近壁圆柱绕流积沙线的形成机理研究

应用粒子图像测速(PIV)系统进行近壁圆柱绕流实验,探讨壁面积沙现象的机理.分别在两个动量损失厚度雷诺数1 092和796下,对两个不同直径的圆柱,取间隙比(圆柱与壁面间的距离与圆柱直径之比)0到1.5中的12个值进行实验,总结了不同情况下积沙线的形成特点.研究结果表明:积沙线形成的可能原因是由于圆柱对平板壁面边界层的影响,使得边界层流动在圆柱下游一到两倍圆柱直径的平板壁面处发生壁面分离,在分离区域流体速度减小,并且产生附着涡,流体运动挟带到此处的粒子速度减小,发生沉积而形成.     

Direct numerical simulation on the particle flow in the wake of circular cylinder

The spectral-element approach is used to simulate the gas-solid two-phase flow behind of the circular cylinder. Based on the method of a high accuracy calculation for the gas phase flow, the particle dynamic field is put into practice. Two key influence factors, Stokes number and Reynolds number, are investigated. The simulation results give a clear pattern of the physical characteristics of gas-particle flow. Due to the construction properties of the eddies in the wake of the circular cylinder, the suction is the main dispersion mechanism of particles near to the centric axis. This effect can make the small particle sucted to the near wake of the circular cylinder. The particle dispersion is also induced by the pressure gradient which is caused by the strong velocity gradient of gas phase.     

水下圆柱体带空泡轴向绕流研究

研究了水下圆柱体带空泡轴向绕流问题.用数值方法研究了不同长细比圆柱体水下运动产生空泡的形态及圆柱体水下带空泡绕流的阻力特性,圆柱体绕流空泡形态以及阻力系数数值计算结果与试验对比,符合较好.圆柱体长细比对空泡形态影响可以忽略.随长细比增大:空化数较高时,阻力系数先减小后增大;空化数较小时,其阻力系数基本保持不变.小空化数条件下,给定长细比,空化数越小,阻力系数越小.     

二维圆柱层流绕流及其控制数值模拟

采用有限体积法求解二维N-S方程,通过改变时间、空间计算参数,对雷诺数100的二维圆柱非定常流场进行了数值模拟,将所得结果与实验数据以及已有的计算结果进行了对比.并对在尾部多个位置加入不同长度阻隔板控制流动的圆柱流场进行了考察.结果发现:在合适的位置放置阻隔板,可以有效抑制尾迹中涡脱落的形成.     

应用粒子图像速度场仪测试圆柱绕流涡的结构

利用粒子图像速度场仪（PIV）的2帧互相关技术,在风洞中测量雷诺数为500的圆柱绕流.通过展示一个涡的产生、发展及脱落的连续瞬时速度矢量场、流线图、速度量级等势线图和涡量等势线图,分析圆柱后涡系发展及涡量输运规律.     

Effect of Mach number on transonic flow past a circular cylinder

The effect of Mach number on transonic flow past a circular cylinder is investigated numerically for the free-stream Mach number M∞ from 0.85 to 0.98 and the Reynolds number 2×10^5 based on the diameter of the cylinder. The work provides an insight into several salient features, including unsteady and quasi-steady flow state, formation of local supersonic zone, and evolution of turbulent shear layer. Results show that there exist two flow states dependent of a critical Mach number Mcr around 0.9. One is an unsteady flow state characterized by moving shock waves interacting with the turbulent flow in the near region of the cylinder for M∞〈Mcr, and the other is a quasi-steady flow state with nearly stationary shock waves formed in the near wake for M∞〉Mcrs, suppressing vortex shedding from the cylin- der. Some flow behaviors in the unsteady and quasi-steady flow states are revealed. From time evolu- tion of flow structures, local supersonic zones are identified in the wake and generated by two typical processes, i.e. reverse flow behind the cylinder and shed vortices in the near wake. The convective Mach number Mc of turbulent shear layers shed from the cylinder is identified nearly as Mc〈I in the unsteady flow regime and Mc〉I in the quasi-steady flow regime, resulting in different evolutions of the shear layers.     

尾部喷射对流向振荡柱体尾流旋涡脱落的抑制

强迫振荡柱体绕流旋涡脱落的抑制具有重要工程意义,但比静止柱体尾流的抑制更加困难,乍前这方面的研究很少．本文采用尾部喷射方法对流向振荡圆柱尾流旋涡脱落进行抑制实验,雷诺娄Re=V∞D／慌围为2700-9800,柱体振荡幅值A／D=O．2,柱体振荡频率范围feD／V∞=0-0．36,其中亿为来沥速度,D为柱体直径．沿圆柱母线开一个与圆柱等长、宽度为h／D=O．015的缝隙,用于喷射空气．喷射麦度比W％范围为0-18,相应的流量比hVb／DV∞范围为0-0．27．风洞中的烟线显示和热线测量结果表明当喷射速度比Vb／比（或hVblDV∞）介于其下临界值和上临界值之间时,振荡柱体两侧的尾流旋涡脱落被辛效抑制．发现在非锁频和锁频两种状态下均能抑制旋涡脱落．在振频fe／V∞和喷射速度比W亿（曼hVb／DV∞）组成的平面坐标系内找出了有效抑制旋涡脱落的区域,研究了有效区域随雷诺数的变化和喷身角对抑制效果的影响,并探讨了旋涡脱落抑制机理．     

剪切层区域旋涡空化的发生机理

为研究高速水流中旋涡空化的形成机理 ,用高速摄影和录像的方法观察了发生在中空射流阀内部流场的空化现象 ,采用数值模拟的方法计算了阀内部非定常粘性流场。发现流场中空化的产生与流动分离以及所伴随的剪切层区域的非定常旋涡运动有关。旋涡空化水流中有两种空穴 ,即空化泡与空化旋涡。在剪切层非定常旋涡从流动分离点产生的过程中 ,旋涡形成区域的压力进一步降低 ,在空化条件下产生大量的空泡 ,部分空泡被旋涡所包容 ,从而形成空化旋涡     

数值分析串列双圆柱绕流

为研究不可压缩流动中二维的串列双圆柱中不同间距对圆柱间相互作用和尾流特征的影响,选取间距比L/D(L为两圆柱中心间的距离,D为圆柱直径)为2、3、4共3个间距进行了数值分析.计算均在Re=200的非定常条件下进行.计算了圆柱的升阻力系数、尾涡脱落频率等描述绕流问题的主要参量.并与参考文献的数值结果比较,验证了用FLUENT分析的有效性.     

圆柱绕流水动力学特性的数值模拟

应用计算流体动力学软件FLUENT对低雷诺数(Re)(Re≤300)下圆柱绕流问题进行数值模拟。采用分区结构化网格及层流模型求解不可压缩Navier-Stokes方程,在未施加任何扰动的条件下获得了圆柱绕流2种特殊的绕流场,系统分析了壁面压力系数、平均阻力系数、脉动阻力、升力系数及旋涡脱落频率等水动力学特性参数随Re数变化的规律,结果与实验研究吻合较好。     

用速度-涡量方法解具有表面抽吸的圆柱绕流问题

用有限差分法计算了不可压缩粘性流体绕具有表面抽吸圆柱的流动，控制方程采用涡量－速度形式的N－S方程，并引入对数有坐标变换，以使近壁处的网格加密，其中涡量输运方程采用二步R－K方法求解，速度泊松方程采用LSOR方法求解，并对速度进行了无散修正，计算表明合理选择抽吸的位置与强度，可有效减少阻力和升力，得到较好的流动控制效果。     

有限流道内低雷诺数二维圆柱绕流数值模拟

为揭示尾迹流场特性及其演化规律,采用多块辐射型网格,以计算流体力学软件FLUENT为平台,对有限流道内低雷诺数二维圆柱绕流进行数值模拟,讨论压力速度耦合算法、压力离散格式和动量方程离散格式对模拟结果的影响。研究结果表明:动量方程离散格式对数值模拟误差的形成起主要作用,较佳数值模拟算法为SIMPLEC压力速度耦合、二阶压力离散和QUICK动量方程离散的组合。尾迹流场中静压在沿轴向2.6～12倍流道宽度范围内波动较显著;并且随着流速增大,轴向压降最大点越靠近圆柱,径向静压幅度变化越大。     

Open-loop and optimal control of cylinder wake via electromagnetic fields

The experimental and numerical investigations on electromagnetic control of cylinder wake have been performed in this paper. Experiments were conducted in a rotating annular tank filled with a low-conducting electrolyte. A cylinder with an electromagnetic actuator mounted on the surface was placed into the electrolyte. Force measurements have been carried out by strain gages attached to a fixed beam to which the hydrofoil is suspended and flow fields are visualized by dye markers. Based on the Navier-Stokes equations considering the electromagnetic body force, i.e. Lorentz force, in the exponential-polar coordinates, the numerical investigations were carried out by means of an Alternative-Direction Implicit algorithm and a Fast Fourier Transform algorithm. Experimental results have shown the same tendency with the numerical results. For the constant Lorentz forces, called open-loop control, the vortex shedding was fully suppressed. Meanwhile, the weak street disappeared and the drag force was reduced. Based on the Navier-Stokes equations, an adjoint-based ensemble optimization of control algorithms was developed and adjoint equations in the exponential-polar coordinates were derived. The equations were solved by numerical algorithm as mentioned above. The evolutions of the flow field in the control process were discussed according to the calculated variable optimal interaction parameters.     

聚焦波浪对直立圆柱作用的试验研究

为研究聚焦波浪对直立圆柱墩的作用情况,根据波的传播原理,采用JONSWAP谱生成不同参数下的聚焦波浪,用波峰波谷聚焦相加减的方法分析出聚焦波浪对直立圆柱墩的二阶绕射作用强于一阶波浪的绕射作用.波浪涌高数据统计分析表明:波浪涌高随波陡及结构物相对尺度的增大而增大;圆柱周围不同受浪角度的涌高也是变化的.     

Numerical Simulation of Uniform Flow past an In-Line Oscillating Circular Cylinder

IntroductionOscillation of cylinders in the in- line or cross- flowdirection relative to an incident flow is a commonoccurrence in industry. Understanding vortex-induced vibrations is of great importance in thedesign of a variety of offshore engineeringstructures and nuclear plant components,forexample,heat- exchangers. To understand thebehavior of this complex interactive vibrationsystem,a number of researchers have examinedthe somewhat simpler and more tractable problemof circular cylinder f…     

The stratification phenomena in the thermal and solutal fields of double-diffusive convection in a circular cylinder

Natural convection due to spatial variations of fluid density is of fundamental importance in many scientific and engineering problems. In the past, investigators always pay attention to convection driven by thermal buoyancy force induced by temperature g…     

二维平行剪切层中声扰动下不稳定波与声波的解析求解研究

以Lilley方程为基础,对二维平行剪切层的不稳定性,以及剪切层中声波的激发与传播的问题进行了研究,求解了某剪切层的不稳定波的激发频率范围。对扰动频率ω=76 rad/s,核心区平均流马赫数Ma=0.756的情况,分别计算了剪切层中扰动声源本身的声传播以及由扰动激发出的不稳定波引起的附加声波。求解途径主要借助于傅立叶变换、格林函数构造和复数域上的数值积分。通过对Agarwal等提出的关于这一问题的解析求解方法的仔细分析,指出了其方法中所存在的一些数学缺陷,并给出了改正后的解析方法与计算结果。     

波流作用下大尺度圆柱周围局部冲刷深度简化数值模型

利用数模研究了波流共同作用下大尺度孤立圆柱周围的局部冲刷问题．该数模包括波浪场模型、流场模型、剪应力模型和冲淤形态模型．在数值计算中,通过分别求解缓坡方程和浅水环流方程得到波浪场和流场的分布情况,据此计算出水质点的底流速,得到底床剪切应力场的分布情况．可通过底面剪应力与泥沙起动应力的比较来调节底床的地形．计算了不同条件下孤立圆柱附近的局部冲刷情况,据此研究了波高、流速对局部冲刷的影响,发现最大冲刷深度随流速、波高的增大而增长．数模采用有限元方法,结果比较合理．     

稀薄气体中高超速圆柱绕流仿真研究

高速尤其是高超音速飞行是航空航天发展的主流方向.目前,70 km以上高超音速飞行器的需求越来越大.当飞行高度达到或超过70 km时,稀薄效应明显,此时连续介质假设失效,传统的连续流体运动方程(NS方程)和相应的CFD方法已经失效.利用连续流体运动方程(NS方程)和直接模拟蒙特卡洛方法(DSMC),对四个典型Kn(Kn分别为0.001、0.01、0.1和1)下的圆柱绕流进行了计算.分析比较发现,随着Kn的增大,流场中的激波间断结构变弱变粗,甚至消失,圆柱后方的分离区也逐渐变小直到消失.     

相交柱锥表面展开图的计算机绘制

根据曲面到平面的等距变换原理，运用可展曲面及其曲面上的截交线或相贯线变换到平面上的方法，使曲面展开变得更为简捷、精确，且更有利于计算机辅助几何设计中建立曲面展开的数学模型和合理的算法，尤其对开展精度要求高的曲面展开更为有利。通过对轴线相交的圆柱体和圆锥体数学模型的研究，建立了展开曲线方程，用VBA语言结合Atutomation技术编制了通用的计算机程序，将展开图在AutoCAD2000上加以绘制，实现了任意大小的圆柱与圆锥展开图的参数化CAD，从而在理论上开发了面向对象的参数化设计系统，并介绍了具体实现的方法、过程。在实际工程中，对计算机在相贯件下料中的应用，具有快速、准确、修改方便的特点。