effects. This provides a simple way to an amplitude calibration with good accuracy when measuring an average of a stationary oscillating velocity. The phase calibration is proposed here by considering the phase difference between the microphone and the hot-wire anemometer output signals. The results obtained by using a simple fluid-filled resonant cavity are encouraging on the feasibility of this method to carry out a first-order acoustic velocity measurement. However, the complexity of the dynamic calibration due to that of the heat transfer mechanism around the hot-wire probe in various frequency ranges clearly merits more investigation.     

简易高精度的平面五点摄像机标定方法

为了进一步提高相机参数精度,简化标定过程,在张正友平面标定算法的基础上,提出了一种较简单的5点标定算法。本文利用一个矩形作为标定模板,将其4个角点和中心点作为待匹配点。仅利用不同角度拍摄的10(10~20幅均可)幅图像,即可求解全部相机内外参数。首先,为了减小数据对结果的影响,对获取的5个点的图像坐标进行归一化,将点坐标控制在以原点为中心,2~(1/2)为半径的圆内;其次,相机成像模型未考虑畸变,考虑到单应矩阵可能会有零元素,故按照9个自由度来求解;再次,求解出相机的内外参数,将求得结果的平均值作为非零因子λ的值;最后利用Levenberg Marquarat(LM)算法对所有内外参数进行整体优化。选用不同噪声水平的模拟实验和真实图像进行测试,结果显示该算法比张正友棋盘格算法的精度要高。     

Improvement of the five-hole probe calibration using artificial neural networks

In the present study, the artificial neural networks (ANNs) technique was implemented to link non-dimensional pressure coefficients and flow characteristics to calibrate a five-hole probe. The experimental data of this work were obtained from a subsonic open-circuit wind tunnel at the velocity of 10 m/s. Here, the efficiency of ANNs was compared with two conventional data reduction methods, including linear interpolation technique and 5^th-order polynomial surface fit algorithm. Based on the statistical parameters of calibration data, it was concluded that the radial basis function (RBF) algorithm was more accurate and had more flexibility compared to the multi-layer perceptron (MLP) regression algorithm, the linear interpolation and 5^th-order polynomial methods. In the RBF method, the mean absolute errors of 0.11, 0.64, 0.02 and 0.03 were achieved for α, β, Cp_t and Cp_s , respectively. Furthermore, the effects of training data reduction and data selection on the performance of RBF were studied. The accuracy of the proposed RBF method was analyzed at different α angles and for random test data. Finally, the influence of increasing number of test data on the efficiency of calculated RBF method was evaluated.     

Measuring the angular dependent energy distribution of backscattered electrons at variable geometry

An aluminium semisphere system with 120 points of entry and eight detection areas, assembled on a meridian covering 0.0026 steradian each, was put over a solid bulk sample (e.g., aluminium), which was mounted in the eucentric point so that the incident electron beam could be varied by a polar rotation of the sphere in steps of 11.25 degrees. The complete angular distribution of the backscattered electrons became available by a rotation in steps of 11.25 degrees azimuthally. For this particular setup, the signals from the detection areas as well as the signal from the rest of the semisphere were amplified by operational amplifiers (Burr-Brown OPA128LM). However the signal of the semisphere was not available at that time. Specimen current measurements made the total amount of electrons accessible, providing a possibility for normalization of the results and comparison with total backscattering coefficients. By use of counter voltage variable up to 10 kV inside the detection assembly, it was possible to measure an energy resolution of the backscattered electrons for each detection area at the same time. Details of the construction and calibration procedures, possible errors, and sources of systematic deviations as well as first test results are discussed.     

Accurate determination of spring constant of atomic force microscope cantilevers and comparison with other methods

We present calibration results of commercial AFM cantilevers using the KRISS nanoforce calibrator (NFC) that can determine traceably spring constants with an uncertainty better than 1%, along with the results obtained from other four calibration methods: the dimensional method, the cantilever-on-cantilever method, the Sader method, and the thermal noise method. Two types (contact and tapping mode) of beam-shaped AFM cantilevers with nominal spring constants of 0.9 N m⁻¹ and 42 N m⁻¹, respectively, were investigated in this study. Because of its small uncertainty, the NFC method was used to assess the uncertainties of other four methods through comparisons between values obtained from other methods and those from the NFC method for the same cantilever. Results from other methods were generally in good agreement with those from the NFC method within the uncertainties of other methods claimed in other literatures, but values obtained from the Sader method were differed by up to 40% from the NFC values, which is 2 times worse than the known uncertainty.     

Unsteady boundary layer for a pitching airfoil at low Reynolds numbers

An experimental study was conducted in order to investigate unsteady boundary layers for a pitching airfoil. An NACA0012 airfoil sinusoid-pitched at quarter chord was employed, and its mean angle-of-attack and oscillation amplitude were 0° and 6°, respectively. To explore the unsteady boundary layers, smoke-wire visualization and surface-mounted probe measurements were pursued for three different cases, varying with Reynolds numbers (Re_c=2.3×10⁴, 3.3×10⁴, and 4.8×10⁴). A reduced frequency of 0.1 was identically set in all cases. Results show that in the presented Reynolds number range, the separation bubble dependent on both angle-of-attack and Reynolds number was observed, accompanied with unsteady laminar separation after reattachment. The unsteady laminar separation occurred at the saddle point, which was formed by the two vortices, the wall, and the external flow, and it was independent of reverse flow. This result indicates that the unsteady laminar separation occurs during the process of transition after the reattachment of separated boundary layer for an unsteady flow. The reverse flow observed over the trailing edge significantly interacted with the trailing edge vortex that rotates in the streamwise direction. This trailing edge vortex prevents the uppermost of the reverse flow from reaching to the unsteady laminar separation point during the upstroke, and this induces that the boundary layer breakdown does not occur in spite of the occurrence of laminar separation. The discrete vortices are formed by unsteady laminar separation, and its formation is ultimately affected by the Reynolds number. Consequently, it is obvious that the unsteady boundary layers are ultimately sensitive to Reynolds number in a low Reynolds number regime.     

Discharge coefficients of CFVN predicted for high Reynolds numbers based on low-Re-calibration

In 2016, PTB introduced a function for the representation of the discharge coefficient c_D of critical flow venturi nozzles (CFVN) (versus the Reynolds number Re) which covers the operating range for both laminar and turbulent boundary layers. It contains the parameters a for the impact of the core flow, b_lam for the Re-dependency in case of laminar and b_turb in case of turbulent boundary layers. These parameters are not independent from each other but have the fixed relation of b_turb = 0.003654b_lam^1.736.Furthermore, the parameter a and the parameter b_lam are both direct functions of the local curvature radius R_c,throat of the nozzle at the throat. These relationships to R_c,throat are described by theoretical models. Consequently, the overall dependency of the discharge coefficient c_D on Reynolds number Re can be derived from only one parameter.The paper describes how these relationships can be used to extrapolate the calibration values of a CFVN determined with atmospheric air to high pressure gas flow applications covering a Reynolds range of about 1:60. It is shown in detail by examples and the reliability is demonstrated by comparison data for low and high pressure for 33 nozzles. Finally, aspects of preconditions for such extrapolation and uncertainties are discussed.     

A multi-tube pressure probe calibration method for measurements of mean flow parameters in swirling flows

A simple and sensitive measurement method of multi-tube pressure probes applicable in swirling flow fields is presented in this paper. Determination of flow direction associated with local pitch, , and yaw, ψ, angles, magnitudes of local static and dynamic pressures can be achieved through a calibration method used with 3- and 5-tube versions of a multi-tube pressure probe. The 5-tube probe was tested in a conventional air cyclone where a strong rotational flow prevailed while the 3-tube probe was used in a low swirl flow field in a pipe internally fitted with a helical coiled wire insert. The method is based on the rotational sensitivity of the pressure probe handled through non-dimensional calibration parameters.     

Improved system for the automatic calibration of standard resistors in the meg-ohm range

An automated measuring system has been developed to improve the calibration of high value standard resistors in the meg-ohm range at the National Institute for Standards (NIS), Egypt. This system is suitable for the calibration of the standard resistors from 100 kΩ to 100 MΩ using the DMM-based method by the substitution technique where the unknown resistor and the standard resistor are indirectly compared in the same position using a dummy resistor as a short-term reference standard. The system operation is automatically controlled by using a Lab VIEW program which is especially developed for this purpose. The uncertainty for the high value standard resistors measurement of this system is estimated. The performance of this system is also evaluated by comparing the measurement results obtained from this technique with those obtained by the direct comparison DMM-based method. It is found that the measurement uncertainty of with this method spans from 4.1 × 10⁻⁶ to 27 × 10⁻⁶, while it spans from 40 × 10⁻⁶ to 110 × 10⁻⁶ for the direct comparison method. The relative differences of the deviation from nominal values of the working standards resistors measured by the two methods are found to be within their expanded uncertainties.     

一种改进的挠性陀螺POS标度因数误差补偿方法

针对航空遥感的作业环境特点,分析了一类位置姿态测量系统(position and orientation system,POS)用挠性陀螺的标度因数与输入角速度之间的关系.通过实验发现了在小角速率范围内陀螺标度因数与输入角速度呈规律性的“双曲线”关系.提出了一种改进的多位置动静混合误差标定与补偿方法.首先根据输入角速度的正负分别标定陀螺标度因数并建立两者的对应关系,然后在误差补偿时根据输入角速度的方向和数值变化更新标度因数及其他误差系数,进而提高误差补偿精度.实验结果表明,利用改进方法进行误差补偿后POS角测量精度可以提升约20％.     

Low flow regime measurements with an automatic pulse tracer velocimeter (APTV) in heterogeneous aquatic environments

Cost-effective velocity measurements at lab and field scales are required for understanding and modeling the flow characteristics in aquatic environments such as constructed wetlands, coastal marshes, lakes and reservoirs. This paper presents a new measurement device—the automatic pulse tracer velocimeter (APTV) that is designed to measure water velocities for low flow regimes (0.2–5.0 cm s⁻¹) in heterogeneous aquatic environments using NaCl pulse tracer measurements. Hydraulic data collected in a laboratory-scale flume and field-scale constructed wetland were analyzed to determine velocity, directional flow and dispersion coefficients measured by using a cross-type and arc-type APTV. Acoustic Doppler velocimeters (ADVs) were used to collect calibration measurements in a hydraulic flume to gain fundamental understanding in support of field experiments. To test the effects of vegetation, four scenarios of laboratory-scale tests having both submerged and emergent artificial vegetation were conducted in a flume including; (1) no artificial vegetation (NAV), (2) submerged artificial vegetation (SAV) (3) emergent artificial vegetation (EAV), and (4) mix artificial vegetation (MAV). Directional flow detection and simulated storm event flow tests were conducted using an arc-type APTV data in the flume to gain perspectives of APTV performance in variable flow conditions. Cross-type APTV pulse data were eventually analyzed to determine dispersion coefficients based on the tracer curves. Finally APTVs were tested alongside an ADV for a three-day duration in a constructed wetland nearby the Everglades, Florida. Operating advantages of the APTV compared to other similar sensors were summarized in the end to enhance the application potential. Results indicate that APTVs are ideal device for affordable measurements of velocities in a 0.2–4.5 cm s⁻¹ range with the prediction of both velocity field, direction and dispersion coefficients, and capable of autonomous deployment and control in a sensor network.     

Micro-scale hole profile measurement using rotating wire probe and acoustic emission contact detection

The development of a new probing method to inspect the inner diameter of micro-scale holes is presented in this paper. This was accomplished by contact detection using acoustic emission with a Ø170 μm rotating wire probe tip. Contact is detected when the rotating probe approaches and impacts the hole’s inner surface. The effective diameter of the rotating probe is calibrated by using a high precision grade 0 Mitutoyo gauge block. The wire rotating probe used was fabricated with micro stainless steel wire and micro tubes. The probe’s effective diameter was compensated for in the measurement of the hole. The probe was used to measure the diameter and the roundness of micro-scale holes. Probes used in previous publications have different geometry than the probe in this paper and are used almost exclusively for external dimensions. Micro-scale holes of less than 1.0 mm in diameter and 10 mm in depth are successfully measured and the 3D profile is created accordingly. Also, the out-of-roundness values of each level spacing, 50 μm apart in height, are calculated.     

Calibration of an ultrasonic flow meter for hot water

If we want to keep the number of necessary characterisation measurements within acceptable limits, we need to be confident that a flow instrument design reacts in a predictable and straightforward way to systematic influences. In this paper, the important systematic influences for an ultrasonic flow meter (UFM) for feed water flow are identified to decide which characterisations have to be carried out in addition to a typical baseline calibration with water at 20 °C. In heat metering applications where there are temperatures up to 120 °C it is for example known that the temperature influence on the flow instrument is important and this also applies to higher temperatures such as in the feed water control of power plants. One of the critical systematic temperature influences that affects most flow instruments is the thermal expansion of the meter body. From June 2009 to March 2010, the “Heat and Vacuum” department of the Physikalisch-Technische Bundesanstalt conducted a measurement campaign to characterise the influence of thermal expansion of a meter body on the calibration of an 8 inch (DN 200) five chord UFM for feed water application in the temperature range from 4 °C to 85 °C and flow range from 50 m³ h⁻¹ to 900 m³ h⁻¹. An overview of the procedures and facility used for the calibration is given and the measurement conditions under which the calibrations were performed are detailed. It is shown that a linear model of the thermal expansion effect is appropriate for the investigated conditions.