串列静子叶片流动机理研究

提高级负荷水平一直是压气机气动设计领域不断追求的目标。串列叶片可以突破常规布局气动负荷的限制，且具有良好的工程应用前景。为了探索串列叶片三维流动机理及前后排相互影响机制，利用数值模拟方法对来流马赫数为0.8的串列静子叶片近端壁流动特性展开研究，分析了前后排相互影响机制，主要是针对前/后排叶片单排工作与串列条件下进行对比。通过研究表明，以后排叶片势作用、缝隙射流、尾迹扩散为代表的典型流动现象显著地影响了前后排叶片的扩压过程，进而影响了气动负荷沿流向的分配及端壁损失，串列静子近端壁的气动设计需要考虑前后排相互干涉的影响。     

宽高比为0.62的矩形柱绕流特性研究

为研究高雷诺数Re=19000下宽高比临界值R=0.62时矩形柱流场及气动特性,基于计算流体力学(Computational Fluid Dynamic,CFD)方法,采用基于动态亚格子模型的大涡模拟(Large Eddy Simulation,LES)对均匀来流下绕流情况进行仿真计算.首先进行网格无关性验证,并针对基...     

高速列车受电弓气动噪声分析与降噪研究

随着列车速度的大幅提升,气动噪声问题愈发凸显。受电弓噪声在整车噪声中占较高位置,为研究高速列车受电弓气动噪声特性,通过Lighthill声学理论的宽频噪声模型对高速列车气动噪声源进行识别,利用定常SST k-w湍流方法分析高速列车受电弓的流场特性;基于大涡模拟与FW-H声学比拟理论计算高速列车受电弓远场气动噪声。数值算例结果表明,受电弓部位的碳滑板、弓头为受电弓主要噪声源;以轨道中心线为对称线,远场气动噪声监测点的声压级及频谱特性表现出较高的对称性;在同一列车运行速度下,监测点声压级随离轨道中心线距离增大而减小,列车以不同速度运行时,其声压级降低的幅值相差较小;高速列车远场气动噪声为宽频噪声,主要能量集中在500Hz~5000Hz。提出一种射流降噪方法,在350km/h速度下,监测点总声压级值降低了15.2dB。     

典型工况下回转体流噪声特性实验对比探究

研究潜艇流水孔阻力及噪声影响,针对对艇体流噪声特性的影响,根据回转体声辐射以及声绕射理论,对水下航行器回转体模型的光体模型、底部进水孔模型、纵缝模型以及全孔模型进行了流噪声数值仿真。针对三种不同的来流速度研究四组模型流噪声的速度特性。结果表明,四组模型之间噪声级的从高到低依次为全孔模型、纵缝模型、底部进水孔模型以及光体模型,并与水洞实验数据相比较,结果相吻合,为水下航行器流水孔流噪声的研究提供了参考。     

串列双索气弹模型的风洞试验研究

为研究斜拉桥串列拉索或悬索桥无吊杆串列主缆在风荷载作用下的相互干扰情况,通过自行设计的拉索试验装置,对两串列拉索进行了一系列的气弹模型风洞试验.试验得到索间距W/D在5.85～20变化(W为拉索中心距,D为拉索直径),风偏角在-90°～90°范围内变化时上下游索的一些响应特性.试验观测到了明显的尾流驰振现象,且试验结果表明索间距与风偏角的变化对串列拉索是否出现尾流驰振都有明显的影响.在发生尾流驰振时,以下游索面外的振动为主,且其临界风速随索间距W/D变小而降低;在同一索间距下,0°风偏角为最不利状态,且负风偏角比正风偏角更容易发生尾流驰振.     

圆柱单自由度和双自由度涡激振动特性研究

对圆柱绕流的涡激振动过程进行了数值模拟,研究了单、双自由度下涡激振动的力学特性、振幅特性、频谱特性,探讨了单、双自由度的适用条件.结果表明,单自由度条件下,随着约化速度的增加,阻力系数时均值先增大后减小,升力系数幅值先增大后减小再增大,且进入和离开“锁定”区间时二者均会产生波动.双自由度条件下,横向与流向无量纲振幅均随雷诺数的增大先增大后减小.低质量比时,流向振动的影响不可忽略,而高质量比时,可忽略流向振动的影响.     

圆柱单自由度和双自由度涡激振动特性研究

对圆柱绕流的涡激振动过程进行了数值模拟，研究了单、双自由度下涡激振动的力学特性、振幅特性、频谱特性，探讨了单、双自由度的适用条件。结果表明，单自由度条件下，随着约化速度的增加，阻力系数时均值先增大后减小，升力系数幅值先增大后减小再增大，且进入和离开“锁定”区间时二者均会产生波动。双自由度条件下，横向与流向无量纲振幅均随雷诺数的增大先增大后减小。低质量比时，流向振动的影响不可忽略，而高质量比时，可忽略流向振动的影响。     

带狭缝圆柱钝体流量测量特性研究

涡街流量计的流量特性与旋涡发生体的形状和几何尺寸密切相关,本文提出了一种新型的带狭缝圆柱发生体结构并应用于涡街流量计。理论分析表明狭缝可以看作是一个反馈通道,可有效加快旋涡脱落并增强旋涡强度。在内径为50mm的管道中进行实验,采集不同流量下带狭缝圆柱与梯形柱绕流产生的涡街信号,重点讨论带狭缝圆柱的小流量测量性能。实验表明,与梯形柱相比,带狭缝圆柱涡街信号更强,信噪比高,雷诺数测量范围可低至9.5?103,斯特劳哈尔数线性度更好。理论分析与实验结果表明,带狭缝圆柱具有较好的流量测量特性,可应用于涡街流量计。     

基于仿真与实测的列车远场气动噪声分析

随着高速列车气动噪声诱发的铁路沿线噪声污染问题变得日益明显,需对高速铁路诱发的远场噪声特性进行研究。基于Lighthill声学理论,应用LES大涡模拟和FW-H声学模型对高速列车整车的气动噪声进行数值模拟,实测高速列车以300 km/h运行时的通过噪声,将仿真与实测进行对比分析。高速列车诱发的远场气动噪声是宽频带噪声,能量主要集中在200~1500 Hz的中低频带范围内。实测与仿真的噪声声压级频谱分析具有相似的变化趋势,但声压级数值不同;由于实测噪声数据不仅包括气动噪声,还包括轮轨、集电系统噪声等,所以实测数据普遍大于仿真结果。通过对比分析验证了仿真结果的科学性,为数值模拟方法研究高速列车气动噪声问题提供了科学依据。     

一种有效的格子Boltzmann方法格点判断法

绕流问题中若物体边界不规则会给格子Boltzmann方法中离散边界的格点类型判断以及后续边界处理带来一定的困难.本文提出了简单的三角形不包含算法来有效判断不规则离散边界点的格点类型.针对离散边界,通过改进虚拟平衡态分布函数插值法中的虚拟速度,提高了格子Boltzmann方法在边界处的数值稳定性和精度.通过对经典的二维圆柱,方柱和椭圆柱绕流问题的数值模拟,验证了本文方法的有效性.     

Numerical simulation of the flow around rows of cylinders

Two-dimensional, laminar, unsteady, water flow around cylinder arrays of unequal sizes was simulated using FLUENT™ at Reynolds numbers below 150 (based on the free-stream velocity and first row cylinder diameter). The flow pattern through two rows of inline cylinders showed incomplete vortex shedding behind the first row at a separation distance less than 2d. Karman vortices were not formed and a near-stagnant separated flow region appeared between the aligned cylinders. Cylinders in staggered arrangements shed Karman vortices regardless of the separation between the two rows. This research has shed light on the detailed flow through paper machine forming fabrics.     

流场中沿轴向运动圆柱的附加质量计算

分别计算理想流体和黏性流体中沿轴向运动圆柱的附加质量.基于相对运动原理得出在无限流体域中不同长细比圆柱的附加质量,验证附加质量与流体黏性无关的这一结论,并发现长细比越大,附加质量因数越小.利用动网格技术的数值模拟结果表明:圆管中沿轴向运动圆柱的附加质量随管径比减小而增大,且流体的流动形态会对物体的附加质量产生一定的影响.以长细比和管径比为参数给出无限和有限流体域中圆柱附加质量与相应参变量的拟合函数.     

Numerical prediction of aerodynamic characteristics of prismatic cylinder by finite element method with Spalart–Allmaras turbulence model

Aerodynamic characteristic of prismatic cylinders is numerically investigated by using finite element method with Spalart–Allmaras turbulence model. The developed model is verified against the available experimental and numerical results for turbulent flow past a square cylinder. The flow behaviors for prismatic cylinders with different section-shapes are compared in terms of instantaneous and time-averaged streamlines. The trends of aerodynamic quantities, including drag and lift forces and Strouhal number with the change of the section-shape are in reasonable agreement with the existing experimental results. The results show that the fluctuating pressure is more sensitive to the change of the afterbody shape.     

Diffusioosmosis of electrolyte solutions in fibrous porous media

An analytical study is presented for the diffusioosmotic flow of an electrolyte solution in the fibrous medium constructed by an ordered array of parallel charged circular cylinders at the steady state. The prescribed electrolyte concentration gradient is constant but can be oriented arbitrarily with respect to the axes of the cylinders. The electric double layer surrounding each cylinder may have an arbitrary thickness relative to the radius of the cylinder. A unit cell model which allows for the overlap of the double layers of adjacent cylinders is employed to account for the effect of fibers on each other. The electrostatic potential distribution in the fluid phase of a cell is obtained by solving the linearized Poisson–Boltzmann equation, which applies to the case of low surface potential of the cylinders. The macroscopic electric field induced by the imposed electrolyte concentration gradient through the fluid phase in a cell is determined as a function of the radial position. A closed-form formula for the fluid velocity profile of the electrolyte solution due to the combination of electroosmotic and chemiosmotic contributions as a function of the porosity of the array of cylinders correct to the second order of their surface charge density or zeta potential is derived as the solution of a modified Navier–Stokes equation. The diffusioosmotic velocity can have more than one reversal in direction over a small range of the zeta potential. For a given electrolyte concentration gradient in a cell, the fluid flow rate does not necessarily increase with an increase in the electrokinetic radius of the cylinder, which is the cylinder radius divided by the Debye screening length. The effect of the radial distribution of the induced axial electric field in the double layer on the diffusioosmotic flow is found to be of dominant significance in most practical situations.     

Numerical study of interference between simple-shape bodies in hypersonic flows

Hypersonic rarefied-gas flows near two side-by-side plates and cylinders, toroidal balloon, plate and cylinder over a plane surface, and plate behind a cylinder in argon, nitrogen, oxygen, and carbon dioxide have been studied numerically using the direct simulation Monte-Carlo technique under the transition flow conditions at Knudsen numbers from 0.004 to 10. Strong influences of the geometrical factor (the ratio of a distance between bodies to a body length) and the Knudsen number on the flow structure about the bodies (shock-wave shapes, the configuration of subsonic flow zones), skin friction, pressure distribution, lift, and drag have been found.     

Flow-induced forces on two circular cylinders in proximity

Flow-induced forces on two nearby circular cylinders of equal diameter immersed in the cross flow at Re = 100 were numerically studied. We consider all possible arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle of the line connecting the cylinder centers with respect to the direction of the main flow. It turns out that significant changes in the characteristics of flow-induced forces are noticed depending on how the two circular cylinders are positioned, resulting in quantitative changes of force coefficients on both cylinders. Collecting all the numerical results obtained, we propose contour diagrams for mean force coefficients and rms values of force coefficient fluctuations for each of the two cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate flow-induced forces on two circular cylinders of equal diameter arbitrarily positioned in physical space with respect to the main flow direction.     

Flow patterns past two circular cylinders in proximity

Flow patterns past two nearby circular cylinders of equal diameter immersed in the cross-flow at low Reynolds numbers (Re ? 160), were numerically studied using an immersed boundary method. We considered all possible arrangements of the two cylinders in terms of the distance between the two cylinders and the inclination angle of the line connecting the cylinder centers with respect to the direction of the main flow. Ten distinct flow patterns were identified in total based on vorticity contours and streamlines, which are Steady, Near-Steady, Base-Bleed, Biased-Base-Bleed, Shear-Layer-Reattachment, Induced-Separation, Vortex-Impingement, Flip-Flopping, Modulated Periodic, and Synchronized-Vortex-Shedding. Collecting all the numerical results obtained, we propose a general flow-pattern diagram for each Re, and a contour diagram on vortex-shedding frequency for each cylinder at Re = 100. The perfect symmetry implied in the geometrical configuration allows one to use these diagrams to identify flow pattern and vortex-shedding frequencies in the presence of two circular cylinders of equal diameter arbitrarily positioned in physical space with respect to the main-flow direction.     

Variational multiscale large-eddy simulations of the flow past a circular cylinder: Reynolds number effects

Variational multiscale large-eddy simulations (VMS–LES) of the flow around a circular cylinder are carried out at different Reynolds numbers in the subcritical regime, viz. Re = 3900, 10,000 and 20,000, based on the cylinder diameter. A mixed finite-element/finite-volume discretization on unstructured grids is used. The separation between the largest and the smallest resolved scales is obtained through a variational projection operator and finite-volume cell agglomeration. The WALE subgrid scale model is used to account for the effects of the unresolved scales; in the VMS approach, it is only added to the smallest resolved ones. The capability of this methodology to accurately predict the aerodynamic forces acting on the cylinder and in capturing the flow features are evaluated for the different Reynolds numbers considered. The sensitivity of the results to different simulation parameters, viz. agglomeration level and numerical viscosity, is also investigated at Re = 20,000.     

Creeping motion of a cylinder through incompressible fluid bounded by a coaxial closed cylinder

The finite element method based on the Galerkin process is used to study the translation of a cylinder through fluid occupying the space between it and a co-axial cylindrical container under incompressible creeping flow conditions. The resistance force on the inner cylinder is calculated for the case of cylinders with diameters equal to their lengths, at the instant when their centroids are coincident. These resistance forces are compared with those for concentric spheres having equal radii or surface areas or volumes to the cylinders. The resistance force is also determined for the more general case when the inner cylinder approaches the end of the container for a range of aspect ratios (both cylinders having the same aspect ratio). The ratio of the pressure drag to the wall friction is also studied.     

High-order accurate simulation of low-Mach laminar flow past two side-by-side cylinders using spectral difference method

This paper reports development of a two-dimensional solver for compressible viscous flow using spectral difference (SD) method and its applications on simulating laminar flow past two side-by-side cylinders at various spacings. The high-order spectral difference solver is based on unstructured quadrilateral grids. High-order curved wall boundary representation is developed for cylinders. Nine different spacings (center-to-center distance/diameter s = 1.1, 1.4, 1.5, 1.7, 2, 2.5, 3, 3.4 and 4) are investigated. The simulation results are compared to experimental results and other numerical results. As s increases, single bluff-body, flip-flopping, anti-symmetric and symmetric wake patterns are predicted.