Two‐dimensional prediction of time dependent,turbulent flow around a square cylinder confined in a channel

This paper presents two‐dimensional and unsteady RANS computations of time dependent, periodic, turbulent flow around a square block. Two turbulence models are used: the Launder–Sharma low‐Reynolds number k–ε model and a non‐linear extension sensitive to the anisotropy of turbulence. The Reynolds number based on the free stream velocity and obstacle side is Re=2.2×10⁴. The present numerical results have been obtained using a finite volume code that solves the governing equations in a vertical plane, located at the lateral mid‐point of the channel. The pressure field is obtained with the SIMPLE algorithm. A bounded version of the third‐order QUICK scheme is used for the convective terms. Comparisons of the numerical results with the experimental data indicate that a preliminary steady solution of the governing equations using the linear k–ε does not lead to correct flow field predictions in the wake region downstream of the square cylinder. Consequently, the time derivatives of dependent variables are included in the transport equations and are discretized using the second‐order Crank–Nicolson scheme. The unsteady computations using the linear and non‐linear k–ε models significantly improve the velocity field predictions. However, the linear k–ε shows a number of predictive deficiencies, even in unsteady flow computations, especially in the prediction of the turbulence field. The introduction of a non‐linear k–ε model brings the two‐dimensional unsteady predictions of the time‐averaged velocity and turbulence fields and also the predicted values of the global parameters such as the Strouhal number and the drag coefficient to close agreement with the data. Copyright © 2009 John Wiley & Sons, Ltd.     

椭圆柱电缆单位长度的自感计算

利用复数坐标系z上的儒可夫斯基变换,计算长直椭圆柱电缆单位长度的自感,并对结果进行讨论.     

液压油缸缓冲装置动态过程仿计算机真分析

本文从液压回路中,采取了措施进行油缸缓冲,首先用功率键合图法,建立了缓冲回路的数学模型,然后用四阶龙格-库塔法定步长(0.0001s),在长城机上进行了计算仿真,并绘出了相应的曲线,找出了缓冲效果与运动部件原速度、运动部件质量等因素的关系,为改善缓冲回路的动态特性提供了理论依据。     

Fluid forces on a square cylinder in oscillating flows with non‐zero‐mean velocities

The unsteady forces on a square cylinder in sinusoidally oscillating flows with non‐zero‐mean velocities are investigated numerically by using a weakly compressible‐flow method with three‐dimensional large eddy simulations. The major parameters in the analysis are Keulegan–Carpenter number (KC) and the ratio between the amplitude and the mean velocities of the approaching flow (A_R). By varying the values of KC and A_R the resulting drag and lift of the cylinders are analyzed systematically at two selected approaching‐flow attack angles (0 and 22.5^°). In the case of the non‐zero attack angle, results show that both the drag and lift histories can be adequately described by Morison equations. However, Morison equations fail to correctly describing the lift history as the attack angle is zero. In addition, when the ratio of A_R/KC is near the Strouhal number of the bluff‐body flow, the resulting drag is promoted due to the occurrence of resonance. Based on the results of systematic analyses, finally, the mean and inertia force coefficients at the two selected attack angles are presented as functions of KC and A_R based on the Morison relationships. Copyright © 2008 John Wiley & Sons, Ltd.     

也谈液体温度计液柱的表观尺寸——兼与舒幼生先生商榷

指出《物理学难题集萃》一书中对该问题解释的缺陷，并给出圆柱形液体温度计液柱表观尺寸的几种确定方法。     

Flow past a cylinder: shear layer instability and drag crisis

Flow past a circular cylinder for Re=100 to 10⁷ is studied numerically by solving the unsteady incompressible two‐dimensional Navier–Stokes equations via a stabilized finite element formulation. It is well known that beyond Re ～ 200 the flow develops significant three‐dimensional features. Therefore, two‐dimensional computations are expected to fall well short of predicting the flow accurately at high Re. It is fairly well accepted that the shear layer instability is primarily a two‐dimensional phenomenon. The frequency of the shear layer vortices, from the present computations, agree quite well with the Re^0.67 variation observed by other researchers from experimental measurements. The main objective of this paper is to investigate a possible relationship between the drag crisis (sudden loss of drag at Re ～ 2 × 10⁵) and the instability of the separated shear layer. As Re is increased the transition point of shear layer, beyond which it is unstable, moves upstream. At the critical Reynolds number the transition point is located very close to the point of flow separation. As a result, the shear layer eddies cause mixing of the flow in the boundary layer. This energizes the boundary layer and leads to its reattachment. The delay in flow separation is associated with narrowing of wake, increase in Reynolds shear stress near the shoulder of the cylinder and a significant reduction in the drag and base suction coefficients. The spatial and temporal power spectra for the kinetic energy of the Re=10⁶ flow are computed. As in two‐dimensional isotropic turbulence, E(k) varies as k^?5/3 for wavenumbers higher than energy injection scale and as k^?3 for lower wavenumbers. The present computations suggest that the shear layer vortices play a major role in the transition of boundary layer from laminar to turbulent state. Copyright © 2004 John Wiley & Sons, Ltd.     

多级油缸及其设计计算

多级油缸可以做到柱塞总行程等于油缸长度的二至四倍.因此具有广阔的应用前景。本文以作者自行设计研制成功的双级油缸为例,详细提供了这种油缸的技术参数、结构及设计计算方法.为保证运动平稳性,作者在油缸内装有流量控制阀,并推导给出了其计算公式。 上述理论亦可应用于三级、四级油缸的设计计算。     

新型螺栓球柱节点静力承载性能试验研究

在传统网架螺栓球节点的基础上,研发了一种可用于无檩网架的新型节点——螺栓球柱节点.进行了13个螺栓球柱节点的承载力试验.试验结果表明,螺栓球柱节点主要有圆柱筒壁压扁破坏、圆柱筒壁冲切破坏、螺栓拔出破坏、焊缝拉裂破坏等4种破坏模式;在压力和拉力荷载作用下,圆柱筒壁主要承受环向应力;设置加劲肋可以较大幅度地提高节点承载力和增强节点刚度.     

水平旋转圆筒表面局部对流换热特性实验

以旋转圆筒型热工设备为研究对象,设计了大直径水平旋转圆筒实验装置.利用微型热电偶,测量了高格拉晓夫数(1×108)下圆筒表面各个方位角处空气热边界层的温度分布.实验结果表明:旋转对圆筒表面0°和180°处的局部对流传热系数的影响有明显差异;旋转使得圆筒表面温度和局部对流传热系数的分布不均匀,尤其当旋转雷诺数大于临界雷诺数时的影响尤为突出.确定了临界雷诺数的准则数关联式.