离心叶轮中滑移系数的研究与评估

在离心叶轮中,影响叶片对气体做功能力的因素中滑移系数占有很大的比重.分析了离心叶轮中气体的理想流动和实际流动,阐述了滑移系数的概念、本质及国内外针对离心叶轮滑移系数的研究,比较了各个公式的精度以及使用范围,并在此基础上提出了加载规律和黏性对滑移系数的影响.最后通过数值试验进行了验证.     

Discharge coefficient for vertical sluice gate under submerged condition using contraction and energy loss coefficients

A novel method is suggested for the determination of flow discharge in vertical sluice gates with considerably small bias. First, in order to derive an equation for the discharge coefficient, energy-momentum equations are implemented to define the physical realization of the phenomenon. Afterward, the discharge coefficient is presented in terms of contraction and energy loss coefficients. Subsequently, discharge coefficient, contraction, and energy loss coefficients were determined through an implicit optimization technique on the data. Data analysis illustrated that there is a meaningful power relationship between the contraction and energy loss coefficients. Thereafter, dimensional analysis is performed and an explicit best-fit regression equation is developed for defining the energy loss coefficient. The obtained equations for contraction and energy loss coefficients were then used in the computation of the discharge coefficient and determination of the flow discharge in the vertical sluice gate. The performance of the developed approach is validated against the selected benchmarks existing in the literature.     

Effective parameters for calculating discharge coefficient of sluice gates

The present work demonstrates the characteristics of flow from sluice gates under free and submerged flow conditions using Energy and Momentum Equations (EMEs). The experimental data was used from the research works reported by different investigators to calibrate the proposed equations. An equation for estimation energy loss factor of sluice gate at free flow was presented and effect of this parameter on increasing discharge coefficient's accuracy was demonstrated. It was derived a theoretical equation for variations of sluice gate's discharge coefficient with relative opening and relative tailwater depth. Effects of energy loss factor on discharge coefficient and distinguishing limit were investigated. In this research the concepts of submergence limit of the gate and the submergence limit of hydraulic jump will be distinguished. By determining effective pressure on the gate and using EMEs, equations for variations of sluice gate's contraction coefficient with relative opening and relative submergence were presented. The result shows that at free flow condition, a minimum contraction coefficient obtained under a certain value of relative gate opening. At submerged flow condition, contraction coefficient would be either increased or decreased depending on the level of flow submergence. This paper carefully considered stage-discharge relationships for estimation gate discharge under free and submerged flow conditions.     

球阀流量系数的研究

针对球阀中液流流动情况提出了计算球阀收缩系数μ的简化模型及流量系数计算方法，并进行了实验分析。     

超声波气体流量计检测精度影响因素分析

在天然气的管道运输过程中,提高气体流量测量的精度是提高运输效率、避免安全事故发生的关键技术。利用流体力学仿真（CFD）方法建立组合双弯管及变径管道模型,定量计算修正系数,对双声道超声波流量计结构和安装位置对于管道内气体速度场的影响进行研究。通过仿真得出超声波流量计的最优声道位置,并结合实验验证了仿真结果的可信性。模拟结果表明,双弯管和变径管与超声波流量计的安装位置至少为10D才能保证流体充分流动;通过修正系数随雷诺数的变化情况得出双声道超声波流量计的最优声道位置为距管道截面中心0.25D处。研究结论对于不同性质气体的流量检测同样适用,为工业中气体运输检测精度的提高以及超声波流量计的优化提供了依据。     

空气压缩机模型级用于不同真实气体的气动性能研究

基于机器马赫数相等的相似变换准则,对不同真实气体工质同一离心压缩机模型级进行常温常压及高温高压下气动性能的数值研究。除了空气,选取的气体工质还包括二氧化碳和丙烯两个重介质以及一个轻介质甲烷。通过分析不同工质的物性和模型级气动性能变化规律,寻找影响不同工质模型级性能变化的主要因素。结果表明:在机器马赫数相等的条件下,工质远离临界区时,模型级内部流场受比热比影响较大,导致不同真实气体的级性能随比热比的变化而改变,流场内部流动损失及压力随比热比的增大而增大。当模型级进出口比热比变化较小时,比热比越大,级效率越低,压比越高,但能头系数变化较小;进出口比热比变化较大时,级性能变化比较大。     

Static Performance of Finite Hydrodynamic Journal Bearings Lubricated by Magnetic Fluids with Couple Stresses

Based upon the Stokes micro-continuum theory, the problem of lubrication of finite hydrodynamic journal bearing lubricated by magnetic fluids with couple stresses is investigated. By taking into account the couple stresses due to the microstructure additives and the magnetic effects due to the magnetization of the magnetic fluid, modified Reynolds equation is obtained. The effects of couple stresses are studied by defining the couple stress parameter L that can be considered as a measure of the chain length of the additive molecule. The magnetic effects of the magnetic fluid are investigated by the magnetic coefficient γ. Using the finite-difference technique and for different values of couple stress parameter and magnetic coefficient, the Reynolds equation is solved, and pressure distributions are obtained. The bearing static characteristics namely load carrying capacity, attitude angle, friction coefficient, and side leakage flow are determined. The results indicate that the influence of couple stresses and magnetic effects on the bearing characteristics are significantly apparent. It is concluded that fluids with couple stresses are better than Newtonian fluids. The improvement of the bearing characteristics is enhanced if the magnetic effects are present.     

Experimental and theoretical modeling of a quarter-circular gate flow

Gates are important hydraulic structures and used for flow measurement, water delivery, and water level regulation in open channels and irrigation networks. In this study, the quarter-circular gate is introduced and investigated. The cross section of this gate consists of a quarter circular arc and the lip angle of the gate equals to zero. Discharge coefficient, variation of downstream flow depth, and velocity distribution at opening section of gate were experimentally measured. Using potential flow theory supported by dimensional analysis, equations for discharge coefficient and velocity distribution at gate opening section of quarter-circular gate were derived and then validated using experimental data. The mean percentage error (MPE) of obtained equation for discharge coefficient of quarter-circular gate was calculated as 2.24%, indicating the high precision of the proposed theory. Based on obtained results, downstream flow depth of quarter-circular gate is uniform. Also, velocity distribution at gate opening section is nearly uniform. Discharge coefficient of quarter-circular gate was averagely obtained 55% larger than that of sluice gate. It was also obtained larger than that of radial gate. Elimination of contraction section at downstream of gate opening, which is the main source for energy loss and therefore discharge capacity reduction, is the main reason for larger discharge coefficient of quarter-circular gate.     

Frictional behaviour of non-Newtonian lubricants

This investigation is concerned with the prediction of the frictional behavior of non-Newtonian fluids in a statically loaded journal bearing. The pressure distribution, friction and bearing load capacity are obtained for various values of the flow behaviour index, n. For the pseudoplastic fluids (n<1) the load carrying capacity and the friction forces are decreased, while shear thickening fluids (n>1) exhibited increases in the friction forces and load. The coefficient of friction was found to decrease as the value of n is increased, provided the dimensionless load exceeded a certain value     

The consistency of pressure effects between three identical Coriolis flow meters

Coriolis flow meters are one of the most popular flow measurement technologies in the world today for high accuracy measurement of single-phase liquids, gases and even slurries. They are capable of measuring both mass and density directly and can also infer the volume flow. They can be installed in challenging process environments and have been successfully deployed with non-Newtonian fluids, high viscosity fluids, pulsating flows and even at extreme temperatures and pressures.However, it is known that operating most Coriolis flow meters at a pressure which differs from the original calibration pressure requires compensation else significant measurement errors will occur. Pressure compensation coefficients appear to vary by manufacturer, meter geometry and sensor material. Furthermore, the manufacturer published pressure compensation coefficients are not fully traceable. To date, there has not been sufficient research exploring the consistency of the pressure compensation for identical Coriolis flow meters.This paper presents the findings of a research conducted at the TÜV SÜD National Engineering Laboratory (NEL) Elevated Pressure and Temperature (EPAT) oil flow facility to investigate the pressure effect uniformity for matching Coriolis devices. The first stage of the experimental programme calibrated three identical DN80 Coriolis flow meters at a range of pressures with no pressure compensation applied. A pressure compensation coefficient was then derived from the data and the Coriolis meters were then calibrated at two alternative pressures to ascertain the robustness of the coefficients and whether the compensation could be extrapolated successfully.From the experimental results, it can be concluded that the pressure effect for the three DN80 Coriolis flow meters was extremely repeatable and consistent with a discrepancy of less than 0.025% between the devices at 80 bar. Whilst the mass flow was significantly affected by fluid pressure, the fluid density did not appear to be influenced. The pressure corrected results were also well within the manufacturer specification of ±0.1%.     

A study of the lubricating effectiveness of micropolar fluids in a dynamically loaded journal bearing (T1516)

The lubricating effectiveness of micropolar fluids in a dynamically loaded journal bearing is studied. On the basis of the theory of micropolar fluids, the modified Reynolds equation for dynamic loads is derived. Results from the numerical analysis indicated that the effects of micropolar fluids on the performance of a dynamically loaded journal bearing depend on the size of material characteristic length and the coupling number. It is shown, compared with Newtonian lubricants, that under a dynamic loading the micropolar lubricants produce an obvious increase in the oil film pressure and oil film thickness, but a decrease in the side leakage flow. It is also shown that the friction coefficient for a dynamically loaded journal bearing with micropolar fluids is in general higher than that of Newtonian fluids, which is not the same as the results for a steadily loaded journal bearing. Furthermore, a parametric study of flow and friction for different mass parameters keeping micropolar parameters fixed is undertaken. It is indicated that, with the increase of the mass parameters, the crank angles corresponding to the maximum flow are changed and the maximum friction coefficients are obviously decreased either for the Newtonian fluids or for the micropolar fluids.     

Deducing the stage-discharge relationship of rectangular broad and sharp-crested contraction devices

Flumes with a local contraction of the channel width are a common way for accurately measuring the flow discharge. In this paper, the outflow process of rectangular broad and sharp-crested contraction devices is modeled using the dimensional analysis and the incomplete self-similarity condition. The proposed theoretical stage-discharge relationship is tested using measurements available in the literature. The proposed power equation is characterized by a value of the exponent close to 1.5 and a coefficient depending on the contraction ratio. The proposed flow-measuring flumes are characterized by a good accuracy of the measured discharge (ranging from −2.71 to 3.28% for the broad-crested contraction device and in the range from −0.24 to 0.31% for the sharp-crested one). Even if both flume types have good accuracy of the measured discharge (less than the limit of ±5% suggested in the literature), the developed analysis demonstrated that the sharp-crested device is characterized by the lowest values of the errors in the estimate of discharge, and this result increases the interest of this device in practical applications. The advantage of the proposed approach is combining an accurate estimate of the flow discharge and working regardless of the discharge coefficient estimate.     

Further results on non-Newtonian power-law flows past a two-dimensional flat plate with finite length

The flow of a non-Newtonian, power-law fluid directed either tangentially or normally to a flat plate of finite length and infinite width (two-dimensional flow) is considered. The problem is investigated numerically using the code ANSYS FLUENT. This problem has been investigated in the past but only for shear-thinning fluids (n < 1). We extend the investigation for the case of shear-thinning, Newtonian and shear-thickening fluids, covering a wide range of Reynolds numbers (from very low to very high). For low Reynolds numbers and low power-law index (n < 0.6) the drag coefficient obeys the relationship c _D = A/Re, both for tangential and normal flow. Equations for the quantity A have been derived as functions of the power-law index. For normal flow, the drag coefficient tends to become independent of the power-law index, both for shear-thinning and shear-thickening fluids at high Reynolds numbers.     

Inertia effects in laminar radial flow of power law fluids

An approximate expression for the pressure distribution for the radial flow of a non-Newtonian fluid (power law) between two parallel disks is obtained by using the momentum and energy integral methods. It is shown that inertia has a significant effect on the pressure distribution especially for those fluids with a power law index, n 1.     

Rheological measurement of untreated sewage by straight tube

Sewage contains abundant low-grade heat energy, and recycling it using a heat pump system is an effective way to reduce carbon emissions. The particles in sewage will cause untreated sewage to exhibit non-Newtonian characteristics, and accurate rheological measurement is important for sewage transmission and distribution system design. The traditional rotary rheometer deforms, agglomerates, or breaks the solid particles in sewage, which affects the measurement results. Therefore, in this study, a horizontal tube rheological test bench was built for urban sewage. Constitutive equations and viscosity expressions of untreated and prepared urban sewage at different temperatures and particle concentrations were tested. The results show that untreated and prepared sewage conforms to the shear-thinning model of power-law fluids in non-Newtonian fluids even at particle wet mass concentration as low as 0.103%. The flow characteristic index n of sewage is unrelated to temperature, and its influence is mainly reflected in the consistency coefficient k. However, the sewage flow characteristic index n increases with a decrease in particle concentration. In the laminar flow range of 0.02–0.2 m/s, the flow resistance obtained by treating untreated sewage as a Newtonian fluid was approximately 1.36–1.99 times that of the non-Newtonian fluid model, which will result in a larger power system design and higher energy consumption. Under turbulent flow conditions, the drag coefficient of the Newtonian model was approximately 1.13 times that of the non-Newtonian model. This shows that when designing a sewage source heat pump system, the power-law fluid shear-thinning characteristics of untreated sewage must be fully considered, which helps reduce the calculated energy consumption of transportation.     

基于单V锥节流装置的湿气气液流量在线测量

提出采用两相质量流量系数对V锥节流装置湿气测量误差进行修正,试验研究洛克哈特-马蒂内利参数、气体密度弗鲁德数以及气液密度比对V锥节流装置两相质量流量系数的影响规律。V锥节流装置的节流比为0.55,试验介质为压缩空气和水,气液密度比为0.002 445~0.006 083,气体密度弗鲁德数为0.3~2.0,洛克哈特-马蒂内利参数为0.01~0.34。结果表明,两相流量系数随洛克哈特-马蒂内利参数增加而线性增大,同时还受气体密度弗鲁德数和气液密度比的影响。获得了两相质量流量系数与洛克哈特-马蒂内利参数、气体密度弗鲁德数和气液密度比的定量关系,建立湿气流量测量的半经验关联式。利用V锥节流装置前后锥体对湿气具有不同的差压响应特性,获得了其差异性的影响规律,建立单节流元件双差压的湿气气液流量双参数测量方程。在试验范围内,测得的气相质量流量相对误差小于±5.0%,平均误差为2.2%;液相质量流量相对误差小于±20.0%,平均误差为9.8%。该方法具有系统简单、成本低廉、精度较高的特点。     

An experimental apparatus measuring convective heat transfer coefficient from a heated fine wire traversing in nanofluids

Most of the previous convection experiments for nanofluids have been performed for internal tube flow with constant heat flux boundary condition. In contrast, a simple experimental apparatus measuring convective heat transfer coefficient from a heated wire to external nanofluids is proposed and its working principles are explained in detail. The convective heat transfer coefficient provided by the present system might be used as a useful indication justifying the adoption of prepared nanofluids as new efficient heat transfer fluids. Validation experiments by comparing convective heat transfer coefficients between the conventional correlation and measured values are carried out for base fluids. Also the effect of increased thermal conductivity of nano lubrication oil on the enhancement of convective heat transfer coefficient is investigated.     

Numerical analysis of journal bearings lubricated with micropolar fluids including thermal and cavitating effects

A numerical study of the non-Newtonian behavior for a finite journal bearing lubricated with micropolar fluids is undertaken considering both thermal and cavitating effects. The modified Reynolds equation and energy equation are derived based on Eringen's micropolar fluid theory. The solution to the modified Reynolds equation is determined using the Elord's cavitation algorithm. The effects of the size of material characteristic length and the coupling number on the thermohydrodynamic performance of a journal bearing are investigated. It is shown, compared with Newtonian fluids, that micropolar fluids exhibit the increase in load capacity and temperature, but the decrease in coefficient of friction and side leakage flow. It is also indicated that, in the full film region, micropolar fluids increase the values of non-dimensional density, while in the cavitated region, both micropolar fluids and Newtonian fluids yield the same values of the fractional film content.     

Analysis of Journal Bearing with Double-Layer Porous Lubricant Film: Influence of Surface Porous Layer Configuration

This article presents an analysis of a long journal bearing with a double-layer porous lubricant film using couple stress and Newtonian fluids. The porous layer with infinite permeability analyzed in this study simulates the surface layer. The Brinkman model was utilized to model the flow in the porous region. The effects of couple stresses were analyzed based on Stokes microcontinuum theory. A double-layer porous lubricant film configuration, with a low-permeability porous layer on top of a high-permeability bearing adherent porous layer, improved the journal bearing performance characteristics. A surface porous layered lubricant film configuration increased the load-carrying capacity and reduced the coefficient of friction in a journal bearing.     

Online rheological measurement of dilute liquid-solid two-phase flow with ultrasound Doppler technique

An online and non-invasive ultrasound Doppler based rheometric method is proposed to measure the flow parameters in a dilute liquid-solid two-phase flow and analyze its rheological behaviours. The flow rate is obtained by integrating the ultrasound Doppler velocity profiles through annuluses formed across the cross-sectional area of the pipe while the pressure drop is calculated by choosing suitable models that captures the working conditions of quasi-homogeneous and heterogeneous dilute liquid-solid flows. Wall shear rate and wall shear stress are obtained from the above measurements with the rheological measurement models established. An experimental platform is built to form polystyrene-water and sand-water liquid-solid two-phase fluids for tests. The proposed method has mean absolute errors of 2.53% and 3.49% in flow rate measurement and 3.67% and 5.87% in pressure measurement for polystyrene-water and sand-water fluids, respectively. The experimental results have shown that the rheological characteristics of both fluids fit well with the power law fluid model.