流量测量临界流文丘里喷嘴的进展

简介颁布国际标准ISO9300《临界流文丘里喷嘴测量气体流量》(1990年)，十余年来国际上对该流量计的研究情况。主要在以下几方面有显著的进展：雷诺数使用范围的拓宽；流量方程中系数的研究；小型音速喷嘴的开发应用；小型音速喷嘴组合方法的研究；绝对测量法的探索等。国际标准化组织正在为修订ISO9300进行准备工作。     

Hydraulics of free overfall in Δ-shaped channels

In this paper, two methods are presented to analyse the free overfall in δ-shaped (equilateral triangle-shaped) channels. First, the flow upstream of a free overfall from smooth horizontal or mildly sloping Δ-shaped channels is analysed theoretically to determine the end-depth-ratio (EDR), applying the momentum equation based on the Boussinesq approximation. Second, an alternate method for analysing free overfall in Δ-shaped channels is also presented where the flow over a free overfall in a Δ-shaped channel is simulated by that over a sharp-crested weir to calculate the EDR. The method of estimation of discharge from the known end depth is also presented for both the methods. These approaches eliminate the need of an experimentally determined pressure coefficient. Experiments are conducted to verify the results obtained from the present methods. Comparisons of the computed and experimental results are satisfactory     

Choke-free flow in trapezoidal channels with change in bed elevation

Solutions for choke-free flow in a trapezoidal channel, with rise in bed elevation that may occur with partial filling up of the channel bottom, are discussed. In this analysis, the side slopes of the channel are assumed to be the same before and after the transition. Considering smooth and gradual transition zones, equations of energy and continuity are solved for subcritical and supercritical upstream flow conditions to determine the maximum limiting rise in bed elevation. The ranges of the upstream flow depths are also obtained for the choke-free condition, using the continuity equation of the upstream flow. A list of symbols is given at the end of the paper     

Velocity and turbulence at a wing-wall abutment

Experimental investigation of the 3D turbulent flow field around a 45‡ wing-wall abutment, resting on a rough rigid bed, is reported. The experiment was conducted in a laboratory flume using the Acoustic Doppler Velocimeter (ADV). Profiles of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy and Reynolds stresses at different azimuthal planes are presented. Vector plots of flow fields at azimuthal and horizontal planes show the presence of a primary vortex associated with the downflow in the upstream side of the abutment and a wake vortex on the downstream side. The shear stresses acting on the bed around the abutment are estimated from the Reynolds stresses and velocity gradients. The data presented in this study would be useful to researchers for future development and comparison of theoretical models of flow fields around bridge abutments.     

Local scour at abutments: A review

Failure of bridges due to local scour has motivated many investigators to explore the causes of scouring and to predict the maximum scour depth at abutments. In this paper, a detailed review of the up-to-date work on scour at abutments is presented including all possible aspects, such as flow field, scouring process, parameters affecting scour depth, time-variation of scour and scour depth estimation formulae.     

临界流文丘里喷嘴流量计的原理与应用

提出了流出系数和临界流函数实用公式和图表对临界流文丘里喷嘴的实际应用能起到指导作用     

A critical note on histogram testing of data acquisition channels

Histogram testing is used to measure the transfer characteristic of a digitizer in order to quantify and to analyze its nonlinear behavior. In this paper it is shown that this method is very insensitive to the out-of-phase components of the digitizers' response to a sine wave excitation. This can lead to an underestimate of the nonlinear behavior of the digitizer     

柱塞式校准器检定临界流喷嘴的实验研究

介绍了一种采用标准柱塞结构的临界流喷嘴校准器的原理和组成.根据临界流喷嘴的流量特性建立了检定数学模型,同时建立工作腔气体状态方程,并进行分析.对该校准器工作腔的压力和温度进行了大量实验研究,结果表明,工作腔内气体的压力和温度在检定过程中能够保持稳定,有益于提高检定的精度和效率.利用该校准器进行临界流喷嘴背压比试验,调节被测喷嘴背压比,检测其实际流量,得到与理论曲线相一致的流量特性曲线,从而为临界流喷嘴的特性研究提供了一个良好的手段.     

A note on a plane creeping corner flow

Abstract

A simple method of similarity transformation is formulated to analyze a two‐dimensional creeping corner flow. By this peculiar transformation, governing equations for the plane velocity are reduced to a pair of ordinary differential equations. With a particular selection of appropriate boundary conditions, the field variables of velocity, pressure, vorticity, and stream function are obtained analytically. A special case with constant velocity at one boundary is explored. The salient characteristics of this example are used to compare with previous investigations. The present study shows that both approaches provide exactly the same solutions. A very interesting feature is that the velocity components in the coordinate system are independent of the radial direction.     

On solute dispersion from an elevated line source in an open-channel flow

The streamwise dispersion of contaminant molecules due to a turbulent shear flow over a gravel-bed surface is examined when the solute is released from an elevated line source. A finite-difference, implicit method is used to solve the unsteady turbulent convection-diffusion equation, employing a combined scheme of central and four-point upwind differences for the steady-state condition and the Alternating Direction Implicit (ADI) method for the unsteady equation. It is shown how the mixing of contaminant is effected by the mean velocity due to the `log-wake law' and the corresponding eddy-diffusivity, when the solute is released in terms of a -function. The results for the steady-state condition are compared with existing experimental data and some other numerical results. The results obtained by the present method are in much better agreement with the experimental data than those obtained by the previous solution scheme, when the `log-wake-law' and the corresponding eddy-diffusivity are used. Far from the source, the concentration increases with time (the rate of increase is rapid near the source), asymptotically approaching a steady state after a certain time; concentrations are about two thirds of those near the source. The behaviour of iso-concentration lines in the vertical plane is also studied.     

Internal waves in an elliptical channel

Abstract

Internal waves in open channels of various depths are studied, in this paper, and a wetted cross section with an elliptical bottom is considered. The frequencies of the first three sloshing modes of internal waves in two superposed fluids contained in an elliptical channel are calculated for various ratios of the depths of the two layers. Numerical solutions converge to analytical solutions based on the shallow water theory as the depth of the thin lower layer approaches zero. Also, solutions for the frequencies of the longitudinal modes of progressive internal waves in two superposed fluid layers contained in an elliptical channel are calculated for various ratios of the depths of the two layers and for two different wave numbers k.     

流式细胞仪样品流速及聚焦流测量方法研究

为提高流式细胞仪的探测分辨率和数据检测的稳定性,需要精确控制样品流速,并分析样品流速和鞘液流速对样品聚焦流的影响,可通过样品聚焦流直径和样品聚焦流在流动室流道中的相对位置来评价样品的聚焦状况。利用蠕动泵运动特点,设计了一种平均流量称重法测量样品流速的方法,并与微流量传感器测量结果作比较;采用最小二乘法线性拟合蠕动泵的控制电压和样品流速之间的函数关系,并采用显微成像法直接测量和分析样品流速和鞘液流速对样品聚焦流直径、偏离流动室流道中心线的距离的影响。实验结果显示,采用平均流量称重法与微流量传感器测得的样品流速的线性相关系数高达0.982 8;蠕动泵的样品流速与其控制电压的线性相关系数高于0.99,说明利用该线性关系可以实现样品流速的精确控制;采用的显微成像法能快速方便地测得样品聚焦流的直径及位置,为流式细胞仪样品流速、鞘液流速的调控以及液流器件组装精度的测试提供了指导方法。     

A note on the velocity of granular flow down a bumpy inclined plane

The velocity distribution of granular flow down a bumpy inclined plane is theoretically studied. The characteristic length scale of local transient cluster plays an important role in determining the flow rheology. After discussing the factors influencing the cluster size, we reproduce all observed velocity distributions successfully.This research was supported by the National Key Basic Research and Development Foundation of the Ministry of Science and Technology of China No. G2000048702.     

Effects of shear flow on long-ranged correlations,spinodal demixing kinetics,and the location of the critical point and cloud point

A derivation of an expression for the shear rate-dependent Ornstein Zernike structure factor is discussed, together with the resulting anomalous behavior of the turbidity. The predicted scaling behavior of the turbidity, comprising the effect of both temperature and shear rate, is in good agreement with experiments on binary fluids. Then initial spinodal decomposition is discussed, and an explicit expression for the time- and shear rate-dependent effective diffusion coefficient is derived, which shows all the typical characteristics of anisotropic light scattering patterns that are observed experimentally for binary fluids. Next it is shown that the spinodal is shifted linearly with the (bare) Peclet number for not too large Peclet numbers, whereas the cloud point is singularly displaced into the unstable region due to a shear now. This is in agreement with an experiment on a two-polymer/solvent mixture and binary fluid mixtures. It is argued that light scattering is useless to determine the location of the spinodal of a sheared system.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

模拟海深条件下提升阀流动特性的实验研究

水压传动技术应用于深海环境可以直接从海洋中吸水加压，高压水作功之后可以直接排入海洋，不需要水箱和回水管道，大大简化了系统，具有独特的优势。然而，在深海作业时，液压元件的工况同陆地相比有较大的差异，海深压力相当于在元件出口加了一个背压。文中用背压来模拟海水压力，对以水作介质时背压对提升阀口流量特性的影响进行了实验研究。研究结果表明，背压使得流量饱和更容易发生；有背压时的流量系数比没有背压时的流量系数大；当阀芯和阀座有叠合时，背压对阀口流量特性的影响比阀芯和阀座没有叠合时的影响大。     

A complex‐variable boundary element approach to fully developed flow and heat transfer in ducts of general cross‐section

The complex‐variable boundary element method (CVBEM) is used to analyse forced convection in cooling passages with general, convex cross‐sections. Quadratic spline interpolation is employed for the modelling of coupled velocity and temperature fields. The method is well‐suited for ducts with curved surfaces and high geometric aspect ratios. The method is illustrated for ducts with rounded rectangular, elliptical and rounded diamond cross‐sections. General correlations are presented for the fully developed Nusselt number and Moody friction factor, and the Hagenbach entrance region factor. Copyright © 1999 John Wiley & Sons, Ltd.     

Steady flow simulation in irrigation canals

A mathematical model is developed for the analysis of spatially varied steady flow in irrigation canals. The model accounts for canal seepage and effect of control structures at the upstream and downstream ends of the canal. Two computational methods developed to solve the spatially varied steady flow equations for the irrigation canals are presented here. The governing differential equations are solved iteratively using fourth order explicit Runge-Kutta method. The model results are verified with experimentally observed water surface profiles available in literature. The effects of bed seepage, canal condition and backwater curves on the discharge carrying capacity and variation of flow depth are studied through model application on a canal reach. It is found, that in most of the situations the backwater curves spread sufficiently upstream and significantly affect the performance of the control structure at the upstream end. In many situations, it may not even be possible to operate the canal at design discharges.     

钟形口流量管入口段速度型面研究

航空发动机试验中通常使用钟形口流量管对进气流量进行试验。在测量过程中,针对测点布置不准确造成测量结果不准确及测量成本增加的问题,开展了管内入口段测量截面上的速度分布情况研究。本文分析了钟形口流量管的测量原理以及湍流状态下管内气流的流动状态,研究了测量截面沿直径方向上速度的变化,建立了管内径向速度分布的数学模型,最终通过试验与仿真的方法对速度分布模型进行了分析与验证,为准确得到管内空气流量提供了一种基于速度分布模型的新方法,即通过试验测得流量管测量截面上少数点的数据信息得到管内速度分布模型,从而得到更准确的管内空气流量值。研究结果对进气流量的测量以及发动机性能的评定试验有重要意义。     

Analysis of transients in a canal network

A generalised formulation of the mathematical model developed for the analysis of transients in a canal network, under subcritical flow, with any realistic combination of control structures and their multiple operations, has been presented. The model accounts for a large variety of control structures such as weirs, gates, notches etc. discharging under different conditions, namely submerged and unsubmerged. A numerical scheme to compute and approximate steady state flow condition as the initial condition has also been presented. The model can handle complex situations that may arise from multiple gate operations. This has been demonstrated with a problem wherein the boundary conditions change from a gate discharge equation to an energy equation and back to a gate discharge equation. In such a situation the wave strikes a fixed gate and leads to large and rapid fluctuations in both discharge and depth. An erratum to this article is available at .