Revisit the Pitot static tubes in the standards

A Pitot tube is a popular device used for the measurements of flow fields. To control the accuracy of the Pitot tube coefficient, the international standard organization (ISO), the American Society for Testing and Materials (ASTM), and the Japanese Industrial Standards (JIS) issued guidelines that recommended the shape and working conditions of these devices. However, many Pitot tubes on the market do not follow these guidelines. In the present study, various types of Pitot tubes in the market were tested at the National Metrology Institute of Japan (NMIJ) to determine the effects of the geometry and flow characteristics. The results revealed certain limitations in the existing ISO and JIS standards, specifically with regard to the recommended design parameters of the AMCA Pitot tube, the reference coefficient value for the JIS Pitot tube, and the redefinition and limitation of Reynolds numbers pertaining to Pitot tube working conditions.     

Large eddy simulation on the flow characteristics of an argon thermal plasma jet

Large eddy simulations based on the CFD software OpenFOAM have been used to study the effect of Reynolds number and turbulence intensity on the flow and mixing characteristics of an argon thermal plasma jet.Detailed analysis was carried out with respect to four aspects:the average flow field,the instantaneous flow field,turbulence statistical characteristics and the self-similarity.It was shown that for the argon thermal plasma jet with low Reynolds number,increasing the turbulence intensity will increase the turbulent transport mechanism in the mixing layer rather than in the jet axis,leading to the faster development of turbulence.The effect of the turbulent transport mechanism increases with increasing Reynolds number.However,the characteristics of flow and mixing are not affected by turbulence intensity for high Reynolds number situations.It was also found that the mean axial velocity and mean temperature in the axis of the turbulent thermal plasma jet satisfy the self-similarity aspects downstream.In addition,decay constant K is 1.25,which is much smaller than that(5.7-6.1)of the turbulent cold gas jet and has nothing to do with the Reynolds number or turbulence intensity in the jet inlet.     

液压阻尼孔的宽温度范围流动特性试验研究

研制一种适合对各种液压孔口或缝隙进行高低温流体力学试验的新型试验装置，运用该装置对具有不同几何参数的液压阻尼孔进行在-50~80℃宽温度范围内的流动特性试验，研究以普通抗磨液压油HM46和低温抗凝减振器油TITAN SAF 5045为工质及其温度变化时对液压阻尼孔流量-压力特性曲线、幂指数和流量系数的影响，研究表明，在低温条件下，液压阻尼孔的流量系数均因油液黏度增大、流动性变差而呈线性下降的趋势，从宏观上看，HM46通过液压阻尼孔时的流动稳定性较差，其对应流量系数的下降幅度明显大于TITAN SAF 5045对应的下降幅度，厚壁小孔流量系数的下降幅度明显大于薄壁小孔对应的下降幅度。研究所获得的新型试验装置、试验数据分析方法和具体理论公式为深入研究和优化现代液压元件在宽温度范围内的动态性能提供新型试验平台与理论基础。     

Heat and mass transfer analysis of combined convection in a horizontal rectangle

In this study, the heat and mass transfer of combined free and forced convection in the horizontal rectangle is explored. The governing equations together with the boundary conditions are solved numerically by using the finite volume method. The innovative idea in this study is to appropriately modify the Semi-Implicit Method for Pressure-Linked Equations algorithm and thereby, the numerical solutions of the flow variables such as the temperature and the concentration in addition to the components of velocity and the pressure are computed. The Richardson numbers (Ri) for distinct gases and liquids are calculated for different Rayleigh numbers at low (Re = 50) and high (Re = 5000) Reynolds numbers. The dimensionless parameters, such as the Reynolds number (Re), the Prandtl number (Pr), and the Schmidt number (Sc) are appropriately chosen to calculate the Richardson numbers. Consequently, combined free and forced convection effects are analyzed. Furthermore, the heat and mass transfer aspect for distinct gases and liquids is critically examined using empirical correlations. The accuracy and the validation of these results are ensured owing to the solutions obtained from correlations being advised in this study and those are existing in the literature.     

表面形貌对粗糙接触界面流体润滑特性的影响

为探究不同表面形貌对粗糙接触界面液体润滑特性的影响，基于有限差分法结合雷诺方程和膜厚方程，研究阶梯形貌、波纹形貌、随机形貌和峡谷形貌4种不同粗糙接触界面液体润滑时的载荷分布及规律。研究发现：4种粗糙表面的三维载荷分布规律都与其表面形貌相对应，在波“峰”处载荷大，摩擦力随载荷的增大而增大，在波“谷”载荷小，摩擦力随载荷减小而减小；4种粗糙表面的载荷随表面展开面积比的变化趋势却有所不同；随表面展开面积比的增大，阶梯形貌表面的载荷呈线性增大，波纹形貌表面的载荷基本不变，随机分布形貌表面的载荷呈增大趋势，峡谷形貌表面的载荷呈先增大后减小的变化趋势。研究结果可以进一步补充现有表面形貌表征和流体润滑等相关研究理论。     

Qualification of an ultrasonic flow meter as a transfer standard for measurements at Reynolds numbers up to 4×106 between NMIJ and PTB

The quality of any laboratory intercomparison depends to a large extent on the performance of the used flow meter. To find a flow meter that is capable of reaching a reproducibility better than 0.05% requires bounding all involved influence quantities down to the required level. The present paper describes the efforts performed while qualifying a time-of-flight ultrasonic flow meter as a transfer standard. It was determined that the most relevant influence quantity besides the flow profile within the bulk flow is the effect caused by the transducer pockets in the meter body. By taking advantage of a specially designed window chamber, it was possible to determine the magnitude of the errors introduced by the transducer pockets and to define, based on the findings, a procedure to perform a bilateral comparison between the hot water calibration facilities of the Physikalisch-Technische Bundesanstalt and the National Institute of Advanced Industrial Science and Technology. The results of the bilateral comparison are presented.     

Effect of vegetative bed on flow structure through a pool-riffle morphology

Natural habitats are created and developed through pool-riffle sequences in rivers, while vegetation cover could play a critical role in the sediment transfer and its quantity and quality. In this study, the effect of vegetation cover on the flow structure in a pool-riffle sequence is investigated in a laboratory flume under bed formation to compare with non-vegetated cover. In this context, instantaneous point velocities were measured by ADV to determine averaged velocity, shear velocity, root mean square velocity, friction factor, Reynolds shear stress and turbulence intensities. Results showed that the vegetation cover increases the thickness of the wall law. Meanwhile, the length of the flow separation zone in the vegetated bedform is more than in the non-vegetated bedform. Variation in roughness coefficients may cause a new boundary layer in which local flow velocities decrease. In both cases (vegetated and non-vegetated bedforms), the momentum is mostly transferred by ejection and sweep phenomena between flow and bedform.     

雷诺方程的数值计算方法概述

作为流体力学中的基本公式,雷诺方程的数值求解一直是流体润滑领域研究的重要方向之一。以雷诺方程的基本形式为基础,分别介绍有限差分法、有限元法和有限体积法求解雷诺方程的过程,讨论各自的特点及存在的问题;介绍多重网格法同上述方法结合在求解雷诺方程中的应用,指出多重网格法在求解雷诺方程的高效性方面有了很大程度的突破,但在求解精度上并未有显著改善;讨论等几何分析方法在求解雷诺方程上的应用,指出等几何分析方法求解雷诺方程具有较高的效率和求解精度,但仍存在如样条基函数的不可插值性和IGA在雷诺方程求解方面的普适性等问题,探讨IGA的研究方向,如针对特定雷诺方程引入适于IGA的新型样条表征求解空间、修改IGA理论与雷诺方程的离散模式引入新型边界条件加载模式等;因数值求解雷诺方程时在边界处理、复杂求解域等问题上仍没有一个稳定适用面广的方法,建议可尝试联合IGA与多重网格法来求解雷诺方程,以进一步提高求解效率和精度。     

微机械槽板结构空气压膜阻尼的修正雷诺方程

推导出了一个适用于槽板结构压膜空气阻尼的微分方程.该方程与传统雷诺方程的区别是在雷诺方程的左边增加了一个用以表示气体从槽流出所引起的阻尼效应的修正项,并考虑了槽中有限气流通道长度的端头修正.在适当的边界条件下,利用此方程可以求解槽板压膜阻尼的压强分布、阻尼力和阻尼力系数.该槽板结构压膜空气阻尼的微分方程对槽板的厚度和横向尺度没有限制,为分析有限尺寸和有限厚度槽板的压膜空气阻尼提供了一个有用的方法.