Flow resistance and its prediction methods in compound channels

A series of experiments was carried out in a large symmetric compound channel composed of a rough main channel and rough floodplains to investigate the resistance characteristics of inbank and overbank flows. The effective Manning, Darcy–Weisbach, Chezy coefficients and the relative Nikuradse roughness height were analyzed. Many different representative methods for predicting the composite roughness were systematically summarized. Besides the measured data, a vast number of laboratory data and field data for compound channels were collected and used to check the validity of these methods for different subsection divisions including the vertical, horizontal, diagonal and bisectional divisions. The computation showed that these methods resulted in big errors in assessing the composite roughness in compound channels, and the reasons were analyzed in detail. The error magnitude is related to the subsection divisions. The project supported by the Major State Basic Research and Development Program of China (973 Program) (2003CB415202) and the National Natural Science Foundation of China (50579040, 50579041). The English text was polished by Yunming Chen.     

Large-scale turbulence phenomena in compound rectangular channels

In this article we investigate turbulent flow of air through compound rectangular channels to experimentally investigate the turbulence phenomena in compound channels. Detailed experimental data of axial mean velocity, wall shear stresses, five of six Reynolds stresses, auto- and cross-spectral densities, and two-point space correlations were measured by hot-wire anemometry in 18 geometrical configurations.

The symmetry of the present flow appears to be better than that of previous measurements and the range of measurments is more extensive. The most interesting result is the existence of a quasi-periodic large-scale turbulence structure in most of the geometries investigated. This structure is stationary and independent of the axial position in the channel. It exists in any longitudinal slot or groove in a wall or a connecting gap between two flow channels, provided its depth is more than approximately twice its width. The frequency of this flow oscillation is determined by the geometry of the slot and is linearly dependent on the bulk velocity.     

内锥流量计流出系数预测方法研究

采用标准k-ε模型、RNG(Renormalization Group)k-ε模型、Realizable k-ε模型和Reynolds应力方程模型 RSM(Reynolds Stress Model) 对100 mm口径6种结构的内锥流量计内流场进行了数值模拟.在等效直径比β值为0.65的三种结构内锥流量计流出系数的仿真计算中,四种湍流模型计算结果与物理实验结果误差的平均值分别为4.19%,2.84%,2.88%和-0.822%;对β值为0.85的情况,各模型计算误差的平均值分别为11.8%,9.62%,9.30%和4.76%.研究结果表明,RSM模型在6种结构内锥流量计流出系数的预测中,计算精度较高,表现出了较好的性能,优于三种k-ε涡粘模型,更适于内锥流量计流场数值模拟与流出系数的预测.     

多梁式波形钢腹板工字钢组合梁荷载横向分布系数研究

为探讨多梁式波形钢腹板工字钢组合梁横向分布系数计算方法,同时考虑波形钢腹板抗扭刚度、剪切变形及钢混滑移效应,对传统的偏心压力法、修正偏心压力法及刚接梁法进行修正,并结合有限元模型通过一座典型的4主梁波形钢腹板工字钢组合梁桥对比分析了上述方法的适用性,最后基于参数分析研究了横隔板数量及刚度对其横向荷载分布系数的影响。结果表明,考虑剪切变形及滑移效应的刚接梁法得到的荷载横向分布系数与有限元值符合最好;当桥梁宽跨比小于2时,宜采用刚接梁法计算各主梁荷载横向分布系数,当宽跨比大于2时,宜采用更为简洁的修正偏心压力法进行计算;横隔板的设置可改善各主梁荷载横向均匀分布,但跨间横隔板间距和刚度对其荷载横向分布系数影响较小,实桥设计时可仅在端部及跨中位置布置横隔板,横隔板刚度及其余部位横隔板数量可根据结构稳定性要求进行布置。     

页岩气储层暂堵转向压裂直井段暂堵球运移特性研究

考虑附加质量力、相间阻力、Basset力、重力、浮力等力学条件,建立了暂堵球运移过程动量守恒模型,通过四阶龙格-库塔方法对其求解,并以长宁区块气井直井段为例进行研究.结果表明:在直井段,暂堵球呈现先加速后减速,最后匀速运动的规律,暂堵球加速度ab≤0阶段,暂堵球运移速度达到最大峰值;随着暂堵球直径、密度及排量增大,暂堵...     

静水中气泡上升运动及阻力系数研究

采用模型计算法与实验法结合的方式对静水中气泡上升运动行为进行研究。通过牛顿运动定律,基于不同物理模型,建立气泡在水中运动的微分方程;假设气泡在运动过程中的关键参数取值,推导小气泡在水中浮升过程中的气泡行为预测公式;针对不同流态下的气泡上升关键参数进行适应性分析和算例计算。通过设计气泡上升运动实验,对气泡上升运动公式进行适应性分析,修正关键参数的取值。据此提出一种小气泡上升运动规律的计算方法以及关键参数取值方式及参考区间。     

Study of the Effect of the Depth of the Cavity of a Braking Device on the Aerodynamic Drag of a Model in Transonic and Supersonic Flow

The flowfield and the aerodynamic drag of a model consisting of a pair of bodies (leading body a cylinder and trailing body a hollow cylinder) connected by a cylindrical bar along the axis of symmetry is experimentally investigated at Mach numbers ranging from 0.6 to 1.7. In the course of the experiments, the trailing body cavity depth and the connecting bar length were varied.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 186–192.Original Russian Text Copyright © 2005 by Pilyugin and Khlebnikov.