管道内差压驱动机器人相关流场数值模拟研究

管道内流场对机器人的驱动力是设计管内机器人外形尺寸的基本依据,本文用数值方法计算了管道内检测机器人所受的差压驱动力。在合理提出一些基本假设后,用一阶迎风和中心差分格式离散管道内检测机器人附近流场的控制方程,用SIMPLE算法求得了不同入口流速下机器人附近的流场分布,以及流场对机器人的驱动力。结果表明雷诺数为1875时,机器人下游流场变为湍流;当雷诺数为60000时,机器人下游流场变为非定常流,出现周期性流动;计算数据还表示驱动力只与管内平均流速有关而与运行压力无关。     

高速列车紊态外流场的数值模拟研究

高速列车是近地运行的细长、庞大物体,它的空气绕流问题有其特殊性,本文以不可压缩粘性流体的Navier-Stokes方程和k-ε两方程紊流模型为基础,采用有限元方法求解了高速列车三维紊态外流场,针对有限元法应用于流场计算时常出现的问题,采用分离式解法,非对称矩阵一维变带宽压缩存储及带宽极小化等方法,最大限度地降低计算存储量;并采用罚函数法,集中质量矩阵,缩减积分法,带参数迭代法以及 引入松弛因子等技术,提出了一套用有限元法计算非线性问题的求解方法,提高了收敛速度的计算严谨,计算方法和计算结果对列车空气动力学的深入研究有一定的帮助。     

Scour Hole Influence on Turbulent Flow Field around Complex Bridge Piers

Experimental results of detailed flow measurements using an Acoustic-Doppler Velocimeter (ADV) around a complex bridge pier (CBP) are presented. The pier consists of a column, a pile cap (PC) and a 2×4 pile group. The time-averaged velocities, turbulence intensities, and Reynolds stresses are studied and presented at different horizontal and vertical planes. Streamlines obtained from the velocity fields are used to show the complexity of the flow around the pier. It is shown that the main feature of the flow responsible for the entrainment of the bed sediments is a contracted (pressurized) flow below the PC toward the piles. A deflected flow around the PC and a strong down-flow along its sides are observed and have been measured. It is shown that these flow patterns also cause sediment entrainment. Vortex flow behind the PC and amplification of turbulence intensity along its sides near the downstream region can be other reasons for the scour hole (SH) development. Turbulence intensities and Reynolds shear stresses are presented and discussed. A comparison is made between the flow field measured with the equilibrium SH and that measured on the fixed flat-bed. The results show that the flow field around the PC is considerably influenced by the development of the SH. The extent of the wake region at the rear of the PC is about 1.4 times larger for the fixed bed (FB) than for the scoured bed (SB). Moreover, the size of the core of high turbulent kinetic energy K, as well as the maximum values of K behind the column for the FB case is larger than that of the SB case. When a scour hole develops, the flow below the PC around the piles is considered to be the main cause of the scour. This is the first time that these observations about the flow and turbulence field around a complex bridge pier are reported and analyzed. In addition to improving the understanding of the flow structure, the present detailed measurements can also be used for benchmarking and verification of numerical models.     

侧柱与串列双柱绕流之间的干扰

本文给出了关于串列双柱与创柱间流动干扰的实验研究结果。当三个圆柱排成等边三角形并靠得很近时，由于三圆柱间强烈的缝隙流动，大大地改变了绕流其中的串列双圆柱的流态。特别，当三圆柱中心距等于二倍圆柱直径时，在串列双柱的前、后柱之间形成了强烈的偏斜的缝隙流，出现了独特的压力分布以及要比单柱高出三倍以上的旋涡脱落频率。     

Remark on Single Exponential Bound of the Vorticity Gradient for the Two-Dimensional Euler Flow Around a Corner

In this paper, we consider the two–dimensional Euler flow under a simple symmetry condition, with hyperbolic structure in a unit square \({D = \{(x_1,x_2):0 < x_1+x_2 < \sqrt{2},0 < -x_1+x_2 < \sqrt{2}\}}\). It is shown that the Lipschitz estimate of the vorticity on the boundary is at most a single exponential growth near the stagnation point.     

High Velocity Flow in and Around Long Perforation Tunnels

In oil industries, wells are mostly cased and perforated rather than completing the producing formation as open-hole. This study concentrates on the steady-state flow behaviour of a single-phase fluid in and around perforated completion tunnels (up to 50 inches long) including inertial effects (Non-Darcy flow). It is shown that the pressure drop inside long perforated tunnels under high flow velocity conditions is negligible compared to that around the perforated region within the porous medium. The results also indicate that the impact of perforation parameters varies with increasing fluid velocity but approaches an asymptotic value at very high flow velocity. The perforation length is the most important parameter whereas perforation radius, rock and fluid properties have little impact on the perforation performance.     

单柱单锥型液—液旋流分离管内流场的LDV诊断

应用二维激光多普勒仪（ＬＤＶ）对一种单柱单锥型液－液旋流分离管内流场进行了测量,考察了流量、溢流比、压力比和气芯等参数对流场的影响。测量结果表明：切向速度分布呈典型的Ｒａｎｋｉｎｅ涡结构,沿轴向衰减很少,表明所用锥角是合适的;因该旋流管的水力直径较大,切向速度的总体水平较低,由于对了离特性带来了不利影响。此外,没有观察到切向速度分布的的双峰分布现象。轴向速度的总体水平较低,尤其是在锥形管的上游更为     

Measurement and Modelling of Gas Condensate Flow Around Rock Perforation

In the petroleum production industry wells are mostly cased and perforated in the producing formation. Perforation characteristics such as size, length, number of perforation tunnels and their arrangements as well as fluid and rock properties determine fluid flow behaviour in the wellbore region, hence, well productivity. Flow of gas and condensate around a perforation tunnel (including the damaged zone) has been studied by performing steady-state core experiments and simulating the results numerically, using a finite element modelling approach. The model allows for the changes in fluid properties and accounts for the coupling of the two phases and the inertial effect using a fractional flow based correlation. The results indicated that different sets of thickness-permeability (h−k) values obtained from matching single-phase flow performance could be assigned to the damaged zone around perforation to represent the two-phase flow performance. The status of the tip of the perforation for two extreme cases of totally closed and fully open was investigated and found to have a minimal effect on the performance of the system.     

Large Eddy Simulations and Experiments of Flow Around Finite-Height Cylinders

The paper presents experimental and numerical results for the flow around a surface-mounted circular cylinder at the two height-to-diameter ratios of 2.5 and 5. The Reynolds number based on approach flow velocity and cylinder diameter is 43,000 and 22,000 for these two cases and the boundary layer of the approach flow has a thickness of about 10% of the cylinder height. The experiments comprise both flow visualizations with dye and laser Doppler velocimeter measurements of all mean velocity and fluctuation components. The numerical study is performed by an elaborate large eddy simulation on a staggered Cartesian grid using the immersed boundary method. The instantaneous flow behaviour including the shedding is analysed with information based on animations. For the long cylinder alternating shedding is found to occur over most of the height while for the shorter cylinder the shedding is observed mainly near the ground where it is also mostly alternating but intermittently also symmetrical. The mean-flow behaviour is analysed with the aid of streamlines and contour plots of mean-velocity and fluctuation components in various planes and a detailed comparison of LES and LDV results is provided, showing generally good agreement. The LES with very fine resolution near the free end allow a detailed study of the complex flow in this region with owl-face topology on the end wall previously observed in experiments. Behind the cylinder, the longitudinal recirculation region, the downstream development of tip vortices and the emergence of trailing vortices further downstream are analysed. The sum of the results, together with those from previous studies that were reviewed extensively, provides a comprehensive picture of the very complex flow behaviour.     

Supersonic Flow Around a V-Shaped Wing at Incidence and Yaw

A solution of the problem of the flow around a V-wing with supersonic leading edges at low angles of attack and yaw is obtained within the framework of the linear theory. Possible patterns of nonsymmetric flow around the wing are analyzed as functions of the wing geometry and the freestream velocity direction, and the ranges of angles of attack and yaw on which these patterns are realized are established. Some previously undescribed shock wave configurations are found to exist in the wing-induced conical flows.     

聚碳酸酯板裂纹顶端的弹塑性研究

本文研究了聚碳酸酯板的延性断裂特征;提出了修正的强化Dugdale条带屈服模型,并用实验-数值计算混合法确定了强化弹塑性材料裂纹顶端附近的应力场参数.实验测定结果与理论等色线,计算的裂纹前沿塑性区长度相符合.由此,验证了所提出的修正强化Dugdale条带屈服模型的合理性.     

Three Dimensional Numerical Flow Simulation Around Parallel Rectangular Cylinders

Noises of flow around parallel rectangular cylinders are likely to be caused by wind flow. According to the wind tunnel experiment, it is known that there are three kinds of special noises. Two kinds of noises occur when the wind comes from a perpendicular direction to the cylinders. These noises are caused by the vortex excited oscillation. Another noise occurs when the wind comes from an inclined direction to the cylinders. This noise is very high frequency, and its mechanism is not clear. Therefore in this study, the three dimensional numerical flow simulation is performed to clarify the high frequency noise of flow around parallel rectangular cylinders.     

Flow Around a Crack in a Porous Matrix and Related Problems

The equations governing plane steady-state flow in heterogeneous porous body containing cracks are presented first. Then, a general transformation lemma is presented which allows extending a particular solution obtained for a given flow problem to another configuration with different geometry, behaviour and boundary conditions. An existing potential solution in terms of discharges along the cracks, established by Liolios and Exadaktylos (J Solids Struct 43:3960–3982, 2006) for non-intersecting cracks in isotropic matrix, is extended to intersecting cracks in anisotropic matrix. The basic problem of a single straight crack in an infinite body submitted to a pressure gradient at infinity is then investigated and a closed-form solution is presented for the case of void cracks (infinite conductivity), as well as a semi-analytical solution for the case of cracks with Poiseuille type conductivity. These solutions, derived first for an isotropic matrix, are then extended to anisotropic matrices using the general transformation lemma. Finally, using the solution obtained for a single crack, a closed-form estimation of the effective permeability of micro-cracked porous materials with weak crack density is derived from a self-consistent upscaling scheme.     

Experimental Study of Supersonic Flow Around Truncated Cones at Incidence

Results of an experimental study of supersonic flow around truncated cones with cone half-angles of 20, 30, and 40°, performed at Mach numbers M = 2, 3, and 4 within the range of angles of attack up to 20°, are presented. A relationship is established between the emergence of an internal shock wave and the character of pressure distribution along the generatrix of the truncated cone. It is shown that the known boundaries of regimes obtained for axisymmetric flow around sharp and blunt cones can be used to predict flow regimes in the vertical plane of symmetry of the truncated cone at incidence.     

Steady Flow of a Navier-Stokes Fluid Around a Rotating Obstacle

Let ? be a body immersed in a Navier-Stokes liquid ? that fills the whole space. Assume that ? rotates with prescribed constant angular velocity ω. We show that if the magnitude of ω is not “too large”, there exists one and only one corresponding steady motion of ? such that the velocity field v(x) and its gradient grad?v(x) decay like |x|^?1 and |x|^?2, respectively. Moreover, the pressure field p(x) and its gradient grad?p(x) decay like |x|^?2 and |x|^?3, respectively. These solutions are “physically reasonable” in the sense of Finn. In particular, they are unique and satisfy the energy equation. This result is relevant to several applications, including sedimentation of heavy particles in a viscous liquid.     

Predictive Pore-Scale Modeling of Single and Multiphase Flow

We show how to predict flow properties for a variety of rocks using pore-scale modeling with geologically realistic networks. The pore space is represented by a topologically disordered lattice of pores connected by throats that have angular cross-sections. We successfully predict single-phase non-Newtonian rheology, and two and three-phase relative permeability for water-wet media. The pore size distribution of the network can be tuned to match capillary pressure data when a network representation of the system of interest is unavailable. The aim of this work is not simply to match experiments, but to use easily acquired data to estimate difficult to measure properties and to predict trends in data for different rock types or displacement sequences.     

Numerical Investigation of Active Flow Control Around a Generic Truck A-Pillar

Large Eddy Simulations (LES) are conducted to study the actuated flow field around a bluff body. The model is a simplified section of a truck. The aim of the work is to model the separation of the flow acting at the front rounded corners, the so called A-pillars, and to minimize the separation of the flow by means of Zero Net Mass Flux synthetic jets. LES data show the interaction of the flow main structures, the separation mechanism and the effects of the actuation on the flow field. The flow is post processed using modal and frequency decompositions. Relevant results in terms of drag reduction were observed for the actuated flow. The principle flow mechanisms are discussed and an optimal actuation frequency, in terms of induced fluctuations and drag reduction, is identified.     

Third-Order Upwind Finite Element Simulation of Flow Around Two Square Cylinders

The aerodynamic behavior of the flow around two square cylinders is presented on the basis of the numerical simulation of the incompressible Navier-Stokes equations using a third-order upwind finite element scheme. It is well known that flow patterns around the two square cylinders are more complicated than flow patterns around one square cylinder because of interference between the Karman vortices behind the two square cylinders. In this paper, two kinds of cylinder arrangements are chosen as computational models. One type is that of two square cylinders arranged vertically to the direction of a uniform flow, and the other is arranged horizontally to the direction of a uniform flow.