High temperature fast response pressure probe for use in liquid metal droplet dispensers

A miniature fast response high temperature pressure probe, with demonstrated use in liquid metals up to 255 °C (528 K), has been developed. Innovative packaging technologies have been applied to integrate a conventional piezoresistive silicon pressure sensor into the probe, without the need of an auxiliary water-cooling system. In situ static calibrations are used to verify the linearity of the pressure signal and the stability of the pressure sensitivity (0.5% standard deviation over 70 min at 255 °C). Dynamic calibration, completed in an air shock tube facility, yields the probe's natural frequency. This frequency, when corrected for probe operation in liquid tin, is found to be 100 kHz. The reliability and accuracy of the probe is assessed by mounting it in a tin droplet dispenser for use in an extreme ultraviolet light source. Droplet dispensers typically include an excitation mechanism, which can be based on the generation of acoustic pressure waves to impose a desired droplet frequency. The probe accuracy is verified by the comparison of pressure measurements with laser Doppler vibrometry measurements of the pressure generating structure. A reference pressure measurement, conducted at representative conditions, shows a complex frequency response, with peaks distributed over three orders of magnitude and maximum amplitude of 440 mbar. Time variance of the excitation mechanism due to thermal transients is studied by monitoring the pressure response during operation. Finally, the linearity of the excitation system, with respect to the excitation amplitude, is verified by response measurements. In conclusion, the developed probe is capable of characterizing the excitation mechanism of a liquid metal droplet dispenser. Additionally, real-time monitoring of the performance of the excitation system during long-term operation is possible.     

Total pressure fluctuations and two-phase flow turbulence in self-aerated stepped chute flows

Current knowledge in high-velocity self-aerated flows continues to rely upon physical modelling. Herein a miniature total pressure probe was successfully used in both clear-water and air-water flow regions of high-velocity open channel flows on a steep stepped channel. The measurements were conducted in a large size facility (θ=45°, h=0.1 m, W=0.985 m) and they were complemented by detailed clear-water and air-water flow measurements using a Prandtl-Pitot tube and dual-tip phase-detection probe respectively in both developing and fully-developed flow regions for Reynolds numbers within 3.3×10⁵ to 8.7×10⁵. Upstream of the inception point of free-surface aeration, the clear-water developing flow was characterised by a developing turbulent boundary layer and an ideal-flow region above. The boundary layer flow presented large total pressure fluctuations and turbulence intensities, with distributions of turbulence intensity close to intermediate roughness flow data sets: i.e., intermediate between d-type and k-type. The total pressure measurements were validated in the highly-aerated turbulent shear region, since the total pressure predictions based upon simultaneously-measured void fraction and velocity data agreed well with experimental results recorded by the total pressure probe. The results demonstrated the suitability of miniature total pressure probe in both monophase and two-phase flows. Both interfacial and water phase turbulence intensities were recorded. Present findings indicated that the turbulence intensity in the water phase was smaller than the interfacial turbulence intensity.     

Beta ratio, swirl and Reynolds number dependence of wall pressure in orifice flowmeters

Experimental work has been performed in an effort to gain a better understanding of the flow field inside orifice flowmeters and the pressure field generated on the walls of the pipe and orifice plate. As a part of a larger study, extensive wall pressure measurements have been made on the pipe wall from four pipe diameters upstream of the orifice plate to six pipe diameters downstream, as well as on both the upstream and downstream faces of the orifice plate. These measurements were performed for Reynolds numbers of 54 700; 91 100 and 122 800; for beta ratios of 0.50 and 0.75 with air as the working fluid. An adjustable swirl plate was installed, which was used to impart varying amounts of swirl into the flow upstream of the orifice plate. For each swirl case, Pitot and static pressure probes were used to characterize the upstream flow field while the pipe wall and orifice plate surface pressures were measured.     

Experimental and Numerical Studies in a Vortex Tube

The present investigation deals with the study of the internal flow phenomena of the counter flow type vortex tube using experimental testing and numerical simulation. Visualization was carried out using the surface tracing method, injecting dye on the vortex tube wall using a needle. Vortex tube is made of acrylic to visualize the surface particle tracing and the input air pressure was varied from 0.1 MPa to 0.3 MPa. The experimentally visualized results on the tube show that there is an apparent sudden changing of the trajectory on the vortex tube wall which was observed in every experimental test case. This may indicate the stagnation position of the vortex flow. The visualized stagnation position moves towards the vortex generator with increase in cold flow ratio and input pressure. Three-dimensional computational study is also conducted to obtain more detailed flow information in the vortex tube. Calculated total pressure, static pressure and total temperature distributions in the vortex tube were in good agreement with the experimental data. The computational particle trace on the vortex tube wall is very similar to that observed in experiments.     

An examination of suitability of multi-hole pressure probe technique for skin friction measurement in turbulent flow

The problems of misalignment to flow direction and the need to drill a tapping hole on a measurement surface to obtain total and static pressures make the use of Preston probe in skin friction measurement in a turbulent flow a cumbersome task. The suitability of a multi-hole pressure probe in a non-nulling mode to overcome these problems was, therefore, investigated. The near-wall effect on multi-hole pressure probe readings was examined both experimentally and theoretically. The results indicate that the presence of the wall had negligible overall effect. Experiments were carried out in a pipe, on a flat plate and on a swept forward facing step to simulate one-, two-, and three-dimensional turbulent flows. The skin friction coefficient determined using the multi-hole pressure probe was found to have good agreement with published data. Since the technique is based on similarity principle with probe diameter as a characteristic parameter, it is expected that the method would be effective with probe geometries of different sizes provided that they are small enough to be submerged in the boundary layer and that their calibration coefficients are accurately determined.     

气流声源稳态流场的PIV实验研究

对大功率调制气流声源的内流场开展了初步的实验研究,包括设计二维声源实验模型,基于单点静压和粒子图像测速（PIV）技术获取喷口下游喉道内的稳态流场数据。实验测得速度场分布和静压值变化趋势均与理论分析结果保持一致,表明采用的实验方案能够确定声源稳态流场特性。喉道内部以负压为主,同一截面上静压值基本相近,外壁面流动分离和近壁面高低压区域交替成为典型工况下声源内流场的重要特征。     

PSC-100型导叶式旋风管内的气相流动分析

采用五孔球探针对不同结构参数和操作参数下PSC-100型导叶式旋风管的流动参数进行了测量,得到旋风管内气相流场的三维速度和静压的分布情况。试验结果表明,切向速度在大部分分离空间沿径向更加趋近于等速流;轴向速度有明显的上下行流分界,且分界位置靠近边壁,沿轴向分界位置逐渐向边壁移动;径向速度的方向在绝大部分分离空间近壁处沿径向向外,中内区域沿径向向内;静压沿径向从边壁到中心逐渐降低。当改变结构参数时,导流锥的开缝面积比对流动参数中切向速度的影响最为显著,即导流锥开缝面积比越大,所对应流场的切向速度值越大,因而旋风管的旋转强度越大,分离效率越高。实验研究的结果为天然气净化用多管式旋风分离器的结构优化与工程设计提供了参考依据。     

脉冲爆震发动机引射器的实验研究

实验采用汽油为燃料,压缩空气为氧化剂,对多循环脉冲爆震发动机(PDE)引射器的性能参数进行了实验研究。研究的特性参数包括引射器的冲量、平均推力和引射空气量。实验结果表明引射系统可以利用排出爆震管的强激波所储存的能量使爆震管单独产生的平均推力增加,平均推力增益最高可达38%。爆震频率越高,引射空气量越大,当爆震频率为35Hz时引射比达4.62。     

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.     

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.     

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.     

Analysis of the impact of flow characteristics on the separation efficiency and pressure drop of a cyclone-type oil separator

The effects of flow structure on the separation efficiency and pressure drop in a cyclone-type oil separator were investigated via Reynolds-averaged Navier-Stokes (RANS) simulations and large eddy simulations (LES), and the results were compared with experiments. Compared with the RANS simulations, the LES results were more similar to the experimental data as they simulated the complex flow structure more realistically. Swirling flow with strong turbulent kinetic energy (TKE) at the top section hindered the flow of particles toward the separator wall. In addition, a decrease in tangential velocity along the wall at the bottom reduced the centrifugal force, resulting in a decreased separation efficiency as particles were able to flow directly toward the outlet. The LES also predicted the pressure drop slightly better than the RANS simulation did, due to increased pressure drop caused by collision of the flow with the helix and outlet tube, which led to the formation of vortical flow structures with strong TKE.

     

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。     

Fabrication and calibration of a sub-miniature 5-hole probe with embedded pressure sensors for use in extremely confined and complex flow areas in turbomachinery research facilities

Multi-hole pressure probes are often employed in experimental facilities to measure the three dimensional flow field due to their ability to simultaneously provide the distributions of the static and total pressures as well as the three components of the velocity vectors. In cases where these probes are employed in turbomachinery research facilities it is essential for them to be accurate, respond to local parameter disturbances quickly and exhibit a high flow angle spatial sensitivity. Thus, the physical dimensions of the probe must be as small as possible. In addition the small size of the probe reduces the flow blockage and the corresponding local disturbances of the flow, especially when it approaches the solid boundaries of the blade channels. The present study refers to the fabrication and calibration of a sub-miniature in dimensions 5-hole probe, for use in complex internal flow areas arising in turbomachinery research. In order to reduce the need for a longer sampling time as the size of the probe gets smaller, the length of the stem that transfers the pressure from the tip of the probe to the sensor has to be minimized. This effect was compensated by embedding the pressure sensors right at the end of the probe׳s stem. This minimizes the air volume and thus the oscillations inside the flexible connecting tubes that usually connect each port of the probe to its corresponding pressure sensor. The fabrication methodology of the probe and data acquisition system is extensively described, as well as the non-nulling method employed for the calibration. Furthermore, application of the probe on a reference configuration geometry often used in turbomachinery research is illustrated in order to validate the effectiveness and novel characteristics of the probe. The result is a construction and calibration technique that allows the relevant laboratories to build on their own such instruments that may cost several thousand dollars (or euros) when bought from the open market.     

Computational modeling of bubbly flows in differential pressure flow meters

This paper addresses bubbly flow modeling within Venturi tubes and nozzles using the two-fluid model. The effects of non-drag forces as virtual mass and the so-called “transversal forces” such as lift and wall lubrication are investigated in the context of the two-fluid model. As expected, the transversal forces have an important influence on void distribution as long as the virtual mass affects the pressure drop along the contraction, which is the main parameter for the flow rate measurement. Models for the virtual mass and lift forces were implemented via user routines in commercial computational fluid dynamics (CFD) software, as the models embedded within these packages, specifically for virtual mass, were found not to be adequate for the purpose of this study. The models are validated against results from the literature and pressure drop measurements along a Venturi tube, developed in this work. Additionally, some experimental visualizations were used to make a qualitative comparison with predicted void distribution.     

位移式超高压测量装置的设计研究

针对应变管压力传感器的不足,该文设计了一种位移式超高压测量装置,该测量装置的弹性体是半球封头与厚壁圆管的组合结构。工作时,弹性体将压力转换成位移,使用高精度位移传感器测量出弹性体的轴向位移,建立压力与位移的关系。该测量装置的工作范围和性能主要由弹性体的结构和材料决定,因此,对弹性体的结构、线性进行了有限元仿真和分析。最后通过实验测得静态性能。结果表明:该测量装置具有良好的线性,满足静态超高压测量需求。     

Static pressure recovery analysis in the vane island diffuser of a centrifugal pump

The overall performance of a vane-island type diffuser of a centrifugal pump model was obtained by means of directional probe traverses. These measurements were performed in an air model of a real hydraulic pump for five volume flow rates. Directional probe traverses are performed with a classical three-hole probe to cover most of the complete inlet section of the diffuser from hub to shroud and from pressure to suction side. Existing Particle image velocimetry (PIV) measurement results are also used to compare probe measurement results between the inlet and outlet throats of vane island diffuser at mid-span. Some assistance from already existing unsteady calculation, including leakage effects, is used to evaluate the numerical approach capability and to correctly define the mean initial conditions at impeller’s outlet section. Pressure recovery and the measured total pressure loss levels inside this particular vane diffuser geometry are then calculated. Detailed analysis of the flow structure at the inlet section of the vane island diffuser is presented to focus on pressure evolution inside the entire diffuser section for different flow rates. The combined effects of incidence angle and blockage distributions along hub to shroud direction are found to play an important role on loss distribution in such a diffuser.     

An experimental and numerical study on hydrodynamic characteristics of horizontal annular type water-air ejector

A water-driven annular type ejector loop is designed and constructed for air absorption. Fabricated ejector unit is horizontally installed in the loop, and annular water jet at the throat entrained atmospheric air through the circular pipe placed at the center of the ejector. The tested range of water flow rate is 160 L/min to 320 L/min and volumetric flow rate of water and air and local pressure are quantitatively measured using LabVIEW signal express program. For the quantitative measurement of bubble velocity, cinematic PIV technique using a high speed camera is adapted. In post processing, each bubble is used as seeding particles and ensemble averaged bubble velocity field at vertical plane of the ejector system is finally acquired. In the range of experiment, the bubble size distribution at downstream of the ejector seems to be quite uniform so that the flow can be classified as a homogeneous bubbly flow. In case of low range of water flow rate, the transition from bubbly flow to stratified flow occurs at the atmospheric outlet condition. As a comparative study, a numerical simulation on the same ejector shape is performed to understand the more detail hydrodynamic characteristics in the annular type ejector system. Homogeneous bubbly flow regime is used as default two-phase flow regime, and void fraction at the vertical plane of the ejector system is qualitatively compared with that of experiment. In volume flow rate comparison, numerical prediction agrees well with that of experiment where the homogeneous bubbly flow is maintained.     

Effect of the Pitot microtube diameter on pressure measurement in plane supersonic microjets

The article reports on results of estimating the Pitot tube diameter effect on the streamwise and lateral pressure distributions in plane supersonic air microjets. The study is aimed at obtaining reliable information on the microjet structure. The nozzles with the size of 22.3 × 2593 μm and 83.3 × 3823 μm are used in experiments. The supersonic flow from that nozzles is investigated by glass Pitot tubes in inner/outer diameters of 24/70 and 16/42 μm. Additional measurements are performed by a Pitot microtube 8 μm in outer diameter and ≈0.1 μm wall thickness. The value ranges for accuracy determination of supersonic jets main characteristics (shock cell sizes and supersonic core length) have been found.     

某防暴喷射管管内流场数值模拟

采用流固耦合的方法,基于COMSOL仿真平台对某防暴喷射管内部流场进行了数值模拟,分析了发射管结构和气室初始压强对管内冲击挤压流动过程的影响.结果表明:在气室初始压强为20MPa,战剂容量为10ml的情况下,发射管内径越小,管流阻力越小,活塞运动时间越短,战剂出口速度越小,能量利用率越高;增大气室初始压强能缩短管内流动...